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

High-voltage LiCoO 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 LiCoO 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 LiCoO cathodes. The coordination between the sulfonate groups and Li as well as the amine-based derivatives and Lewis acid of PF is expected to disrupt the Li solvation shell and deactivate the PF 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 LiCoO provide a compensating charge to Co, inhibiting the surface cobalt dissolution, irreversible oxygen redox reaction, and the detrimental LiCoO phase transition from O3 to H1-3. The use of a tiny amount of polymer additive presents an effective approach to stabilizing high-voltage LiCoO, offering valuable insights for the design of high-energy battery materials.