Facile synthesis and high rate capability of Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript>/C composite materials with controllable carbon content

A modified ball-milling-assisted green solid reaction method is provided to prepare Li₄Ti₅O₁₂/C composite materials with controllable carbon content. Thermal analysis was utilized to investigate the reaction process and the temperature for eliminating carbon. The added carbon and the time for eliminating the carbon can affect the particle size and greatly improve the cycling stability and rate performance. Besides, the particle size can reach ~60 nm, the Li₄Ti₅O₁₂ eliminated carbon at 600 °C has ~178% higher discharge capacity than that without added carbon after 500 cycles under the same conditions. As for the Li₄Ti₅O₁₂ with a carbon weight of 10.6%, the second discharge capacity can reach 177.2 and 120.8 mAh g⁻¹ at 1 and 20 C rates, respectively. Its discharge capacity still remains at 118.3 mAh g⁻¹ after 500 cycles under various current rates. The results are comparable to those of the reported Li₄Ti₅O₁₂/PAS composite.     

Effects of surface area on electrochemical performance of Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript> cathode material

The effect of surface area on the electrochemical properties and thermal stability of Li[Ni_0.2Li_0.2Mn_0.6]O₂ powders was characterized using a charge/discharge cycler and DSC (Differential Scanning Calorimeter). The surface area of the samples was successfully controlled from ~4.0 to ~11.7 m² g⁻¹ by changing the molar ratio of the nitrate/acetate sources and adding an organic solvent such as acetic acid or glucose. The discharge capacity and rate capability was almost linearly increased with increase in surface area of the sample powder. A sample with a large surface area of 9.6–11.7 m² g⁻¹ delivered a high discharge capacity of ~250 mAh g⁻¹ at a 0.2 C rate and maintained 62–63% of its capacity at a 6 C rate versus a 0.2 C rate. According to the DSC analysis, heat generation by thermal reaction between the charged electrode and electrolyte was not critically dependent on the surface area. Instead, it was closely related to the type of organic solvent employed in the fabrication process of the powder.     

Enhanced electrochemical performance of FeS<Subscript>2</Subscript> synthesized by hydrothermal method for lithium ion batteries

Iron disulfide (FeS₂) powders were successfully synthesized by hydrothermal method. Cetyltrimethylammonium bromide (CTAB) had a great influence on the morphology, particle size, and electrochemical performance of the FeS₂ powders. The as-synthesized FeS₂ particles with CTAB had diameters of 2–4 μm and showed a sphere-like structure with sawtooth, while the counterpart prepared without CTAB exhibited irregular morphology with diameters in the range of 0.1–0.4 μm. As anode materials for Li-ion batteries, their electrochemical performances were investigated by galvanostatic charge–discharge test and electrochemical impedance spectrum. The FeS₂ powder synthesized with CTAB can sustain 459 and 413 mAh g⁻¹ at 89 and 445 mA g⁻¹ after 35 cycles, respectively, much higher than those prepared without CTAB (411 and 316 mAh g⁻¹). The enhanced rate capability and cycling stability were attributed to the less-hindered surface layer and better electrical contact from the sawtooth-like surface and micro-sized sphere morphology, which led to enhanced process kinetics.     

Improved performances of mechanical-activated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript>/MWNTs cathode for aqueous rechargeable lithium batteries

LiMn₂O₄/multi-walled carbon nanotubes (MWNTs) composite was synthesized by mechanical activation reaction followed by a heat-treatment (500 °C). The LiMn₂O₄ and LiMn₂O₄/MWNTs as cathodes were investigated in 1 M Li₂SO₄ by cyclic voltammetry (CV), galvanostatic charge/discharge (GC), and electrochemical impedance spectroscopy (EIS). The LiMn₂O₄/MWNTs cathode delivered higher discharge capacity (117 mAh g⁻¹) than LiMn₂O₄ (84.6 mAh g⁻¹). Furthermore, the results from EIS showed that LiMn₂O₄/MWNTs had a faster kinetic process for lithium ion intercalation/de-intercalation than LiMn₂O₄. Besides, LiMn₂O₄/MWNTs had better cycling stability and rate capability than LiMn₂O₄, which was confirmed by GC testing. SEM images showed that a three-dimensional network structure was formed during the mechanical activation, giving a decrease of particle size.     

Study of electrochemical properties and the charge/discharge mechanism for Li<Subscript>4</Subscript>Mn<Subscript>5</Subscript>O<Subscript>12</Subscript>/MnO<Subscript>2</Subscript>-AC hybrid supercapacitor

Spinel Li₄Mn₅O₁₂ was prepared by a sol–gel method. The manganese oxide and activated carbon composite (MnO₂-AC) were prepared by a method in which KMnO₄ was reduced by activated carbon (AC). The products were characterized by XRD and FTIR. The hybrid supercapacitor was fabricated with Li₄Mn₅O₁₂ and MnO₂-AC, which were used as materials of the two electrodes. The pseudocapacitance performance of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor was studied in various aqueous electrolytes. Electrochemical properties of the Li₄Mn₅O₁₂/MnO₂-AC hybrid supercapacitor were studied by using cyclic voltammetry, electrochemical impedance measurement, and galvanostatic charge/discharge tests. The results show that the hybrid supercapacitor has electrochemical capacitance performance. The charge/discharge test showed that the specific capacitance of 51.3 F g⁻¹ was obtained within potential range of 0–1.3 V at a charge/discharge current density of 100 mA g⁻¹ in 1 mol L⁻¹ Li₂SO₄ solution. The charge/discharge mechanism of Li₄Mn₅O₁₂ and MnO₂-AC was discussed.     

Three-dimensional porous Sn-Cu alloy anode for lithium-ion batteries

A binder-free three-dimensional (3D) porous Cu₆Sn₅ anode was prepared for lithium-ion batteries. In this novel approach, tin was deposited by electroless-plating on copper foam which was served as anode current collector as well as the source of copper for Cu₆Sn₅ alloy formation. With optimized post-treatment condition, Cu₆Sn₅ alloy with thickness of 1.2 μm was formed on the surface of copper foam network. 3D porous Sn-Cu₆Sn₅ and Cu₃Sn-Cu₁₀Sn₃-Cu₆Sn₅ composite anodes were also prepared for comparison. Electrochemical tests showed that 3D porous Cu₆Sn₅ anode exhibits the best electrochemical performance in terms of specific capacitance and cycleability, which delivers a rechargeable capacity of 404 mAh g⁻¹ over 100 cycles.     

The compatibility of transition metal oxide/carbon composite anode and ionic liquid electrolyte for the lithium-ion battery

Three types of transition metal oxide/carbon composites including Fe₂O₃/C, NiO/C and CuO/Cu₂O/C synthesized via spray pyrolysis were used as anode for lithium ion battery application in conjunction with two types of ionic liquid: 1 M LiN(SO₂CF₃)₂ (LiTFSI) in 1-ethyl-3-methyl-imidazolium bis(fluorosulfonlyl)imide (EMI-FSI) or 1-methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide (Py13-FSI). From the electrochemical measurements, the composite electrodes using Py13-FSI as electrolyte show much better electrochemical performance than those using EMI-FSI as electrolyte in terms of reversibility. The Fe₂O₃/C composite shows the highest specific capacity and the best capacity retention (425 mAh g⁻¹) under a current density of 50 mA g⁻¹ for up to 50 cycles, as compared with the NiO/C and CuO/Cu₂O/C composites. The present research demonstrates that Py13-FSI could be used as an electrolyte for transition metal oxides in lithium-ion batteries.     

One-step electrodeposition synthesis and electrochemical properties of Cu6Sn5 alloy anodes for lithium-ion batteries

Cu₆Sn₅ alloys were successfully electrodeposited on rough Cu foils and smooth Cu sheets using a facile one-step electrodepositing method, and their structural and electrochemical properties were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charging/discharging testing and electrochemical impedance spectroscopy (EIS). The influence of surface morphology of the current collectors on the cycleability and the interfacial performance of the Cu₆Sn₅ alloy electrode are both discussed. The results demonstrate that the Cu₆Sn₅ alloy electrode on the rough Cu foil presented better electrochemical performance than that on the smooth Cu sheet because its rough surface could buffer the volume changes to some extent. The first discharging (lithiation) and charging (delithiation) capacities were measured at 462 and 405 mAh g⁻¹ respectively with high initial coulomb efficiency of 88%, with charging capacity in the 50th cycle remaining 76% of that in the first cycle. The phase transformation during initial lithiation was detected by electrochemical impedance spectroscopy (EIS) and its trend versus electrode potential is also discussed.     

Preparation and electrochemical performance of Li-rich layered cathode material,Li[Ni<Subscript>0.2</Subscript>Li<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>]O<Subscript>2</Subscript>, for lithium-ion batteries

The Li-rich layered cathode material, Li[Ni_0.2Li_0.2Mn_0.6]O₂, was synthesized via a “mixed oxalate” method, and its structural and electrochemical properties were compared with the same material synthesized by the sol–gel method. X-ray diffraction (XRD) shows that the synthesized powders have a layered O₃–LiCoO₂-type structure with the R-3m symmetry. X-ray photoelectron spectroscopy (XPS) indicates that in the above material, Ni and Mn exist in the oxidation states of +2 and +4, respectively. The layered material exhibits an excellent electrochemical performance. Its discharge capacity increases gradually from the initial value of 228 mA hg⁻¹ to a stable capacity of over 260 mA hg⁻¹ after the 10th cycle. It delivers a larger capacity of 258 mA hg⁻¹ at the 30th cycle. The dQ/dV curves suggest that the increasing capacity results from the redox-reaction of Mn⁴⁺/Mn³⁺.     

Electrochemical oxidation of an acid dye by active chlorine generated using Ti/Sn<Subscript>(1−<Emphasis Type="Italic">x</Emphasis>)</Subscript>Ir<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> electrodes

The generation of active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes, with different compositions of Ir (x = 0.01, 0.05, 0.10 and 0.30 ), was investigated by controlled current density electrolysis. Using a low concentration of chloride ions (0.05 mol L⁻¹) and a low current density (5 mA cm⁻²) it was possible to produce up to 60 mg L⁻¹ of active chlorine on a Ti/Sn_0.99Ir_0.01O₂ anode. The feasibility of the discoloration of a textile acid azo dye, acid red 29 dye (C.I. 16570), was also investigated with in situ electrogenerated active chlorine on Ti/Sn_(1−x)Ir _x O₂ anodes. The best conditions for 100% discoloration and maximum degradation (70% TOC reduction) were found to be: NaCl pH 4, 25 mA cm⁻² and 6 h of electrolysis. It is suggested that active chlorine generation and/or powerful oxidants such as chlorine radicals and hydroxyl radicals are responsible for promoting faster dye degradation. Rate constants calculated from color decay versus time reveal a zero order reaction at dye concentrations up to 1.0 × 10⁻⁴ mol L⁻¹. Effects of other electrolytes, dye concentration and applied density currents also have been investigated and are discussed.     

Spherical natural graphite coated by a thick layer of carbonaceous mesophase for use as an anode material in lithium ion batteries

A method for coating a thick layer of carbonaceous mesophase was developed to treat spherical natural graphite (SNG) for use as anodes in lithium ion batteries. The carbonaceous mesophase layer was fabricated by heat treatment of a mixture of SNG and coal tar pitch. The thickness of the carbonaceous mesophase on the surface of the SNG was approximately 2.5 μm, which is effective for enhancing the strength of the carbonaceous mesophase shell and for allowing the shell to maintain good integrity at a high anode density (1.6 g cm⁻³). The mesophase layer increased the initial columbic efficiency from approximately 90% to 95%, dramatically improved the capacity retention and reduced the irreversible capacity by greatly decreasing the SNG surface area. The initial efficiency, cycle life and rate capability for the SNG anode covered by a thick mesophase layer gave comparable results as the mesocarbon microbeads (MCMB) anode, while the SNG anode reversible capacity of 341 mAh g⁻¹ was higher than that of MCMB, 319 mAh g⁻¹. Electrochemical measurements showed that SNG particles coated by a thick carbonaceous mesophase layer are strong candidates for use as possible anode materials in high energy density lithium ion batteries.     

Facile Solvothermal Synthesis Ni(OH)<Subscript>2</Subscript> Nanostructure for Electrochemical Capacitors

Nickel hydroxide nanosheets were successfully synthesized by facile solvothermal method without any template. The structure and morphology of the as-prepared sample were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The observations revealed the formation of hexagonal phase β-Ni(OH)₂ nanosheets with an average diameter of about 100–120 nm. Electrochemical studies were carried out using cyclic voltammetry and galvanostatic charge–discharge tests, respectively. A maximum specific capacitance of 2,342 F g⁻¹, which is the highest reported for a β-Ni(OH)₂ electrode, could be achieved in 6 mol L⁻¹ KOH electrolyte within the potential range of 0–0.50 V (vs. SCE) for the obtained β-Ni(OH)₂ electrode at 0.4 A g⁻¹, suggesting its potential application in the electrode material for electrochemical capacitors.     

Synthesis and Characterization of Cobalt-Doped WS<Subscript>2</Subscript> Nanorods for Lithium Battery Applications

Cobalt-doped tungsten disulfide nanorods were synthesized by an approach involving exfoliation, intercalation, and the hydrothermal process, using commercial WS₂ powder as the precursor and n-butyllithium as the exfoliating reagent. XRD results indicate that the crystal phase of the sample is 2H-WS₂. TEM images show that the sample consists of bamboo-like nanorods with a diameter of around 20 nm and a length of about 200 nm. The Co-doped WS₂ nanorods exhibit the reversible capacity of 568 mAh g⁻¹ in a voltage range of 0.01–3.0 V versus Li/Li⁺. As an electrode material for the lithium battery, the Co-doped WS₂ nanorods show enhanced charge capacity and cycling stability compared with the raw WS₂ powder.     

DSA electrochemical treatment of olive mill wastewater on Ti/RuO<Subscript>2</Subscript> anode

The electrochemical oxidation of olive mill wastewater (OMW) over a Ti/RuO₂ anode was studied by means of cyclic voltammetry and bulk electrolysis and compared with previous results over a Ti/IrO₂ anode. Experiments were conducted at 300–1,220 mg L⁻¹ initial chemical oxygen demand (COD) concentrations, 0.05–1.35 V versus SHE and 1.39–1.48 V versus SHE potential windows, 15–50 mA cm⁻² current densities, 0–20 mM NaCl, Na₂SO₄, or FeCl₃ concentrations, 80 °C temperature, and acidic conditions. Partial and total oxidation reactions occur with the overall rate being near first-order kinetics with respect to COD. Oxidation at 28 Ah L⁻¹ and 50 mA cm⁻² leads to quite high color and phenols removal (86 and 84%, respectively), elimination of ecotoxicity, and a satisfactory COD and total organic carbon reduction (52 and 38%, respectively). Similar performance can be achieved at the same charge (28 Ah L⁻¹) using lower current densities (15 mA cm⁻²) but in the presence of various salts. For example, COD removal is less than 7% at 28 Ah L⁻¹ in a salt-free sample, while addition of 20 mM NaCl results in 54% COD reduction. Decolorization of OMW using Ti/RuO₂ anode seems to be independent of the presence of salts in contrast with Ti/IrO₂ where addition of NaCl has a beneficial effect on decolorization.     

Determination of cadmium (II) using H<Subscript>2</Subscript>O<Subscript>2</Subscript>-oxidized activated carbon modified electrode

Pristine activated carbon (AcC) was oxidized by H₂O₂ under ultrasonic conditions. Compared with pristine AcC, the H₂O₂-oxidized AC possesses higher accumulation ability to trace levels of Cd²⁺. Based on this, a highly sensitive, simple and rapid electrochemical method was developed for the determination of Cd²⁺. In 0.01 mol L⁻¹ HClO₄ solution, Cd²⁺ was effectively accumulated at the surface of H₂O₂-oxidized AcC modified paste electrode, and then reduced to Cd under −1.10 V. During the following potential sweep from −1.10 to −0.50 V, reduced Cd was oxidized and a sensitive stripping peak appears at −0.77 V. The stripping peak current of Cd²⁺ changes linearly with concentration over the range 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ mol L⁻¹. The limit of detection was found to be 3.0 × 10⁻⁸ mol L⁻¹ for 2-min accumulation. Finally, this new sensing method was successfully used to detect Cd²⁺ in waste water samples.     

Thermoelectric Properties of <Emphasis Type="Italic">x</Emphasis>PbTe/Yb<Subscript>0.2</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> Hot-Pressed Samples

The xPbTe/Yb_0.2Co₄Sb₁₂ compounds were prepared by the ball-milling and hot-pressed process. Electrical conductivity of the composite samples are reduced with a increase in PbTe content; and, their temperature dependence coefficients show the positive values. The maximum electrical conductivity of composite materials is ~80000 Sm⁻¹ at 800 K. The Seebeck coefficient (absolute value) of the composite material is obviously improved with an increase in the dispersed phase (PbTe) content; the Seebeck coefficient (absolute value) of the 10PbTe sample is ~260 μVK⁻¹ at 700 K, which increases by 13.6% relative to that of the Yb_0.2Co₄Sb₁₂ sample. The thermal conductivity of the composite samples is improved due to introduction of PbTe, and the thermal conductivity of the 10PbTe sample is ~3 Wm⁻¹ K⁻¹ at 550 K. The maximum value of ZT is 0.78 at 700 K for the 2.5PbTe sample.     

Preparation and properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods as supercapacitor material

Co₃O₄ nanorods have been successfully synthesized by thermal decomposition of the precursor prepared via a facile and efficient microwave-assisted hydrothermal method, using cetyltrimethylammonium bromide (CTAB) with ordered chain structures as soft template for the first time. The obtained Co₃O₄ was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electrochemical measurements. The results demonstrate that the as-synthesized nanorods are single crystalline with an average diameter of about 20 to 50 nm and length up to several micrometers. Preliminary electrochemical studies, including cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) measurements, are carried out in 6 M KOH electrolyte. Specific capacitance of 456 F g⁻¹ for a single electrode could be achieved even after 500 cycles, suggesting its potential application in electrochemical capacitors. This promising method could provide a universal green chemistry approach to synthesize other low-cost and environmentally friendly transition metal hydroxide or oxide.     

Preparation and electrochemical performance of SiCN–CNTs composite anode material for lithium ion batteries

The composite of silicon carbonitride (SiCN) and carbon nanotubes (CNTs) was synthesized by sintering the mixture of polysilylethylenediamine-derived amorphous SiCN and multi-walled CNTs at a temperature of 1,000 °C for 1 h in argon. The as-prepared SiCN–CNTs material, which was used as anode active substance in a lithium ion battery, showed excellent electrochemical performance. Charge–discharge tests showed the SiCN–CNTs anode provided a high initial specific discharge capacity of 1176.6 mA h g⁻¹ and a steady specific discharge capacity of 450–400 mA h g⁻¹ after 30 charge–discharge cycles at 0.2 mA cm⁻². Both of the abovementioned values are higher than that of pure polymer-derived SiCN, CNTs, and commercial graphite at the same charge–discharge condition. It was deduced that the CNTs in the composite not only improved the electronic conductivity and offered channels and sites for the immigrating and intercalating of Li⁺ but also stabilized the structure of the composite.     

Preparation and characterization of three-dimensional tin thin-film anode with good cycle performance

Three-dimensional tin thin-film anode was prepared by electroless plating tin onto three-dimensional (3D) copper foam (which served as current collector), and characterized physically by SEM, EDS and XRD. Its electrochemical property and mechanism were studied by charge-discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The SEM and EDS results indicated that tin film with 500 nm thickness was formed over the whole surface of copper branches. The XRD results suggested that a new phase of Cu₆Sn₅ was formed between copper and tin. Besides the tin microflake structure of 500 nm thickness, the interaction effects of the copper foam and Cu₆Sn₅ phase formed between copper and tin resulted in good cycle performance with first discharge capacity of 737 mAh g⁻¹, 97% capacity retention after 20 cycles and still 84% after 40 cycles.     

Electrochemical performances of Al-based composites as anode materials for Li-ion batteries

Al-C, Al-Fe and Al-Fe-C composite materials have been prepared by high-energy ball milling technique. The electrochemical measurements demonstrated that the Al-Fe-C composites have greatly improved electrochemical performances in comparison with Al, Al-C and Al-Fe anode. For example, Al₇₁Fe₉C₂₀ can deliver the reversible capacity of 436 mAh g⁻¹ at first cycle and 255 mAh g⁻¹ at 15th cycle. This improved electrochemical performance could be attributed to the alloying formation of Al with Fe and the buffering effect by the graphite matrix. This suggests that the Al-Fe-C composite has a potential possibility to be developed as an anode material for lithium-ion batteries.