3D amorphous carbon and graphene co-modified LiFePO_4 composite derived from polyol process as electrode for high power lithium-ion batteries

Amorphous carbon and graphene co-modified LiFePO_4 nanocomposite has been synthesized via a facile polyol process in connection with a following thermal treatment.Various characterization techniques,including XRD.Mossbauer spectra,Raman spectra,SEM,TEM,BET,O_2-TPO,galvano charge-discharge,CV and EIS were applied to investigate the phase composition,carbon content,morphological structure and electrochemical performance of the synthesized samples.The effect of introducing way of carbon sources on the properties and performance of LiFePO_4/C/graphene composite was paid special attention.Under optimized synthetic conditions,highly crystalized olivine-type LiFePO_4was successfully obtained with electron conductive Fe_2P and FeP as the main impurity phases.SEM and TEM analyses demonstrated the graphene sheets were randomly distributed inside the sample to create an open structured LiFePO_4 with respect to graphene,while the glucosederived carbon mainly coated over LiFeP04 particles which effectively connected the graphene sheets and LiFePO_4 particles to result in a more efficient charge transfer process.As a result,favorable electrochemical performance was achieved.The performance of the amorphous carbon-graphene co-modified LiFePO_4 was further progressively improved upon cycling in the first 200 cycles to reach a reversible specificcapacity as high as 97 mAh·g~(-1) at 10 C rate.     

Facile low-temperature polyol process for LiFePO4 nanoplate and carbon nanotube composite

Crystalline LiFePO₄ nanoplates were incorporated with 5 wt.% multi-walled carbon nanotubes (CNTs) via a facile low temperature polyol process, in one single step without any post heat treatment. The CNTs were embedded into the LiFePO₄ particles to form a network to enhance the electrochemical performance of LiFePO₄ electrode for lithium-ion battery applications. The structural and morphological characters of the LiFePO₄–CNT composites were investigated by X-ray diffraction, Fourier Transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. The electrochemical properties were analyzed by cyclic voltammetry, electrochemical impedance spectroscopy and charge/discharge tests. Primary results showed that well crystallized olivine-type structure without any impurity phases was developed, and the LiFePO₄–CNT composites exhibited good electrochemical performance, with a reversible specific capacity of 155 mAh g⁻¹ at the current rate of 10 mA g⁻¹, and a capacity retention ratio close to 100% after 100 cycles.     

新方法合成LiFePO4/C

以Fe(NO3)3·9H2O、LiNO3、NH4H2PO4和蔗糖为原料,在超临界CO2流体中反应合成,进而经二次焙烧制得LiFePO4/C。 结果表明,在超临界CO2流体中经50 ℃反应24 h,在350和600 ℃焙烧后制得粒径分布在0.5~1.0 μm的纯LiFePO4/C,该材料作为锂离子电池正极的放电比容量达156.6 mA·h/g,经50次循环后容量几乎没有衰减。     

Synthesis,characterization and electrochemical performances of LiFePO4/graphene cathode material for high power lithium-ion batteries

LiFePO₄/graphene (LiFePO₄/G) cathode with exciting electrochemical performance was successfully synthesized by liquid phase method. LiFePO₄ nanoparticles wrapped with multi-layered grapheme can be fabricated in a short time. This method did not need external heating source. Heat generated by chemical reaction conduct the process and removed the solvent simultaneously. The LiFePO₄/G were analyzed by X-ray diffraction (XRD) analysis, scanning electron microscope (SEM), transmission electron microscopy (TEM), magnetic properties analysis and electrochemical performance tests. The LiFePO₄/G delivered a capacity of 160 mAh g⁻¹ at 0.1C and could tolerate various dis-charge currents with a capacity retention rate of 99.8%, 99.2%, 99.0%, 98.6%, 97.3% and 95.0% after stepwise under 5C, 10C, 15C, 20C, 25C and 30C, respectively.     

Graphene-encapsulated Fe3O4 nanoparticles with 3D laminated structure as superior anode in lithium ion batteries

Fe₃O₄–graphene composites with three‐dimensional laminated structures have been synthesised by a simple in situ hydrothermal method. From field‐emission and transmission electron microscopy results, the Fe₃O₄ nanoparticles, around 3–15 nm in size, are highly encapsulated in a graphene nanosheet matrix. The reversible Li‐cycling properties of Fe₃O₄–graphene have been evaluated by galvanostatic discharge–charge cycling, cyclic voltammetry and impedance spectroscopy. Results show that the Fe₃O₄–graphene nanocomposite with a graphene content of 38.0 wt % exhibits a stable capacity of about 650 mAh g^?1 with no noticeable fading for up to 100 cycles in the voltage range of 0.0–3.0 V. The superior performance of Fe₃O₄–graphene is clearly established by comparison of the results with those from bare Fe₃O₄. The graphene nanosheets in the composite materials could act not only as lithium storage active materials, but also as an electronically conductive matrix to improve the electrochemical performance of Fe₃O₄.     

Dispersing SnO2 nanocrystals in amorphous carbon as a cyclic durable anode material for lithium ion batteries

We demonstrate a facile route for the massive production of SnCb/carbon nanocomposite used as high-capacity anode materials of nextgeneration lithium-ion batteries.The nanocomposite had a unique structure of ultrafine SnO2 nanocrystals（5 nm,80 wt%） homogeneously dispersed in amorphous carbon matrix.This structure design can well accommodate the volume change of Li＋ insertion/desertion in SnO2,and prevent the aggregation of the nanosized active materials during cycling,leading to superior cycle performance with stable reversible capacity of 400 mAh/g at a high current rate of 3.3 A/g.     

Hydrothermal synthesis of spindle-like Li2FeSiO4-C composite as cathode materials for lithium-ion batteries

In this paper,we report on the preparation of Li_2FeSiO_4,sintered Li_2FeSiO_4,and Li_2FeSiO_4-C composite with spindle-like morphologies and their application as cathode materials of lithium-ion batteries.Spindle-like Li2FeSi04 was synthesized by a facile hydrothermal method with(NH_4)_2Fe(SO_4)_2 as the iron source.The spindle-like Li_2FeSiO_4 was sintered at 600 ℃ for 6 h in Ar atmosphere.Li_2FeSiO_4-C composite was obtained by the hydrothermal treatment of spindle-like Li_2FeSiO_4 in glucose solution at 190 ℃ for 3 h.Electrochemical measurements show that after carbon coating,the electrode performances such as discharge capacity and high-rate capability are greatly enhanced.In particular.Li_2FeSiO_4-C with carbon content of 7.21 wt%delivers the discharge capacities of 160.9 mAh·g~(-1) at room temperature and 213 mAh·g~(-1) at45℃(0.1 C),revealing the potential application in lithium-ion batteries.     

Interconnected sandwich structure carbon/Si-SiO2/carbon nanospheres composite as high performance anode material for lithium-ion batteries

In the present work,an interconnected sandwich carbon/Si-SiO2/carbon nanospheres composite was prepared by template method and carbon thermal vapor deposition（TVD）.The carbon conductive layer can not only efficiently improve the electronic conductivity of Si-based anode,but also play a key role in alleviating the negative effect from huge volume expansion over discharge/charge of Si-based anode.The resulting material delivered a reversible capacity of 1094 mAh/g,and exhibited excellent cycling stability.It kept a reversible capacity of 1050 mAh/g over 200 cycles with a capacity retention of 96%.     

新一代动力锂离子电池磷酸锰锂正极材料的研究现状与展望

磷酸锰锂（LiMnPO₄）正极材料具有能量密度高、成本低、安全性高和热稳定性好等优点,目前已成为锂电产业界研究的热点,有望成为继磷酸铁锂（LiFePO₄）之后的新一代正极材料. 然而,磷酸锰锂的电子电导率和锂离子扩散率均很低,其电化学性能提高较为困难,至今尚无法制备出满足实际应用的高性能LiMnPO₄正极材料,严重制约了LiMnPO₄材料及其电池的发展. 本文从LiMnPO₄的结构特性出发,对近年来国内外在碳包覆、离子掺杂、纳米化和控制晶体形貌等改性研究、全电池研究、专利情况以及商业化尝试等多方面进行了综述,并对LiMnPO₄的发展进行了展望.     

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.     

Graphitized carbon and graphene modified Fe2O3/Li4Ti5O12 as anode material for lithium ion batteries

Graphitized carbon (GC) and graphene (GE) modified Fe₂O₃/Li₄Ti₅O₁₂ (LTO) composites have been synthesized via a solid‐state reaction, respectively. The structure, morphology and electrochemical performance of the materials have also been characterized with X‐ray diffraction (XRD), scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) system, X‐ray photoelectron spectrometer (XPS), Fourier transform infrared spectroscopy (FTIR) and electrochemical measurements. The discharge capacities of Fe₂O₃/LTO, GC/Fe₂O₃/LTO and GE/Fe₂O₃/LTO are 100.2 mAh g^?1, 207.5 mAh g^?1 and 238.9 mAh g^?1 after 100 cycles at the current density of 176 mA g^?1. The cyclic stability and rate capability are in the order of GE/Fe₂O₃/LTO > GC/Fe₂O₃/LTO > Fe₂O₃/LTO because of the synergistic effect between GC (GE) and Fe₂O₃/LTO. Copyright © 2016 John Wiley & Sons, Ltd.     

A feasibility study on the use of Li(4)V(3)O(8) as a high capacity cathode material for lithium-ion batteries

Li(4)V(3)O(8) materials have been prepared by chemical lithiation by Li(2)S of spherical Li(1.1)V(3)O(8) precursor materials obtained by a spray-drying technique. The over-lithiated vanadates were characterised physically by using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and electrochemically using galvanostatic charge-discharge and cyclic voltammetry measurements in both the half-cell (vs. Li metal) and full-cell (vs. graphite) systems. The Li(4)V(3)O(8) materials are stable in air for up to 5 h, with almost no capacity drop for the samples stored under air. However, prolonged exposure to air will severely change the composition of the Li(4)V(3)O(8) materials, resulting in both Li(1.1)V(3)O(8) and Li(2)CO(3). The electrochemical performance of these over-lithiated vanadates was found to be very sensitive to the conductive additive (carbon black) content in the cathode. When sufficient carbon black is added, the Li(4)V(3)O(8) cathode exhibits good cycling behaviour and excellent rate capabilities, matching those of the Li(1.1)V(3)O(8) precursor material, that is, retaining an average charge capacity of 205 mAh g(-1) at 2800 mA g(-1) (8C rate; 1C rate means full charge or discharge of a battery in one hour), when cycled in the potential range of 2.0-4.0 V versus Li metal. When applied in a non-optimised full cell system (vs. graphite), the Li(4)V(3)O(8) cathode showed promising cycling behaviour, retaining a charge capacity (Li(+) extraction) above 130 mAh g(-1) beyond 50 cycles, when cycled in the voltage range of 1.6-4.0 V, at a specific current of 117 mA g(-1) (C/3 rate).     

A Superior Na3V2(PO4)3‐Based Nanocomposite Enhanced by Both N‐Doped Coating Carbon and Graphene as the Cathode for Sodium‐Ion Batteries

A superior Na₃V₂(PO₄)₃‐based nanocomposite (NVP/C/rGO) has been successfully developed by a facile carbothermal reduction method using one most‐common chelator, disodium ethylenediamintetraacetate [Na₂(C₁₀H₁₆N₂O₈)], as both sodium and nitrogen‐doped carbon sources for the first time. 2D‐reduced graphene oxide (rGO) nanosheets are also employed as highly conductive additives to facilitate the electrical conductivity and limit the growth of NVP nanoparticles. When used as the cathode material for sodium‐ion batteries, the NVP/C/rGO nanocomposite exhibits the highest discharge capacity, the best high‐rate capabilities and prolonged cycling life compared to the pristine NVP and single‐carbon‐modified NVP/C. Specifically, the 0.1 C discharge capacity delivered by the NVP/C/rGO is 116.8 mAh g^?1, which is obviously higher than 106 and 112.3 mAh g^?1 for the NVP/C and pristine NVP respectively; it can still deliver a specific capacity of about 80 mAh g^?1 even at a high rate up to 30 C; and its capacity decay is as low as 0.0355 % per cycle when cycled at 0.2 C. Furthermore, the electrochemical impedance spectroscopy was also implemented to compare the electrode kinetics of all three NVP‐based cathodes including the apparent Na diffusion coefficients and charge‐transfer resistances.     

Inorganic Sol-Gel Preparation of Medium Sized Microparticles of Li2TiO3 from TiCl4 as Tritium Breeding Material for Fusion Reactors

Microspheres of Li₂TiO₃ were fabricated by a classical, inorganic sol-gel process from commercially available TiCl₄. Elaborated process consists of the following main steps: (1) dissolving of TiCl₄ in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl₄ by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li₂TiO₃ microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.     

Electrochemical sensors for the simultaneous determination of zinc,cadmium and lead using a Nafion/ionic liquid/graphene composite modified screen-printed carbon electrode

A simple, low cost, and highly sensitive electrochemical sensor, based on a Nafion/ionic liquid/graphene composite modified screen-printed carbon electrode (N/IL/G/SPCE) was developed to determine zinc (Zn(II)), cadmium (Cd(II)), and lead (Pb(II)) simultaneously. This disposable electrode shows excellent conductivity and fast electron transfer kinetics. By in situ plating with a bismuth film (BiF), the developed electrode exhibited well-defined and separate peaks for Zn(II), Cd(II), and Pb(II) by square wave anodic stripping voltammetry (SWASV). Analytical characteristics of the BiF/N/IL/G/SPCE were explored with calibration curves which were found to be linear for Zn(II), Cd(II), and Pb(II) concentrations over the range from 0.1 to 100.0 ng L⁻¹. With an accumulation period of 120 s detection limits of 0.09 ng mL⁻¹, 0.06 ng L⁻¹ and 0.08 ng L⁻¹ were obtained for Zn(II), Cd(II) and Pb(II), respectively using the BiF/N/IL/G/SPCE sensor, calculated as 3σ value of the blank. In addition, the developed electrode displayed a good repeatability and reproducibility. The interference from other common ions associated with Zn(II), Cd(II) and Pb(II) detection could be effectively avoided. Finally, the proposed analytical procedure was applied to detect the trace metal ions in drinking water samples with satisfactory results which demonstrates the suitability of the BiF/N/IL/G/SPCE to detect heavy metals in water samples and the results agreed well with those obtained by inductively coupled plasma mass spectrometry.     

Conducting Graphene Decorated Li3V2(PO4)3/C for Lithium‐Ion Battery Cathode with Superior Rate Capability and Cycling Stability

In this study, core‐shell structured Li₃V₂(PO₄)₃/C wrapped in graphene nanosheets has been successfully prepared. The reduction of graphene oxide and the synthesis of Li₃V₂(PO₄)₃/C are carried out simultaneously using a chemical route followed by a solid‐state reaction. The effects of conducting graphene are studied by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectra and electrochemical measurements. The results reveal that the graphene sheets not only form a compact and uniform coating layer throughout the Li₃V₂(PO₄)₃/C, but also stretch out and cross‐link into a conducting network around the Li₃V₂(PO₄)₃/C particles. Thus, the graphene decorated Li₃V₂(PO₄)₃/C electrode exhibits superior high‐rate capability and long‐cycle stability. It delivers a reversible discharge capacity of 178.2 mAh·g^?1 after 60 cycles at a current density of 0.1 C, and the rate performances of 176, 169.3, 156.1 and 135.7 mAh·g^?1 at 1, 2, 5 and 10 C, respectively. The superior electrochemical properties make the graphene decorated Li₃V₂(PO₄)₃/C composite a promising cathode material for high‐performance lithium‐ion battery.     

Heteroatoms self-doped porous carbon from cottonseed meal using K2CO3 as activator and DES electrolyte for supercapacitor with high energy density

Biomass had been extensively explored and applied in many fields due to their abundance, attractive structure, low cost, renewability, and environmental friendliness. Cottonseed meal (CM), one of the by-products of cotton, consisted of much crude protein, fiber, and inorganic ions, was a potential carbon precursor. In this work, CM was used to prepare N, S, and O self-doped carbon materials by two steps (hydrothermal pre-carbonization and K₂CO₃ carbonization–activation) processes. The optimized material displayed high capacitive performance, which benefited from the large surface area (2361 m²/g), hierarchical porous structure and rich multi-heteroatoms doping of the prepared porous carbon. What's more, we prepared a new-type K₂CO₃-based deep eutectic solvent (DES) electrolyte. The assembled symmetric device using DES electrolyte displayed a superior energy density (34.4 Wh/kg) at room temperature. Furthermore, the energy density could reach 36.5 Wh/kg when the temperature rose to 50 °C. Even under extreme conditions, the device delivered a not particularly bad energy density (11.8 Wh/kg at ?25 °C and 8.6 Wh/kg at 105 °C). This study provided an efficient and simple method to prepare CM-based heteroatoms self-doped porous carbon materials and uncovered a new possibility for the exploitation of carbon-based supercapacitors with high energy density.     

Simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using a carbon composite electrode modified with Cu3(PO4)2 immobilized in polyester resin

A simple electrochemical method was developed for the single and simultaneous determination of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) in food samples using square-wave voltammetry (SWV). A carbon composite electrode modified (MCCE) with copper (II) phosphate immobilized in a polyester resin was proposed. The modified electrode allowed the detection of BHA and BHT at potentials lower than those observed at unmodified electrodes. A separation of about 430 mV between the peak oxidation potentials of BHA and BHT in binary mixtures was obtained. The calibration curves for the simultaneous determination of BHA and BHT demonstrated an excellent linear response in the range from 3.4 × 10⁻⁷ to 4.1 × 10⁻⁵ mol L⁻¹ for both compounds. The detection limits for the simultaneous determination of BHA and BHT were 7.2 × 10⁻⁸ and 9.3 × 10⁻⁸ mol L⁻¹, respectively. In addition, the stability and repeatability of the electrode were determined. The proposed method was successfully applied in the simultaneous determination of BHA and BHT in several food samples, and the results obtained were found to be similar to those obtained using the high performance liquid chromatography method with agreement at 95% confidence level.