Self‐Healing Polymer Electrolyte for Dendrite‐Free Li Metal Batteries with Ultra‐High‐Voltage Ni‐Rich Layered Cathodes

Practical applications of polymer electrolytes in lithium (Li) metal batteries with high-voltage Ni-rich cathodes have been hindered by the dendrite growth and poor oxidative stability of electrolytes. Herein, a self-healing polymer electrolyte is developed by in situ copolymerization of 2-(3-(6-methyl4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate (UPyMA) and ethylene glycol methyl ether acrylate (EGMEA) monomers. With the electrolyte, the dendrite growth is inhibited by spontaneously repairing dendrite-induced defects, cracks, and voids at the Li/electrolyte interface; the suppressed dendrite growth and associated electro-chemo behaviors are visualized by the kinetic Mont-Carlo simulation. Benefitting from the high ionic conductivity, wide electrochemical window and good interfacial stability, the self-healing polymer electrolyte enables stable cycling of the LiNi_0.8 Mn_0.1 Co_0.1 O₂ (NMC811) cathode under 4.7 V, achieving a high specific capacity of ≈228.8 mAh g^-1 and capacity retention of 80.4% over 500 cycles. The new electrolyte is very promising for developing highly safe and dendrite-free Li metal batteries with high energy density.