A NiCo₂O₄ nanosheet-mesoporous carbon composite electrode for enhanced reversible lithium storage

As a member of the ternary metal oxide family, nickel cobaltite is considered as a promising electrode material. This is due to its high theoretical capacity, low diffusional resistance to protons, ease of electrolyte penetration, superior ionic/electronic conductivity and higher electrochemical activity compared to single metallic oxides such as NiO or Co₃O₄. However, NiCo₂O₄'s relatively low electrical conductivity and its tendency to pulverize due to the volume changes experienced during the charge-discharge process remain a pressing issue to be solved. Here we demonstrate a simple co-precipitation and calcination routine to graft ultrathin NiCo₂O₄ nanosheets onto highly-ordered mesoporous carbon CMK-3 to form a new mesoporous-nanosheet structure which can accommodate stresses induced by volume changes and provide favourable conducting paths. The material exhibits a high specific surface area and excellent electrochemical performance, which can be ascribed to the ultrathin NiCo₂O₄ nanosheets and the interconnected conductive network of the mesoporous matrix. The nanosheets and the inner channels of CMK-3 are more beneficial to the diffusion of Li⁺ while the interconnected conductive network favours fast electron conduction.