Protons Inside the LiCoO2 Electrode Largely Increase Electrolyte-Electrode Interface Resistance in All-Solid-State Li Batteries

Formation of an electrolyte-electrode interface that allows smooth Li-ion transport is essential for the further development of all-solid -state Li batteries. Water vapor is recognized as one critical origin of increased resistance at the electrolyte-electrode interface. However, the detailed mechanism of the degradation remains unclarified. This study uses a thin-film battery with a LiCoO2 electrode to investigate how protons at the interface contribute to the degradation. Protons were introduced to the LiCoO2 by exposing the surface to water vapor. Electrochemical, composi-tional, and structural investigations reveal that the protons induce the mixing of Li and Co during the first charging process. The mixing induces the formation of low-temperature-phase LiCoO2; this layer acts as an interphase layer that degrades battery performance. Understanding these interfacial phenomena contributes to increasing the power density of all-solid-state Li batteries.

Automated summary

The formation of an electrolyte-electrode interface that allows smooth Li-ion transport is crucial for the development of all-solid-state Li batteries. Water vapor is identified as a critical factor causing increased resistance at the interface, but the specific degradation mechanism remains unclear. This study investigates the contribution of protons to the degradation by introducing them to the LiCoO2 electrode through exposure to water vapor. Electrochemical, compositional, and structural analyses reveal that protons induce the mixing of Li and Co, leading to the formation of a low-temperature-phase LiCoO2 interphase layer that deteriorates battery performance. Understanding these interfacial phenomena enhances the power density of all-solid-state Li batteries.