The preparation and electrochemical storage behavior of MoS2 nanodots--more precisely single-layered ultrasmall nanoplates--embedded in carbon nanowires has been studied. The preparation is achieved by an electrospinning process that can be easily scaled up. The rate performance and cycling stability of both lithium and sodium storage were found to be outstanding. The storage behavior is, moreover, highly exciting from a fundamental point of view, as the differences between the usual storage modes--insertion, conversion, interfacial storage--are beneficially blurred. The restriction to ultrasmall reaction domains allows for an almost diffusion-less and nucleation-free "conversion", thereby resulting in a high capacity and a remarkable cycling performance.

Even though signifi cant enhancement of secondary lithium batteries has been achieved in the last decades, it remains a challenge to develop safe batteries for electric/hybrid vehicles with high energy and power density at lower cost. [1][2][3] As far as the anode is concerned, graphite, still the dominant anode material in commercial batteries, suffers from low kinetics at high power. [ 4 , 5 ] In addition, the passivating solid electrolyte interphase (SEI) formed on graphite in the initial charge due to the electrolyte decomposition, consumes a signifi cant amount of lithium irreversibly. The fact that the potential for lithium intercalation in graphite is close to metallic lithium is favorable for achieving a high voltage of the battery but also leads to the possibility of lithium plating during fast charge. Thus, lithium dendrite formation has to be concerned with which is an enormous safety hurdle for application in large electric vehicles. To avoid lithium plating, the anode charging potential must be less negative.In this regard, Li 4 Ti 5 O 12 appears to be an attractive alternative owing to phase thermodynamics structure and chemical stability. However, the theoretical capacity of Li 4 Ti 5 O 12 is relatively low (175 mAh/g) according to only three lithium atoms being insertable into the spinel structure at 1.5 V. [ 6-, 10 ] Recently, Goodenough et al. proposed TiNb 2 O 7 as a competitor for Li 4 Ti 5 O 12 with a higher capacity and an operating voltage range in which SEI formation does not occur. [ 1 ] TiNb 2 O 7 has a layered monoclinic structure in the space group C2/m, in which Ti 4 + and Nb 5 + both occupy octahedral sites sharing corners and edges. Anti-site disorder is probable owing to similar ionic radii of Ti 4 + and Nb 5 + . According to ref [12], lithium can be reversibly inserted into the ( -I10) plane of the TiNb 2 O 7 primitive cell and occupying the interstitial site there. [ 11 , 12 ] The theoretical capacity for TiNb 2 O 7 is 387.6 mAh/g according to the 5 electron transfer reaction (Ti 4 + /Ti 3 + , Nb 5 + /Nb 3 + ). Previous studies showed a reversible capacity of 280 mAh/g at 0.1C in the voltage range of 1-3 V, already a marked enhancement compared to Li 4 Ti 5 O 12 . [ 11 ] However, the development of rechargeable lithium ion batteries with TiNb 2 O 7 as an anode has been limited due to its low electronic conductivity and ionic conductivity, [ 12 ] which restricts the electrochemical kinetics. Ti doping (through Nb substitution, Ti Nb ′ ) and carbon coating improved the composite electronic conductivity, such that a reversible capacity of ∼ 150 mAh/g was achieved for TiNb 2 O 7 at a 2C rate. [ 11 ] It has been well demonstrated that nanostructure plays a prominent role in lithium insertion kinetics, by facilitating transport owing to shorter or simpler diffusion paths for lithium ions. [13][14][15] Specifi cally, one-dimensional (1D) nanostructures such as nano-wires, -fi bers, -rods or -tubes are quite attractive for electrode materials due to large surface-to-volume ratio, fa...

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To improve the energy/power density of energy storage materials, numerous efforts have focused on the exploration of new structure prototypes, in particular metal-organic fameworks, Prussian blue analogues, open-framework oxides, and polyanion salts. Here we report a novel pyrochlore phase that appears to be useful as a high-capacity cathode for Li and Na batteries. It is an iron fluoride polymorph characterized by an intersecting tunnel structure, providing the space for accommodation and transport of Li and Na ions. It is prepared using hydrolyzable ionic liquids, which serve as reaction educts and structure-directing agents not only as far as the chemical structure is concerned but also in terms of morphology (shape, defect structure, electrode network structure). A capacity higher than 220 mA h g(-1) (for Li and Na storage) and a lifetime of at least 300 cycles (for Li storage) are demonstrated.

On the one hand, conversion reactions can typically transfer more than one electron per transition metal ion. On the other hand, nucleation and diffusion associated with it are severe.As a typical 2D layered materials, molybdenum disulfi de (MoS 2 ) is considered as an attractive host for energy storage, [4][5][6][7][8] besides its applications in other fi elds such as lubrication, [ 9 ] transistor technology, [ 10 ] photovoltaics [ 11 ] and catalysis. [ 12 ] Several studies have demonstrated its great potential as an anode material for lithium ion batteries because the reversible capacity for MoS 2 can reach a high value of 800-1000 mAh g −1 at low current density through proper morphology modifi cation. [13][14][15][16] In addition to the inherent problems of conversion reactions, MoS 2 suffers from various disadvantages. First, the poor electronic conductivity [ 17 ] of MoS 2 limits its rate performance. Second, substantial volume changes in the host matrix during charge-discharge cycle leads to pulverization and aggregation of electrode particles. [ 18 ] The way out of this problem is to use small mechanically isolated but electrochemically well connected particles. The better the electrochemical contacting, the lesser the geometrical demands with respect to the geometry of the electroactive mass. Some groups have attempted to reduce the size of MoS 2 particle, modify the morphology or synthesize few-layered or even single-layered MoS 2 in order to relax the strain, shorten the transport length and lower the barrier for lithium storage. [ 4,7,19,20 ] While others have tried to construct various MoS 2 -carbon composites [ 18,21 ] to buffer the volume change during cycling. In this context, various carbonaceous materials were chosen, such as graphene, [ 22,23 ] carbon nanotube, [ 24,25 ] conductive polymer [ 13 ] and porous carbon. [ 21 ] Excellent cycling performance has been achieved by using single-layered ultrasmall nanoplates of MoS 2 embedded in electrospun carbon nanofi bers. [ 8 ] Among the carbonaceous materials, graphene is considered as the most promising matrix because of its pronounced advantages, such as high electronic conductivity, good fl exibility and high chemical stability. [ 26 ] Until now, several MoS 2graphene composites with different structures have been designed and synthesized successfully, which demonstrates A 3D porous composite consisting of nano-0D MoS 2 , nano-1D carbon nanotubes (CNTs), and nano-2D graphene is successful prepared using an electrostatic spray deposition (ESD) technique. Depending on the preparation procedure either nanodots of amorphous MoS 2 (0.5-5 nm) or nanocrystalline few-layered MoS 2 (5-10 nm) bonded to graphene-carbon nanotubes backbone are obtained. These functionalized carbon nanotubes adhere to a porous graphene-based network. Such composites can be directly deposited on the current collectors without any binder or conductive additives to assemble a battery that shows superior rate performance and cycling stability. For nanodots, nucleation and diffusio...