Study On Preparation And Coating Modification Of LiNi_0.6Co_0.1Mn_0.3O₂ Cathode Material For Lithium-ion Batteries

At present,the goal of carbon peaking and neutrality has become the consensus and collective action of all countries in the world and has triggered a revolution in the global energy system and promoted the transformation to a green and low-carbon economy.Electric vehicles（EVs）have gradually become a research hotspot in various countries due to their advantages of green,clean,and diversified power sources,high capacity conversion rate,and sustainable development.Lithium-ion batteries（LIBs）have become the mainstream commercial vehicle batteries in the current market due to their high energy density（200–250Wh/kg）,discharge efficiency,and endurance.Cathode materials are one of the key components of LIBs and are an important factor in determining the battery’s energy density,fabrication cost,and safety performance.Among the many cathode materials（lithium cobalt oxide,lithium iron phosphate,lithium nickel cobalt manganese oxide,and lithium nickel cobalt aluminate）,the nickel-rich ternary layered cathode material(LiNi_1-x-yCo_xMn_yO₂)is preferred due to its high energy density and low temperature.Its advantages of strong adaptability and good charging and discharging performance have attracted the attention of researchers.However,cathode materials still face a series of problems,such as irreversible phase transition,electrode polarization,surface lithium residues,and poor thermal stability,which greatly affect their cycling stability and safety and limit their wider applications.To solve the above problems,this work aimed to investigate the effects of lithiation ratio and calcination temperature on the physical and electrochemical properties of nickel-rich LiNi_0.6Co_0.1Mn_0.3O₂ anode materials through solid-phase calcination.Results showed that under the optimal calcination conditions(Li OH·H₂O to Ni_0.6Co_0.1Mn_0.3（OH）₂molar ratio of 1.05:1 and 750°C for 15 h),the prepared LiNi_0.6Co_0.1Mn_0.3O₂cathode material has a goodα-Na Fe O₂ layered structure.Its secondary particles are spherical,which is beneficial to Li⁺migration.This finding lays the foundation for the subsequent modification of the material.Aqueous NH₄H₂PO₄solution impregnation and low-temperature solid-phase method were used to successfully coat a Li₃PO₄ layer on LiNi_0.6Co_0.1Mn_0.3O₂.Among the samples,the modified0.5NCM613@LPO exhibited the best structural stability and electrochemical properties.Its specific capacity of the discharge at 0.2 C current density was as high as 205.01 m Ah g^-1 with a coulombic efficiency of 85.93%.After 100 cycles at 1.0 C current density,the capacity was 164.10 m Ah g^-1 with a capacity decay rate of 6.92%.Even at a current density of 5 C,the discharge capacity was still 147.83 m Ah g^-1,implying the excellent electrochemical performance of modified0.5NCM613@LPO compared with that of bare NCM613.This improved performance was attributed to the 3D Li⁺diffusion channels in Li₃PO₄that provide high-speed channels for Li⁺de-embedding and increase the lithium ion mobility.In addition,the formed Li₃PO₄ coating reduces the residual lithium compounds on the surface of the secondary particles,protects the internal core material from corrosion by hydrofluoric acid in the electrolyte,stabilizes the laminate structure of the material body,and increases the safety of the battery during use.LiNi_0.6Co_0.1Mn_0.3O₂ materials with Nb₂O₅ powder coating were successfully prepared by ball milling and low-temperature solid-phase method.On the basis of the study on the physical and electrochemical properties of the samples before and after modification,the optimal coating amount was 0.75%.The results showed that bare NCM613 and modified 0.75NCM613@Nb₂O₅ have typicalα-Na Fe O₂-type layered structures and spherical secondary particles that have aggregated from primary particles.EDS results showed that Ni,Co,Mn,and Nb were uniformly distributed on the surface of the material particles.Combined with the results of TEM,this finding confirmed the existence of Nb₂O₅surface coating.The study on the electrochemical properties of the material showed that the discharge specific capacity of0.75NCM613@Nb₂O₅ was 237.39 m Ah g^-1 in the first cycle at a current density of 0.2 C and 176.43 m Ah g^-1 after 100 cycles at a current density of 1 C.The loss rate was only 14%.Compared with the bare NCM613,the modified sample showed a significantly reduced ionic impedance and reduced electrochemical polarization degree and irreversible reaction.This finding was attributed to the successful coating with Nb₂O₅ that improves the structural stability and electrochemical performance of the material.