Cosintering the Anode Active Material with Li ₇ La ₃ Zr ₂ O ₁₂ Solid Electrolyte for the All-Solid-State Battery: How to Predict the Interfacial Reaction at Elevated Temperatures

Cosintered-type all-solid-state batteries composed of Li7La3Zr2O12 (LLZ) have garnered significant attention as next-generation batteries that offer both high energy density and long cycle life. However, achieving low-resistance interfaces through cosintering of electrode materials, particularly between the anode active material and LLZ, remains a big challenge due to the formation of reaction phases caused by interdiffusion during high-temperature sintering. In this study, we demonstrated the lithium concentration within the materials (CLi: mol/cm3) as a key factor for predicting the reactivity between the anode active material and LLZ during high-temperature sintering. Various kinds of anode active materials with different CLi values were mixed with LLZ, and the reactivity during sintering at 850 °C was carefully investigated. XRD results show that interfacial reaction proceeds between LLZ and low CLi materials due to the occurrence of Li loss in LLZ. Contrarily, Li2SnO3, Li2TiO3, and Li3SbO4 in the high CLi group (larger than that of LLZ) achieve interaction suppression against the LLZ electrolyte during high-temperature sintering. However, lattice parameter characterization and TEM images reveal that interdiffusion and side reactions occurred at the interface layer in the composite LLZ/high CLi material. Densified composite LLZTBO–Li2SnO3 (relative density ∼ 89%) and LLZTBO–Li2TiO3 pellets (∼95%) were successfully obtained under 900 °C sintering for 15 h. Charge–discharge tests using the half-cell assembled with the cosintered composite anode and liquid electrolyte reveal the superior capacity of 550 mAh/g with nearly 92% Coulombic efficiency for the LLZTBO–Li2SnO3 cosintered anode. The approach reported herein has the potential to rapidly screen possible cosintered electrodes for garnet-type solid-state electrolytes and achieve cosintered-type all-solid-state batteries with high energy density.