Synthesis and electrochemical performance of doped LiCoO2 materials

Layered intercalation compounds LiM_0.02Co_0.98O₂ (M = Mo⁶⁺, V⁵⁺, Zr⁴⁺) have been prepared using a simple solid-state method. Morphological and structural characterization of the synthesized powders is reported along with their electrochemical performance when used as the active material in a lithium half-cell. Synchrotron X-ray diffraction patterns suggest a single phase HT-LiCoO₂ that is isostructural to α-NaFeO₂ cannot be formed by aliovalent doping with Mo, V, and Zr. Scanning electron images show that particles are well-crystallized with a size distribution in the range of 1–5 μm. Charge–discharge cycling of the cells indicated first cycle irreversible capacity loss in order of increasing magnitude was Zr (15 mAh g⁻¹), Mo (22 mAh g⁻¹), and V (45 mAh g⁻¹). Prolonged cycling the Mo-doped cell produced the best performance of all dopants with a stable reversible capacity of 120 mAh g⁻¹ after 30 cycles, but was inferior to that of pure LiCoO₂.     

A new SiO/C anode composition for lithium-ion battery

A new anode composition comprising SiO and graphite(C) is prepared through a high-energy ball milling process. During the first cycle, the anode delivers high discharge and charge capacity values of 1556 and 693 mAh g⁻¹, respectively. The electrode shows a reversible charge capacity value of 688 mAh g⁻¹ at the 30th cycle with 99% Coulombic efficiency. X-ray diffraction analysis reveals that ball milling does not produce any new compound, but only causes a reduction in particle size. The irreversible and reversible capacities appear to be interdependent.     

Preparation and electrochemical properties of carbon-doped TiO2 nanotubes as an anode material for lithium-ion batteries

Carbon-doped TiO₂ nanotubes were synthesized through a sol–gel and subsequent hydrothermal process. Transmission electron microscopy and X-ray diffraction showed that the products are uniformly straight tubes with the diameter around 10 nm in anatase-type. The electrochemical performances of the nanotubes were tested by constant current discharge/charge, cyclic voltammetry, and electrochemical impedance spectroscopy. The initial discharge capacity reaches 291.7 mAh g⁻¹ with a coulombic efficiency of 91.7% at a current density of 70 mA g⁻¹. There is a distinct potential plateau near 1.75 and 1.89 V (versus Li⁺/Li) in the lithium intercalation and extraction processes, respectively, and the lithium insertion capacity is about 204 mAh g⁻¹ over the plateau of 1.75 V region in the first cycle. From the 2nd to the 30th cycles, the average reversible capacity loss is less than 1.73 mAh g⁻¹ per cycle. After 30 cycles, the reversible capacity still remains 211 mAh g⁻¹ with a coulombic efficiency larger than 99.7%, implying a perfect reversibility and cycling stability.     

Electrochemical performance of mesoporous TiO2 anatase

Mesoporous TiO₂ was prepared via a sol–gel method from an ethylene glycol-based titanium-precursor in the presence of a non-ionic surfactant at pH 2. Only the anatase structure was detected after annealing, while the BET specific surface area was measured as being 90 m² g⁻¹ with a rather monomodal pore diameter close to 5 nm. Electrochemical performances were investigated by cyclic voltammetry and galvanostatic techniques. Mesoporous TiO₂ exhibits excellent rate capability (184 mAh g⁻¹ at C/5, 158 mAh g⁻¹ at 2C, 127 mAh g⁻¹ at 6C, and 95 mAh g⁻¹ at 30C) and good cycling stability.     

Surfactant based sol–gel approach to nanostructured LiFePO4 for high rate Li-ion batteries

Porous nanostructured LiFePO₄ powder with a narrow particle size distribution (100–300 nm) for high rate lithium-ion battery cathode application was obtained using an ethanol based sol–gel route employing lauric acid as a surfactant. The synthesized LiFePO₄ powders comprised of agglomerates of crystallites <65 nm in diameter exhibiting a specific surface area ranging from 8 m² g⁻¹ to 36 m² g⁻¹ depending on the absence or presence of the surfactant. The LiFePO₄ obtained using lauric acid resulted in a specific capacity of 123 mAh g⁻¹ and 157 mAh g⁻¹ at discharge rates of 10C and 1C with less than 0.08% fade per cycle, respectively. Structural and microstructural characterization were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray (EDX) analysis while electronic conductivity and specific surface area were determined using four-point probe and N₂ adsorption techniques.     

Preparation of nanostructures NiO and their electrochemical capacitive behaviors

Nanocrystalline NiO was synthesized by high temperature solid-state (HTSS) method and microwave (MW) method. The structure of the samples was examined by X-ray. Electrochemical properties were examined by galvanostatic charge–discharge measurements, cyclic voltammetry and electrical impedance spectroscopy. The results showed that the particle sizes of the NiO prepared by MW and HTSS were 34.6 and 75.5 nm. The specific capacitance of MW and HTSS were 186 and 97 F g⁻¹, which decreased to 170 and 74 F g⁻¹ after 1000 cycles. It revealed that the NiO materials prepared by MW exhibited good specific capacitance and cycling performance, which had the high surface redox reactivity due to its special nanostructures.     

Sulfides organic polymer: Novel cathode active material for rechargeable lithium batteries

Two novel sulfide polymers, poly(2-phenyl-1,3-dithiolane) and poly[1,4-di(1,3-dithiolan-2-yl)benzene], were prepared via facile oxidative-coupling polymerization under ambient conditions, characterized by FT-IR, XRD, TGA and elemental analysis, and were tested as cathode materials in rechargeable lithium battery. The charge–discharge tests showed that the specific capacity of poly[1,4-di(1,3-dithiolan-2-yl)benzene)] was 378 mAh g⁻¹ at the third cycle, and retained at 300 mAh g⁻¹ after 20 cycles. The specific capacity of poly(2-phenyl-1,3-dithiolane) was 117 mAh g⁻¹ at the second cycle, and retained at 100 mAh g⁻¹ after 20 cycles. The results indicated that thiolane group could be used as cathode active function group for lithium secondary batteries and the novel electrode reaction is proposed tentatively.     

Nanostructured Fe2O3 and CuO composite electrodes for Li ion batteries synthesized and deposited in one step

Nanostructured composite electrodes based on iron and copper oxides for applications in Li-ion batteries are produced by Electrostatic spray pyrolysis (ESP). The electrodes are directly formed by electrospraying precursor solutions containing either iron or copper salts dissolved in N-methylpyrrolidone (NMP) together with polyvinylidene fluoride (PVdF) as binder. The morphology and the structure of the deposited electrodes are investigated by X-ray diffraction (XRD) and Transmission electron microscopy (TEM), which show that sub-micrometric deposits are formed as a composite of oxide nanoparticles of a few nanometers in a PVdF polymer matrix. Electrochemical characterization by cyclic voltammetry (CV) and galvanostatic charge-discharge tests demonstrate that the conversion reactions in these electrodes enable initial discharge capacities of about 800 mAh g⁻¹ and 1550 mAh g⁻¹ for CuO and Fe₂O₃, respectively. The capacity retention in both cases needs further improvements.     

Preparation and electrochemical properties of Li4Ti5O12 thin film electrodes by pulsed laser deposition

Spinel Li₄Ti₅O₁₂ thin film anode material for lithium-ion batteries is prepared by pulsed laser deposition. Thin film anodes are deposited at ambient temperature, then annealed at three different temperatures under an argon gas flow and the influence of annealing temperatures on their electrochemical performances is studied. The microstructure and morphology of the films are characterized by XRD, SEM and AFM. Electrochemical properties of the films are evaluated by using galvanostatic discharge/charge tests, cyclic voltammetry and a.c. impedance spectroscopy. The results reveal that all annealed films crystallize and exhibit good cycle performance. The optimum annealing temperature is about 700 °C. The steady-state discharge capacity of the films is about 157 mAh g⁻¹ at a medium discharge/charge current density of 10 μA cm⁻². At a considerably higher discharge/charge current density of 60 μA cm⁻² (about 3.45 C) the discharge capacity of the films remains steady at a relative high value (146 mAh g⁻¹). The cycleability of the films is excellent. This implies that such films are suitable for electrodes to be used at high discharge/charge current density.     

Electrochemical properties of carbon-coated Si/B composite anode for lithium ion batteries

Carbon-coated Si and Si/B composite powders prepared by hydrocarbon gas (argon + 10 mol% propylene) pyrolysis were investigated as the anodes for lithium-ion batteries. Carbon-coated silicon anode demonstrated the first discharge and charge capacity as 1568 mAh g⁻¹ and 1242 mAh g⁻¹, respectively, with good capacity retention for 10 cycles. The capacity fading rate of carbon-coated Si/B composite anode decreased as the amounts of boron increased. In addition, the cycle life of carbon-coated Si/B/graphite composite anode has been significantly improved by using sodium carboxymethyl cellulose (NaCMC) and styrene butadiene rubber (SBR)/NaCMC mixture binders compared to the poly(vinylidene fluoride, PVdF) binder. A reversible capacity of about 550 mAh g⁻¹ has been achieved at 0.05 mAm g⁻¹ rate and its capacity could be maintained up to 450 mAh g⁻¹ at high rate of 0.2 mAm g⁻¹ even after 30 cycles. The improvement of the cycling performance is attributed to the lower interfacial resistance due to good electric contact between silicon particles and copper substrate.     

A study on the electrochemical characteristics of LiFePO4 cathode for lithium polymer batteries by hydrothermal method

Phospho-olivine LiFePO₄ cathode materials were prepared by hydrothermal reaction at 150 °C. Carbon black was added to enhance the electrical conductivity of LiFePO₄. LiFePO₄-C powders (0, 3, 5 and 10 wt.%) were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). LiFePO₄-C/solid polymer electrolyte (SPE)/Li cells were characterized electrochemically by charge/discharge experiments at a constant current density of 0.1 mA cm⁻² in a range between 2.5 and 4.3 V vs. Li/Li⁺, cyclic voltammetry (CV) and ac impedance spectroscopy. The results showed that initial discharge capacity of LiFePO₄ was 104 mAh g⁻¹. The discharge capacity of LiFePO₄-C/SPE/Li cell with 5 wt.% carbon black was 128 mAh g⁻¹ at the first cycle and 127 mAh g⁻¹ after 30 cycles, respectively. It was demonstrated that cycling performance of LiFePO₄-C/SPE/Li cells was better than that of LiFePO₄/SPE/Li cells.     

Morphology effect on the electrochemical performance of NiO films as anodes for lithium ion batteries

NiO films were prepared by chemical bath deposition and electrodeposition method, respectively, using nickel foam as the substrate. The films were characterized by scanning electron microscopy (SEM) and the images showed that their morphologies were distinct. The NiO film prepared by chemical bath deposition was highly porous, while the film prepared by electrodeposition was dense, and both of their thickness was about 1 μm. As anode materials for lithium ion batteries, the porous NiO film prepared by chemical bath deposition exhibited higher coulombic efficiency and weaker polarization and its specific capacity after 50 cycles was 490 mAh g⁻¹ at the discharge–charge current density of 0.5 A g⁻¹, and 350 mAh g⁻¹ at 1.5 A g⁻¹, higher than the electrodeposited film (230 mAh g⁻¹ at 0.5 A g⁻¹, and 170 mAh g⁻¹ at 1.5 A g⁻¹). The better electrochemical performances of the film prepared by chemical bath deposition are attributed to its highly porous morphology, which shorted diffusion length of lithium ions, and relaxed the volume change caused by the reaction between NiO and Li⁺.     

Temperature-controlled microwave solid-state synthesis of Li3V2(PO4)3 as cathode materials for lithium batteries

Monoclinic Li₃V₂(PO₄)₃ can be rapidly synthesized at 750 °C for 5 min (MW5m) by using temperature-controlled microwave solid-state synthesis method (TCMS). The carbon-free sample MW5m presents well electrochemical properties. In the cut-off voltage 3.0-4.3, MW5m presents a charge capacity 132 mAh g⁻¹, almost equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹), and discharge capacity 126.4 mAh g⁻¹. In the cut-off voltage 3.0-4.8 V, MW5m shows an initial discharge capacity of 183.4 mAh g⁻¹, near to the theoretical discharge capacity. In the cycle performance, the capacity fade of Li₃V₂(PO₄)₃ is dependent on the cut-off voltage and the preparation method.     

A doped activated carbon prepared from polyaniline for high performance supercapacitors

A novel doped activated carbon has been prepared from H₂SO₄-doped polyaniline which is prepared by the oxypolymerization of aniline. The morphology, surface chemical composition and surface area of the carbon have been investigated by scanning electron microscope, X-ray photoelectron spectroscopy and Brunaner-Emmett-Teller measurement, respectively. Electrochemical properties of the doped activated carbon have been studied by cyclic voltammograms, galvanostatic charge/discharge, and electrochemical impedance spectroscopy measurements in 6 mol l⁻¹ KOH. The specific capacitance of the carbon is as high as 235 F g⁻¹, the specific capacitance hardly decreases at a high current density 11 A g⁻¹ after 10,000 cycles, which indicates that the carbon possesses excellent cycle durability and may be a promising candidate for supercapacitors.     

Cerium and zinc: Dual-doped LiMn2O4 spinels as cathode material for use in lithium rechargeable batteries

Pristine spinel lithium manganese oxide (LiMn₂O₄) and zinc- and cerium-doped lithium manganese oxide [LiZn_xCe_yMn_2−x−yO₄ (x = 0.01–0.10; y = 0.10–0.01)] are synthesized for the first time via the sol–gel route using p-amino benzoic acid as a chelating agent to obtain micron-sized particles and enhanced electrochemical performance. The sol–gel route offers shorter heating time, better homogeneity and control over stoichiometry. The resulting spinel product is characterized through various methods such as thermogravimetic and differential thermal analysis (TG/DTA), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrochemical galvanostatic cycling studies. Charge–discharge studies of LiMn₂O₄ samples heated at 850 °C exhibit a discharge capacity of 122 mAh g⁻¹ and a corresponding 99% coulombic efficiency in the 1st cycle. The discharge capacity and cycling performance of LiZn_0.01Ce_0.01Mn_1.98O₄ is found to be superior (124 mAh g⁻¹), with a low capacity fade (0.1 mAh g⁻¹ cycle⁻¹) over the investigated 10 cycles.     

Effects of magnesium doping on electronic conductivity and electrochemical properties of LiFePO4 prepared via hydrothermal route

Carbon free composites Li_1−xMg_xFePO₄ (x = 0.00, 0.02) were synthesized from LiOH, H₃PO₄, FeSO₄ and MgSO₄ through hydrothermal route at 180 °C for 6h followed by being fired at 750 °C for 6 h. The samples were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), flame atomic absorption spectroscopy and electronic conductivity measurement. To investigate their electrochemical properties, the samples were mixed with glucose as carbon precursors, and fired at 750 °C for 6 h. The charge–discharge curves and cycle life test were carried out at 23 ± 2 °C. The Rietveid refinement results of lattice parameters of the samples indicate that the magnesium ion has been successfully doped into the M1 (Li) site of the phospho-olivine structure. With the same order of magnitude, there is no material difference in terms of the electronic conductivities between the doped and undoped composites. Conductivities of the doped and undoped samples are 10⁻¹⁰ S cm⁻¹ before being fired, 10⁻⁹ S cm⁻¹ after being fired at 750 °C, and 10⁻¹ S cm⁻¹ after coated with carbon, respectively. Both the doped and undoped composites coated with carbon exhibit comparable specific capacities of 146 mAh g⁻¹ vs. 144 mAh g⁻¹ at 0.2 C, 140 mAh g⁻¹ vs. 138 mAh g⁻¹ at 1 C, and 124 mAh g⁻¹ vs. 123 mAh g⁻¹ at 5 C, respectively. The capacity retention rates of both doped and undoped samples over 50 cycles at 5 C are close to 100% (vs. the first-cycle corresponding C-rate capacity). Magnesium doping has little effects on electronic conductivity and electrochemical properties of LiFePO₄ composites prepared via hydrothermal route.     

Optimized performances of core-shell structured LiFePO4/C nanocomposite

A nanosized LiFePO₄/C composite with a complete and thin carbon-shell is synthesized via a ball-milling route followed by solid-state reaction using poly(vinvl alcohol) as carbon source. The LiFePO₄/C nanocomposite delivers discharge capacities of 159, 141, 124 and 112 mAh g⁻¹ at 1 C, 5 C, 15 C and 20 C, respectively. Even at a charge-discharge rate of 30 C, there is still a high discharge capacity of 107 mAh g⁻¹ and almost no capacity fading after 1000 cycles. Based on the analysis of cyclic voltammograms, the apparent diffusion coefficients of Li ions in the composite are in the region of 2.42 × 10⁻¹¹ cm² s⁻¹ and 2.80 × 10⁻¹¹ cm² s⁻¹. Electrochemical impedance spectroscopy and galvanostatic intermittent titration technique are also used to calculate the diffusion coefficients of Li ions in the LiFePO₄/C electrode, they are in the range of 10⁻¹¹-10⁻¹⁴ cm² s⁻¹. In addition, at −20 °C, it can still deliver a discharge capacity of 122 mAh g⁻¹, 90 mAh g⁻¹ and 80 mAh g⁻¹ at the charge-discharge rates of 0.1 C, 0.5 C and 1 C, respectively.     

Preparation of LiFePO4/C composites by co-precipitation in molten stearic acid

The olivine type LiFePO₄ is synthesized via a simple and inexpensive route by aqueous co-precipitation of an Fe(II) precursor material in molten stearic acid and subsequent heat treatment at different temperatures. Stearic acid serves as both chelating agent and carbonaceous material. The obtained composites with carbon are characterized by X-ray powder diffraction, field emission scanning electron microscopy, and Mössbauer spectroscopy. Electrochemical characteristics of the composites are evaluated by using galvanostatic charge/discharge tests. The powder obtained at 700 °C delivers discharge capacity of 160 mAh g⁻¹, quite near the theoretical value.     

Long-term cycling studies on 4 V-cathode, lithium vanadium fluorophosphate

Lithium vanadium fluorophosphate, LiVPO₄F is prepared by two-step carbothermal reduction method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), density and surface area. Its cathodic behaviour is examined by galvanostatic charge-discharge cycling up to 1260 cycles, cyclic voltammetry (CV) and impedance spectra using Li-metal as the counter and reference electrode. When cycled between 3.0 and 4.5 V at 15 mA g⁻¹ (0.12C), a reversible and stable capacity of 130 (±3) mAh g⁻¹ is observed in the range 20-200 cycles. Slow capacity fading occurs between 200 and 360 cycles. When cycled at the 0.92C rate (1C = 130 mA g⁻¹), a reversible and stable capacity of 122 (±3) mAh g⁻¹ is obtained at 200-800 cycles. The capacity degrades slowly over 800-1260 cycles and the total loss is ∼14%. Coulombic efficiency increases to 96-98% after the first 10-15 cycles. The CV data show that the charge-discharge process, a two-phase reaction, occurs between 4.2 and 4.5 V, in agreement with literature data. Impedance spectra, up to 90 cycles are fitted to an equivalent circuit and the variation of impedance parameters is interpreted.     

All-solid-state lithium secondary batteries with high capacity using black phosphorus negative electrode

Black phosphorus was prepared from red phosphorus by using mixer mill and planetary ball-mill apparatuses. The composites with black phosphorus and acetylene black (AB) were also prepared by using the mixer mill apparatus. The mechanical milling of black phosphorus and AB brought about a decrease in size of secondary particles of the composites. The all-solid-state lithium cells with the composite and the Li₂S-P₂S₅ glass-ceramic electrolyte exhibited the first discharge capacity of 1962 mAh g⁻¹ and the coulombic efficiency of 89% at the current density of 0.064 mA cm⁻² (24 mA g⁻¹). The all-solid-state cells worked at 3.8 mA cm⁻² (1.47 A g⁻¹) at 25 °C and showed the excellent cycle performance with a high capacity of over 500 mAh g⁻¹ for 150 cycles. Black phosphorus is one of the most attractive negative electrodes with both high capacity and high-rate performance in all-solid-state lithium rechargeable batteries with sulfide electrolytes.