Synthesis of LiFePO4/C cathode material from ferric oxide and organic lithium salts

LiFePO₄/C cathode material has been simply synthesized via a modified in situ solid-state reaction route using the raw materials of Fe₂O₃, NH₄H₂PO₄, Li₂C₂O₄ and lithium polyacrylate (PAALi). The sintering temperature of LiFePO₄/C precursor is studied by thermo-gravimetric (TG)/differential thermal analysis (DTA). The physical properties of LiFePO₄/C are then investigated through analysis using by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and the electrochemical properties are investigated by electrochemical impedance spectra (EIS), cyclic voltammogram (CV) and constant current charge/discharge test. The LiFePO₄/C composite with the particle size of ∼200 nm shows better discharge capacity (156.4 mAh g⁻¹) than bare LiFePO₄ (52.3 mAh g⁻¹) at 0.2 C due to the improved electronic conductivity which is demonstrated by EIS. The as-prepared LiFePO₄/C through this method also shows excellent high-rate characteristic and cycle performance. The initial discharge capacity of the sample is 120.5 mAh g⁻¹ and the capacity retention rate is 100.6% after 50 cycles at 5 C rate. The results prove that the using of organic lithium salts can obtain a high performance LiFePO₄/C composite.     

Properties of Li-graphite and LiFePO4 electrodes in LiPF6–sulfolane electrolyte

Sulfolane (also referred to as tetramethylene sulfone, TMS) containing LiPF₆ and vinylene carbonate (VC) was tested as a non-flammable electrolyte for a graphite |LiFePO₄ lithium-ion battery. Charging/discharging capacity of the LiFePO₄ electrode was ca. 150 mAh g⁻¹ (VC content 5 wt%). The capacity of the graphite electrode after 10 cycles establishes at the level of ca. 350 mAh g⁻¹ (C/10 rate). In the case of the full graphite |1 M LiPF₆ + TMS + VC 10 wt% |LiFePO₄ cell, both charging and discharging capacity (referred to cathode mass) stabilized at a value of ca. 120 mAh g⁻¹. Exchange current density for Li⁺ reduction on metallic lithium, estimated from electrochemical impedance spectroscopy (EIS) experiments, was j_o(Li/Li⁺) = 8.15 × 10⁻⁴ A cm⁻². Moreover, EIS suggests formation of the solid electrolyte interface (SEI) on lithium, lithiated graphite and LiFePO₄ electrodes, protecting them from further corrosion in contact with the liquid electrolyte. Scanning electron microscopy (SEM) images of pristine electrodes and those taken after electrochemical cycling showed changes which may be interpreted as a result of SEI formation. No graphite exfoliation was observed. The main decomposition peak of the LiPF₆ + TMS + VC electrolyte (TG/DTA experiment) was present at ca. 275 °C. The LiFePO₄(solid) + 1 M LiPF₆ + TMS + 10 wt% VC system shows a flash point of ca. 150 °C. This was much higher in comparison to that characteristic of a classical LiFePO₄ (solid) + 1 M LiPF₆ + 50 wt% EC + 50 wt% DMC system (T_f ≈ 37 °C).     

Improving the rate performance of LiFePO4 by Fe-site doping

LiFePO₄ doped by bivalent cation in Fe-sites show improved rate performance and cyclic stability. Under 10 C rate at room temperature, the capacities of LiFe_0.9M_0.1PO₄ (M = Ni, Co, Mg) maintain at 81.7, 90.4 and 88.7 mAh/g, respectively, in comparison with 53.7 mAh/g for undoped LiFePO₄ and 54.8 mAh/g for carbon-coated LiFePO₄ (LiFePO₄/C). The capacity retention is 95% after 100 cycles for doped samples while this value is only 70% for LiFePO₄ and LiFePO₄/C. Such a significant improvement in electrochemical performance should be partially related to the enhanced electronic conductivities (from 2.2 × 10⁻⁹ to <2.5 × 10⁻⁷ S cm⁻¹) and probably the mobility of Li⁺ ions in the doped samples.     

Synthesis of spindle-shaped nanoporous C–LiFePO4 composite and its application as a cathodes material in lithium ion batteries

In this work, LiFePO₄/C composites were prepared in hydrothermal system by using iron gluconate as iron source, and two feeding sequences during the preparation were comparatively studied. The morphology, crystal structure and charge–discharge performance of the prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and galvanostatic charge–discharge testing. The results showed that the feeding sequences and iron gluconate seriously affected the microstructures and electrochemical properties of the resulting LiFePO₄ cathodes in lithium ion batteries. The spindle-shaped LiFePO₄ with hierarchical microporous structure self-assembled by nanoparticles has been successfully synthesized by synthesis route B. In addition, the cell performance of the synthesized LiFePO₄ by synthesis route B was better than that of LiFePO₄ by synthesis route A. Specially at high rates, the superior rate performance of the spindle-shaped LiFePO₄/C microstructure (LFP/C-B) was revealed. And special reversible capacities of ∼118 and ∼95 mAh g⁻¹ were obtained at rates of 2 C and 5 C, comparing to ∼96 and ∼68 mAh g⁻¹ for LFP/C-A.     

Emulsion drying synthesis of olivine LiFePO4/C composite and its electrochemical properties as lithium intercalation material

The electroactive LiFePO₄/C nano-composite has been synthesized by an emulsion drying method. During burning-out the oily emulsion precipitates in an air-limited atmosphere at 300 °C, amorphous or low crystalline carbon was generated along with releasing carbon oxide gases, and trivalent iron as a cheap starting material was immediately reduced to the divalent one at this stage as confirmed by X-ray photoelectron spectroscopy, leading to a low crystalline LiFePO₄/C composite. Heat-treatment of the low crystalline LiFePO₄/C in an Ar atmosphere resulted in a well-ordered olivine structure, as refined by Rietveld refinement of the X-ray diffraction pattern. From secondary electron microscopic and scanning transmission electron microscopic observations with the corresponding elemental mapping images of iron and phosphorous, it was found that the LiFePO₄ powders are modified by fine carbon. The in situ formation of the nano-sized carbon during crystallization of LiFePO₄ brought about two advantages: (i) an optimized particle size of LiFePO₄, and (ii) a uniform distribution of fine carbon in the product. These effects of the fine carbon on LiFePO₄/C composite led to high capacity retention upon cycling at 25 and 50 °C and high rate capability, resulting from a great enhancement of electric conductivity as high as 10⁻⁴ S cm⁻¹. That is, the obtained capacity was higher than 90 mAh (g-phosphate)⁻¹ by applying a higher current density of about 1000 mA g⁻¹ (11 C) at 50 °C.     

Synthesis and electrochemical characterization of LiCoxMn1−xPO4/C nanocomposites

LiCo_xMn_1−xPO₄/C nanocomposites (0 ≤ x ≤ 1.0) were prepared by a combination of spray pyrolysis at 300 °C and wet ball-milling followed by heat treatment at 500 °C for 4 h in 3% H₂ + N₂ atmosphere. X-ray diffraction analysis indicated that all samples had the single phase olivine structures indexed by orthorhombic Pmna. The lattice parameters linearly decreased with increasing cobalt content, which confirmed the existence of solid solutions. It was clearly seen from the scanning electron microscopy observation that the LiCo_xMn_1−xPO₄/C samples were agglomerates with approximately 100 nm primary particles. The LiCo_xMn_1−xPO₄/C nanocomposites were used as cathode materials for lithium batteries, and electrochemical performance was comparatively investigated with cyclic voltammetry and galvanostatic charge–discharge test using the Li?1 M LiPF₆ in EC:DMC = 1:1?LiCo_xMn_1−xPO₄/C cells at room temperature. The cells at 0.05 C charge–discharge rate delivered first discharge capacities of 165 mAh g⁻¹ (96% of theoretical capacity) at x = 0, 136 mAh g⁻¹ at x = 0.2, 132 mAh g⁻¹ at x = 0.5, 125 mAh g⁻¹ at x = 0.8 and 132 mAh g⁻¹ (79% of theoretical capacity) at x = 1.0, respectively. While the first discharge capacity increased with the cobalt content at high charge–discharge rates more than 0.5 C due to higher electronic conductivity of LiCoPO₄ in comparison with LiMnPO₄, the cycleability of cell became worse with increasing the amount of cobalt. The existence of Mn²⁺ seemed to enhance the cycleability of LiCo_xMn_1−xPO₄/C nanocomposite cathode.     

Enhanced performance of LiFePO4 through hydrothermal synthesis coupled with carbon coating and cupric ion doping

A hydrothermal reaction has been adopted to synthesize pure LiFePO₄ first, which was then modified with carbon coating and cupric ion (Cu²⁺) doping simultaneously through a post-heat treatment. X-ray diffraction patterns, transmission electron microscopy and scanning electron microscopy images along with energy dispersive spectroscopy mappings have verified the homogeneous existence of coated carbon and doped Cu²⁺ in LiFePO₄ particles with phospho-olivine structure and an average size of 400 nm. The electrochemical performances of the material have been studied by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The carbon-coated and Cu²⁺-doped LiFePO₄ sample (LFCu5/C) exhibited an enhanced electronic conductivity of 2.05 × 10⁻³ S cm⁻¹, a specific discharge capacity of 158 mAh g⁻¹ at 50 mA g⁻¹, a capacity retention of 96.4% after 50 cycles, a decreased charge transfer resistance of 79.4 Ω and superior electrode reaction reversibility. The present synthesis route is promising in making the hydrothermal method more practical for preparation of the LiFePO₄ material and enhancement of electrochemical properties.     

Tuning fermi level and band gap in Li4Ti5O12 by doping and vacancy for ultrafast Li+ insertion/extraction

Li₄T_i5O₁₂ (LTO) attracts great interest due to the “zero strain” during cycles but the poor electronic and ionic conductivity critically impede the practical application. Herein, we report a synergy strategy of tuning localized electrons to shift Fermi level and band gap by Mg/Zr co-doping and oxygen vacancy incorporation, which significantly improves Li⁺ and electronic transport. More importantly, the intrinsic synergistic mechanism has been revealed by neutron diffraction, X-ray absorption spectra, and first-principles calculations. The “elastic effect” of lattice induced by Mg/Zr co-doping allows LTO to accommodate more oxygen vacancies to a certain degree without a severe lattice distortion, which largely improves the electronic conductivity. Mg/Zr co-doping and oxygen vacancy incorporation effectively enhanced the dynamic characteristics of LTO electrode, achieving the excellent rate performance (90 mAh/g at 20C) and cycle stability (96.9% after 500 cycles at 10C). First-principles calculations confirm Fermi level shifts to the conduction band, and the band gap becomes narrowed due to the synergistic modulation, and the intrinsic mechanism of the enhanced electronic and Li-ion conductivity is clarified. This study offers some insights into achieving the fast Li⁺ insertion/extraction by tuning the crystal and electronic structure with lattice doping and oxygen vacancy engineering.     

High power performance of nano-LiFePO4/C cathode material synthesized via lauric acid-assisted solid-state reaction

A nano-LiFePO₄/C composite has been directly synthesized from micrometer-sized Li₂CO₃, NH₄H₂PO₄, and FeC₂O₄·2H₂O by the lauric acid-assisted solid-state reaction method. The SEM and TEM observations demonstrate that the synthesized nano-LiFePO₄/C composite has well-dispersed particles with a size of about 100–200 nm and an in situ carbon layer with thickness of about 2 nm. The prepared nano-LiFePO₄/C composite has superior rate capability, delivering a discharge capacity of 141.2 mAh g⁻¹ at 5 °C, 130.9 mAh g⁻¹ at 10 C, 121.7 mAh g⁻¹ at 20 °C, and 112.4 mAh g⁻¹ at 30 °C. At −20 °C, this cathode material still exhibits good rate capability with a discharge capacity of 91.9 mAh g⁻¹ at 1 °C. The nano-LiFePO₄/C composite also shows excellent cycling ability with good capacity retention, up to 100 cycles at a high current density of 30 °C. Furthermore, the effect of lauric acid in the preparation of nano-LiFePO₄/C composite was investigated by comparing it with that of citric acid. The SEM images reveal that the morphology of the LiFePO₄/C composite transformed from the porous structure to fine particles as the molar ratio of lauric acid/citric acid increased.     

An optimized Ni doped LiFePO4/C nanocomposite with excellent rate performance

Both Ni doping and carbon coating are adopted to synthesize a nano-sized LiFePO₄ cathode material through a simple solid-state reaction. It is found that the Ni²⁺ has been successfully doped into LiFePO₄ without affecting the phospho-olivine structure from the XRD result. The images of SEM and TEM show that the size of particles is distributed in the range of 20-60 nm, and all the particles are coated with carbon completely. The results of XPS show the valence state of Fe and Ni in the LiFePO₄. The electronic conductivity of the material is as high as 2.1 × 10⁻¹ S cm⁻¹, which should be ascribed to the coefficient of the conductive carbon network and Ni doping. As a cathode material for lithium-ion batteries, the Ni doped LiFePO₄/C nanocomposite delivers a discharge capacity of 170 mAh g⁻¹ at 0.2 C, approaching the theoretical value. Moreover, the material shows excellent high-rate charge and discharge capability and long-term cyclability. At the high rates of 10 and 15 C, this material exhibits high capacities of 150 and 130 mAh g⁻¹, retaining 95% after 5500 cycles and 93% after 7200 cycles, respectively. Therefore, the as-prepared material is capable of such large-scale applications as electric vehicles and plug-in hybrid electric vehicles.     

Enhanced electrochemical performance of carbon nanospheres-LiFePO4 composite by PEG based sol-gel synthesis

The carbon nanospheres-LiFePO₄ (CNSs-LiFePO₄) composite has been synthesized by PEG (polyethylene glycol, mean molecular weight of 30,000) based sol-gel route. Highly conductive CNSs (30-40 nm) were adopted to improve the electronic conductivity of LiFePO₄. PEG was used to promote the dispersion of CNSs with the surface functionalization of CNSs, which could facilitate the coating of CNSs on the surface of the LiFePO₄ particles. The sample was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and Raman scattering. Electrochemical performance of the CNSs-LiFePO₄ composite was characterized by the charge-discharge test and electrochemical impedance spectra measurement. The results indicated that LiFePO₄ particles were well coated with the conductive CNSs to overcome the intrinsic low electronic conductivity problem of LiFePO₄. The CNSs-LiFePO₄ composite delivered an enhanced rate capability (146, 128 and 113 mAh g⁻¹ at 0.1 C, 1 C and 5 C rate). The PEG based sol-gel route enables LiFePO₄ networked with CNSs, which offered a higher electrochemical performance.     

Synthesis and characterization of LiFePO4/(Ag + C) composite cathodes with nano-carbon webs

LiFePO₄/(Ag + C) composite cathodes with a new type of nano-sized carbon webs were synthesized by two methods of an aqueous co-precipitation and a sol-gel process, respectively. Simultaneous thermogravimetric-differential thermal analysis indicates that the crystallization temperature of LiFePO₄ is about 455-466 °C, which is close to the pyrolysis temperature of polypropylene, 460 °C. The silver and carbon co-modifying does not affect the olivine structure of LiFePO₄ but improves its kinetics in terms of discharge capacity and rate capability. Discharge capacities were improved from 153.4 mA h g^− 1 of LiFePO₄/C to 160.5 mA h g^− 1and 162.1 mA h g^− 1 for LiFePO₄/(Ag + C) cathodes synthesized by the co-precipitation and sol-gel methods, respectively. The possible reasons for the small difference in discharge capacity of two LiFePO₄/(Ag + C) cathodes were discussed. AC impedance measurements show that the Ag + C co-modification decreases the charge transfer resistance of LiFePO₄/(Ag + C) cathodes.     

1-Alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids as highly safe electrolyte for Li/LiFePO4 battery

Several 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquids (alkyl-DMimTFSI) were prepared by changing carbon chain lengths and configuration of the alkyl group, and their electrochemical properties and compatibility with Li/LiFePO₄ battery electrodes were investigated in detail. Experiments indicated the type of ionic liquid has a wide electrochemical window (−0.16 to 5.2 V vs. Li⁺/Li) and are theoretically feasible as an electrolyte for batteries with metallic lithium as anode. Addition of vinylene carbonate (VC) improves the compatibility of alkyl-DMimTFSI-based electrolytes towards lithium anode and LiFePO₄ cathode, and enhanced the formation of solid electrolyte interface to protect lithium anodes from corrosion. The electrochemical properties of the ionic liquids obviously depend on carbon chain length and configuration of the alkyl, including ionic conductivity, viscosity, and charge/discharge capacity etc. Among five alkyl-DMimTFSI-LiTFSI-VC electrolytes, Li/LiFePO₄ battery with the electrolyte-based on amyl-DMimTFSI shows best charge/discharge capacity and reversibility due to relatively high conductivity and low viscosity, its initial discharge capacity is about 152.6 mAh g⁻¹, which the value is near to theoretical specific capacity (170 mAh g⁻¹). Although the battery with electrolyte-based isooctyl-DMimTFSI has lowest initial discharge capacity (8.1 mAh g⁻¹) due to relatively poor conductivity and high viscosity, the value will be dramatically added to 129.6 mAh g⁻¹ when 10% propylene carbonate was introduced into the ternary electrolyte as diluent. These results clearly indicates this type of ionic liquids have fine application prospect for lithium batteries as highly safety electrolytes in the future.     

Enhanced rate performance of nano–micro structured LiFePO4/C by improved process for high-power Li-ion batteries

A spherical carbon-coated nano–micro structured LiFePO₄ composite is synthesized for use as a cathode material in high-power lithium-ion batteries. The composites are synthesized through carbothermal reduction with two sessions of ball milling (before and after pre-sintering of precursor) followed by spray-drying with the dispersant of polyethylene glycol added. The structure, particle size, and surface morphology of the cathode active material and the properties of the coated carbon are investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Results indicate that the LiFePO₄/C composite has a spherical micro-porous morphology composed of a large number of carbon-coated nano-spheres linked together with an ordered olivine structure. The carbon on the surface of LiFePO₄ effectively reduces inter-particle agglomeration of the LiFePO₄ particles. A galvanostatic charge–discharge test indicates that the LiFePO₄/C composites exhibit initial discharge capacities of 155 mAh g⁻¹ and 88 mAh g⁻¹ at 0.2 C and 20 C rates with the end of discharge voltage of 2.5 V, respectively. This behavior is ascribed to the unique spherical structure, which shortens lithium ions diffusion length and improves the electric contact between LiFePO₄ particles.     

Insight into the improvement of rate capability and cyclability in LiFePO4/polyaniline composite cathode

A simple and efficient strategy was employed to enhance high-rate performance for carbon-coated LiFePO₄ (C-LFP) by incorporating with conducting polymer polyaniline (PANI). C-LFP was synthesized via a solid state reaction whereas PANI was formed in situ by chemical oxidative polymerization of aniline with ammonium persulfate as an oxidizer to achieve the C-LFP/PANI composites. Specific capacities as high as 165 mAh g⁻¹ at 0.2 C, 133 mAh g⁻¹ at 7 C and 123 mAh g⁻¹ at 10 C were obtained in C-LFP/7 wt.% PANI composite. Moreover, the composite exhibits remarkably improved cyclability as compared with the parent C-LFP. The mechanism has been carefully investigated for the improvement in the electrochemical performance. Experimental results show that the charge transfer impedance decreases significantly and the cathode surface becomes much smooth over cycling with modification of conductive PANI. The incorporated PANI can work not only as an additional host for Li⁺-ion insertion/extraction, but also as a binder to modify the electrode surface and a container for electrolyte to penetrate into C-LFP particles.     

Rechargeable Li/LiFePO4 cells using N-methyl-N-butyl pyrrolidinium bis(trifluoromethane sulfonyl)imide-LiTFSI electrolyte incorporating polymer additives

We have incorporated polymer additives such as poly(ethylene glycol) dimethyl ether (PEGDME) and tetra(ethylene glycol) dimethyl ether (TEGDME) into N-methyl-N-butylpyrrolidinium bis(trifluoromethane sulfonyl)imide (PYR₁₄TFSI)-LiTFSI mixtures. The resulting PYR₁₄TFSI + LiTFSI + polymer additive ternary electrolyte exhibited relatively high ionic conductivity as well as remarkably low viscosity over a wide temperature range compared to the PYR₁₄TFSI + LiTFSI binary electrolytes. The charge/discharge cyclability of Li/LiFePO₄ cells containing the ternary electrolytes was investigated. We found that Li/PYR₁₄TFSI + LiTFSI + PEGDME (or TEGDME)/LiFePO₄ cells containing the two different polymer additives showed very similar discharge capacity behavior, with very stable cyclability at room temperature (RT). Li/PYR₁₄TFSI + LiTFSI + TEGDME/LiFePO₄ cells can deliver about 127 mAh/g of LiFePO₄ (74.7% of theoretical capacity) at 0.054 mA/cm² (0.2C rate) at RT and about 108 mAh/g of LiFePO₄ (63.4% of theoretical capacity) at 0.023 mA/cm² (0.1C rate) at −1 °C for the first discharge. The cell exhibited a capacity fading rate of approximately 0.09-0.15% per cycle over 50 cycles at RT. Consequently, the PYR₁₄TFSI + LiTFSI + polymer additive ternary mixture is a promising electrolyte for cells using lithium metal electrodes such as the Li/LiFePO₄ cell reported here. These cells showed the capability of operating over a significant temperature range (∼0-∼30 °C).     

One-step microwave synthesis and characterization of carbon-modified nanocrystalline LiFePO4

The precursors of LiFePO₄ were prepared by a sol-gel method using lithium acetate dihydrate, ferrous sulfate, phosphoric acid, citric acid and polyethylene glycol as raw materials, and then the carbon-modified nanocrystalline LiFePO₄ (LiFePO₄/C) cathode material was synthesized by a one-step microwave method with the domestic microwave oven. The effect of microwave time and carbon content on the performance of the resulting LiFePO₄/C material was investigated. Structural characterization by X-ray diffraction and scanning electron microscopy proved that the olivine phase LiFePO₄ was synthesized and the grain size of the samples was several hundred nanometers. Under the optimal conditions of microwave time and carbon content, the charge-discharge performance indicated that the nanosized LiFePO₄/C had a high electrochemical capacity at 0.2 C (152 mAh g⁻¹) and improved capacity retention; the exchange current density was 1.6977 mA cm⁻². Furthermore, the rate capability was improved effectively after LiFePO₄ was modified with carbon, with 59 mAh g⁻¹ being obtained at 20 C.     

Synthesis and characterization of high-density LiFePO4/C composites as cathode materials for lithium-ion batteries

To achieve a high-energy-density lithium electrode, high-density LiFePO₄/C composite cathode material for a lithium-ion battery was synthesized using self-produced high-density FePO₄ as a precursor, glucose as a C source, and Li₂CO₃ as a Li source, in a pipe furnace under an atmosphere of 5% H₂-95% N₂. The structure of the synthesized material was analyzed and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical properties of the synthesized LiFePO₄/carbon composite were investigated by cyclic voltammetry (CV) and the charge/discharge process. The tap-density of the synthesized LiFePO₄/carbon composite powder with a carbon content of 7% reached 1.80 g m⁻³. The charge/discharge tests show that the cathode material has initial charge/discharge capacities of 190.5 and 167.0 mAh g⁻¹, respectively, with a volume capacity of 300.6 mAh cm⁻³, at a 0.1C rate. At a rate of 5C, the LiFePO₄/carbon composite shows a high discharge capacity of 98.3 mAh g⁻¹ and a volume capacity of 176.94 mAh cm⁻³.     

In situ construction of carbon nano-interconnects between the LiFePO4 grains using ultra low-cost asphalt

LiFePO₄/C composite cathode materials with carbon nano-interconnect structures were synthesized by one-step solid state reaction using low-cost asphalt as both carbon source and reducing agent. Based on the thermogravimetry, differential scanning calorimetry, transmission electron microscopy and high-resolution transmission electron microscopy, a growth model was proposed to illustrate the formation of the carbon nano-interconnect between the LiFePO₄ grains. The LiFePO₄/C composite shows enhanced discharge capacity (150 mAh g⁻¹) with excellent capacity retention compared with the bare LiFePO₄ (41 mAh g⁻¹) due to the electronically conductive nanoscale networking provided by the asphalt-based carbon. The results prove that the asphalt is a perfect carbon source and reduction agent for cost-effective production of high performance LiFePO₄/C composite.     

Investigation on a core–shell nano-structural LiFePO4/C and its interfacial CO interaction

Core–shell LiFePO₄/C nanocomposite has been prepared by a sol–gel method. The mean size of the spherical core LiFePO₄ is about 30 nm, and thickness of carbon shell is about 3 nm. The bonding character on the interface of core–shell was revealed by soft X-ray absorption spectroscopy (XAS). The as-prepared sample was characterized by X-ray diffraction (XRD), Raman spectrum, Transmission electron microscope (TEM) and High-resolution transmission electron microscopy (HRTEM). Charge-discharge tests show the core–shell LiFePO₄/C demonstrates high rate capability (106 mAh g⁻¹ at 20 C) and good cycling performance (negligible capacity loss after 250 cycles).