Preparation And Electrochemical Performance Of Ternary Ni-Co-Al Cathode Materials

Lithium-ion batteries（LIBs）are one of the hottest new products under the current new century,which have given people more options in terms of energy usage.The popular materials with Ni-rich content(Li Ni_xMn_yCo_1-x-yO₂,Li Ni_xCo_yAl_1-x-yO₂,x≥0.6)have improved to a great extent compared to the previous Li Co O₂ in terms of environmental protection and usage cost and economic benefits.However,problems related to stoichiometric ratio,structural defects and cycling performance still hinder its practical application.Therefore,in this paper,NCA,a Ni-rich ternary cathode material,is chosen as the research object,and a series of experiments and characterization tests are conducted to address some existing problems such as uneven element dispersion,cycling performance,and large surface alkalinity.Firstly,the ternary cathode material precursors were synthesized by solvent thermal method with three different solvent states,such as water,ethanol,ethanol and water,to investigate the effects of different solvents on the electrochemical performance of the cathode material.The results showed that the ternary cathode materials prepared when ethanol was used as the solvent had the optimal electrochemical properties.The crystallinity of the material is good and the distribution of elements is uniform.The first discharge capacity at 0.1 C was 203.3m Ah g^-1;the capacity after 100 cycles at 1 C was 123.2 m Ah g^-1 with a capacity retention rate of 66.7%;and the capacity at 5 C was 121.7 m Ah g^-1in the multiplicity performance test,which showed a significant improvement in electrochemical performance compared with the other two solvents.Next,the cathode material precursors were synthesized by"co-precipitation and freeze-drying"using oxalic acid as the precipitant,and then the target products were synthesized by combining freeze-drying with wet lithium blending in a tube furnace under oxygen conditions to investigate the differences in electrochemical properties of the materials at different solution concentrations.The results showed that the obtained material has excellent layered structure and low Ni²⁺/Li⁺under the experimental condition of 0.15 mol L^-1;its first discharge specific capacity at 0.1 C was 195.7 m Ah g^-1;its capacity after 100 cycles at 1 C was 158.6 m Ah g^-1with a capacity retention rate of 88.75%;in the multiplicative performance test,the capacity was 139.7 m Ah g^-1 at 5 C.Both the cycling performance and the discharge capacity at high multipliers were improved to a certain extent.Finally,the effect of this modification on the electrochemical performance of the material was investigated by using H₃BO₃ and Al₂O₃ to improve the surface alkalinity of the Ni-rich material by"wet coating and heat treatment"and to produce a cladding layer.It was found that when the material was coated on the surface of the cathode material,the surface alkalinity of the material was significantly reduced,which would be very beneficial to reduce the side reactions to improve the electrochemical performance;The initial discharge capacity of Al₂O₃/B@NCA modified composite is 202.4 m Ah g^-1 at 0.1 C.the capacity after 100 cycles at1 C was 165.6 m Ah g^-1 with a capacity retention rate of 89.3%;and the capacity at 5 C was160.9 m Ah g^-1 in the multiplicative performance test.