Owing to the high theoretical capacities and high abundance, the binary and ternary transition metal oxides (TMOs) have been widely studied as the next generation anode materials for rechargeable lithium-ion batteries (LIBs). However, TMOs electrodes still have some fatal flaws, such as large volume, poor cycling stability and detrimental structural collapse during the charge/discharge process. Development of hybrid carbon-based TMOs nanocomposites is one of the promising ways to solve the above limitations to promote the energy storage performance for the needs of high-power electric vehicles (EVs) and LIBs.

Among the polynary TMOs, cubic spinel crystallize ZnCo₂O₄ has drawn considerable attention because of its unique crystalline structure and electrochemical reaction mechanism. Although different preparation methods for the specific electrochemical performance have been reported, those special morphologies of ZnCo₂O₄ electrodes are still needed to further improve to meet the needs of high-power applications.

Two-dimensional reduced graphene oxide (rGO) is known to be one of the promising carbon-based materials as an excellent building block and an ideal conductive platform for anode materials. Besides, oxygen-containing groups are abundant on the surface of the rGO so that these groups are very reactive to oxidize the electrolyte and subsequently minimize the electrochemical instabilities. Furthermore, rGO sheets have a relatively low volumetric change during the electrochemical process. It is expected that intimate interactions between TMOs and rGO cannot only promote Li⁺/electrons transfer, but also inhibit the volume expansion and aggregation during the electrochemical cyclic process.

Chemically integrated hybrid ZnCo₂O₄/rGO nanocomposites have been synthesized through a polyol process. Ultrafine ZnCo₂O₄ particles grow and embed on the surface of rGO sheets. Owing to the special nanoparticles-on-sheets structure, the composites exhibit the excellent initial electrochemical discharge capacity for rechargeable LIBs (~1300 mAh g^-1 at the current density of 200 mA g^-1), high rate stability (~500/550 mAh g^-1 at 4000 mA g^-1) and outstanding electrochemical cyclic performance (~650/~660 mAh g^-1 at 2000 mA g^-1 after 2000 cycles with a capacity retention of ~65 %). The superior performance of the synthesized composites can be ascribed to the advantage of nanoparticles. With the successful synthesis of hybrid ZnCo₂O₄/rGO nanocomposites, the facile strategy can extend to synthesize the composites with other TMOs for much promising storage applications.