Yan Xuedong, Xin Liqing, Wang Hang, Cao Changhe, Sun Shanshan
College of Chemical Engineering, Ningbo Polytechnic Ningbo 315800 PR China.
School of Metallurgy and Environment, Central South University Changsha 410000 PR China.
RSC Adv. 2019 Mar 12;9(15):8222-8229. doi: 10.1039/c8ra10646k.
Carbon coated Li Na V(PO)/C ( = 0.04, 0.06, 0.10, 0.12, 0.18) cathode materials for lithium-ion batteries were synthesized a simple carbothermal reduction reaction route using methyl orange as the reducing agent, which also acted as the Na and carbon sources. The influence of various Na-doping levels on the structure and electrochemical performance of the Li Na V(PO)/C composites was investigated. The valence state of vanadium, the form of residual carbon and the overall morphology of the LiNaV(PO)/C, which showed the highest initial specific discharge capacity of 128 mA h g at the current density of 0.1C (1C = 132 mA g) among this series of composites, were further examined by X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and high-resolution transmission electron microscopy, respectively. The results indicated that a well crystallized structure of Na-doped LiNaV(PO) coated by a carbon matrix is obtained. In the further electrochemical measurements, the LiNaV(PO)/C cathode material shows superior discharge capacities of 124, 118, 113, 106 and 98 mA h g at 0.3, 0.5, 1, 2 and 5C, respectively. High capacity retention of 97% was obtained after 1100 cycles in long-term cyclic performance tests at 5C. The reason for such a promising electrochemical performance of the as-prepared LiNaV(PO)/C has also been explored, which revealed that the synergetic effect of the Na-doping and carbon coating provide enlarged Li diffusion channels and the increased electronic conductivity.
采用简单的碳热还原反应路线，以甲基橙作为还原剂（其同时作为钠源和碳源）合成了用于锂离子电池的碳包覆LiNaV(PO₄)₂/C（x = 0.04、0.06、0.10、0.12、0.18）正极材料。研究了不同钠掺杂水平对LiNaV(PO₄)₂/C复合材料结构和电化学性能的影响。通过X射线光电子能谱、拉曼光谱、扫描电子显微镜和高分辨率透射电子显微镜，分别进一步研究了该系列复合材料中钒的价态、残余碳的形态以及LiNaV(PO₄)₂/C的整体形貌，该复合材料在0.1C（1C = 132 mA g⁻¹）电流密度下的初始比放电容量最高，为128 mA h g⁻¹。结果表明，获得了由碳基体包覆的钠掺杂LiNaV(PO₄)₂的良好结晶结构。在进一步的电化学测试中，LiNaV(PO₄)₂/C正极材料在0.3C、0.5C、1C、2C和5C时的放电容量分别为124、118、113、106和98 mA h g⁻¹。在5C的长期循环性能测试中，经过1100次循环后容量保持率高达97%。还探究了所制备的LiNaV(PO₄)₂/C具有如此优异电化学性能的原因，结果表明钠掺杂和碳包覆的协同效应提供了更大的锂扩散通道并提高了电子电导率。
