Researchs On The Prepareation And Modification Of LiNi_1/3Co_1/3Mn_1/3O₂ Cathode Material For Lithium-Ion Battery

LiNi 1/3 Co 1/3 Mn 1/3 O2 was emerging as the most promising cathode material to replace LiCoO2, because of its lower cost, easily prepared, higher reversible capacity, wider voltage range, milder thermal stability and less toxicity. However, the main difficulties we meet in the investigation were its low tap-density and worse cyclic performance when charged to higher cut-off voltage and discharge at different C-rates. Analysis showed that LiNi 1/3 Co 1/3 Mn 1/3 O2 materials will have better electrochemical properties after doping and surface modification. In this paper we studied the preparation and doping modification of LiNi 1/3 Co 1/3 Mn 1/3 O 2 material in detail.The layered LiNi 1/3 Co 1/3 Mn 1/3 O2 powder was prepared by hydroxide co-precipitation method. The effects of pH value, concentration of NH 3·H2O, synthesized time, calcination temperature and extra Li amount on the morphology, structure and electrochemical properties of the cathode material were investigated in detail. Meanwhile, the modified materials were also conducted on the basis of LiNi 1/3 Co 1/3 Mn 1/3 O2 material. We analyzed the material's superficial morphology, structure and phase composition by using Tap-Density, Particle Size Distribution, Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD); X-ray Photoelectron Spectra (XPS) was used to analyze the valence states of Ni, Co and Mn ironic in material; Charge-Discharge test was used to study the specific capacity and cyclic properties of cathode material. Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscope (EIS) were used to discuss electrochemical reactive mechanism. The results showed that the layered Li[Ni 1/3 Co 1/3 Mn 1/3 ]O2 powder had spherical shape and narrow particle size distribution and the tap-density was 2.09g·cm-3 . The highest initial discharge capacity of 147.04mAh g -1(2.8~4.3V) and 173.27mAh g-1 (2.8~4.6V) and 100 th capacity retention of 94.95%(2.8~4.3V) and 77.02%(2.8~4.6V) were obtained as pH value was 12, concentration of NH 3·H 2 O was 0.36mol·L-1, synthesized time was 24h, calcination temperature was 900℃and the Li/M(Ni+Co+Mn) ratio was 1.1. Form the XPS results we found that in Ni 1/3 Co 1/3 Mn 1/3 (OH) 2 the valence states of Ni, Co and Mn were 2+; and in Li[Ni 1/3 Co 1/3 Mn 1/3 ]O2 the valence states of Ni, Co and Mn were 2+, 3+ and 4+, respectively. After doped Cr, the tap-density could reach 2.51 g·cm-3 and its volumetric capacity was 327.18mAh·cm-3. EIS results indicated that material electrochemical reaction resistance had sharply decreased after doping Cr and F, so in the voltage range of 2.8~4.6V the highest 50th capacity retention were 87.69% and 108.67% respectively, which was higher than the bared one(83.35%). Meanwhile the capacity retention was highly improved by 55.1% as doped Cr and 63.2% as doped F, when the cathode material was discharged at 720mA·g-1 current density.