尿素改性对钠离子电池负极材料NaTi2（PO4）3电化学性能的影响
Effect on the electrochemical performance of NaTi2(PO4)3 modified by CO(NH2)2 as anode materials for rechargeable Na-ion batteries

为提高水溶液钠离子电池负极材料NaTi2（PO4）3（NTP）的导电性和倍率性能，以尿素（CO（NH2）2）为碳源采用溶剂热法合成了CO（NH2）2/NaTi2（PO4）3（C/NTP）复合负极材料。采用XRD、SEM、TEM、Raman和恒流充放电等手段分析了材料的结构、C/NTP形貌和电化学性能。研究了不同阶段升温速率对C含量、包覆层石墨化程度及对电化学性能的影响。实验结果表明，低于400℃升温速率越小，C/NTP残碳量越高；400~650℃之间升温速率越小，包覆层石墨化程度越高，并提高了其电化学性能；在5C倍率下2℃/min热处理的样品首圈放电比容量为114.9 mAh·g-1，循环30次后容量保持在91.9 mAh·g-1；10C下放电比容量为87 mAh·g-1，20C下放电比容量仍保持在71 mAh·g-1，展现出高倍率下优异的循环性能。 In order to enhance the electrical conductivity and rate capability of NaTi2(PO4)3 (NTP)as anode materials for aqueous rechargeable Na-ion batteries, the C/NTP composites were prepared by the solvothermal strategy using CO(NH2)2 as the carbon source. The crystal structure, surface morphology and electrochemical properties of the obtained CO(NH2)2/NaTi2(PO4)3(C/NTP)composites were investigated by the XRD, SEM, TEM, Raman and constant current charge-discharge testing. The effect of heating rate at different stage on the content of carbon, the graphitization degree of coating layer and the electrochemical performance of C/NTP composites was carefully studied. The results show that below 400℃ the lower of the heating rate, the higher content of carbon remains in C/NTP, and the lower of the heating rate between 400℃ and 650℃, the higher graphitization degree of carbon coating obtained, which also can improve the electrochemical performance of C/NTP composites. The initial discharge capacity of the C/NTP composites treated at the heating rate of 2℃/min reaches 114.9 mAh·g-1 at the current of 5C and maintain as 91.9 mAh·g-1 after 30 cycles, and the discharge capacity even keeps 87 mAh·g-1 at the current of 10C and 71 mAh·g-1 at the current of 20C, which exhibites excellent cycle performance at high current rate. 湖北省自然科学基金（2014CFB781）