A Multifunctional Potent Lewis Acid for In Situ Formation of Poly‐Dioxolane Electrolytes Toward High‐Performance Quasi‐Solid State Lithium Metal Batteries

Conventional polymer electrolytes based on poly‐dioxolane (PDOL) suffer from low ion mobility and unstable interfaces. Here, AlCl3‐initiated in situ polymerized gel PDOL electrolytes (AGPE) form a facile Li+ conduction path and hybrid SEI layers, thus enabling high Li+ conductivity and uniform Li deposition. These findings establish AlCl3‐initiated AGPE as a promising platform for the development of high‐performance but safe LMBs. Abstract Quasi‐solid‐state polymer electrolytes represent a promising strategy for Li metal batteries (LMBs) with superior safety and energy density. However, Li dendrite formation and unstable interfaces significantly hinder their practical application. Here, an AlCl3‐initiated gel polymer electrolyte (AGPE) is developed via in situ ring‐opening polymerization of 1,3‐dioxolane (DOL) to directly generate poly(1,3‐dioxolane) (PDOL) electrolyte in battery cells. AlCl3 acts both as polymerization initiator and a multifunctional additive, enhancing polymer network stability and facilitating selective Li+ transport through an AlCl3‐mediated multi‐coordination framework. Additionally, AlCl3 spontaneously generates a hybrid SEI layer composed of LiF, LiCl, and LiAl, significantly enhancing interfacial stability and suppressing dendritic growth. Consequently, the AGPE achieves excellent ionic conductivity (≈5.0 mS cm−1 at room temperature) and an outstanding Li+ transference number (tLi+ = 0.75). Li||LiFePO4 full cells employing AGPE exhibit superior electrochemical stability, retaining 92.7% capacity after 280 cycles at 0.5 C and delivering a high capacity of 118.2 mAh g−1 at 5 C. These results highlight AGPE as an attractive quasi‐solid electrolyte, demonstrating substantial promise for safe and high‐performance next‐generation LMBs. Conventional polymer electrolytes based on poly-dioxolane (PDOL) suffer from low ion mobility and unstable interfaces. Here, AlCl 3 -initiated in situ polymerized gel PDOL electrolytes (AGPE) form a facile Li + conduction path and hybrid SEI layers, thus enabling high Li + conductivity and uniform Li deposition. These findings establish AlCl 3 -initiated AGPE as a promising platform for the development of high-performance but safe LMBs. Abstract Quasi-solid-state polymer electrolytes represent a promising strategy for Li metal batteries (LMBs) with superior safety and energy density. However, Li dendrite formation and unstable interfaces significantly hinder their practical application. Here, an AlCl 3 -initiated gel polymer electrolyte (AGPE) is developed via in situ ring-opening polymerization of 1,3-dioxolane (DOL) to directly generate poly(1,3-dioxolane) (PDOL) electrolyte in battery cells. AlCl 3 acts both as polymerization initiator and a multifunctional additive, enhancing polymer network stability and facilitating selective Li + transport through an AlCl 3 -mediated multi-coordination framework. Additionally, AlCl 3 spontaneously generates a hybrid SEI layer composed of LiF, LiCl, and LiAl, significantly enhancing interfacial stability and suppressing dendritic growth. Consequently, the AGPE achieves excellent ionic conductivity (≈5.0 mS cm −1 at room temperature) and an outstanding Li + transference number (t Li+ = 0.75). Li||LiFePO 4 full cells employing AGPE exhibit superior electrochemical stability, retaining 92.7% capacity after 280 cycles at 0.5 C and delivering a high capacity of 118.2 mAh g −1 at 5 C. These results highlight AGPE as an attractive quasi-solid electrolyte, demonstrating substantial promise for safe and high-performance next-generation LMBs. Advanced Science, EarlyView.