Preparation And Modification Of Concentration-gradient LiNi_0.9Co_0.083Mn_0.017O₂ For Li-ion Battery Cathode Material

Because of the specific capacity and working voltage,LiNi_xCo_yMn_zO₂ is considered to be one of the most valuable cathode materials for research and application.However,it is faced with many challenges in practical application,and many factors will lead to the degradation of material properties and failure.The surface instability of electrode active material,moisture and carbon dioxide in the air are seriously affect the performance of the materials.In order to solve the problems of nickel-lithium mixing in high-nickel terpolymer,this paper synthesized the material LiNi_0.9Co_0.083Mn_0.017O₂ with concentration gradient structure through experimental design,and carried out coating modification.The main research was as follows:（1）High nickel cathode material LiNi_0.9Co_0.083Mn_0.017O₂ with its precursors were prepared by coprecipitation method and high temperature calcination.The morphology and structure of the materials with gradient structure and the general materials were analyzed by the characterization test.The nickel content on the surface of the samples with gradient structure was lower while the nickel content in the center part was higher,and the obtained product was determined as the target product.Compared with the ordinary material,the metal cation mixing degree of the gradient material is lower,and the layered structure is better.In terms of electrochemical performance,the specific initial discharge capacity of the gradient sample at0.2C current density is 221.2 m A h g^-1.The discharge specific capacity can reach 161.1 m A h g^-1 at 5C,the capacity retention rate is 92.6%after 100 cycles,higher than the general material74.8%.The galvanostatic intermittent titration technique test has proved that the concentration gradient design is conducive to the diffusion of lithium ions,increase the interfacial stability of materials,and improve the electrochemical performance.（2）The gradient precursor was coated with zirconium nitrate,and the concentration gradient material coated with Li₂Zr O₃ was obtained by calcination at high temperature.The influence of different Li₂Zr O₃ coating amounts on the material characteristics and electrochemical performance were explored.The characterization results show that the positive electrode material coated with Li₂Zr O₃ is successfully synthesized.When the molar ratio of Zr to active substance is 0.02,the mixing degree of Ni²⁺/Li⁺is the lowest.At the current density of 0.2C,1C,2C and 5C,the specific discharge capacity can reach 219.44 m A h g^-1,195.49 m A h g^-1,189.45 m A h g^-1,165.70 m A h g^-1.The test results show that suitable Li₂Zr O₃ coating treatment can effectively improve the transmission rate of lithium ions in the cathode material,reduce the side reaction between the electrode surface and electrolyte,and improve the electrochemical performance of high nickel cathode.（3）In order to solve the problem that water and carbon dioxide in the air seriously affect the performance of high-nickel terpolymer,the positive material LiNi_0.9Co_0.083Mn_0.017O₂ with concentration gradient structure is mixed with anhydrous ethanol and different amounts of tetraethyl silicate.Finally,the ethoxy-functional polysiloxane coating concentration gradient LiNi_0.9Co_0.083Mn_0.017O₂ was obtained.Under simulated humid conditions,compared with the sample without coating treatment,when the Si molar ratio of coating layer to active substance is 0.03,the discharge capacity increased from 88.30 m A h g^-1（0.1C）,49.27 m A h g^-1（1C）,32.71m A h g^-1（2C）and 12.56 m A h g^-1（5C）to 191.94 m A h g^-1（0.1C）,156.74 m A h g^-1（1C）,129.94m A h g^-1（2C）and 71.48 m A h g^-1（5C）.The results of electrochemical testing and characterization proved that the appropriate amount of EPS coating could effectively reduce the influence of water on the properties of the high-nickel ternary material and reduce the corrosion of HF in the electrolyte.