Coherent 1T-Phase Surface Architecture Unlocks Ultrafast and Durable High-Voltage LiCoO₂ Cathodes

Nowadays, fast-charging capability in battery materials is intensively pursued in both academia and industry, yet the crystallographic factors that fundamentally determine rapid Li⁺ transport remain unclear. Here, we identify the theoretical structural capacity for collective Li⁺ transport, defined by the availability of crystallographically accessible Li diffusion sites, as a decisive but previously underappreciated structural origin governing interfacial Li⁺ transport, and introduce Li-site density (ρ_Li-site) as a quantitative descriptor to guide surface architecture design for accelerated Li⁺ migration. Guided by this principle, we construct a coherent and fluorinated 1T-Li_{1 + x}CoO_{2 - y}F_y surface structure on LiCoO₂, which simultaneously preserves crystallographic compatibility with the O3 matrix and provides an exceptionally high ρ_Li-site (∼48 sites·nm^-3), substantially exceeding those of commonly employed frameworks (≤ 31 sites·nm^-3). The modified cathode delivers unprecedented rate capability, achieving 183 and 175 mAh g^-1 at 10C and 20C, respectively. In-situ synchrotron x-ray and neutron diffraction results further reveal that the 1T phase effectively suppressed O3 to H1-3 phase transitions and stabilized oxygen frameworks, enabling outstanding cycling stability with 87% capacity retention after 500 cycles. This work establishes Li site density-guided surface engineering as a general structural principle for simultaneously improving interfacial reaction kinetics and structural durability in high-voltage layered oxide cathodes.