Study On The Surface Modification Of LiNi_0.6Co_0.2Mn_0.2O₂ As Cathode Material For Lithium Ion Batteries

Lithium-ion batteries have been considered as excellent storage carriers for new clean renewable energy sources due to their high energy density,long service life,and environmental friendliness.In order to reduce the dissolution of the transition metal ions of cathode material in the electrolyte and the volume change of the cathode material during charge and discharge,the surface modification of the material is very important.Since LiN i_0.6Co_0.2Mn_0.2O₂ has excellent comprehensive performance in terms of cycle performance and discharge capacity,it was selected as a base material for coating.The synthesized LiN_i0.6Co_0.2Mn_0.2O₂ cathode material is used as the base material to be coated,while ZnO,CoO,FeF₃·3H₂O,FeF₃·0.33H₂O and LiN i_1/3Co_1/3Mn_1/3O₂ which are also ternary cathode materials were used as the clad materials to modify the surface of the substrate.EDS,SEM,XRD,and charge-discharge tests were used to analyze the Morphology,material structure and charge-discharge performance of materials before and after the surface coating.LiN_i0.6Co_0.2Mn_0.2O₂ cathode material was prepared by co-precipitation method,and ZIF-8@Zn and ZIF-67@Co were self-assembled on the surface of the cathode material by the liquid phase method.Through the surface EDS analysis of the pure ZnO,CoO and the coated material,it was confirmed that ZnO and CoO were formed on the surface of the cathoed material particle.The charge-discharge test results show that the CoO-coated cathode material has lower capacity attenuation compared to ZnO-coated and uncoated materials,and has a higher discharge specific capacity at high rates.Using Fe?NO₃?₃·9H₂O and NH₄HF₂ as raw materials,FeF₃·3H₂O was formed on the surface of the substrate cathode material at room temperature,and then the coated material was heated at 180?for 3 hours under N₂ atmosphere to prepare cathode material coated with FeF₃·0.33H₂O.The results of charge and discharge show that FeF₃·3H₂O and FeF₃·0.33H₂O coating can increase the specific discharge capacity of the material,but it does not significantly reduce the capacity attenuation between different rates of the cathoed material,and the cycle stability is slightly improved.The co-precipitation method was also used to form N i_1/3Co_1/3Mn_1/3??OH2 coating on the surface of LiN i_0.6Co_0.2Mn_0.2O₂ material particles.Then the product was washed and dried and then mixed with Li₂CO₃.LiN i_1/3Co_1/3Mn_1/3O₂ coated cathode materials were prepared after furnace cooling.The charge and discharge test results show that the initial discharge capacities of LiN i_1/3Co_1/3Mn_1/3O₂ coated cathode materials at0.5C,1C,2C,and 5C are 166.39,154.42,144.13,and 131.11 mAhg^-1,respectively,the first discharge capacity at 1C,2C,5C holds 92.80%,86.62%,78.79%of 0.5C?.Combined with the cycle performance chart,it can be concluded that the discharge capacity,rate performance,and cycle stability of the cathode material after coating LiNi_1/3Co_1/3Mn_1/3O₂ material has been significantly improved.