In-Situ synthesized Non-flammable gel polymer electrolyte enable highly safe and Dendrite-Free lithium metal batteries.

[Display omitted] • Acidified-Al 2 O 3 initiated the polymerization of 1,3-dioxolane in a liquid electrolyte. • The gel polymer electrolyte possesses an excellent ionic conductivity. • The gel polymer electrolyte affords a satisfactory Li+ transference number. • As-prepared gel polymer electrolyte exhibits excellent flame retardation. • Dendrite-free solid-state lithium batteries has been achieved. Safety issues resulting from flammable organic solvent and lithium (Li) dendrite formation have seriously impeded Li metal batteries development. Here, the H+ generated by acid-treated Al 2 O 3 functions as an initiator, promotes the polymerization of 1,3-dioxolane (DOL) in a commercial liquid electrolyte (LE) which contains 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a mixed organic solution of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME) (1:1, v/v) to form gel polymer electrolyte (GPE). Owing to the fire-retarding property of Al 2 O 3 , the oxygen index of as-prepared GPE can reach up to 22.2%. Furthermore, a high Li+ transference number of 0.74 has been achieved by acid-treated nano Al 2 O 3. The –OH on the surface of acid-treated nano Al 2 O 3 can attract TFSI‐ anions by Lewis acid-base interaction and promote the dissolution of LiTFSI and enhance the mobility of Li+. Sequentially, the Li-Li symmetric cells based on as-prepared GPE show no evident polarization enlargement after 1000 h cycling under the current density of 1 mA cm−2, which means as-prepared GPE can effectively suppress the Li dendrite formation during the Li plating/stripping process. The lithium metal batteries (LMBs) using LiFePO 4 as a cathode deliver excellent rate performance with capacity retention up to 97% after a sequence of current density attributing to Li's good interfacial stability anodes. [ABSTRACT FROM AUTHOR]