Country：Japan

Country：Japan

Country：Japan

Country：Japan

Country：Japan

Country：Japan

Country：Japan

Country：Japan

Kind of work：Joint Work  

DOI： https://doi.org/10.1016/j.ssi.2023.116412

Repository URL： http://hdl.handle.net/10466/0002001028

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DOI： https://doi.org/10.1002/batt.202300427

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DOI： https://doi.org/10.5796/electrochemistry.23-00030

Repository URL： http://hdl.handle.net/10466/0002001239

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DOI： https://doi.org/10.1007/s10008-023-05714-4

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DOI： https://doi.org/10.1039/d3ta05426h

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DOI： https://doi.org/10.1021/acs.chemmater.3c00185

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DOI： https://doi.org/10.1021/acsaem.3c01858

Repository URL： http://hdl.handle.net/10466/0002001237

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DOI： https://doi.org/10.1016/j.ssi.2023.116361

Repository URL： http://hdl.handle.net/10466/0002001234

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DOI： https://doi.org/10.1021/acs.jpcc.3c03766

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DOI： https://doi.org/10.1021/acs.jpcc.3c03876

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DOI： https://doi.org/10.5796/electrochemistry.23-00054

Repository URL： http://hdl.handle.net/10466/0002001238

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DOI： https://doi.org/10.1021/acs.jpcc.3c02143

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DOI： https://doi.org/10.1021/acs.jpcc.3c02851

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DOI： https://doi.org/10.1021/acs.jpcc.3c02277

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DOI： https://doi.org/10.2109/jcersj2.23014

Repository URL： http://hdl.handle.net/10466/0002001242

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DOI： https://doi.org/10.2109/jcersj2.23015

Repository URL： http://hdl.handle.net/10466/0002001233

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DOI： https://doi.org/10.1016/j.ssi.2023.116287

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DOI： https://doi.org/10.1016/j.ssi.2023.116288

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DOI： https://doi.org/10.1021/acs.inorgchem.3c01415

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DOI： https://doi.org/10.1021/acsami.3c03552

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DOI： https://doi.org/10.1021/jacs.3c03827

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DOI： https://doi.org/10.1103/PhysRevResearch.5.023203

Repository URL： http://hdl.handle.net/10466/0002001240

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DOI： https://doi.org/10.1021/acs.jpcc.3c02399

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DOI： https://doi.org/10.1039/d2cc05224e

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DOI： https://doi.org/10.1515/zkri-2023-0013

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DOI： https://doi.org/10.1016/j.jallcom.2023.170600

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DOI： https://doi.org/10.1021/acs.jpcc.3c01740

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DOI： https://doi.org/10.5796/electrochemistry.23-00029

Repository URL： http://hdl.handle.net/10466/0002001243

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DOI： https://doi.org/10.1016/j.jpowsour.2023.232739

Repository URL： http://hdl.handle.net/10466/0002001027

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DOI： https://doi.org/10.1016/j.ssi.2023.116162

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DOI： https://doi.org/10.1002/smll.202302179

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DOI： https://doi.org/10.5796/electrochemistry.23-00003

Repository URL： http://hdl.handle.net/10466/0002001241

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DOI： https://doi.org/10.5796/electrochemistry.23-00009

Repository URL： http://hdl.handle.net/10466/0002001235

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DOI： https://doi.org/10.1021/acs.jpcc.3c00414

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DOI： https://doi.org/10.1002/eem2.12612

Repository URL： http://hdl.handle.net/10466/0002001236

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DOI： https://doi.org/10.1021/acs.jpcc.2c06593

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DOI： https://doi.org/10.1021/acsaem.2c02627

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DOI： 10.5796/ecsjkansai.2022.2.023

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DOI： 10.5796/ecsjkansai.2022.2.001

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DOI： https://doi.org/10.2320/matertrans.MT-M2022094

Repository URL： http://hdl.handle.net/10466/0002001033

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DOI： https://doi.org/10.1021/acs.chemmater.2c02645

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DOI： https://doi.org/10.5796/electrochemistry.22-66075

Repository URL： http://hdl.handle.net/10466/0002001030

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DOI： https://doi.org/10.5796/electrochemistry.22-66088

Repository URL： http://hdl.handle.net/10466/0002001029

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DOI： https://doi.org/10.1016/j.jpowsour.2022.231821

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DOI： https://doi.org/10.1002/smll.202203383

Repository URL： http://hdl.handle.net/10466/0002001032

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DOI： https://doi.org/10.2109/jcersj2.22056

Repository URL： http://hdl.handle.net/10466/0002001031

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DOI： https://doi.org/10.1246/cl.220132

Repository URL： http://hdl.handle.net/10466/0002001009

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DOI： https://doi.org/10.2109/jcersj2.22035

Repository URL： http://hdl.handle.net/10466/0002001035

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DOI： https://doi.org/10.1021/acsaem.2c00978

Repository URL： http://hdl.handle.net/10466/0002001008

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DOI： https://doi.org/10.2109/jcersj2.22017

Repository URL： http://hdl.handle.net/10466/0002001036

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DOI： https://doi.org/10.1021/acs.jpcc.2c02497

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DOI： https://doi.org/10.1016/j.nocx.2022.100089

Repository URL： http://hdl.handle.net/10466/0002001042

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DOI： https://doi.org/10.1016/j.jpowsour.2022.231313

Repository URL： http://hdl.handle.net/10466/0002001028

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DOI： https://doi.org/10.5796/electrochemistry.22-00037

Repository URL： http://hdl.handle.net/10466/0002001037

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DOI： https://doi.org/10.1007/s10971-022-05824-x

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DOI： https://doi.org/10.1021/acsami.2c05090

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DOI： https://doi.org/10.1016/j.ssi.2022.115869

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DOI： https://doi.org/10.2109/jcersj2.21177

Repository URL： http://hdl.handle.net/10466/0002001039

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DOI： https://doi.org/10.1021/acs.jpcc.2c00421

Kind of work：Joint Work  

DOI： https://doi.org/10.5796/electrochemistry.22-00016

Repository URL： http://hdl.handle.net/10466/0002001038

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DOI： https://doi.org/10.5796/electrochemistry.22-00013

Repository URL： http://hdl.handle.net/10466/0002001040

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DOI： https://doi.org/10.1016/j.ssi.2021.115848

Repository URL： http://hdl.handle.net/10466/0002001058

Kind of work：Joint Work  

DOI： https://doi.org/10.5796/electrochemistry.22-00007

Repository URL： http://hdl.handle.net/10466/0002001041

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DOI： https://doi.org/10.1039/D1MA01228B

Repository URL： http://hdl.handle.net/10466/0002001034

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DOI： https://doi.org/10.1007/s10971-021-05524-y

Repository URL： http://hdl.handle.net/10466/0002001024

Kind of work：Joint Work  

DOI： https://doi.org/10.1021/acsaem.1c03166

Kind of work：Joint Work  

DOI： https://doi.org/10.1002/adfm.202106174

Repository URL： http://hdl.handle.net/10466/0002001043

Kind of work：Joint Work  

DOI： https://doi.org/10.1021/acsaem.1c02452

Publishing type：Research paper (scientific journal)  

Sulfide-based solid electrolytes (SEs) exhibiting high ionic conductivity are indispensable battery materials for next-generation all-solid-state batteries. However, sulfide-based SEs have a major drawback in their low chemical stability in air. When exposed to H2O or O2 gas, toxic H2S is generated, and their ionic conductivity considerably declines. However, their degradation mechanism caused by air exposure has not been understood yet. To clarify the degradation process, in this study, we developed a transmission electron microscope (TEM) system to evaluate the air stability of battery materials. Using a vacuum transfer double-tilt TEM holder with a gas-flow system, the in situ observation of the degradation process was conducted for a sulfide-based Li4SnS4 glass ceramic under an air-flow environment. Consequently, electron diffraction (ED) patterns and TEM images could clearly capture morphological changes and the amorphization process caused by air exposure. Moreover, based on the analysis of ED patterns, it is observed that Li4SnS4 is likely to decompose because of the reaction with H2O in air. Therefore, this airtight and air-flow TEM system should be effective in clarifying the process of the deterioration of sulfur-based SEs during exposure to air.

DOI： 10.1093/jmicro/dfab022

PubMed

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

All-solid-state batteries using sodium are promising candidates for next-generation rechargeable batteries due to the limited lithium resources. A practical sodium battery requires an electrolyte with high conductivity. Cubic Na3PS4 exhibiting high conductivity of over 10−4 S cm−1 is obtained by crystallizing amorphous Na3PS4 synthesized by ball milling. Amorphous Na3PS4 crystallizes in a cubic structure and then is transformed into a tetragonal phase upon heating. In this study, in situ observation by transmission electron microscopy demonstrates that the crystallite size drastically increases during the transition from the cubic phase to the tetragonal phase. Moreover, an electron diffraction analysis reveals that amorphous domains and nano-sized crystallites coexist in the cubic Na3PS4 specimen, while the tetragonal phase contains micro-sized crystallites. The nano-sized crystallites and the composite formed by crystallites and amorphous domains are most likely responsible for the increase in conductivity in the cubic Na3PS4 specimens.

DOI： 10.1016/j.jpowsour.2021.230444

All-solid-state sodium batteries are attracting attention as next-generation batteries, owing to their improved safety and abundance of sodium resources. To realize all-solid-state sodium batteries, solid electrolytes with high sodium-ion conductivities are required. In this study, Na3PS4 electrolytes with partial substitution of P5+ with W6+ were investigated. The Na3–xP1–xWxS4 sulfide-based solid electrolytes were prepared via a mechanochemical process and consecutive heat treatment. The Na2.85P0.85W0.15S4 electrolyte with Na vacancies exhibited an ionic conductivity of 8.8 × 10−3 S cm−1 at 25 °C, which was higher than that of Na3PS4 solid electrolyte. The all-solid-state batteries (Na-Sn/Na2.85P0.85W0.15S4/TiS2) exhibited a reversible capacity of 140 mA h g−1 at a current density of 0.038 mA cm−2 and retained the capacity of 115 mAh g−1 for 40 cycles at 0.130 mA cm−2 at 25 °C. The Na3–xP1–xWxS4 samples prepared via mechanochemistry are homogeneous electrolytes free of crystalline WS2 impurities and are effective for application to all-solid-state sodium batteries.

DOI： 10.1016/j.jpowsour.2021.230100

J-GLOBAL

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

All-solid-state lithium batteries that use lithium metal as the anode have extremely high energy densities. However, for lithium metal anodes to be used, lithium dendrite formation must be addressed. Recently, the addition of lithium iodide (LiI) to sulfide solid electrolytes was found to suppress lithium dendrite formation. It is unclear whether the cause of this suppression is the improvement of the ionic conductivity of the solid electrolyte itself or the electrochemical properties of the lithium metal/solid electrolyte interface. In this study, the cause of the suppression was quantitatively elucidated. The effect of the interphase on the dendrite growth of doping LiI into Li3PS4 was determined using X-ray absorption spectroscopy and X-ray computed tomography measurements. The results revealed that LiI-doped Li3PS4 suppressed the dendrite formation by maintaining the interface due to inhibition of the reductive decomposition of Li3PS4. In addition, annealed LiI-doped Li3PS4 showed a greater dendrite suppression ability as the ionic conductivity increased. From these results, we not only found that the physical properties of the lithium metal/solid electrolyte interface and the bulk ionic conductivity contribute to lithium dendrite suppression but also quantitatively determined the proportions of the contributions of these two factors.

DOI： 10.1021/acs.chemmater.1c00270

Publishing type：Research paper (scientific journal)  

Understanding the differences in the structures and defects in the stable crystalline phase and metastable phase is important for increasing the ionic conductivities of a solid electrolyte. The metastable phase often has higher conductivity than the stable phase. In this study, metastable lithium thiogallate, Li5GaS4, was synthesizedviamechanochemistry and stable Li5GaS4was obtained by heating the metastable phase. The metastable Li5GaS4sample was found to have an antifluorite-type crystal structure with cationic disorder, while the stable phase was found to have a monoclinic crystal structure, similar to that of another solid electrolyte, Li5AlS4. In both the structures, the Ga3+cations were surrounded by four S2−anions in tetrahedral coordination. The conductivity of the metastable phase was determined to be 2.1 × 10−5S cm−1at 25 °C, which is 1000 times greater than that of the monoclinic phase. The high conductivity of the metastable phase was achieved owing to cation disorder in the crystal structure.

DOI： 10.1039/d1ra03194e

Publishing type：Research paper (scientific journal)  

All-solid-state batteries using oxide electrolytes are regarded as safe batteries. However, most crystalline oxide solid electrolytes require high-temperature sintering for densification. Oxide electrolytes with high formability, which enable the construction of high-performance batteries, are thus required. In this study, Li4SiO4Li2SO4 glasses and glass-ceramics were prepared by mechanochemical treatment and subsequent heat treatment at 270 °C to achieve electrolytes with high formability. As the Li2SO4 content was increased, the formability of the electrolyte increased. The 90Li4SiO4·10Li2SO4 glass-ceramic electrolyte with a hexagonal structure (a P63/mmc space group) showed the highest ionic conductivity of 2.2 © 1016 S cm11 at 25 °C. In this crystal structure, oxygen anions form a hexagonal close-packed structure, and silicon and sulfur cations randomly occupy the tetrahedral sites formed by oxygen anions. An all-solid-state LiIn/LiNi1/3Mn1/3Co1/3O2 cell using a 90Li4SiO4·10Li2SO4 glass-ceramic electrolyte operated at 100 °C as a secondary battery without high-temperature sintering. These oxide materials are promising solid electrolytes for oxide-type all-solid-state batteries.

DOI： 10.2109/jcersj2.21027

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

To develop all-solid-state lithium batteries, high-capacity positive electrode materials are necessary. An antifluorite-type material, Li2S, exhibits a high theoretical capacity. However, Li2S cannot be used as a positive electrode for the all-solid-state cell because of its insulating behavior. To provide electronic and ionic conduction, recently, antifluorite-type Li3CuS2 has been developed by activation of Li2S by Cu substitution. Li3CuS2 is a favorable candidate for positive electrodes as sulfide-based all-solid-state cells with Li3CuS2 exhibit high charge-discharge performance. However, structural changes and redox species during the charge-discharge cycle have not been understood yet. To clarify the charge-discharge mechanism of Li3CuS2, in this study, we examined the microstructural changes in a Li3CuS2-Li3PS4 positive electrode composite during charge and discharge by transmission electron microscopy (TEM). The hollow-cone dark-field imaging technique was employed to evaluate the crystallite size distribution. The result shows that the crystallite size of Li3CuS2 reversibly decreases and increases in the charging and discharging states, respectively. The electron diffraction pattern shows that LiCuS2 was formed during charging, which is attributed to Li+ extraction from Li3CuS2. In the discharging state, the crystallite size increased and Li3CuS2 was reproduced. The TEM results suggest that the reversible structural changes (Li3CuS2 ⇆ LiCuS2 + 2Li+ + 2e-) would contribute to high charge-discharge characteristics.

DOI： 10.1021/acsaem.1c01074

Publishing type：Research paper (scientific journal)  

Solid electrolytes are important materials for enhancing the performance of all-solid-state sodium rechargeable batteries. Na10+xSn1+xP2-xS12 (0 ≤ x ≤ 1.2) samples were prepared using a mechanochemical process, followed by heat treatment and their structures and ionic conductivities were investigated. Glassy samples were obtained via the mechanochemical process; the samples with the Na11Sn2PS12 type crystal structure were obtained for all the prepared compositions through the heat treatment of the glasses. The Na11Sn2PS12 (x = 1) sample obtained by heat treatment at 300°C exhibited an ionic conductivity of 2.6

DOI： 10.2109/jcersj2.21010

Kind of work：Joint Work  

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Kind of work：Joint Work  

Kind of work：Joint Work  

Repository URL： http://hdl.handle.net/10466/0002001026

Publishing type：Research paper (scientific journal)  

The electronic and ionic conductivities of the interphase that forms between Li metal and solid electrolytes (SEs) are key parameters in determining battery cell performance. In this study, we evaluated the effect of the interphase on Li dissolution/deposition behaviors. The reduction of Li2S-P2S5 glasses to Li2S and Li3P by Li metal occurred at the Li/SE interface. The Li dissolution/deposition performance at 100 °C was improved by increasing the Li3P content in the interphase, and the cell with a Li4P2S6 glass electrolyte functioned without short-circuiting at a current density of 1.3 mA cm-2. The ionic conductivity of the Li/SE interphase was evaluated by preparing Li-SE compounds using mechanochemical processing. The milled sample prepared from Li metal and Li4P2S6 glass showed a one order of magnitude higher conductivity of 10-4 S cm-1 at 100 °C than that of the Li-Li3PS4 milled sample, indicating that the ionic conductivity of the interphase formed at the Li/SE interface is an important factor for improving the short-circuiting tolerance of all-solid-state Li-metal batteries.

DOI： 10.1149/1945-7111/ac0995

Publishing type：Part of collection (book)  

DOI： 10.1016/B978-0-12-803581-8.12133-2

A new lithium-ion conducting oxide, hexagonal Li4GeO4, with a space group of P63/mmc, was prepared by mechanochemical treatment and subsequent heat treatment at 250 °C. The crystal structure was found in sulfide Li4SnS4, and this is the first study to report an oxide system. In addition, (100-x)Li4GeO4·xLi2MO4 (M = S or W; x = 10, 20, 30, and 40 mol%) glass-ceramic electrolytes with the hexagonal phase were prepared by crystallization of their mother glasses. The formability of the electrolytes improved as the quantity of Li2SO4 increased, and the 90Li4GeO4·10Li2SO4 glass-ceramic electrolyte showed the highest ionic conductivity of 2.9 × 10−6 S cm−1 at 25 °C. Compared with the experimental results, the bond valence sum (BVS) analysis results indicated that ionic conduction paths are easily connected along the c-axis in the hexagonal phase, suggesting that the relatively small lattices in the a- and b-axes are more advantageous for three-dimensional ionic conduction.

DOI： 10.1016/j.ssi.2021.115605

J-GLOBAL

Kind of work：Joint Work  

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

DOI： https://doi.org/10.1021/acsaem.1c01074

Repository URL： http://hdl.handle.net/10466/0002001045

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

Recently, several sulfide solid electrolytes have been synthesized by liquid-phase synthesis for the commercialization of all-solid-state batteries. Unfortunately, the ionic conductivity for most of these electrolytes is unsatisfactory compared to that of solid electrolytes synthesized by conventional ball milling. This problem is attributed to different mechanisms between the liquid phase and the solid phase in reaction and formation. However, to the best of our knowledge, the effect of the solvent on the ionic conductivity of solid electrolytes has not been extensively investigated, although the identification of these properties is a key point in understanding the liquid-phase synthesis. Herein, the correlation between ionic conductivity and crystallinity originating from the solvents used has been investigated. As a result, the ionic conductivity of the electrolyte was found to be strongly dependent on polarity (δP) with low crystallinity. The highest ionic conductivity (5.09 × 10-4 S cm-1 at 25 °C) was obtained using butyl acetate, which exhibited the lowest δP. Moreover, the highest ionic conductivity of Li3PS4 produced by liquid-phase synthesis using butyl acetate was very comparable to that obtained by ball milling (5.14 × 10-4 S cm-1).

DOI： 10.1021/acsaem.0c02771

Publishing type：Research paper (scientific journal)  

Liquid-phase synthesis for solid electrolytes has received considerable attention owing to its shape control, with the potential to produce particles easily on a large scale, and its low cost and energy consumption. However, solid electrolytes prepared through liquid-phase synthesis have been shown to have lower ionic conductivity than solid electrolytes prepared through the mechanical milling method. Recently, following various efforts, our group found that the crystallinity and remaining intermediate are the reasons for the low ionic conductivity of these materials. By using tetrahydrofuran (THF), we successfully improved the ionic conductivity of Li3PS4 to 1.85 × 10−4 S cm−1 at 25 °C, higher than that afforded by ethyl propionate, which was reported to produce the highest ionic conductivity among the solvents used for liquid-phase synthesis. High-energy X-ray diffraction (XRD) measurements coupled with pair distribution function (PDF) analysis were employed to analyze the synthesized materials in order to determine why the ionic conductivity was higher than that of a sample prepared using ethyl propionate. The PDF analysis revealed that the crystallization of Li3PS4 can be suppressed using THF, which has a lower boiling point than ethyl propionate. Moreover, it was revealed that the solvent could not be removed completely when the material has an amorphous structure, and thus, the ionic conductivity was lower than that of a material prepared using the solid-phase synthesis method.

DOI： 10.1016/j.ssi.2021.115568

Publishing type：Research paper (scientific journal)  

Studies on local conduction paths in composite electrodes are essential to the realization of high-performance sulfide all-solid-state lithium batteries. Here, we directly evaluate the electrical properties of individual LiNi1/3Mn1/3Co1/3O2 (NMC) electrode active material particles in composite positive electrodes by scanning probe microscopy (SPM) techniques. Kelvin probe force microscopy (KPFM) and scanning spreading resistance microscopy (SSRM) are combined. The results indicate that all NMC particles exhibit a charged state with increasing potential, but low electronic conduction paths exist at point of contacts of some NMC particles. Furthermore, the I-V characteristics measured by conductive atomic force microscopy (C-AFM) suggest that these specific NMC particles show low charge-discharge reactivity. The results of the SPM techniques indicate that poor conduction locally limits the charge-discharge reactivity of electrode active materials, leading to the degradation of battery performance. Such an SPM combination accelerates the morphological optimization of composite electrodes by facilitating the investigation of the intrinsic electrical properties of the electrodes.

DOI： 10.1021/acs.jpcc.0c10148

Publishing type：Research paper (scientific journal)  

The application of lithium metal as a negative electrode in all-solid-state batteries shows promise for optimizing battery safety and energy density. However, further development relies on a detailed understanding of the chemo-mechanical issues at the interface between the lithium metal and solid electrolyte (SE). In this study, crack formation inside the sulfide SE (Li3PS4: LPS) layers during battery operation was visualized using in situ X-ray computed tomography (X-ray CT). Moreover, the degradation mechanism that causes short-circuiting was proposed based on a combination of the X-ray CT results and scanning electron microscopy images after short-circuiting. The primary cause of short-circuiting was a chemical reaction in which LPS was reduced at the lithium interface. The LPS expanded during decomposition, thereby forming small cracks. Lithium penetrated the small cracks to form new interfaces with fresh LPS on the interior of the LPS layers. This combination of reduction-expansion-cracking of LPS was repeated at these new interfaces. Lithium clusters eventually formed, thereby generating large cracks due to stress concentration. Lithium penetrated these large cracks easily, finally causing short-circuiting. Therefore, preventing the reduction reaction at the interface between the SE and lithium metal is effective in suppressing degradation. In fact, LPS-LiI electrolytes, which are highly stable to reduction, were demonstrated to prevent the repeated degradation mechanism. These findings will promote all-solid-state lithium-metal battery development by providing valuable insight into the design of the interface between SEs and lithium, where the selection of a suitable SE is vital.

DOI： 10.1021/acsami.0c18314

PubMed

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

Sulfur is one of the promising next-generation cathode materials because of its low cost and high theoretical gravimetric capacity. However, the reaction mechanism of the sulfur cathode is largely influenced by the electrolyte and the intermediate sulfur species during the first discharge process has not been quantitatively explored in different electrolytes. In this study, we elucidated the reaction mechanism of sulfide cathodes by using three different electrolyte systems, viz., a conventional liquid electrolyte [LiPF6/ethylene carbonate (EC)/ethylene-methyl carbonate (EMC)], a concentrated liquid electrolyte [lithium bis(trifluorosulfonyl)amide (LiTFSA)/tetraglyme (G4):1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE)], and a solid-state electrolyte (Li3PS4). Soft X-ray absorption spectroscopy was used to examine the reaction mechanism of the sulfur cathode in the liquid and solid-state electrolytes during the first discharge process. In the conventional electrolyte, the sulfur cathode was reduced to long-chain polysulfide (S62-) during the first discharge process, and the polysulfide subsequently dissolved into the electrolyte. In the concentrated electrolyte, the sulfur cathode was reduced to midchain polysulfide (S42-) at the initial stage of the first discharge process and then reduced to short-chain polysulfide (S22-) and Li2S, followed by the formation of long-chain polysulfide (S62-). In the solid-state electrolyte, the sulfur cathode was reduced to long-chain polysulfide (S62-) at the initial stage of the first discharge process and was gradually reduced to mid-chain polysulfide (S42-), short-chain polysulfide (S22-), and Li2S. The differences in these reaction pathways govern electrochemical properties such as the difference in discharge voltage.

DOI： 10.1021/acsaem.0c02063

Publishing type：Research paper (scientific journal)  

All-solid-state batteries using flame-retardant inorganic solid electrolytes boast of advantages such as safety and wide usable temperature ranges. Although Li2S with an antifluorite-type structure has a high theoretical capacity, it is challenging to use in all-solid-state batteries because of the insulating nature. Here, we report an antifluorite-type Li3CuS2 as a sulfide positive electrode active material with high electronic conductivity. All-solid-state batteries using Li3CuS2 were successfully operated without the addition of conductive additives to the positive electrode. The Li3CuS2 exhibited an initial charge-discharge capacity of 380 mAh g-1 with an average discharge voltage of 2.1 V vs Li+/Li.

DOI： 10.1021/acsaem.0c02657

Kind of work：Joint Work  

Kind of work：Joint Work  

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Publishing type：Research paper (scientific journal)  

Amorphous VS4(a-VS4) electrode material was synthesized by mechanical milling of crystalline VS4(c-VS4). The columbic efficiency of the a- VS4cell was significantly improved (ca. 86 %) at the first cycle as compared with the c-VS4cell (ca. 77 %), resulting in the improved capacity retention for prolonged cycling. Pair distribution function (PDF) analysis obtained from X-ray total scattering data, revealed that the radial atomic distribution of a-VS4at initial stage was similar to that of the low-crystalline VS4appeared after the first cycle of c-VS4. This is suggestive that the amorphization via mechanical milling process gave rise to the preparation of "first cycled VS4" which would contribute to the improved columbic efficiency at the first cycle and the resulting improved capacity retention for prolonged cycling. The structure of a-VS4could be visualized by first-principles molecular dynamic calculation of "first-cycled VS4".

DOI： 10.5796/electrochemistry.21-00015

Publishing type：Research paper (scientific journal)  

Development of oxide solid electrolytes for all-solid-state batteries is attracting increasing attention. In this study, amorphous Li2O-LiI materials are prepared via a mechanochemical process to achieve high lithium ionic conductivity and good compatibility to lithium metal. Amorphous 66.7Li2O·33.3LiI (mol%) electrolyte shows a high ionic conductivity of 3.1 × 10−5 S cm−1 at 25 °C with a relative density of 96 %. An all-solid-state Li symmetric cell (Li/66.7Li2O·33.3LiI/Li) operates without an increase in overvoltage. A simple combination of lithium oxide and lithium iodide exhibits high ionic conductivity, ductility, and stability to lithium metal.

DOI： 10.5796/electrochemistry.21-00049

Publishing type：Research paper (scientific journal)  

To realize all-solid-state sodium-ion batteries, the ionic conductivities and stabilities of solid electrolytes must be improved. The sulfide Na3SbS4 electrolyte is known to show a high sodium-ion conductivity of over 10-3 S cm-1 at room temperature. In this study, cation-substituted Na3SbS4 solid electrolytes with excess Na or Na vacancies were prepared, and the effects of substitution on the material conductivity were examined. The ionic conductivities of the Na3+xSb1-xMxS4 (M = Si, Ge, Sn) electrolytes, which were doped with excess Na, were lower than that of the Na3SbS4 electrolyte; in contrast, the conductivities of the Na3-xSb1-xMoxS4 electrolytes, which were doped with Na vacancies, were higher. The Na2.88Sb0.88Mo0.12S4 electrolyte showed the highest room-temperature ionic conductivity of 3.9 × 10-3 S cm-1 and the lowest activation energy for conduction of 21 kJ mol-1. To improve the ionic conductivity of the Na3SbS4 electrolyte, introducing Na vacancies instead of excess Na was found to be effective.

DOI： 10.1021/acsaem.0c01823

Publishing type：Research paper (scientific journal)  

© 2020 Elsevier B.V. A positive electrode containing Li3PS4 (LPS) glasses and LiNi1/3Mn1/3Co1/3O2 (NMC) is a promising candidate for sulfide-based all-solid-state lithium batteries owing to its excellent charge–discharge cycle characteristics. However, sulfide-based solid electrolytes exhibit low chemical stability in air. This disadvantage affects process cost and thermal stability of all-solid-state cells. To resolve these issues, in this study, we focus on solid electrolytes, Li4SnS4 (LSS), that do not generate H2S gas in air. The thermal behavior and microstructure of LSS–NMC positive electrode composites before and after the initial charge–discharge cycle are investigated. The initially charged LSS–NMC composites exhibit several exothermal reactions above 250 °C. However, pristine and initially discharged samples do not show any considerable exothermal reactions. For LPS–NMC composites, by contrast, exothermal reactions are detected regardless of the charging and discharging state. To clarify the exothermic factors of initially charged LSS–NMC composites, we performed ex situ transmission electron microscopy observation and X-ray diffraction measurements. It is determined that SnS2, transition metal sulfides, and metal oxides are formed above 300 °C, which is attributable to LSS and NMC decomposition reactions. On the basis of the relation between thermal behavior and corresponding structural changes, exothermic factors and thermal stability of LSS–NMC composites are discussed in comparison with LPS–NMC composites.

DOI： 10.1016/j.jpowsour.2020.228827

Kind of work：Joint Work  

Compressive pressure applied during the operation of all-solid-state batteries that employ a sulfide solid electrolyte (SE) assists particle contact, thereby maintaining the ionic and electronic conduction network. The relationship between compressive pressure and volume variation in active materials is critical for designing practical full-cells with enhanced cell-based energy densities. However, studies into these aspects are rare. Here, we systematically investigate the effects of volume change of active materials [silicon, graphite, and LiNi1/3Mn1/3Co1/3O2 (NMC)] at different pressures (75 and 50 MPa) on electrochemical performance, cell internal resistance, and microstructure of full-cells with a thin SE layer (approximately 75-μm-thick). Pressurization at 75 MPa and use of graphite with lower expansion ratios improves capacity and capacity retentions. Increasing variation in the negative electrode volume increases charge-transfer resistance and crack formation in the NMC-composite layer. This indicates that the buffering effect via the elastic deformation of the thin SE layer is insufficient. Pressure facilitates plastic deformation of LixSi and SE, resulting in their improved contact, while perpendicular cracks appear throughout the Si-composite layer, effectively alleviating stress derived from variations in the volume of Si. This study provides important mechanistic insights into the design of advanced active materials and batteries required for industrial applications.

DOI： 10.1016/j.jpowsour.2020.228595

J-GLOBAL

Publishing type：Research paper (scientific journal)  

© 2020 American Chemical Society. The guiding principle for the design of inorganic compounds with high ionic conductivity has been extensively sought to realize next-generation all-solid-state batteries (ASSBs). Recently, a sulfide-type Na+ ion conductor, cubic Na3SbS4 with W doping (Na2.88Sb0.88W0.12S4), was reported with unprecedentedly high ionic conductivity of 3.2 × 10-2 S cm-1, making it now a champion solid electrolyte for Na-ASSB (A. Hayashi et al., Nat. Commun. 2019, 10, 5266). Herein, density functional theory molecular dynamics (DFT-MD) calculations were performed for pristine, W-doped, and Mo-doped Na3SbS4 to examine the ionic conduction mechanism (Boltzmann factor vs prefactor) and the aliovalent cation dopant effects in Na3SbS4. We showed that Na vacancies induced by cation doping play crucial roles in superionic conductivity, while the diffusion process is rather characterized by the concerted motion of Na+ ions. A comparison between the two dopants, Mo6+ and W6+, revealed that the conductivity enhancement can be primarily explained by a decrease of Na+ ion activation energy, which is found to be strongly correlated to the enlargement of Na Wyckoff site cages brought upon by the smaller WS4/MoS4 tetrahedral volume relative to the host SbS4 volume. This descriptor of the pathway free volume can suggest a general guiding principle for superionic conduction that can be applied to other cations, in addition to explaining the superior performance of W-doped Na3SbS4.

DOI： 10.1021/acs.chemmater.0c02318

Publishing type：Research paper (scientific journal)  

All-solid-state lithium batteries using inorganic sulfide solid electrolytes have good safety properties and high rate capabilities as expected for a next-generation battery. Presently, conventional preparation methods such as mechanical milling and/or solid-phase synthesis need a long time to provide a small amount of the product, and they have difficult in supplying a sufficient amount to meet the demand. Hence, liquid-phase synthesis methods have been developed for large-scale synthesis. However, the ionic conductivity of sulfide solid electrolytes prepared via liquid-phase synthesis is typically lower than that prepared via solid-phase synthesis. In this study, we have controlled three factors: (1) shaking time, (2) annealing temperature, and (3) annealing time. The factors influencing lithium ionic conductivity of Li3PS4 prepared via liquid-phase synthesis were quantitatively evaluated using high-energy X-ray diffraction (XRD) measurement coupled with pair distribution function (PDF) analysis. It was revealed from PDF analysis that the amount of Li2S that cannot be detected by Raman spectroscopy or XRD decreased the ionic conductivity. Furthermore, it was revealed that the ionic conductivity of Li3PS4 is dominated by other parameters, such as remaining solvent in the sample and high crystallinity of the sample.

DOI： 10.1021/acsomega.0c04307

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

© 2020 Ceramic Society of Japan. All rights reserved. Solid electrolytes have become important materials for improving the performance of next-generation all-solidstate sodium rechargeable batteries. Therefore, sodium vacancy doping for Na3SbS4electrolytes was performed by partially substituting Cl for S. Na3-xSbS4-xClxelectrolytes were prepared using a mechanochemical process and consecutive heat treatment. The structures, ionic conductivities, and air safety of the prepared Na3-x- SbS4-xCxl electrolytes were evaluated via X-ray diffraction and impedance, air stability, and electrochemical tests. The Na2.9375SbS3.9375Cl0.0625electrolyte showed a higher room-temperature ionic conductivity of 2.9 × 10-3Scm-1than that of the Na3SbS4electrolyte. An all-solid-state Na15Sn4/Na2.9375SbS3.9375Cl0.0625/TiS2cell showed a reversible capacity of approximately 100mAh g-1at room temperature. Thus, the Na2.9375SbS3.9375Cl0.0625solid electrolyte has the potential for application as a solid electrolyte in all-solid-state batteries.

DOI： 10.2109/jcersj2.20089

Publishing type：Research paper (scientific journal)  

©2020 The Ceramic Society of Japan. All rights reserved. Composite quasi-solid electrolytes comprising Li3PS4 (LPS) glass and various organic carbonates were prepared, and the effects of these carbonates on the glass were investigated. Compared to LPS glass, the conductivity decreased for composites with highly dielectric cyclic carbonates and increased slightly for composites with a poorly dielectric linear carbonate. Scanning electron microscopy observations indicated that the addition of a poorly dielectric linear carbonate slightly improved the formability of LPS glass.

DOI： 10.2109/jcersj2.20114

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

© 2020 American Chemical Society. Long-lasting all-solid-state batteries can be achieved by preventing side reactions in the composite electrodes comprising electrode active materials and solid electrolytes. Typically, the battery performance can be enhanced through the use of robust solid electrolytes that are resistant to oxidation and decomposition. In this study, the thermal stability of sulfide solid electrolytes Li3PS4 and Li4SnS4 toward oxide positive electrode active materials was estimated by investigating the occurrence of side reactions at the electrolyte-electrode interfaces when the composite electrodes are heated in an accelerated aging test: Li4SnS4 showed higher thermal stability because of the suppression of the substitution reaction between S and O. Moreover, thermally stable sulfide solid electrolytes are amenable to an improved cell construction process. The sintering (pelletizing and subsequent heating) of the composite electrodes with Li4SnS4 as the solid electrolyte allowed the manufacture of dense electrodes that exhibited increased ionic conductivity, thereby enhancing the battery performance.

DOI： 10.1021/acsami.0c05050

PubMed

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

© 2020 The Authors The need for an effective design of composite electrodes in all-solid-state Na-S batteries is warranted because of their slow charge–discharge reactions. By employing a composite of activated carbon MSP20, sulfur, and Na3SbS4 as the positive electrode material, we developed an effective all-solid-state Na-S battery that demonstrated the advantages of exhibiting a high capacity and good cyclability. Further, we discovered that filling the carbon micropores with sulfur and combining with highly conductive Na3SbS4, results in a reversible two-electron reaction between S and Na2S. This all-solid-state Na-S battery, operating at room temperature, demonstrates a high capacity of 1560 mAh per gram of sulfur (ca. 330 mAh per gram of positive electrode) and a capacity retention of 93% after 50 cycles. Decreasing the size of the S-MSP20 particles coated with Na3SbS4 in a liquid phase process was observed to reduce the volume change of the particles during charge and discharge cycles, which resulted in an excellent electrochemical performance.

DOI： 10.1016/j.elecom.2020.106741

Publishing type：Research paper (scientific journal)  

Capacity degradation mechanism of graphite in sulfide-based all-solid-state lithium batteries has been investigated by adopting three different press conditions for cell assembling. Reversible redox reaction and stage transition of graphite were recognized from cyclic voltammetry and X-ray diffraction measurement. Initial charge and discharge capacity of graphite in the thus obtained three cells were ca. 310 and 270 mAh g-1, respectively, indicating that the press conditions did not affect the initial charge and discharge capacity of graphite. After 50 cycles, the cell pressed at the highest pressure maintained over 95% of the capacity of that obtained at the 10th cycle. The capacity of the cell pressed at the lowest pressure, on the other hand, faded near 90%. The increase of resistance assigned to bulk solid electrolyte during cycling was detected by the impedance spectroscopy, and the cell pressed at the lowest pressure exhibited the largest resistance increase among all of the cells. Cross-sectional scanning electron microscope observation revealed formation of the voids in the bulk solid electrolyte, especially in the cell pressed at the lowest pressure, after 50 cycles, which resulted in the increase of the resistance for bulk solid electrolyte and capacity degradation of graphite.

DOI： 10.1021/acsaem.0c00460

Publishing type：Research paper (scientific journal)  

© the Owner Societies. The reaction uniformity of LiCoO2 composite positive electrodes in all-solid-state cells was compared quantitatively by investigating the Raman band shifts corresponding to the state-of-charge (SOC) of LiCoO2. The quantitative SOC analysis was conducted using the Raman imaging data of composite electrodes with smaller or larger solid electrolytes. The electrodes exhibited different reaction uniformity although the cells showed similar initial charge capacities and average SOC. In the case of larger solid electrolytes, most LiCoO2 particles showed higher or lower SOC than the average SOC, and lower battery performance. The quantitative analysis of SOC in each LiCoO2 electrode demonstrated that a variable SOC outside the average SOC resulted in larger irreversible capacity and lower rate performance. The quantitative SOC analysis newly developed in the present study is a useful technique for designing composite electrodes showing higher battery performance.

DOI： 10.1039/d0cp00508h

PubMed

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

An all-solid-state lithium battery using inorganic solid electrolytes requires safety assurance and improved energy density, both of which are issues in large-scale applications of lithium-ion batteries. Utilization of high-capacity lithium-excess electrode materials is effective for the further increase in energy density. However, they have never been applied to all-solid-state batteries. Operational difficulty of all-solid-state batteries using them generally lies in the construction of the electrode-electrolyte interface. By the amorphization of Li₂RuO₃ as a lithium-excess model material with Li₂SO₄, here, we have first demonstrated a reversible oxygen redox reaction in all-solid-state batteries. Amorphous nature of the Li₂RuO₃-Li₂SO₄ matrix enables inclusion of active material with high conductivity and ductility for achieving favorable interfaces with charge transfer capabilities, leading to the stable operation of all-solid-state batteries.

DOI： 10.1126/sciadv.aax7236

PubMed

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

©2020 The Ceramic Society of Japan. All rights reserved. All-solid-state lithium-sulfur batteries are promising from the perspective of high safety, low cost, and high capability. Herein, composites of sulfur and microporous carbon (MSP20, MSC30) are prepared by a melt diffusion process, and their performance as electrode materials are compared with that of composites based on nanocarbons. In addition to the type of carbon, the degree of mixing with solid electrolytes is an important factor in the formation of ionic/electronic conduction pathways. The all-solid-state cell using S-MSC30-Li3PS4 shows a high initial discharge capacity of 1488 mAh per gram of sulfur at 25 °C at a current density of 1.3 mA cm12 and operates reversibly at a high current density of 12.7 mA cm12 (3C) at 100 °C. The amorphization of sulfur is effective for obtaining high capacity and sulfur impregnated into the meso- and micropores of carbon is more active than sulfur that forms nanocom osites with nanocarbon

DOI： 10.2109/jcersj2.20003

Kind of work：Joint Work  

DOI： 10.1021/acsenergylett.9b02764

Publishing type：Research paper (scientific journal)  

Copyright © 2020 American Chemical Society. The dynamic changes of ionic conduction path in the cross-sectional graphite composite electrodes of bulk-type all-solid-state lithium batteries have been monitored using operando confocal microscopic observations for color changes of graphite in response to their stage structures. The ionic conduction path decreased in the cross-sectional direction as cycle numbers increased, with simultaneous capacity degradation. The local reactivity of lithiation and delithiation was evaluated by image analysis considering state-of-charge (SOC) values. Electrode thickness changes were examined from the confocal microscope images obtained in the operando observations. The results revealed that voids and cracks were formed during cycle tests and that the thickness gradually increased. These cracks and voids were one of the main contributors to the limitation of ionic conduction paths in the depth direction. Operando microscopic observation and subsequent image analysis elucidated not only the morphological changes of active materials but also the differences in local SOC changes in the electrode.

DOI： 10.1021/acs.jpclett.9b03456

PubMed

Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. In this study, we present a dry coating process to produce a core-shell composite particle for an all-solid-state lithium battery, where a single particle of the active material is coated with solid electrolytes. LiNi1/3Co1/3Mn1/3O2 (NCM) and Li3PS4 (LPS), which are typical cathode active material and sulfide solid electrolyte, were used. A dry impact-blending device was employed for the dry coating process. We demonstrated that a single particle of NCM was uniformly coated with a continuous layer of LPS by the dry coating process without any breakage or attrition of NCM, to produce an NCM@LPS core-shell particle. The charge-discharge cycling tests showed that the rate and cycle performances of an all-solid-state half-cell prepared with the NCM@LPS core-shell particles significantly improved. The three-dimensional internal structure of the composite cathode was subsequently analyzed using FIB-SEM with an image reconstruction technique. The results revealed that the composite cathode prepared with the NCM@LPS core-shell particles had a (i) high interfacial contact area between NCM and LPS and (ii) well-percolated ion transport pathway. In conclusion, the core-shell composite particle contributed to the structure of the composite cathode, thus resulting in improved cell performance.

DOI： 10.1016/j.jpowsour.2019.227579

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

© 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited. Composite quasi-solid electrolytes composed of Li3PS4 (LPS) glass and a carboxylate ester were prepared via planetary ball milling, and the influence of the molecular structure of the carboxylate esters on their ion-conduction was investigated. The results revealed that filling the voids in the solid electrolyte with a bulky carboxylate ester, which hardly reacted with the LPS glass, effectively maintains the high ionic conductivity of the LPS glass even when the relative density of LPS decreases. The use of this composite quasi-solid electrolyte is an effective approach to maintain the ion-conduction in not only an electrolyte separator layer but also a composite electrode layer in an all-solid-state battery.

DOI： 10.1149/1945-7111/abacec

Kind of work：Joint Work  

Kind of work：Joint Work  

All-solid-state Na–S secondary batteries that use sodium and sulfur, both available in abundance, are the most attractive next-generation batteries. In this study, two types of amorphous MoS3 (a-MoS3) were prepared as electrode active materials for use in all-solid-state sodium secondary batteries using the thermal decomposition (TD) of (NH4)2MoS4 and mechanochemical (MC) processes, denoted a-MoS3 (TD) and a-MoS3 (MC), respectively. X-ray diffraction, thermogravimetric-differential thermal analysis, and X-ray photoelectron spectroscopy (XPS) analyses revealed that a-MoS3 (TD) and a-MoS3 (MC) had different local structures. The a-MoS3 (TD) and a-MoS3 (MC) electrodes showed high reversible capacities of 310 mAh g−1 and 260 mAh g−1, respectively, for five cycles in all-solid-state sodium secondary batteries. XPS analysis of the discharge–charge products suggested that the dissociation and formation of disulfide bonds occurred during the discharge–charge reaction. The results show that a-MoS3 is a promising active electrode material for all-solid-state sodium batteries.

DOI： 10.1016/j.powera.2021.100061

J-GLOBAL

In order to find suitable solid electrolytes for all-solid-state sodium batteries, sulfide electrolytes composed of tetrahedral structural units such as PS4, SnS4 and SbS4 have been widely studied. In this paper, the ionic conductivities of Na3BS3ortho-thioborate electrolytes with triangular BS3 units are firstly reported. Na3BS3 glass was prepared via a mechanochemical process from crystalline Na3BS3 (monoclinic phase). The crystalline Na3BS3 was pre-synthesized from a mixture of Na2S, B, and S due to the instability of the B2S3 compound. A new metastable phase of trigonal Na3BS3 was precipitated as the primary phase by crystallization of the Na3BS3 glass. The prepared glass-ceramic electrolyte showed a higher ionic conductivity than the monoclinic Na3BS3 phase. The Na3BS3 glass showed the highest conductivity of 1.1 × 10-5 S cm-1, which was higher than that of conventional Na3PS4 glass. Futhermore, the Na3BS3 glass showed a superior formability and electrochemical stability to Na15Sn4 negative electrode. An all-solid-state cell with the Na3BS3 glass as an electrolyte successfully operated as a secondary battery at 60 °C. It is concluded that the Na3BS3 glass with triangular structural units has appropriate properties as a solid electrolyte for application to all-solid-state sodium batteries. The results of this study extend research on multi-component sulfide electrolytes with triangular BS3 structural units and contribute to the development of solid electrolytes for all-solid-state batteries. This journal is

DOI： 10.1039/d0ma00777c

J-GLOBAL

Publishing type：Research paper (scientific journal)  

© The Royal Society of Chemistry. We report a route for the synthesis of Na3SbS4-Na2WS4 superionic conductors from aqueous solution. Na3SbS4-Na2WS4 has the highest high sodium-ion conductivity (4.28 mS cm-1 at 25 °C) of reported sulfide-based solid electrolytes prepared via liquid-phase methods. The antimony in Na3SbS4 is replaced by tungsten in a higher valence state, which is charge-compensated by sodium vacancies in the form Na3-xSb1-xWxS4. Introducing sodium vacancies while maintaining the 3D conduction pathways increases the pre-exponential factor in the Arrhenius plots of ionic conduction. The development of a facile synthetic protocol, as well as the high ionic conductivity and excellent chemical stability of Na3SbS4-Na2WS4 in the presence of water, is a major step towards the realization of all-solid-state sodium batteries.

DOI： 10.1039/c9ta02246e

Publishing type：Research paper (scientific journal)  

Solid electrolytes are key materials to enable solid-state rechargeable batteries, a promising technology that could address the safety and energy density issues. Here, we report a sulfide sodium-ion conductor, Na2.88Sb0.88W0.12S4, with conductivity superior to that of the benchmark electrolyte, Li10GeP2S12. Partial substitution of antimony in Na3SbS4 with tungsten introduces sodium vacancies and tetragonal to cubic phase transition, giving rise to the highest room-temperature conductivity of 32 mS cm−1 for a sintered body, Na2.88Sb0.88W0.12S4. Moreover, this sulfide possesses additional advantages including stability against humid atmosphere and densification at much lower sintering temperatures than those (>1000 °C) of typical oxide sodium-ion conductors. The discovery of the fast sodium-ion conductors boosts the ongoing research for solid-state rechargeable battery technology with high safety, cost-effectiveness, large energy and power densities.

DOI： 10.1038/s41467-019-13178-2

PubMed

Other URL： http://www.nature.com/articles/s41467-019-13178-2

Authorship：Lead author   Publishing type：Research paper (scientific journal)  

© 2019 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim All-solid-state lithium–sulfur batteries have attracted much attention because of their large capacity and long life. However, their rate capability is not sufficiently high, prompting a great demand for improvement. Herein, a sulfur-based composite electrode is fabricated for the high-rate operation of all-solid-state lithium–sulfur batteries. The electrode is made of a carbon material having a large number of “interconnected mesopores” with a diameter of 5 nm. The highly mesoporous structure is conducive to electrode reactions and the formation of conduction pathways. Consequently, the rate capability of the composite electrode is drastically improved compared with that of an electrode made of conventional conducting nanocarbon. The all-solid-state lithium–sulfur battery with this composite electrode shows a high capacity of 1100 mA h g −1 per sulfur after 400 cycles at a high current density of 1.3 mA cm −2 at 25 °C. These findings are expected to contribute toward the development of practical all-solid-state lithium–sulfur batteries.

DOI： 10.1002/ente.201900077

Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. Al-doped Li7La3Zr2O12 (LLZ) sintered ceramics with two grain sizes were prepared to investigate the relationship between their microstructure and conducting properties. The X-ray diffraction patterns showed no difference in the peak shift and intensity between the two prepared LLZ ceramics, suggesting that their bulk conductivities were almost the same. Scanning electron microscopy and energy dispersive X-ray spectrometry were used to observe their microstructure. Neither of the ceramics had an obvious impurity phase along grain boundaries. One of LLZ (LLZ_LG) had a larger grain size of 5–20 μm and showed intergranular fracture. The other LLZ (LLZ_SG) had a smaller grain size of primarily &lt;1 μm and showed intragranular fracture. LLZ_LG showed a total conductivity of 3.6 × 10−4 S cm−1 and an activation energy, Ea, for conduction of 32 kJ mol−1, while LLZ_SG showed conductivity of 4.4 × 10−4 S cm−1 and Ea of 26 kJ mol−1. It is noteworthy that the grain boundary composed of small grains showed lower grain boundary resistance than that composed of large grains. As a result, it is clarified that LLZ ceramics with higher ion-conductivity and lower Ea can be prepared by suppressing grain growth.

DOI： 10.1016/j.ssi.2019.115047

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. Novel nitride glass electrolyte Li3BN2 was prepared from Li3N and BN via a mechanochemical process using planetary ball milling. Raman and X-ray photoelectron spectroscopies revealed that the glass was composed of Li+ and BN23− ions. The Li3BN2 glass exhibited good ductility, and the powder-compressed pellet showed a relative density of 84%. The hot-pressed pellet of the Li3BN2 glass showed a conductivity of 1.3 × 10−5 S cm−1 at 25 °C, which is much higher than that of oxide-based glass electrolytes such as Li3BO3 glass and LiPON thin films. Moreover, Young&#039;s modulus of the Li3BN2 glass was 51.1 GPa, which is an intermediate value between sulfides and oxides. The Li symmetric cell using the Li3BN2 glass electrolyte was cycled stably at 100 °C without short-circuiting. Nitride glassy materials are promising electrolytes for all-solid-state batteries because of their high conductivity, good mechanical properties, and electrochemical stability.

DOI： 10.1016/j.ssi.2019.05.020

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

Drastically higher conductivity was found in the amorphous lithium-ion conducting nitride relative to the crystal. The amorphous Li2CN2 prepared by a mechanochemical process has the conductivity of 1.1 © 1016 S cm11 at 25°C, which is more than 1000 times higher than that of the crystalline form. The nitride has a better deformability compared to Li3BO3 oxide glass.

DOI： 10.2109/jcersj2.19077

Publishing type：Research paper (scientific journal)  

Mechanochemical (MC) process is one of the most effective methods to produce amorphous and cation disordered electrode active materials. We individually synthesized amorphous and cation disordered cubic rocksalt Na2TiS3 by controlling the preparation conditions of the MC process. Cubic rocksalt Na2TiS3 and ordered monoclinic Na2TiS3 were also obtained via the heat treatment of amorphous Na2TiS3. The all-solid-state cell with cubic rocksalt Na2TiS3 showed a high reversible capacity of 270 mAh g11, which corresponds to the theoretical capacity of Na2TiS3. The cell maintained the capacity for more than 30 cycles, indicating that the active materials can endure long operation life. The MC methods for transition metal sulfides and the search for ordered monoclinic polymorphs are necessary for the pursuit of novel electrode materials.

DOI： 10.2109/jcersj2.19086

Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. All-solid-state sodium batteries with sulfide-based solid electrolytes are attracting attention as next-generation energy storage systems to replace Li-ion batteries, owing to their improved safety and the abundant sodium resources. Na 3 PS 4 -based materials, which have relatively high conductivities and favorable mechanical properties, make promising Na-ion solid electrolytes for realizing all-solid-state sodium batteries. However, it is essential to establish a further simple and effective protocol for manufacturing such solid electrolytes and composite electrodes. In this study, Na 3-x PS 4-x Cl x (x = 0, 0.0625) was prepared by a liquid-phase (suspension) process from Na 2 S, P 2 S 5 , and NaCl using 1,2-dimethoxyethane as a reaction media. Na 3 PS 4 heated at 400 °C and Na 2.9375 PS 3.9375 Cl 0.0625 heated at 480 °C exhibited Na-ion conductivities of 2.6 × 10 −4 and 4.3 × 10 −4 S cm −1 at 25 °C, respectively. A homogenous composite electrode was prepared with TiS 2 active material and Na 3 PS 4 solid electrolyte via the simple liquid-phase process, resulting in large contact areas between electrode and electrolyte particles. The electrode obtained by liquid-phase provided an all-solid-state cell with higher reversible capacity of 161 mAh g −1 than a conventional mechanically mixed electrode. Suspension syntheses of Na 3-x PS 4-x Cl x are useful for the simple production of solid electrolytes and are highly applicable to all-solid-state sodium batteries.

DOI： 10.1016/j.jpowsour.2019.04.069

Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. Highly safe all-solid-state batteries are constructed using oxide electrolytes because of their high chemical and electrochemical stabilities. Previously, we have developed various Li 3 BO 3 -based glass-ceramic electrolytes with high ductility and conductivity. In this study, we focus on the importance of electrode/electrolyte interfacial contacts in all-solid-state batteries. All-oxide solid-state cells (Li-In/LiNi 1/3 Mn 1/3 Co 1/3 O 2 ) with Li 3 BO 3 -based glass-ceramic electrolytes, are fabricated simply by pressing at room temperature. Furthermore, the effects of the ductility and ionic conductivity of glass-ceramic electrolytes on the charge-discharge properties of all-solid-state batteries are investigated. The 33Li 3 BO 3 ·33Li 2 SO 4 ·33Li 2 CO 3 (mol%) glass-ceramic electrolyte shows lower ionic conductivity and better ductility than the 90Li 3 BO 3 ·10Li 2 SO 4 electrolyte. The all-solid-state cells using these electrolytes operate as secondary batteries at 100 °C. However, better cycle performance is obtained with cells using the former electrolyte. Formation of well-contacted electrode/electrolyte interfaces when using highly ductile electrolytes leads to enhanced electrochemical performance of bulk-type all-solid-state batteries.

DOI： 10.1016/j.jpowsour.2019.03.083

Kind of work：Joint Work  

Kind of work：Joint Work  

Publishing type：Research paper (scientific journal)  

© 2019 American Chemical Society. All-solid-state batteries (ASSBs) are potentially safe energy storage devices. The 90Li3BO3·10Li2SO4 (mol %) glass-ceramic is one of the promising oxide electrolytes due to its high ductility and ionic conductivity. Utilization of Li metal negative electrode enhances the energy density of ASSBs. Herein, the high electrochemical stability of the 90Li3BO3·10Li2SO4 electrolyte against Li metal negative electrode was demonstrated. The symmetric cells using a dense electrolyte body with relative density of 99% synthesized by the hot-pressing technique showed excellent cycle performance for the Li dissolution and deposition reactions. Finally, the all-solid-state (Li/80LiNi0.5Mn0.3Co0.2O2·20Li2SO4) full cell operated as a secondary battery at 100 °C.

DOI： 10.1021/acsaem.9b00470

Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. Li 3 SbS 4 glass was prepared by a mechanochemical process and a glass-ceramic was prepared by heating the glass above the crystallization temperature. The glass-ceramic had a crystal structure similar to that of γ-Li 3 PS 4 . As indicated by the Raman spectra, both electrolytes contained an SbS 4 unit. The conductivity of the pelletized Li 3 SbS 4 glass was 1.5 × 10 −6 S·cm −1 at 25 °C, which was higher than that of its glass-ceramic. The amount of H 2 S generated from Li 3 SbS 4 glass in humid air was considerably lower than that from the Li 3 PS 4 glass.

DOI： 10.1016/j.ssi.2019.01.017

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Publishing type：Research paper (scientific journal)  

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim All-solid-state batteries attract significant attention owing to their potential to realize an energy storage system with high safety and energy density. In this paper, a mechanochemical synthesis of novel amorphous positive electrode materials of the Ni-rich LiNi 1−x−y Mn x Co y O 2 (NMC)–Li 2 SO 4 system suitable for oxide-type all-solid-state batteries is reported. Through the mechanochemical treatment with Li 2 SO 4 , excellent formabilities of the electrode materials as those of ductile solid electrolytes are obtained. Owing to the deformability of the active material, a good electrode/electrolyte interface is provided simply by pressing at room temperature. In all-oxide solid-state cells using 80NMCs·20Li 2 SO 4 (mol%) positive electrode materials, the cell capacity increases with the Ni content in the NMC. The all-solid-state cell using the 80NMC811·20Li 2 SO 4 positive electrode active material exhibits a high capacity larger than 250 mAh g −1 in a voltage range of 1.6–4.8 V versus Li at 100 °C. Furthermore, bulk-type all-oxide solid-state batteries (Li 4 Ti 5 O 12 /80NMC532·20Li 2 SO 4 (mol%)) successfully function as secondary batteries with excellent cycle performances.

DOI： 10.1002/admi.201802016

Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. All-solid-state cells are safe, and have high energy densities and power densities. Sulfide-based solid electrolytes (SEs) exhibit high ionic conductivities and favorable mechanical properties allowing for the facile preparation of all-solid-state cells via simple mixing and cold-pressing processes. For practical applications, it is necessary to produce SEs and all-solid-state cells more efficiently. Herein, a novel fabrication process for homogeneous composite electrodes used in all-solid-state cells was successfully demonstrated using an infiltration technique. The Li 4 Ti 5 O 12 and carbon nanotube (LTO@CNT) porous electrode was infiltrated with a precursor solution containing an argyrodite Li 6 PS 5 Br SE, and the solvent was removed by drying at 150 °C under vacuum to prepare an infiltrated SE-LTO@CNT electrode. The process without conventional mixing formed an electrochemically active interface with a large contact area and favorable conduction pathways. The all-solid-state cell with the SE-LTO@CNT electrode showed an improved capacity of 163 mAh g −1 compared to those prepared with the dry-mixed electrodes at 25 °C, and the high capacity was maintained for 500 cycles. Moreover, the cell with the SE-LTO@CNT electrode showed a reversible capacity of 100 mAh g −1 or more at 4 C-rate and 100 °C. Thus, the infiltration process is effective for the practical fabrication and application of all-solid-state cells.

DOI： 10.1016/j.jpowsour.2019.01.070

Publishing type：Research paper (scientific journal)  

© 2019 American Chemical Society. For the application of lithium-ion batteries (LiBs) to a large-scale power source for electric vehicles, positive electrode materials with high energy and power densities should be developed. Although Li-excess materials are regarded as high-capacity positive electrodes, there are several issues in the anionic redox reactions, such as oxygen gas evolution and large resistance, which lead to capacity fading and limitation of high-current operation. Here, we report the high-current operation of an electrochemical cell using the Li 2 RuO 3 -Li 2 SO 4 positive electrode in LiBs. The cell using Li 2 Ru 0.8 S 0.2 O 3.2 showed a high capacity of 350 mAh g -1 with an average discharge voltage of 2.9 V vs Li at 25 °C. By introducing an amorphous matrix based on Li 2 SO 4 , a high diffusion coefficient was maintained during the whole charge-discharge process, and low charge-transfer resistance was maintained even at a high oxidation state up to 4.2 V vs Li. As a result, extremely high current operation, such as 40 C rate, was achieved.

DOI： 10.1021/acsaem.8b02163

© 2019, Springer Nature Limited. Solid sulfide electrolytes are key materials in all-solid-state lithium batteries because of their high lithium-ion conductivity and deformability, which enable the lithium-ion path to be connected between the material’s grain boundaries under pressure near room temperature. However, sulfur species are moisture-sensitive and exhibit high vapour pressures; therefore, syntheses of sulfide electrolytes need to be carefully designed. Liquid-phase reactions can be performed at low temperatures in controlled atmospheres, opening up the prospect of scalable processes for the preparation of sulfide electrolytes. Here, we review liquid-phase syntheses for the preparation of sulfide-based solid electrolytes and composites of electrolytes and electrodes, and we compare the charge–discharge performances of the all-solid-state lithium batteries using these components.

DOI： 10.1038/s41570-019-0078-2

Publishing type：Research paper (scientific journal)  

© 2019 American Chemical Society. In sheet-type all-solid-state lithium-ion batteries with the sulfide-based solid electrolyte, composite electrodes consist of active material, solid electrolyte, conductive additive material, and binder. Thus, they form a three-dimensional ionic and electronic conduction pass. In composite electrodes, the reaction inhomogeneity derived from their morphology exerts a remarkable effect on battery performance. In this study, we prepared sheet-type composite electrodes for all-solid-state lithium-ion batteries with the sulfide-based solid electrolyte using different binder materials with different solvents and investigated the reaction distribution within the electrodes using the 2D-imaging X-ray absorption spectroscopy. Thus, we demonstrated that the dominant factor of the reaction distribution formation is the ionic conduction, depending on the structure of the composite electrode, and that the structure is influenced by the combination between the binder and the solvent used in the preparation of the sheet-type composite electrode.

DOI： 10.1021/acs.jpcc.8b09569

Kind of work：Joint Work  

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Publishing type：Research paper (scientific journal)  

© 2019 The Chemical Society of Japan. Amorphous transition metal polysulfides are promising high capacity electrode active materials for sodium secondary batteries. Here we report the superior electrode performance of amorphous Na 2 TiS 3 . Crystalline (c-) and amorphous (a-) Na 2 TiS 3 were prepared by solid phase reaction with heat treatment and mechanochemical reaction, respectively. a-Na 2 TiS 3 showed 10 fold higher ionic conductivity (1.5 © 10 16 S cm 11 ) than that of c-Na 2 TiS 3 . The all-solid-state cells using c-Na 2 TiS 3 and a-Na 2 TiS 3 showed reversible capacities of 110 mAh g 11 and 250 mAh g 11 , respectively. Amorphization of Na 2 TiS 3 is a powerful way to improve electrode performance in all-solid-state sodium secondary batteries.

DOI： 10.1246/cl.180895

Authorship：Lead author  

Copyright © The Japan Institute of Electronics Packaging Mechanochemistry is a study that deals with the interaction between mechanical energy and chemical energy. Mechanochemical reaction is a chemical reaction by mechanical energy. We have synthesized various next-generation battery materials using the mechanochemical method and evaluated their unique properties. In this paper, we review our recent researches on mechanochemical syntheses of sulfide materials as next-generation battery materials.

DOI： 10.4164/sptj.56.452

J-GLOBAL

Publishing type：Research paper (scientific journal)  

© The Author(s) 2019. Published by ECS. Lithium dissolution/deposition behavior of Al-doped Li7La3Zr2O12 (LLZ) was investigated in terms of grain size of LLZ-sintered bodies. One LLZ had smaller grain sizes of primarily less than 1 μm (LLZ_SG), and the other one had larger grain sizes of 5-20 μm (LLZ_LG). The total resistance of a Li symmetric cell using LLZ_SG was smaller than that using LLZ_LG at 100◦C. The cell using LLZ_SG was stably cycled at 100◦C without short-circuiting at a high current density of 1.3 mA cm−2, while the cell using LLZ_LG was stably cycled at current densities below 0.26 mA cm−2. Stronger bonding at grain boundaries for LLZ_SG was expected to contribute to the improvement of cyclability.

DOI： 10.1149/2.0661903jes

Publishing type：Research paper (scientific journal)  

© 2019 The Chemical Society of Japan. A novel Li2NaPS4 crystal was successfully prepared from tetragonal Na3PS4 via Na+/Li+ ion-exchange in an acetonitrile solution of lithium bis(fluorosulfonyl)amide at room temperature. Its crystal structure was analyzed by powder X-ray diffraction. The Li2NaPS4 crystal maintained the basic anion framework of tetragonal Na3PS4 (P421c). The chemical environment of PS43- units in the ion-exchanged product was similar to that in the Li3PS4 crystal. Ion-exchange synthesis is a promising approach to develop novel sulfide-based materials.

DOI： 10.1246/cl.190135

Publishing type：Research paper (scientific journal)  

© 2018 The Royal Society of Chemistry. Sulfide-based solid electrolytes with halide elements are essential components of advanced all-solid-state batteries. Argyrodite crystals are viable candidates as solid electrolytes for realizing all-solid-state batteries. However, a simple and effective route for the synthesis of these solid electrolytes is required. Herein, argyrodite Li 6 PS 5 Br superionic conductors were synthesized from a homogeneous solution by a liquid-phase technique. The Li 6 PS 5 Br solid electrolyte was prepared in a shorter synthesis time of one day using tetrahydrofuran and ethanol as compared with the solid-phase method. More importantly, of all the sulfide-based solid electrolytes prepared by liquid-phase techniques, Li 6 PS 5 Br showed the highest ionic conductivity of 3.1 mS cm -1 at 25 °C. The obtained particle size of 1 μm is suitable for application in all-solid-state cells. Moreover, coating electrode active materials with the solid electrolyte using the precursor solution led to a large contact area between the electrode and electrolyte and improved the cell performance. In addition, infiltrating a porous electrode with the precursor solution of the solid electrolyte is suitable for forming homogeneous composite electrodes to improve the cell performance. The all-solid-state cell using the Li 6 PS 5 Br fine powder with a high conductivity of 1 mS cm -1 or more exhibited a reversible capacity of 150 mA h g -1 . This technique is effective for the industrial production of solid electrolytes and is applicable to all-solid-state batteries.

DOI： 10.1039/c8ta09477b

Publishing type：Research paper (scientific journal)  

© The Electrochemical Society of Japan, All rights reserved. Materials with metastable structures often exhibit high stability up to a certain temperature, despite not being thermodynamically stable. Therefore, it is important to use the excellent physical properties generated by metastable structure. Secondary batteries are an energy device that stores chemical energy by producing thermodynamically metastable materials. Metastable materials can also be directly utilized as the electrode active materials and the solid electrolytes. The rapid quenching and mechanochemical processes are useful to obtain room temperature metastable materials. This review provides an overview of our research progress on glassy and metastable crystalline materials for all-solid-state batteries.

DOI： 10.5796/electrochemistry.19-H0002

Publishing type：Research paper (scientific journal)  

© The Electrochemical Society of Japan, All rights reserved. Na-Sb alloy was synthesized as an advanced negative electrode material for all-solid-state sodium batteries by a mechanochemical process. An all-solid-state symmetric cell using a composite of an Na-Sb alloy and Na3PS4 solid electrolyte operated reversibly with a high reversible capacity of 370 mAh g−1 at room temperature under a current density of 0.064 mA cm−2. The composite electrode showed an effective ionic conductivity of 3.4 × 10−5 S cm−1. The cell also operated at 60°C under the same current density with low polarization compared to room temperature operation. The sodiation process from NaSb to Na3Sb was examined by ex situ X-ray diffraction (XRD) measurements. An all-solid-state half-cell using a TiS2 composite electrode and a Na3Sb composite electrode showed a high reversible capacity of 200 mAh g−1 at room temperature under a constant current density of 0.064 mA cm−2. Na-Sb alloys are a suitable negative electrode material for all-solid-state sodium batteries.

DOI： 10.5796/electrochemistry.19-00014

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© 2020 Elsevier B.V. Mechanical properties and ionic conductivities of solid electrolytes are important factors influencing the performance of all-solid-state batteries. This study investigates composite quasi-solid electrolytes composed of Li2S–P2S5 glass and a phosphate ester, prepared via planetary ball milling, and the relative densities of the powder-compressed pellets, formed using the composite quasi-solid electrolytes. Dense pellets of the Li2S–P2S5 glass electrolyte are obtained via addition of phosphate esters; the relative densities increase from 90.6% to 93.1%, without the ionic conductivities decreasing, upon addition of a small quantity of tris (2, 2, 2-trifluoroethyl) phosphate to the Li3PS4 glass. The addition of small quantities of phosphate esters to sulfide solid electrolytes is effective in improving the formability of these solid electrolytes.

DOI： 10.1016/j.jpowsour.2020.228826

J-GLOBAL

Publishing type：Research paper (scientific journal)  

© 2019 The Royal Society of Chemistry. Liquid-phase synthesis is a useful technique for preparing argyrodite sulfide-based solid electrolytes, and the synthesis conditions such as heat treatment strongly affect the conductivity. Because the understanding of structural changes reveals crucial information about their properties, it is necessary to evaluate this change during heat treatment to determine the factors that affect the conductivity. In this study, X-ray diffraction measurements and transmission electron microscope observations reveal the effects of heat treatment on the crystallinities and ionic conductivities in the synthesis process of argyrodite electrolytes with tetrahydrofuran and ethanol. The amorphous material is in the main phase when heated at low temperatures below 200 °C and exhibits relatively low conductivities of ca. 2 × 10-4 S cm-1 despite precipitation of the argyrodite crystals. As the heat treatment temperature increases, the ratio of argyrodite crystals increases, involving nucleation and grain growth, leading to high conductivities of over 10-3 S cm-1. It is critical to control the ratio of the amorphous and crystal phases to achieve high conductivities in the synthesis of argyrodite electrolytes via liquid-phase processing.

DOI： 10.1039/c9ra00949c

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