A Surface Se‐Substituted LiCo[O₂₋<i>_δ</i>Se<i>_δ</i>] Cathode with Ultrastable High‐Voltage Cycling in Pouch Full‐Cells

Abstract

Abstract Cycling LiCoO 2 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 &lt; 2) migration, causing oxygen loss, phase collapse, and electrolyte decomposition that severely degrade the battery cyclability. Hereby, commercial LiCoO 2 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 LiCoO 2 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 LiCoO 2 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 ).