Additive‐Regulated Interface Chemistry Enables Depolarization for Ultra‐High Capacity LiCoO ₂

Abstract

Abstract Unlocking the capacity potential of mainstream LiCoO 2 (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/H 2 O, 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.