A mechanistic investigation of the Li 10 GeP 2 S 12 |LiNi 1-x-y Co x Mn y O 2 interface stability in all-solid-state lithium batteries

All-solid-state batteries are intensively investigated, although their performance is not yet satisfactory for large-scale applications. In this context, the combination of Li 10 GeP 2 S 12 solid electrolyte and LiNi 1-x-y Co x Mn y O 2 positive electrode active materials is considered promising despite the yet unsatisfactory battery performance induced by the thermodynamically unstable electrode|electrolyte interface. Here, we report electrochemical and spectrometric studies to monitor the interface evolution during cycling and understand the reactivity and degradation kinetics. We found that the Wagner-type model for diffusion-controlled reactions describes the degradation kinetics very well, suggesting that electronic transport limits the growth of the degradation layer formed at the electrode|electrolyte interface. Furthermore, we demonstrate that the rate of interfacial degradation increases with the state of charge and the presence of two oxidation mechanisms at medium (3.7 V vs . Li + /Li < E < 4.2 V vs . Li + /Li) and high ( E ≥ 4.2 V vs . Li + /Li) potentials. A high state of charge (>80%) triggers the structural instability and oxygen release at the positive electrode and leads to more severe degradation.