Preparation And Modification Of Cathode Material LiFe_xMn_1-xPO₄/C For Lithium Ion Batteries

With the rapid development of modern technology,energy and environmental issues have become increasingly prominent,which requires the performance of the battery to further improve.Since Lithium-ion battery has high operating voltage,energy density,long cycle life,no memory effect and good environmental influence,it is considered to be the first choice for mobile power.LiMnPO4 has a high energy density because of its high discharge potential(4.1 V)with respect to Li+/Li,but its practical application is limited because of its poor conductivity.In order to overcome these problems,LiFexMn1-xPO4 has now been studied.A large number of studies have shown that the way to increase the rate of diffusion of lithium ions is mainly to reduce and control the morphology of the particles.The improvement in conductivity is generally achieved by coating the conductive layer.In this paper,LiFexMn1-xPO4/C cathode material was prepared by high temperature mechanochemical method.The influence of milling temperature,carbon coating amount and molar ratio of Fe to Mn on the properties of the powders was studied by XRD,SEM,PSD,cyclic voltammetry and electrochemical impedance spectroscopy(EIS).LiFexMn1-xPO4/C could be obtained by milling under the optimal conditions of molar ratio Fe:Mn=8:2 and carbon coating amount of 10 wt.%at 720?.The initial discharge specific capacity was 120.369 mAh·g-1,97.181 mAh·g-1 and 90.386 mAh·g-1 at 0.1 C,0.5 C and 1 C rate,respectively.At-25? the specific discharge capacity was 61.101 mAh·g-1.Based on the above research,LiFexMn1-xPO4/C powder was modified by ion-doping(F-,Ti4+,V5+,Al3+,Mg2+),and the electrochemical properties of LiFexMn1-xPO4/C were researched.The results showed that the initial discharge capacity of the material was greatly improved compared with the undoped LiFexMn1-xPO4/C powder.The results showed that vanadium doping can effectively improve the performance of LiFe0.8Mn0.2PO4/C.The capacity of the samples with vanadium doping content of x=1.5%tested at 0.1 C under-25? was increased to 79.178 mAh·g-1.