Lithium-Borate Interphase Enables High-Rate and Long-Lifespan Ni-Rich Layered Oxide Cathodes

The growing demand for fast-charging and high-power electric vehicles is shifting Ni-rich cathode design from maximizing energy density alone toward sustaining rapid Li-ion transport over long cycling. LiNi_xCo_yAl_zO₂ is well suited to this target because its Mn-free, Al-stabilized layered framework offers high capacity and structural robustness, yet residual alkaline lithium species on the particle surface compromise electrode processing, interfacial kinetics and long-term durability. Here we convert these residual lithium species on LiNi_0.88Co_0.09Al_0.03O₂ (NCA) surface into a functional lithium-borate interphase through a boric-acid-mediated surface reaction (NCA-B). Rather than simply removing surface residues, this strategy suppresses parasitic interfacial chemistry while maintaining efficient Li-ion transport. In Ah-level NCA-B||graphite pouch cells, the modified cathode retains 76.9% capacity after 2000 cycles at 1 C and sustains nearly decay-free cycling for 2400 cycles under 1 C charge and 10 C discharge, with a voltage-fade rate of 0.0375 mV per cycle. These results establish residual-lithium conversion as a practical interfacial design principle for high-rate, long-life NCA batteries.