LiNi_0.8Co_0.1Mn_0.1O₂ Coating-modified With LiAlO₂ And PPy And Electrochemical Performance

Energy density is one of the main parameters of rechargeable batteries,compared with other materials which currently used on a large scale,the high-nickel ternary material LiNi_0.8Co_0.1Mn_0.1O₂ has a high specific capacity,which has attracted widespread attentions.However,the cycle properties and thermal stability of the material are poor,and residual lithium compounds are present on the surface of the material,and the electrode/electrolyte interface is liable to cause side reactions,causing deterioration of the layered structure of the material.In this paper,the ternary material coated with material which have excellent ionic conductivity or electronic conductivity to improve electrochemical properties of the material,and a composite coating which has excellent ionic conductivity and electronic conductivity is build to coat the ternary material,comparing modification effect of single coating and composite coating.Among the lithium ion conductor compounds,the LiAlO₂ compound has a good modification effect,and the aluminum compound is relatively inexpensive.In this paper,LiNi_0.8Co_0.1Mn_0.1O₂ was coated with?-LiAlO₂ by solid-phase methode and hydrothermal-hydrothermal method.The effects of coating amount and calcination temperature on the electrochemical properties of the materials were investigated.Lithium residues on the surface of LiNi_0.8Co_0.1Mn_0.1O₂ are partially consumed as raw materials to synthesize LiAlO₂ coating layer,and the LiAlO₂coating has excellent lithium ion conductivity due to its three-dimensional transmission channel of Li⁺,which simultaneously improves the rate performance and cycle performance of the material.The surface-coated materials prepared by hydrolysis-hydrothermal method have the best performance.When the coating amount of LiAlO₂ is 1mol%and the calcination temperature is 500°C,the specific capacity of the surface-coated material at 0.1 C can reach 189.5 mAh g^-1,and the specific capacity of 10 C can reach 112 mAh g^-1,while the raw material is only 87mAh g^-1.After 200 cycles at 1 C rate,the specific capacity of the surface-coated material was 144 mAh g^-1,while the raw material was only 122.8 mAh g^-1.Among the conductive polymers materials,polypyrrole?PPy?has excellent electronic conductivity and excellent environmental stability,and polypyrrole can resistant to HF corrosion.The NCM811 was coated with polypyrrole by in-situ chemical oxidation polymerization.Among all the surface-coated samples,the material which the coating amount of pyrrole was 2mass%has the best electrochemical performanc,the specific capacity of the material at 10 C was 117mAh g^-1.After 200 cycles at 1 C rate,the specific capacity was 136.3 mAh g^-1,and the capacity retention was 79.5%.On the basis of the above research results,NCM811 was coated with the PPy-LiAlO₂ composite coating were synthesized by the integrated use of hydrolysis–hydrothermal approach and in-situ chemical polymerization,and the electrochemical performance of the material was better than the single coating layer modified material.The discharge specific capacity reached 127.9 mAh g^-1 at 10 C rate,after 200 cycles at 1 C rate,the discharge specific capacity was 149.1 mAh g^-1,and the capacity retention ratio was 85.6%.These results indicate that this composite multi-functional coating design strategy is feasible,and this surface modification strategy could be extended to other cathode materials.