Synergistic impact of a low band gap polyanionic-cluster (NaCuPO4) and super-high surface area activated carbon on rechargeable Na-ion battery performance

Abstract

Sodium-ion batteries (SIBs) attract significant interest and demonstrate great potential for energy storage applications due to their abundant resources and excellent electrochemical performance. NaCuPO₄ (NCP), a polyanionic material, is synthesized to utilize the role of Cu²⁺ in modifying the electronic structure and facilitating Na ⁺ diffusion through Cu–O bonding interactions, thereby contributing to the stability of the 3D framework. The NCP/nitrogen-doped activated carbon (NAC) (NCP/NAC) composite forms through high-energy ball-milling technology. The combined impacts of incorporating high-surface-area NAC and the NaCuPO₄ (NCP) result in a high-performance and stable sodium-ion battery. This approach promotes fast electron migration and enhances interfacial contact with the electrolyte. Density functional theory (DFT) studies of NCP reveal a low band gap (0.378 eV), primarily caused by Cu 3d and other p orbitals. The NCP/NAC cathode exhibits an initial discharge capacity of 145.98 mAh g⁻¹ at 1C. Even after 800 cycles, the capacity retention rate remains at 67 %. We believe this work significantly inspires the advancement of polyanionic cathodes in high-performance SIBs.