A Combustion Synthesis Method To Preare LiNi_0.5Mn_1.5O₄ As Cathode Materials For Lithium Ion Battery

There are intensive efforts to develop new cathodes for Li-ion batteries.A major impetus is to find cheaper cathode materials than LiCoO₂ which is the main cathode material used in commercial Li-ion batteries.Among those materials,LiNi_0.5Mn_1.5O₄ received great attentions for it showed the higher discharge capacity with stable cycle-ability at around 4.7V potential.In general,LiNi_0.5Mn_1.5O₄ prepared by a conventional solid-state reaction method,has poor electrochemical behaviors.Sol-gel,co-precipitation,emulsion drying,composite carbonate process,molten salt synthesis,and solution combustion synthesis can obtain high-quality LiNi_0.5Mn_1.5O₄.However,these methods are yet too complicated involving large quantities of solvent,molten salt and organic materials such as citric acid,ethylene glycol, polyvinyl alcohol,lithium chloride,etc.To overcome these disadvantages,Urea combustion synthesis(UCS)method and carbon combustion Synthesis(CCS)were employed for the preparation of LiNi_0.5Mn_1.5O₄.Synthetic variables on the character and performance of LiNi_0.5Mn_1.5O₄ were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM)and electrochemical method.The results showed that the heat generated by carbon combustion or urea combustion could accelerate the formation of spinel LiNi_0.5Mn_1.5O₄(Fd3m)from Li₂CO₃,NiO and Mn₃O₄.The optimal synthesis conditions of LiNi_0.5Mn_1.5O₄ prepared by UCS were found to be a preheating temperature 500℃,the mole ratio of urea/Li 0.57,annealing temperature 900℃and annealing time 4h.The material synthesized using the optimal conditions provided an initial discharge capacity of 133mAh·g^-1and capacity retention of 99.6%after 20 cycles at 25℃.The preheating temperature 800℃,and the mole ratio of carbon/Li is 0.25 in the CCS. Other conditions were similar with the UCS.The material prepared by CCS delivered a discharge capacity of 131.7 mAh·g^-1and capacity retention of 99.3%after 20 cycles at 25℃.Compared with the solid reaction method and the wet method,LiNi_0.5Mn_1.5O₄ can be prepared by UCS and CCS at the shorter time.The research provided here can be considered as the base for developing the simple and effective route to prepare high performance LiNi_0.5Mn_1.5O₄.