A propylene carbonate based gel polymer electrolyte for extended cycle life and improved safety performance of lithium ion batteries

A poly(vinylidene difluoride-co-hexafluoropropylene) (PVdF-HFP)-based gel polymer electrolyte (GPE) containing propylene carbonate (PC)-based liquid electrolyte was developed to enhance the safety performance of LiNi0.5Mn0.3Co0.2O2/graphite (NMC532/graphite) lithium ion batteries. The PC-based liquid electrolyte (PEV-LE) consists of 1 mol L−1 LiPF6 as lithium salt, PC as the main solvent and ethylene sulfite (ES, 2% by weight) as well as vinylene carbonate (VC, 2% by weight) as solid electrolyte interphase (SEI) forming additives. Electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) revealed that the combination of ES and VC additives facilitates the formation of effective interphases at the respective electrolyte/electrode interfaces, thus contributing to a remarkable cycle life of NMC532/graphite cell comprising PEV-GPE. Flash point measurements and differential scanning calorimetry (DSC) confirmed significantly improved safety performance of PEV compared to the state-of-the-art electrolyte. PEV-GPE is a promising alternative to state-of-the-art electrolyte as it shows extended cycle life and enhanced thermal stability in NMC532/graphite lithium ion cells.