Improvement Of Electronic Conductivity Research Articles

Sulfur encapsulated in porous carbon nanospheres and coated with conductive polyaniline as cathode of lithium–sulfur battery

We report a novel composite, sulfur (S) encapsulated in porous carbon nanospheres (PCNS) and coated with conductive polyaniline (PANI) (PCNS-S@PANI), as cathode of lithium–sulfur battery. PCNS is prepared by convenient and controllable hydrothermal synthetic route and loaded with S via chemical deposition and then coated with conductive polyaniline via in situ polymerization under the control of ascorbic acid. The physical and electrochemical performances of the resulting PCNS-S@PANI are investigated by scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption–desorption isotherms, thermogravimetric analysis, electronic conductivity measurement, galvanostatic charge–discharge test, and electrochemical impedance spectroscopy. It is found that PCNS-S@PANI exhibits excellent charge–discharge performances as cathode of lithium–sulfur battery: delivering a discharge capacity of 881 mAh g−1 at 0.2 C (1 C = 1672 mA g−1) with a capacity retention of 72 % after 100 cycles and a rate capacity of 324 mAh g−1 at 2 C. These natures can be attributed to the co-contribution of PCNS and conductive PANI to the improvement in electronic conductivity and chemical stability of sulfur cathode.

Sn02 Aerogels: Towards Performant and Stable PEFC Catalyst Supports

Keywords: Fuel Cells, Catalysts support, Metal oxides, Sol-gel, Aerogels. Carbon blacks supported Pt, currently widely used as electrocatalysts in Polymer Electrolyte Fuel Cells (PEFC) are thermochemically unstable in PEFC operating conditions. This is especially true at the cathode side where, on top of relatively elevated temperature (80°C) and acidic conditions, both the potential and the relative humidity may be high. The resulting carbon oxidation is partially responsible for the PEFC performance decrease observed over time. Hence, long term durability still needs to be improved in order to consider PEFC as credible alternatives to conventional power sources for automotive, stationary or portable applications. Tin dioxide has already been studied as an alternative catalyst support to replace carbon (1, 2). We will show how SnO2 aerogels may even be more promising candidates. Due to their remarkable nanotexturation, aerogels have indeed already proven their ability to efficiently support catalyst for PEMFC application (3). Our SnO2 aerogels were obtained from supercritical CO2 drying of gels synthetized following an acid catalyzed sol-gel route, starting from metal alkoxides precursors. Nb or Sb doping were realized adding the corresponding dopant alkoxide to the sol. The nanoscale morphology can be controlled during the sol-gel synthesis route and is retained after drying. The effect of doping with Nb5+ or Sb5+ on the structure and the morphology of the material was investigated by XRD, SEM and nitrogen sorption. Our materials showed reasonable specific surface areas (80-90 m²/g). The bimodal narrow pore size distribution, centered on around 25 and 45 nm after calcination at 600 °C, is particularly well adapted to the foreseen application. Such morphology (see Figure 1) was directed to i) favor both good dispersion and high activity of the catalyst (Pt) and ii) efficiently manage the water produced at the cathode during the oxygen reduction reaction (ORR). All Sb doped samples exhibited an impressive improvement of electronic conductivity, reaching 1 S/cm for 5 at.% Sb. This is representing a 5 orders of magnitude increase compared to pure SnO2. This level of conductivity is almost equivalent to that of carbon Vulcan XC-72R measured in the same conditions (4 S/cm). These properties make SnO2: Sb a very promising material as catalyst support for PEFC cathode. Our latest results, including platinum deposition and electrochemical activity, will be discussed with respect to the foreseen application. This work is funded by the FP7 NANOCAT European program (SP1-JTI-FCH.2012.1.5). REFERENCES 1. A. Masao, S. Noda, F. Takasaki, K. Ito, K. Sasaki, Carbon-Free Pt Electrocatalysts Supported on SnO2 for Polymer Electrolyte Fuel Cells. Electrochemical and Solid State Letters 12, B119-B122 (2009). 2. K. Kakinuma, M. Uchida, T. Kamino, H. Uchida, M. Watanabe, Synthesis and electrochemical characterization of Pt catalyst supported on Sn0.96Sb0.04O2-delta with a network structure. Electrochimica Acta 56, 2881-2887 (2011). 3. M. Ouattara-Brigaudet, C. Beauger, S. Berthon-Fabry, P. Achard, Carbon Aerogels as Catalyst Supports and First Insights on Their Durability in Proton Exchange Membrane Fuel Cells. Fuel Cells 11, 726-734 (2011). Figure 1

Flake structured SnSbCo/MCMB/C composite as high performance anodes for lithium ion battery

SnSbCo/MCMB/C composite with flake structure were prepared by stepwise synthesis method. Firstly, SnSbCo nanoparticles were fabricated by co-precipitation, and then nanosized SnSbCo alloy were embedded in mesocarbon microbeads (MCMB) by ball-milling to synthesize primitive SnSbCo/MCMB hybrids, followed by carbonization of phenolic resin to produce an outer layer of carbon coating. The crystal structure, morphology and electrochemical properties of the SnSbCo/MCMB/C composite were evaluated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and galvanostatical cycling tests. Compared with bare SnSbCo alloy and SnSbCo/MCMB hybrids, the efficiently enhanced electrochemical performance of SnSbCo/MCMB/C composite were mainly ascribed to the improved electron conductivity and volume buffering effect provided by the amorphous carbon coating. The resultant SnSbCo/MCMB/C composite delivered an initial discharge capacity of 848 mAh g−1 under 100 mA g−1, with a good capacity retention of 85.6% after 70 cycles. The composite also exhibited excellent rate capability of 603 mAh g−1 and 405 mAh g−1 at the current density of 200 mA g−1 and 1000 mA g−1, respectively.

Electrocatalytic oxidation of ascorbic acid on mesostructured SiO2-conducting polymer composites

The conducting self-doping copolymer poly(aniline-co-ABA) preserves its redox activity at pH values as high as 7. This observation was the starting point to synthesize an organic–inorganic hybrid composite able to electrochemically oxidize ascorbic acid molecules at that pH. The inorganic part of the catalytic element was an ordered mesoporous electrodeposit of SiO2, which has been used as the template for the electrochemical insertion of the self-doping copolymer. The oxidation of ascorbate ions at a fixed potential on this composite was studied by means of the kinetic model proposed by Bartlett and Wallace (2001). It was observed that the effective kinetic constant KME increased significantly but, simultaneously, k′ME remained almost constant when the composite was employed as the electrocatalytic substrate. These results were interpreted in the light of two combinations of kinetic constants, which strongly suggested that the increase in KME should be ascribed to the improvement in electronic conductivity of the copolymer induced by the highly ordered silica template.

Non-isothermal electrochemical model for lithium-ion cells with composite cathodes

Transition metal oxide cathodes for Li-ion batteries offer high energy density and high voltage. Composites of these materials have shown excellent life expectancy and improved thermal performance. In the present work, a comprehensive non-isothermal electrochemical model for a Lithium ion cell with a composite cathode is developed. The present work builds on lithium concentration-dependent diffusivity and thermal gradient of cathode potential, obtained from experiments. The model validation is performed for a wide range of temperature and discharge rates. Excellent agreement is found for high and room temperature with moderate success at low temperatures, which can be attributed to the low fidelity of material properties at low temperature. Although the cell operation is limited by electronic conductivity of NCA at room temperature, at low temperatures a shift in controlling process is seen, and operation is limited by electrolyte transport. At room temperature, the lithium transport in Cathode appears to be the main source of heat generation with entropic heat as the primary contributor at low discharge rates and ohmic heat at high discharge rates respectively. Improvement in electronic conductivity of the cathode is expected to improve the performance of these composite cathodes and pave way for its wider commercialization.

Facile Synthesis of Graphene@NiO/MoO3 Composite Nanosheet Arrays for High-performance Supercapacitors

Graphene@NiO/MoO3 composite nanosheet arrays (CSAs) were grown on the nickel foam via a one-step hydrothermal way. The composite of NiO and MoO3 showed a promising synergistic effect for capacitors. Graphene had been integrated to the composite nanosheets to further enhance the electrochemical performance. The prepared samples were characterized by scanning electron microscopy and transmission electron microscopy, X-ray diffraction spectroscopy and Raman spectroscopy. A possible growth mechanism was proposed to explain the formation of the composite nanosheets by carrying out a series of time-dependent experiments. Benefiting from the improved electron conductivity and effective buffering of the volume variation induced by redox reactions, the composite exhibited a high area capacitance of 1.372F cm−2 even at a high current density of 42mAcm−2, and showed excellent cycle stability (62.7% of the initial capacitance after 7500 cycles, while 87.9% remained in the latter 7000 cycles).

High performance of mesoporous γ-Fe2O3 nanoparticle/Ketjen Black composite as anode material for lithium ion batteries

A type of γ-Fe2O3 nanoparticle/Ketjen Black (KB) composite material is synthesized by a solvothermal method combined with precursor thermal transformation. The structure and morphology are characterized by XRD, raman spectra, TG, nitrogen sorption, SEM, TEM and EDS. The results show that the composite has a uniform nanoporous network and well-dispersed γ-Fe2O3 particles with a size of ca. 5nm are embedded in the mesopores of KB. The γ-Fe2O3/KB exhibits superior eletrochemical performances to the bare γ-Fe2O3, especially at high current rate. The discharge capacity of the composite is 1100 mAh·g−1 at the first cycle and remains 988.8 mAh·g−1 after 100 cycles at 0.2C. Moreover, it also maintains a high discharge capacity of 697.8 mAh·g−1 at 2C and 410.1 mAh·g−1 at 5C after 100 cycles, respectively. Such improved electrochemical performances could be attributed to the superior conductivity and favorable structure of KB, which contributes to the improvement in electronic conductivity and structure stability of γ-Fe2O3 during the lithium ion insertion/desertion process.

Enhanced electrochemical performance of sodium lithium titanate by coating various carbons

To improve the electrochemical performance of Na2Li2Ti6O14, carbon black (CB), graphene (GN) and carbon nanotube (CNT) are introduced to fabricate high conductive Na2Li2Ti6O14/CB, Na2Li2Ti6O14/GN, Na2Li2Ti6O14/CNT and Na2Li2Ti6O14/CB/GN/CNT by a solid state method. It can be found that only CNT forms a complete three-dimensional conductive network which embeds the randomly distributed Na2Li2Ti6O14 particles, leading to an improvement of electronic conductivity. The results of cyclic voltammetry, electrochemical impedance spectroscopy and charge–discharge tests reveal that Na2Li2Ti6O14/CNT obtains the lowest redox polarization and the highest peak current among all the five samples. As a result, Na2Li2Ti6O14/CNT shows the best cycling and rate performances among all the five samples. It reveals a charge capacity of 111.4 mAh g−1 at 100 mA g−1, 110 mAh g−1 at 200 mA g−1, 103.9 mAh g−1 at 300 mA g−1 and 98.9 mAh g−1 at 400 mA g−1. For comparison, bare Na2Li2Ti6O14 only displays a charge capacity of 89.9 mAh g−1 at 100 mA g−1, 79.7 mAh g−1 at 200 mA g−1, 73.7 mAh g−1 at 300 mA g−1 and 69.4 mAh g−1 at 400 mA g−1. It indicates that the introduction of CNT is more effective to improve the performance of Na2Li2Ti6O14 than CB, GN and CB/GN/CNT.

Synthesis and Morphological Influence on High Capacity LiMnBO3 Cathode Material for New Generation Lithium Ion Batteries

In search of new cathode material, Borate based electrode, LiMBO3 (M= Fe, Mn and Co) for lithium ion battery offer several attractive features, such as low molar mass, abundant, environmental friendliness and relatively high theoretical capacities (222 mAh/g) [1]. In this view,an effort towards improvement in electronic conductivity of LiMnBO3material via reduction in particle size and appropriate synthesis condition is reported in this paper.A simplified Sol gel method was adopted for the synthesis of LiMnBO3cathode material. High Purity, analytical grade LiNO3, Mn(NO3)2. 6H2O and H3BO3 were used as precursors. The synthesized powders were annealed at 700oC for 3 hrs under different atmosphere.Powder X –ray diffraction pattern of the LiMnBO3 revealed the presence of mixed phases of hexagonal and monoclinic in which hexagonal phase is dominant in both Ar and N2atm. [2]. The crystallite size (Debye –Scherrer) calculation indicated nanoparticle formation (~ 38 nm).The SEM images of LiMnBO3 (Fig.1a) showed elongated spherical shaped particle in Ar atmosphere whereas peculiar tetragonal rod shaped particles was observed for N2atmosphere (fig.1b). The influence of morphological changes on the electrochemical performance is reported in this paperCycling profile of LiMnBO3 cells are given in fig.2. The cells were cycled between 1.5 to 4.8V at room temperature at a C rate of C/20. Fig.2, revealed that the capacity was maintained at 198mAh g-1for the first three cycles followed by a good capacity retention upto 35 cycles with a capacity deliverance of 190mAh/g (figure not shown).From the results, we report a sol gel derived LiMnBO3 that delivers a first discharge capacity of 198mAh g-1 at C/20 rate, the best result reported so far for LiMnBO3to our knowledge.

Synthesis of carbon nanotube/mesoporous TiO2 coaxial nanocables with enhanced lithium ion battery performance

Well-organized hybrid nanocables consisting of carbon nanotube (CNT) core and mesoporous TiO2 sheath has been synthesized through a combined sol–gel and hydrothermal process. By using hexadecylamine as a structure directing agent, mesoporous TiO2 with thickness ranging from 40 to 70nm was uniformly deposited on multi-walled CNTs. The resultant one dimensional CNT core/mesoporous TiO2 sheath (CNT@mesoporous TiO2) hybrid nanocables shows well-crystallized quality, porous feature and large surface area, favoring its electrochemical performance. Compared with reference TiO2 without CNTs, the CNT@mesoporous TiO2 hybrid nanocables shows largely enhanced rate performance, which could be attributed to its unique structure as well as the improvement of electronic conductivity by adding conductive CNTs.

Electrospinning of "Welded" Carbon Fiber Paper for Lithium Ion Battery Current Collectors

An approach for electrospinning interconnected (“welded”) carbon fiber mats for improved electronic conduction in 3D porous positive electrode current collectors for lithium ion batteries is presented. Although individual carbon fibers have high axial electronic conductivity, when used as current collectors in lithium ion batteries and other electrochemical storage/conversion systems, their electronic conductivity is largely limited by the interconnectivity of the carbon fibers. Active electrode materials for lithium ion batteries have low electronic conductivity and can block the carbon fiber interconnectivity when loaded onto the fibers. Interconnectivity in commercial carbon fiber paper (CFP) (d ≈ 10μm) is achieved by bonding of individual carbon fibers using additional polymer precursor and subsequent carbonization. In some reports of CFP current collectors in electrochemical devices additional carbon additives are mixed with the active material slurry and then pressed into the CFP in order to improve interconnectivity and electronic conductivity [1]. When carbon fiber paper is used directly in an electrode without an addition of carbon additives, the electrode is reported to suffer from low electronic conductivity due to low interconnectivity of carbon fibers [2]. Additionally, for application in lithium ion battery electrodes, CFP should be composed of small diameter fibers. Decreasing carbon fiber diameter can improve mass loadings for active material coated carbon fiber current collectors, and reduces the path length for ionic conductivity, however this also increases the number of junction points of carbon fibers in the CFP and decreases interconnectivity. In a typical carbon fiber paper (CFP) electrode, hundreds of fiber-to-fiber contact points are encountered along the path of the electron to the external circuit. A multitude of junction points creates a tortuous electronic pathway, decreasing the interconnectivity of the fibers. In order to improve electronic conductivity in small diameter CFP based LIB electrodes we have used an electrospinning method that allows us to weld the carbon fiber junctions together, increasing the conductivity and maintaining the integrity of the connections during coating of ceramic active materials. In this study, welded CFP paper was created by electrospinning polyacyrlonitrile (PAN) precursor solution into fiber mats followed by carbonization to create carbon fiber paper. LiMn2O4 active materials were grown directly on the welded CFP using a hydrothermal synthesis technique. The individual fibers were approximately 1 μm diameter and the fibers were loaded with approximately 60wt% active material. The LiMn2O4 loaded electrodes were used directly as positive electrodes in lithium ion batteries without additional binder or carbon additive. The improvement in electronic conductivity of the welded fibers dramatically improved the performance of the lithium ion battery (Li metal / 1 M LiPF6 in 1:1 EC:DMC / LiMn2O4) at intermediate rates.[1] Kercher, Andrew K., J. O. Kiggans, and Nancy J. Dudney. "Carbon Fiber Paper Cathodes for Lithium Ion Batteries." Journal of The Electrochemical Society157.12 (2010): A1323-A1327.[2] Kim, Chan, et al. "Fabrication of Electrospinning‐Derived Carbon Nanofiber Webs for the Anode Material of Lithium‐Ion Secondary Batteries." Advanced Functional Materials 16.18 (2006): 2393-2397.

Graphene–TiO2 nanocomposite photocatalysts for selective organic synthesis in water under simulated solar light irradiation

Heterogeneous photocatalysis offers a promising route to realize green oxidation processes in organic synthesis because such selective organic transformation processes can be enabled under solar light irradiation with ambient conditions. In this research, graphene–TiO2 nanocomposites have been utilized for aerobic selective oxidation of benzylic alcohols to corresponding aldehydes and acids in water under simulated solar light irradiation. The photocatalytic performance and related properties of solvent exfoliated graphene–TiO2 (SEG–TiO2) and reduced graphene oxide–TiO2 (RGO–TiO2) have been comparatively studied. It has been found that decreasing the defect density of graphene, by using SEG instead of graphene oxide (GO) as the precursor of RGO, can enhance the photoactivity of graphene–TiO2 nanocomposites due to the improved electron conductivity of SEG as compared to that of RGO. It is hoped that this work would stimulate further interest in utilizing graphene–semiconductor nanocomposite photocatalysts in the field of green-chemistry-oriented photocatalytic selective organic transformation.

Fe2O3 nanorods/carbon nanofibers composite: Preparation and performance as anode of high rate lithium ion battery

A novel Fe2O3/carbon composite is prepared using a facile one-step hydrothermal method. Its structure, morphology and performance as anode of lithium ion battery are investigated with X-ray diffraction, scanning electron microscopy, thermogravimetry, cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. It is found that the as-prepared composite is composed of α-Fe2O3 nanorods of about 75 nm in diameter and 1 μm in length, which are enwrapped with soft and curly carbon nanofibers, and exhibits superior charge/discharge performance compared to bare α-Fe2O3 nanorods, especially at high current rate. The discharge capacity is 1069 mAh g−1 at the first cycle and remains 560 mAh g−1 after 30 cycles at 0.2C for the bare nanorods, but improved to 1278 mAh g−1 and 960 mAh g−1 for the composite. At 12C, the discharge capacity is only 798 mAh g−1 initially and becomes 98 mAh g−1 after 30 cycles for the bare nanorods, while 844 mAh g−1 and 292 mAh g−1 for the composite. The improved performance of the composite is attributed to the bondage from carbon nanofibers, which contributes to the improvement in electronic conductivity and structure stability of α-Fe2O3 nanorods.

Facile synthesis of novel two-dimensional silver-coated layered double hydroxide nanosheets as advanced anode material for Ni–Zn secondary batteries

Silver-coated layered double hydroxide (Ag-coated LDH) nanosheets are successfully prepared by a facile silver mirror reaction and their electrochemical performance has been evaluated as anode materials for Ni–Zn secondary batteries. The microstructure and morphology of as-prepared Ag-coated Zn/Al-LDH are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). As anode material for Ni–Zn secondary batteries, Ag-coated Zn/Al-LDH exhibits high specific capacity (400 mAh g−1), good charge–discharge properties and excellent cycling performance, which is attributed to the effect of the electron conductivity improvement by the Ag coating on the surface of Zn/Al-LDH nanosheet. This newly designed Ag-coated Zn/Al-LDH may offer a promising anode candidate for high-performance Ni–Zn secondary batteries.

Lithium deficient mesoporous Li2−xMnSiO4 with significantly improved electrochemical performance

Li2−xMnSiO4 compounds with mesoporous structure are first proposed in the present work. It is interesting to note that the lithium deficient compounds exhibit much higher electrochemical performance in comparison with the stoichiometric one. Among these compounds, Li1.8MnSiO4 shows the best electrochemical performance. It is found that mesoporous Li1.8MnSiO4 without carbon coating delivers a maximum discharge capacity of 110.9 mAh g−1 at 15 mA g−1, maintaining 90.8 mAh g−1 after 25 cycles, while that of the stoichiometric one is only 48.0 mAh g−1, with 12.5 mAh g−1 remaining. The superior properties are mainly due to the great improvement of electronic conductivity and structure stability, as well as suppressed charge-transfer resistance.

CdS–graphene nanocomposites as visible light photocatalyst for redox reactions in water: A green route for selective transformation and environmental remediation

A series of CdS–graphene (GR) nanocomposites with different weight addition ratios of GR have been fabricated via a facile one-step solvothermal approach. CdS–GR nanocomposites are proven to serve as selective visible light photocatalysts toward aerobic selective oxidation of alcohols and reduction of heavy ions Cr(VI), instead of being nonselective in water. Furthermore, we find that decreasing the defect density of GR by using the solvent-exfoliated graphene (SEG) instead of graphene oxide (GO) as the precursor of GR can efficiently enhance the photocatalytic activity of CdS–GR nanocomposites due to its improved electron conductivity as compared to reduced GO (RGO). In addition, the hybridization of CdS with GR (RGO, SEG) via an intimate interfacial interaction can also effectively inhibit the photocorrosion of CdS during the photocatalytic redox reaction. It is hoped that this work can draw attention to making better use of graphene to synthesize more efficient GR-based nanocomposite photocatalysts for solar energy conversion, especially in the field of diverse redox processes in water in the framework of green chemistry.

High rate performance of the composites of Li4Ti5O12–Ketjen Black and Li4Ti5O12–Ketjen Black–multi-walled carbon nanotubes for Li-ion batteries

Composites of Li4Ti5O12–Ketjen Black (Li4Ti5O12–KB) and Li4Ti5O12–Ketjen Black–multi-walled carbon nanotubes (Li4Ti5O12–KB–MWCNTs) are prepared by a simple solution method. Their morphologies and structures are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and thermogravimetric analysis. Their electrochemical properties are investigated by galvanostatic charge–discharge test. Li4Ti5O12 particles in Li4Ti5O12–KB and Li4Ti5O12–KB–MWCNT composite have a diameter of ca. 40–60nm. The discharge specific capacity is 157 (0.1C), 110 (20C) and 93 (30C) mAhg−1 for Li4Ti5O12–KB composite, and 157 (0.1C), 133 (20C) and 105 (30C) mAhg−1 for Li4Ti5O12–KB–MWCNT composite. After 100cycles at 5C, the discharge capacity retention of Li4Ti5O12–KB and Li4Ti5O12–KB–MWCNTs is 94% and 96%, respectively. Li4Ti5O12 shows asymmetric behavior between charge and discharge. The excellent high rate performance of Li4Ti5O12–KB and Li4Ti5O12–KB–MWCNT composites can be attributed to the reduction of Li4Ti5O12 particle size and the improvement of electronic conductivity due to the uniform distribution of Li4Ti5O12 particles within the carbon matrix conductive network.

Facile synthesis of Ag/AgVO3 hybrid nanorods with enhanced electrochemical performance as cathode material for lithium batteries

Ag/β-AgVO3 hybrid nanorods have been successfully prepared by a facile one-step solid-state approach and their electrochemical performance has been evaluated as cathode materials for lithium batteries (LBs). The effects of calcinations temperatures to the morphologies of the material and the content of Ag in the hybrid have been investigated. The Ag/AgVO3 hybrid synthesized at 420 °C shows well-separated nanorods anchored with Ag nanoparticles. The existence of Ag nanoparticles has been demonstrated to improve the conductivity of the electrode. As a cathode material for lithium batteries, it exhibits high specific capacity, good rate capability and improved cycle stability. Initial specific discharge capacities of 242, 228, 203, 202, 198 mA h g−1 can be achieved at the current densities of 50, 100, 200, 400, 800 mA g−1, respectively. The superior performance is attributed to the combined effect of the electron conductivity improvement by the Ag nanoparticles and the well-separated β-AgVO3 nanorod structures. The results demonstrate the advantages of the Ag/AgVO3 hybrid for primary lithium batteries, and the possible application in rechargeable lithium batteries.

A Sol–Gel Process for Fabrication of NiO/NiCo2O4/Co3O4Composite with Improved Electrochemical Behavior for Electrochemical Capacitors

Transition metal oxides possess multiple oxidation states that enable rich redox reactions for pseudo capacitanc. They have been investigated as promising electrode materials to achieve high energy density. In this study, NiO/NiCo(2)O(4)/Co(3)O(4) composite with high specific surface and mesoporous structure is fabricated by a sol-gel process then calcined at 250 °C. Benefits from the improved electron conductivity and effective mesoporous structure, the fabricated composite exhibits high specific capacitance (1717 F g(-1)), enhanced rate capability, and excellent electrochemical stability (94.9% retention after 1000 cycles). Interestingly, the specific capacitance of the composite is higher than that of NiO, NiCo(2)O(4), and Co(3)O(4), which indicates a synergistic effect of the composite on improvement of electrochemical performance. The findings demonstrate the importance and great potential of NiO/NiCo(2)O(4)/Co(3)O(4) composite in development of high-performance energy-storage systems.

Synthesis of sandwich-like TiO2@C composite hollow spheres with high rate capability and stability for lithium-ion batteries

Novel sandwich-like TiO2@C composite hollow spheres with {001} facets exposed are obtained through hydrothermal carbon-coating treatment for the first time. Based on investigations by transmission electron microscopy (TEM), scanning electron microscopy (FESEM), XRD, laser Raman spectra, and N2 adsorption–desorption isotherms, TiO2 shells are proved to be wrapped in porous carbon layers, which provide conductive support for TiO2, resulting the improvement in electronic conductivity and diffusion of Li+. Moreover, these TiO2 shells expose the reactive {001} facets, which facilitate Li+ insertion/extraction. Through combining the above advantages, TiO2@C composite hollow spheres show more superior rate capability and higher stability than TiO2 nanoparticles (Degussa P25), TiO2 nanosheets with {001} facets exposed, and TiO2 hollow spheres before carbon-coating. This method may be extended to synthesize other sandwich-like composite hollow spheres for energy storage.