A Li₁₀GeP₂S₁₂-type lithium-ion conductor Li₁₀P₃S₁₂Br was investigated as a potential solid electrolyte for composite anodes in all-solid-state lithium-ion batteries. Cyclic voltammetry measurements using an Au/Li₁₀P₃S₁₂Br/Li cell revealed that Li₁₀P₃S₁₂Br possesses a sufficiently wide electrochemical window, making it suitable for anode reactions at low potentials. Spherical graphite-Li₁₀P₃S₁₂Br composite anodes, fabricated via rotary mixing, exhibited lithium (de)intercalation activity, demonstrating the feasibility of Li₁₀P₃S₁₂Br as an electrolyte for all-solid-state battery anodes. Composite anodes with a higher proportion of Li₁₀P₃S₁₂Br relative to graphite exhibited improved cycle retention of charge-discharge capacities. A composite comprising graphite (d₅₀: 8 µm) and Li₁₀P₃S₁₂Br (d₅₀: 0.3 µm) in a 20:80 wt.% ratio achieved a discharge capacity of 365 mAh g⁻¹ at the 30th cycle. In contrast, the 50:50 wt.% composite exhibited a notable decrease in lithium intercalation capacity in the stage 2 (LiC₁₂) and stage 1 (LiC₆) regions. These results suggest that reducing the lithium diffusion distance within graphite particles is crucial for enhancing the intercalation properties of graphite/Li₁₀P₃S₁₂Br composite anodes.

Li₁₀GeP₂S₁₂ solid electrolytes, which exhibit ionic conductivity comparable to that of organic electrolytes, have attracted attention. An excess sulfur solution method for short-time synthesis of Li₁₀GeP₂S₁₂ has been proposed, and it has been revealed that the heat treatment process using a titanium boat improves ionic conductivity compared to other combustion boats, such as quartz boats. To elucidate the mechanism, analysis including X-ray diffraction and Raman spectroscopy were conducted, and they revealed the formation of lattice distortion related to the enhanced ionic conductivity. Furthermore, applying a Ge-rich composition precursor successfully achieved the liquid-phase synthesis of Li₁₀GeP₂S₁₂ solid electrolyte with high ionic conductivity.

A model cathode interface for sulfide all-solid-state lithium-ion batteries consisting of a LiCoO₂(104) epitaxial film, LiNbO₃ buffer layer, and Li₃PS₄ film was fabricated using physical vapor deposition. In situ thin-film X-ray diffraction were applied to observe the crystal structure changes in the bulk and surface regions of LiCoO₂ during the initial lithium (de)intercalation. The Li₃PS₄/LiNbO₃/LiCoO₂ interface exhibited an irreversible capacity during the first charge-discharge cycle, followed by reversible lithium (de)intercalation in the second cycle. The bulk and surface structures of LiCoO₂ showed reversible structural changes during charging and discharging without significant degradation, suggesting that the initial irreversible capacity was due to the oxidation side reactions in the LiNbO₃ and/or Li₃PS₄ layers. The crystal structure of the LiCoO₂ surface differs from that of the bulk region and undergoes greater structural change than the bulk region. These results indicate that the surface structure of LiCoO₂ depends on structural changes at the electrolyte-side interface, where side reactions occur. Direct observation of the crystal structure changes is crucial for achieving a deeper understanding of the reactions occurring at the oxide cathode/sulfide electrolyte interface.