Bimetallic Oxide Coated LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials For Lithium Ion Batteries

LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）has been one of the most promising cathode materials for lithium ion batteries,but some disadvantages of poor cycle stability and thermal stability significantly obviously limit its commercialization.In this thesis,monometallic oxides（Bi₂O₃ and TiO₂）/bimetallic oxide(Bi₄Ti₃O₁₂)coated NCM811 cathode materials are studied in detail,and the influence of two types of coating structure,interface characteristics,thickness and other factors on the electrochemical performance of NCM811 are further explored:（1）The monometallic oxides/bimetallic oxide coating layers may not damage the crystal structure of NCM811.Both types of coating layers highly improve the electrochemical performance of the cathode materials,moreover,bimetallic oxide coating shows better effect on electrochemical performance of NCM811.（2）1%mol Bi₄Ti₃O₁₂ coated NCM811 is with the best cycle stability and rate performance.After 100 cycles at 3.0-4.5 V,compared with that of NCM811,the discharge specific capacity of the modified sample is increased by 17.7 mAh g^-1,and the capacity retention rate is increased by 11.3%.（3）Compared with monometallic oxides（Bi₂O₃ and TiO₂）,the Bi₄Ti₃O₁₂ coating shows better lithium ion transport kinetics properties,i.e.diffusion barrier of bimetallic oxide is only 425.8 meV.As a result,one bimetallic oxide coating can significantly improve the rate performance of NCM811.