Ion-exchangeable functional binders and separator for high temperature performance of Li_1.1Mn_1.86Mg_0.04O₄ spinel electrodes in lithium ion batteries

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, LiNi_1/3Mn_1/3Co _1/3O₂ and LiNi_0.5Co_0.2Mn _0.3O₂. However, LiMn₂O₄ spinel electrodes severely degrade at high temperature due to Mn dissolution. Also, the dissolved Mn²⁺ ions causes self-discharge where reduction of Mn ²⁺ 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 LiMn₂O ₄ 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.