Ion-Exchangeable Functional Binders and Separator for High Temperature Performance of Li1.1Mn1.86Mg0.04O4 Spinel Electrodes in Lithium Ion Batteries

Abstract

Since LiMn2O4 spinel materials are inexpensive, environmentally-friendly, and safe, they are considered a promising cathode candidate for lithium ion batteries in EVs to replace commercialized materials such as LiCoO2, LiNi1/3Mn1/3Co1/3O2 and LiNi0.5Co0.2Mn0.3O2. However, LiMn2O4 spinel electrodes severely degrade at high temperature due to Mn dissolution. Also, the dissolved Mn2+ ions causes self-discharge where reduction of Mn2+ ions into Mn metals occurs on a graphite anode surface accompanied by oxidation of lithiated graphite at a charged state, and this results in severe capacity fading at high temperature. In this study, ion-exchangeable binders and a separator having functional groups of sodium carboxylate or sulfonate are, for the first time, examined to solve the Mn dissolution problem of LiMn2O4 spinel materials at high temperature. Ion exchange between Na+ ions of the functional groups of the binders and the separator and dissolved Mn2+ ions of the LiMn2O4 electrodes inhibits self-discharge, resulting in improved cycle performance. This result is supported by the IR spectra of the binders, an ICP analysis of the electrolytes, and ex situ XRD patterns of lithiated graphite electrodes.