Improved Electrochemical Performance of LiMn2O4 via Ni and Co Gradient Doping

Ni and Co were successfully gradient doped in Mn3O4 (GM) via co-precipitation method. Then, gradient doped lithium manganate (LGM) was synthesized with GM and Li2CO3 as raw materials. To investigate the influence of gradient doping elements on the structure, morphology and the value state of LGM, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscope (XPS) were employed. The results demonstrated that the structure of LGM after gradient doping was almost the same as LiMn2O4 with JCPDS Card No. 35-0782. The SEM figure indicated that the morphology of all prepared samples was spherical grain. From the results of charge-discharge test, it demonstrated that both of the cycle performance and capacity were improved through gradient doping. When the doping content was Co = Ni = 1%, the initial discharge capacity of LGM reached 119.8 mAh/g at discharge current of 148 mA/g between 3 and 4.3 V at room temperature. The capacity still retained 115.8 mAh/g after 200 cycles. The results of impedance spectroscopy (EIS) indicated the R-Omega value of LGM increased with the augment of doping content. XPS curves revealed the valance of Ni and Co were +2 and +3, respectively.