| LiCoO2 has been widely used as a cathode material in commerciallithium ion battery production at present. Due to the high cost andshortcoming on security of LiCoO2, many efforts have been made toreplace it. The research development of cathode materials for Li-ionbattery was summarized, this dissertation emphasizes on layeredLiNi1/3Co1/3Mn1/3O2 cathode material. The synthesis, performance, dopingand kinetics of lithium insertion-extraction process of layeredLiNi1/3CO1/3Mn1/3O2 cathode materials were studied.Using NaOH+NH3·H2O as precipitating agent, controling the pHvalue of solution as 10.5, the ratio of NH3 : M2+(M= Ni1/3Co1/3Mn1/3) as0.75:1, precursor has a narrow particle distribution. More over, theparticles are ball-like with big bulk density and tap density. XRD andTG-DTA studies showed (Ni1/3CO1/3Mn1/3)3O4 was prepared at 450℃withNi1/3CO1/3Mn1/3(OH))2.The effects of different precursors, temperature, time and the ratio ofLi/M(M=Ni1/3CO1/3Mn1/3) on layered LiNi1/3CO1/3Mn1/3O2 cathodematerials were studied. On this basis, the best synthesis conditions wereobtained: Li2CO3 and (Yi1/3CO1/3Mn1/3)3O4 were mixed with the ratio ofLi/M(M=Ni1/3CO1/3Mn1/3) being 1/1.08, the mixed materials were calcinedat 500℃; for 6h and then calcined at 950℃for 12h.The cathode materials LiNi1/3Co1/3Mn1/3O2 synthesized at aboveconditions showed that the initial discharge capacity was 133.8 mAh·g-1in 4.2～2.75V at 1C rate and after 100 cycles the capacity retention ratewas 96.3%.The kinetics studies showed that the reversible performance of thismaterial was good, diffusion coefficient related to the discharged statedecreased with the going-on of discharge, and the impedance picture ofLiNi1/3Co1/3Mn1/3O2 was made up of three parts, film impedance of SEI,electrochemical impedance and Warburg impedance caused by diffusionof Li+, the film impedance of SEI is not changed with the voltage whilethe electrochemical impedance is increased with the reducing of voltage.With La, Ce, Zr as doping elements, doping effects on the performance of layered cathode material LiNi1/3Co1/3Mn1/3O2 werestudied. The results showed that Li(Ni1/3Co1/3Mn1/3)0.98Zr0.02O2 had abetter performance. Its cycle performance improved, although itselectrochemical activity was not so better at initial cycles, after 350cycles the capacity retention rate was 97.0％, the capacity discharged to3.4V at 1C rate was 103.5 mAh·g-1. Moreover its cycle performance at60℃was better, after 100 cycles the capacity retention rate was 92.4％. |
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