Resynthesis of Ni-rich Li[Ni0.9Co0.05Mn0.05]O2 in simulated Li-ion battery leachate after saline discharge

Abstract

A discharge step is a crucial process to avoid any danger of explosion from residual electricity inside spent Li-ion batteries (LIBs). Saline discharge using a NaCl solution has been widely used due to its low energy cost and high discharge efficiency. Therefore, residual NaCl impurities from the saline discharge can be flowed into successive LIB recycling processes and their impacts need to be examined on the structural characterization and electrochemical performance of resynthesized cathode active materials. The state-of-the-art Ni-rich Li[Ni0.9Co0.05Mn0.05]O2 (NCM955) is resynthesized by a coprecipitation reaction in simulated LIB leachate after the saline discharge. The impurity levels of Na and Cl in resynthesized precursors significantly decrease after washing 1 time and almost unchanged up to 6 time washing. Whereas the electrochemical performance of unwashed resynthesized NCM955 is inferior to pristine NCM955, residual NaCl after the sufficient washing enhances discharge capacity, cyclability, and rate capability. In particular, the cycling performance is improved significantly due to strong transition metal-Cl bonds, suppressed Ni dissolution, and a less degree of phase transition to rock-salt and spinel phases. While sufficient washing is necessary in the resynthesis of cathode active materials from spent LIBs undergoing the saline discharge, residual NaCl would be beneficial to the electrochemical performance of resynthesized cathode active materials.