Influence of sintering temperature on the performance of garnet-based all-solid-state Li-metal batteries

All-solid-state Li-metal batteries (ASSLMBs) based on Li 7 La 3 Zr 2 O 7 (LLZO) solid electrolytes (SEs) are promising candidates for next-generation energy storage devices. Although the composite cathode obtained by sintering well-mixed LiCoO 2 (LCO) and LLZO at high temperature can overcome the problem of low ionic conductivity within the cathode, the capacity and cycling stability of such LLZO-based ASSLMBs are still not satisfactory. Systematically investigating the impact of sintering conditions on ASSLMB helps identify limiting factors and guides further optimization. Herein, we investigated the influence of sintering temperature on the phase composition, microstructure and electrochemical performance of LLZO-based ASSLMBs. It was found that low sintering temperature leads to a loose microstructure within the composite cathode, resulting in high impedance, low LCO utilization and rapid capacity degradation. Increasing the sintering temperature results in a denser composite cathode, thereby reducing impedance and improving cycling stability. Meanwhile, side reactions within the composite cathode become severer, lowering the initial Coulombic Efficiency (CE). Continuously increasing the sintering temperature ultimately leads to early battery failure, likely due to excessive stress in the overly dense cathode. Overall, our study shows that sintering temperature has multiple influences on the performance of LLZO-based ASSLMBs. Further performance optimization requires balancing trade-offs among multiple limiting factors. • LCO/LLZO composite cathode was co-sintered onto LLZO to build ASSLMB. • < 895 °C, loose cathode structure, high impedance, fast capacity degradation. • Higher sintering temperature, denser microstructure but severer side reactions. • ≥ 995 °C, early battery failure, likely due to excessive stress. • Side reaction byproduct Li-La-Co-O was identified by Raman-EDX-mapping and XRD.