A viscoelastic oxyhalide catholyte for 4.5 V all-solid-state batteries under low stack pressures

Deployment of all-solid-state lithium batteries is hindered by high stack pressure (>200 MPa) and interfacial chemo-mechanical instability. Herein, we propose a moderate-temperature (180 °C) sintering strategy based on a viscoelastic oxyhalide catholyte LiAlCl2.5O0.75 (LACO) to construct the composite cathode capable of operating under low stack pressure (10 MPa) and a cutoff voltage of 4.5 V. Benefiting from the polymer-like thermoplasticity and viscoelasticity, the LACO exhibits an ionic conductivity of 1.52 mS cm−1 at 30 °C without external pressure and enables conformal and homogeneous contact throughout the composite cathode. Moreover, the thermally driven co-sintering process triggers the gradient cross-diffusion of Al and Cl from LACO into the subsurface of the single-crystal LiNi0.8Co0.1Mn0.1O2 (NCM811). The localized elemental co-doping significantly mitigates Li+/Ni2+ antisite defects and the H2−H3 phase transition. Simultaneously, it constructs a robust in situ passivation shield on the cathode surface, suppressing the continuous oxidative degradation pathways of the electrolyte at 4.5 V. With enhanced mechanical and electrochemical stability, the NCM811/LACO composite cathodes achieve 800 cycles at 4.3 V and 275 cycles at 4.5 V with 80% capacity retention under a low stack pressure of 10 MPa.