Study On The Preparation Process And Modification Of LiMn_xFe_1-xPO₄ As Cathode Material For Lithium Ion Batteries

Lithium iron phosphate?Li Fe PO4?and lithium manganese phosphate?Li Mn PO 4?have similar crystal structures and theoretical specific capacity and several priorities,such as rich in raw materials,low cost,environmental benignity and good thermal stability.However,the energy d ensity of lithium iron phosphate(578Wh kg^–1)is lower than the energy density of lithium manganese phosphate(701Wh kg^–1),which restricts the further development of lithium phosphate.While at the same time,the electronic conductivity,ionic conductivit y and cyclic properties of lithium manganese phosphate have also affected its application.In order to improve the energy density of lithium iron phosphate,we hope to combine the advantages of lithium iron phosphate and lithium manganese phosphate to synt hesize lithium iron–manganese phosphate.The main research of preparation and modification of material are described as follows:1.To synthesize Li Fe1–x Mnx PO4?x=0.15,0.25,0.35,0.45,0.55,0.65,0.75,0.85?,analytical reagents of Li 2CO3,Fe C2O4·2H2O,NH4H2PO4 and Mn C2O4·4H2O were used as raw materials with stoichiometric calculation by planetary ball milling.The experiment shows better electrochemical performance when x=0.55.The further research about the influence of synthesized temperature and time indicates the heat at650?for 12h shows better cycle–life stability and rate capability.2.Study the effect of manganese source on Li Fe 0.45Mn0.55PO4 by replacing different sources of manganese?Mn CO 3,Mn O2,Mn C2O4·4H2O?.The experimental results show that the energy density of manganese dioxide is much lower than that of manganese carbonate and manganese acetate.Manganese acetate has better electrochemical performance than manganese carbonate,and the different source of manganese will affect the performa nce of the material.On the condition of x=0.35,the Li Fe0.65Mn0.35PO4 composition by manganese dioxide as manganese source shows better rate capability and cycle performance than manganese acetate in a certain range of iron and manganese.3.The effects of carbon sources on the electrochemical properties of the materials were studied by adding 3 wt%different carbon sources?glucose,sucrose,citric acid?.And the different weight ratio of carbon in a certain carbon resource could affect the electrochemical properties of the composition.The result indicates sucrose as carbon adding 1wt%exhibited better electrochemical performance.