Lithium Ion Insertion Research Articles

Graphene‐Encapsulated Copper tin Sulfide Submicron Spheres as High‐Capacity Binder‐Free Anode for Lithium‐Ion Batteries

AbstractSn‐based sulfides are potential anode materials for lithium‐ion batteries (LIBs); nevertheless, they typically suffer from poor cycle stability resulted from the huge volume variation during lithium‐ion insertion and extraction. Herein, we successfully fabricated the multiphase Cu2Sn3S7/Cu2SnS3/SnS2 (CTS) submicron spheres uniformly incorporated with reduced graphene oxide nanosheets (CTS@RGO). This binder‐free hybrid CTS@RGO paper exhibits favorable capacity retention as an anode of LIBs (965 mAh g−1 after 300 cycles at current density of 500 mA g−1), as well as better rate capability and high initial coulombic efficiency compared with that of a pristine CTS anode. The enhanced electrochemical performance can be ascribed to the introduction of graphene as a buffer to accommodate large volume changes and to maintain structural integrity of electrode.

Graphene-doped carbon/Fe3O4 porous nanofibers with hierarchical band construction as high-performance anodes for lithium-ion batteries

Porous graphene-doped carbon/Fe3O4 (GN@C/Fe3O4) nanofibers are synthesized via in-situ electrospinning and subsequent thermal treatment for use as lithium-ion battery anode materials. A polyacrylonitrile (PAN)/polymethyl methacrylate (PMMA) solution containing ferric acetylacetone and graphene oxide nanosheets is used as the electrospinning precursor solution. The resulting porous GN@C/Fe3O4 nanofibers show unique dark/light banding and a hierarchical porous structure. These nanofibers have a Brunauer–Emmett–Teller (BET) specific surface area of 323.0m2/g with a total pore volume of 0.337cm3/g, which is significantly greater than that of a sample without graphene and C/Fe3O4 nanofibers. The GN@C/Fe3O4 nanofiber electrode displays a reversible capacity of 872 mAh/g at a current density of 100mA/g after 100 cycles, excellent cycling stability, and superior rate capability (455mA/g at 5A/g). The excellent performance of porous GN@C/Fe3O4 is attributed to the material’s unique structure, including its striped topography, hierarchical porous structure, and inlaid flexible graphene, which not only provides more accessible active sites for lithium-ion insertion and high-efficiency transport pathways for ions and electrons, but also accommodates the volume change associated with lithium insertion/extraction. Moreover, the zero-valent iron and graphene in the porous nanofibers enhance the conductivity of the electrodes.

Pressure-induced abnormal insulating state in triangular layered cobaltite LixCoO2 (x = 0.9)

Lithium cobaltite oxides (LixCoO2) have been serving as an important rechargeable battery material with reversible extraction and insertion of lithium ions.

Synthesis and Ionic Conductivity Studies of In- and Y-Doped Li6Hf2O7 as Solid-State Electrolyte for All-Solid State Li-Ion Batteries

The development of all solid-state lithium batteries is reliant on suitable high performance solid state electrolytes. Here, we present the synthesis and ionic conductivity of the In- and Y-doped Li6Hf2O7 materials; Li6+xHf2-xMxO7 (M = In3+, Y3+). Microwave-assisted synthesis was used to give phase pure material after heating for 4 hours at 850°C. The ionic conductivity of the materials is increased with the insertion of interstitial lithium ion within the structure from 0.02 to 0.25 mS cm−1 at 174°C and the activation energy for ionic conduction is lowered from 0.97(4) eV to 0.42(3) eV with respect to the undoped material.

Combustion synthesized macroporous structure MFe2O4 (M= Zn, Co) as anode materials with excellent electrochemical performance for lithium ion batteries

ZnFe2O4 and CoFe2O4 materials are successfully prepared via solution combustion synthesis with glycine as fuel and complexing agent. The final products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The average diameter of the prepared particles is in the range of 80–100 nm. Cyclic voltammetry (CV), galvanostatic cycling and electrochemical impedance spectroscopy (EIS) studies are used to investigate the electrochemical properties of the MFe2O4 (M = Zn, Co) particles. The reversible capacities of ZnFe2O4 and CoFe2O4 are 1037.2 mAh g−1 and 994.3 mAh g−1, respectively, after 80 cycles at a current density of 200 mA g−1. The capacity retentions are up to 104.2% and 106.6% compared to the second cycle. The as-synthesized samples also exhibit outstanding rate capability and long cycle life. After 300 cycles at a high current density of 1000 mA g−1, the capacity retention are 109.3% and 87.4% compared to the second cycle with almost no capacity fading but increasing. It could still maintain reversible capacities of 794.7 mAh g−1 and 746.5 mAh g−1, respectively. The superior electrochemical performance can be attributed to the macroporous structure in pure phase without any impurities, which can not only ease the volume expansion during the charge/discharge processes but also provide more interstices for lithium ions insertion. What is more, the high crystallinity of two samples is able to stabilize the microstructure no collapse after plenty of lithiation-delithiation processes. The results suggest that this method is a facile, effective and general way to synthesize excellent electrochemical properties of macroporous structure spinel Fe-based binary transition metal oxides as anode material for lithium ion batteries.

Maxwell stress to explain the mechanism for the anisotropic expansion in lithiated silicon nanowires

This computational research study attempts to explain the process that leads to volume expansion during insertion of lithium ions into a silicon nanowire. During lithiation, electrons flow through the nanowire in the opposing direction of lithium ions insertion. This causes an applied electromagnetic field which is described as being a quantum mechanical version of photon density wave theory. A series of events are calculated as the individual electrons and photons travels through the lithiated silicon nanowire. The hypothesis that will be presented employs the Maxwell stress tensor to calculate the refractive indices in three orthogonal directions during lithiation. The quantum harmonic oscillator and the electromagnetic intensity will be utilized in this presentation to calculate the energy of electrons and optical amplification of the electromagnetic field respectively. The main focus of this research study will use electron scattering theory, spontaneous and stimulated emission theory to model the breaking of cohesion bonds between silicon atoms that ultimately leads to excessive volume expansion that is witnessed during the lithiation process in Si nanowires.

Cotton/rGO/carbon-coated SnO2 nanoparticle-composites as superior anode for Lithium ion battery

The three-dimensional carbonized cotton framework covered by reduced graphene oxide (rGO) was uniformly decorated by the SnO2 nanoparticles encapsulated by a layer of the amorphous carbon and was directly used in the anode materials for the lithium ion battery. The carbonized frameworks covered by rGO are interconnected and the pores are enriched, facilitating the diffusion of electron and releasing the strain of lithium ions insertion and extraction. The rGO sheets with better mechanical and foldable characterization increase the conductive and buffer the electrode expansion during the cycling process. Furthermore, the amorphous carbon coating effectively prevents the direct contact between the SnO2 nanoparticles and the electrolyte, which can format a stable solid electrolyte interphase and greatly reduce the irreversible reaction. As a result, the capacity of composite is as high as 496.3mAhg−1 (1.72mAhcm−2) after 200cycles at current density of 100mAg−1, which means that the product as free-standing and binder-free electrode exhibits the stable cycle performance and will be a promising material for the application of lithium ion battery.

Microsized Porous SiOx@C Composites Synthesized through Aluminothermic Reduction from Rice Husks and Used as Anode for Lithium-Ion Batteries.

Microsized porous SiOx@C composites used as anode for lithium-ion batteries (LIBs) are synthesized from rice husks (RHs) through low-temperature (700 °C) aluminothermic reduction. The resulting SiOx@C composite shows mesoporous irregular particle morphology with a high specific surface area of 597.06 m2/g under the optimized reduction time. This porous SiOx@C composite is constructed by SiOx nanoparticles uniformly dispersed in the C matrix. When tested as anode material for LIBs, it displays considerable specific capacity (1230 mAh/g at a current density of 0.1 A/g) and excellent cyclic stability with capacity fading of less than 0.5% after 200 cycles at 0.8 A/g. The dramatic volume change for the Si anode during lithium-ion (Li+) insertion and extraction can be successfully buffered because of the formation of Li2O and Li4SiO4 during initial lithiation process and carbon coating layer on the surface of SiOx. The porous structure could also mitigate the volume change and mechanical strains and shorten the Li+ diffusion path length. These characteristics improve the cyclic stability of the electrode. This low-cost and environment-friendly SiOx@C composite anode material exhibits great potential as an alternative for traditional graphite anodes.

Ultra-thin anatase TiO2 nanosheets with admirable structural stability for advanced reversible lithium storage and cycling performance

Anatase TiO2 ultra-thin nanosheets (TiO2-NS) are synthesized by a facile hydrothermal method. Several merits are realized when employing the prepared TiO2-NS as lithium ion battery anode material, compared to TiO2 nanoparticles. Firstly, the as-prepared TiO2-NS has high charge capacities and a specific surface area up to 98.8m2g−1, which is beneficial for the insertion of lithium ion. Secondly, the large specific surface area is helpful in enlarging the electrode/electrolyte interfacial area. Finally, the EIS result verifies short electron transfer paths. More importantly, the stability of the nanosheet structure is indirectly confirmed by the excellent cycling performance of charge capacity and the curve of charge capacities versus cycle number at different current densities. After galvanostatic charge/discharge of the batteries for 1000 cycles, the HRTEM images of post-mortem batteries directly reveal a good reversibility of the lithium ion insertion/extraction process aided by TiO2-NS. Thus, all these advantages and the special structure facilitate an excellent cycling performance: the charge capacity with the maximum value of 250mAhg−1 keeps half after 2000 cycles at a current density of 840mAg−1 (5C).

Electrochemical Properties and In-situ XAFS Observation of Li2O-V2O5-P2O5-Fe2O3 Quaternary-glass and Crystallized-glass Cathodes

Electrochemical properties of Li2O-V2O5-P2O5-Fe2O3 quaternary-glass and crystallized-glass cathodes were compared in terms of the local structural changes of vanadium and iron ions with increasing discharge capacity by in-situ X-ray absorption fine structure (XAFS) measurements. 10.3Li2O-69.2V2O5-10.2P2O5-10.3Fe2O3 glass was prepared by the melt-quenching method. The crystallized glass was produced by heat treatment of the glass at 375°C in air. The crystal phase of the crystallized glass was found to be a single phase of β-vanadium bronze. The glass exhibited a discharge capacity of around 300 mAh g−1 and a capacity retention of 66% after 100cycles. On the other hand, the crystallized glass exhibited a capacity of around 340 mAh g−1 and a capacity retention of 68% after 100cycles. In the cases of glass and crystallized glass, in-situ X-ray absorption near-edge spectroscopy (XANES) spectra revealed that a redox reaction of vanadium and iron ions occurs as a compensation reaction for lithium-ion insertion. In addition, the absorption-energy shift of the vanadium and iron K-edges in the case of glass was larger than that in the case of crystallized glass despite the same discharge capacity. The analysis of pre-edge peak intensities and extended X-ray absorption fine structure (EXAFS) analysis revealed that the vanadium and iron coordination symmetry of the glass can transform more easily than that of the crystallized glass under lithium-ion insertion. These results imply that the origin of good cycleability differs in the cases of glass and crystal-phase cathodes.

Novel solvent-thermal preparation of a SnO2 nanoparticles/expanded graphite multiscale composite with extremely enhanced electrical performances for Li-ion batteries

A novel SnO2 nanoparticles (NPs)/expanded graphite (EG) multiscale hybrid composite was prepared via an elaborately designed solvent-thermal reaction and the following anneal treatment. A mixed solvent system of acetone-H2O with volume proportion of 3:1 was employed for the solvent-thermal reaction in order to realize moderate hydrolysis rate of Sn4+ and favorable wettability between solvent molecules and EG surface. Acetone played a very positive role for the uniform nucleation and crystal growth of SnO2-NPs, which could be proved by the ultrafine sizes of 3–6nm and well-crystallized texture of SnO2-NPs, as well as their homogeneous anchor on the surface of EG. As an anode material for Li-ion batteries, the SnO2-NPs/EG composite exhibited excellent long-term cycling stability, e.g. decay-free reversible capacity of 976mAhg−1 after 100 cycles, and good rate capability (>400mAhg−1 at 2000mAg−1). The extraordinary electrochemical performances arise from the structural advantages of the composite: the ultrafine SnO2-NPs with high dispersity on conductive EG matrix supply not only large quantity of accessible active sites for lithium-ion insertion but also good conductivity and short diffusion length for lithium ions. These results suggest the SnO2-NPs/EG composite would be a promising candidate as anode material for next-generation LIBs.

Layered Si-C Nanocomposites Synthesized from Layered Silicate As High Performance Anodes for Lithium-Ion Batteries

1. Introduction Lithium Ion Batteries (LIB) are already widely used for small potable electronics (cellular phone, lab top computer, MP3 etc.) as a main energy part due to light weight, good energy storage rate, and long term stability (cyclaility and durability). Existing LIBs use graphite as an anode material. This carbon material has high cycle stability and electrical conductivity. However, the specific lithiation capacity (370 mA h g-1) of the graphite can’t satisfy the demands for higher energy density batteries. Silicon (Si) has emerged as a promising material to produce high capacity anodes for LIBs, due to its high theoretical capacity (~4200 mA h g-1) which is 10 times higher than that of graphite. However, Si anodes for LIBs have a disadvantage from the large volume change. The expanding to 3-4 times its original size often break the electrical contacts with current collector. Therefore, we focus on making ideal particle size and effective structure of Si. Layered Si particles are prepared by kanemite as a raw material, followed by magnesiothermic reduction. And then, the phenol-formaldehyde liquid resin pyrolyzed carbon coated on the surface of Si particles and inserted into layered Si inner space. In this research, This novel anode active materials exhibit a high reversible specific capacity and good capacity retention. 2. Materials and Method The natural clays with layered Na+ silicates are used in constructing the structure of the silicon layers. A layered silicate kanemite (NaHSi2O5ㆍ3H2O) was prepared by dispersing δ-Na2SiO5 (1.0g) in deionized water (100mL) with stirring for 1h. After that, the kanemite was filtrated, washed, and then dried. The kanemite powder (200mg) was mixed with Mg powder (200mg), and calcined for magnesiothermic reduction at 650°C under Ar atmosphere for 5h. 0.1 M of HCl solution remove redundant Mg, MgO and Mg2Si. We used HF and ethanol solution for remove remained SiO2 in the layered silicon particles. 200 mg of synthesized layered silicon particles, 100ml of Phenol-Formaldehyde (PF) liquid and 1ml of HCl were dispersed in the mixture by ultrasonication for 2h. The mixed solution was filtrated with 0.2mm size of membrane filter. During the filtrate process, dispersed silicon thin plates are stacked like bricks. The filter and mixture become phenolic resin structure after heated at 128°C for 12h. Finally, the silicon-phenolic resin solid compound was calcined at 700°C for 5h in Ar atmosphere in order to be layered Si-C nanocomposites. For the characteristic comparison, we prepare commercial original Si nanoparticles (40~60nm). 3. Results and discussion As shown in Fig. 1a,b, the PF resin pyrolized carbon and carbon black showed constant reversible capacity of 170mA h g-1 and 150mA h g-1 respectively. The layered Si and commercial Si particle showed a first reversible capacity of almost 1100mAhg-1 and 1200mAhg-1 in Fig. 1c,d. however, the reversible capacity in both samples were less that 100mAhg-1 after 25 cycles. On the other hand, the reversible capacity on the layered Si-C nanocomposite is still as high as 792mA h g-1 after 25 cycles at a rate of 100mAg-1 as shown in fig. 1e. This means capacity retention is 90% because the first reversible capacity was 875 mA h g-1. Fig. 1f result indicating that the layered Si-C nanocomposite has an excellent cycling performance. One possibility of the improved performance maybe accounted to the fact that the thin layer structures of nano silicon may have less volumetric changes and restrain the pulverization of the electrode materials during lithium ion insertion and extraction. Another reason for the enhanced behavior could be assigned to the carbon, which can improve the electrical conductivity of the composite and suppress the polarization. 4. Conclusions In summary, layered Si plates were prepared by the means of magnesiothermic reduction of Kanemite. And then, layered Si-C nanocomposites were successfully synthesized by dispersing layered silicon particles in a liquid phenol-formaldehyde followed by a subsequent pyrolysis process. This process enables a strong contact of the silicon layers and carbon sources. The layered Si-C nanocomposites exhibit an initial reversible capacity of 875mAhg-1 and a high retention of 90% after 25cycles at a current density of 100mAg-1. The highly enhanced electrochemical performance of layered Si-C nanocomposite maybe attributed to the intercalated and coated carbon on the composites which suppress the volume change of Si upon cycling, prevent the pulverization of the electrode, and increase the electrical conductivity of nanocomposite. The extremely thin Si layer (<1nm) will also provide better strength than general Si particles from the volume change, as same function as the Si thin film. Figure 1

Cathode Design for High Energy Molten Salt Lithium-Oxygen Batteries

State of the art commercial lithium ion batteries use cathodes such as lithium cobalt oxide which rely on insertion and removal of lithium ions from a host material. However, insertion cathode materials are limited in their capacity, and replacing them with a cathode that employs growth and dissolution of new phases could significantly increase a battery’s energy density. For example, oxygen and sulfur cathodes have been widely researched to this end, with both cases involving the growth of a lithium-rich compound on a current collector/catalyst support. While the lithium-oxygen battery is promising with regard to its energy density, there are many practical challenges that remain to be solved. For instance, traditional organic electrolytes decompose in the presence of superoxide anions, intermediates in the growth of the lithium peroxide discharge product. However, by replacing the organic electrolyte with a molten salt, we can inherently avoid this organic electrolyte decomposition. In addition, the use of a molten salt electrolyte results in a system operating at elevated temperature with a large concentration of lithium ions, encouraging faster diffusion and kinetics. The morphology of the lithium peroxide grown in this molten salt lithium-oxygen battery is notably different from that previously observed in literature. While previous works have observed thin films, platelets, and “toroids” on the order of several hundred nanometers, we observe much larger (several micron) structures which appear to be stacks of hexagonal layers. We believe these stacks to be a new morphology of lithium peroxide growth. These new lithium peroxide morphologies are characterized with SEM, EDS, and XRD. In addition to the lithium-oxygen system described above, we introduce another phase-forming chemistry, whereby a molten nitrate salt serves as both an active material and the electrolyte. Molten nitrate salts have been previously studied as an active material in a primary lithium battery where lithium oxide irreversibly forms as nitrate converts to nitrite. We will describe how the use of a nanoparticle heterogeneous catalyst allows the reversible growth and dissolution of large (several micron) lithium oxide crystals in this system, as substantiated by SEM, XRD, and TEM. After introducing these molten salt lithium batteries, we address the effect of cathode geometry on the discharge capacity. In particular, we note that the growth of such large, solid phase species on the surface of the catalyst support imposes new design restrictions when optimizing a cathode for energy density. For instance, it is not just the surface area of the catalyst support that determines the discharge capacity, but also the amount of usable pore volume to allow this solid phase discharge product to form. As a proof of concept, we design and implement an architected electrode with large pore volume and relatively small surface area. Such cathode design principles could be extended to other phase-forming chemistries.

MoO2/Mo2c Hybrid Nanowires As High Performance Anode Materials for Lithium Ion Batteries

Molybdenum oxides, mainly including MoO3 and MoO2, are attractive materials with potential applications in catalysis, sensors and energy storage. Owing to the good electronic conductivity, high stability and density, MoO2 was proposed as a host material for lithium ions. However, the application of MoO2 as anode material for lithium ion batteries was limited in the early research, due to the low capacity and poor cycling stability resulting from the bulky dimensions, the consequential slow kinetics and huge volume changes during the charge/discharge process. To improve the performance of MoO2, a most promising way is to design and construct nanostructured composites [1-3]. Here we report on MoO2/Mo2C hybrid nanowires synthesized through simple calcination using MoOx/amine nanowires as a precursor. The small diameters of the nanowires ensure fast lithium ion insertion and extraction, while the long dimensions benefit good electron transport between wires. Besides, Mo2C with a high specific conductance distinctly increases the structural stability and electronic conductivity of the hybrid nanowires. As a result, the cycling and rate performance of the hybrid nanowires is remarkably enhanced. At a current density of 1000 mA/g, a discharge capacity of ~700 mAh/g is still retained after 300 cycles, which indicates the MoO2/Mo2C hybrid nanowires a promising anode material for high performance lithium ion batteries. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Nos. 51402110, and 51231003). [1] Q.S. Gao, L. C. Yang, X. C. Lu, J. J. Mao, Y. H. Zhang, Y. P. Wu, Y. Tang, J. Mater. Chem., 2010, 20, 2807. [2] L.C. Yang, L. L. Liu, Y. S. Zhu, X. J. Wang, Y. P. Wu, J. Mater. Chem., 2012, 22, 13148. [3] H. J. Zhang, K. X. Wang, X. Y. Wu, Y. M. Jiang, Y. B. Zhai, C. Wang, X. Wei, J. S. Chen, Adv. Funct. Mater., 2014, 24, 3399.

Electrochemical Properties of Nb-Based Oxides As Active Materials for the Negative Electrode of Lithium Secondary Batteries

During the past twenty years, much effort has been undertaken to obtain lithium secondary batteries with higher energy densities, and a great progress has been made. However, there is still an increasing demand for further lightweight and small-size rechargeable batteries for portable electronic devices. In addition, recent environmental concerns about global warming and the need to reduce CO2 emissions provide us a strong driving force for developing large-scale lithium secondary batteries with high energy densities for use in electric vehicles. One of the important requirements of negative electrode material to get a lithium secondary battery having a large energy density, the redox potential at the negative electrode should be as low as possible. In the present work, we report Nb-based oxides as active materials for the negative electrode of lithium secondary batteries. Composite electrodes were used for charge/discharge tests and cyclic voltammetry (CV). The test electrode was prepared by coating a mixture of the Nb-based oxide powder (80 wt.%) and a carbon black (10 wt.%) and a poly(vinylidene difluoride) binder (10 wt.%) on copper foil. The charge and discharge tests were carried using conventional three-electrode cells at a constant current of 18.1 mA g–1. The electrolyte solution was 1 mol dm–3 (M) LiClO4 dissolved in 1:1 (by volume) mixtures of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC + DEC) (Kishida Chemical Co., Lithium Battery Grade). The counter and reference electrodes were lithium foil. CV was performed between 3.0 and 30.0 V at a sweep rate of 0.5 mV s–1. All electrochemical measurements were carried out in an argon-filled glovebox with a dew point < –60 °C. All potentials are referred to as volts vs. Li/Li+.The electrochemical properties of Li1.1Nb0.9O2-x material was theoretically predicted by first principal method and experimentally tested by electrochemical method. The potential of Li1.1Nb0.9O2-x for lithium ion insertion into and extraction out of the material, as predicted through theoretical calculations, was quite low below 0.3 V vs. Li/Li+, giving high cell voltage as a negative electrode material for lithium secondary batteries. Li1.1Nb0.9O2-x was successfully synthesized by a solid state reaction and shown to have good cycle performance, although there is a large irreversible capacity in the first cycle. The main reversible reaction of the material is occurred at almost 0 V vs. Li/Li+. The low potential is originated from the electronic structure of the Li1.1Nb0.9O2-x; it acts as a favorable factor for an increase in energy density even though the possibility of an increase in electrolyte decomposition is present in initial charging process. The study on the electrochemical properties of Li1.1M0.9O2-x (M=Ti, Cr, Zr, and Mo) might be meaningful because those compounds present low potentials for lithium ion insertion as predicted by the first principal method and show high cell voltage as a negative electrode material for lithium secondary batteries.The NbO2 electrode showed a large irreversible capacity and small discharge capacity. The results of X-ray photoelectron spectroscopy indicate that the poor electrode performance of NbO2 may be caused by niobium pentoxide (Nb2O5) formed on the surface of active material. The Nb2O5 could be removed by chemical etching to some extent, thus improving the electrode performance. In addition, The electrochemical properties of niobium monoxide, NbO, were investigated as a negative electrode material for lithium-ion batteries. Lithium ions were inserted into and extracted from NbO material at potentials < 1.0 V versus Li/Li+. The process involved the formation of a solid electrolyte interface (SEI) on the NbO surface in the first cycle. The reversible capacity was ~67 mAh g–1 with a capacity retention of ~109% after 50 cycles. The magnitude of the charge transfer resistance was greatly decreased by ball-milling the pristine NbO, but the ball-milling had no effect on the SEI resistance. References1) K.T. Jacob, C. Shekhar, M. Vinay, Y. Waseda, J. Chem. Eng. Data, 55,4854 (2010).2) L.-F. Cui, Y. Yang, C.-M. Hsu, Y. Cui, Nano Lett., 9, 3370 (2009).

Electrochemical Performance of Carbon-Coated Cauliflower-like WO3 for Li-Ion Batteries

Metal oxides have been considered and investigated as alternative anodes for use in lithium ion batteries. The research focus is on two different mechanism groups: intercalation–deintercalation reaction and conversion (redox) reaction. The intercalation–deintercalation mechanism is that transition metal oxides and other compounds with a multidimensional layer structure can reversibly intercalate lithium ions into the lattice without destroying their crystal structure. While conversion mechanism usually produces metallic nanoparticles embedded in an insulating Li2O matrix and the shows generally much higher theoretical capacity than that of already-commercialized graphite. Among the metal oxides, tungsten oxides (WO2, WO3, and WO3-x H2O) as one of the important metal oxides with respect to physicochemical properties, have been extensively investigated for such applications as gas sensors, photocatalysis, electrochromic devices, electronic devices, dye-sensitized solar cells, supercapacitors, and lithium ion batteries. Interestingly, the tungsten oxides have better electronic conductivity (10–10-6 S cm-1) than some of the other oxides; in addition, they also rely on designing a nanostructured particle with a small radius and right crystalline phase for fast lithium-ion insertion and superior electrochemical performance. From this point of view, a wide variety of approaches have been pursued over the years for the synthesis of tungsten oxides, such as nanoparticles, nanowires, nanorods, and nanoflowers using various approaches which include a hydrothermal reaction, combustion process, sol–gel process, solution-phase reaction, template directed method, mechanochemical activation, and hot-wire chemical vapor deposition (HWCVD) method. However, most of the previous approaches led to the formation of monoclinic W18O49, hexagonal WO3, and WO3-xH2O nanostructures. There have been very few studies on nanostructured monoclinic WO3 (m-WO3). In this study, we will present a facile hydrothermal process that obtains cauliflower-like carbon-coated WO3 oxide with a high rate-capability and good cycling performance for lithium-ion batteries. The motivation in this study is to explore the possibility of using m-WO3 as an anode material for lithium-ion batteries and to elucidate its reaction mechanism with lithium during the charge–discharge process.

Highly uniform Co9S8 nanoparticles grown on graphene nanosheets as advanced anode materials for improved Li-storage performance

A Co9S8/GNS (graphene nanosheets) nanocomposites has been synthesized via a facile solvothermal approach followed by thermal treatment in nitrogen at 500°C using graphite oxide sheets, CoCl2·6H2O and thiourea as the starting materials. Highly uniform Co9S8 nanoparticles with a size of about 80–90nm are evenly grafted on the surface of GNS, forming a unique Co9S8/GNS hybrid nanostructure. When evaluated as anode materials for lithium ion batteries, impressive electrochemical performances of the as-prepared nanocomposites are achieved compared to that of pure bulk Co9S8, with an high reversible capacity of 1480mAhg−1. Moreover, the as-synthesized nanocomposites present excellent cycling durability and high-rate capability. The improvement in the electrochemical properties could be attributed to the well-designed structure of the Co9S8/GNS nanocomposite which possesses large number of accessible active sites for lithium-ion insertion, fast ion diffusion rate and good electronic conductivity.

Enhanced electrochemical performance of Li-rich low-Co Li1.2Mn0.56Ni0.16Co0.08−x Al x O2 (0≤x≤0.08) as cathode materials

Layered Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 (0 ≤ x ≤ 0.08) cathode materials were successfully synthesized by a sol-gel method. X-ray diffraction and the refinement data indicate that all materials have typical α-NaFeO2 structure with R -3 m space group, and the a -axis has almost no change, but there is a slight decrease in the c lattice parameter as well as the cell volume. Scanning electron microscopy and high resolution transmission electron microscopy prove that all the samples have uniform particle size of about 200–300 nm and smooth surface. The energy-dispersive X-ray spectroscopy mapping shows that aluminum has been homogeneously doped in the Li1.2Mn0.56Ni0.16Co0.08O2 cathode material. The cyclic voltammetry and electrochemical impedance spectroscopy reveal that appropriate Al-doping contributes to the reversible lithium-ion insertion and extraction, and then reduces the electrochemical polarization and charge transfer resistance. Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 ( x = 0.05) shows the lowest charge transfer resistance and the highest lithium-ion diffusion coefficient among all the samples. The Li-rich electrodes with low-level Al doping shows a much higher discharge capacity than the pristine one, especially the Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 ( x = 0.05) sample, which exhibits greater rate capacity and better fast charge-discharge performance than the other samples. Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 ( x = 0.05) also exhibits higher discharge capacity than the pristine one at each cycle at 55°C. These results clearly indicate that the high rate capacity together with a good high rate cycling performance and high-temperature performance of the low-Co Li1.2Mn0.56Ni0.16Co0.08− x Al x O2 ( x =0.05) is a promising alternative to next-generation lithium-ion batteries.

A Core-Shell Fe/Fe2 O3 Nanowire as a High-Performance Anode Material for Lithium-Ion Batteries.

The preparation of novel one-dimensional core-shell Fe/Fe2 O3 nanowires as anodes for high-performance lithium-ion batteries (LIBs) is reported. The nanowires are prepared in a facile synthetic process in aqueous solution under ambient conditions with subsequent annealing treatment that could tune the capacity for lithium storage. When this hybrid is used as an anode material for LIBs, the outer Fe2 O3 shell can act as an electrochemically active material to store and release lithium ions, whereas the highly conductive and inactive Fe core functions as nothing more than an efficient electrical conducting pathway and a remarkable buffer to tolerate volume changes of the electrode materials during the insertion and extraction of lithium ions. The core-shell Fe/Fe2 O3 nanowire maintains an excellent reversible capacity of over 767 mA h g(-1) at 500 mA g(-1) after 200 cycles with a high average Coulombic efficiency of 98.6 %. Even at 2000 mA g(-1) , a stable capacity as high as 538 mA h g(-1) could be obtained. The unique composition and nanostructure of this electrode material contribute to this enhanced electrochemical performance. Due to the ease of large-scale fabrication and superior electrochemical performance, these hybrid nanowires are promising anode materials for the next generation of high-performance LIBs.

Nanostructured MnO2 anode materials for advanced lithium ion batteries

Owing to the high reversible capacity, low-cost, natural abundance and environmental friendliness, manganese dioxide (MnO2) is recognized as one of the most appropriate and promising anode materials. In this work, nanostructured MnO2 anode materials have been achieved via a hydrothermal method. The crystal structure, morphology and specific surface area of as-prepared MnO2 are characterized by XRD, SEM and BET techniques. As anode materials for lithium-ion batteries, MnO2 samples show high initial discharge capacity and relatively excellent cyclic performance. The electrochemical performance of MnO2 samples is related to crystal structure and surface morphology. Monoclinic structure, it is similar to graphene, which is more convenient for the fast ionic transportation into the bulk of the electrode materials. And porous structure, which can accommodate volume expansion, shorten the electron and lithium ion diffusion pathway and provide a large number of electrochemical reactive sites for lithium ion insertion and extraction during cycling.