Lithium Ion Battery Cathode Material Li (Ni <sub> 1/3 </ Sub> The Mn <sub> Of The Co. <sub> 1/3 </ Sub> 1/3 </ Sub>) O <sub> 2 </ Sub > Study The Structure And Electrochemical Properties

The layered LiC_1/3Ni_1/3Mn_1/3O₂ has become a promising cathode material for lithium ion batteries due to its low cost, high specific capacity, good capacity retention, mild thermal behavior and stable structure. In this study, LiCo_1/3Ni_1/3Mn_1/3O₂ and Mg or Cu doped materials Li[Ni_1/3Co_1/3Mn_1/3]_1-xM_xO₂(M=Mg or Cu, x=0.02, 0.04, 0.06,0.1) have been synthesized by co-precipitation. The morphology, crystalstructure and electrochemical properties of synthesized materials were studied by means of SEM, XRD and electrochemical test. The lattice parameters and the composition of particle surface were analyzed. The valence state of transition metals (Co, Ni, Mn) of the doped materials were studied. The relationship between lattice parameters, valence state of transition metals and electrochemical property was discussed.The results show that the Mn content in the material is the most and the molar ratio of Ni:Co:Mn is close to 1:1:1 when co-precipitated under pH=11. All materials have the a-NaFeO₂ structure when precipitated between pH10 and pH12.No impurity phase was found in samples. The highest first discharge capacity is reached as Li/M molar ratio equals 1.1.Mg or Cu doping does not change the structure of materials. For Li[Ni_1/3Co_1/3Mn_1/3]_1-xM_xO₂(x=0.02, 0.04, 0.06, 0.1, M=Mg, Cu), the lattice parameters slightly increase with the increasing of amounts of doping. Mg-doped materials have lower cation mixing compared to the undoped material. Cu-doped materials have higher cation mixing compared to the undoped material when the amount of Cu-doping x>0.02.The oxidation states of transition metals (Ni, Co, Mn) in compounds Li[Ni_1/3Co_1/3Mn_1/3]_1-xMg_xO₂ kept unchange when x≤s 0.02, but parts of transition metals were oxidized to higher state when x≥0.04. In Cu-doped materials, Ni³⁺ was found among with Ni²⁺, and Mn³⁺ was found among with Mn⁴⁺. But Co kept the same state. XPS also shows the enrichment of Mg and Li on the particle surface of Mg-doped materials. Cu-doping can restrain the enrichment of Li.Mg-doped materials have lower first discharge capacity, the first reason is Mg²⁺ is electrochemically inactive. The second reason is some electrochemically active Ni²⁺, Co³⁺ were oxidized. Electrochemical tests show that certain amount Mg-doping can improve the rate capacity of materials.