Electrolyte-Driven Regulation of Oxygen Redox and Interfacial Chemistry in Layered Oxide Cathodes

Abstract

The instability of oxygen redox chemistry in layered oxide cathodes fundamentally limits the achievable energy density and lifetime of lithium-based batteries. The degradation processes associated with oxygen evolution can be viewed from two complementary perspectives. From the cathode surface perspective, highly reactive oxidized oxygen species generated during charging decompose the electrolyte, inducing protonation of the surface and creating oxygen vacancies. These vacancies further drive the migration of bulk lattice oxygen (O²⁻) toward the surface, accelerating structural degradation. From the electrolyte perspective, oxygen released from the cathode exists as reactive oxygen species (ROS), such as singlet oxygen and superoxide radicals, which escape into the electrolyte and trigger secondary decomposition reactions. In this study, electrolyte-driven strategies were developed to regulate oxygen redox and mitigate such degradation processes from both perspectives. First, to deactivate oxygen radicals in the electrolyte, the working principles of proton-donating phenolic antioxidants were analyzed in Li-containing organic solvents, leading to the design of an organic superoxide dismutase mimic (SODm), guaiacol. Through associative binding of its hydroxyl and methoxy groups with LiO₂ radicals, guaiacol efficiently promoted lithium-assisted disproportionation, forming a thin polymeric cathode–electrolyte interphase (CEI) that suppressed electrolyte decomposition and enhanced interfacial stability. Second, beyond radical removal, oxygen evolution was further suppressed by introducing electrolyte components, anthracene, capable of anchoring oxidized oxygen species prior to oxygen dimerization, thereby preventing the formation of molecular oxygen. Third, a reduction-driven strategy was proposed to construct a stable inorganic-rich CEI that restrains surface oxygen release. Incorporation of divalent cations such as Mg²⁺ modulated the solvation structure of anions, elevating their reduction potential above 2 V vs. Li/Li⁺ and enabling controlled formation of LiF-rich CEIs through reduction of anion without inducing cathode overlithiation. Collectively, this work establishes an integrated framework for the electrolyte-driven regulation of oxygen redox and interfacial chemistry in layered oxide cathodes. By combining radical scavenging, oxygen anchoring, and reduction potential modulation, this dissertation provides fundamental insights and design principles for achieving structurally stable, long-life, high-energy lithium batteries.