磷酸铜表面修饰富锂层状正极材料的制备及电化学性质

用溶胶 凝胶法制备富锂锰基层状正极材料Li_1.18Ni_0.15Co_0.15Mn_0.52O₂, 并对其进行Cu₃(PO₄)₂表面修饰. 用X射线衍射, 扫描电子显微镜和红外光谱测试样品的表面形貌, 并对样品进行恒电流充放电测试及电化学阻抗谱测试. 结果表明: Cu₃(PO₄)₂均匀包覆在材料表面, 以非晶态存在, 修饰后Li+在过渡金属层中的有序排列被破坏; 表面修饰后富锂材料的首圈库仑效率由77%提高至94%； 表面修饰前后材料的初始放电比容量均为244 mA·h/g, 100圈循环后经Cu₃(PO₄)₂表面修饰的富锂材料的放电比容量为203 mA·h/g, 容量保持率为83%； 表面修饰后的材料在3.0,2.7 V出现了一对氧化还原峰, 相对应在充放电曲线出现新平台; Cu₃(PO₄)₂修饰后富锂层状正极材料的阻抗明显减小.

Preparation and Electrochemical Properties of Cu3(PO4)2 Modified Li Rich Layered Cathode Material

Lithium rich layered cathode material Li_1.18Ni_0.15Co_0.15Mn_0.52O₂ was synthesized by the sol gel method, then surface coated using Cu₃(PO₄)₂. The surface morphology of the samples was measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy, and the samples were tested by constant current charge discharge and electrochemical impedance spectroscopy. The results show that Cu₃(PO₄)₂ distributes uniformly on the surface of the material. Cu₃(PO₄)₂ exists in amorphous form and the ordered arrangement of Li⁺ in transition metal layer is destroyed after modification. The initial Coulomb efficiency of the material is increased from 77% to 94% after surface modification. The initial discharge capacity of the all materials is 244 mA·h/g, the specific discharge capacity of the Cu₃(PO₄)₂ modified material is 203 mA·h/g after 100 cycles, and  the capacity retention is 83%.  A pair of redox peaks appear at 30, 27 V while the charge/discharge curve appear a new platform after surface modification. The impedance of surface modified lithium rich layered cathode material is obviously reduced.