Deep Eutectic Polymer Electrolyte with Competitive Hydrogen‐Bonding Coordination for High‐Voltage Nickel‐rich Lithium Metal Batteries

ABSTRACT The pursuit of high‐energy‐density solid‐state batteries using Li metal anodes and high‐voltage Ni‐rich cathodes is hindered by severe interfacial degradation. Conventional polymer electrolytes with electronegative groups strongly adsorb high‐valent nickel, accelerating cathode decomposition and oxygen release. Here, we develop a deep‐eutectic polymer electrolyte (p‐DEPE) via in situ copolymerization of cyanoacrylate and butyl acrylate within a LiTFSI/LiDFOB dual‐salt network to reshape the interfacial chemistry. This design creates an intermolecular hydrogen‐bonding matrix that establishes a competitive coordination environment at the cathode interface, effectively weakening Ni ⁴⁺ adsorption on electronegative sites. The suppression of high‐value Ni inhibits the growth of a high‐resistance cathode–electrolyte interphase and retards the detrimental phase transition from a layered to a rock‐salt structure. Furthermore, the locally confined interaction between the cyano‐group and the cathode surface at high states of charge minimizes parasitic chemical reactions with lattice oxygen, thereby substantially reducing oxygen release. Consequently, Li||LiNi _0.8 Co _0.1 Mn _0.1 O ₂ cells with p‐DEPE deliver outstanding high‐rate performance, cycling over 200 cycles at 2 C at room temperature and at 3 C at 70°C. Moreover, a 4.5 V high‐loading Li||NCM811 pouch cell retains 97.3% of its initial capacity after 100 cycles. This work demonstrates a scalable polymer electrolyte strategy for high‐energy‐density lithium metal batteries.