| Ternary materialof LiNixCo1-2xMnxO2is synthesisedusing nickel salt, cobalt salt and manganese salts,and the proportion of nickel, cobalt and manganese can be adjusted according to the actual requirement. LiNixCo1-2xMnxO2, relative to the LiCoO2, has the higher reversible capacity and thermal stability, the lower cost and toxicity, which has caused more and more researchers’interest. In many research of layered structure of LiNixCo1-2xMnxO2, LiNi1/3Co1/3Mn1/302, which has the higher initial discharge capacity and more stable cycle performance, has became the most promising high energetic anode materials. However, LiNi1/3Co1/3Mn1/3O2material exist such problems like the higher irreversible capacity for the first time, the lower compaction density and the poor rate capability and so on, so in order to improve the electrical properties of LiNi1/3Co1/3Mn1/3O2, the electrode materials must be modified.The research used acetate of Ni, Co, Mn as raw materials, citric acid as complexingagent to fabricate the LiNi1/3Co1/3Mn1/3O2materials which have a single layer of hexagonal system by the sol-gel method. The crystal structure and morphology of synthetic samples are observed by XRD, SEM. Charging and discharging in the constant current, combined with CV, are used to analyze the electrochemical properties of the samples.Using sol-gel method, combining with the secondary calcinations, optimizing the synthesis conditions, the LiNi1/3Co1/3Mn1/3O2materials of better structure and electrical performance are prepared. Some research has shown that when the ratio of C6H8O7·H2O and Li+is1:0.75, the samples which get the better electrochemical performance have the ideal type of a-NaFeO2layered structure whose particles are equally distributed (about200nm) after preheating at400℃for4hours, roasting at800℃for12hours. When the discharge rate is0.1C, the initial discharge specific capacity is168.4mAh·g-1, and after30cycles, the capacity retention is95.1%. Besides, at the discharge rate of0.5C,1C and2C,the stable circulating discharge specific capacity are167.3mAh·g-1,151.9mAh·g-1and137.9mAh·g·1respectively. After50times cycle, the capacity retention is94.7%,86.3%and76.4%respectively, showing good ratio performance.Based on the optimization of process, the samples of Li(Ni1/3Co1/3Mn1/3)1-xMxO2(x=0,0.02,0.05,0.08; M=Zn、Cu) with different doping amount are prepared. With the help of XRD,SEM, charge-discharge tester and electrochemical workstation, the phase microstructure and electrochemical properties of the synthetic samples have been characterized and tested. When the Zn doping amount<2%, samples show the single layer structure. When the Zn content≥5%, the diffraction peak of ZnO has occurred in the atlas, showing that the zinc doping has no obvious effect on particle size and electrical properties. When x=0.02, charging-discharging for the first time has slightly increased at O.1C.At the discharge rate of0.5C, the capacitance drop to155.6mAh·g-1by163.6mAh·g-1after50cycles of discharge and the capacity retention is95.1%.At the discharge rate of1C and2C, the discharge capacity decreased from154.9mAh·g-1,145.1mAh·g-1to132.3mAh·g-1,108.5mAh·g-1,and the capacity retention is85.4%,74.8%respectively. Cu element doping on the material have a greater influence on the particle size and the electrical properties, doping makes the electrode material particle size appeared together and there is an obvious decline in specific capacity at the same time. And the irreversible capacity increased with the increase of doping amount increased rapidly. After doping Cu element, the first discharge capacity under different ratio are lower compared with the pure phase; after50cycles at the0.5C to charge and discharge,, the discharge capacity of mixed Cu samples dropped to143.4mAh·g-1from155.4mAh·g-1capacity at a rate of92.3%,1C and2C to charge and discharge, the discharge capacity of samples by142.9mAh·g-1and126.1mAh·g-1, respectively dropped to129.0mAh·g-1,1and97.4mAh·g-1, capacity remains at a rate of90.27%and77.2%.On the basis of the optimization process, using copper nitrate as raw materials, LiNi1/3Co1/3Mn1/3O2composite with different CuO coating content is prepared by method of chemical deposition. XRD analysis shows that the diffraction peak of LiNi1/3Co1/3Mn1/3O2with different CuO content is consistent with standard JCPDS card (PDF#50-0653), showing the intact a-NaFeO2layered structure. The CuO coating is unable to change the crystal structure of LiNi1/3Co1/3Mn1/3O2, having no significant effect on the particle size and distribution. When the CuO coating content is2%, the materials have the best cycle performance, and the charge-discharge capacity for the first time is171.9mAh/g at0.1C. At the discharge rate of0.5C, the capacity retention is93.3%after50cycles of discharge. At the discharge rate of1C and2C, the capacity retention is96.7%and90.5%respectivelyafter50cycles of discharge, with the battery showing good cycle performance and rate capacity. |
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