High Pseudocapacitance-Driven CoC 2 O 4 Electrodes Exhibiting Superior Electrochemical Kinetics and Reversible Capacities for Lithium-Ion and Lithium-Sulfur Batteries.

In this study, cuboid-like anhydrous CoC O particles (CoC O -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 CoC O -HK delivers a high reversible capacity (≈1360 mAh g at 0.1 A g ), good rate capability (≈650 mAh g at 5 A g ) and outstanding cycling stability (835 mAh g after 1000 cycles at 1 A g ). Characterizations illustrate that the Li -intercalation pseudocapacitance dominates the charge storage of CoC O -HK electrode, together with the reversible reaction of CoC O +2Li +2e →Co+Li C O on discharging and charging. In addition, CoC O -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 at 2 C and a low decay rate of 0.079% per cycle after 500 cycles. The density functional theory (DFT) calculations show that CoC O /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 CoC O as the high-performance electrode materials for rechargeable Li-ion and Li-S batteries.