High rate sodium ion battery anodes from block copolymer templated mesoporous nickel–cobalt carbonates and oxides

Abstract

Micelle-templated ordered mesoporous nickel–cobalt carbonates and oxides are fabricated using a metal nitrate–citric acid strategy, which avoids the hydrolysis and aging requirements associated with sol–gel chemistry. A series of mesoporous Ni_xCo_(3−x)(CO₃)_y and Ni_xCo_(3−x)O₄ films with varying Ni–Co compositions and 14 ± 4 nm mesopores are fabricated with the same block copolymer template. AFM and GISAXS analysis indicates that the mesostructure is maintained through the formation of the carbonate and oxide, while GIXD profiles confirm formation of pure spinel phases of semi-crystalline Ni_xCo_(3−x)O₄. The micelle templated mesopores are interconnected and provide transport paths for the electrolyte to minimize the solid-state diffusion requirements associated with battery electrodes. These materials exhibit good performance as sodium ion battery anodes even at high current densities of 4 A g⁻¹. Amongst the mixed-metal oxides, Ni₂CoO₄ exhibits the highest specific capacity of 239 mA h g⁻¹ after galvanostatic cycling at a current density of 1 A g⁻¹ for 10 cycles. We attribute the superior performance of Ni₂CoO₄ at high rates to the high surface area and short ion-diffusion paths of the nanoporous anode architecture, while the higher nickel content in the mixed metal oxide provides enhanced stability during oxide formation along with enhanced electronic conductivity, leading to improved cycling stability of the anode. This micelle template metal nitrate–citric acid method enables new possibilities for fabricating variety of ordered mesoporous mixed-metal carbonates and oxides that could be used in a wide range of applications.