Chemically Active Sulfonate Additive with Transition Metal and Oxygen Dual-Site Deactivation for High-Voltage LiCoO₂

Modulating a solid electrolyte interphase (SEI) through additives represents a crucial approach for stable operation of cathode materials. Traditional perspectives focus on the electrochemical decomposition of the additive itself while underestimating the reactivity and catalytic ability from cathode surfaces. Inspired by the sulfur-containing species causing catalyst poisoning, the catalytic effects of LiCoO2 (LCO) for the sulfur-based molecule (−SOx) additives have been investigated. We elucidate the mechanism of additives by assessing multiple interactions with the LCO surface, which are primarily characterized by chemical ring-opening reactions. Furthermore, decreasing the saturated carbon in molecules can enhance its reactivity, while the −SOx groups deactivate both the lattice oxygen and transition metal center through dual-site bond formation. Benefiting from the chemically passivated surface, the sulfonate additive enables LCO cycling at a high temperature and a high voltage of 4.65 V. This provides new insights into the mechanisms for stabilizing the cathode interface and molecular design for additives.