Chemical reduction-induced oxygen deficiency in Co₃O₄ nanocubes as advanced anodes for lithium ion batteries

Cobalt (II, III) oxide (Co₃O₄) nanostructures have attracted much attention as a candidate for anode materials in lithium-ion batteries (LIBs) due to its unique physical/chemical properties and high specific capacity. However, critical issues, such as low electronic conductivity, inefficient ionic diffusion, and large volume change during battery operation, have to be addressed before practical applications. In this work, we report a facile chemical reduction approach to modify Co₃O₄ nanocubes by NaBH₄ solution treatment. The microstructure and chemical composition analysis indicate that the modified Co₃O₄ nanocubes are oxygen deficient and other secondary phases are not formed during the processing. The degree of oxygen deficiency can be well controlled by altering the concentration of NaBH₄ solution. When evaluated as the anodes for LIBs, the optimized sample shows a reversible capacity of 873.5 mAhg⁻¹ after 50 cycles at a current density of 0.1 Ag⁻¹, and a charge-discharge capacity of 569.1 mAhg⁻¹ at a higher current density of 5 Ag⁻¹. The balanced oxygen deficiency and crystallinity in the chemically reduced nanostructured electrodes are supposed to be responsible for the improved lithium storage properties. We believe that the facile solution-based chemical reduction strategy provides an alternative way to control the defects in different functional nanostructures for broader applications.