Improved Performance of LiNi_0.5Mn_1.5O₄Cathodes with Electrolytes Containing Dimethylmethylphosphonate (DMMP)

The cycling performance of Li/LiNi 0.5 Mn 1.5 O 4 cells with 1.0 M LiPF 6 in ethylene carbonate (EC)/ethyl methyl carbonate (EMC) (3:7) with and without added dimethyl methylphosphonate (DMMP) (0.5–1.0%) was investigated. Addition of DMMP resulted in improved capacity retention during cycling to high voltage (4.9 V vs Li). Ex-situ surface analysis of LiNi 0.5 Mn 1.5 O 4 electrodes after cycling via Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Infrared (IR) spectroscopy suggest that addition of DMMP inhibits electrolyte decomposition on the surface of the cathode. Addition of DMMP also inhibits the dissolution of Mn from LiNi 0.5 Mn 1.5 O 4 particles stored in electrolyte at 85 °C.