合成温度对全梯度正极材料LiNi0.7Co0.15O2的结构和电化学性能影响

通过控制结晶法和浓度梯度进料的方式制备了Ni、Co和Mn三元素组分含量呈全梯度分布的类球形Ni_0.7Co_0.15Mn_0.15（OH）₂前驱体，与LiOH·H₂O均匀混合并焙烧后获得LiNi_0.7Co_0.15O₂正极材料，系统研究了不同焙烧温度对材料Ni、Co和Mn三元素扩散情况、晶体结构及电化学性能的影响规律。通过能谱仪（EDXS）分析不同焙烧温度下材料颗粒中Ni、Co、Mn三元素的扩散程度。研究结果表明，在800℃下焙烧得到的正极材料梯度分布特征明显且电化学性能最佳，首次放电比容量为186.1 mAh·g^-1（2.8~4.3 V，0.2C），2C大倍率充放电条件下循环200次后容量保持率为90.1%。这种材料兼具高比容量及良好的循环稳定性，可以用作下一代高能量密度锂离子电池正极材料。

Effect of Synthesis Temperature on the Structural and Electrochemical Properties of a Full Concentration Gradient LiNi0.7Co0.15O2 Cathode Material

Spherical Ni0.7Co0.15Mn0.15(OH)2 precursor with a full concentration gradient of Ni, Co and Mn elements was obtained via co-precipitation method. The precursor was evenly mixed with LiOH?H2O and then sintered at 750~900 ℃ for 12 h in oxygen to synthesize LiNi0.7Co0.15Mn0.15O2 cathode material with the Ni rich in core and Mn rich in the outer layer. The diffusion of Ni, Co, and Mn under different calcination temperatures led to various elements homogeneity, analyzed by energy-dispersive X-ray spectroscopy (EDXS). Then, the electrochemical properties of samples were investigated by the charge-discharge test and electrochemical impedance spectroscopy (EIS) test. The results indicated that the cathode material sintered at 800 ℃ had an obvious concentration-gradient distribution with a shell of LiNi0.52Co0.24Mn0.24O2 and exhibited the optimal electrochemical performance. Under the voltage range 2.8~4.3 V and, it delivered an initial discharge of 186.1 mAh?g-1 at a charge-discharge rate of 0.2C, and showed an excellent capacity retention of 90.1% after 200 cycles at a high rate of 2C.