Anion-trapping composite gel electrolyte for safer and more stable anode-free lithium-metal batteries

Lithium-metal battery advancement has been restricted due to increasing apprehensions about leakage-related safety issues and the unavoidable formation of dendrites connected with liquid electrolytes. Gel polymer electrolytes (GPEs) have the benefits of both solid polymer and liquid electrolytes and thus appear to be a more viable alternative in energy storage devices. Poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP)-based GPE is known for its high dielectric constant and wide potential window. Fluorinated polyimide (F-PI) has outstanding thermal and oxidative stability. Herein, we prepare a composite GPE exhibiting a porous 3D cross-linked structure by combining these two polymers via thermal treatment, enabling H-bonding interaction between F-PI (N-H) and (-F) PVDF-HFP. Further, upon gelation, the amide bond (N-H moiety) in F-PI possesses unique anion-trapping (FSI-) by strong H-bonding interaction. This interaction restricts anion's dynamics, making them immobile and facilitating Li-ion transport. It improves the Li-ion kinetics and uniformity during the plating/stripping in an anode-free lithium metal battery (AFLMB) (Cu||NMC811). With a high Li+ transference number of 0.7, this GPE displays exceptional cycling stability with a retention of ∼ 70 % after 100 cycles.