One Stone for Multiple Birds: Copolymer with Multifunctional Groups Boosts the Cycling Stability of Lithium Cobalt Oxide Cathodes at 4.5 V

High-voltage LiCoO₂ is a promising cathode material for ultrahigh-energy lithium-ion batteries, particularly in the commercialization of 5G technology. However, achieving long-term operational stability remains a significant challenge. Herein, a quaterpolymer additive with multiple functional groups is introduced to enhance the electrochemical performance of LiCoO₂ cathode at 4.5 V. The capacity remains 96% after 100 cycles at room temperature and 94.4% after 50 cycles even at 45 °C. The sulfonate and ester groups of the quaterpolymer additive serve as lithium carriers, providing high voltage resistance and fast ionic conductivity with increased lithium-ion diffusion coefficients during the charge/discharge processes. The incorporation of a quaterpolymer additive also improves the dispersion properties and peel strength of the LiCoO₂ cathodes. The coordination between the sulfonate groups and Li⁺ as well as the amine-based derivatives and Lewis acid of PF₅ is expected to disrupt the Li⁺ solvation shell and deactivate the PF₅ reactivity, therefore suppressing electrolyte decompositions. Furthermore, the superior interactions between sulfate ester (O atoms)/amide (N atoms) groups of copolymer additive and superficial cobalt atoms of LiCoO₂ provide a compensating charge to Co, inhibiting the surface cobalt dissolution, irreversible oxygen redox reaction, and the detrimental LiCoO₂ phase transition from O3 to H1-3. The use of a tiny amount of polymer additive presents an effective approach to stabilizing high-voltage LiCoO₂, offering valuable insights for the design of high-energy battery materials.