Growth of ultrafine CuCo2O4 nanoparticle on graphene with enhanced lithium storage properties

Nanosized anode materials have been shown to be successful in addressing the problems of metal oxide anodes during electrochemical reactions. However, issues with low Coulombic efficiencies and poor cyclability of nanostructured metal oxide anodes still need to be resolved. Ultrafine CuCo2O4 nanoparticles of 6∼9 nm uniformly anchored on graphene have been synthesized. CuCo2O4/graphene (CuCo2O4/G) composites show superior lithium-storage performances. A high reversible capacity of 1040 mAh g−1 is achieved at 0.1 C after 80 cycles, and can retain 211 mAh g−1 at a current density of 2 C. Furthermore, the lithiation process of CuCo2O4/G was recorded by TEM. It suggests the Li+ diffuse through an individual CuCo2O4 nanoparticle consists of three stages: (1) the insertion of Li+ without crystalline structure change, (2) the nanoparticle's crystalline lattice collapses, and (3) nanograins grow and reform from the collapsed nanoparticle. The lithium conversion resulting in the formation of a network of many ultrafine nanograins (2 nm) embedded in the Li2O matrix; also these ultrafine nanograins are confined in a layer of crystal, which is beneficial for the improved electrochemical performance. The macroscopic electrochemical performance of CuCo2O4/G was further correlated with the microcosmic in situ TEM results.