Influence of carbon additive on the properties of spherical Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> and LiFePO<Subscript>4</Subscript> materials for lithium-ion batteries

Preparing spherical particles with carbon additive is considered as one effective way to improve both high rate performance and tap density of Li₄Ti₅O₁₂ and LiFePO₄ materials. Spherical Li₄Ti₅O₁₂/C and LiFePO₄/C composites are prepared by spray-drying–solid-state reaction method and controlled crystallization–carbothermal reduction method, respectively. The X-ray diffraction characterization, scanning electron microscope, Brunauer–Emmett–Teller, alternating current impedance analyzing, tap density testing, and electrochemical property measurements are investigated. After hybridizing carbon with a proper quantity, the crystal grain size of active materials is remarkably decreased and the electrochemical properties are obviously improved. The Li₄Ti₅O₁₂/C and LiFePO₄/C composites prepared in this work are spherical. The tap density and the specific surface area are as high as 1.71 g cm⁻³ and 8.26 m² g⁻¹ for spherical Li₄Ti₅O₁₂/C, which are 1.35 g cm⁻³ and 18.86 m² g⁻¹ for spherical LiFePO₄/C powders. Between 1.0 and 3.0 V versus Li, the reversible specific capacity of the Li₄Ti₅O₁₂/C is more than 150 mAh g⁻¹ at 1.0-C rate. Between 2.5 and 4.2 V versus Li, the reversible capacity of the LiFePO₄/C is close to 140 mAh g⁻¹ at 1.0-C rate.     

A carbon–LiFePO<Subscript>4</Subscript> nanocomposite as high-performance cathode material for lithium-ion batteries

A cathode material of an electrically conducting carbon–LiFePO₄ nanocomposite is synthesized by wet ball milling and spray drying of precursor powders prior to a solid-state reaction. The structural characterization shows that the composite is composed of LiFePO₄ crystals and 4.8 wt.% amorphous carbon. Galvanostatic charge/discharge measurements indicate that the composite exhibits a superior high energy and high cycling stability. This composite delivers a discharge capacity of 159.1 mAh g⁻¹ at 0.1 C, 150.8 mAh g⁻¹ at 1 C, and 140.1 mAh g⁻¹ at 2 C rate. The capacity retention of 99% is achieved after 200 cycles at 2 C. The 18,650 cylindrical batteries are assembled using the composite as cathode materials and demonstrate the capacity of 1,400 mAh and the capacity retention of 97% after 100 cycles at 1 C. These results reveal that the as-prepared LiFePO₄–carbon composite is one of the promising cathode materials for high-performance, advanced lithium-ion batteries directed to the hybrid electric vehicle and pure electric vehicle markets.     

LiFePO<Subscript>4</Subscript>/C with high capacity synthesized by carbothermal reduction method

The olivine-type LiFePO₄/C cathode materials were prepared via carbothermal reduction method using cheap Fe₂O₃ as raw material and different contents of glucose as the reducing agent and carbon source. Their structural and morphological properties were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, and particle size distribution analysis. The results demonstrated that when the content of the carbon precursor of glucose was 16 wt.%, the synthesized powder had good crystalline and exhibited homogeneous and narrow particle size distribution. Even and thin coating carbon film was formed on the surface of LiFePO₄ particles during the pyrolysis of glucose, resulting in the enhancement of the electronic conductivity. Electrochemical tests showed that the discharge capacity first increased and then decreased with the increase of glucose content. The optimal sample synthesized using 16 wt.% glucose as carbon source exhibited the highest discharge capacity of 142 mAh g⁻¹ at 0.1C rate with the capacity retention rate of 90.4% and 118 mAh g⁻¹ at 0.5C rate.     

Synthesis of the LiFePO<Subscript>4</Subscript> by a solid-state reaction using organic acids as a reducing agent

Olivine LiFePO₄ using organic acid as a reducing agent has been synthesized utilizing a solid-state method. Samples were characterized by an X-ray diffraction and a scanning electron microscope. The single-phase LiFePO₄ and small grain size of the crystallite were obtained without the use of a carbon-coating process. In such LiFePO₄ powder, the initial specific capacity was 142 mAhg⁻¹ at a current rate of 0.1 C. After the 50th cycle test, the reversible specific capacity was 132 mAhg⁻¹ at a 2 C rate, showing a retention ratio to the initial capacity as 98.4%.     

Stability of LiFePO4 in water and consequence on the Li battery behaviour

The stability of LiFePO₄ in water was investigated. Changes upon exposure to water can have several important implications for storage conditions of LiFePO₄, aqueous processing of LiFePO₄-based composite electrodes, and eventually for utilisation in aqueous lithium batteries. A Li₃PO₄ layer of a few nanometers thick was characterised at the LiFePO₄ grains surface after immersion in water, accompanied by an increase of Fe^III percentage in the grains. For first charge–discharge cycles in a lithium battery, no effect was observed on electrochemical performances for a sample of LiFePO₄ immersed for 24 h at a concentration of 50 g L⁻¹ without any pH modification. To limit the aging of LiFePO₄ during aqueous electrode processing, it is advised to reduce the immersion duration, to concentrate the LiFePO₄ suspensions, and not to modify the pH. In addition, since immersion in water mimics an accelerated exposure to air humidity, LiFePO₄ should be stored in a dry atmosphere. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Improved of cathode performance of LiFePO<Subscript>4</Subscript>/C composite using different carboxylic acids as carbon sources for lithium-ion batteries

Among the several materials under development for use as a cathodes in lithium-ion batteries olivine-type LiFePO₄ is one of the most promising cathode material. However, its poor conductivity and low lithium-ion diffusion limits its practical application. In this study, we report seven different carboxylic acids used to synthesize LiFePO₄/C composite, and influences of carbon sources on electrochemical performance were intensively studied. The structure and electrochemical properties of the LiFePO₄/C were characterized by X-ray diffraction, scanning electron microscopy, electrical conductivity, and galvanostatic charge–discharge measurements. Among the materials studied, the sample E with tartaric acid as carbon source exhibited the best cell performance with a maximum discharge capacity of 160 mAh g⁻¹ at a 0.1 C-rate. The improved electrochemical properties were attributed to the reduced particle size and enhanced electrical contacts by carbon.     

A PEG-assisted rheological phase reaction synthesis of 5LiFePO<Subscript>4</Subscript>⋅Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C as cathode material for lithium ion cells

5LiFePO₄⋅Li₃V₂(PO₄)₃/C composite cathode material is synthesized by a polyethylene glycol (PEG)-assisted rheological phase method. As a surfactant and dispersing agent, PEG can effectively inhabit the aggregation of colloidal particles during the formation of the gel. Meanwhile, PEG will coat on the particles to play the role of carbon source during the sintering. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy, and electrochemical methods. XRD results indicate that the 5LiFePO₄⋅Li₃V₂(PO₄)₃/C composites are well crystallized and contain olivine-type LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ phases. The composite synthesized at 650 °C exhibits the initial discharge capacities of 134.8 and 129.9 mAh g⁻¹ and the capacity retentions of 96.2 and 97.1 % after 50 cycles at 1C and 2C rates, respectively.     

Polarized Raman spectroscopy study of NiSi film grown on Si(001) substrate

We report on the growth of NiSi film on Si(001) substrate with an orientation of NiSi[200]//Si[001]. Polarized Raman spectroscopy was used to assign the symmetry of the NiSi Raman peaks. Raman peaks at 213 cm⁻¹, 295 cm⁻¹, and 367 cm⁻¹ are assigned to be A _g symmetry and peaks at 196 cm⁻¹, and 254 cm⁻¹ are B _3g symmetry.     

EPR and Optical Absorption Studies of Cu2+-Doped Bis(l-Asparaginato)Mg(II)

The electron paramagnetic resonance study of Cu²⁺-doped bis(l-asparaginato)Mg(II) is performed at room temperature. Two magnetically non-equivalent sites for Cu²⁺ are observed. The spin-Hamiltonian parameters evaluated by fitting spectra to the crystalline field of rhombic symmetry are as follows: g _x  = 2.0420 ± 0.0002, g _y  = 2.0808 ± 0.0002, g _z  = 2.3600 ± 0.0002, A _x  = (99 ± 2) × 10⁻⁴ cm⁻¹, A _y  = (108 ± 2) × 10⁻⁴ cm⁻¹, A _z  = (140 ± 2) × 10⁻⁴ cm⁻¹. The ground state wave function of Cu²⁺ is also determined. The g-anisotropy is estimated and compared with the experimental value. Further, with the help of optical study the nature of bonding of a metal ion with different ligands in the complex is discussed.     

EPR and Optical Study of Cu<Superscript>2+</Superscript> Ions Doped in Sodium Zinc Sulfate Tetrahydrate Single Crystals

Electron paramagnetic resonance (EPR) study of Cu²⁺-doped sodium zinc sulfate tetrahydrate is done at liquid nitrogen temperature. Two magnetically equivalent sites for Cu²⁺ are observed. The spin-Hamiltonian parameters determined by fitting the EPR spectra to the rhombic-symmetry crystalline field are g _x  = 2.2356, g _y  = 2.0267, g _z  = 2.3472, A _x  = 27 × 10⁻⁴ cm⁻¹, A _y  = 54 × 10⁻⁴ cm⁻¹and A _z  = 88 × 10⁻⁴ cm⁻¹. The ground state wave function is also determined. The g-anisotropy is evaluated and compared with the experimental value. With the help of optical study, the nature of bonding in the complex is discussed.     

ESR of V4+ in α-RbTiOPO4 single crystals

We have recorded and investigated the ESR spectrum of vanadium-doped α-RbTiOPO₄ single crystals in the temperature interval 77–300 K. Two types of structurally distinct centers, V1 and V2, with a 4:1 ratio of the peak intensities were observed. The angular dependences of the resonance magnetic fields are described by a spin Hamiltonian corresponding to axial symmetry with the parameters g _∥1=1.9305, g _⊥1=1.9565, A _∥1=−168.2×10⁻⁴cm⁻¹, and A _⊥1=−54.3×10⁻⁴cm⁻¹ for V1 centers and g _∥2=1.9340, g _⊥2=1.9523, A _∥2=−169.0×10⁻⁴cm⁻¹, and A _⊥2=−55.2×10⁻⁴cm⁻¹ for V2 centers. A model of a paramagnetic center is proposed: The vanadium ions replace titanium ions in two structurally distinct positions Ti1 and Ti2 (V1 and V2 centers, respectively). The possibility that a VO²⁺ ion forms when α-RbTiOPO₄ crystals and crystals of the KTP group (KTiOPO₄, NaTiOPO₄, α-and β-LiTiOPO₄), studied earlier, are doped with vanadium is discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 534–536 (March 1998)     

A novel approach to employ Li<Subscript>2</Subscript>MnSiO<Subscript>4</Subscript> as anode active material for lithium batteries

In the present paper, we describe utilization of cathode active material as anode active material, for example, Li₂MnSiO₄. The lithium manganese silicate has been successfully synthesized by solid-state reaction method. The X-ray diffraction pattern confirms the orthorhombic structure with Pmn2 ₁ space group. The Li/Li₂MnSiO₄ cell delivered the initial discharge capacity of 420 mA h g⁻¹, which is 110 mA h g⁻¹ higher than graphitic anodes. The electrochemical reversibility and solid electrolyte interface formation of the Li₂MnSiO₄ electrode was emphasized by cyclic voltammetry.     

Synthesis of Co-coated lithium manganese oxide and its characterization as cathode for lithium ion battery

Co-coated LiMn₂O₄ was synthesized by electroless plating. The phase identification, surface morphology, and electrochemical properties of the synthesized powders were studied by X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, and galvanostatic charge–discharge experiments, respectively. The result shows that Co-coated LiMn₂O₄ particle has a coarse surface with a lot of holes. The specific capacity of Co-coated LiMn₂O₄ is 118 mAh g⁻¹, which is a bit less than 123 mAh g⁻¹ for the uncoated LiMn₂O₄. The capacity retention of Co-coated LiMn₂O₄ is 11% higher than the uncoated LiMn₂O₄ when the electrode is cycled at room temperature for 20 times. When cycled at the temperature of 55 °C, the capacity retention of Co-coated LiMn₂O₄ becomes 15% higher than the uncoated one.     

Studies on lithium bis(oxalato)-borate/propylene carbonate-based electrolytes for Li-ion batteries

Lithium bis(oxalato)-borate (LiBOB) is a promising salt for Li-ion batteries owing to its various characteristics such as non-fluorine, non-toxicity, low cost, and safety. It has the unique merits such as the stability at high temperature and the film-forming characteristics in propylene carbonate (PC)-based electrolyte. In this work, the utilization of PC as the basal solvent and dimethyl carbonate, γ-butyrolactone and ethylene carbonate as co-solvents for LiBOB have been investigated. The results indicate that the co-solvent has conducive effects on the conductivities, viscosities, and battery performance. The conductivity and viscosity of 0.7 mol L⁻¹ LiBOB in PC+GBL+EC+DMC (1:1:1:1, v/v) are 6.22 mS cm⁻¹ and 3.74 mPa s, respectively, and it is very stable in 0–5 V range. The capacity of Li/LiFePO₄ battery is about 160 mAh g⁻¹ at 0.5 °C. Moreover, the battery has exhibited the excellent rate performance.     

Fluorescent Method for the Determination of Sulfide Anion with ZnS:Mn Quantum Dots

Water-soluble Mn²⁺-doped ZnS quantum dots (QDs) were prepared using mercaptoacetic acid as the stabilizer. The optical properties and structure features were characterized by X-Ray, absorption spectrum, IR spectrum and fluorescence spectrum. In pH 7.8 Tris-HCl buffer, the QDs emitted strong fluorescence peaked at 590 nm with excitation wavelength at 300 nm. The presence of sulfide anion resulted in the quenching of fluorescence and the intensity decrease was proportional to the S²⁻ concentration. The linear range was from 2.5 × 10⁻⁶ to 3.8 × 10⁻⁵ mol L⁻¹ with detection limit as 1.5 × 10⁻⁷ mol L⁻¹. Most anions such as F⁻, Cl⁻, Br⁻, I⁻, CH₃CO₂ ⁻, ClO₄ ⁻, CO₃ ²⁻, NO₂ ⁻, NO₃ ⁻, S₂O₃ ²⁻, SO₃ ²⁻ and SO₄ ²⁻ did not interfere with the determination. Thus a highly selective assay was proposed and applied to the determination of S²⁻ in discharged water with the recovery of ca. 103%.     

Recoil distance half-life measurements of the excited states in 145Sm

A recoil distance method was used to measure half-lives of the excited states of ₁₄₅Sm. The reaction used was ₁₃₉La(₁₀B, 4n)₁₄₅Sm. A plunger system was used. Half-lives were determined for two excited states for the first time. The yrast 27/2₊ state was found to have a half-life of 1.1 ± 0.2 ns corresponding to the retardation of 3.1 × 10₋₄ comparing with the single particle estimate of M1. The excitation energy of this state was well reproduced by the shell model calculation having a mixed configuration of [π{h^11/2(g^7/2)₋₂ (d^5/2)₋₁}¹⁰⁻, νf^7/2] + [π{h^11/2(g^7/2)₋₁}⁹⁻,νh^9/2]. Another retarded E1 transition was also found in a decay of a 21/2₊ state. Its retardation was 1.6 × 10₋₄ comparing with the single particle value. Received: 9 September 1997 / Revised version: 12 June 1998     

Electrochemical performances of FePO<Subscript>4</Subscript>-positive active mass prepared through a new sol–gel method

This investigation is a contribution to the research on alternative cathode materials with much more promising performances for lithium batteries. It deals with the electrochemical properties of iron phosphate compound FePO₄, chemically prepared through the so-called sol–gel Pechini process, terminated by a calcination of the product precursor at temperatures (T _c) ranging between 350°C and 650°C. A crystalline phase was obtained for temperatures ≥400°C. The particle size decreased with the decrease in T _c, giving rise to a Brunauer–Emmett–Teller (BET)-specific surface area, S _BET, as high as 28 m² g⁻¹ for the sample annealed at 400°C. The electrochemical properties of FePO₄-based composite cathodes were characterized on three-electrode laboratory cells. Charge–discharge cycling determined a maximum reversible capacity of 132 mAh g⁻¹, which fell with the increase in T _c. A direct correlation was established between the activity of the material and its active surface area.     

Preparation of MnO<Subscript>2</Subscript>/WMNT composite and MnO<Subscript>2</Subscript>/AB composite by redox deposition method and its comparative study as supercapacitive materials

The manganese oxide/multi-walled carbon nanotube (MnO₂/MWNT) composite and the manganese oxide/acetylene black (MnO₂/AB) composite were prepared by translating potassium permanganate into MnO₂ which formed the above composite with residual carbon material using the redox deposition method and carbon as a reducer. The products were characterized by X-ray diffraction, Fourier transform infrared, and scanning electron microscope. Electrochemical properties of both the MnO₂/MWNT and MnO₂/AB electrodes were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the MnO₂/MWNT electrode has better electrochemical capacitance performance than the MnO₂/AB electrode. The charge–discharge test showed the specific capacitance of 182.3 F·g⁻¹ for the MnO₂/MWNT electrode, and the specific capacitance of 127.2 F·g⁻¹ for the MnO₂/AB electrode had obtained, within potential range of 0–1 V at a charge/discharge current density of 200 mA·g⁻¹ in 0.5 mol·L⁻¹ potassium sulfate electrolyte solution in the first cycle. The specific capacitance of both the MnO₂/MWNT and MnO₂/AB electrodes were 141.2 F·g⁻¹ and 78.5 F·g⁻¹ after 1,200 cycles, respectively. The MnO₂/MWNT electrode has better cycling performance. The effect of different morphologies was investigated for both MnO₂/MWNT and MnO₂/AB composites.     

Laser-based measurements of line strength, self- and pressure-broadening coefficients of the H35Cl R(3) absorption line in the first overtone region for pressures up to 1 MPa

A high-resolution spectrometer based on a vertical-cavity surface-emitting laser (VCSEL) was developed and used to determine the line strength S(T ₀)=12.53(11)×10⁻²¹ cm⁻¹/(molec cm⁻²) and the self-broadening coefficient g⁰_HCl=0.021787(61)\gamma^{0}_{\mathrm{HCl}}=0.021787(61)  cm⁻¹/atm of the R(3) absorption line in the first rovibrational overtone (2←0) band of H³⁵Cl. Furthermore, the first laser-based high-pressure study on the pressure broadening of HCl by He, N₂ and O₂(g⁰_N2=0.07292(5)\mathrm{O}_{2}(\gamma^{0}_{\mathrm{N}_{2}}=0.07292(5)  cm⁻¹/atm, g⁰_He=0.02113(1)\gamma^{0}_{\mathrm{He}}=0.02113(1)  cm⁻¹/atm, g⁰_O2=0.03978(6)\gamma^{0}_{\mathrm{O}_{2}}=0.03978(6)  cm⁻¹/atm) is presented covering pressures of up to 1 MPa. The results are compared to previously available low-pressure data.     

Effects of Li2CO3 as a secondary lithium source on the LiFePO4/C composites prepared via solid-state method

Li₂CO₃ was used as the secondary lithium source for the synthesis of LiFePO₄/C composites via a solid-state reaction method by adopting Li₃PO₄ as the main lithium source. The main purpose of using Li₂CO₃ is to compensate for the partial lithium loss during the sintering while reducing the usage of excess Li₃PO₄. In this study, the effects of Li₂CO₃ amount on the phase, structural and electrochemical properties of LiFePO₄/C material were systematically investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), constant-current charge–discharge test and cyclic voltammetry (CV). The results showed that by adding an appropriate amount of Li₂CO₃, the impurities, e.g. Li₃PO₄, normally appearing in the final product, could be excluded. It was found that LiFePO₄/C with Li₂CO₃ in 6% excess (vs. stoichiometric LiFePO₄) exhibited the best electrochemical performance, which delivered initial discharge capacities of 141.7, 125.2, 119.9 and 108.9 mAh g^?1, respectively, at 0.5, 1, 2 and 5C rates. The capacity was reduced to 113.4 mAh g^?1 after 50 cycles at 2C rate, with capacity retention rate of 94.6%.