Unveiling the enhancement essence on Li2S deposition by the polarized topological β-polyvinylidene fluoride: Beyond built-in electric field effect

Abstract

Electric field from ferroelectric materials was often applied to energy-storage devices to enhance their electrochemical reaction kinetics via the electrostatic interaction. However, traditional ferroelectric materials are difficult to be used commercially for their insulation. Herein, we elucidate a novel strategy to introduce the electrostatic interaction by polarizing the polyvinylidene fluoride (PVDF) binder used in the C/S cathodes for lithium-sulfur batteries. In particular, we show both experimentally and theoretically how an external electric field from β-phase PVDF induces unprecedented performance and stabilities. Density functional theory calculation results indicate that the polarized topological β-phase PVDF possesses not only an strong built-in electric field and an improved conductance that benefits both the deposition of LiPSs and the transport of Li+ ions, but also an enhanced adsorption capability to polysulfide ions. As a result, the specific capacity was improved by over 60 %, the rate capability (from 0.1 to 2.0 C) was enhanced by 138 %, and the capacity decay rate (1000 cycles at 1.0 C) largely decreases from 0.059 % to 0.038 % per cycle. Besides, the enhancement mechanism of Li2S deposition by electrostatic interaction has also been explored. This research would provide some new insight into the ferroelectric enhanced design of high-performance energy-storage devices.