[Show abstract][Hide abstract] ABSTRACT: One new ether-functionalized ionic liquid (IL) composed of pyrazolium cation with one 2-ethoxyethyl group and bis(trifluoromethylsulfonyl)imide anion was synthesized and characterized. The IL showed the lowest viscosity among all the reported pyrazolium ILs, and the value was 38.9 mPa s at room temperature. The conductivity of the IL was 3.48 mS cm−1 at 25 °C, and its electrochemical window was 4.4 V. Cycling performance of symmetric lithium cell was investigated for the IL electrolyte with 0.6 mol kg−1 of LiTFSI. Li/LiMn2O4 cell using the IL electrolyte owned good cycling and rate performances, and it was found for the first time that LiMn2O4 cathode was compatible with electrolyte based on ether-functionalized IL. By the characterizations of X-ray diffraction and scanning electron microscopy for fresh and cycled LiMn2O4 electrodes, it was inferred that the slow dissolution of LiMn2O4 in the IL electrolyte might happen during the charge–discharge processes.
[Show abstract][Hide abstract] ABSTRACT: Mesoporous lithium titanate microsphere anodes have been made by hydrothermal synthesis. Layered hydrous lithium titanate was obtained after hydrothermal reaction and Li4Ti5O12 microspheres assembled from nanosheets were subsequently formed by thermal treatment. This results in improved voltage profiles and charge/discharge dynamics. Mesoporous lithium titanate microspheres showed stable cycling performances, with high capacity retention (140 mAh g−1) even after 4000 cycles. In order to understand the functioning of this promising anode material at the molecular level, we used in-situ X-ray absorption spectroscopy (XAS). The XAS results verify the Ti conversion between Ti4+ and Ti3+ during charge/discharge cycling and demonstrate that this reduction is accompanied by small changes Ti–O distance but no detectable change in Ti–Ti distance. This anion re-arrangement suggests a structural explanation for the fact that this material is electrochemically very stable even under higher current density cycling.
Journal of Power Sources 12/2014; 268:294–300. DOI:10.1016/j.jpowsour.2014.06.018 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A peculiar nanostructure of encapsulation of SnO2/Sn nanoparticles into mesoporous carbon nanowires (CNWs) has been successfully fabricated by a facile strategy and confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffraction (XRD), BET, energy-dispersive X-ray (EDX) spectrometer, and X-ray photoelectron spectroscopy (XPS) characterizations. The 1D mesoporous CNWs effectively accommodate the strain of volume change, prevent the aggregation and pulverization of nanostructured SnO2/Sn, and facilitate electron and ion transport throughout the electrode. Moreover, the void space surrounding SnO2/Sn nanoparticles also provides buffer spaces for the volumetric change of SnO2/Sn during cycling, thus resulting in excellent cycling performance as potential anode materials for lithium-ion batteries. Even after 499 cycles, a reversible capacity of 949.4 mAh g−1 is retained at 800 mA g−1. Its unique architecture should be responsible for the superior electrochemical performance.
Particle and Particle Systems Characterization 09/2014; 32(3). DOI:10.1002/ppsc.201400160 · 3.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Titanium dioxide (TiO2) has received increasing attention as promising anode for lithium ion batteries because it offers a distinct safety advantage in comparison to commercialized graphite anodes, whereas it also suffer from the drawbacks of low practical capacity and relatively low electronic conductivity. Herein, one-dimensional mesoporous anatase TiO2 composed of nanocrystals prepared by a facile procedure is reported for the first time. Such peculiar architecture and intrinsical mesoporous can effectively improve pseudocapacitance charge storage, increase contact interface between the active materials and electrolyte, and enhance the structure stability during cycling, therefore contributing to good lithium storage and excellent cycling stability. A reversible capacity of 202.9 mAhg−1is obtained at 30 mAg−1 after 70 cycles. More importantly, 151 mAhg−1 can be obtained at 200 mAg−1 even after 500 cycles.
[Show abstract][Hide abstract] ABSTRACT: An imidazolium-based polymerized ionic liquid (PIL), poly(1-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonylimide)) is successfully synthesized via a new three-step process comprising the direct radical polymerization of the 1-vinylimidazole monomer, and subsequent quaternization reaction followed by an anion exchange procedure. Furthermore, polymer electrolytes are prepared by blending as-obtained PIL as the polymer host with an ionic liquid and LiTFSI salt. Electrochemical measurements demonstrate that compared with polymer electrolytes containing the PIL host synthesized by the conventional route, polymer electrolytes containing the PIL host obtained by new synthetic process exhibit significantly improved capacity and cycling performance, which is due to higher ionic liquid content.
Journal of Power Sources 07/2014; 258:150–154. DOI:10.1016/j.jpowsour.2014.02.057 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report here for the first time Sn-contained N-rich carbon nanowires, which are prepared via a facile and scalable procedure using poly-pyrrole as the carbon source. As-obtained nanowires with a diameter of about 50 nm crosslink with each other with enough void space, beneficial to accommodating lithiation induced volumetric change and mechanical stress. In particular, this product contains abundant nitrogen (9.8 wt.%), favorable for Li+ diffusion and storage. It therefore exhibits excellent cycling stability of 682.6 and 760.1 mAhg(-1) at 500 mAg(-1) after 200 and 600 cycles, respectively. It also delivers great high rate performance even at 10 Ag-1.
[Show abstract][Hide abstract] ABSTRACT: In this work, a new nanostructure of SnO2 nanoparticles (NPs) encapsulated into hollow TiO2 nanowires (SnO2@TiO2) has been successfully fabricated. This unique architecture intrinsically possess void space in between the TiO2 shell and SnO2 nanoparticle cores, as confirmed by XRD, XPS, SEM, TEM and HRTEM characterizations. The TiO2 shell of the composite can not only alleviate the pulverization and drastic volume change of the SnO2 NPs and maintain the structural integrity, but also contribute to the total capacity of the composite. Moreover, the void space can also accommodate the volume expansion of SnO2 and provide highly efficient channels for the fast transport of both electrons and lithium ion during discharge/charge cycling process. When tested as potential anode materials for lithium ion batteries, the as-prepared hollow TiO2 nanowires shell encapsulating SnO2 NPs architecture exhibits good lithium storage performance and excellent cyclability (which delivers a higher reversible capacity of 445 mAh g−1 at 800 mA g−1 after 500 cycles). The unique architecture should be responsible for the superior electrochemical performance.
Journal of Power Sources 05/2014; 253:9–16. DOI:10.1016/j.jpowsour.2013.12.049 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The mesoporous Li3V2(PO4)3@CMK-3 nanocomposite has been firstly synthesized by a sol–gel method. The X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen adsorption–desorption measurements show that the Li3V2(PO4)3@CMK-3 nanocomposite exhibits the pure monoclinic structure and mesoporous morphology. Li3V2(PO4)3 has particle sizes of <50 nm, and are embedded in the mesoporous channels as well as well dispersed on the CMK-3 surface. Electrochemical measurements demonstrate that the Li3V2(PO4)3@CMK-3 nanocomposite shows significantly better rate capability and cycling performance than the bulk Li3V2(PO4)3. In the potential range of 3.0–4.3 V, the Li3V2(PO4)3@CMK-3 nanocomposite delivers high initial discharge capacity of 130.0 mAh g−1 at 0.2 C, and maintain an initial discharge capacity of 119.5 and 107.8 mAh g−1 at 5 C and 10 C, respectively. After 300 cycles, it can still retain a discharge capacity of 95.4 and 73.5 mAh g−1 at 5 C and 10 C, respectively. The good electrochemical performance for the Li3V2(PO4)3@CMK-3 nanocomposite are related to the special mesoporous structure, nanosized particles, and the existence of conductive carbon matrix, thus leading to improvement in electron and lithium ion diffusivity.
Journal of Power Sources 05/2014; 253:294–299. DOI:10.1016/j.jpowsour.2013.12.080 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Li2MnSiO4/C composite is prepared by sol–gel method with Mn3O4 nanoparticle, and its carbon content, structure, and morphology are characterized. The results show that Li2MnSiO4/C exhibits pure phase with orthorhombic structure and the size of Li2MnSiO4 (20–30 nm) is smaller than Mn3O4 nanoparticle. As the cathode material of lithium-ion battery, Li2MnSiO4/C delivers an initial discharge capacity of about 240 mAh g−1 at the current density of 8 mA g−1, corresponding to 1.44 mol of Li+ per formula unit. The cycle performance of Li2MnSiO4/C at different current densities from 8 mA g−1–320 mA g−1 is studied, and it is found that the capacity retention is improved with the increasing of current density. Basing on the results of ex-situ X-ray diffraction measurement, it is inferred that low degree of irreversible distortion for Li2MnSiO4 may result in the improved capacity retention at high current density.
Journal of Power Sources 04/2014; 252:169–175. DOI:10.1016/j.jpowsour.2013.11.076 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Twenty-four new functionalized ionic liquids (ILs) based on trialkylimidazolium cations with the alkoxymethyl group at the N-1 position were synthesized and characterized. Physicochemical properties of these ILs, such as melting point, thermal stability, density, viscosity, conductivity, and electrochemical stability, were studied systematically. Twenty-one ILs appeared in the liquid state at room temperature, and 14 ILs showed a melting point lower than −60 °C. Introduction of the alkoxymethyl group at the N-1 position of trialkylimidazolium cations could not be more beneficial than that of the alkoxyethyl group for reducing viscosity. Li/LiFePO4 cells employing three trialkylimidazolium ILs with methoxymethyl-group-based electrolytes showed good discharge capacity and cycle stability at a current rate of 0.1 C. This is the first report of ILs with the alkoxymethyl group used as electrolytes without an additive for a lithium ion battery.
[Show abstract][Hide abstract] ABSTRACT: In this work, a new morphological nanostructure of the CNWs@ultrathin
SnO2 NSs@C composite has been successfully fabricated,
realizing the integration of two-dimensional ultrathin SnO2
NSs and one-dimensional CNWs. The nanosized ultrathin SnO2
NSs (thickness of ca. 1-3 nm) are uniformly distributed between one
dimension CNWs core and C shell, as confirmed by XRD, SEM, TEM and HRTEM
characterizations. When tested as potential anode materials for LIBs,
the as-prepared coaxial nanocable-like CNWs@ultrathin SnO2
NSs@C composite exhibits outstanding reversible capacity for lithium
storage (695 mAh g-1 after 40 cycles at 160 mA
g-1, 651 and 618 mAh g-1 after 80 cycles at 400
and 800 mA g-1, respectively). This intriguing architecture,
which integrates both electronic conductivity and buffering matrix
design strategies, contributing to enhanced lithium storage performance.
Journal of Power Sources 01/2014; 246:587-595. DOI:10.1016/j.jpowsour.2013.08.009 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Si has the second highest theoretical capacity among all the known anode materials for lithium ion batteries, whereas it is vulnerable to pulverization and crumbling upon lithiation/delithiation. Herein, Si mesoporous nanowires prepared by a scalable and cost-effective procedure are reported for the first time. Such nanowire morphology and mesoporous structure can effectively buffer the huge lithiation-induced volume expansion of Si, therefore contributing to excellent cycling stability and high-rate capability. Reversible capacities of 1826.8 and 737.4 mA h g(-1) can be obtained at 500 mA g(-1) and a very high current density of 10 A g(-1), respectively. After 1000 cycles at 2500 mA g(-1), this product still maintains a high capacity of 643.5 mA h g(-1).
[Show abstract][Hide abstract] ABSTRACT: Two series of room temperature ionic liquids, 1-alkyl-3-methylimidazolium tetrafluoroborate and 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (n = 2–4) as electrolytes were prepared and fundamental electrochemical properties of the neat ionic liquids and those mixed with an organic solvent (EC-DMC-DEC, 1:1:1, mass ratio) were investigated. It was found that the Arrhenius equation is approximately fit for the relationship between conductivity and temperature for neat ionic liquids within lower temperature range (298–323 K). The VTF interpretation describes the conductivity temperature dependence for the ionic liquids containing tetrafluoroborate anion more accurately than those containing bis(trifluoromethylsulfonyl)imide anion within wider temperature range. The potential windows are approximately 4.0 V for all these ionic liquids. Conductivities of the mixed electrolytes show a maximum value as the solution concentrations increase.
Chinese Science Bulletin 09/2013; 50(18). DOI:10.1007/BF03322792 · 1.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Graphene/Cu6Sn5 nanocomposite is successfully prepared via a facile one-pot method. Cu6Sn5 nanoparticles with the average size below 10 nm are homogeneously encapsulated into graphene nanosheets. Inactive Cu can release the volume expansion of Sn, prevent Sn from aggregation, and accommodate structural stress. Graphene can enhance mechanical properties, prevent the aggregation between Cu6Sn5 nanoparticles, and provide enough void space to buffer volume change of Cu6Sn5. Part of Cu6Sn5 nanoparticles possesses hollow structure, which is also favorable for volume buffer and stress accommodation. Due to such intriguing structure, it delivers great long term cycling stability and excellent high rate performance. Up to 411.4 mAh g−1 is obtained after 1600 cycles at a high current density of 500 mA g−1. The reversible capacity is as large as 220 mAh g−1 at 10,000 mA g−1 (merely 80 s for discharge or charge).
[Show abstract][Hide abstract] ABSTRACT: A new family of C-2 functionalized trialkylimidazolium ionic liquids with alkoxymethyl groups were synthesized and characterized. Their physicochemical properties including melting point, thermal stability, viscosity, conductivity, and electrochemical windows were systematically investigated. All of these functionalized trialkylimidazolium ionic liquids were liquids at room temperature, and most of them had melting points lower than −60 °C. At room temperature, 24 ionic liquids had viscosities lower than 90 cP, and the viscosities of IM2(1o2)2TFSA and IM1(1o2)2TFSA were 50.3 and 53.3 cP.
[Show abstract][Hide abstract] ABSTRACT: Using amorphous TiO microspheres as precursors, we obtain mesoporous TiO-Sn@C core-shell microspheres. Sn is encapsulated into a TiO matrix, and carbon is coated outside. This intriguing architecture can effectively buffer volume change and structural stress, thus contributing to excellent long-term cycling stability and superior high-rate cyclability.
Chemical Communications 03/2013; 49(27):2792-4. DOI:10.1039/c3cc40671g · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Six low-viscosity ionic liquids based on trialkylimidazolium cation with one or two ether groups and TFSA− anion are used as new electrolytes for lithium battery, and compared with three typical trialkylimidazolium ILs without ether group. It is found that ether group in trialkylimidazolium cation can have an obvious effect on properties of electrolyte and performances of lithium battery. Introducing of ether group into trialkylimidazolium cation can be benefit for lithium redox behavior on Ni electrode, and affect passivation layer between IL electrolyte and lithium metal. Li/LiFePO4 cells using these ether-functionalized IL electrolytes without additive have good battery performance, and IM(2o1)1(2o2)-TFSA electrolyte owns better rate property.
Journal of Power Sources 03/2013; 226:210–218. DOI:10.1016/j.jpowsour.2012.10.076 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fe2O3 microsphere is used as iron source and template to prepare Li2FeSiO4/C nanocomposite by a sol–gel method. The carbon content, structure, and morphology of the sample are characterized by carbon–sulfur inferred analysis (CSI), X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscopy (TEM) techniques. The results show that the Li2FeSiO4/C owns pure phase and sphere-like morphology as a result of an agglomeration of nanoparticles with an average particle size of about 50 nm. The Li2FeSiO4/C exhibits stable cycle performance at different rates from 0.1 C to 2 C, and its capacity at 0.1 C rate can reach 160 mAh g−1.
Journal of Power Sources 11/2012; 217:243–247. DOI:10.1016/j.jpowsour.2012.05.093 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Two new functionalized ILs based on pyrazolium cations and bis(trifluoromethylsulfonyl)imide anions (TFSI−) were synthesized and characterized. Their physicochemical and electrochemical properties, including melting point, thermal stability, density, viscosity, conductivity, and electrochemical window were investigated. The two ILs had low melting points and wide electrochemical windows. Behaviors of lithium redox, chemical stability against lithium metal, and charge–discharge cycle performance of lithium battery were also examined for the two IL electrolytes with 0.4 mol kg−1 LiTFSI. The IL electrolytes showed good chemical stability against lithium metal, and Li/LiFeO4 cells using the two IL electrolytes without additives owned good capacity and cycle property at the current rate of 0.1 C.
Journal of Power Sources 10/2012; 66:67–74. DOI:10.1016/j.electacta.2012.01.059 · 6.22 Impact Factor