Overcoming Chemo-Mechanical Instability at Silicon-Solid Electrolyte Interfaces in Solid-State Batteries

Silicon is the preferred choice for lithium-ion battery anodes due to its high theoretical capacity and low lithiation potential. However, achieving high areal capacity with silicon anodes in solid-state batteries (SSBs) is challenging because of poor electronic and ionic conductivity, as well as chemo-mechanical instability at the silicon|solid electrolyte (Si|SE) interfaces. Here, we propose fabricating and testing composite anodes made of nanosized Si powder embedded in partially fluorinated graphene (Si-FG) and Li₆PS₅Cl (LPSCl) sulfide SE. X-ray photoelectron spectroscopy revealed that the in situ formation of LiF-rich SEI can protect against SE decomposition at the interface in the Si-FG-LPSCl composite anode. FIB-SEM and EIS analyses also indicate a stable structure and low interfacial resistance after one cycle for a composite anode containing FG. The incorporation of partially FG enhances both electronic (through heterojunction formation with Si) and ionic conductivities, buffers significant volume changes, and ensures chemo-mechanical stability in the composite anode. The Si-FG-LPSCl composite anode in SSBs delivered high discharge/charge capacities of 3499/2994 mAh g^-1 at a C-rate of C/20 and an ICE of 85.6% in a half cell. This work provides valuable insights for advancing high-capacity Si composite anodes to meet future energy needs.