Amphiphilic Polymer Electrolyte Blocking Lattice Oxygen Evolution from High-Voltage Nickel-rich Cathodes for...

Ni-rich cathodes have been intensively adopted in Li-ion batteries to pursuit high energy density, which still suffering irreversible degradation at high voltage. Some unstable lattice O^2- species in Ni-rich cathodes would be oxidized to singlet oxygen ¹O₂ and released at high volt, which lead to irreversible phase transfer from the layered rhombohedral (R) phase to a spinel-like (S) phase. To overcome the issue, the amphiphilic copolymers (UMA-F_x) electrolyte were prepared by linking hydrophobic C-F side chains with hydrophilic subunits, which could self-assemble on Ni-rich cathode surface and convert to stable cathode-electrolyte interphase layer. Thereafter, the oxygen releasing of polymer coated cathode was obviously depressed and substituted by the Co oxidation (Co³⁺→Co⁴⁺) at high volt (>4.2 V), which could suppressed irreversible phase transfer and improve cycling stability. Moreover, the amphiphilic polymer electrolyte was also stable with Li anode and had high ion conductivity. Therefore, the NCM811//UMA-F₆//Li pouch cell exhibited outstanding energy density (362.97 Wh/kg) and durability (cycled 200 times at 4.7 V), which could be stalely cycled even at 120°C without short circuits or explosions.