To improve the cycle performance of spinel LiMn204 as the cathode material of 4 V class Li secondary batteries, LiNixMn2-xO4 （x=0-0.3） samples were prepared using a simple precipitation method, and the effects of Ni doping on the physical properties and electrochemical performance of the samples were investigated using various methods. All LiNixMn2-xO4 （x=0-0.3） compounds show a single spinel phase, and the lattice parameter （a）, the unit cell volume （v） and particle size decrease with increasing Ni content. The results of the electrochemical experiments showed that the initial charge-discharge capacity of LiNixMn2-xO4 samples in the 3.0-4.4 V range decreases with increasing Ni content except for pure LiMn2O4; however, the capacity in the 4.4-4.9 V range increases with the increasing Ni content. For spinel samples Ni substitution can contribute to the improvement of their cycle performance due to the formation of the stronger Ni-O bond, homogeneous morphology, and sub-micron sized particles, and the sample with x=0.05 has larger peak currents, higher initial capacity and better cycling capability due to its lower electrochemical and diffusion polarization than those of other samples.
Guoguang WANJianming WANGWenqu MAOJianqing ZHANGChunan CAO
The MnO2 samples coated with Ca（OH）2 were prepared by a liquid-phase surface treatment method. The physical properties of the samples were examined by SEM, EDAX and chemical analysis, and their electrochemical performances were investigated by means of galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy （EIS）. The SEM results show that the samples coated with Ca（OH）2 display a porous surface structure. The electrochemical experiments indicate that the surface modification decreases the polarization of MnO2 electrodes and improves their discharge potentials and discharge capacities.
