SEI layer-forming additives for LiNi0.5Mn1.5O4/graphite 5 V Li-ion batteries

This study demonstrates that proper SEI layer on graphite anode is essential in LiNi_0.5Mn_1.5O₄(LNMO)/graphite 5 V lithium-ion batteries. Succinic anhydride (SA) and 1,3-propane sultone (PS) were found to greatly extend cycle life and suppress swelling behavior of LNMO/graphite cells. The benefits of SA and PS were ascribed not only to the stable SEI layer they form on graphite but also to their stability toward the oxidation at high voltage. Using 1 M LiPF₆ EC/EMC (1/2, v/v) solutions with SA and PS, LNMO/graphite Al-laminated pouch cell with nominal capacity of 600 mA h exhibited about 80% capacity retention after 100 cycles. This is the first report on the successful LNMO/graphite 5 V LIB to our best knowledge.     

Investigation of interfacial processes in graphite thin film anodes of lithium-ion batteries by both in situ and ex situ infrared spectroscopy

Graphite thin film anodes with a high IR reflectivity have been prepared by a spin coating method. Both ex situ and in situ microscope FTIR spectroscopy (MFTIRS) in a reflection configuration were employed to investigate interfacial processes of the graphite thin film anodes in lithium-ion batteries. A solid electrolyte interphase layer (SEI layer) was formed on the cycled graphite thin film anode. Ex situ MFTIRS revealed that the main components of the SEI layer on cycled graphite film anodes in 1 mol L -1 LiPF6 /ethylene carbonate + dimethyl carbonate (1:1) are alkyl lithium carbonates (ROCO2 Li). The desolvation process on graphite anodes during the initial intercalation of lithium ion with graphite was also observed and analyzed by in situ MFTIRS.     

X-ray photoelectron study of fluorinated graphite intercalation compounds

Intercalated compounds of fluorinated graphite C₂F·yR, where R is benzene, hexafluorobenzene, acetone, or germanium tetrachloride, are studied by X-ray photoelectron spectroscopy. The binding energies of the C1s and F1s inner levels indicate that the C-F chemical bond in fluorinated graphite differs dramatically from the covalent bond in graphite monofluoride. The binding energies of the inner levels in atoms of the graphite fluoride matrix and GeCl₄ are analyzed and it is concluded that there is no chemical binding between the host matrix and the guest molecule. Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 6, pp. 1127–1133, November–December, 1998.     

Natural graphite enhanced the electrochemical performance of Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode material for lithium ion batteries

Natural graphite treated by mechanical activation can be directly applied to the preparation of Li₃V₂(PO₄)₃. The carbon-coated Li₃V₂(PO₄)₃ with monoclinic structure was successfully synthesized by using natural graphite as carbon source and reducing agent. The amount of activated graphite is optimized by X-ray diffraction, scanning electron microscope, transmission electron microscope, Raman spectrum, galvanostatic charge/discharge measurements, cyclic voltammetry, and electrochemical impedance spectroscopy tests. Our results show that Li₃V₂(PO₄)₃ (LVP)-10G exhibits the highest initial discharge capacity of 189 mAh g^?1 at 0.1 C and 162.9 mAh g^?1 at 1 C in the voltage range of 3.0–4.8 V. Therefore, natural graphite is a promising carbon source for LVP cathode material in lithium ion batteries.     

Effect of pretreatment of graphite oxide on activity of platinum supported catalysts in liquid-phase hydrogenation

The effect of the reduction procedure of graphite oxide (GO) on activity of platinum supported catalysts in liquid-phase hydrogenation of nitrobenzene and dec-1-ene was studied. The following methods were applied to prepare the catalysts: simultaneous reduction of graphite oxide and H₂PtCl₆; deposition of platinum on graphite oxide which was preliminary subjected to reduction with sodium tetrahydroborate or hydrazine hydrate, or to thermal reduction at 1000 and 1050 °С. It was shown that at equal Pt particles size of ca. 2 nm the catalyst supported on thermally reduced graphite oxide is more active in the model reactions than the catalysts supported on chemically reduced graphite oxide. The catalyst prepared by simultaneous reduction was the least active.     

异质双碳源对LiMn0.8Fe0.2PO4复合材料电化学性能的影响

采用水基流变相辅助的固相法,以异质碳蔗糖和石墨为碳源,合成了LiMn_0.8Fe_0.2PO₄/C复合材料,研究了不同石墨加入方式对所制复合材料电化学性能的影响,并对所制备的LiMn_0.8Fe_0.2PO₄/C复合材料进行了X射线衍射(XRD)、比表面积测试、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等表征。结果表明,不同石墨包覆工艺对材料结构和电化学性能具有显著影响。前驱体煅烧后再加入石墨获得的样品纯度高,形貌呈均一的椭圆形,在0.1C下的放电比容量为149 mAh·g^-1,达到其理论比容量的 87%;在 5C 下最大的放电比容量为 133 mAh·g^-1;在 2C 倍率下经过 300 次循环后比容量维持在 127 mAh·g^-1,衰减率仅为1.9%,表现出了优良的循环稳定性。     

异质双碳源对LiMn0.8Fe0.2PO4复合材料电化学性能的影响

采用水基流变相辅助的固相法,以异质碳蔗糖和石墨为碳源,合成了LiMn_0.8Fe_0.2PO₄/C复合材料,研究了不同石墨加入方式对所制复合材料电化学性能的影响,并对所制备的LiMn_0.8Fe_0.2PO₄/C复合材料进行了X射线衍射(XRD)、N₂吸附-脱附测试、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等表征。结果表明,不同石墨包覆工艺对材料结构和电化学性能具有显著影响。前驱体煅烧后再加入石墨获得的样品纯度高,形貌呈均一的椭圆形,在0.1C下的放电比容量为149 mAh·g^-1,达到其理论比容量的87%;在5C下最大的放电比容量为133 mAh·g^-1;在2C倍率下经过300次循环后比容量维持在127 mAh·g^-1,衰减率仅为1.9%,表现出了优良的循环稳定性。     

Understanding High-Rate K+-Solvent Co-Intercalation in Natural Graphite for Potassium-Ion Batteries

Graphite shows great potential as an anode material for rechargeable metal-ion batteries because of its high abundance and low cost. However, the electrochemical performance of graphite anode materials for rechargeable potassium-ion batteries needs to be further improved. Reported herein is a natural graphite with superior rate performance and cycling stability obtained through a unique K⁺-solvent co-intercalation mechanism in a 1 m KCF₃SO₃ diethylene glycol dimethyl ether electrolyte. The co-intercalation mechanism was demonstrated by ex situ Fourier transform infrared spectroscopy and in situ X-ray diffraction. Moreover, the structure of the [K-solvent]⁺ complexes intercalated with the graphite and the conditions for reversible K⁺-solvent co-intercalation into graphite are proposed based on the experimental results and first-principles calculations. This work provides important insights into the design of natural graphite for high-performance rechargeable potassium-ion batteries.     

Thermal reduction of graphite oxide derivatives for preparation of supports for platinum hydrogenation catalysts

Thermal reduction of graphite oxide and its derivatives under argon atmosphere has been studied by means of thermogravimetric analysis. Carbon materials prepared via thermal reduction of graphite oxide derivatives in argon at 900°С during 3 h have been used for deposition of platinum from H₂PtCl₆ solutions. Pt particles supported on the support catalyze liquid-phase hydrogenation of nitrobenzene and dec-1-ene under atmospheric pressure of H₂. Thermal reduction of the supports based on graphite oxide results in the formation of the structural defects significantly enhancing the catalytic activity.     

氧化环境和比例对改性Hummers法制备GO的影响

以鳞片石墨(GR)为原料,采用改性Hummers法液相氧化方法制备氧化石墨,通过超声剥离的方法剥离出片状的氧化石墨烯(GO),探讨了H₂SO₄环境与H₂SO₄+H₃PO₄混酸环境和KMnO₄与GR的比例对GO制备的影响。采用FTIR、UV、TG、XRD、SEM和XPS等分析手段对制备的GO进行分析。结果表明：GO外貌是呈褶皱片状,在片层上主要有C=O、C-OH、-COOH和C-O-C等官能团,以共价键形式存在石墨层间;通过TG与XPS数据分析表明在H₂SO₄ H₃PO₄混酸环境下制备的GO含氧官能团较多,并且(KMnO₄)与鳞片石墨的最佳比例是1:4。     

SnO2 sheet/graphite composite as anode material with improved electrochemical performance for lithium-ion batteries

The SnO₂ sheet/graphite composite was synthesized by a hydrothermal method for high-capacity lithium storage. The microstructures of products were characterized by XRD and FE-SEM. The electrochemical performance of SnO₂ sheet/graphite composite was measured by galvanostatic charge/discharge cycling and EIS. The first discharge and charge capacities are 1,072 and 735 mAh g^?1 with coulombic efficiency of 68.6 %. After 40 cycles, the reversible discharge capacity is still maintained at 477 mAh g^?1. The results show that the SnO₂ sheet/graphite composite displays superior Li-battery performance with large reversible capacity and good cyclic performance.     

双相碳改性硅酸铁锂正极材料研究

以活化的天然石墨为碳源,采用固相辅助回流法成功合成了双相碳改性的Li₂FeSiO₄复合材料。采用XRD、SEM、HRTEM和Raman光谱分析了Li₂FeSiO₄/(C+G)复合材料的物相、形貌及其微观结构;并研究了活化石墨用量对Li₂FeSiO₄/(C+G)复合材料的电化学性能的影响。结果表明：活化石墨以石墨微晶和无定形碳的形态共存于Li₂FeSiO₄/(C+G)材料中,活化石墨用量为5%时所得样品的首次放电容量较高(170.3mAh·g^-1),循环50次后其容量保持率为88.7%,表现出了良好的电化学性能。     

Polyethylene/graphite nanocomposites obtained by in situ polymerization

The synthesis of polyethylene/graphite nanocomposites by in situ polymerization was achieved using the catalytic system Cp₂ZrCl₂ (bis(cyclopentadienyl)zirconium(IV) dichloride)/methylaluminoxane (MAO). Graphite with nano dimensions, previously treated with MAO, was added into the reactor as filler at percentages of 1, 2, and 5% (w/w). XRD analysis showed that the chemical and thermal treatments employed preserve the structure of the graphite sheets. The formation of graphite nanosheets and nanocomposites was confirmed by TEM and AFM. TEM micrographics showed that the polyethylene grew between the graphene nanosheets, giving intercalated and exfoliated graphite nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 692–698, 2010     

Preparing graphene oxide–copper composite material from spent lithium ion batteries and catalytic performance analysis

The wide use of lithium ion batteries (LIBs) has created much waste, which has become a global issue. It is vital to recycle waste LIBs considering their environmental risks and resource characteristics. Anode graphite from spent LIBs still possess a complete layer structure and contain some oxygen-containing groups between layers, which can be reused to prepare high value-added products. Given the intrinsic defect structure of anode graphite, copper foils in LIB anode electrodes, and excellent properties of graphene, graphene oxide–copper composite material was prepared in this work. Anode graphite was firstly purified to remove organic impurities by calcination and remove lithium. Purified graphite was used to prepare graphene oxide–copper composite material after oxidation to graphite oxide, ultrasonic exfoliation to graphene oxide (GO), and Cu²⁺ adsorption. Compared with natural graphite, preparing graphite oxide using anode graphite consumed 40% less concentrated H₂SO₄ and 28.6% less KMnO₄. Cu²⁺ was well adsorbed by 1.0 mg L^?1 stable GO suspension at pH 5.3 for 120 min. Graphene oxide–copper composite material could be successfully obtained after 6 h absorption, 3 h bonding between GO and Cu²⁺ with 3/100 of GO/CuSO₄ mass ratio. Compared to CuO, graphene oxide–copper composite material had better catalytic photodegradation performance on methylene blue, and the electric field further improved the photodegradation efficiency of the composite material.     

Studying lithium intercalation into graphite particles via in situ Raman spectroscopy and confocal microscopy

The electrochemical intercalation of lithium into single graphite particles was studied in situ using Raman microscopy combined with confocal microscopy. The degree of intercalation during cycling was obtained from changes in the Raman bands of carbon. Confocal microscopy was used to image the graphite electrode in order to monitor the intercalation into single graphite particles. An industrial button cell was modified such that Raman spectra and microscopic images of the back side of the negative electrode could be taken through a window in the cup of the cell. The liquid electrolyte consisted of a 1:1 mixture of ethylenecarbonate/dimethylcarbonate (EC/DMC) with 1 M LiPF₆. The spectroscopy and microscopy showed that lithium does not intercalate into the graphite in a homogeneous manner. Inhomogeneous lithium intercalation was even observed in single graphite particles.     

Effect of mild oxidation of natural graphite (NG7) on anode-electrolyte thermal reactions

The effect of mild oxidation of natural graphite (NG7) and some other parameters on the reaction between a fully lithiated graphite anode (Li _x C₆, x=1.0–1.1) and 1 M lithium hexafluoroarsenate in ethylene carbonate and diethyl carbonate electrolyte (1:2, v/v) were studied by differential scanning calorimetry (DSC). It was found that mild oxidation of the graphite suppressed the exothermic reaction of the fully lithiated anode with the electrolyte, most probably as a result of the formation of a more stable and chemically bonded solid electrolyte interphase. Separation and removal of the small graphite particles from the anode mixture suppressed this reaction further. It was also found that the copper current collector, the amount of electrolyte and binder as well as other parameters have a significant influence on the heat evolution as measured by DSC. Received: 11 October 1999 / Accepted: 1 March 2000     

Electrochemically Driven Transformation of Amorphous Carbons to Crystalline Graphite Nanoflakes: A Facile and Mild Graphitization Method

Although, in the carbon family, graphite is the most thermodynamically stable allotrope, conversion of other carbon allotropes, even amorphous carbons, into graphite is extremely hard. We report a simple electrochemical route for the graphitization of amorphous carbons through cathodic polarization in molten CaCl₂ at temperatures of about 1100 K, which generates porous graphite comprising petaloid nanoflakes. This nanostructured graphite allows fast and reversible intercalation/deintercalation of anions, promising a superior cathode material for batteries. In a Pyr₁₄TFSI ionic liquid, it exhibits a specific discharge capacity of 65 and 116 mAh g⁻¹ at a rate of 1800 mA g⁻¹ when charged to 5.0 and 5.25 V vs. Li/Li⁺, respectively. The capacity remains fairly stable during cycling and decreases by only about 8 % when the charge/discharge rate is increased to 10000 mA g⁻¹ during cycling between 2.25 and 5.0 V.     

双相碳改性硅酸铁锂正极材料研究

以活化的天然石墨为碳源,采用固相辅助回流法成功合成了双相碳改性的Li2FeSiO4复合材料。采用XRD、SEM、HRTEM和Raman光谱分析了Li2FeSiO4/(C+G)复合材料的物相、形貌及其微观结构;并研究了活化石墨用量对Li2FeSiO4/(C+G)复合材料的电化学性能的影响。结果表明:活化石墨以石墨微晶和无定形碳的形态共存于Li2FeSiO4/(C+G)材料中,活化石墨用量为5%时所得样品的首次放电容量较高(170.3 mAh·g-1),循环50次后其容量保持率为88.7%,表现出了良好的电化学性能。     

Decreasing Irreversible Capacity of Graphite Electrodes in Lithium-Ion Batteries by Direct Contact of Graphite with Metallic Lithium

The feasibility of reducing the irreversible capacity of negative graphite electrodes in lithium-ion batteries by a direct contact of such electrodes with lithium in the electrolyte is studied. It is shown that the dynamics of the formation of the passive film on graphite and the degree of the decrease in the irreversible capacity depend on the ratio between weights of graphite and lithium in contact. This method of reducing the irreversible capacity does not diminish the reversible capacity of graphite during the cycling. The irreversible capacity of the initial graphite cycled in 1 M LiPF₆ in a mixture of propylene carbonate and diethyl carbonate at a current density of 20 mA g^–1 is 550–1150 mA h g^–1. The reversible capacity of electrodes cycled in the same conditions reaches 290 mA h g^–1.     

Formation of Compressed and Mixed-Layered Graphite on Heating Impact Diamonds

The graphitization process of impact diamonds in the helium atmosphere at 1900–1960 °C is investigated. It is shown that when an impact diamond particle with a large number of lonsdaleite defects is kept at 1900 °C for 1 min, ~5 wt.% of graphite are formed (in the paralle experiment with a particle without lonsdaleite defects the graphite formation is not observed). With an increase in the temperature to 1930 °С and 1940 °С the graphite amount increases to 70 wt.% and 80 wt.% respectively. In both cases, a mixture of two graphite phases forms: the first is turbostratic graphite with d₀₀₂ = 3.38 Å; the second is compressed graphite with d₀₀₂ = 3.21 Å. On heating a particle to 1960 °C graphite is formed in which the layer packing contains a large amount of defects and is a mixture of 2Н and 3R polytypes (the ratio 40:60) with a small degree of turbostratic disordering.