Co3O4 hollow nanospheres doped with ZnCo2O4 via thermal vapor mechanism for fast lithium storage

Abstract

Binary metal oxides offer improved anode materials in lithium ion batteries owing to enhanced electrical conductivity but suffer from large volume expansion on lithiation. A novel route to hollow Co<inf>3</inf>O<inf>4</inf> nanospheres doped with ZnCo<inf>2</inf>O<inf>4</inf> is demonstrated that mitigates the expansion issue and shows excellent performance at high current densities. The synthetic route is based on the pyrolysis of binary metal-organic-frameworks (MOFs) with the controlled loss of zinc tuning the micro and nanostructure of the material through a thermal vapor mechanism. The optimal structures, that contain hollow Co<inf>3</inf>O<inf>4</inf> spheres of ca. 50 nm diameter doped with ZnCo<inf>2</inf>O<inf>4</inf>, show a specific capacity of 890 mAh g⁻¹ at a current rate of 0.1 A g⁻¹ and show a similar specific capacity at 1 A g⁻¹ after 120 cycles at high current densities. The kinetics of lithiation/delithiation changes from diffusion-controlled to a surface-controlled process by the nanosizing of the particles. The resultant faster ion diffusion and capacitive storage for lithium ions are responsible for the extraordinary high-rate performance of the hollow structures.