Preparation And Electrochemical Performances Of Mn-based Hollow Spherical Cathode Materials For Lithium-ion Batteries

Lithium-ion batteries are now considered to be the technology of choice for future hybrid electric and full electric vehicles to address global warming.Spinel lithium manganese oxide?LiMn2O4?as a cathode material for lithium-ion batteries has been paid much attention due to its low cost,low toxicity,and relatively high energy density.However,LiMn2O4 suffers from a poor cycling behavior due to Jahn-Teller effect and the dissolution of Mn3+.In order to improve the energy density of the lithium manganate cathode material,it is a way to improve its performance by preparing the binary composite material to improve its charge and discharge voltage.For the electrode material,controllable shape and uniform size of the material may prevent local polarization and increase the diffusion of lithium ions.Therefore,we first study the preparation and electrochemical performance of hollow spherical lithium manganate material by precipitation method.Then,we studied the crystal structure,ion diffusion and electrochemical properties of LiNi_0.33Mn_1.67O₄ hollow microsphere by in-situ doping of nickel ions into the lattice of lithium manganite.On this basis,a high voltage LiNi_0.5Mn_1.5O₄ hollow microsphere cathode material was prepared and its electrochemical performance was studied.The main research work is as follows:1.A spinel lithium manganate cathode material with hollow spherical structure was prepared by carbonate precipitation and solid phase sintering.SEM results show that the hollow sphere has a particle size between 3.0-4.0 ?m and has a porous structure with a smooth surface.Lithium manganese ratio of 0.53 obtained by the sample has excellent electrochemical performance,in the first charge and discharge cycle of 0.2 C under the first discharge specific capacity of 134.58 mAh g^-1,the first charge and discharge coulomb efficiency of 96.6%.At 0.2 C after 100 cycles,the capacity retention rate was 95.1%.It shows good cycle stability.2.The spinel LiNi_0.33Mn_1.67O₄ with hollow spherical structure was prepared by in-situ doping of Ni_0.17Mn_0.83CO₃ hollow sphere by carbonate coprecipitation method.And a small amount of nickel ion was substituted for the Mn3+ of lithium manganite.The electrostatic interaction of nickel ions stabilize the of lithium manganese oxide crystal structure,thereby improving its cycle stability.SEM results show that the size of the hollow sphere is between 2.0-4.0 ?m,and the reaction conditions research show that the morphology of the prepared product prepared at 55 ? is more uniform.The initial discharge capacity of the material at 0.5 C is 134.49 mAh g^-1,the capacity retention rate is 97.2% at 1.0 C after 200 cycles.The discharge capacity is 124.11 mAh g^-1 at 5.0 C,and the capacity decay is less than 6.4% after 200 cycles,with good cycle stability.Compared with the lithium manganate prepared by the precipitation method,the material exhibits better magnification performance.3.The study of the second part found that LiNi_0.33Mn_1.67O₄ material is the mixture of the lithium manganese oxide and the high voltage LiNi_0.5Mn_1.5O₄ microcrystalline hollow microspheres structure.The LiNi_0.5Mn_1.5O₄ hollow microspheres were prepared by increasing the content of nickel ions in LiNi_0.33Mn_1.67O₄.SEM results show that the hollow sphere has a pore size between 3.5 and 4.5 ?m and has a porous structure.EDS results show that nickel ions and manganese ions in the material distribution is very evenly.The first discharge specific capacity of the obtained material is 135.01 mAh g^-1 at 0.5 C.The capacity retention rate is 92.0% after 300 cycles at 0.5 C,which has high specific capacity and better cycle performance.The discharge specific capacity at 2.0 C is 124.47 mAh g^-1.After 200 cycles,capacity decay is less than 1.5%,indicating that it has a very excellent rate performance.