Effects of a Thermally Electrochemically Activated β-PVDF Fiber on Suppression of Li Dendrite Growth for Anode-Free Batteries

Abstract

Organic electrolytes react aggressively with lithium (Li) active materials, especially at 60 °C, exhibiting uncontrolled dendrite growth. Herein, β-poly(vinylidene difluoride) (PVDF) polymer conformal coating on copper (Cu) is successfully prepared via electrospinning. The charge/discharge performance of the anode-free full cell configuration, either Cu@β-PVDF∥NMC or Cu@α-PVDF∥NMC, is very poor at room temperature. Interestingly, when the Cu@β-PVDF∥NMC cell treated with five charge/discharge cycles at 60 °C, termed thermal–electrochemical activation (TEA), achieves the capacity retention of 68.36 and 78.45% at the 20th cycle, it progresses in the following cycles at 25 and 60 °C, respectively. Even though it is treated with TEA, the Cu@α-PVDF∥NMC cell attains the capacity retention of only 35.36% at the 20th cycle at 60 °C. The adsorption of β-PVDF on the Li surface is more thermodynamically favorable than α-PVDF from the density functional theory calculation, whereas polar β-PVDF is seen as more effective in guiding the lithium cation flux. β-PVDF and the plated Li react to form a robust LiF-rich solid electrolyte interface . Unlike what is commonly perceived, TEA of β-PVDF can improve the interfacial chemistry and result in a compact deposition of lithium and stable cycling performance. The findings can apply to the conformal coating on Cu in anode-free batteries and other lithium metal batteries with liquid or solid electrolytes.