Preparation Of Cathode Materials LiNi_0.5Mn_1.5O₄ With Special Morphologies By Coprecipitation Method

After years of development,lithium ion battery has become the most popular energy storage equipment because of its high energy density,long storage time,no memory effect and environmental friendliness.In the past few decades,lithium-ion battery has been used only in small electronic products,but with the further development of the society,lithium ion battery is exploited to meet higher power requirements for electric vehicles.The power supply system for some large equipment is in urgent need of high power and high energy density lithium-ion battery.Cathode material is an important component of the lithium ion battery,which is the key factor to determine the electrochemical performanc e of lithium ion battery.The voltage platform of spinel cathode material lithium manganese nickel（Li Ni0.5Mn1.5O4）is 4.7 V,which meets the requirements of high power.Currently,most of Li Ni0.5Mn1.5O4 on the market is nano level,which is easy to be eroded by the electrolyte,resulting in capacity attenuation.In addition,the calcination temperature during the preparation of the material will affect the growth of the crystal form,and then affect the electrochemical properties of the material.It is found that the nano-and micro spherical and hollow nano-and micro-structure Li Ni0.5Mn1.5O4 own a stable spherical structure,which reduces the contact between the electrode and the electrolyte and improves the electrochemical performance of the material.In this paper,the nano-and micro-structure of Li Ni0.5Mn1.5O4 materials are prepared by co precipitation method successfully and the effect of calcination temperature on the electrochemical properties of the batteries was explored.And then the ratio of precipitation agent is optimized,achieving the preparation of the hollow nano-and micro-structure of Li Ni0.5Mn1.5O4 cathode material with adjustable wall thickness.The results show that the co precipitation method is simple,and the particle size distribution of the material is uniform,and the hollow nano-and micro-structure is easy to be prepared.The calcination temperature has an effect on the electrochemical properties of the material.The optimum calcination temperature of the material is determined by selecting three roasting temperatures.LNMO800 has a regular spherical morphology,good cycle performance and excellent rate performance due to co precipitation method and optimum calcination temperature.In particular,the material possesses good structure stability when the material is calcined 800 ^oC due to its P4332 space group.At the same time,the precipitant has some influence on the morphology of the material and electrochemical performance of batteries.In this paper,the effect of different contents of sodium hydroxide（Na OH）in precipitator on the morphology and electrochemical performance of Li Ni0.5Mn1.5O4 are studied.The hollow structure Li Ni0.5Mn1.5O4 materials with adjustable wall thickness are prepared by adjusting the molar ratio of Na OH and Na2CO3 in solution.After analyzing the data,it is concluded that the spherical precursor particles become smaller with the molar ratio of sodium hydroxide increases.However,it is easy to agglomerate in the calcination process when the molar ratio of Na2CO3 to Na OH is less than or equal to 8.Hollow structure Li Ni0.5Mn1.5O4 owns thinner wall thickness and larger surface pore interval.with the increase of the content of Na OH in the original precipitant.This is because the size of the spherical precursor particles becomes smaller,which can effectively shorten the free path of internal and external atoms,and promote the Kirkendall effect in the reaction process.It is found that the electrochemical performance is the best when the molar ratio of Na2CO3 to Na OH was 10:1（LNMO-C）.The discharge capacity of LNMO-C at 0.2 C is 120 m Ah g^-1,and the discharge capacity is 97.3 m Ah g^-1 at 6 C.