Low Volume Expansion Research Articles

Electrochemical performance of 2D polyaniline anchored CuS/Graphene nano-active composite as anode material for lithium-ion battery

Lithium-ion battery (LIB) is a revolutionary step in the electric energy storage technology for making green environment. In the present communication, a LIB anode material was constructed by using graphene/polyaniline/CuS nanocomposite (GR/PANI/CuS NC) as a high-performance electrode. Initially, pure covellite CuS nanoplates (NPs) of the hexagonal structure were synthesized by hydrothermal route and then GR/PANI/CuS NC was fabricated by in-situ polymerization of aniline in the presence of CuS NPs and graphene nanosheets (GR NSs) as host matrix. GR/PANI/CuS NC-based LIB has shown the superior reversible current capacity of 1255mAhg−1, a high cycling stability with more than 99% coulombic efficiency over 250 cycles even at a high current density of 5Ag−1, low volume expansion, and excellent power capabilities. Galvanostatic charge/discharge tests and cyclic voltammetry analysis were used to investigate electrochemical properties. The electrochemical test proves that GR/PANI/CuS NC is promising anode material for LIB. The crystal phases and purity of the GR/PANI/CuS NC were confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) were employed to examine the morphology, size, chemical composition, and phase structure of the synthesized GR/PANI/CuS NC.

Scalable Template-Free Synthesis of Na2Ti3O7/Na2Ti6O13 Nanorods with Composition Tunable for Synergistic Performance in Sodium-Ion Batteries

Sodium-ion batteries are regarded as one of the potential candidates to substitute lithium ion batteries in large-scale electric energy storage applications in the near future. Several forms of sodium titanates including Na2Ti3O7, Na2Ti6O13 and Na4Ti5O12 have recently been applied as anode in sodium ion batteries. Here, we present an energy-efficient solid-state synthesis, via the addition of carbon, to mass-produce a series of uniform and single-crystalline Na2Ti3O7/Na2Ti6O13 nanorods with tunable composition as anode materials for sodium-ion batteries.1 Due to the extra local heat generation and CO2/CO release from carbon oxidation, the carbon added in the synthesis provides an alternative low-temperature route for the Na2Ti3O7 formation at 450 °C, a reaction temperature much lower than that of conventional solid-state methods (750–1000 °C), and Na2CO3 is regenerated to be recycled in the synthesis. The high theoretical capacity of Na2Ti3O7 and low volume expansion of Na2Ti6O13 upon charge–discharge are synergistically exploited to achieve high electrochemical performance and stability.

Structural and vibrational characterization of anhydrous and dihydrated species of trehalose based on the FTIR and FTRaman spectra and DFT calculations

In this study, three anhydrous species of trehalose and their dihydrated form were studied using the Fourier Transform Infrared (FTIR) and Raman spectroscopy combined with theoretical calculations derived from the theory of the functional of the density (DFT). Here, the structural and vibrational properties were predicted using the hybrid B3LYP/6-31G∗ method. The complete vibrational assignments were performed using the scaled mechanical force fields (SQMFF) methodology and their internal normal coordinates. The natural bond orbital (NBO) and atoms in molecules (AIM) calculations predicted high stabilities for the dihydrated species in gas and aqueous solution phases. The little variation observed in the dipole moment for the dihydrated species in solution could be related to a small perturbation of water hydration shell and short hydrogen bonds, as revealed by NBO and AIM studies. The lower volume expansion, low solvation energy and the higher nucleophilicity index observed for trehalose species in solution, in relation to maltose and sucrose could probably explain that different water molecules are around of trehalose/water mixtures generating higher “rigidity” in trehalose, as was experimentally reported in the literature. On the other hand, the low f(νO–H)H2O force constant value for trehalose, as compared with maltose and lactose could justify the very fragile character from the trehalose/water system to the temperature and concentration changes, as was experimentally observed from viscosity and Raman scattering studies.

Two-step ball-milling synthesis of a Si/SiOx/C composite electrode for lithium ion batteries with excellent long-term cycling stability

SiOx-based anodes have attracted tremendous attention owing to their low cost, higher theoretical capacity than graphite and lower volume expansion than pure silicon.

Pomegranate-like porous carbon coated CuxSny/Sn/SnO2 submicrospheres as superior lithium ion battery anode

The Cu-Sn alloy compounds have low volume expansion but suffer from poor cycling performance as anode materials for lithium ion batteries (LIBs). In order to improve the electrochemical performance, the pomegranate-like porous carbon coated CuxSny/Sn/SnO2 submicrospheres assembled by nanoparticles (abbreviated as pomegranate-like CuxSny/Sn/SnO2/C submicrospheres) were facilely prepared by in situ polymerization of dopamine (DA) on the surface of CuSn(OH)6 submicrospheres, followed by carbonization and reduction in H2/Ar atmosphere. Based on the advantages of nanometer-sized particle, porous structure and amorphous carbon coated, the as-prepared pomegranate-like CuxSny/Sn/SnO2/C submicrospheres behaved excellent cycling and rate performance as anode materials for LIBs. At the current density of 200mAg−1, the electrode materials could keep a capacity of 604mAhg−1 after 150 cycles. Importantly, pomegranate-like CuxSny/Sn/SnO2 submicrospheres could maintain the initial structure after 150 cycles. Relied on the excellent electrochemical performance, the pomegranate-like CuxSny/Sn/SnO2/C submicrospheres were expected to become a promising anode material for LIBs.

Scalable Template-Free Synthesis of Na2Ti3O7/Na2Ti6O13 Nanorods with Composition Tunable for Synergistic Performance in Sodium-Ion Batteries

Solid-state reactions are a simple and scalable synthetic method, but they lack controlled nanostructures at present. Here, we report an energy-efficient solid-state synthesis, via the addition of carbon, to mass-produce uniform, single-crystalline, one-dimensional metal oxide nanorods with tunable composition according to performance demands. The carbon added in the solid-state reaction provides an alternative low-temperature route for the metal oxide formation due to the extra local heat generation and CO2/CO release from carbon oxidation. To demonstrate the methodology, a series of single-crystalline Na2Ti3O7/Na2Ti6O13 nanorods with tunable composition are synthesized and applied in sodium-ion batteries. The local heat generated from carbon allows formation of Na2Ti3O7 at 450 °C, a reaction temperature much lower than that of conventional solid-state methods (750–1000 °C), and Na2CO3 is regenerated to be recycled in the synthesis. The high theoretical capacity of Na2Ti3O7 and low volume expansion of Na...

Alkali Metal Ion Storage Properties of Single-Walled Carbon Nanotube Encapsulation Systems

Single-walled carbon nanotube (SWCNT) encapsulation systems have been paid much attention since the discovery of C60 peapod in 1998. So far, several kinds of molecules (e.g. coronene, β-carotene, 9,10-dichloroanthracene, water, iodine) have been encapsulated. The eager studies on structural and electronic properties of the encapsulation systems revealed that some of the encapsulated molecules show properties different from their bulk forms. Due to such findings, it has been concluded that the tube interior provides a unique field to the encapsulated molecules to alter their properties. However, there are not many reports describing the applications of encapsulation systems. Lithium ion batteries (LIBs) have been widely used in portable electronic devices such as cell phones and lap-top computers, owing to their high energy density. However, new energy source with higher capacity and better rate performance is required because LIBs are not good enough for larger and higher power machines such as electric vehicles. Recently, metal-air, lithium-sulfur (LIS), sodium-ion batteries and others have been attracting much attention as post-LIB energy devices. LIS battery is one alternative that has higher energy density than LIB has, and is expected to be used for large-scale devices. However, in order for the practical use of LIS battery to be realized, we have to solve the problem that polysulfide ions (Sn−) are easily dissolved in electrolyte. This dissolution problem leads to capacity fading with charge-discharge cycles. Several investigations have been carried out to improve the cycle performance of LIS battery. For example, Kaneko et al. reported the encapsulation of sulfur into the hollow core of single-walled carbon nanotube (SWCNT) [1]. Another post-LIB is sodium-ion battery (SIB) that has received increasing attention in the recent years, because SIB is very advantageous in regards to cost and resources. However, good anode materials having high capacity for SIBs have not been found yet. Graphite, which is used as a negative electrode of LIBs, does not adsorb Na ions. So far, SIB negative electrode properties of several kinds of carbon materials have been studied. Although some kinds of hard-carbons and Na alloys can adsorb and desorb sodium ions, we should explore better anode materials to realize SIBs. Phosphorus is also expected as alternative electrode materials because of its high theoretical capacity (2596 mAh/g) and relatively low volume expansion when adsorbing sodium ions. However, phosphorus electrode still suffers from instability problems, despite the numerous attempts that have been made with different phosphorus polymorphs and/or different kinds of electrode support materials. In the present study, we use the unique environment provided by the hollow core inside SWCNTs to encapsulate both sulfur and phosphorous molecules, in order to address some of the unanswered questions and performance issues of both LIS and SIB. First, we compare the physical stability of sulfur molecules inserted in SWCNTs having different tube diameters, then we report the LIS battery electrode properties of sulfur encapsulated SWCNTs (S@SWCNTs). We also report on the negative electrode properties of phosphorus encapsulated single-walled carbon nanotubes (P@SWCNTs), in which phosphorus atoms are inserted into the pores of SWCNT [2]. Since SWCNTs have good electric conductivity, they should work as a conductive component for the highly resistive phosphorus electrode. In the conference, I will also talk about another types of SWCNT encapsulation systems.

Development of a Core Void Shell Silicon Nanoparticle for Use in High Capacity Anodes

In the field of energy there is a continuous drive to increase available capacity. To satisfy this growing need for energy storage, the capacity available for Li-ion batteries should increase appropriately. For the cathode of LIB's a continuous exploration of new materials is in effect, while for the construction of the anode, carbonaceous materials have been in use since the first LIB’s commercialized by Sony in 1991. This material was not chosen because of its high capacity (approx. 372 mAh/g), but because of its stability against degradation due to a low volume expansion (10%). [1,2]In the differentiation towards new elements as to replace graphitic carbon as the anode in LIB's, silicon stands out due to its high volumetric (8330 mAh/cm³) and gravimetric (3579 mAh/g) capacity. This large increase in capacity being a full order of magnitude can be understood by looking at the reaction mechanism as Si undergoes an alloying reaction with Li rather than an intercalation reaction such as with carbonaceous materials. Unfortunately there is also a negative side to this alloying reaction which has prohibited its use in commercial batteries up until this point. Namely the anode material expands widely in volume (up to 275%). A bulk layer of Si would crack up when cycling the battery. A method to circumvent this volume-expansion problem exists, consisting of nanosizing the Si to spherical particles of a few 100 nanometres. These particles survive cycling during charge and discharge cycles, yet reveal a new problem. Due to the large volume changes no stable SEI can be formed on the particles. As with each volume expansion the SEI would crack and reveal new exposed silicon surface to the electrolyte. Thus each cycle more SEI is formed and lithium is irreversibly consumed. Using this silicon in a full cell would quickly deplete the available lithium. In order for silicon to be considered an alternative for commercial batteries a solution to this problem must be found. [3-6] In this work the authors demonstrate a novel way to combine the high capacity of silicon and the stable surface of carbon. The route of preference for this goal is the synthesis of a core/shell particle. However conventional core/shell particles would have the same problem as the SEI formation. Namely the shell would crack with each volume expansion rendering the protective surface ineffectual. To alleviate this problem free space must be introduced in the core/shell particle into which the silicon can expand freely to allow for the large volume expansion. This has been accomplished by the conformal coating of a sacrificial alumina layer on top of the silicon particles using a surfactant controlled synthesis step via the thermal decomposition route of a suitable aluminium precursor. Controlling the reaction time and precursor concentration allows for optimal control of the resulting coating so this can be matched to accommodate the volume expansion.On top of these silicon alumina core/shell particles a carbon layer is deposited by firing an aliphatic precursor. Conformal coating is achieved by dispersion in solution using the precursor as a surfactant. In a final step the alumina layer can be removed by a mild acidification. This technique results in a core/void/shell particle which can absorb the volume expansion internally and present a stable SEI forming carbon surface to the electrolyte. Electrochemical characterizations were carried out on the coin cell level showing a decrease in the irreversible capacity on the first cycles as well as enhanced capacity retention during lifetime testing. Total capacity was less than for pure silicon based anodes due to the need to incorporate inactive material in the formation of the core/shell particles. The novelty of this research lies in the use of alumina as the sacrificial layer, thus requiring only a mild acid treatment. As previous core/shell designs have made extensive use of TEOS based silica growth, thus requiring an aggressive hydrogen fluoride. In contrast the here proposed route requires only hydrogen chloride which does not corrode the underlying silicon particles. [7,8] [1] T. Nagaura and K. Tozawa, Prog. Batteries Sol. Cells. 9, 209[2] J.L. Tirado, Mater. Sci. Eng. R. 40, 103[3] A. N. Dey, J Electrochem. Soc. 118(10), 1547[4] Tian et. al., J. Electrochem. Soc. 156(3) A187-A191[5] Besenhard et. al., J. Power Sources 67, 87[6] Winter et. al., Adv. Mat. 10, 725[7] Hiu et. Al., Nano Lett. 2012, 12, 904−909[8] Cui et. Al., Nature Nanotech 2012, 7, 310-315

Nanostructured Si Alloys Via Ethanol Delithiation

Introduction Si-based alloys are potential candidates as high energy density negative electrodes in Li-ion batteries. Such alloys have high theoretical capacity but also have high volume expansion, which can lead to cell fade. It has been shown previously that amorphous Si (a-Si) synthesized by chemical or physical deposition has improved cycling performance compared to crystalline Si (cr-Si) [1, 2]. Typically, a-Si is made by ball milling or atomic deposition techniques. Templating methods have also been employed to make nanostructured Si alloys that include void space in which the Si can expand [3, 4]. Such alloys can perform well as negative electrodes in Li cells. An inexpensive route for synthesizing bulk quantities of a-Si or nanostructured Si alloys is desirable. In this study, a new chemical delithiation method employing ethanol as an oxidizing agent was applied to prepare bulk quantities of a-Si from Li-Si compounds. The a-Si formed was found to have a unique exfoliated layered structure, which has lower volume expansion than cr-Si and improved cycling characteristics. C-Si and Fe-Si alloys were also synthesized by the delithiation of C-Li-Si and Fe-Li-Si alloys using this chemical delithiation method. When tested as negative electrodes in Li cells, the C-Si and Fe-Si alloys showed superior electrochemical characteristics and lower volume expansion than cr-Si. Experimental Li12Si7, Li7Si3, Li13Si4 or Li22Si5 compounds were first prepared in an arc furnace from the elements. Ethanol was then used to delithiate the Li-Si compounds under an Ar atmosphere. After the resulting slurry was washed with distilled water, a-Si was recovered with a 70% yield. C-Li-Si and Fe-Li-Si precursors with serial C: Si or Fe: Si stoichiometric ratios were prepared by ball milling. Ethanol was then used to delithiate the C-Li-Si or Fe-Li-Si alloys under an Ar atmosphere. After the resulting products were washed with distilled water, C-Si and Fe-Si alloys were recovered with 79% and 70% yields, respectively. Electrode slurries were prepared by mixing active materials (a-Si, C-Si or Fe-Si), carbon black and polyimide in a volume ratio of 62.5/18/19.5 in N-methyl pyrrolidinone. Electrode disks were punched from the coating foil and heated in a tube furnace for 3h at 300 °C under an Ar flow. 2325 coin-type cells were assembled in an Ar-filled glovebox with a Li counter/reference electrode. All cells were cycled between 5~900 mV with a Maccor Series 4000 Automated Test System. Results a-Si prepared from ethanol delithiation of Li12Si7, Li7Si3, Li13Si4, and Li22Si5 resulted in layered products, except in the case of Li22Si5, which was composed of dense particles. Figure 1 shows an SEM image of a-Si prepared from ethanol delithiation of Li12Si7. a-Si prepared from ethanol delithiation of Li12Si7 had the most orderly layered structure, with the layers being highly exfoliated. All a-Si samples had superior cycling performance and lower volume expansion compared to cr-Si. Figure 2 shows the cycling performance of an a-Si electrode prepared from ethanol delithiation of Li12Si7 and a cr-Si electrode. It is thought that the porous layered structure of these delithiated materials can accommodate the Si volume expansion during lithiation, resulting in low overall particle expansion and improved cycling performance. Remarkably, C-Si and Fe-Si alloys made by the delithiation of ball milled C-Li-Si or Fe-Li-Si alloys contained very low silicide or carbide content. Instead the alloys were primarily composed of a nano-composite of elemental C and Si or Fe metal and Si. This was confirmed by X-ray diffraction and Mössbauer spectroscopy. These alloys have a completely different nanostructure than conventional ball milled Si-based alloys, in which carbon and Fe are typically completely reacted to form carbides and silicides. Conclusions The alcohol delithiation method represents an effective means of producing Si-based alloys as negative electrode materials for Li cells. The unique nanostructures of these alloys and their electrochemical performance will be discussed.

High Energy and Stable Li-Ion Battery Anodes Enabled with 3D Si/C Particulate Nanocomposites Intenally-Wired with Graphene Networks

Silicon is very promising anode materials not only for boosting the energy density of lithium-ion batteries (LIBs) but for replacing the dendrite forming lithium metal anodes in lithium metal free Li-O2and Li-S batteries [1-3]. However, it is challenging to design silicon-based anodes exhibiting stable cycling behavior, high volumetric and specific capacity, and low volume expansion. In this study, we proposed that a sol–gel process can serve as a facile platform for composite materials of high lithium storage capacity. These composite materials consist of silicon nanoparticles (SiNPs) coated with carbon, a small graphene network interconnecting these nanoparticles to form condensed micro-sized particles, and a large fraction of void spaces between nanoparticles and graphene networks in these composites. Since, Si/C composites are internally wired with graphene networks, they are denoted as Si/C-IWGNs hereafter. The Si/C-IWGN samples were simply prepared by carbonizing the composite gels formed in aqueous mixtures consisting of SiNPs and resorcinol (R)–formaldehyde (F) as the carbon precursor and a small amount of graphene oxide (GO) in one-pot reactions. Various Si/C-IWGN samples were prepared with different contents of SiNPs (40 or 50 wt%) and graphene (1, 5 and 10 wt%). Two types of gelation catalysts (C), Na2CO3 or NH4OH, with different concentrations (R/C ratio = 100–500 in molar) were used for forming composite gels. Various electrochemical responses of Si/C-IWGNs, such as cycling stability, volumetric as well as specific capacity, coulombic efficiency, and electrode thickness increase, are thoroughly compared with those of the following reference samples: (1) control composites, Si/C composites, which were prepared without GO addition in the gel formation process and (2) commercial graphite. Finally, we have demonstrated a hybrid strategy to develop a reliable and low cost anode material consisting of mixtures of high capacity Si/CIWGNs and commercial graphite. The characterization and electrochemical responses of this novel composite suggest that graphene networks in Si/C-IWGNs not only provide electrical networks but also generate void spaces (Fig. 1a~c), which are very effective in absorbing large volume expansions of Si to the level comparable to that of commercial graphite (Fig. 1d, inset). Thereby, graphene networks effectively tackled the issue of common electrode pulverization and ensured the cycling stability of Si-based anodes (Fig. 1d) [4]. Compared to commercial graphite, a properly designed Si/C-IWGN composite material exhibited about 420% increase in specific capacity and about 141% increase in volumetric capacity, which was determined on the basis of electrode weight or volume. We devised a reliable and cost-effective hybrid anode using a mixture of Si/C-IWGN and commercial graphite. Si–Gr is a hybrid that offers the capacity level (800–1000 mAh g-1) required to improve the energy density of current LIB cells. Moreover, the volumetric capacity of the Si–Gr electrode is 161% higher than that obtained from commercial graphite [4]. The Si–Gr hybrid also has excellent cycling stability. We conclude that the preparation of Si/C-IWGNs is a scalable process. Moreover, owing to the remarkable electrochemical responses of Si/C-IWGNs, it could be used in manufacturing energy storage devices of high energy density and long cycle life. [1] N.Liu, Z. Lu, J. Zhao, M.T. McDowell, H.-W. Lee, W. Zhao, and Yi Cui, Nat. Nanotechnol., 9, 187-192 (2014). [2] C. Chae, H.-J. Noh, J. K. Lee, B. Scrosati, and Y.-K. Sun, Adv. Funct. Mater,, 24, 3036-3042 (2014). [3] S.-K. Lee, S.-M. Oh, E. Park, B. Scrosati, J. Hassoun, M.-S. Park, Y.- J. Kim, H. Kim, I. Belharouak, and Y.-K. Sun, Nano Lett., 15, 2863-2868 (2015). [4] J. Kim, C. Oh, C. Chae, D.-H. Yeom, J. Choi, N. Kim, E.-S. Oh, and J. K. Lee, J. Mater. Chem. A., 3,18684-18695 (2015). Figure 1. (a) SEM image, (b) TEM image, (c) SEM image of particle cross-section and (d) cycling stability of Si/C and Si/C-IWGNs (Inset shows electrode thickness changes). Figure 1

Flower-like Coo Microstructures Embedded in 3D Interconnected Graphene Hydrogel As Efficient Anode Material for Lithium-Ion Batteries

Although numerous rechargeable battery technologies have been developed and successfully demonstrated, Lithium-ion batteries still remain at the forefront, both in terms of its performance, and in its span of applications. However, despite their commercialization, the Li-ion industry is still limited by the choices available for anode materials. Graphite, with its high specific capacity, good rate capability, low irreversible capacity, low volume expansion during lithiation, and good electronic conductivity, still remains an ideal choice as an anode material for Li-ion batteries.[1] Nevertheless, owing to the safety issues with graphite,[2] an alternative for its use as an anode material has always been sought after. A considerable effort has already gone into the development of Li-alloys and other intermetallic alloys such as tin, antimony, aluminium etc. with their attractive gravimetric capacity.[3] However, with the huge volume expansion issues, alloying materials have their own limitation that prevented their widespread application and commercialization. Further, research efforts began on metal oxides of the type MO as anodes for Li-ion batteries,[4] owing to their widespread availability, ease in synthesis and only moderate safety concerns in comparison to the graphite materials. Among these metal oxides, Cobalt oxide, CoO is of particular interest because of its high theoretical capacity of 715 mAh g-1.[5] Several morphologies of CoO have been shown to have a high specific capacity and excellent cyclic stability against lithium, and there is a continued interest in developing innovative morphologies for their successful application in Li-ion batteries. However, as is the case with several other materials, Cobalt oxide suffers from particle aggregation and huge volume change upon Li-ion insertion and extraction during the conversion reactions.[6]This consequentially leads to deterioration of electrical contact between CoO particles and eventually causes the capacity to fade. Therefore, it becomes important to develop appropriate methods and composite materials that improve conduction between the cobalt oxide particles, and thereby enable them to be considered as ideal candidates for Li-ion battery anodes. Numerous carbonaceous composites of cobalt oxides have been shown to improve the capacity and maintain the cyclic stability of cobalt oxide particles. Graphene hydrogel is a new class of material that possesses inherent mechanical stability and still retains the superior conducting properties of graphene.[7] This would act as a three-dimensional support for materials embedded in it thereby addressing the volume expansion issue in addition to providing improved conductivity. Herein, we report the synthesis of a new 3D networked completely interconnected hybrid material with flower-like cobalt oxide (CoO) embedded on graphene hydrogel matrix, by using hydrothermal technique, and its subsequent application as anodes for Li-ion batteries. The electrochemical studies were carried out in the voltage range of 0.01–3.0 V versus Li/Li+ by using galvanostatic cycling, cyclic voltammetry and electrochemical impedance spectroscopy. The electrochemical performance of this hybrid material has been compared with the pristine cobalt oxide flowers. The 3D CoO–graphene hydrogel sample exhibited excellent electrochemical properties when studied as an anode for LIB, with high reversible specific capacity (1010 mAh g − 1 over 100 cycles), long cycling lifetime, and good rate capability (300 mAh g − 1 at 1.6 A g − 1). The unique flower-like morphology and its cross-linking with the rGO sheets enable enhanced interfaces leading to shorter Li + diffusion and buffering against volume expansion upon lithiation/delithiation, thus resulting in improved electrochemical performances for such CoO microstructures. The obtained electrochemical results are promising and the synthesis strategy could easily be extended to form 3D networked macrostructures with other metal oxides.

Novel Li-Titanate Anode Thin Film Structures for Li-Garnet All Solid State Batteries

Next generation energy storage devices for stationary as well as mobile electronics will not only need high gravimetric and volumetric capacity, but also long term stability even in rough environments at elevated temperature. Here, all solid state batteries based on Li-garnet structures are shown as interesting model systems that: i.) can partially use industrial waste heat to increase charging times (increased Li+ diffusion) for stationary, ii.) can integrate new high capacity electrode materials which show conventionally a low stability in standard liquid/polymer based Li-batteries, iii.) are easy transferrable to model thin film battery structures for powering of portable electronics. Going all-solid-state opens up completely new pathways for chip integration and downscaling to the sub-micron range for high energy densities to battle supercapacitors. From a materials perspective, cubic garnet Li7La3Zr2O12-based structures are among the fastest conducting solid state electrolytes[1]. Moreover, their inherent compatibility with metallic Lithium, stability in a wide voltage range as well as their Arrhenius-activated conduction mechanism support their prospering interest for all solid state large-scale and future microbatteries. On the electrode side, Li4Ti5O12 is known as one of the most stable anode material due to its remarkably low volume expansion upon lithiation/delithiation and its good cycle performance [2]. We hereby report our latest progress on nanostructuring different promising anode thin films of Li4Ti5O12 / TiO2 mixed-phase deposited by pulsed laser deposition and constructed bilayer half-cells batteries systems with Li7La3Zr2O12 pellets as the electrolyte. Rate capability studies as well as galvanostatic cycling of this system showed promising initial capacity and acted as a case study for the well-known Li4Ti5O12 thin film anode, shown its good compatibility with the investigated solid garnet electrolyte. Near-order phenomena could be tracked by Raman spectroscopy and gave insight into the process of lithiation and delithiation. To the best of our knowledge, no such study has yet been reported in literature. However, degradation and ageing effects still remain challenging and will be discussed.

Fe3O4 Nanoparticles on MWCNTs Backbone for Lithium Ion Batteries

A composite electrode made of iron oxide nanoparticles/multi-wall carbon nanotube (iNPs/M) delivers high specific capacity and cycle durability. At a rate of 200 mA g−1, the electrode shows a high discharge capacity of ~ 664 mAh g−1 after 100 cycles, which is ~ 70% of the theoretical capacity of Fe3O4. Carbon black, carbon nanotube, and graphene as anode materials have been explored to improve the electrical conductivity and cycle stability in Li ion batteries. Herein, iron oxide nanoparticles on acid treated MWCNTs as a conductive platform are combined to enhance the drawbacks of Fe3O4 such as low electrical conductivity and volume expansion during the alloying/dealloying process. Enhanced performance was achieved due to a synergistic effect between electrically 3D networks of conductive MWCNTs and the high Li ion storage ability of Fe3O4 nanoparticles (iNPs). Key words: Iron oxide, Nanaocomposite, Microwave synthesis, Anode

Nitrogen-doped Carbon Coated Porous Silicon as High Performance Anode Material for Lithium-Ion Batteries

An effective approach to generate nitrogen-doped carbon coating layer on porous silicon (CN@P-Si), one of most promising anode materials for lithium-ion batteries, was addressed in this study to minimize their intrinsic drawbacks of low electrical conductivity and large volume expansion. The resulting enhanced electrochemical performance of the cell using the prepared CN@P-Si materials is attributed to the suppression of volume expansion and formation of the stable solid electrolyte interface by the combination of the porous structure and nitrogen-doped carbon coating layer during the repeated lithiation and delithiation process. After 100 cycles at 0.8Ag−1, the capacity retention is 82% in contrast to 69% for the non-coated samples. Even at the increased discharge current of 20Ag−1, the cell with CN@P-Si electrode delivers a high specific capacity of 1904mAhg−1. After 100 cycles, the P-Si electrode with pores shows huge pulverization; in contrast the CN@P-Si electrode remains intact with reasonably low volume expansion. Nitrogen-doped carbon coating layer on porous Si surface successfully suppress the pulverization of CN@P-Si electrode owing to its shielding capability. These results suggest that CN@P-Si is an attractive candidate for a high-capacity anode for lithium-ion batteries.

Ab Initio Study of Phosphorus Anodes for Lithium- and Sodium-Ion Batteries

Phosphorus has received recent attention in the context of high-capacity and high-rate anodes for lithium- and sodium-ion batteries. Here, we present a first-principles structure prediction study combined with NMR calculations, which gives us insights into its lithiation/sodiation process. We report a variety of new phases found by the ab initio random structure searching (AIRSS) and the atomic species swapping methods. Of particular interest, a stable Na5P4–C2/m structure and locally stable structures found less than 10 meV/f.u. from the convex hull such as Li4P3–P212121, NaP5–Pnma, and Na4P3–Cmcm. The mechanical stability of Na5P4–C2/m and Li4P3–P212121 has been studied by first-principles phonon calculations. We have calculated average voltages, which suggest that black phosphorus (BP) can be considered as a safe anode in lithium-ion batteries due to its high lithium insertion voltage, 1.5 V; moreover, BP exhibits a relatively low theoretical volume expansion compared with other intercalation anodes, 2...

Theoretical prediction, preparation, and mechanical properties of YbB6, a candidate interphase material for future UHTCf/UHTC composites

High melting point, low shear deformation resistance and high volume expansion upon oxidation are the basic requirements for interphase materials of future ultrahigh-temperature ceramic fiber reinforced ultrahigh-temperature ceramic matrix (UHTCf/UHTC) composites. YbB6 is one of the materials that possesses a combination of these properties. In this work, using a combination of first-principles calculations based on density functional theory and experimental investigations, low shear deformation resistance of YbB6 (theoretically predicted 81GPa, experimentally determined 80GPa) is confirmed. In addition, YbB6 has low Pugh's ratio G/B, low brittleness index M=Hv/KIC, but high damage tolerant index Dt=KIC×E/σb×Hv, which endow that cracks are arrested or deflected when propagated from the matrix if it was used as an interphase material for UHTCf/UHTC composites. Details on the preparation, structural features and mechanical properties (hardness, strength, fracture toughness) of YbB6 are also given.

Two-dimensional transition-metal oxide monolayers as cathode materials for Li and Na ion batteries.

Two-dimensional monolayers are attractive for applications in metal-ion batteries because of their low ion-diffusion barrier and volume expansion. In this work, we carry out a first-principles study on electrochemical and structural properties of two-dimensional (2D) oxide monolayers and investigate their applications in metal-ion batteries. 2D transition-metal oxide monolayers (MO2; M = Mn, Co, and Ni) with various ion-intercalation densities are systematically studied. Our calculations show that Li and Na atoms can easily be transported on the surfaces of the monolayers with low diffusion barriers because of the long binding distance. We find that Li2MO2 and Na2MO2 are stable because of negative intercalation energies and unsaturated specific energies. We show that MnO2 has the lowest diffusion barrier, highest specific capacity, and smallest lattice expansion under Li-intercalation, but lowest cell voltage. We also find that CoO2 shows the largest cell voltages in a wide range of ion-intercalation densities and smallest lattice expansion under Na-intercalation, and NiO2 only gives the highest cell voltage in Li2NiO2 and has the largest volume expansion. We further show that Li and Na atoms in Li2MO2 and Na2MO2 move from stable-adsorption sites to metastable sites on the surfaces of oxide monolayers to reduce lattice expansion, leading to reduced cell voltages. It is expected that metal-ion batteries with particular applications and performances can be achieved in the design of these oxide monolayers.

The effect of pH on the interlayer distances of elongated titanate nanotubes and their use as a Li-ion battery anode

Titanate nanotubes are promising materials for Li-ion battery anodes because of their special morphology and high specific surface areas. These titanates provide high rate capability and low volume expansion upon lithiation. More importantly, their tubular structure helps the transport of ions through the crystal. In this study, we synthesized elongated titanate nanotubes and modified their interlayer distances by changing the pH (2–13). For the structural characterization XRD, BET, SEM and TEM techniques were used. In addition, the effect of interlayer distance on energy capacity and rate capability was investigated. The highest interlayer distance was obtained at pH 10 and with decreasing pH, the interlayer distance dropped until reaching a pH value of 4. Conversely, the specific surface area reached its maximum value of 204 m2 g−1 at a pH of 4. Different from anatase (TiO2), titanate nanotubes had broad peaks in cyclic voltammograms suggesting a pseudocapacitive behavior. The sloping profiles of potential-capacity results also supported the pseudocapacitive property. For the titanate nanotubes obtained at pH 10, an initial discharge capacity of 980 mAh g−1 was achieved. More importantly, titanate nanotubes showed exceptional rate capabilities and the capacities stayed almost constant at high current rates because of their elongated structure. It was found that the interlayer distance and the elongated structure play an important role in the electrochemical performance of the material.

C-Doped TiO2-B Nanowires Derived from TiC As an Anode Materials for Lithium Ion Batteries with High Rate Performance

In the recent past nanostructured materials have been attracting much interest owing to their physical and chemical characteristics, which make them extremely suitable for a number of applications. In particular, one of the most promising applications is their use as electrode materials for rechargeable lithium ion batteries (LIB)1-2. Among the anode materials, Titanium dioxide (TiO2) has been deeply investigated for lithium intercalation/de-intercalation due to high rate capability, very good reversible capacity, low volume expansion ( <2% ) upon cycling and furthermore lost cost, high abundant and very safe lithium reaction potential ~ 1.5 V vs Li/Li+, owing to these characteristics, TiO2 anodes have been considered to target in EVs and HEVs application1-3. Recently, the various polymorphs of TiO2 (anatase, rutle, brookite and bronze) have been explored as efficient anodes for LIB3. In particular, TiO2-Bronze (TiO2-B) has been receiving significant interest due to its theoretical capacity of 335 mAh g-1. Importantly, TiO2-B manifests the major advantages of fast charging-discharging through a pseudo-capacitive mechanism in addition to the bulk diffusion, whereas other polymorphs of TiO2 mostly show intercalation of Li-ion through bulk diffusion controlled mechanism3. However, the low electronic conductivity and low rate of Li-ion diffusivity of TiO2 are key issues for a high rate capable anode. To overcome these issues, we report synthesis of carbon-doped TiO2-B nanowires by facile and inexpensive method without using external carbon source. The carbon doping was verified by UV–visible and X-ray photoelectron spectroscopy and further structure and morphology was investigated with X-ray diffraction, Raman spectroscopy and Scanning and Transmission microscopies. The electrochemical performances of the C doped and undoped TiO2-B nanowires were tested by galvanostatic charge/discharge cycling, cyclic voltammetry, and electrochemical impedance spectroscopy. This novel C-doped materials presented high capacities and higher rate capability in electrochemical cycling experiments with respective to undoped material. This is attributed to the reduction of Li-ion diffusion path lengths along with improving electrical conductivity of TiO2-B nanowires. The electrochemical experiments demonstrated that C-TiO2-B nanowires electrodes exhibited superior lithium storage capacity of ~306 mAh g-1 at current rate of 0.1C as well as excellent rate ability of ~160 mAh g-1even at high current rate of 10C after 1000 cycle in lithium-ion batteries.

Nanotube-Constructed Li4Ti5O12-TiO2 Hybrid Spheres for Lithium Ion Batteries

Introduction Spinel Li4Ti5O12 and anatase TiO2 have been regarded as two typical alternative anode materials for rechargeable lithium-ion batteries (LIBs) to the commercial graphite because of their better safety and low volume expansion.1-3 The flat lithium insertion potential plateau of spinel Li4Ti5O12 locates at 1.55 V, which is above the solid electrolyte interface (SEI) and the lithium dendrite formation potentials, thus making it much safer. Also, the spinel Li4Ti5O12 is “zero strain” insertion, which endows the material a high potential of long cycle life. Similarly, anatase TiO2 features a potential plateau of ~1.7 V along with a low volume expansion of 3-4%. More importantly, the reduction of the particle size to nanoscale allows nearly 1 Li+ insertion into the anatase host structure, resulting in a high capacity of more than 300 mA h g- 1 theoretically. By combining the two materials, high safety and long cycle life as well as high capacity are expected. However, the instinct electronic conductivity for both materials is very low.4-7 Here, we report on the large-scale fabrication of nanotube-constructed Li4Ti5O12-TiO2 hybrid spheres (L-T-SPs), and the evaluation of their lithium storage properties. The hybrid exhibits a high capacity and long cycle life, benefitting from the tiny tubular morphology, defects in the grain boundary of the Li4Ti5O12-TiO2 hybrid and the synergistic effects of the two phases. Experimental Typically, the L-T-SPs product was prepared by a modified hydrothermal route, followed by an ion-exchange and post annealing processes. The microstructure of the L-T-SPs product were determined by scanning electron microscopy (SEM). The working electrodes were fabricated by mixing the L-T-SPs material, super P and polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone (8:1:1), and then coated onto a Cu foil. A lithium foil was used as the counter and reference electrode, Celgard 2300 as the separator, and 1 M LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1) as the electrolyte. Galvanostatic charge-discharge measurements were performed on a Land Battery Measurement System (Land, China) at various current densities. Results and Discussion The synthesis process is schematically illustrated in Fig. 1a. The titanic acid (HTO) precursor was firstly treated by LiOH to exchange the H+ ions with Li+ ions, forming an intermediate containing Li, Ti and O elements (Li-Ti-O spheres). The Li4Ti5O12-TiO2 product was obtained by post annealing the intermediate. The SEM images in Fig. 1b and 1c shows the spherical morphology of the product. Each individual urchin-like microsphere consists of numerous tiny nanotubes. The lithium storage performance of the as-prepared L-T-SPs product was evaluated using lithium half-cells. Fig. 1d demonstrates the initial two cycles of the galvanostatic charge-discharge profiles. There are two distinct voltage plateaus located at ~1.7 and 1.55 V in the discharge process, assigned to the insertion of lithium into the anatase and the Li4Ti5O12 host structures, respectively. The cycle performances of the L-T-SPs electrode are presented in Fig. 1e. Capacities of ~140 mA h g- 1 at 5 C and ~110 mA h g- 1 at 20 C can be obtained. Moreover, the capacity at 20 C retained for 100 cycles without obvious decay, indicating excellent cyclability of the L-T-SPs electrode. The tiny tubular microstructure integrated with the defects in the grain boundary and the synergy between the spinel Li4Ti5O12 and anatase TiO2 contribute to the enhanced lithium storage performance of the L-T-SPs electrode. Figure captions: Figure 1. (a) Schematic illustration of the formation process for the L-T-SPs product, (b,c) SEM images of the L-T-SPs product, (d,e) The charge-discharge profiles of the L-T-SPs electrodes in the initial two cycles and their cycle performances at 5 and 20 C. References 1 M. Wagemaker, W. J. H. Borghols and F. M. Mulder, J . Am . Chem . Soc . 2007, 129, 4323-4327. 2 V. Gentili, S. Brutti, L. J. Hardwick, A. R. Armstrong, S. Panero and P. G. Bruce, Chem. Mater. 2012, 24, 4468-4476. 3 Y. Q. Wang, L. Gu, Y. G. Guo, H. Li, X. Q. He, S. Tsukimoto, Y. Ikuhara and L. J. Wan, J . Am . Chem . Soc . 2012, 134, 7874-7879. 4 C. J. Chen, X. L. Hu, P. Hu, Y. Qiao, L. Qie, Y. H. Huang, Eur. J. Inorg. Chem . 2013, 30, 5320. 5 A. G. Dylla, G. Henkelman, K. J. Stevenson, Acc. Chem. Res. 2013, 46, 1104. 6 C. J. Chen, X. L. Hu, Y. Jiang, Z. Yang, P. Hu, Y. H. Huang, Chem . Eur. J. 2014, 20, 1383. 7 E. Kang, Y. S. Jung, G. H. Kim, J. Chun, U. Wiesner, A. C. Dillon, J. K. Kim and J. Lee, Adv . Funct . Mater . 2011, 21, 4349-4357. Figure 1