Preparation And Modification Of Lithium-rich Layered Cathode Materials

Lithium-rich layered cathode material Li_1.2[Mn_0.54Ni_0.13Co_0.13]O₂（LMNC）is one of the potential cathode materials,which has attracted much attention from researchers because of its high current density,high working potential,environmental friendly and low cost.Despite the advantages of this positive material,they still have disadvantages such as low Coulomb efficiency for the first time,dissolution of transition metals,voltage hysteresis,slow kinetics and severe voltage decay,which lead to deterioration of energy efficiency,power density and cycle performance,thus limiting their practical application.In order to effectively solve the above problems,the materials were prepared by ball milling spray drying method,and the optimum calcination temperature and atmosphere were explored.The bulk ion doping and anion-cation co-doping technology were also used to improve the structural stability of the materials,which restrained voltage decay and phase change to a certain extent,thus improving their electrochemical properties.Specific research contents are as follows:（1）The LMNC positive material was condensed by the ball rolling spray drying method.The effect of the different temperature and the burning atmosphere on the performance of the LMNC material was investigated.The results shown that when the calcination temperature was set to 900℃in oxygen atmosphere,the mixture of Li and Ni in the precursor was the lowest and the structure was more stable.Moreover,the electrochemical performance is prominent.At 1 C,the initial capacity is as high as 179.9 m Ah g^-1,and after 100 laps,the capacity remains at 64.31%.（2）Li[Li_0.2-xMn_0.54-xNi_0.13-xCo_0.13-x]B_xO₂（x=0;0.01;0.02）Li-rich cathode materials were prepared by the same preparation method on the basis of previous experiments.The results show that B³⁺doping in LMNC materials can improve the crystallinity of lithium ions,as well as the cycling and multiplicity properties of the cathode materials by bulk doping to stabilize the structure of the crystals and increasing the lattice parameters.When the amount of B³⁺was0.01,the material had the best electric performance.Under the condition of 1 C,the capacity of the half cell and the full cell was 168.7 m Ah g^-1and 135.2 m Ah g^-1after 100 circles,with the capacity reservations of 87.1%and 72.2%respectively.（3）Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]_1-xMo_xO_2-yF_y（x=0/0.005,y=0/0.01）lithium-rich positive material was successfully synthesized by the same preparation method.The results show that MF-LR samples exhibit the most excellent cyclic stability.Co-doping of Mo and F does not destroy the material structure,but also enlarges the lithium layer spacing,accelerates the diffusion rate of lithium ions,reduces the content of Mn³⁺and the occurrence of Jahn-Teller effect,which stabilizes the material structure.At 1 C rate,the initial capability of MF-LR sample was still 194.7 m Ah g^-1,and after 100 cycles,the capacity decreased by only 8.2%.And for the whole battery,the capacity of the first cycle is 190.7 m Ah g^-1,the capability persist rate is 77.40%after 100 cycles.