In Situ Forming Gel Polymer Electrolyte for High Energy‐Density Lithium Metal Batteries

In situ forming gel polymer electrolyte (GPE) is one of the most feasible ways to improve the safety and cycle performances of lithium metal batteries with high energy density. However, most of the in situ formed GPEs are not compatible with high‐voltage cathode materials. Here, this work provides a novel strategy to in situ form GPE based on the mechanism of Ritter reaction. The Ritter reaction in liquid electrolyte has the advantage of appropriate reaction temperature and no additional additives. The polymer chains are cross‐linked by amide groups with the formation of GPE with superior electrochemical properties. The GPE has high ionic conductivity (1.84 mS cm−1), wide electrochemical stability window (>5.25 V) and high lithium ion transference number (≈0.78), compatible with high‐voltage cathode materials. The Li|LiNi0.6Co0.2Mn0.2O2 batteries with in situ formed GPE show excellent long‐term cycle stability (93.4%, 300 cycles). The density functional theory calculation and X‐ray photoelectron spectroscopy results verify that the amide and nitrile groups are beneficial for stabilizing cathode structure and promoting uniform Li deposition on Li anode. Furthermore, the in situ formed GPE exhibits excellent electrochemical performance in Graphite|LiMn2O4 and Graphite|LiNi0.5Co0.2Mn0.3O2 pouch batteries. This approach is adaptable to current battery technologies, which will be sure to promote the development of high energy‐density lithium‐ion batteries. Gel polymer electrolyte with high ionic conductivity, wide electrochemical stability window and high lithium‐ion transference number is developed. It can improve the cycle performance of lithium metal batteries by stabilizing cathode structure and promoting uniform Li deposition, which is also applicable to current battery technologies.