Calendar Life Enhancement of Commercial Ultra-High-Rate LiFePO4/Graphite Batteries for Electromagnetic Launch

Abstract Due to the advantages of ultra-high-power density, long cyclic life, and desirable safety, ultra-high-rate LiFePO4/graphite batteries (U-LIBs) are used as the energy storage system for electromagnetic launchers. However, the short calendar life of U-LIB limits its further application in the field of electromagnetic launch. In this study, the calendar life of commercial U-LIB is improved through the optimization design of anode materials and electrolytes. The calendar life is successfully improved without affecting the battery performances by appropriately increasing the particle size of graphite in the anode and properly reducing the proportion of dimethyl carbonate (DMC), which has low stability in the electrolyte. The average particle size of graphite is increased from 5 μm to 8 μm with a compaction density of 1.3 g cm−3 as the best option. The electrolyte formulation is optimized from 30% ethylene carbonate (EC), 60% DMC, and 10% ethyl methyl carbonate (EMC) to 30% EC, 50% DMC, and 20% EMC. After comprehensive optimization, the calendar life of commercial U-LIB was significantly improved at different temperatures and states of charge (SOCs). For example, the 1-month-storage capacity retention of U-LIB increased from 96.9% to 98% under the temperature of 45 °C at 50% SOC (meaning 35.5% decrease on capacity loss), and increased from 98.2% to 98.8% under the temperature of 25 °C at 100% SOC (33.3% decrease on capacity loss).