The precursor of LiNi0.5MnSubscript text1.5O4cathode material with high density was synthesized by two-dryness co-precipitation method. The optimized parameters were found out by studying the relationship between the density of precursor and the concentration of reactants, the manner of adding agglomerating agent, the remaining water in filter cake and the manner of dryness. The highest density (1.74 g/cm3) of precursor can be achieved under optimized condition: NiSO40.375 mol/L, coagulation agent added with little amount but many times, 28% of water in filter cake and two-step dryness, which is much better than that made by other methods. Our experiment provides a significant reference for the synthesis of excellent-performance cathode materials of lithium-ion battery. LiNi0.5MnSubscript text1.5O4has a good cycle performance, a higher discharge capacity and a discharge platform of 4.7v, so it has become a research focus of 5-voltage cathode materials in the field of lithium ion battery recently.[1-4] However, LiNi0.5Mn1.5O4 prepared by common methods usually has a lower tap volume capacity.[5-9] HiroyuKi Ito[6] reported a continuous fabricated high-density cobalt-manganese-doped nickel hydroxide method with which the density of product was between 1.5-1.91g/cm3, however the used ammonia as a complexation agent in the preparation process not only increased the cost of the preparation, but also led to environmental pollution. Research results show that the cathode material synthesized using high-density precursor has a higher tap density, a larger volume capacity and a good electrochemical performance.[10] In this paper, we find out the optimized parameters of preparation of precursor of LiNi0.5MnSubscript text1.5O4by studying the relationship between the density of precursor and concentration of reactants, the manner of adding agglomerating agent, the remaining water in filter cake and the manner of dryness.
The carbon materials prepared by PVDF carbonization at different temperatures have similar BET surface area and pores volume. The content of fluorine in the carbons decreased with the carbonization temperature from 1.46% (atm %) at 600°C to 0.18 %( atm %) at 1000°C. The first cycle specific capacity and the initial coulombic efficiency decreases with the decrease of fluorine content in the samples. The first cycle discharge capacity decreased from 982 mAh/ g at 600°C to 752 mAh/ g at 1000°C and the initial coulombic efficiency decreased from 31.8% at 600°C to 24% at 1000°C. It is believed that fluorine contained in the carbon materials has a positive effect to improve the electrochemical properties as anode materials for Li-ion batteries.
Carbon onions including Fe3C were synthesized by the catalytic decomposition of acetylene at 400 °C using iron supported on sodium chloride as catalyst. The samples were examined by high resolution transmission electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. The results show that carbon onions including Fe3C core with a structure of stacked graphitic fragments and diameters in the range 15-50 nm were obtained. When the product was further heat-treated under vacuum at 1100 °C, carbon onions with a clear concentric graphitic layer structure were obtained.
The reactions were carried out by decomposing acetylene at 1000 °C in a two-stage furnace system for 10 min. In the first furnace no catalyst was placed and an AAO template with the average diameter about 50 nm was placed in the second furnace whose temperature was designed to be 500 °C, 600 °C and 700 °C. The samples were characterized by scanning electron microscopy and high resolution transmission electron microscopy. The results show that carbon spheres with average diameter about 50 nm on the AAO template surface were obtained when the temperature of the second furnace was designed to be 700 °C. These carbon spheres are composed of unclosed graphene layers with an interlayer distance of 0.33–0.35 nm between the layers.
Catalytic decomposition of acetylene was carried out at 400 °C using iron supported on sodium chloride as catalyst and the product was heat-treated at 650 °C under an argon atmosphere for 2 h directly. The sample was examined by scanning electron microscopy, high resolution transmission electron microscopy and X-ray diffraction. The results show that nano onion-like fullerenes encapsulating Fe cores with diameters in the range 20-50 nm were obtained.
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