碳包覆对LiNi_(0.5)Mn_(1.5)O_4电化学性能的影响

以蔗糖为碳源,采用溶液沉积-真空热解法制备了LiNi_(0.5)Mn_(1.5)O_4/C复合材料。用热重与差热分析、X射线衍射分析、扫描电镜分析及电化学测试等手段对LiNi_(0.5)Mn_(1.5)O_4/C的微观结构、表面形貌和电化学性能进行了研究。结果表明,蔗糖热分解后在LiNi_(0.5)Mn_(1.5)O_4颗粒的表面包覆形成了一层无定形碳。无定形碳可以有效阻止LiNi_(0.5)Mn_(1.5)O_4颗粒的聚集,增加电极的导电面积,降低电池极化,从而改善LiNi_(0.5)Mn_(1.5)O_4的电化学性能。与未包覆的LiNi_(0.5)Mn_(1.5)O_4粉末相比,LiNi_(0.5)Mn_(1.5)O_4/C复合材料具有更高的可逆容量、更稳定的循环性能和更好的倍率性能。0.2C放电时,LiNi_(0.5)Mn_(1.5)O_4/C复合材料的首次放电容量达到144.8mA.h.g-1,经60次循环后平均每次循环的容量损失仅为0.0081%。而1.0C和2.0C放电时,LiNi_(0.5)Mn_(1.5)O_4/C复合材料的首次放电容量分别保持在131.9mA.h.g-1和122.4mA.h.g-1。

Effect of C-coating on Electrochemical Performances of LiNi_(0.5) Mn_(1.5) O_4

LiNi_(0.5) Mn_(1.5) O_4/C composite was prepared by the solution deposition-vacuum pyrolysis method using LiNi_(0.5) Mn_(1.5) O_4 and sucrose as raw materials.The microstructure,surface morphology and electrochemical properties were characterized by various electrochemical methods in combination with thermogravimetric (T_G) analysis and differential thermal analysis (DTA),X-ray diffraction (XRD) and scanning electron microscope (SEM).It was found that the amorphous carbon layer is coated on the surface of LiNi_(0.5) Mn_(1.5) O_4 due to the pyrolysis of sucrose.The amorphous carbon can prevent the LiNi_(0.5) Mn_(1.5) O_4 particles from aggregation,increase the conductive area of electrode,decrease the polarization of cell and improve the electrochemical properties of LiNi_(0.5) Mn_(1.5) O_4 effectively.Compared to LiNi_(0.5) Mn_(1.5) O_4,the LiNi_(0.5) Mn_(1.5) O_4/C composite has increased the reversible capacity,stabilized the cycling performance and improved the rate performance.The first discharge capacity of LiNi_(0.5) Mn_(1.5) O_4/C is more than 144.8 mA·h·g~(-1) and the capacity loss per cycle is only 0.008 1% after cycling 60 times at 0.2 C.While the first discharge capacity of LiNi_(0.5) Mn_(1.5) O_4/C keeps at 131.9 mA·h·g~(-1) and 122.4 mA·h·g~(-1) respectively even cycling at 1.0 C and 2.0 C.