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

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 Ni4+ 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||LiNi0.8Co0.1Mn0.1O2 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.