Ultrathin dense LiF coverage coupled with a near-surface gradient fluorination lattice enables fast-charging long-life 4.6 V LiCoO2

Abstract

LiCoO₂ (LCO) is a leading cathode material of lithium-ion batteries in consumer electronics. However, practical applications of high-voltage fast charging are hampered by unstable interfacial structures and unfavorable phase transitions arising from the superimposed high-flux Li⁺ diffusion of LCO during deep de-lithiation. Here, we report a universal cathode interface engineering strategy of stabilizing 4.45 V commercial LCO by surface fluorination (F-LCO) towards fast-charging long-life cyclability at a high voltage of 4.6 V. It is experimentally observed that the resulting near-surface structure with a ∼1 nm ultrathin dense LiF covering layer and a 10–20 nm gradient fluorination lattice, together with a trace amount of phosphates, provides extraordinary stabilization to the surface lattice oxygen. F-LCO achieves a record capacity retention of 92% after 1000 cycles at 3C, far outperforming the commercial LCO (31%) and reported 4.6 V LCOs. Further, it is theoretically revealed that the antibonding orbital electron transfer in Co–F bonding greatly inhibits cobalt migration as the de-lithiation approaches 4.6 V. We unravel that the reconstructed high-energy barrier F-rich interface with enhanced charge transfer capability ultimately prevents high-valent oxygen species (Oⁿ⁻, 0 < n < 2) from migrating along vacancies and evolving into oxygen to generate interfacial side reactions. Our pouch-type full cells of graphite||F-LCO offer superior high voltage (4.5 V) cyclability without capacity fading over 1100 cycles at a fast-charging rate of 5C. Therefore, this strategy of cathode interface fluorination provides new insights into the commercial realization of high-voltage fast-charging LCOs.