In-situ formation of LiF-rich composite interlayer for dendrite-free all-solid-state lithium batteries

Polyethylene oxide (PEO)-based composite electrolytes are considered as competent candidates to achieve high energy density all-solid-state lithium batteries (ASSLBs) due to good flexibility, which can effectively solve the problem of large interfacial resistance with electrodes. However, poor mechanical strength and low Li+ transference number can’t restrain the formation and growth of Li dendrites, leading to parasitic reaction between electrolyte and Li anode and unsatisfied coulombic efficiency. Herein, Li metal is pre-treated by poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP)/CuF2 composite to form a stable interlayer on the anode. In-situ reaction of CuF2 with Li greatly improves the contact between PVDF-HFP layer and Li anode, forming a LiF-rich modified layer. The interlayer with high mechanical strength and ionic conductivity can not only suppress the formation of Li dendrites, but also achieve the growth restriction and elimination of dendrites. Moreover, excellent elasticity and strong adhesion with Li anode can ensure the structure stability of modified layer during dynamic plating/stripping of Li. Applied in ASSLBs with PEO-based electrolyte, PVDF-HFP/CuF2 modified symmetrical Li cells demonstrate increased critical current density and extended cycle life than that of bare Li or single CuF2 treated Li. Furtherly, the ASSLBs with LiFePO4 cathode show excellent cycle stability and high coulombic efficiency over 1000 cycles at 1 C.