An efficient gel polymer electrolyte for dendrite-free and long cycle life lithium metal batteries

Lithium metal batteries (LMBs) are plagued with non-uniform and dendritic electrodeposition of Li when used with liquid electrolytes, resulting in poor cycle life and Coulombic efficiency, and safety hazards. Herein, we report a novel gel polymer electrolyte (GPE) for LMBs enabling uniform and nondendritic Li electrodeposition, long cycle life, and high Columbic efficiency. The GPE is made by immobilization of liquid electrolytes within a crosslinked polymer matrix. At ambient temperature, the GPE shows a Li ion conductivity of 1.5 mS cm−1. Topology and morphology of the electrochemically deposited Li in the GPE were studied by operando optical microscopy and scanning electron microscopy (SEM). Cryogenic transmission electron microscopy (cryo-TEM) and X-ray photon spectroscopy (XPS) characterizations indicate that the solid electrolyte interphase (SEI) layer at the Li/GPE interface is a thin and LiF-rich while the SEI layer is thick and LiF-poor at the Li/liquid electrolyte interface. Density functional theory (DFT) calculations show that LiF crystals facilitate and regulate Li ions transport. Lithium|lithium iron phosphate (Li|LFP) cells with our GPE deliver an initial specific capacity of ∼130 mAh g−1 and ∼70% capacity retention after 1000 cycles at 2C charge/discharge rate. This study offers a promising approach for engineering a stable and conductive Li/polymer electrolyte interface for dendrite-free LMBs.