Use of a solid polymer/ceramic electrolyte coating to promote uniform Li flux and a LiF-rich interphase for lithium metal batteries

Abstract

Li metal batteries have been considered promising candidates for next-generation high-energy-density batteries due to their high theoretical capacity and low redox potential. However, the uneven Li flux causes the formation of Li dendrites, and “dead lithium” caused by the reaction with the liquid electrolyte hinders their practical application. Herein, a PVDF-HFP/LiTFSI polymer electrolyte was designed and fabricated to stabilize the interfaces of the Li metal anode. LiTFSI could participate in the formation of inorganic LiF-rich interphases through preferential reduction of TFSI⁻ to effectively restrain the growth of lithium dendrites. The PVDF-HFP/LiTFSI polymer electrolyte coating showed a uniform morphology that induced uniform Li⁺ flux and dendrite-free Li deposition and stripping. Consequently, the polymer electrolyte-modified PE separator enabled a high rate and stable cycling performance of Li metal batteries. The PVDF-HFP/LiTFSI-modified PE separator showed an ionic conductivity of 5.7 × 10⁻⁴ S cm⁻¹ with a lithium ion transference number of 0.47. Paired in Li‖Li symmetric cells, a long-duration cycling performance of 1100 h at 0.2 mA cm⁻² was achieved. The polarization voltage remained at 0.013 V due to a low interfacial resistance of 70.6 Ohm cm² in the Li metal anode. In Li‖LFP full cells, the polymer/ceramic electrolyte-modified separator enabled stable cycling over 700 cycles while maintaining 81% capacity retention after 500 cycles. Even at a high rate of 10C, the cell delivered a specific capacity of 74.7 mA h g⁻¹. This work provides a new approach for developing high-performance Li metal batteries using a polymer/ceramic electrolyte-modified separator.