Thiol‐ene click reaction is an intriguing strategy for preparing polymer electrolytes due to its high activity, atom economy and less side reaction. However, the explosive reaction rate and the use of non‐electrolytic amine catalyst hamper its application in in‐situ batteries. Herein, a nitrogen‐containing eutectic solution is designed as both the catalyst of the thiol‐ene reaction and the plasticizer to in‐situ synthesize the gel polymer electrolytes, realizing a mild in‐situ gelation process and the preparation of high‐performance gel electrolytes. The obtained gel polymer electrolytes exhibit a high ionic conductivity of 4 × 10−4 S cm−1 and lithium‐ion transference number () of 0.51 at 60 °C. The as‐assembled Li/LiFePO4 (LFP) cell delivers a high initial discharge capacity of 155.9 mAh g−1, and a favorable cycling stability with the capacity retention of 82% after 800 cycles at 1 C is also obtained. In addition, this eutectic solution significantly improves the rate performance of the LFP cell with high specific capacity of 141.5 and 126.8 mAh g−1 at 5 C and 10 C, respectively, and the cell can steadily work at various charge–discharge rate for 200 cycles. This powerful and efficient strategy may provide a novel way for in‐situ preparing gel polymer electrolytes with desirable comprehensive performances.

As an emerging and potential replacement system for liquid electrolytes, polymer electrolytes (PEs) exhibit unique capacity in suppressing metal dendrite formation and leakage risks. However, the most used polymer matrix, including polyether, polyester, and polysiloxane, still cannot meet the practical demands for metal electrode compatibility and long lifespan. In this study, gel polymer electrolytes consisting of a polyurea network with abundant hydrogen bonds and deep eutectic electrolyte (DEE) are designed and prepared in-situ. The hydrogen bonding between polyurea chains and polyurea-DEE provides good interfacial stability between PEs and lithium metal. As a result, the assembled Li/LiFePO 4 cells based on this electrolyte deliver a long cycle life with 90 % retention after 500 cycles and 76.5 % retention after 1000 cycles at 1 C. In addition, the flexible design characteristics of polyurea structure permit easy operation for performance optimization by modulating the composition of hard and soft segments, and enhanced ionic conductivity and self-healing efficiency are obtained. This study provides a novel method for preparing advanced polymer electrolytes for lithium metal batteries.