Electrochemical study of NiO nanoparticles electrode for application in rechargeable lithium-ion batteries

Nickel oxide nanoparticles were synthesized via a simple and inexpensive microwave-assisted synthesis method within a fast reaction time of less than 20 min. The calcination of as-prepared precursor at 600 °C produces single phase nickel oxide. The lattice structure and morphology of the sample were investigated by X-ray diffraction, field-emission scanning electron microscopy and field-emission transmission electron microscopy. The particle size range of the nickel oxide nanoparticles varied from 50 to 60 nm. Nickel oxide nanoparticles exhibited good electrochemical performances as an anode material for lithium-ion batteries. The prepared nickel oxide anode revealed a large initial discharge capacity of 1111.08 mAh g⁻¹ at 0.03 C rate and retained 80% of initial capacity (884.30 mAh g⁻¹) after 20 cycles. Furthermore, at elevated rate of 3.7 C, the charge capacity of the nickel oxide electrode was as high as 253.1 mAh g⁻¹, which was 35% greater than that of commercial bulk nickel oxide (188 mAh g⁻¹). The enhancement of the electrochemical performance was attributed to the high specific surface area, good electric contact among the particles and easier lithium ion diffusion.     

Porous polythiophene as a cathode material for lithium batteries with high capacity and good cycling stability

Polythiophene (PTh) has been synthesized by chemical oxidative polymerization and used as an active cathode material in lithium batteries. The lithium batteries are characterized by cyclic voltammetry (CV), galvanostatic charge/discharge cycling and electrochemical impedance spectroscopic studies (EIS). The lithium battery with the PTh cathode exhibits a discharge voltage of 3.7 V compared to Li⁺/Li and excellent electrochemical performance. PTh can provide large discharge capacities above 50 mA h g⁻¹ and good cycle stability at a high current density 900 mA g⁻¹. After 500 cycles, the discharge capacity is maintained at 50.6 mA h g⁻¹. PTh is a promising candidate for high-voltage power sources with excellent electrochemical performance.     

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.     

Electrochemical and spectroscopic measurements for stable nitroxyl radicals

A nitroxyl radical, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), is known to be oxidized electrochemically at 3.5 V versus lithium [4] and [5]. Since this reaction is reversible in the aprotic electrolyte, we can use it as a cathode reaction in lithium rechargeable battery. Some nitroxyl radical compounds which have different structures have been prepared and their electrochemical behavior and spectroscopic properties have been studied. The electrochemical measurements in aprotic electrolyte revealed that most nitroxyl radical compounds show reversible redox behavior similar to that of TEMPO independent of their structures in the range of −0.15-0.20 V versus Ag/Ag⁺ (3.69-4.04 V versus Li/Li⁺). The redox potentials for these materials were found to be predictable approximately by quantum calculations. Thus, various molecular designs tailored to desired redox potentials would be possible as active materials for lithium rechargeable batteries, and their specific capacities, mechanical properties and colors can be controlled within limits.     

Electrochemical reaction of the SiMn/C composite for anode in lithium ion batteries

The SiMn-graphite composite powder was prepared by mechanical ball milling and its electrochemical performances were evaluated as the candidate anode materials for lithium ion batteries. It is found that the cyclic performance of the composite materials is improved significantly compared to SiMn alloy and pure silicon. The heat treatment of the electrodes is beneficial for enhancing the cyclic stabilities. The SiMn-20 wt.% graphite composite electrode after annealing at 200 °C has an initial reversible capacity of 463 mAh g⁻¹ and a charge-discharge efficiency of 70%. Moreover, the reversible capacity maintains 426 mAh g⁻¹ after 30 cycles with a coulomb efficiency of over 97%. The phase structure and morphology of the composite were analyzed by X-ray diffraction (XRD) and scanning electron microscopy. The lithiation/delithiation behavior was investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composite materials appear to be promising candidates as negative electrodes for lithium rechargeable batteries.     

Lithium-ion battery anode properties of TiO2 nanotubes prepared by the hydrothermal synthesis of mixed (anatase and rutile) particles

From mixed (anatase and rutile) bulk particles, anatase TiO₂ nanotubes are synthesized in this study by an alkaline hydrothermal reaction and a consequent annealing at 300-400 °C. The physical and electrochemical properties of the TiO₂ nanotube are investigated for use as an anode active material for lithium-ion batteries. Upon the first discharge-charge sweep and simultaneous impedance measurements at local potentials, this study shows that interfacial resistance decreases significantly when passing lithium ions through a solid electrolyte interface layer at the lithium insertion/deinsertion plateaus of 1.75/2.0 V, corresponding to the redox potentials of anatase TiO₂ nanotubes. For an anatase TiO₂ nanotube containing minor TiO₂(B) phase obtained after annealing at 300 °C, the high-rate capability can be strongly enhanced by an isotropic dispersion of TiO₂ nanotubes to yield a discharge capacity higher than 150 mAh g⁻¹, even upon 100 cycles of 10 C-rate discharge-charge operations. This is suitable for use as a high-power anode material for lithium-ion batteries.     

A novel polymer electrolyte based on PMAML/PVDF-HFP blend

A gel polymer electrolyte based on the blend of poly(methyl methacrylate-co-acrylonitrile-co-lithium methacrylate) (PMAML) and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was prepared and characterized. The synthesized PMAML were characterized by FTIR and NMR, respectively, and the surface morphology of the PMAML and PVDF-HFP blend membrane was also observed by scanning electron microscope (SEM). The electrochemical properties of composite electrolyte membranes were studied. The ionic conductivity of the polymer electrolyte composed of 75 wt.% 1 M LiBF₄ in ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:1 by weight) was about 2.6×10⁻³ S cm⁻¹ at ambient temperature. The electrochemical window of the polymer electrolyte was about 4.6 V determined from the linear sweep voltammetry plot. The lithium ion polymer batteries were assembled by sandwiching gel polymer electrolyte between LiCoO₂ cathode and mesophase carbon fibre (MPCF) anode. Charge-discharge test results display that lithium ion batteries with these gel polymer electrolytes have good electrochemical performance.     

Electrochemical properties of heat-treated polymer-derived SiCN anode for lithium ion batteries

Silicon-carbon-nitrogen material (SiCN) is pyrolyzed from polysilylethylenediamine (PSEDA) derivation, followed by a heat-treating process at 1000 °C in Ar atmosphere. This heat-treated SiCN material has an excellent electrochemical performance as an anode for lithium ion batteries. Charge-discharge cycle measurements show that the heat-treated SiCN material exhibits a high first cycle discharge capacity of 829.0 mAh g⁻¹ and stays between 400 and 370 mAh g⁻¹ after 30 cycles. The discharge capacity remains above 300 mAh g⁻¹ at the high current density of 80 and 160 mA g⁻¹. These values are higher than untreated SiCN and commercial graphite anodes, which indicates that the heat-treating process improves the charge-discharge capacity, cycle stability and high-rate ability of SiCN anode. It is seemed that changes of SiCN structure, the formation of loose nano-holes on material surface and the formation of graphitic carbon phase in heat-treating process contribute to the improvement of electrochemical properties for SiCN anode.     

Novel tin-graphite composites as negative electrodes of Li-ion batteries

For the purpose of obtaining an improved performance of the graphite negative electrode of Li-ion batteries, a novel graphite-tin composite has been synthesized by reduction of tin chloride (SnCl₂) with KC₈ in THF medium. This composite contains nano-sized tin particles dispersed on the graphite surface and free tin aggregates. Lithium electrochemical insertion occurs both in graphite and in tin. An experimental reversible specific charge of 489 mA h g⁻¹ is found stable upon cycling. Such a value is lower than the maximum theoretical one of 609 mA h g⁻¹ suggesting that only a part of tin is involved in the lithium insertion/extraction process. This part of active tin responsible for the stable capacity could be that bound to graphite. To the contrary, free tin aggregates could contribute to an extra capacity that decreases upon cycling in relation with the volume changes that occurs during alloying/dealloying.     

Synthesis of sawtooth-like Li4Ti5O12 nanosheets as anode materials for Li-ion batteries

Hierarchical layered hydrous lithium titanate and Li₄Ti₅O₁₂ microspheres assembled by nanosheets have been successfully synthesized via a hydrothermal process and subsequent thermal treatment. The electrochemical properties of the two samples have been investigated by galvanostatic methods. The former, with the obvious layered structure and a large surface area, delivers a reversible capacity of 180 mA h g⁻¹ after 200 cycles at 200 mA g⁻¹. As for Li₄Ti₅O₁₂, with the intriguing and unique sawtooth-like morphology, it presents exceptional high rate performance and excellent cycling stability. Up to 132 mA h g⁻¹ is obtained after 200 cycles at 10,000 mA g⁻¹ (57 C), proving itself promising for high-rate applications.     

Three-dimensional reticular tin-manganese oxide composite anode materials for lithium ion batteries

Tin-manganese oxide film with three-dimensional (3D) reticular structure has been prepared by electrostatic spray deposition (ESD). X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that the film is amorphous. X-ray-photoemission spectroscopy (XPS) demonstrates that the 3D grid is composed of tin-manganese oxide. As an anode electrode for the lithium ion battery, the tin-manganese oxide film has 1188.3 mAh g⁻¹ of initial discharge capacity and very good capacity retention of 656.2 mAh g⁻¹ up to the 30th cycle. Such a composite film can be used as an anode for lithium ion batteries with higher energy densities.     

Highly crystalline macroporous β-MnO2: Hydrothermal synthesis and application in lithium battery

A highly crystalline macroporous β-MnO₂ was hydrothermally synthesized using stoichiometric reaction between KMnO₄ and MnCl₂. The as-prepared material has a pore size of ca. 400 nm and a shell thickness of 300-500 nm. The formation of the macroporous morphology is related to self-assembling from nanowires of α-MnO₂, and could be obtained at high reactant concentrations (e.g., 0.8 M KMnO₄) but not at low ones (e.g., below 0.04 M KMnO₄). Compared to conventional bulk β-MnO₂ processing very low capacity, our macroporous material exhibits good electrochemical activity, e.g., obtaining an initial discharge capacity of 251 mAh g⁻¹ and sustaining as ca. 165 mAh g⁻¹ at 10 mA g⁻¹. The electrochemical activity of the as-prepared β-MnO₂ is related to its macroporous morphology and small shell thickness; the former leads to that electrolyte can flood pore of the material and its inner surface is available for lithium ion diffusion, while the latter helps to release the stress from phase transformation during the initial discharging. The X-ray diffraction characterizations of the macroporous β-MnO₂ electrodes suggest that, upon initial discharging, such a β-MnO₂ will be irreversibly transformed to an orthorhombic Li_xMnO₂ and then cycled within the new developed phase in the subsequent lithium insertion/extraction processes.     

Rheological phase reaction synthesis and electrochemical performance of Li3V2(PO4)3/carbon cathode for lithium ion batteries

Monoclinic lithium vanadium phosphate/carbon (Li₃V₂(PO₄)₃/C) cathode has been synthesized for applications in lithium ion batteries, via a rheological phase reaction (RPR) method. The sample is characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). This material exhibits high initial discharge capacity of 189 and 177 mAh g⁻¹ at 0.1 and 0.2 C between 3.0 and 4.8 V, respectively. Moreover, it displays good fast rate performance, which discharge capacities of 140, 133, 129 and 124 mAh g⁻¹ can be delivered after 100 cycles between 3.0 and 4.8 V vs. Li at a different rate of 0.5, 1, 2 and 5 C, respectively. The electrochemical impedance spectroscopy (EIS) is also investigated.     

Large reversible capacity of high quality graphene sheets as an anode material for lithium-ion batteries

High quality graphene sheets were prepared from graphite powder through oxidation followed by rapid thermal expansion in nitrogen atmosphere. The preparation process was systematically investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and Brunauer-Emmett-Teller (BET) measurements. The morphology and structure of graphene sheets were characterized by scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The electrochemical performances were evaluated in coin-type cells versus metallic lithium. It is found that the graphene sheets possess a curled morphology consisting of a thin wrinkled paper-like structure, fewer layers (∼4 layers) and large specific surface area (492.5 m² g⁻¹). The first reversible specific capacity of the prepared graphene sheets was as high as 1264 mA h g⁻¹ at a current density of 100 mA g⁻¹. Even at a high current density of 500 mA g⁻¹, the reversible specific capacity remained at 718 mA h g⁻¹. After 40 cycles, the reversible capacity was still kept at 848 mA h g⁻¹ at the current density of 100 mA g⁻¹. These results indicate that the prepared high quality graphene sheets possess excellent electrochemical performances for lithium storage.     

Preparation and characterization of nano-sized LiFePO4 by low heating solid-state coordination method and microwave heating

The precursors of LiFePO₄ were prepared by low heating solid-state coordination method using lithium acetate, ammonium dihydric phosphate, ferrous oxalate and citric acid as raw materials. Olivine phase LiFePO₄ as a cathode material for lithium-ion batteries was successfully synthesized by microwave heating in a few minutes. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to characterize its structure and morphology. Cyclic voltammetry (CV) and charge-discharge cycling performance were used to characterize its electrochemical properties. The results showed that the grain size of the optimal sample was about 40-50 nm, and the as-prepared particles were homogeneous. The nano-sized LiFePO₄ obtained has a high electrochemical capacity (125 mAh g⁻¹) and stable cycle ability.     

Characterization of structure and electrochemical properties of lithium manganese oxides for lithium secondary batteries hydrothermally synthesized from δ-KxMnO2

Lithium manganese oxides have attracted much attention as cathode materials for lithium secondary batteries in view of their high capacity and low toxicity. In this study, layered manganese oxide (δ-K_xMnO₂) has been synthesized by thermal decomposition of KMnO₄, and four lithium manganese oxide phases have been synthesized for the first time by mild hydrothermal reactions of this material with different lithium compounds. The lithium manganese oxides were characterized by powder X-ray diffraction (XRD), inductively coupled plasma emission (ICPE) spectroscopy, and chemical redox titration. The four materials obtained are rock salt structure Li₂MnO₃, hollandite (BaMn₈O₁₆) structure α-MnO₂, spinel structure LiMn₂O₄, and birnessite structure Li_xMnO₂. Their electrochemical properties used as cathode material for secondary lithium batteries have been investigated. Of the four lithium manganese oxides, birnessite structure Li_xMnO₂ demonstrated the most stable cycling behavior with high Coulombic efficiency. Its reversible capacity reaches 155 mAh g⁻¹, indicating that it is a viable cathode material for lithium secondary batteries.     

Synthesis and electrochemical performance of lithium vanadium oxide nanotubes as cathodes for rechargeable lithium-ion batteries

A new kind of cathode materials for rechargeable lithium-ion batteries, lithium vanadium oxide nanotubes synthesized by a combined sol-gel reaction and hydrothermal treatment procedure is reported in this paper. SEM, TEM, XRD and XPS techniques were performed to investigate the morphology and structure of the resulting materials. The results confirmed that the synthetic materials are composed of uniformly open-ended multiwalled nanotubes with a length from 1 to 3 μm. The inner and the outer diameters of the obtained nanotubes vary from 30 to 50 nm and 50 to 120 nm, respectively. The electrochemical performance as a cathode material was examined and evaluated by cyclic voltammetry, galvanostatic charge-discharge cycling and AC impedance spectroscopy techniques. The results indicated that the resultant lithium vanadium oxide nanotubes have a high initial discharge capacity of 457 mAh g⁻¹ in the potential range of 1.0-4.0 V (vs. Li/Li⁺) and good cycling performance. The improved electrochemical performance of the products should be due to its special one-dimensional multiwalled tubular structure and the contribution of lithium-ions.     

Lithium storage performance of carbon nanotubes prepared from polyaniline for lithium-ion batteries

Carbon nanotubes with large surface area and surface nitrogen and oxygen functional groups are prepared by carbonizing and activating of polyaniline nanotubes, which is synthesized by polymerization of aniline with the self-assembly method in aqueous media. The physicochemical properties of the carbon nanotubes are characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, elemental analyses and X-ray photoelectron spectroscopy measurements. The surface area and pore diameter are 618.9 m² g⁻¹ and 3.10 nm. The electrochemical properties of the carbon nanotubes as anode materials in lithium ion batteries are evaluated. At a current density of 100 mA g⁻¹, the activated carbon nanotube shows an enormously first discharge capacity of about 1370 mAh g⁻¹ and a charge capacity of 907 mAh g⁻¹. After 20 cycling tests, the activated carbon nanotube retains a reversible capacity of 728 mAh g⁻¹. These indicate it may be a promising candidate for an anode material for lithium secondary batteries.     

Effect of surface modified porous inorganic-organic hybrid polyphosphazene nanotubes on the properties of polyethylene oxide based solid polymer electrolytes

2-(2-methyloxyethoxy)ethanol modified poly (cyclotriphosphazene-co-4,4′-sufonyldiphenol) (PZS) nanotubes were synthesized and solid composite polymer electrolytes based on the surface modified polyphosphazene nanotubes added to PEO/LiClO₄ model system were prepared. Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM) were used to investigate the characteristics of the composite polymer electrolytes (CPE). The ionic conductivity, lithium ion transference number and electrochemical stability window can be enhanced after the addition of surface modified PZS nanotubes. The electrochemical investigation shows that the solid composite polymer electrolytes incorporated with PZS nanotubes have higher ionic conductivity and lithium ion transference number than the filler SiO₂. Maximum ionic conductivity values of 4.95 × 10⁻⁵ S cm⁻¹ at ambient temperature and 1.64 × 10⁻³ S cm⁻¹ at 80 °C with 10 wt % content of surface modified PZS nanotubes were obtained and the lithium ion transference number was 0.41. The good chemical properties of the solid state composite polymer electrolytes suggested that the inorganic-organic hybrid polyphosphazene nanotubes had a promising use as fillers in solid composite polymer electrolytes and the PEO₁₀-LiClO₄-PZS nanotubes solid composite polymer electrolyte can be used as a candidate material for lithium polymer batteries.     

Electrochemical performance of flowerlike CaSnO3 as high capacity anode material for lithium-ion batteries

Nanosized CaSnO₃ is synthesized by a hydrothermal process and characterized by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The SEM observation shows the sample has a porous flowerlike morphology. The electrochemical results exhibit that the stable and reversible capacity of 547 mAh g⁻¹ is obtained after 50 cycles at 60 mA g⁻¹ (0.1 C) and the corresponding charge capacity is determined to be 316 mAh g⁻¹ at the current density of 2.5 C. Cyclic voltammetry and electrochemical impedance spectroscopy data are analyzed to complement the galvanostatic results. The observed excellent performance is attributed to the porous structure and large surface area of flowerlike CaSnO₃.