| Improved preparation method,doping and modification technology were carried out as follow in this paper,in order to obtain LiNi1/3Co1/3Mn1/3O2 with high rate capability.The results showed that all the measures could improve its rate capability,and modification technology indicated best inproved rate capability.LiNi1/3Co1/3Mn1/3O2 was prepared by a carbonate co-precipitation methode combined with a ultrasonic technique,followed by a high temperature solid state reaction,and the effect of calcined temperature and ultrasonic technique to material were also taken.Scanning electron macroscopy(SEM),X-ray diffraction(XRD),cyclic voltammetry(CV) and charge-discharge cycling were used to investigate the material's characters and electrochemical performance.The particle size was about 200nm and its distribution was uniform,as observed by SEM.Initial discharge capacity of LiNi1/3Co1/3Mn1/3O2 prepared with above method combined with a ultrasonic technique and then calcined at 900℃was 156.3 mAh/g at 0.1 C-rate.That of 137.8 mAh/g,129.3 mAh/g,114.4 mAh/g,95.5 mAh/g were also gotten at 1 C,2 C,5 C,10 C,respectively. The electrode showed good rate capability since little capacity fade appeared after 5 cycles at such different rates,even at 10C and 96%of initial discharge capacity was maintained after 40 cycles at 1 C.The layered LiNi1/3Co1/3Mn1/3O2 cathode materials doped by A1 and Mg were prepared,taking glycol as dispersant.The effects of different doped element(Al,Mg)on electrochemical properties of the synthesized materials were also studied.The bare material showed 11%capacity fade of its first discharge capacity after 10 cycles at 0.1 C-rate.Cycling properties of the doped element(Al,Mg)materials were improved.Their capacity fade rates were only 2.5%and 3.3%,respectively,after 10 cycles. At 1 C-rate,the capacity fade of bare material,Mg and Al dopant ones after 10cycles were 24.8%,14.6%and 15.9%,which indicated that the dopant material had better rate capability than that bare one.Al2O3 and AlF3 were coated on the surface of LiNi1/3Co1/3Mn1/3O2 particle,respectively,by chemical precipitation method and the effects of different coated contents on their electrochemical performance were studied.The thicknesses of Al2O3 and AlF3 coated layer were about 10 nm and 3 nm,respectively,displaying by TEM.It's found that the material with 1.5 wt%coated content has best electrochemical performance.The 1.5 wt%Al2O3 coated LiNi1/3Co1/3Mn1/3O2 at 2 C-rate showed 90.9% capacity retention of its initial discharge capacity,while the bare one showed only 47.4%.At 5 C-rate,the capacity retention of coated one after 20 cycles was 87.6%,while the bare one's was 64.5%.As for the AlF3 coated one,the capacity retention at 2 C-rate was 90.2%。At 5 C-rate, the capacity retention after 50 cycles of the bare and AlF3 coated ones were 52.6%and 91.4%,respectively.It's obviously that the AlF3 coated one showed better rate capability than Al2O3 coated one.The results of EIS showed that the little change of charge transfer resistance of both Al2O3 and AlF3-coated LiNi1/3Co1/3Mn1/3O2 at higher charge-discharge rate was the main reason why the electrochemical performance improved obviously.Besides,Al2O3 and AlF3 coated layer could improve the cyclic stability at high cut-off voltage or high operating temperature. |
