Synthesis And Electrochemical Performances Of Cathode Materials For Lithium-ion Battery

Lithium ion battery has been widely used as the power source for portable electronicssuch as digital cameras, mobile phones and laptop computers, and is also considered theleading candidate for electric vehicles (EV) and hybrid electric vehicles (HEVs). However,there are still some challenges related to cathode material. Although the capacity of somecathode materials is more than300mAh/g, the actual capacity of cathode material is lowercompared with anode material (graphite:372mAh/g). These challenges limit theapplication of lithium battery, especially the development of power battery. So it isnecessary to develop new cathode material or modification to exist material to meet therequirement for such applications.Our research is as follows:(1) To improve the electrochemical properties of spinel LiMn2O4cathode material,LiMn2O4coated with Al doped ZnO (AZO) was prepared by sol–gel method. The effectsof AZO coating on the structural and electrochemical properties were investigated by XRD,SEM, EDS, TEM, EIS, ICP-AES and charge-discharge test. The results demonstrate thatAZO coating can effectively obstruct the direct contact between the cathode electrode andelectrolyte and suppress the dissolution of manganese into the electrolyte. It is shown that1.5wt%AZO-coated LiMn2O4delivers a capacity of114mAh g-1with a capacityretention of95.4%after100cycles operated at1C rate and55℃, which is obviouslyhigher than that of bare LiMn2O4(70.6%). Moreover,1.5wt%AZO-coated LiMn2O4presents an excellent high-rate capability with the discharge capacity of99mAh/g at10Crate.(2) The precursor of LiNi1/3Mn1/3Co1/3O2was synthesized by reverse microemulsiontechnique. We get size-regulated nanopaticles by this method and the particle size is about5~10nm. Finally, we sintered the precursor to synthesize the target cathode material (LiNi1/3Mn1/3Co1/3O2). It is shown that LiNi1/3Mn1/3Co1/3O2which was synthesized byreverse microemulsion technique delivers a high initial discharge capacity of228.3mAh/g.Although it shows a high discharge capacity, the cycle performance is not very good. Toimprove the electrochemical properties of LiNi1/3Mn1/3Co1/3O2cathode material,LiNi1/3Mn1/3Co1/3O2coated with Al2O3was prepared by sol–gel method. The effects ofAl2O3coating on the structural and electrochemical properties were investigated by XRD,SEM, TEM, EIS and charge-discharge test. It is shown that1.5wt%Al2O3-coatedLiNi1/3Mn1/3Co1/3O2delivers a capacity of184.3mAh/g with a capacity retention of94%after50cycles operated at20mA/g. Moreover,1.5wt%Al2O3-coated LiNi1/3Mn1/3Co1/3O2presents an excellent high-rate capability with the discharge capacity of166mAh/g at800mA/g.