Investigating the Local Structure of Deuterium-exchanged LiNiO2 to Study Degradation in Li-ion Batteries

Li-ion batteries are becoming an ever more important technology in modern society and crucial in the widespread adoption of renewal energy, with a drive for electrode materials offering greater energy density and prolonged lifetime. Increasing the nickel-content of the commercially relevant cathode material lithium nickel manganese cobalt oxide (NMC) offers higher practical gravimetric capacity and operating voltages, culminating in lithium nickel oxide, LiNiO2 (LNO), the end member of the family. However, its successful application is challenged by the tendency to form unwanted surface species which are detrimental to electrode manufacturing, cell performance, and battery safety. They are therefore typically washed with water or alcohols, but this washing is accompanied by an unwanted lithium/proton cation exchange, yielding a partially protonated LNO (HxLi1-xNiO2). This decreases the lithium inventory, and results in resistance build-up deteriorating the cycle life. It is therefore critical to determine the location, the local environment, and the mobility of protons within the layered structure in order to develop strategies to mitigate the cathode degradation, maximise energy density, and extend lifetime. This study aims to identify the characteristic hydrogen sites by comparing a series of samples exhibiting bulk Li+/H+ exchange up to ~50%.