Embedding NiCo₂O₄ Nanoparticles into a 3DHPC Assisted by CO₂‑Expanded Ethanol: A Potential Lithium-Ion Battery Anode with High Performance

Abstract

A high-performance anode material, NiCo₂O₄/3DHPC composite, for lithium-ion batteries was developed through direct nanoparticles nucleation on a three-dimensional hierarchical porous carbon (3DHPC) matrix and cation substitution of spinel Co₃O₄ nanoparticles. It was synthesized via a supercritical carbon dioxide (scCO₂) expanded ethanol solution-assisted deposition method combined with a subsequent heat-treatment process. The NiCo₂O₄ nanoparticles were uniformly embedded into the porous carbon matrix and efficiently avoided free-growth in solution or aggregation in the pores even at a high content of 55.0 wt %. In particular, the 3DHPC was directly used without pretreatment or surfactant assistance. As an anode material for lithium-ion batteries, the NiCo₂O₄/3DHPC composite showed high reversible capacity and improved rate capability that outperformed those composites formed with single metal oxides (NiO/3DHPC, Co₃O₄/3DHPC), their physical mixture, and the composite prepared in pure ethanol (NiCo₂O₄/3DHPC-E). The superior performance is mainly contributed to the unique advantages of the scCO₂-expanded ethanol medium, and the combination of high utilization efficiency and improved electrical conductivity of NiCo₂O₄ as well as the electronic and ionic transport advantages of 3DHPC