Preparation And Electrochemical Propertiers Of LiMn_2-2xM（Ⅱ）Ti_xO₄ As Cathode Materials For Li-ion Battery

The equimolar bivalent ion and tetravalent ion co-doped LiMn2O4 samples are synthesized via sol-gel method and ultrasonic-assisted sol-gel(UASG) method.. The influence of pre-sintering temperature, sintering mechanism, lithium manganese molar ratio and different lithium sources are investigated in detail. According to the research results, the optimal synthesis condition is preferentially selected. The bivalent ions such as Mg2+, Ni2+ and Zn2+ were chosen respectively, and the structures, morphologies and electrochemical performance of spinel LiMn2-2xMxTixO4(M=Mg、Ni、Zn, x=0.01, 0.03, 0.05, 0.07, 0.10) were characterized by X-ray diffraction(XRD), Scanning electron microscopy(SEM), Transmission electron microscope(TEM), X-ray photoelectron spectroscopy(XPS), cyclic voltammetry(CV), AC impedance spectroscopy(EIS) and electrochemical tests.The experimental results show that the samples synthesized by UASG method have improved cycle stability. The sample has good capacity retention of 99.4% after 30 cycles. However, we choose sol-gel method for further research, because of the lower discharge specific capacity. The co-doped samples present a single spinel structure without any other impurity. For the co-doped samples, the particle diameter is smaller and the distribution is even. The Mg2+ and Ti4+ ions co-doping improves effectively the cycling stability and discharge specific capacity. For the optimal LiMn1.90Mg0.05Ti0.05O4, the highest discharge specific capacity was 143.4 mAh/g, about 95% of the theoretical specific capacity, and remained 137.9 mAh/g after 30 cycles at 0.5 C in the voltage range of 3.3~4.35 V. The capacity retention could reach 96.2 %, which was far higher than that of the undoped LiMn2O4. The sample can deliver the highest discharge specific capacity of 154.1 mAh/g, in the voltage range of 3.3~4.5 V. By contrast, the small amount of Ni2+ and Ti4+ co-doping can cause the deep discharge and enhance the discharge specific capacity of obtained samples, but the cycle performance can be decreased. With the increasing of co-doping quantity, the initial discharge capacity can be reduced, while the cycle performance is improved to some extent. For the equimolar Zn2+ and Ti4+ co-doped sample, the cycle stability and rate performance, especially the high rate discharge performance, can be improved. At high rate of 4 C, the LiMn1.9Zn0.05Ti0.05O4 can show the best electrochemical performance.