Synthesis And Modification Of LiNi_0.5Co_0.2Mn_0.3O₂ Cathode Material For Lithium Battery

Lithium-ion batteries have been indispensable as a key component of portable electronic devices,electric vehicles（EVs）and efficient energy storage systems to overcome the global warming problem.Cathode materials play a decisive role in increasing the specific energy of Lithium-ion batteries.Ni_0.5Co_0.2Mn_0.3O₂ have become a research hotspot in recent years,due to its high reversible capacity,lower cost,safety and environment friendliness.In this paper,conditions for the preparation of Ni_0.5Co_0.2Mn_0.3（OH）₂ precursorss using coprecipitating method were investigated,including pH value,feed time,solid content and NH₄OH concentration.Ni_0.5Co_0.2Mn_0.3（OH）₂ with a spherical shape and dense surface,a diameter of about 10 μm,and a uniform particle size could be obtained when the pH value was 11.0 and the stirring time was 30 hours.In addition,the concentration of NH₄OH has an important impact on the morphology,structure and the final composition.The Ni_0.5Co_0.2Mn_0.3（OH）₂ prepared at high ammonia concentration of 0.30 mol L^-1 has good crystallinity,dense surface,uniform secondary particle size distribution and high tap density.The solid state method is used to prepare Ni_0.5Co_0.2Mn_0.3O₂ material.After investigations of the different synthesis factors,the optimal conditions were obtained and the synthesis parameters are shown in the following:the Li⁺/Ni²⁺ mixed samples prepared at the current sintering and lithium salt molar ratio of 1:1.05 show lower crystallinity and excellent electrochemical performance.The lithium salt molar ratio is 1:1.05 and the concentration of NH₄OH is 0.30 mol L^-1.The resultant Ni_0.5Co_0.2Mn_0.3O₂ has shown.good layered-structure,high crystallinity and good crystallinity.The material delivers high initial discharge capacity of 156.1 mAh g^-1.After 150 cycles the discharge capacity can retain 137.8 mAh g^-1 with a high first-time Coulombic efficiency（82.5%）.Layered Nd-doped Ni_0.5Co_0.2Mn_0.3O₂ compounds were also successfully synthesized via a coprecipitation-assisted solid-phase method in this work.The effects of Nd doping on the crystal structure,morphology,and electrochemical properties were characterized thoroughly using XRD,SEM,TEM,EDX,and electrochemical tests.Rietveld refinement of the X-ray diffraction data indicated that the Nd-doped samples had lower cation mixing than the raw Ni_0.5Co_0.2Mn_0.3O₂.The SEM and EDX mapping characterization results demonstrated that Nd atoms were uniformly distributed in Ni_0.5Co_0.2Mn_0.3O₂.At 1 C and 10 C,the Li(Ni_0.5Co_0.2Mn_0.3)0.992Nd0.008O2 materials exhibited initial discharge capacities of 189.7 and 101.5 mAh g^-1,respectively,with capacity retentions of 83.3%and 88%,respectively,compared to those of Ni_0.5Co_0.2Mn_0.3O₂（68.1%and 52.5%,respectively）with a cutoff voltage of 4.8 V after 100 cycles.It was found that Ni_0.5Co_0.2Mn_0.3O₂ doped with Nd³⁺ ions can expand lithium ion diffusion channels in the layered structure and stabilize the structure of the material.