Surface fluorination and electrochemical behavior of petroleum cokes graphitized at medium and high temperatures for secondary lithium battery

The surface structure and electrochemical performance have been investigated of petroleum cokes heat-treated at 2100 and 2600 °C (abbreviated to PC2100 and PC2600) and those fluorinated by elemental fluorine at 200 and 300 °C. XPS study indicated that surface fluorine was covalently bonded to carbon and surface fluorine contents were in the range of 4.9-17.8 at.%. Surface oxygen was reduced by fluorination. BET surface areas were nearly the same before and after fluorination. Fluorination enhanced D-band intensity in two Raman shifts observed at 1580 cm⁻¹ (G-band) and 1360 cm⁻¹ (D-band), indicating the increase in the surface disordering. At a high current density of 150 mA/g, the capacity increase was observed for PC2100 fluorinated at 200 °C and for PC2600 fluorinated at 200 and 300 °C. The most interesting result was the increase in first coulombic efficiencies by surface fluorination. First columbic efficiencies for PC2600 fluorinated at 300 °C were increased by 12.1% at 60 mA/g and by 25.8% at 150 mA/g, respectively. The impedance measurements showed that the resistances of surface films on carbon electrodes were increased by fluorination, however, the charge transfer resistances were decreased by 12.3% for PC2100 fluorinated at 200 °C, and by 27.5 and 6.4% for PC2600 fluorinated at 200 and 300 °C, respectively. The reduction of the charge transfer resistances was consistent with increase in the charge capacities for PC2100 fluorinated at 200 °C and PC2600 fluorinated at 200 and 300 °C.     

Surface fluorination of the cathode active materials for lithium secondary battery

LiMn₂O₄ was treated with F₂ at room temperature (RT), 373 and 473 K under 1.3, 6.6 and 13.2 kPa-F₂. XPS data indicate that two kinds of fluorine species may exist on the sample surface and the ratio of these fluorines is affected by choosing the reaction condition. The peak indicating Mnⁿ⁺ bonded to fluorine appeared in the XPS spectra of Mn2p3/2 electron. From the results of the charge/discharge measurements, the efficiency of charge/discharge process for the sample fluorinated under 1.3, 6.6 and 13.2 kPa-F₂ below 373 K was larger than that of untreated one. The discharge capacity of the fluorinated sample was also larger than that of untreated one. The discharge capacity, the loss of discharge capacity during 50 charge/discharge cycles, F/O ratio measured from XPS data and the intensity of the peak indicating Mnⁿ⁺ bonded to fluorine in the XPS spectra were closely related to each other. The optimal fluorination condition was under 1.3 kPa-F₂ at RT for 1 h.     

Surface structure and electrochemical characteristics of natural graphite fluorinated by ClF3

Natural graphite samples with average particle sizes of 5, 10 and 15 μm (NG5 μm, NG10 μm and NG15 μm, respectively) were fluorinated by ClF₃ (3 × 10⁴ Pa) at 200 and 300 °C for 2 min. X-ray photoelectron spectra of surface-fluorinated samples showed that surface fluorine concentration increased with increase in the particle size of graphite and reaction temperature. Small amounts of chlorine were also detected in all the fluorinated samples. Raman spectra of original and surface-fluorinated samples indicated that the surface disordering was increased for NG10 μm and NG15 μm. Surface areas were decreased by the fluorination for NG5 μm and NG10 μm but unchanged for NG15 μm. The mesopores with diameter of 1.5-2 nm increased while those of 2-3 nm decreased for all the samples. First coulombic efficiencies for NG10 μm and NG15 μm were highly increased by surface fluorination in 1 mol/dm³ LiClO₄-EC/DEC/PC (EC: ethylene carbonate, DEC: diethyl carbonate, PC: propylene carbonate) solution.     

Effect of surface fluorination on the electrochemical behavior of petroleum cokes for lithium ion battery

Surface structure change and electrochemical behavior of fluorinated petroleum coke samples (petroleum cokes: petroleum coke and those heat-treated at 1860 °C, 2300 °C and 2800 °C, abbreviated to PC, PC1860, PC2300 and PC2800, respectively) have been investigated. Surface oxygen of petroleum coke was decreased by the fluorination using elemental fluorine. Raman and EPR spectroscopies revealed that surface fluorination increased surface disorder and lattice defects. ¹⁹F NMR spectrum suggests that distribution of fluorine atoms in PC fluorinated 300 °C was similar to that in graphite fluoride with covalent CF bonds. Surface areas of fluorinated petroleum cokes were nearly the same as those of non-fluorinated ones or only slightly increased by fluorination, except PC fluorinated at 300 °C. It is noted that first coulombic efficiencies of PC2300 and PC2800 were highly increased to 80-84% by the fluorination at 300 °C. These values of 80-84% were 12-18% higher than those of non-fluorinated PC2300 and PC2800.     

Effect of surface fluorination and conductive additives on the electrochemical behavior of lithium titanate (Li4/3Ti5/3O4) for lithium ion battery

Effect of surface fluorination and conductive additives on the charge/discharge behavior of lithium titanate (Li_4/3Ti_5/3O₄) has been investigated using F₂ gas and vapor grown carbon fiber (VGCF). Surface fluorination of Li_4/3Ti_5/3O₄ was made using F₂ gas (3 × 10⁴ Pa) at 25-150 °C for 2 min. Charge capacities of Li_4/3Ti_5/3O₄ samples fluorinated at 70 °C and 100 °C were larger than those for original sample at high current densities of 300 and 600 mA/g. Optimum fluorination temperatures of Li_4/3Ti_5/3O₄ were 70 °C and 100 °C. Fibrous VGCF with a large surface area (17.7 m²/g) increased the utilization of available capacity of Li_4/3Ti_5/3O₄ probably because it provided the better electrical contact than acetylene black (AB) between Li_4/3Ti_5/3O₄ particles and nickel current collector.     

锂离子二次电池碳负极材料的改性

作为锂离子二次电池的碳负极材料，其改性方面的研究内容主要有：引入非金属元素，引入金属元素，处理表面及其它方面。纺入的非金属元素有硼，硅，氮，磷和硫。引入的金属元素有钾，铝，镓和钒，镍，钴，铜，铁等过渡金属元素。表面处理的方法包括氧化，形成表面层等。     

Electrochemical properties and structures of surface-fluorinated graphite for the lithium ion secondary battery

Surface modification of graphite powder has been performed by elemental fluorine and radiofrequency (rf) plasma fluorination. Both methods give rise to an enlargement of the surface areas of graphite samples and a change of the pore volume distribution. The capacities of surface-fluorinated graphite samples are higher than those of original samples and even more than the theoretical capacity of graphite, 372 mAh g⁻¹, without any reduction of the first colombic efficiencies. The increments of the capacities are ∼5, 10, and 15% for graphite samples with average particle diameters of 7, 25 and 40 μm, respectively.     

Synthesis of carbon nanofibers@MnO2 3D structures over copper foil as binder free anodes for lithium ion batteries

A 3D structured composite of carbon nanofibers@MnO₂ on copper foil is reported here as a binder free anode of lithium ion batteries, with high capacity, fast charge/discharge rate and good stability. Carbon nanofiber yarns were synthesized directly over copper foil through a floating catalyst method. The growth of carbon nanofiber yarns was significantly enhanced by mechanical polishing of the copper foils, which can be attributed to the increased surface roughness and surface area of the copper foils. MnO₂ was then grown over carbon nanofibers through spontaneous reduction of potassium permanganate by the carbon nanofibers. The obtained composites of carbon nanofibers@MnO₂ over copper foil were tested as an anode in lithium ion batteries and they show superior electrochemical performance. The initial reversible capacity of carbon nanofibers@MnO₂ reaches up to around 998 mAh·g^?1 at a rate of 60 mmA·g^?1 based on the mass of carbon nanofibers and MnO₂. The carbon nanofibers@MnO₂ electrodes could deliver a capacity of 630 mAh·g^?1 at the beginning and maintain a capacity of 440 mmAh·g^?1 after 105 cycles at a rate of 600 mA·g^?1. The high initial capacity can be attributed to the presence of porous carbon nanofiber yarns which have good electrical conductivity and the MnO₂ thin film which makes the entire materials electrochemically active. The high cyclic stability of carbon nanofibers@MnO₂ can be ascribed to the MnO₂ thin film which can accommodate the volume expansion and shrinking during charge and discharge and the good contact of carbon nanofibers with MnO₂ and copper foil.     

Surface modification of thermoplastics by atomic layer deposition of Al2O3 and TiO2 thin films

Al₂O₃ and TiO₂ thin films were deposited by atomic layer deposition at 80-250 °C on various polymeric substrates such as polymethylmethacrylate (PMMA), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE) and ethylenetetrafluoroethylene (ETFE). The films were studied with FESEM, EDX, XRD, contact angle measurements and adhesion tests. The film growth rates on the thermoplastics were close to the corresponding growth rates on Si substrates. The adhesion of the films was good on PEEK and poor on PTFE. All coated surfaces showed lower water contact angles than the uncoated thermoplastics. Furthermore, the water contact angles on all TiO₂-coated surfaces decreased upon UV illumination, most efficiently with crystalline TiO₂ coatings.     

The fluorination of scheelite with ammonium bifluoride

The interaction of scheelite with ammonium bifluoride was studied. It was shown that sheelite reacts with NH₄HF₂ at room temperature, in contrast with tungstic oxide and other tungsten compounds. Two complexes are formed (NH₄)₃WO₃F₃ and the previously unknown (NH₄)₂WO₃F₂. The compounds obtained were fluorinated to (NH₄)₃WO₂F₅ (endothermic peaks at 170° and 90°C, respectively).Cubic monocrystals of (NH₄)₃WO₂F₅ were obtained. The cubic form is unstable and underwent a lattice transformation at room temperature to the more stable tetragonal form, which was transformed reversibly into the cubic form at 140°C. The thermal decomposition of (NH₄)₂WO₃F₂ was studied.

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Zusammenfassung Es wird die Wechselwirkung von Scheelit und Ammoniumhydrogenfluorid untersucht. Im Gegensatz zu Wolframoxid und anderen Wolframverbindungen geht Scheelit mit Ammoniumhydrogenfluorid bei Raumtemperatur eine chemische Reaktion ein, wobei zwei verschiedene Komplexe gebildet werden: (NH₄)WO₃F₃ und der bisher unbekannte Komplex (NH₄)₂WO₃F₂. Die erhaltenen Verbindungen werden zu (NH₄)₃WO₂F₅ fluoriert (endotherme Peaks bei 170° bzw. 90°C).Man erhält die kubischen Einkristalle (NH₄)₃WO₂F₅. Die unstabile kubische Form wandelte sich bei Raumtemperatur in die stabilere tetragonale Form um, die bei 140°C reversibel wieder in die kubische Form überführt werden kann.Es wird weiterhin die thermische Zersetzung von (NH₄)₂WO₃F₂. untersucht.

     

Fabrication of carbon microcapsules containing silicon nanoparticles-carbon nanotubes nanocomposite by sol-gel method for anode in lithium ion battery

Carbon microcapsules containing silicon nanoparticles (Si NPs)-carbon nanotubes (CNTs) nanocomposite (Si-CNT@C) have been fabricated by a surfactant mediated sol-gel method followed by a carbonization process. Silicon nanoparticles-carbon nanotubes (Si-CNT) nanohybrids were produced by a wet-type beadsmill method. To obtain Si-CNT nanocomposites with spherical morphologies, a silica precursor (tetraethylorthosilicate, TEOS) and polymer (PMMA) mixture was employed as a structure-directing medium. Thus the Si-CNT/Silica-Polymer microspheres were prepared by an acid catalyzed sol-gel method. Then a carbon precursor such as polypyrrole (PPy) was incorporated onto the surfaces of pre-existing Si-CNT/silica-polymer to generate Si-CNT/Silica-Polymer@PPy microspheres. Subsequent thermal treatment of the precursor followed by wet etching of silica produced Si-CNT@C microcapsules. The intermediate silica/polymer must disappear during the carbonization and etching process resulting in the formation of an internal free space. The carbon precursor polymer should transform to carbon shell to encapsulate remaining Si-CNT nanocomposites. Therefore, hollow carbon microcapsules containing Si-CNT nanocomposites could be obtained (Si-CNT@C). The successful fabrication was confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). These final materials were employed for anode performance improvement in lithium ion battery. The cyclic performances of these Si-CNT@C microcapsules were measured with a lithium battery half cell tests.     

Property control of new forms of carbon materials by fluorination

Multiwall carbon nanotubes (MWNTs) based on the template carbonization technique were fluorinated in a temperature range 323-473 K by elemental fluorine. The fluorination of the carbon nanotubes results in functionalization and modification of pristine nanotubes with respect to adsorption and electrochemical properties. Selective fluorination of the inner surface of the carbon nanotubes, brings about a decrease in the surface free energy of the inner surface of the tubes and an increase in colombic efficiency of Li/nanotubes rechargeable cells in an aprotic medium. Electrochemical fluoride-ion doping of fullerene C₆₀ thin films (250-450 nm) was carried out in a fluoride-ion conductive solution, MeCN solution of 1 M Et₄NF·4HF. Galvanostatic oxidation yielded C₆₀F_ca.1-3 where fluorine exists as a semi-ionic species in the cavity surrounded by C₆₀ molecules without forming covalent CF bonds     

Electrochemical properties and synthesis of LiAl0.05Mn1.95O3.95F0.05 by a solution-based gel method for lithium secondary battery

The cathode materials, LiMn₂O₄, LiAl_0.05Mn_1.95O₄ and LiAl_0.05Mn_1.95O_3.95F_0.05 were firstly prepared by a simple solution-based gel method using the mixture of acetate and ethanol as the chelating agent. The synthesized samples were investigated by X-ray diffraction, scanning electronic microscope and differential and thermal analysis. The as-prepared powders were used as positive materials for lithium-ion battery, whose discharge capacity and cycle voltammogram properties were examined. The results revealed that LiAl_0.05Mn_1.95O_3.95F_0.05 synthesized by the solution-based gel method had higher initial capacity than LiAl_0.05Mn_1.95O₄ and better capacity retention rate (92%) than that of LiAl_0.05Mn_1.95O₄ and LiMn₂O₄, which revealed that Al and F dual-doped LiMn₂O₄ could gain better electrochemical properties of LiMn₂O₄ than only the Al-doped LiMn₂O₄.     

二氧化硅栅绝缘层的制备与表面修饰

研究了有机薄膜晶体管的二氧化硅栅绝缘层的性质。二氧化硅绝缘层的制备采用热生长法，氧化气氛是O₂(g)+H₂O(g)，工艺为干氧-湿氧-干氧的氧化过程。制得的绝缘层漏电流在10^-9 A左右。以该二氧化硅作为有机薄膜晶体管的栅绝缘层，并五苯作为有源层制作了有机薄膜晶体管器件。实验表明采用十八烷基三氯硅烷(OTS)进行表面修饰的器件具有OTS/SiO₂双绝缘层结构，可以有效地降低SiO₂栅绝缘层的表面能并改善表面的平整度。修饰后器件的场效应迁移率提高了1.5倍、漏电流从10^-9 A降到10^-10 A、阈值电压降低了5 V、开关电流比从10⁴增加到10⁵。结果显示具有OTS/SiO₂双绝缘层的器件结构能有效改进有机薄膜晶体管的性能。     

Effects of fluorination modification on pore size controlled electrospun activated carbon fibers for high capacity methane storage

Electrospun carbon fibers were prepared as a methane storage medium. Chemical activation was carried out using potassium carbonate to develop the pore structure, which can provide sites for the uptake of methane, and then fluorination surface modification was conducted to enhance the capacity of storage. Chemical activation provided a highly microporous structure, which is beneficial for methane storage, with a high specific surface area greater than 2500 m²/g. The pore size distribution showed that the prepared samples have pore sizes in the range of 0.7–1.6 nm. The effect of fluorination surface modification was also investigated. The functional groups, which were confirmed by XPS analysis, played an important role in guiding methane gas into the carbon silt pores via the attractive force felt by the electrons in the methane molecules due to the high electronegativity of fluorine. Eventually, the methane uptake increased up to 18.1 wt.% by the synergetic effects of the highly developed micropore structure and the guiding of methane to carbon pores by fluorine.     

Electrolytic Co3O4 for thin-layer anodes of lithium-ion batteries

Electrolytic (e) cobalt oxide of a spinel structure, e-Co₃O₄, is obtained from the sulfate and nitrate (aqueous, water-alcohol) solutions containing Co²⁺ with the aim of using it in thin-layer anodes of lithium-ion batteries. The physicochemical and structural properties of the synthesized compounds are examined using thermal and x-ray diffraction analyses, absorption IR spectroscopy, and atomic force microscopy. The electrochemical characteristics of e-Co₃O₄ are determined in breadboards of lithium power sources and in the lithiumion system LiCoO₂/e-Co₃O₄.     

核壳结构MoOx/C微球的制备及储锂性能

采用水热法合成了MoO_3/酚醛树脂前驱体,然后在空气中进行煅烧处理,成功制备了一种新型核壳MoOx/C微球。对材料的晶体结构、形貌和元素价态进行分析表明,该材料的主要成分是单斜相MoO_2、正交晶系MoO_3和碳。树脂在空气中的煅烧碳化将MoO_3/酚醛树脂前驱体中的六方晶系的MoO_3还原为单斜相MoO_2。其中少量的MoO_2会在空气中重新被氧化成正交晶系的MoO_3,形成了MoO_2/MoO_3异质结构。在这一系列反应的综合作用下,形成这种表面有裂纹的核壳MoOx/C微球复合材料。将该材料用作锂离子电池负极材料,表现出了循环稳定性高、倍率性能好等优异的电化学性能。在100 mA·g-1的电流密度下充放电循环100次之后,可逆容量达640.6 mAh·g-1。     

CNTs表面改性与TiO2-CNTs异质结光催化性能

碳纳米管(CNTs)混酸(H₂SO₄/HNO₃, 体积比为3:1)超声辅助纯化及氧化植入活性基团－COOH, 进一步借助其转化为酰氯基团, 分别于CNTs 表面共价嫁接亲水性赖氨酸及亲脂性正十八胺基团, 赋予赖氨酸表面改性CNTs 显著水溶(6.85 mg·mL-1)和十八胺表面改性CNTs 显著醇溶(10.15 mg·mL^-1)性能. 运用低温水热法以亲水性CNTs 复合TiO₂, 溶胶-凝胶法以亲脂性CNTs 复合TiO₂, 观察到复合催化剂光催化性能随CNTs 溶剂分散性能增加而明显提升. 运用傅里叶变换红外(FTIR)、激光拉曼、X射线衍射(XRD)、Brunauer-Emmett-Teller 低温氮气吸附、透射电镜(TEM)及X光电子能谱(XPS)等手段表征, 系统探讨CNTs 的表面改性机制及CNTs 溶解分散性能与复合催化剂的光活性的关联. 认为表面改性CNTs 借助Ti－O－C键合促进其与纳米TiO₂的异质结合, 从而充分利用CNTs的大比表面积及电荷传输性能促进催化剂的污染物光催化降解.     

N掺杂MnO2/碳布复合材料的制备及储锂性能

采用碳布（CC）为柔性基底,通过水热法制备了MnO₂/CC及N掺杂MnO₂/CC无黏结剂负极材料,借助X射线衍射（XRD）、扫描电镜（SEM）、X射线光电子能谱（XPS）、比表面积测试和恒电流充放电对材料进行了结构表征及电化学性能测试。结果表明N掺杂MnO₂/CC具有良好的倍率性能和循环稳定性。在0.1 A·g^-1的电流密度下,其首次充电比容量为948.8 mAh·g^-1,经过不同倍率测试后电流密度恢复至0.1 A·g^-1时仍然保持有907.9 mAh·g^-1的可逆比容量,容量保持率为95.7%。在1 A·g^-1的大电流密度下,其首次充电比容量为640.3 mAh·g^-1,循环100次后仍然保持有529.9 mAh·g^-1的可逆比容量,容量保持率为82.8%,可逆比容量远高于商用MnO₂。     

Zinc-containing zeolite catalysts for ethane aromatization prepared by solid-state modification

Solid-state modification was used to prepare zinc-containing zeolite catalysts based on pentasils with different framework SiO₂/Al₂O₃ ratios. The catalysts were studied by X-ray diffraction analysis and IR spectroscopy. The activity and selectivity of the Zn—pentasil systems prepared by the solid-state modification and impregnation methods were compared in the aromatization of ethane. The active and stable zeolite catalysts modified by transition metal ions can be obtained by the topochemical method.