Excellent electrochemical performance of PVDF based composite electrolyte by incorporating ZIF with different entropy for lithium metal batteries

Composite solid-state electrolytes (CSEs) with high safety and flexibility are promising candidates for high-energy-density energy storage devices. However, the low ionic conductivity, low ion transference number, and poor interfacial stability of CSEs greatly reduce the electrochemical performance of lithium-ion batteries (LIBs). In this work, ZIFs with low, medium and high entropy prepared using mechanical ball grinding are introduced into polyvinylidene fluoride (PVDF) as fillers. The effect of ZIFs with different entropy on the structure, ionic conductivity of CSEs as well as electrochemical performance of cells is investigated. The CSE with high-entropy ZIF (PLL-HE) showcases optimal comprehensive properties, with mechanical strength as high as 11.2 MPa, high room-temperature ionic conductivity of 7.76 × 10 −4  S cm −1 , high ionic transference number of 0.84, and low activation energy of 0.14 eV. The Li/PLL-HE/Li symmetric cell does not experience short-circuit phenomena after cycling for 1400 h at a current density of 0.2 mA cm −2 . The LiFePO 4 /PLL-HE/Li full cell has an initial discharge specific capacity of 152.3 mA h g −1 at a rate of 0.2 C and exhibits a capacity retention rate of 99.44 % after 130 cycles. This study provides a novel strategy using high-entropy ZIF to boost CSE performance for Li-metal cells.