No abstract

No abstract

Taking advantage of zeolitic imidazolate framework (ZIF-8), ZnS-SbS@C core-double shell polyhedron structure is synthesized through a sulfurization reaction between Zn dissociated from ZIF-8 and S from thioacetamide (TAA), and subsequently a metal cation exchange process between Zn and Sb, in which carbon layer is introduced from polymeric resorcinol-formaldehyde to prevent the collapse of the polyhedron. The polyhedron composite with a ZnS inner-core and SbS/C double-shell as anode for sodium ion batteries (SIBs) shows us a significantly improved electrochemical performance with stable cycle stability, high Coulombic efficiency and specific capacity. Peculiarly, introducing a carbon shell not only acts as an important protective layer to form a rigid construction and accommodate the volume changes, but also improves the electronic conductivity to optimize the stable cycle performance and the excellent rate property. The architecture composed of ZnS inner core and a complex SbS/C shell not only facilitates the facile electrolyte infiltration to reduce the Na-ion diffusion length to improve the electrochemical reaction kinetics, but also prevents the structure pulverization caused by Na-ion insertion/extraction. This approach to prepare metal sulfides based on MOFs can be further extended to design other nanostructured systems for high performance energy storage devices.

No abstract

attracted increased attention as a new rechargeable battery system as an alternative to LIBs because of the abundant sodium resources in the earth and low cost of sodium compounds. [3][4][5][6] However, it should be stressed that the lower energy capacity and poor cycling stability of SIBs than that of LIBs are the major obstacles for their potential large scale energy storage applications.In order to improve the energy density of SIBs, it is of great importance to rationally design electrode materials with high specifi c capacities and appropriate redox potentials. Up to date, various interlayered transition metal cathode materials for SIBs have been developed successfully, including NaCoO 2 , [ 7 ] NaFePO 4 , [ 8 ] NaMnO 2 , [ 9 ] and Na 3 V 2 (PO 4 ) 3 [10][11][12] by replacing Li ions with Na ions. However, high performance SIBs anodes are still challenging. Previous study shows that pure graphite SIBs anode does not demonstrate an excellent performance. [ 4 ] Ge and Fouletier [ 13 ] reported the electrochemical behavior of graphite SIBs anode only shows a capacity of only about 35 mA h g −1 . Kim et al. [ 14 ] improved the Na ion storage performance of SIBs anode based on natural graphite by using an ether-based electrolyte system. However, the reversible capacity is still lower, only about 150 mA h g −1 . Therefore, in order to obtain SIBs with high specifi c capacity, new anode materials with high capacity and low redox potential should be introduced. [ 4 ] Na alloy-based anodes have attracted much attention owing to the appropriate redox potentials and higher gravimetric and volumetric specifi c capacities, such as Sb, [15][16][17][18][19] Ge, [ 20 ] Sn, [21][22][23] and P [24][25][26][27][28] based materials. Sb shows excellent stable capacity retention performance because of its smaller volume expansion and reduced anisotropic mechanical stress. [ 19 ] However, it is hindered by its low theoretical specifi c capacity of 660 mA h g −1 and high price. [ 4,[15][16][17][18] Ge also cannot meet the requirement of SIBs due to its lower theoretical capacity of only 396 mA h g −1 . [ 6,20 ] Sn has the high electrical conductivity, low cost, environmental friendliness, and appropriate low chargedischarge potentials versus Na + /Na. [21][22][23] Sn can theoretically deliver a high capacity of 847 mA h g −1 , which corresponds to Different from previously reported mechanical alloying route to synthesize Sn x P 3 , novel Sn 4 P 3 /reduced graphene oxide (RGO) hybrids are synthesized for the fi rst time through an in situ low-temperature solution-based phosphorization reaction route from Sn/RGO. Sn 4 P 3 nanoparticles combining with advantages of high conductivity of Sn and high capacity of P are homogenously loaded on the RGO nanosheets, interconnecting to form 3D mesoporous architecture nanostructures. The Sn 4 P 3 /RGO hybrid architecture materials exhibit signifi cantly improved electrochemical performance of high reversible capacity, high-rate capability, and excellent cycling performance as sodium ion batterie...

We develop a facile synthesis route to prepare Cu doped hollow structured manganese oxide mesocrystals with controlled phase structure and morphology using manganese carbonate as the reactant template. It is shown that Cu dopant is homogeneously distributed among the hollow manganese oxide microspherical samples, and it is embedded in the lattice of manganese oxide by substituting Mn(3+) in the presence of Cu(2+). The crystal structure of manganese oxide products can be modulated to bixbyite Mn2O3 and tetragonal Mn3O4 in the presence of annealing gas of air and nitrogen, respectively. The incorporation of Cu into Mn2O3 and Mn3O4 induces a great microstructure evolution from core-shell structure for pure Mn2O3 and Mn3O4 samples to hollow porous spherical Cu-doped Mn2O3 and Mn3O4 samples with a larger surface area, respectively. The Cu-doped hollow spherical Mn2O3 sample displays a higher specific capacity of 642 mAhg(-1) at a current density of 100 mA g(-1) after 100 cycles, which is about 1.78 times improvement compared to that of 361 mA h g(-1) for the pure Mn2O3 sample, displaying a Coulombic efficiency of up to 99.5%. The great enhancement of the electrochemical lithium storage performance can be attributed to the improvement of the electronic conductivity and lithium diffusivity of electrodes. The present results have verified the ability of Cu doping to improve electrochemical lithium storage performances of manganese oxides.

Nitrogen-doped carbon (NDC) spheres with abundant 22 nm mesopores and 0.5 nm micropores are obtained by directly carbonization of nitrogen-contained metal organic framework (MOF) nanocrystals. Large S8 and small S2-4 molecules are successfully infiltrated into 22 nm mesopores and 0.5 nm micropores, respectively. We successfully investigate the effect of sulfur immobilization in mesopores and micropores on the electrochemical performance of lithium-sulfur (Li-S) battery based on NDC-sulfur hybrid cathodes. The large S8 molecules in 22 nm mesopores can be removed by a prolonged heat treatment, with only small molecules of S2-4 immobilized in micropores of NDC matrices. The NDC/S2-4 hybrid exhibits excellent cycling performance, high Coulombic efficiency, and good rate capability as cathode for Li-S batteries. The confinement of smaller S2-4 molecules in the micropores of NDS efficiently avoids the loss of active sulfur and formation of soluble high-order Li polysulfides. The porous carbon can buffer the volume expansion and contraction changes, promising a stable structure for cathode. Furthermore, N doping in MOF-derived carbon not only facilitates the fast charge transfer but also is helpful in building a stronger interaction between carbon and sulfur, strengthening immobilization ability of S2-4 in micropores. The NDS-sulfur hybrid cathode exhibits a reversible capacity of 936.5 mAh g(-1) at 100th cycle with a Coulombic efficiency of 100% under a current density of 335 mA g(-1). It displays a superior rate capability performance, delivering a capacity of 632 mAh g(-1) at a high rate of 5 A g(-1). This uniquely porous NDC derived from MOF nanocrystals could be applied in related high-energy storage devices.

To eliminate capacity-fading effects due to the loss of sulfur cathode materials as a result of polysulfi de dissolution in lithium-sulfur (Li-S) cells, 3D carbon aerogel (CA) materials with abundant narrow micropores can be utilized as an immobilizer host for sulfur impregnation. The effects of S incorporation on microstructure, surface area, pore size distribution, and pore volume of the S/ CA hybrids are studied. The electrochemical performance of the S/CA hybrids is investigated using electrochemical impedance spectroscopy, galvanostatical charge-discharge, and cyclic voltammetry techniques. The 3D porous S/CA hybrids exhibit signifi cantly improved reversible capacity, high-rate capability, and excellent cycling performance as a cathode electrode for Li-S batteries. The S/CA hybrid with an optimal incorporating content of 27% S shows an excellent reversible capacity of 820 mAhg −1 after 50 cycles at a current density of 100 mAg −1 . Even at a current density of 3.2C (5280 mAg −1 ), the reversible capacity of 27%S/CA hybrid can still maintain at 521 mAhg −1 after 50 cycles. This strategy for the S/CA hybrids as cathode materials to utilize the abundant micropores for sulfur immobilizers for sulfur impregnation for Li-S battery offers a new way to solve the long-term reversibility obstacle and provides guidelines for designing cathode electrode architectures.