Study On Synthesis And Modification Of Nickel-cobalt Lithium Aluminate(NCA) Cathode Materials

Nickel cobalt aluminate(LiNi_xCo_yAl_1-x-yO₂,NCA,x≥0.8)ternary cathode materials of lithium ions batteries possess the advantages of high capacity,good thermal stability,low cost,and environmentally friendly,in which LiNi_0.8Co_0.15Al_0.05O₂cathode materials are widely investigated and commercialized.High-nickel with low-cobalt or cobalt-free anode materials become a research hotspot at present.However,some fatal flaws,such as rigorous preparation processes and difficult coating due to a high alkalinity,hinder the further production and application of ternary cathode materials.The research and analysis about the synthesis process and comprehensive performance of LiNi_0.88Co_0.09Al_0.03O₂（NCA88）precursors and cathode materialsare carried out in this paper,which are aiming to yield high-density spherical NCA88precursors and high-electrochemical performance NCA88 cathode materials by exploring the optimal process conditions.Firstly,NCA88precursors are prepared by the co-precipitation method,and the effects of synthesis process conditions,such as ammonia concentration,pH,reaction time,and aging time,on the precursor performance are mainly investigated by through the particle size test,tap density test,ICP,SEM,XRD and other characterization analyses.The optimal process conditions are:ammonia concentration of 1.0 mol/L,pH=11.0,reaction time of 24 h,and aging time of 9 h.The finally obtained NCA88 precursor presents a regular sphere with aβ-Ni（OH）₂ type structure,which demonstrates a uniform size distribution with D₅₀=12.8μm and up to 2.15 g/cm³ of the tap density.Secondly,the NCA88 cathode materials are synthesized by a high-temperature solid-phase method,in which the effects of sintering temperature,sintering time,and Li ratio on the morphology,crystal structure and electrochemical performance of the synthesized NCA88 cathode material are detailed investigated.The characterization results show that the as-prepared NCA88 cathode materials can deliver the best electrochemical performance when the precursor powders are sintered at 700℃ for 12 h with 1.05 of Li ratio,in which the assembled coin cell can deliver an initial discharge specific capacity of 203.3 m Ah/g with an initial coulombic efficiency of 85.74%at 0.1 C,and retain a discharge specific capacity of 147.7 m Ah/g with a retention rate of 79.45%after 100cycles at 1.0 C.Finally,NCA88 powders are modified with Li₃PO₄ powders to improve the cycling stability of the cathode materials.By comparing the properties of the materials before and after being coated,the optimal coating amount of Li₃PO₄ powders and the corresponding coating modification mechanism are investigated.The coin cell with the modified sample with the optimal coating content of 0.5%shows the best electrochemical performance,in which the cell can retain a discharge specific capacity of 160.9 m Ah/g with an improved retention rate of 89.74%after 100 cycles at 1.0 C.