Propylene carbonate based electrolyte for extended cycle life lithium-ion batteries

Lithium-ion batteries (LIBs) are rapidly taking over the electric vehicle (EV) industry as the main energy storage system. They provide high energy efficiency, long cycle life, and low self-discharge compared to other battery chemistries. LIB is generally made up of a lithium metal oxide or phosphate cathode, a graphite anode, a polymer separator and a liquid electrolyte solution. The electrolyte is comprised of a lithium salt dissolved in a mixture of carbonates, such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. The melting point of ethylene carbonate (EC, 36.4°C) is higher than that of its analogue propylene carbonate (PC, –48 °C). Therefore, PC is an attractive candidate to improve the low temperature charge/discharge capacity and the fast charge capability of LIBs. Several groups have attempted to replace EC by PC. However, co-intercalation of PC-solvated Li+ ions results in serious exfoliation of graphite layers and a faster degradation of battery cycle life. We used a combination of additives in PC based liquid electrolyte containing LiPF6 salt, to address this issue. The developed electrolyte offers superior cycle life for the NMC/graphite pouch cell. The rationale for improved performance was analyzed with the help of characterization techniques such as ultra-high precision coulometry (UHPC), EIS, XPS and gas analysis