The improvement effect of LiF on stability of Li anode in PVDF-HFP gel polymer electrolyte

Abstract

The porous composite polymer membranes, based on poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) polymer matrix and lithium fluoride (LiF) inorganic additive, were prepared by phase inversion method and gel polymer electrolytes (GPEs) were obtained by immersing membranes into liquid electrolyte. GPEs containing LiF additive exhibited a high ionic conductivity of 1.10 10-3 S cm-1 and a high lithium ion transference number of 0.65 because of the lower crystallinity degree of GPEs. Moreover, we disclosed distinct merits including enhanced migration of Li+ and suppressed Li-ion concentration gradient in GPE near the surface of Li electrode. These merits ameliorated electrochemical performance of Li metal anode by retarding Li dendrite. LiF-GPEs effectively improved the cyclability and rate performance of symmetrical Li cells in a wide current densities rage. Pairing with LiFePO4 cathode, full cells containing LiF-GPEs showed excellent rate performance and cycling stability. This work effectively demonstrates that LiF-GPEs could suppress lithium dendrite by boosting electrochemical characters of mass transfer, and kinetic parameters.