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.     

Surface modification of carbon anodes for secondary lithium battery by fluorination

Recent results on the surface modification of petroleum cokes and their electrochemical properties as anodes of secondary lithium batteries are summarized. The surface of petroleum coke and those heat-treated at 1860-2800 °C were fluorinated by elemental fluorine (F₂), chlorine trifluoride (ClF₃) and nitrogen trifluoride (NF₃). No surface fluorine was found except only one sample when ClF₃ and NF₃ were used as fluorinating agents while surface region of petroleum coke was fluorinated when F₂ was used. Transmission electron microscopic (TEM) observation revealed that closed edge of graphitized petroleum coke was destroyed and opened by surface fluorination. Raman spectra showed that surface fluorination increased the surface disorder of petroleum cokes. Main effect of surface fluorination with F₂ is the increase in the first coulombic efficiencies of petroleum cokes graphitized at 2300-2800 °C by 12.1-18.2% at 60 mA/g and by 13.3-25.8% at 150 mA/g in 1 mol/dm³ LiClO₄-ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1, v/v). On the other hand, main effect of the fluorination with ClF₃ and NF₃ is the increase in the first discharge capacities of graphitized petroleum cokes by ∼63 mAh/g (∼29.5%) at 150 mA/g in 1 mol/dm³ LiClO₄-EC/DEC.     

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.     

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.     

高压锂离子电池电解液的研究进展

电极/电解液界面不稳定是高压锂离子电池发展的主要瓶颈.提高界面稳定性是高压锂离子电池得以应用的前提.本文综述了碳酸酯基电解液氧化分解反应机理、新型耐高压溶剂体系和新型成膜添加剂实验与理论的研究进展.     

Development of polyaniline–lithium secondary battery

A series of coin-type lithium secondary batteries with polyaniline positive electrodes was developed and commercialized which might be not only the first practical polymer battery but also the first industrial application of conducting polymers. Performances of the commercialized batteries were described in detail in this paper. In order to achieve the development the most important thing was the optimization of molecular structure and molphology of multiguise polyaniline as the electrode material. According to the findings obtained during the development, polyaniline sheet was prepared substantially to be composed of imino-1,4-phenylene (IP) and the cation radical of IP (IP⁺) by the novel procedure, not to include quinoid configuration of polyaniline (NP) which was proved to be electrochemically inactive in non-aqueous systems.     

锂离子电池用复合导电剂浆料制备与性能

采用超声波混合、抽滤的方法把多壁碳纳米管（MWCNTs）和乙炔黑混合制备了锂离子电池用复合导电剂浆料，用扫描电子显微镜（SEM）和恒流充放电测试考察了复合导电剂的结构和其作为导电剂对LiCoO2电极放电比容量的影响。SEM的分析结果表明MWCNTs和乙炔黑实现了纳米层次的均匀混合。复合导电剂悬浮液和浆料分别被用作导电剂制成了两种LiCoO2电极，前一种电极为Cathode A，后一种电极为Cathode B，考察了不同MWCNTs含量时，两种电极0．5C第10次放电比容量的差异。实验结果表明，随着MWCNTs含量的增加，两种电极放电比容量的差值增大，说明低含量MWCNTs的复合导电剂浆料是一种理想的锂离子电池导电剂。     

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。     

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.     

Improvements of the electrochemical features of graphite fluorides in primary lithium battery by electrodeposition of polypyrrole

Improvements of the electrochemical features of CF_x cathode materials in primary lithium battery were obtained by the electrodeposition of polypyrrole (PPy) performed in acetonitrile with Py monomer. The electrodeposition does not affect the core of the CF_x powder as revealed by XRD and TEM. The maximum discharge rate which is 1C for pristine CF_x increases for PPy–CF_x and reaches 4C in the case of PPy–CF_0.80 1 M LiPF₆–EC:DMC (1:1) electrolyte. A maximum power density of 5235 W/kg (4C-rate) has been achieved with PPy–CF_0.80, a value around 3.8 times higher than for CF_0.80 (1C-rate).     

锂离子电池负极材料铜锌锡硫纳米颗粒的制备及其电化学性能

以金属氯化物为金属源,硫脲为硫源,聚乙二醇和乙二醇为混合溶剂,采用溶剂热法一步合成了球形的铜锌锡硫纳米颗粒.利用X射线衍射仪(XRD),扫描电子显微镜(SEM)和透射电子显微镜(TEM)分析了铜锌锡硫纳米颗粒的物相、结构、形貌;利用电池测试系统对以铜锌锡硫纳米颗粒为锂离子电池负极材料组装的锂离子电池的电化学性能进行了测试.结果表明:所得到的产物为具有锌黄锡矿结构的纯相铜锌锡硫,颗粒直径在300～500nm.铜锌锡硫纳米颗粒作为锂离子电池的负极材料具有较好的稳定性,有望在锂离子电池研究和应用中得到推广.     

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.     

锂离子动力电池隔膜的研究及发展现状

锂离子动力电池作为新能源汽车的动力之源受到广泛关注.本文对动力电池的重要组件之一——电池隔膜进行了介绍.围绕提高安全性和能量密度的设计目标,综述了其新材料、新技术的发展及现状.     

用于锂离子电池的中空无机非金属纳米材料的研究进展

锂离子电池电极材料在充放电过程中由于锂离子嵌入和脱嵌,电极材料在膨胀和收缩过程中极易粉化而导致电池失效.无机中空纳米材料具有较高的比表面积,可调的空腔体积以及壳层厚度,并且每一个中空颗粒都可以作为一个微反应室,从而增加了反应界面,作为锂电池电极材料,无机中空纳米材料能够适应充放电过程中颗粒的膨胀和收缩,表现出优异的性能.面对传统模板法的局限性,基于Kirkendall效应等新的机理或方法以其操作步骤简单、无模板等优点,有望实现低成本的规模化生产.本文综述了利用Kirkendall效应,Oswald熟化和溶剂热3种机理或方法制备中空无机纳米材料作为锂离子电池电极材料的最新研究进展,并对其应用前景进行了展望.     

Synthesis and electrochemical study of Li-Mn-Ni-O cathodes for lithium battery applications

Cathode powders of the Li–Mn–Ni–O system have been prepared at a Mn/(Mn+Ni) ratio varying from 0 to 1. The solid state reaction method was used to obtain the cathode materials by mixing MnO₂, LiCO₃ and NiO. A 20% excess of lithium was used in the precursors. The materials produced were examined by X-rays to identify their structure. Batteries were assembled by using these materials as cathode with a liquid electrolyte consisting of EC/DC 1:1, 1 LiPF₆ and Li anode. Their capacity, cycle fading and charge-discharge conditions were evaluated.Presented at the 3rd International Meeting "Advanced Batteries and Accumulators", June 16th–June 20th 2002, Brno, Czech Republic     

Development of direct fluorination technology for application to materials for lithium battery

Direct fluorination of 1,3-dioxolan-2-one with elemental fluorine was successfully carried out to provide 4-fluoro-1,3-dioxolan-2-one, which was expected as an additive for lithium ion secondary battery. 4-Fluoro-1,3-dioxolan-2-one was also further fluorinated with elemental fluorine to give three isomers of difluoro derivatives by the same methodology. Another topic is the preparation of trifluoromethanesulfonyl fluoride, an intermediate of lithium battery electrolyte, by the reaction of methanesulfonyl fluoride with elemental fluorine. The use of perfluoro-2-methylpentane as a solvent gave satisfactory selectivity of trifluoromethanesulfonyl fluoride.     

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.     

Impacts of fluorine on the electrochemical properties of Li[Ni0.5Mn0.5]O2 and Li[Li0.2Ni0.15Co0.1Mn0.55]O2

The impact of the fluorine substitution on the electrochemical properties of layered lithium nickel manganese positive electrode materials for lithium ion batteries is summarized. The addition of a controlled amount of fluorine to the oxygen lattice can effectively improve the capacity retention as well as reduce the impedance of the positive electrode materials. The fluorination of the nickel and manganese based layered oxide cathode material has also led to significant improvement in cycle life and power capability of the battery.     

Surface structures and electrochemical characteristics of surface-modified carbon anodes for lithium ion battery

Petroleum coke and those heat-treated at 1860 °C, 2100 °C, 2300 °C 2600 °C and 2800 °C (abbreviated as PC, PC1860, PC2100, PC2300, PC2600 and PC2800) were fluorinated by elemental fluorine of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Natural graphite powder samples with average particle sizes of 5 μm, 10 μm and 15 μm (abbreviated as NG5μm, NG10μm and NG15μm) were also fluorinated by ClF₃ of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Transmission electron microscopic (TEM) observation revealed that closed edge of PC2800 was destroyed and opened by surface fluorination, which increased the first coulombic efficiencies of PC2300, PC2600 and PC2800 by 12.1–18.2% at 60 mA/g and by 13.3–25.8% at 150 mA/g in 1 mol/dm³ LiClO₄–ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1 in volume). Light fluorination of NG10μm and NG15μm increased the first coulombic efficiencies by 22.1–28.4% at 150 mA/g in 1 mol/dm³ LiClO₄–EC/DEC/PC (PC: propylene carbonate, 1:1:1 in volume).     

锂电隔膜研究及产业技术进展

隔膜是锂离子电池的关键材料,在极片间起绝缘和提供离子通道的作用.本文以如何构建耐高温的隔膜、如何提高隔膜的离子电导率为重点,介绍了锂电隔膜研究及产业化技术进展,内容主要包括隔膜性能的影响因素、凝胶聚合物电解质膜、拉伸法制备隔膜及其改性、隔膜制造的新方法和新材料.最后展望了隔膜的发展前景.