Decoding two-stage degradation pathways in sulfide all-solid-state batteries with Ni-rich cathodes

초록

While sulfide-electrolyte-based all-solid-state lithium-ion batteries (ASSLiBs) are highly safe and offer high ionic conductivities, their practical deployment with Ni-rich layered cathodes is limited by issues associated with interfacial reactivity and the structural instability of the cathode, especially when cycled rapidly. This study systematically investigated C-rate-dependent degradation in torque-type cells containing a Li6PS5Cl (LPSCl) solid electrolyte and an NCM811 cathode. Electrochemically, all cells showed two-stage fading behavior: rapid capacity loss during the first 10 cycles followed by slower long-term fading. The initial capacity declined and degradation accelerated markedly with increasing C-rate, with lower capacity retentions observed after 100 cycles. Chemical analysis confirmed that LPSCl oxidatively decomposed at the cathode interface over 10 cycles of use to produce sulfur-rich species, with oxygen-containing sulfite, sulfate, and phosphate species progressively formed during extended cycling, consistent with the participation of oxygen from the cathode during reconstruction. Direct visualization of the surface-initiated reconstruction of NCM811 revealed spinel-like domains after 10 cycles and rocksalt-like surface layers after 100 cycles, with larger reconstructed regions formed at higher C-rates. Taken together, these results reveal a transition in the dominant degradation mode: early-stage capacity loss is governed by interfacial decomposition and contact degradation, whereas loss during prolonged cycling is increasingly controlled by cathode structural reconstruction, which limits Li-ion transport and promotes irreversible capacity loss. These findings highlight the need for integrated strategies that stabilize the interface and cathode, including the use of robust coatings and structural tuning that enable high-rate operation of sulfide-based ASSLiBs with Ni-rich cathode active materials.

키워드