A germanium/single-walled carbon nanotube composite paper as a free-standing anode for lithium-ion batteries

Paper-like free-standing germanium (Ge) and single-walled carbon nanotube (SWCNT) composite anodes were synthesized by the vacuum filtration of Ge/SWCNT composites, which were prepared by a facile aqueous-based method. The samples were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Electrochemical measurements demonstrate that the Ge/SWCNT composite paper anode with the weight percentage of 32% Ge delivered a specific discharge capacity of 417 mA h g-1 after 40 cycles at a current density of 25 mA g-1, 117% higher than the pure SWCNT paper anode. The SWCNTs not only function as a flexible mechanical support for strain release, but also provide excellent electrically conducting channels, while the nanosized Ge particles contribute to improving the discharge capacity of the paper anode.

In-situ one-step hydrothermal synthesis of a lead germanate-graphene composite as a novel anode material for lithium-ion batteries

Lead germanate-graphene nanosheets (PbGeO3-GNS) composites have been prepared by an efficient one-step, in-situ hydrothermal method and were used as anode materials for Li-ion batteries (LIBs). The PbGeO3 nanowires, around 100–200 nm in diameter, are highly encapsulated in a graphene matrix. The lithiation and de-lithiation reaction mechanisms of the PbGeO3 anode during the charge-discharge processes have been investigated by X-ray diffraction and electrochemical characterization. Compared with pure PbGeO3 anode, dramatic improvements in the electrochemical performance of the composite anodes have been obtained. In the voltage window of 0.01–1.50 V, the composite anode with 20 wt.% GNS delivers a discharge capacity of 607 mAh g−1 at 100 mA g−1 after 50 cycles. Even at a high current density of 1600 mA g−1, a capacity of 406 mAh g−1 can be achieved. Therefore, the PbGeO3-GNS composite can be considered as a potential anode material for lithium ion batteries.

Zr4+ doping in Li4Ti5O12 anode for lithium-ion batteries: Open Li+ diffusion paths through structural imperfection

One-dimensional nanomaterials have short Li+ diffusion paths and promising structural stability, which results in a long cycle life during Li+ insertion and extraction processes in lithium rechargeable batteries. In this study, we fabricated one-dimensional spinel Li 4Ti5O12 (LTO) nanofibers using an electrospinning technique and studied the Zr4+ doping effect on the lattice, electronic structure, and resultant electrochemical properties of Li-ion batteries (LIBs). Accommodating a small fraction of Zr4+ ions in the Ti4+ sites of the LTO structure gave rise to enhanced LIB performance, which was due to structural distortion through an increase in the average lattice constant and thereby enlarged Li+ diffusion paths rather than changes to the electronic structure. Insulating ZrO2 nanoparticles present between the LTO grains due to the low Zr4+ solubility had a negative effect on the Li+ extraction capacity, however. These results could provide key design elements for LTO anodes based on atomic level insights that can pave the way to an optimal protocol to achieve particular functionalities. Distorted lattice: Zr4+ is doped into a 1 D spinel Li4Ti5O12 (LTO) nanostructure and the resulting electrochemical properties are explored through a combined theoretical and experimental investigation. The improved electrochemical performance resulting from incorporation of Zr4+ in the LTO is due to lattice distortion and, thereby, enlarged Li+ diffusion paths rather than to a change in the electronic structure.

Solution-Combustion Synthesized Nanocrystalline Li4Ti5O12 As High-Rate Performance Li-Ion Battery Anode

Nanocrystalline Li4Ti5O12 (LTO) crystallizing in cubic spinel-phase has been synthesized by single-step-solution-combustion method in less than one minute. LTO particles thus synthesized are flaky and highly porous in nature with a surface area of 12 m(2)/g. Transmission electron micrographs indicate the primary particles to be agglomerated crystallites of varying size between 20 and 50 nm with a 3-dimensional interconnected porous network. During their galvanostatic charge-discharge at varying rates, LTO electrodes yield a capacity value close to the theoretical value of 175 mA h/g at C/2 rate. The electrodes also exhibit promising capacity retention with little capacity loss over 100 cycles at varying discharge rates together with attractive discharge-rate capabilities yielding capacity values of 140 mA h/g and 70 mA h/g at 10 and 100 C discharge rates, respectively. The ameliorated electrode-performance is ascribed to nano and highly porous morphology of the electrodes that provide short diffusion-paths for Li in conjunction with electrolyte percolation through the electrode pores ensuring a high flux of Li.

Lithium ion transport in Li2SO4-Li2O-B2O3 glasses

Electrical conductivity and dielectric relaxation studies with a wide range of compositions of lithium ion conducting glasses belonging to the ternary glass system Li2SO4-Li2O-B2-O3- have been carried out over the temperature range 150-450 K and between 10 - 10(7) Hz. DC conductivities exhibit two different activation regions. This seems to suggest the presence of a cluster tissue texture in these glasses with weakly ordered clusters of Li2SO4 and lithium berates being held together by a truly amorphous tissue of the same average composition as clusters. AC conductivity behaviour of these glasses has been analysed using both power law and stretched exponential relaxation functions. The variation of the power law exponent s and the stretched exponent beta with temperature seems to be consistent with the presence of a cluster tissue texture in these glasses.

New lithium-ion conductors based on the NASICON structure

Lithium-ion conduction in mixed-metal phosphates, (LiMMIII)-M-V(PO,), [M-V = Nb, Ta; M-III = Al, Cr, Fe], possessing the rhombohedral (R (3) over bar c) NASICON structure has been investigated. Among the phosphates investigated, LiTaAl(PO4)(3) exhibits the highest conductivity, sigma approximate to 1.0 x 10(-2) S cm(-1) at 350 degrees C (E-a = 0.47 eV), comparable to the conductivity of LiTi2(PO4)(3). Unlike LiTi2(PO4)(3) which contains lithium-reducible Ti-IV, LiTaAl(PO4)(3) contains stable Ta-V and Al-III oxidation states and hence deserves further attention towards tailoring new lithium-ion conductors for application as electrolytes in solid state lithium batteries.

Rational design of solid materials: A case study of lithium-ion conductors

In the absence of a reliable method for a priori prediction of structure and properties of inorganic solid materials, an experimental approach involving a systematic study of composition, structure and properties combined with chemical intuition based on previous experience is likely to be a viable alternative to the problem of rational design of inorganic materials. The approach is illustrated by taking perovskite lithium-ion conductors as an example.

Role of PbO in lithium ion transport in Li2O-PbO-B2O3 glasses

Abstract: A wide range of compositions of grasses in the ternary Li2O-PbO-B2O3 glass system was prepared, and de and ac conductivity measurements were carried out on these glasses. The presence of lead leads to a decrease in de conductivities and an increase in the activation energies. This is likely to be due to the increase of the partial charges on the oxygen atoms and to the presence of the lone pair on the Pb atom; both of these factors impede lithium ion motion. The ac conductivity and dielectric behavior of these glasses support such a conjecture. (C) 2000 Elsevier Science Ltd.

The molecular dynamics study of lithium ion conduction in phosphate glasses and the role of non-bridging oxygen

Molecular dynamics (MD) simulation of lithium phosphate (Li2O-P2O5) glasses with varying Li2O content has been carried out. Two different P-O distances corresponding to phosphorus coordination with bridging oxygen (BO) and non-bridging oxygen (NBO) were identified in the simulated glasses. NBO-BO interconversion or bond switching was noted, which results in a dynamic equilibration of the tetrahedral phosphate units (P-n, n = 1,3 indicates the number of bridging oxygen atoms in the coordination of phosphorus). The NBO-BO bond switching is mildly activated with an effective activation barrier of 0.03-0.05 eV. Lithium ion jumps do not appear to be strongly coupled to bond switching. But the number of Li+ ions coordinated to an optimum number of NBOs and the number of Li+ ions jumping out of their sites appear to be correlated. Detailed analysis was made of the dynamics of P-n species and new insights have been obtained regarding ion migration in network-modified phosphate glasses.

Enhanced lithium-ion transport in PEG-based composite polymer electrolyte with Mn0.03Zn0.97Al2O4 nanoparticles

The ion conduction and thermal properties of composite solid polymer electrolyte (SPE) comprising Poly(ethylene) Glycol (PEG, mol wt. 2000), lithium perchlorate (LiClO4) and insulating Mn0.03Zn0.97Al2O4 nanoparticle fillers were studied by complex impedance analysis and DSC techniques. The average size of the nanoparticles was determined by powder X-ray diffraction (XRD) using Scherrer's equation and was found to be similar to 8 nm. The same was also determined by TEM imaging and found to be similar to 12 nm. The glass transition temperature T, as measured by differential scanning calorimeter (DSC), showed a minimum at 5 mol% of narroparticles. Fractional crystallinity was determined using DSC. NMR was used to deter-mine crystallinity of a pure PEG sample, which was then used as the standard. Fractional crystallinity X. was the lowest for 5 mol% and beyond. The ionic conductivity of the composite polymer electrolyte containing 5 mol% Mn0.03Zn0.97Al2O4 nanoparticles was found to be 1.82 x 10(-5) S/cm, while for the pristine one, it was 7.27 x 10(-7) S/cm at room temperature. As a function of nanoparticle content, conductivity was observed to go through two maxima, one at around 5 mol% and another shallower one at around 12 mol%. The temperature dependence of conductivity could be divided into two regions, one consistent with Arrhenius behaviour and the other with VTF. We conclude that the enhancement of ionic conductivity on the addition of Mn0.03Zn0.97Al2O4 nanoparticles is a result of reduction in both the T, and the crystallinity. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of lithium ion irradiation on the transport and optical properties of Bridgman grown n-type InSb single crystals

Single crystal (100) wafers of n-InSb were implanted with 50 MeV Li3+ ions at various fluences ranging from 10(10) to 10(14) ions/cm(2) at room temperature. Investigations of the optical, electrical, and structural properties of the as-grown, irradiated, annealed wafers were carried out by infrared and Raman spectroscopies, Hall measurements, and high resolution x-ray diffraction (HRXRD). In the case of samples irradiated with an ion fluence of 1.6x10(14) ions/cm(2), electrical measurements at 80 K reveal that there is a decrease in carrier concentration from 8.5x10(15) (for unirradiated) to 1.1x10(15)/cm(3) and an increase in mobility from 5.4x10(4) to 1.67x10(5) cm(2)/V s. The change in carrier concentration is attributed to the creation of electron trap centers induced by ion beam irradiation and the increase in mobility to the formation of electrical inactive complexes. Nevertheless, even with the irradiation at 1.6x10(14) ions/cm(2) fluence the crystalline quality remains largely unaffected, as is seen from HRXRD and Raman studies. (C) 2001 American Institute of Physics.

Utilizing an ionic liquid for synthesizing a soft matter polymer ``gel'' electrolyte for high rate capability lithium-ion batteries

A cross-linked polymer ``gel'' electrolyte obtained from free radical polymerization of a vinyl monomer (acrylonitrile; AN) in a room temperature ionic liquid electrolyte (N,N-methyl butyl pyrrolidinium-bis (trifluoromethanesulphonyl)imide-lithium bis(trifluoromethanesulphonyl) imide;LiTFSI-[Py(1,4)-TFSI]) for application in high rate capability rechargeable lithium-ion batteries is discussed here. This is a novel alternative compared to the often employed approach of using a molecular liquid as the medium for performing the polymerization reaction. The polymer ``gel'' electrolytes (AN:Py(1,4)-TFSI = 0.16-0.18, w/w) showed remarkable compliable mechanical strength and higher thermal stability compared to LiTFSI-[Py(1,4)-TFSI]. Despite two orders increase in magnitude of viscosity of polymer ``gels'', the room temperature ionic conductivity of the ``gels'' (1.1 x 10(-3)-1.7 x 10(-3) Omega(-1) cm(-1)) were nearly identical to that of the ionic liquid (1.8 x 10(-3) Omega(-1) cm(-1)). The present ``gel'' electrolytes did not exhibit any ageing effects on ionic conductivity similar to the conventional polymer gel electrolytes (e.g. high molecular weight polymer + salt + high dielectric constant molecular solvent). The disorder (ionic liquid) to a relative order (cross-linked polymer electrolyte) transformation does not at all influence the concentration of conducting species. The polymer framework is still able to provide efficient pathways for fast ion transport. Unlike the ionic liquid which is impossible to assemble without a conventional separator in a cell, the polymer ``gel'' electrolyte could be conveniently assembled without a separator in a Li vertical bar lithium iron phosphate (LiFePO(4)) cell. Compared to the ionic liquid, the ``gel'' electrolyte showed exceptional cyclability and rate capability (current density: 35-760 mA g(-1) with LiFePO(4) electronically wired with carbon (amorphous or multiwalled nanotube [MWCNT]).

The effect of particle size on performance of cathode materials of Li-ion batteries

Beginning with the ‘frog-leg experiment’ by Galvani (1786), followed by the demonstrations of Volta pile by Volta (1792) and lead-acid accumulator by Plante´ (1859), several battery chemistries have been developed and realized commercially. The development of lithium-ion rechargeable battery in the early 1990s is a breakthrough in the science and technology of batteries. Owing to its high energy density and high operating voltage, the Li-ion battery has become the battery of choice for various portable applications such as note-book computers, cellular telephones, camcorders, etc. Huge efforts are underway in succeeding the development of large size batteries for electric vehicle applications. The origin of lithium-ion battery lies in the discovery that Li+-ions can reversibly be intercalated into/de-intercalated from the Van der Walls gap between graphene sheets of carbon materials at a potential close to the Li/Li+ electrode. By employing carbon as the negative electrode material in rechargeable lithium-ion batteries, the problems associated with metallic lithium in rechargeable lithium batteries have been mitigated. Complimentary investigations on intercalation compounds based on transition metals have resulted in establishing LiCoO2 as the promising cathode material. By employing carbon and LiCoO2, respectively, as the negative and positive electrodes in a non-aqueous lithium-salt electrolyte,a Li-ion cell with a voltage value of about 3.5 V has resulted.Subsequent to commercialization of Li-ion batteries, a number of research activities concerning various aspects of the battery components began in several laboratories across the globe. Regarding the positive electrode materials, research priorities have been to develop different kinds of active materials concerning various aspects such as safety, high capacity, low cost, high stability with long cycle-life, environmental compatibility,understanding relationships between crystallographic and electrochemical properties. The present review discusses the published literature on different positive electrode materials of Li-ion batteries, with a focus on the effect of particle size on electrochemical performance.

Hydrothermal synthesis of a monoclinic VO2 nanotube-graphene hybrid for use as cathode material in lithium ion batteries

The hydrothermal reaction of a mixture of a colloidal dispersion of graphite oxide and ammonium vanadate yielded a hybrid made of graphene and a nanotubular metastable monoclinic polymorph of VO2, known as VO2(B). The formation of VO2(B) nanotubes is accompanied by the reduction of graphite oxide. Initially the partially scrolled graphite oxide layers act as templates for the crystallization of VO2(B) in the tubular morphology. This is followed by the reduction of graphite oxide to graphene resulting in a hybrid in which VO2(B) nanotubes are dispersed in graphene. Electron microscopic studies of the hybrid reveal that the VO2(B) nanotubes are wrapped by and trapped between graphene sheets. The hybrid shows potential to be a high capacity cathode material for lithium ion batteries. It exhibits a high capacity (similar to 450 mAh/g) and cycling stability. The high capacity of the hybrid is attributed to the interaction between the graphene sheets and the VO2(B) tubes which improves the charge-transfer. The graphene matrix prevents the aggregation of the VO2(B) nanotubes leading to high cycling stability. (C) 2012 Elsevier Ltd. All rights reserved.