Synthesis And Modifying Of Rich-Lithium Nickel-Manganese-Chromium Cathode Materials

In this research, a series of Li[Li1/3Mn2/3]O2-LiCrO2-Li Ni1/2Mn1/2O2 compounds were investigated, lithium-rich cathode material of manganese–nickel–chromium ternery system Li–Mn–Ni–Cr–O was synthesized by sol gel, the influence of Cr/Mn +Ni(Set up Cr/Mn+Ni for x,x=0.44,0.38,0.29,0.21,0.15, called A-E, hereinafter)on their structures and electrochemical behavior were investigated and choose the best material. The water processing, reaction temperature, mole ratios of citric acid and transition metal, solvent, calcining temperature and time were studied in the preparation process of the best material. Then surface modifications of the best material were studied. Their crystal structures, the content of element and the electrochemical performances were investigated by XRD, ICP, SEM, EIS and CV and so on.The mole ratios of citric acid and transition metal was 1:1,pH=7, A ~ E series precursors were synthesized at 55℃, presintered 4h under 400 ℃, then calcined 12 h under 800 ℃, the samples prepared under the condition had a layered structure,but A~E compounds exhibited strong hygroscopicity; the electrochemical performance of the series of materials obviously improved by water processing and the structure of the material had no obvious change; experiments show chemical composition of the dissolution was Li2CrO4. Among them, the Li1.016Cr0.103Mn0.464Ni0.356O2 sample has good electrochemical performance. Continue to Li1.016Cr0.103Mn0.464Ni0.356O2 optimization, the solvent was water; the mole ratios of citric acid and transition metal was 1:1; the reaction temperature was 85 ℃, then calcined 12 h under 800 ℃. The results showed that Li1.016Cr0.103Mn0.464Ni0.356O2 synthesized at the optimal condition have a typical feature of a rich-Li layered solid solution material in terms of their crystal structures.The initial specific discharge capacity of the material reached 190.2mAh/g in 2.0~4.8V with 0.1C. After 20 cycles at 0.1C, the capacity retention rate was86.0%。With Co, Al as doping element, the effects of doping amount on the structure and electrochemical properties of Li1.016Cr0.103Mn0.464Ni0.356O2 were studied. It was found that 1% Co-doped samples in small-rate discharge capacity increase slightly. At0.1 C and 0.2 C discharge specific capacity up to 192.1 mAh/g and 160.2 mAh/g,respectively; at 0.5 C and 1.0 C, the capacity retention after 10 cycles were 98.7%and 102.0% respectively. Al doping did not improve the capacity of the materials, but2% of Al doped samples at 0.5 C stable performance had improved significantly.In addition, the Li1.016Cr0.103Mn0.464Ni0.356O2 cathode was coated using MgO,Al2O3 materials. The amount of coating is 1%,2%,3%,4% respectively, of these,although the discharge capacity of 4%-Al2O3 coated material in a small-rate was lower than pure sample, but the discharge capacity of samples at 0.5 C and 1 C had improved significantly, the discharge capacity of the material reached 115.1 mAh/g and 95.1 m Ah/g, respectively. The discharge capacity of 1% MgO coated material under high-rate was higher than pure sample, at 0.5 C and 1 C the discharge capacity was the 113.2 m Ah/g s and 100.2 mAh/g, respectively.