Effects of the Mn/Ni ratio on the battery performance of layered Na-Ni-Mn oxide cathode materials in sodium-ion batteries

The development of efficient sodium-ion batteries is essential to overcome the issue of limited lithium sources for preparing lithium-ion batteries. Layered Mn-based cathode materials have significant application potential because of their simple structure and high specific capacities. Serious voltage attenuation and phase transition are the prominent problems of layered manganese-sodium ion batteries. To eliminate these issues, in this study, we investigated the effects of different Mn/Ni ratios in Na-Ni-Mn cathode materials on their structural stability and electrochemical performances. Na 0. 8MnO 2 (NNM-8010), Na 0.8 Ni 0.1 Mn 0.9 O 2 (NNM-819), Na 0.8 Ni 0.2 Mn 0.8 O 2 (NNM-828), and Na 0.8 Ni 0.3 Mn 0.7 O 2 (NNM-837) were synthesized and characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and electrochemical analyses. The addition of Ni 2+ increased the Mn oxidation state from + 3 to + 4, thus reducing the Jahn–Teller effect of Mn 3+ and stabilizing the material structure. NNM-819 exhibited the best electrochemical performance. Its initial discharge-specific capacity was 198.5mAh g −1 at a current density of 0.2C, and the capacity retention rate after 100 cycles was 86.9% at 0.5C. Moreover, its capacity retention rate at 1.0C high-rate cycling after 100 cycles remained high 81.9%. Graphical Abstract