One\nStone for Multiple Birds: Copolymer with Multifunctional\nGroups Boosts the Cycling Stability of Lithium Cobalt Oxide Cathodes\nat 4.5 V

High-voltage LiCoO<sub>2</sub> is\na promising cathode material\nfor ultrahigh-energy lithium-ion batteries, particularly in the commercialization\nof 5G technology. However, achieving long-term operational stability\nremains a significant challenge. Herein, a quaterpolymer additive\nwith multiple functional groups is introduced to enhance the electrochemical\nperformance of LiCoO<sub>2</sub> cathode at 4.5 V. The capacity remains\n96% after 100 cycles at room temperature and 94.4% after 50 cycles\neven at 45 °C. The sulfonate and ester groups of the quaterpolymer\nadditive serve as lithium carriers, providing high voltage resistance\nand fast ionic conductivity with increased lithium-ion diffusion coefficients\nduring the charge/discharge processes. The incorporation of a quaterpolymer\nadditive also improves the dispersion properties and peel strength\nof the LiCoO<sub>2</sub> cathodes. The coordination between the sulfonate\ngroups and Li<sup>+</sup> as well as the amine-based derivatives and\nLewis acid of PF<sub>5</sub> is expected to disrupt the Li<sup>+</sup> solvation shell and deactivate the PF<sub>5</sub> reactivity, therefore\nsuppressing electrolyte decompositions. Furthermore, the superior\ninteractions between sulfate ester (O atoms)/amide (N atoms) groups\nof copolymer additive and superficial cobalt atoms of LiCoO<sub>2</sub> provide a compensating charge to Co, inhibiting the surface cobalt\ndissolution, irreversible oxygen redox reaction, and the detrimental\nLiCoO<sub>2</sub> phase transition from O3 to H1–3. The use\nof a tiny amount of polymer additive presents an effective approach\nto stabilizing high-voltage LiCoO<sub>2</sub>, offering valuable insights\nfor the design of high-energy battery materials.