Oxygen-defective Co3O4 for pseudo-capacitive lithium storage

Transition metal oxide is widely studied type of high-capacity anode material for lithium ion batteries. Herein, oxygen-defective cobalt oxide with attractive lithium storage performance is prepared via a two-step strategy. Experimental results shows that there is certain amount of oxygen vacancies in Co3O4. Reversible conversion between metallic Co and CoO during the charge-discharge process was revealed by ex-situ XRD. Reversible morphology evolution is also confirmed by the ex-situ FE-SEM. The oxygen-defective Co3O4 anode shows attractive stability and rate performance. It possesses a discharge capacity of 1006 mAh.g(-1) in the first cycle, with a high initial Coulombic efficiency of 73.9%. A reversible capacity of 896 mAh.g(-1) can be maintained after 200 cycles at 250 mA g(-1). It could even stably operate at an elevated current density of 5000 mA g(-1) for 500 times. Further kinetic analysis reveals that pseudo-capacitance plays a dominant role in the lithium storage of oxygen-defective Co3O4. Existence of oxygen vacancies could not only facilitate Li+ migration but also enhance electric conductivity to a certain extent, resulting in improved lithium storage performance.