Electrochemical investigation of PVDF: HFP gel polymer electrolytes for quasi-solid-state Li-O2 batteries: effect of lithium salt type and concentration

Among rechargeable lithium batteries, lithium-oxygen batteries (Li-O2) offer remarkable energy densities which make them to be considered as the next generation energy storage systems. However, intrinsic problems arising from the use of liquid electrolytes has to be overcome before their adoption into the market. Gel-polymer electrolytes (GPEs) are now considered as the next-generation electrolytes to be utilized in Li-O2 systems. PVDF-HFP polymers with different lithium salts were successfully utilized as gel-polymer electrolytes to replace liquid electrolytes in Li-O2 batteries. However, the electrochemical performance of different lithium salts dissolved in PVDF-HFP matrices are limited in different aspects, i.e. (electro)chemical stability, ionic conductivity, interfacial stability, cycle stability or lithium-ion transference number. In this study, we systematically observed the effect of different lithium salts at various concentrations on the above mentioned electrochemical properties. Our results indicate that LiPF6 salt imparts best ionic conductivity into GPE systems while LiTFSI has both the widest electrochemical window and highest lithium-ion transference number. Our results indicate that the synthesis of new lithium salts having decent electrochemical performance in all aspects is of great importance in developing GPE systems.