The CxN samples(C14N-C62N) prepared with a nickel catalyst had the higher crystallinity and less pyridine-type nitrogens existing at the edge of graphene layers than CxN prepared in the absence of a catalyst. With increase in the deposition temperature of CxN, the cy-cleability for electrochemical intercalation-deintercalation of lithium ions was improved and the profile of the charge-discharge curve approached that of graphite due to increase in the crystallinity and decrease in the incorporated nitrogens. CxN-coated graphites demonstrated gradual increase in the potential at the last stage of lithium ion deintercalation process.

The effect of fluoroester-mixing in 1 M LiClO4-EC/DEC was also investigated at a low temperature. It was found that CHF2COOCH3 with a low molecular weight and a small number of fluorine atoms was effective as a mixing agent.

This paper reports on some new results on the application of surface sensitive techniques for the study of the correlation of surface chemistry, morphology and electrochemical behavior of lithium and lithiated graphite as anodes for rechargeable batteries. Surface sensitive FTIR spectroscopy, atomic force microscopy (AFM), electrochemical quartz crystal microbalance (EQCM) were applied to Li and Li-graphite electrodes in a variety of electrolyte solutions of interest, in conjunction with standard electrochemical techniques. The similarity in the surface chemistry developed on Li and lithiated graphite in solutions is demonstrated and discussed. We demonstrate the strong impact of the surface chemistry on the morphology of Li deposition-dissolution processes, and the use of in situ EQCM measurements for the choice of optimal electrolyte solutions for rechargeable batteries with Li metal anodes.

Low-potential Li insertion materials comprised of molybdenum oxides (AxMoO3) have been prepared by a “chimie douce” route. Li insertion below 200 mV is associated with dramatic transformation of the structure, leading to a material which displays good cyclability with a high reversible specific capacity of 940 mA/g in the voltage window 3.0–0.005V (volumetric capacity of 4000 mAh/cc), albeit with notable polarization on charge. The structural and compositional changes on discharge to 200 mV have been studied by a combination of XRD, and XAS. The interlayer ions have also been exchanged for Sn, and the electrochemical characteristics of these materials are compared with the alkali derivatives.

The carbon aerogel/carbon paper composites have physical properties similar to those of monolithic carbon aerogels but do not require supercritical extraction during fabrication. The resorcinol-formaldehyde based carbon aerogel phase is intertwined between the fibers of a commercial carbon paper. The resulting composites have variable densities (0.4–0.6 g/cc), high surface areas (300–600 m2/g), and controllable pore sizes and pore distribution. The effects of the resorcinol-formaldehyde concentrations (50–70% w/v) and the pyrolysis temperature (600–1050°C) were studied in an attempt to tailor the aerogel microstructure and properties. The composite physical properties and structure were analyzed by transmission electron microscopy and multipoint-BET analyses and related to electrochemical capacitive data in 5M KOH. These thin carbon aerogel/carbon paper composite electrodes are used in experiments with electrochemical double-layer capacitors and capacitive deionization.

Several carbon materials have been studied for suitability as anode materials in lithium-ion cells. Carbons that have been included in this evaluation are three grades of commercially available mesophase carbon microbeads (MCMB) 6–28, 10–28 and 25–28, two specially prepared mesophase fibers (Amoco), a foreign mesophase fiber and KS-15 graphite (Lonza). Differences in cycling behavior between the three types of MCMB material are shown. Data of full lithium-ion cells demonstrate the effect that the choice of carbon material has on the cell discharge voltage and capacity. Lithium reference electrode experiments in full cells (3.0–4.0Ah capacity), elucidate the dynamics under several charge/discharge regimes and provide a comparison between the performance of carbon fiber and graphite anode materials. These test results indicate that the fibers can be charged at significantly higher rates than graphite without showing polarization at the anode. Full and half cell data also demonstrates the high coulombic efficiencies of the mesophase materials and first cycle efficiencies as compared to graphite. A comparison of two mesophase materials with different textures in full cells under strenuous cycling conditions shows significant differences in capacity retention. SEM photos of fibers showing the different textures are also presented.

Disordered carbons were synthesized at 700°C from methacrylonitrile-divinylbenzene precursors. The disorder, even at the free surface, was confirmed with TAM. These powdered carbons were subjected to rapid surface heating by a pulsed infrared laser. While the bulk structure remained essentially unchanged, there was substantial surface reconstruction to a depth of 0.25μm after heating (5.9 W average power at 10Hz, 10 ns pulse width, 1064nm wavelength). The surface ordering appears similar to the bulk microstructure of carbons isothermally annealed at 2,200°C (i.e., turbostratic). Improvements were observed in first cycle irreversible loss, rate capability, and coulombic efficiencies of the reconstructed carbons, relative to the untreated carbon.

Electric double-layer capacitors based on charge storage at the interface between a high surface area activated carbon electrode and a propylene carbonate solution are widely used as maintenance-free power sources for IC memories and microcomputers. New applications for electric double-layer capacitors have been proposed in recent years. The popularity of these devices is derived from their high energy density compared with conventional capacitors and their long cycle life and high power density relative to batteries.

The performance of the capacitor depends not only on the materials used in the cells but also on the construction of the cells. The performance of power capacitors for large power sources as well as materials and construction of these capacitors are described.

Strontium ruthenates with the perovskite type structure ABO3 have been shown to exhibit attractive capacitive properties. Doping on the A site with La lead to typical capacitance values of 21 F/g. These materials were synthesized by coprecipitating metal hydroxides from a stoichiometric salt solution and subsequent firing at 800 °C in air. In this paper we present a new procedure to synthesize the materials which are crystalline and nevertheless show appreciable capacitances in contrast to ruthenium dioxide material, which only works in a hydrated amorphous structure. The process basically consists in a pyrolysis of concentrated metal salt solutions of the respective chlorides and nitrates at 500 °C for several minutes. Excess soluble phases are removed by washing out with water. X-ray diffraction experiments revealed similar phase purity and crystallinity as known from the coprecipitated materials. However the measured capacitances of undoped perovskites reached high values of 200 F/g exceeding twenty times the value of respective coprecipitated materials. First experiments on doping the materials promise further progress. The new synthesis route introduces a higher surface area by leaving cavities from leached soluble phases and bulk defects into the crystal structure. The first effect increases the number of active sites in contact with the electrolyte while the latter enhances the protonie conduction which is necessary to keep the charge balance within the material during cycling.

Processes for fabricating new high surface area ceramic electrode materials have been developed. These electrode materials have been applied in electrochemical capacitors and related energy storage and conversion devices. Several synthetic approaches have been developed for producing high surface area carbide or nitride active materials. The fabrication methods provide the capability to vary the composition and microstructure of the electrode material. A number of new candidate high surface area electrode materials have been synthesized. Compositional and microstructural information is presented. Electrodes have been evaluated by cyclic voltammetry, chronopotentiometry, and impedance spectroscopy in acidic and basic aqueous electrolyte systems. Single electrode and single cell performance data are presented. Intrinsic properties such as open circuit potential, electrochemical stability and specific capacitance are discussed with respect to electrode composition. The influence on performance of extrinsic factors such as electrode thickness, particle size, and pore structure is also discussed. The performance of these new materials is compared to carbon, with emphasis on advantages with respect to volumetric energy and power density.

Activated carbon fiber cloth (ACFC) electrodes whose surface was modified by “pulsed cold plasma”, i.e., low-temperature plasma generated by a pulsed electric power in argon-oxygen mixed gas at a reduced pressure, were applied to electric double layer (EDL) capacitors with an organic electrolyte composed of propylene carbonate and tetraethylammonium tetrafluoroborate (TEABF4). The treatment of the ACFC electrodes with the pulsed cold plasma increased total capacitance in the EDL capacitors. The observed increase in the total capacitance was ascribed mainly to an ascertained increase in capacitance of a negative ACFC electrode involving TEA+ cation adsorption/desorption with the cold plasma treatment. No obvious increase in capacitance of a positive ACFC electrode involving BF4- anion adsorption/desorption was observed with the plasma treatment. The chemical and electrochemical characteristics of a treated ACFC interface were found to be favorable for TEA+ cation adsorption/desorption.

Various electrochemical capacitors (ultracapacitors) are being developed for hybrid vehicles as candidate power assist devices for the Partnership for a New Generation of Vehicles (PNGV) fast-response engine. The envisioned primary functions of the ultracapacitor are to level the dynamic power loads on the primary propulsion device and recover available energy from regenerative breaking during off-peak power periods. This paper will present test data from selected U.S. Department of Energy (DOE) supported ultracapacitor projects designed to meet the fast response engine requirements.

This paper will address the temperature dependence of test data obtained from a set of three devices provided from Maxwell Energy Products, Inc. These devices are rated at 2300 F at 2.3 V. Constant-current, constant-power, and self-discharge testing as a function of temperature have been conducted. From these tests were determined the capacitance, equivalent series resistance, specific energy and power, and the self-discharge energy loss factor as a function of the device operating temperature.

The electrochemical stability and capacitance in H2SO4, KOH, and propylene carbonate of single phase polycrystalline γ-Mo2N and δMoN thin film electrodes deposited at 350 and 700° C, respectively, at a rate of 0.5 μm/min on Ti substrates have been determined. The films were prepared by chemical vapor deposition at 100 torr using Mo(CO)6 and NH3 flowing at 1.5 standard liters per minute (slm). Cyclic voltammetry referenced to a standard Ag/AgCl electrode indicated that both phases possessed a more positive voltage stability limit in H2SO4 than KOH. Films of γ-Mo2N had voltage stability ranges of -0.3 to 0.6 V and -1.3 to - 0.3 V in 4.4 M H2SO4 and 7.6 M KOH, respectively. Films of δ-MoN possessed voltage stability ranges of -0.3 to 0.7 V and -1.3 to -0.3 V in the same respective electrolytes. Both phases had a voltage stability of approximately one volt in the propylene carbonate electrolyte. These results were used to design and fabricate a hybrid capacitor composed of a Ta/Ta2O5 anode and a δ-MoN cathode contained in an electrolyte of 4.4M H2SO4. The hybrid device had an operating voltage range between 0 and 50 V, a temperature range of -55 to + 90°C, a capacitance of ≈ 5.0 mF and an energy density of ≈ 1.32 J/cm3. This device is now in pre-production at Evans Capacitor Corporation.