High Pseudocapacitance-Driven CoC₂ O₄ Electrodes Exhibiting Superior Electrochemical Kinetics and Reversible Capacities for Lithium-Ion and Lithium-Sulfur Batteries

In this study, cuboid-like anhydrous CoC₂ O₄ particles (CoC₂ O₄ -HK) are synthesized through a potassium citrate-assisted hydrothermal method, which possess well-crystallized structure for fast Li⁺ transportation and efficient Li⁺ intercalation pseudocapacitive behaviors. When being used in lithium-ion batteries, the as-prepared CoC₂ O₄ -HK delivers a high reversible capacity (≈1360 mAh g^-1 at 0.1 A g^-1 ), good rate capability (≈650 mAh g^-1 at 5 A g^-1 ) and outstanding cycling stability (835 mAh g^-1 after 1000 cycles at 1 A g^-1 ). Characterizations illustrate that the Li⁺ -intercalation pseudocapacitance dominates the charge storage of CoC₂ O₄ -HK electrode, together with the reversible reaction of CoC₂ O₄ +2Li⁺ +2e^- →Co+Li₂ C₂ O₄ on discharging and charging. In addition, CoC₂ O₄ -HK particles are also used together with carbon-sulfur composite materials as the electrocatalysts for lithium-sulfur (Li-S) battery, which displays a gratifying sulfur electrochemistry with a high reversibility of 1021.5 mAh g^-1 at 2 C and a low decay rate of 0.079% per cycle after 500 cycles. The density functional theory (DFT) calculations show that CoC₂ O₄ /C can regulate the adsorption-activation of reaction intermediates and therefore boost the catalytic conversion of polysulfides. Therefore, this work presents a new prospect of applying CoC₂ O₄ as the high-performance electrode materials for rechargeable Li-ion and Li-S batteries.