Preparation And Carbon Nanotubes Modification Research Of LiNi_0.5Mn_1.5O₄ Cathode

LiNi_0.5Mn_1.5O₄ cathode material has attracted much attention for rechargeable lithium-ion batteries due to its 4.7 V high voltage plateau and high energy density.It becomes one of the new generation potential high energy density cathodes,which can meet the demand of hybrid electric vehicles and electric vehicles.However,the short cycle life and poor high-rate capability hinder its commercialization.In this paper,we studied the preparation and modifaction of LiNi_0.5Mn_1.5O₄ cathode.We analysed different materials with different structure,morphology and electrochemical performance,which prepared at different stineering temperatures in hydrothermal method,and then modified the material using carbon nanotubes gained at best stineering temperature.Besides,we also studied the influence of different precipitation systems on structure,morphology and electrochemical performance in coprecipitation method,and then modified the material via carbon nanotubes obtained at best precipitation systems.The results are as follows:?1?The LiNi_0.5Mn_1.5O₄ materials obtained at different temperatures in hydrothermal method are all Fd-3m space phases.The hollow spherical structure built from polyhedral nanoparticles can be obtained at calcination temperature of 850 ^oC,which owes the best compositive electrochemical performance.The best capability can be attributed to the reduced diffusion path for lithium ions and the well-accommodated volume variation during repeated lithium insertion/extraction.?2?After modified by 5%carbon nanotubes on the surface of material obtained at 850 ^oC,the modified cathode manifests outstanding cycling stability and rate cability.It delivers an initial discharge capacity of 127 mAh g^-1 at 5 C,maintaining104 mAh g^-1 after 500 cycles.At an even higher rate of 20 C,a discharge capacity of121 mAh g^-1 can be maintained.The excellent electrochemical performance dues to the enhanced electronic conductivity resulting from the introduction of 3D carbon nanotubes network on the surface.?3?The LiNi_0.5Mn_1.5O₄ obtained from Na₂CO₃/NH₄HCO₃,Na₂CO₃/NH₄OH and H₂C₂O₄/NH₄HCO₃ systems in coprecipitation method are all Fd-3m space phases.The morphology and electrochemical performance are different when the coprecipitator and PH change.The homogeneous spherical precursor and uniform spherical LiNi_0.5Mn_1.5O₄ material can be obtained through Na₂CO₃/NH₄HCO₃coprecipitation system,which manifests the best elecrtrochemical performance among three coprecipitation systems.?4?The LiNi_0.5Mn_1.5O₄ obtained from Na₂CO₃/NH₄HCO₃ coprecipitation system is further modified by 5%carbon nanotubes.It delivers an initial discharge capacity of 125.6 mAh g^-1 at 5 C,and the capacity retention is 84.1%after 500 cycles.The discharge capacity of 121 mAh g^-1 can be maintained at an even higher rate of 20 C.The elecrtrochemical performance is obviously improved because of the formation of3D carbon nanotubes network on the surface,which accelerates the transfer rate of the electric and further enhances the electronic conductivity.