Effects of the Mn/Ni Ratio on the Battery Performance of Layered Na-Ni-Mn Oxide Cathode Materials in Sodium-ion Batteries

Abstract 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. However, sodium-ion batteries with these cathode materials demonstrate considerable voltage attenuation and phase transition during battery operation. 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. Na0.8MnO2 (NNM-8010), Na0.8Ni0.1Mn0.9O2 (NNM-819), Na0.8Ni0.2Mn0.8O2 (NNM-828), and Na0.8Ni0.3Mn0.7O2 (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+ increased the Mn oxidation state from + 3 to + 4, thus reducing the Jahn–Teller effect of Mn3+ 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%.