Trigger of the Highly Resistive Layer Formation at the Cathode-Electrolyte Interface in All-Solid-State Lithium Batteries

Interfacial materials design is critical in the development of all-solid-state lithium batteries. We conduct a series of analyses of the highly resistive layer formation process at the interface of a layered cathode: LiCoO2 and a garnet-type solid-state electrolyte: Li6.4La3Zr1.4Ta0.6O12, during the co-sintering process. The reaction between a delithiated LixCoO2 and Li6.4La3Zr1.4Ta0.6O12 starts at 60 °C. The lithium chemical potential gap triggers the lithium migration from the garnet-type solid-state electrolyte to the LixCoO2 below 200 °C. The lithium-extracted garnet decomposes at around 200 °C, and the decomposition completes at 500 °C. Since no transition metal interdiffusion occurs below 500 °C, the reaction product is the decomposed lithium-deficient garnet phase. The present work offers that the lithium migration is the first step of highly resistive layer formation, resulting in the decomposition of the lithium-deficient garnet phase.