Surface Modification And Electrochemical Properties Of LiNi_0.6Co_0.2Mn_0.2O₂ As Cathode Material For Lithium Ion Batteries

With the growing appeal of green energy,the demand for clean energy such as lithium ion batteries is also increasing.Although Lithium-ion batteries have been widely used in production and life,there is still much room for development.It has attracted a large number of new energy scholars around the world to study it.It is urgent to improve the performance of cathode materials which directly restricting the performance of lithium ion batteries.Although,the layered ternary cathode material has become a hot research topic due to the high capacity,low cost and high safety,the negative reaction between cathode materials and electrolyte seriously reduce the rate performance and cycle stability,which is an urgent problem to be solved.Coating modification is a common method to improve the properties of materials through coating the surface with uniform film material,which can suppresses the side reaction between electrode material and electrolyte without changing the structure of the material.In this study,we designed two kinds of ultrathin coating layers(non-solid electrolyte:ZrO2 and solid electrolyte:Li2ZrO3)on the surface of the NCM via a sol-gel-solvent thermal assistant method.We tested the rate performance and the circulation stability.After XRD,SEM,EDS,TEM,XPS test methods,we found that the nanometer ultrathin coating was successfully coated on the surface of the spherical secondary particles without changing the structure of the a-NaFeO2.We performed electrochemical tests in the range of 2.7-4.5 V,under the rate of 0.2 C current density.The result shows that the first cycle discharge capacity of ZrO2-coating material increases to 187.3 mA h/g.Discharge capacity increases to 158.4 mA h/g.Meanwhile,the capacity retention increased to 85.6%after 100 cycles.Especially,the discharge capacity increases to 134 mA h/g at 3C.EIS test showed that the coating layers inhibited the side reaction between electrodes and electrolytes,and reduced the interface impedance.We further investigated the solid electrolyte Li2ZrO3 and its performance on NCM.We added lithium methanol and successfully coated NCM material with the same method without changing the structure.We conduct electrochemical performance tests under the same test parameters.The first cycle capacity of solid electrolyte coated sample increases to 200.1 mA h/g,the capacity after 100 cycles is 172.5 mA h/g,the capacity retention rate is 86.2%,and the capacity at high rate(3 C)is 154.3 mA h/g.The overall performance is better than that of ZrO2 coated samples.The study results show that the electrochemical properties of NCM materials can be effectively improved by coating non-solid electrolyte ZrO2 and solid electrolyte Li2ZrO3,and the effect of solid electrolyte Li2ZrO3 is better.