Improved Capacity Retention of Lithium Ion Batteries Under Fast Charge Via Metal-Coated Graphite Electrodes

Abstract

The need to develop Li-ion batteries which can be charged in approximately 10 minutes is critical for the widespread implementation of electric vehicles. Fast charging capability of current state of the art Li-ion batteries is currently limited by the occurrence of Li plating at the graphite anode, which limits cycle life and negatively impacts safety. To overcome this challenge, we deliberately modify the interface of graphite electrodes with nanoscale layers of Cu and Ni to increase the overpotential for Li deposition and suppress Li plating under high rate charge conditions.1, 2 Due to their nanoscale, the deposited surface films have minimal impact on cell level theoretical energy density. Interfacial properties of the anodes are thoroughly characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and spatially resolved mapping X-ray absorption near edge structure (XANES) spectroscopy. Li plating is quantified by X-ray diffraction and associated electrochemistry measurements revealing that the surface treatment effectively reduces the quantity of plated Li metal by ~50% compared to untreated electrodes. Extended galvanostatic cycling of control and metal-coated electrodes in graphite/NMC622 pouch cells show that the metal films improve capacity retention under fast charge rates. The effect of metal film loading on capacity retention improvement has also been quantified. The findings establish that with rational design of an electrode interface, the overpotential for Li deposition can be modulated, providing a new conceptual approach for reducing Li plating on graphite anodes under fast charge conditions.