A Surface Se-Substituted LiCo[O_2- _δ Se_δ ] Cathode with Ultrastable High-Voltage Cycling in Pouch Full-Cells.

Abstract

Cycling LiCoO₂ to above 4.5 V for higher capacity is enticing; however, hybrid O anion- and Co cation-redox (HACR) at high voltages facilitates intrinsic O^α ^- (α < 2) migration, causing oxygen loss, phase collapse, and electrolyte decomposition that severely degrade the battery cyclability. Hereby, commercial LiCoO₂ particles are operando treated with selenium, a well-known anti-aging element to capture oxygen-radicals in the human body, showing an "anti-aging" effect in high-voltage battery cycling and successfully stopping the escape of oxygen from LiCoO₂ even when the cathode is cycled to 4.62 V. Ab initio calculation and soft X-ray absorption spectroscopy analysis suggest that during deep charging, the precoated Se will initially substitute some mobile O^α ^- at the charged LiCoO₂ surface, transplanting the pumped charges from O^α ^- and reducing it back to O^2- to stabilize the oxygen lattice in prolonged cycling. As a result, the material retains 80% and 77% of its capacity after 450 and 550 cycles under 100 mA g^-1 in 4.57 V pouch full-cells matched with a graphite anode and an ultralean electrolyte (2 g Ah^-1 ).