Preparation And Electrochemical Properties Of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials Coated By Al₂O₃ And LiAlO₂

Lithium-ion batteries are widely used in portable devices,power vehicles and electronic products as energy storage tools due to their environmental friendliness,rechargeable cycles,and high energy density.High-nickel-nickel-cobalt-manganese ternary materials have high discharge specific capacity and are considered to be one of the most promising cathode materials.However,its cycle performance and specific capacity decreased sharply with the increase of cycle times.In this work,the effects of lithium ratio,sintering temperature and time on the structure and electrochemical properties of LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）were explored.The surface of NCM811 was coated with Al₂O₃,LiAlO₂and Al₂O₃-LiAlO₂to explore the change rule and mechanism of its electrochemical properties.Firstly,NCM811 cathode materials with different lithium ratio,calcination temperature and calcination time were synthesized by ball milling mixing and high temperature solid-phase method.When the lithium ratio was 1:1.15,the I_（003）/I_（104）value of NCM811 obtained by calcining at 795°C for 20 h was 1.42,indicating that there was a low lithium-nickel mixing.When charged and discharged at 0.1 C,the initial discharge specific capacity of the cathode material was 193.78m Ah/g.After 100 cycles,the discharge specific capacity was 139.87 m Ah/g,and the capacity retention rate was 72.18%.When discharged at 1.0,2.0 and 5.0 C,the specific capacities of NCM811 were 141.89,117.37 and 83.80 m Ah/g,respectively.Secondly,the Al₂O₃@NCM811 cathode material was prepared by ultrasonic dispersion,ball milling mixing,and solid-phase synthesis.The cathode materials of NCM811 and Al₂O₃@NCM811 were characterized by XRD,XPS,SEM,TEM,EIS,CV and electrochemical properties.The results showed that the Al₂O₃of the cladding layer was amorphous Al₂O₃,and the thickness of the cladding layer formed was 30-70 nm.When the coating amount was 2.0 wt.%,the Al₂O₃@NCM811 material provided an initial discharge specific capacity of 167.39 m Ah/g at 1.0C.After 200 cycles,the discharge specific capacity was 154.94 m Ah/g,and the specific capacity retention rate reached 92.56%.It could be seen that coating Al₂O₃could effectively improve the cycling stability of NCM811 cathode material.Thirdly,LiAlO₂-coated LiAlO₂@NCM811 materials were prepared using Al（OH）₃,LiNO₃and NCM811 as raw materials.The XRD,XPS,SEM,TEM and electrochemical performance test results showed that the thickness of the coating layer formed by LiAlO₂on the surface of the material was 50-70 nm,which was composed of a mixture ofβ-LiAlO₂andα-LiAlO₂.When charged and discharged at 0.1 C,the initial discharge specific capacities of the coated samples with 1.0,2.0,3.0 wt.%and without coating were 170.09,186.58 and 174.27 and 193.78 m Ah/g,respectively.After 100 cycles,the discharge specific capacities were 146.88,160.66,149.32 and139.87 m Ah/g,and the specific capacity retention rates were 86.35,86.07,85.68 and 72.18%,respectively.It was shown that LiAlO₂@NCM811 had higher cycling stability than NCM811 at0.1 C.Finally,double-coated Al₂O₃-LiAlO₂@NCM811 cathode materials were synthesized using Al（OH）₃and LiAlO₂@NCM811 as raw materials.The XRD,XPS,SEM and TEM test results showed that Al₂O₃and LiAlO₂formed a coating layer with a thickness of 10-70 nm on the surface of the material,which could effectively alleviate the lithium-nickel mixing of NCM811 material.When the current density was 0.1 C,the initial discharge specific capacities of the sample with coating amounts of 0.5,1.0 and 1.5 wt.%were 196.26,192.75 and 192.57 m Ah/g,respectively.After 100 cycles,the discharge specific capacities were 189.33,176.88 and 188.04 m Ah/g,and the specific capacity retention rates were 96.47,91.77 and 97.64%,respectively.When the coating amount was 0.5 wt.%,the specific capacity of Al₂O₃-LiAlO₂@NCM811 at 5.0 C was 139.16m Ah/g.The Al₂O₃-LiAlO₂@NCM811 cathode material exhibited higher cycling stability and rate capability.