Breaking the Capacity–Stability Trade-Off in High-Voltage LiCoO2 via Opposite Co/O Redox Activity

LiCoO2 (LCO) suffers from daunting capacity–stability trade-off due to deeper Co oxidation and ensuing O oxidation (O2– → Co4+ electron transfer) at high-voltage (≥4.5 V). Aggressive Co4+ and O2/On– (0 < n < 2) species result in pronounced mechanical/chemical failure and fast capacity decay. Most of the state-of-the-art solutions partially resolve these problems yet sacrificing capacity. Herein, facilitated Co3+/4+ redox and effectively restrained O redox are simultaneously achieved by amplifying Co t2g electron density of states (DOS) near the Fermi level while reducing O 2p electron DOS. Consequently, the engineered cathode harvests a remarkable initial capacity of 212.1 mAh g–1 at 4.6 V (vs 212.9 mAh g–1 of bare LCO). Moreover, advanced multiscale X-ray/electron spectroscopy and imaging techniques reveal that mitigated O redox prevents irreversible phase transitions, lattice O loss, and undesirable surface parasitic reactions. As a result, the cathode has reinforced electrochemical (capacity retention of 88.4% within 330 cycles at 5C) and thermal stability thanks to fatigue-free (de)lithiation channels, less new-generated Co3O4 layer, and inorganic-rich cathode/electrolyte interphase (CEI) film. This work provides a valuable inspiration for the electronic structure engineer of robust LCO cathode toward high operation voltages.