Rational material design on high capacity and long-term-cyclability of graphite/Si-based anodes for room temperature all-solid-state batteries

•A graphite/SiOx composite (GSC) with carbon coating is developed for ASSBs.•The GSC, synthesized via mechano-fusion, offers high capacity retention and minimal volume change.•The carbon coating suppresses interfacial reactions with sulfide electrolytes.•This design achieves enhanced electrochemical performance at room temperature. Graphite, a Li intercalation-type host, is considered the most commercially available anode material for secondary batteries. However, major issues such as poor kinetics, low capacity, and interfacial reactivity with sulfide solid electrolytes hinder the introduction of graphite to all-solid-state batteries (ASSBs). Here, we propose a rational material design on graphite/Si-based anodes for high-capacity and long-cycle-life ASSBs. Hetero-aggregates, where (sub-)micron SiOx particles are anchored on the surface of graphite host particles (10–20 µm), are synthesized by a mechano-fusion process. The as-prepared graphite/SiOx composite (GSC) is covered with a carbon layer (∼10 nm) by pitch coating and thermal treatment (C@GSC). As the ASSB (C@GSC | Li6PS5Cl | Li) tested at 25℃ and under 25 MPa, it delivers an initial discharge capacity of 706mAh g−1 and a high capacity retention of 89 % over 200 cycles. Monitoring of swelling behavior shows only 2 % volume change after charge/discharge, leading to good interfacial solid–solid contacts and electrode integrity. We further reveal that the pitch carbon coating can largely suppress the interfacial reaction between the GSC and the Li6PS5Cl. Our design strategy on materials opens up a new possibility for the graphite/Si-based anode for the room-temperature ASSB.