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 2 O 4 particles (CoC 2 O 4 -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 2 O 4 -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 CoC 2 O 4 -HK electrode, together with the reversible reaction of CoC 2 O 4 +2Li + +2e - →Co+Li 2 C 2 O 4 on discharging and charging. In addition, CoC 2 O 4 -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 CoC 2 O 4 /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 2 O 4 as the high-performance electrode materials for rechargeable Li-ion and Li-S batteries.