Study On The Synthesis And Modification Of High-voltage LiNi_0.5Mn_1.5O₄ Cathode Material For Lithium-ion Battery

Rechargeable lithium-ion battery has many advantages,such as high charge/discharge efficiency,wide operating temperature range,long cycle life and little environmental pollution.Currently,commercialized lithium-ion battery cathode materials are mainly LiCoO₂ and Li Ni_xCo_yMn_1-x-yO₂.Although they have high theoretical capacity,the actual discharge capacity accounts for only 48-65%of the theoretical capacity.Additionally,the reserve of cobalt is not rich in earth,leading to high prices,and the material discharge voltage platform are all below 4 V.In order to meet the demand for electric vehicles preferably,a cathode material for high energy density and high operating voltage is required.LiNi_0.5Mn_1.5O₄ is more studied among the high-voltage materials,because it only shows a4.7 V discharge plateau,corresponding to Ni²⁺/Ni⁴⁺redox.In addition,the three-dimensional tunnel,spinel structure and stable discharge structureis owned by LiNi_0.5Mn_1.5O₄ cathode material,meaning that it is one of the promising cathode material for lithium-ion batteries.In this paper,Li Ni_0.5Mn_1.5O₄ is synthesized by using industrial raw materials.In order to find the optimum preparation of LiNi_0.5Mn_1.5O₄,the ratio of lithium,calcination temperature and calcination time are studied firstly.And the influence of doping Mg²⁺,F^-,Ti⁴⁺as well as co-doping La³⁺and Ti⁴⁺on the structure and electrochemical properties of the material are researched secondly.Finally,LiNi_0.5Mn_1.5O₄ is coated by B₂O₃.The structure,morphology,particle size and electrochemical properties of the particles are characterized by X-ray diffraction,scanning electron microscopy,laser particle size,charge-discharge cycles,cyclic voltammetry and AC impedance.It can be seen that the synthetic materials are all spinel structure,but contains the impurity phase Li_xNi_1-x O or NiO.The condition for the best structure morphology and electrochemical properties of material is 5%excess of lithium as well as synthesized at850?for 12 h.At the rates of 1,2 and 5 C,the intial discharge special capacity is 120.8,118.1 and 111.2 mAh/g with excellent capacity retention after 200 cycles.The discharge capacity decreases after the doping F^-,but the cyclic performance has been improved.Samples prepared by doping Mg²⁺,the discharge capacity is little change,but the area of the discharge capacity at the 4.7 V platform is enhanced significantly.In order to make the Ni and Mn elements better mixing,an appropriate amount of ethanol is added while raw materials are mixing,the discharge capacity of the pure sample is 124.3 mAh/g and the proportion for 4.7 V region is 87.3%.After doping 1%Ti⁴⁺,the intial discharge specific capacity is 128.5 mAh/g,and the retention is 97.3%after 700 cycles at 1 C.When LiNi_0.5Mn_1.5O₄ is doped by Ti⁴⁺and La³⁺simultaneously,the intial discharge capacity is 139.1 mAh/g after doping 3%La³⁺and 1%Ti⁴⁺at 1 C.The initial discharge capacity is 136.6 mAh/g after the pure LiNi_0.5Mn_1.5O₄ coated by 1%B₂O₃ at 1 C.