PNNL

Abstract

It is classically well perceived that cathode-air interfacial reaction, often instantaneous and thermodynamic non-equilibrium, will lead to the formation of an interfacial layer, which subsequently, and often vitally, controls the behaviour and performance of the batteries. However, understanding of the nature of the cathode-air interfacial reaction remains elusive. Here, using atomic-resolution, time-resolved in-situ environmental transmission electron microscopy and density functional theory calculation, we reveal for the first time that the cathode-air interfacial reaction is an element selective reaction, featuring Li+-water interaction driven Li ion de-intercalation and subsequent reaction with water vapour, rather than a direct surface chemical reaction as perceived previously. The surface reaction layer shows a critical thickness beyond which the de-intercalation is arrested, a common behaviour of element selective reaction induced surface passivation. Remarkably, the ultrathin passivation layer can repair the local breakdowns, a feature of self-healing passivation. We discover that the Li+-water interactions driven lithium ion de-intercalation shows strong dependence on the chemical composition and the intrinsic surface structure of the cathode, demonstrating that tailoring of the surface structure can lead to the controlling of the interfacial reaction. The present work provides fundamental guideline for tailoring surface passivation of cathode toward long shelf-life and stable cycling of rechargeable batteries.