Additive-Regulated Interface Chemistry Enables Depolarization for Ultra-High Capacity LiCoO₂

Unlocking the capacity potential of mainstream LiCoO₂ (LCO) cathode materials for stable cycling at a high upper cut-off voltage is undoubtedly one of the most economical approaches to achieving high-energy-density lithium-ion batteries. However, significant polarization issues induced by interfacial and interphase degradation during high-voltage cycling remain well known. This study demonstrates the efficient depolarization effects of cyclic organosiloxane additive 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4) at the cathode-electrolyte interface, facilitating interfacial charge transfer and enhancing the capacity of LCO||Li cells to 220 mA h g^-1 even at 4.55 V (vs Li/Li⁺). Specifically, V4D4 tends to adsorb onto the surface of highly delithiated LCO cathodes, and its preferential oxidation intermediates help stabilize lattice oxygen, eliminate harmful HF/H₂O, and form an ultrathin cathode-electrolyte interphase (CEI) that reduces interface resistance to Li⁺ diffusion and stabilizes the surface structure. Additionally, with the assistance of fluoroethylene carbonate (FEC), long-term cycling produces a homogeneous, chemo-mechanically stable CEI enriched in organic silicon-containing compounds and LiF. This CEI suppresses excessive bulk electrolyte decomposition, reinforces the reversibility of the significantly enhanced O3-H1-3 phase transition, and enables capacity retention of ≈97% after 200 cycles.