Controlling the Surface Chemistry of Cathode Materials for High Energy Rechargeable Batteries

Abstract

Chemical evolution and structural transformations at the surface of an electrode material influence greatly the key performance metrics of lithium batteries, including energy density, power capability, safety and cycle life. This presentation will discuss how we bridge the design principles of surface chemistry in electrode materials with advanced characterization tools, in pursuit of safer and durable lithium batteries. A high-throughput analytical method, based on synchrotron X-ray spectroscopy and transmission electron microscopy, is developed to investigate the surface phase irreversibility of lithium ion battery materials, a phenomenon that has been widely observed yet poorly understood. It is found that, in layered cathode materials, surface reconstruction from a layered to a rock-salt structure is commonly observed under a variety of battery operating conditions, particularly in high energy Ni-rich NMC compositions. This phenomenon, together with electrolyte decomposition and formation of a cathode electrolyte interphase, result in poor high-voltage cycling performance, impeding attempts to improve the energy density by widening the potential window at which these electrodes operate. Subsequently, we propose three methods to improve the surface stability of cathode materials, including selective surface metal segregation, surface coating and electrolyte formulation. This presentation will demonstrate the great importance of controlling surface chemistry of cathode materials for the successful development of high-energy lithium batteries.