Research On Preparation And Electrochemical Performance Of LiFe_0.6Mn_0.4PO₄/C Cathode Material

Lithium-ion batteries?LIBs?are concerned widely for its characteristics such as high energy,long cycle life,no memory effect.Inside of LIBs,the cathode material is one of the key factors which determine the performance and price of LIBs.Olivine-type phosphate cathode materials which have the advantages of high energy density,large discharge specific capacity,high voltage platform etc.are expected to apply in the high-end fields such as PHEVs,but part of them have some issues,such as low conductivity and capacity fading.By contrast,the transition-metal phosphate LiFe_0.6Mn_0.4PO₄ which has two operating potentials,3.5 V and 4.1 V,possesses high conductivity,the energy and power density,but the research on a match with electrolytes should be encouraged.On this actuality,the thesis synthesizes LiFe_0.6Mn_0.4PO₄/C cathode materials by the solid-state and sol-gel methods respectively,and researches their electrochemical performance.The results suggest that the discharge specific capacity of the sample prepared by the sol-gel method is higher than that of the material with the solid-state method,and the capacity are 118.9m Ah g-1and 82.7 m Ah g-1,respectively.Moreover,the sol-gel sample has the better cycle stability and rate performance.Compared with the material prepared with FeSO₄,the sol-gel sample using Fe C2O₄ raw material exhibits the better electrochemical performance.The causes may be that C2O₄2-has the stronger complexing ability and is beneficial to the regularization of the particles and the reduction of resistance.Therefore,the iron source,Fe C2O₄ is more suitable for the preparation of LiFe_0.6Mn_0.4PO₄ cathode material with excellent performance.In addition,this paper pays attention to Li Mn PO₄/C cathode as a comparison,exhibiting that the incorporation of Fe can enhance the reversible capacity and cycling stability.Electrolytes have an important impact on the capacities and cycle performance of LIBs.Commercialized lithium hexafluorophosphate-based electrolytes consist of hexafluorophosphate salt and organic carbonate solvents,which may dissolve the cathode materials and decay the performance of the batteries.To study the compatibility between LiFe_0.6Mn_0.4PO₄ and electrolytes,lithium bis?oxalate?borate is chosen as the lithium salt,based upon ethylene carbonate,dimethyl carbonate,and dimethyl sulfite as the supporting electrolyte solvents.At the same time,the electrochemical performances of hexafluorophosphate-based and lithium bis?oxalate?borate-based electrolytes are compared.The study finds that the combination of lithium bis?oxalate?borate and dimethyl sulfite as an excellent S-containing film-forming additive can facilitate the formation of an surfaceprotective film efficiently.In addition,lithium bis?oxalate?borate-ethylene carbonate/dimethyl sulfite electrolyte exhibits the better cycle and rate performance.The results suggest that lithium bis?oxalate?borate-ethylene carbonate/dimethyl sulfite electrolyte has good compatibility with LiFe_0.6Mn_0.4PO₄,which makes it possess an attractive application perspective in the field of rechargeable LIBs based upon LiFe_0.6Mn_0.4PO₄ cathodes.