| Investigation and improvement of novel cathode material has been one of the main directions of lithium-ion battery. Olivine structured lithium manganese phosphate (LiMnPO4) has the advantage of high operating voltage (4.1V), high energy density (697Wh·kg-1) and low cost etc.. However, LiMnP04has very low conductivity which limits its electrochemical properties at rapid charge/discharge and hinders its commercialization. Therefore, how to improve rate performance of LiMnP04becomes an important and hot point of current research. According to this object, present dissertation gives a systematic research on preparation of LiMnP04, the substitution with cation, the structure and the electrochemical properties. The micro-structures and morphologies of these composites were investigated by XRD SEM and EDS. The electrochemical performance has been evaluated by galvanostatic charge/discharge, cyclic votammetry (CV) and electrochemical impedance spectra (EIS).LiMnPO4/C composites were synthesized by solid state reaction which show significantly enhanced electrochemical performance due to smaller particle size after adding oxalic acid in the raw materials. The sample delivers a discharge capacity of42.54mAh·g-1at0.1C, as well as above twice higher than the capacity of the sample without using oxalic acid. The discharge capacity could be further enhanced when both of the samples were post annealed at550℃for1h. Then in situ carbon coating LiMnPO4composites were synthesized using sucrose as conductive additive and they exhibit better electrochemical performance compared with the sample using Super P as carbon resource.Based on the process research of LiMnPO4/C, Fe, Zn and Mg substituted LiMn1-xxMxPO4(M=Fe,Zn and Mg)solid solutions were synthesized and studied. The results show that the conductivity was increased and the charge-discharge property was improved with obviously reduced electrochemical polarization and the cycle performance was also enhanced after substituting with three cations. The crystallite grains of Fe substituted LiMnPO4grew and became less uniform with an increase Fe contents and synthesis temperatures resulting in a fall in the discharge capacity. Among of them, the sample in situ carbon coating LiMno.9Fe0.1PO4synthesized at650℃for10h shows the optimized performance, delivering the capacity of～130mAh·g-1at0.1C and～90mAhg-1at2C. For Zn substituted LiMnPO4, the results reveal that the Zn substitution is highly beneficial for the performance of LiMnPO4, which is different from those previously reported in the former documents. Compared with the pure C-LiMnPO4, the C-LiMn1-xZnxPO4has higher capacity and better rate capability. C-LiMn0.95Zn0.05PO4synthesized at700℃for10h exhibits the best performance providing capacity of144mAh℉g-1at0.1C and102mAh·g-1at2C. Two different processes, solid-state reaction and co-precipitation, were carried out to prepare Mg substituted LiMnPO4. The samples of C-LiMn1-xMgxPO4synthesized by solid-state reaction possess better electrochemical activity but the samples via two methods shows the highest discharge specific capacity when x=0.03.On the basis of the study on single substitution of LiMnPO4, Fe-Zn, Mg-Zn and Fe-Mg co-substitutions were proposed and a synergistic effect of the cation co-doping or co-substitution has been evidenced by experimental research. Co-substitutions of Mn sites have better modification effect than single substitution and Fe-Mg co-substituted LiMnPO4delivers the highest capacity in all samples. Therefore, C-LiMno.9Fe1-xMgxPO4composites were further optimized showing more higher capacity at0.1,1and10C are154,135and63mAh·g-1, respectively, when*=0.01.Finally, C-LiMn0.9Fe0.09Mg0.01PO4composites were synthesized under vacuum condition. Technological conditions of this synthesis method were investigated systematically and optimized which have a porous characteristic. The sample synthesized at700℃for5h shows optimum electrochemical performance with the smallest polarization and the best rate performance.
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