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

Organic electrolytes react aggressively with lithium (Li) active materials, especially at 60 degrees C, exhibiting uncontrolled dendrite growth. Herein, beta-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@beta-PVDF parallel to NMC or Cu@alpha-PVDF parallel to NMC, is very poor at room temperature. Interestingly, when the Cugfi-PVDF parallel to NMC cell treated with five charge/ discharge cycles at 60 degrees 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 degrees C, respectively. Even though it is treated with TEA, the Cua-PVDF parallel to NMC cell attains the capacity retention of only 35.36% at the 20th cycle at 60 degrees C. The adsorption of beta-PVDF on the Li surface is more thermodynamically favorable than alpha-PVDF from the density functional theory calculation, whereas polar beta-PVDF is seen as more effective in guiding the lithium cation flux beta-PVDF and the plated Li react to form a robust LiF-rich solid electrolyte interface. Unlike what is commonly perceived, TEA of beta-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.

Automated summary

The findings suggest that thermal-electrochemical activation (TEA) of beta-PVDF conformal coating on copper can improve interfacial chemistry with lithium active materials, leading to a robust solid electrolyte interface and enhanced stability and cycling performance of lithium metal batteries.