Core–shell Ni/Fe/Mn@Cu micron particles with high tap density serving as an effective precursor for preparing high-performance cathode materials for sodium-ion battery

Abstract

The layered metal-oxide cathode material, NaCu_1/9Ni_2/9Fe_1/3Mn_1/3O₂ (NaC1N2F3M3), for sodium-ion battery has attracted extensive attention in recent years, due to its low cost, good air stability and excellent electrochemical stability. However, the important precursor, namely Cu_1/9Ni_2/9Fe_1/3Mn_1/3 (denoted as C1N2F3M3), for preparing NaC1N2F3M3 cathode materials is usually prepared through traditional one-step co-precipitation process in industry, which generally affords a low tap density (TD) C1N2F3M3 precursor, and the low TD of the precursor has adverse effects on the electrochemical performance of final cathode materials. In this study, a high TD precursor, C1N2F3M3-H, with a NiFeMn@Cu core–shell structure was prepared by a two-step synthetic procedure. The TD of C1N2F3M3-H is 1.86 g/cm³, which is enhanced by 75% compared with that of C1N2F3M3-L. Importantly, the NaC1N2F3M3-H cathode material prepared from C1N2F3M3-H displays an evidently improved electrochemical performance in the assembled sodium-ion battery compared to NaC1N2F3M3-L prepared from C1N2F3M3-L. The first discharge specific capacity and coulombic efficiency of NaC1N2F3M3-H are 135.34 mAh g⁻¹ and 98.7% in the voltage range of 2.50–4.05 V at 0.1 C. After 100 cycles at 1 C, the capacity retention rate is 89.88%, which is higher than 80.82% for NaC1N2F3M3-L. Moreover, the electrochemical dynamics analysis shows that the NaC1N2F3M3-H electrode has faster Na⁺ diffusivity and lower charge transfer resistance compared to the NaC1N2F3M3-L electrode, indicating that the NaC1N2F3M3-H has better rate performance and higher conductivity. This study develops a two-step method for preparing the high TD precursor containing quaternary metal-oxide components, from which high-performance cathode materials can be obtained.

Graphical abstract