Multiple Ion Rectification Strategy Regulated Polyethylene Glycol‐Based Polymer Electrolyte for Stable High‐Voltage Lithium Metal Batteries

Abstract Polyethylene glycol (PEG)‐based polymer electrolyte has emerged as a class of promising solid electrolytes for lithium metal batteries (LMBs), but suffer from incompatibility with high‐voltage cathodes and uneven plating/stripping of Li metal anode. Herein, a modified C 3 N 4 additive with dual defect sites of cyano‐groups and nitrogen‐vacancies (CN─Nv─C 3 N 4 ) in PEG‐based polymer electrolyte is demonstrated, which can serve as an effective dual functional ion rectifier to mitigate the cathode crosstalk, and optimize ion conductive environment. Experimental characterization and density functional theory (DFT) calculations reveal that the high electronegative cyano‐groups effectively traps the transition metal cations through coordination, while N‐vacancies generate abundant electron‐deficient centers to anchor anions and thus significantly increase Li + transfer number. Specifically, the CN─Nv─C 3 N 4 modulated PEG‐based polymer electrolyte (GPE‐CNC) achieved an ultra‐high Li + transfer number of 0.72 and an Li + conductivity of 0.6 mS cm −1 at room temperature. Moreover, when matched with high‐voltage LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode, GPE‐CNC can operate stably at a rate of 0.5 C, with an outstanding capacity retention rate of 71% after 700 cycles. This multiple ion rectification strategy not only enhances voltage compatibility, but also promotes high Li + transfer number of PEG‐based polymer electrolyte, offering inspiration for the development of high energy density solid‐state batteries.