Chemo-mechanical failure of solid composite cathodes accelerated by high-strain anodes in all-solid-state batteries

Large volume changes in Li-based anodes during repeated charge-discharge cycling, which can exert additional mechanical stresses on cell components, remain a significant bottleneck for realizing all-solid-state batteries (ASSBs). While a few studies have reported the mechanical deformation of solid electrolyte layers induced by the volume changes in anodes, the possible degradation of composite cathodes has been largely overlooked. Herein, we present a comparative experimental-simulation study of sulfide-based ASSBs assembled with high-strain (Li-In) and zero-strain (Li4Ti5O12 (LTO)) anodes to understand the impact of anode volume changes on the chemo-mechanical degradation of composite cathodes. The Li-In cell suffers from severe capacity loss after ∼120 cycles, whereas the LTO cell shows a capacity retention as high as 76 % over 200 cycles. In-depth chemical and microstructural analyses, coupled with impedance decoupling and mechanical simulations, reveal that the combination of the cathode volume changes and the high-strain Li-In anode perturbs the structural integrity of the LiNi0.88Co0.09Al0.03O2 (NCA) composite cathode and facilitates "dynamic" contacts among the cathode constituents upon repeated cycling. This leads to enhanced parasitic interfacial reactions, as evidenced by the increased amount of resistive phases in the cathode. The resulting chemically/electrochemically heterogeneous interfaces between the NCA and Li6PS5Cl lead to accelerated cracking of the NCA aggregates in the presence of anode-induced stresses. This study highlights the accelerated degradation of composite cathodes driven by high-strain anodes and provides insights into the design of ASSBs with long cycle lifetimes.