Robert S. Conell

Electrochemical and Thermal Characterization of Battery Modules Commensurate with Electric Vehicle Integration

A relatively simple mathematical representation of a nickel metal hydride traction battery is developed and implemented. The approach is based in part on an equivalent circuit comprising a resistor element in series with a parallel resistor-capacitor combination. Additional features include self-discharge, current inefficiency, temperature and state-of-charge (SOC) dependencies, and mass-transport limitations. An energy balance is coupled to the electrochemical problem: the energy balance incorporates transient heat-transfer to the battery surroundings as well as reversible and irreversible heat generation. The high-frequency and pseudo-steady-state impedance exhibit an Arrhenius temperature dependence. All the model parameters arc constants or are described by continuous functions of temperature and SOC. Calculated results from the coupled electrochemical and thermal model are compared with charge and discharge experiments conducted over the time scales and current magnitudes of interest for electric-vehicle applications. The paper closes with a brief summary and a discussion of open questions.

The electrochromic properties of hydrous nickel oxide

The electrochromic properties of thin films of nickel hydroxide on conductive tin-oxide-coated glass substrates are reported. Adherent, uniform thin films (⩽ 100 nm) which are cathodically electrodeposited from Ni(NO3)2 solution, can be repeatedly colored and bleached electrochemically in a 1M KOH electrolyte. In the reduced form, the films are essentially transparent, but upon oxidation they absorb light strongly throughout the visible region of the spectrum. Peak coloration efficiency, which occurs at about 450 nm, is estimated to be 50 cm2/C. Variable control of transmittance through the films was achieved by controlling the extent of film oxidation. Intrinsic switching times for coloration and bleaching are each less than one second. Nonuniform coloration and bleaching, due to the resistivity of the conductive glass substrate, increases the effective switching time as the electrode area is increased. The open circuit memory of colored films is on the order of hours in 1M KOH. Increased switching times and a decrease in total coloration are observed after 500 color/bleach cycles.

The Effect of Temperature on the Equilibrium and Transport Properties of Saturated Poly(perfluorosulfonic acid) Membranes

The equilibrium and transport properties of a poly(perfluorosulfonic acid) membrane containing a dilute sulfuric acid solution are investigated over the temperature range from 20 to 90 o C, which is of interest for polymer-electrolyte fuel cells. The membrane porosity, proton diffusion coefficient, and electrokinetic permeability are measured and tabulated as a function of temperature. A combination of electrochemical and radiotracer techniques are employed. The electrokinetic Peclet number, a dimensionless group that characterizes the importance of electro-osmotic water transport by the membrane, is shown to have only a slight dependence on temperature

In situ extended x‐ray absorption fine structure spectroscopy of thin‐film nickel hydroxide electrodes

A convenient in situ electrochemical cell has been developed which permits x‐ray absorption measurements on thin‐film electrodes under electrochemical polarization. Extended x‐ray absorption fine structure spectra from highly disordered α‐Ni(OH)2 films, before and after polarization, provided quantitative results on the lattice contraction accompanying oxidation. Upon oxidation of α‐Ni(OH)2, the Ni‐O distance contracted from 2.05 to 1.86 A, and the Ni‐Ni distance contracted from 3.09 to 2.82 A. The observed 10% contraction in the brucite plane is consistent with the 3.67 nickel valence in a K(NiO2)3 phase. The present technique extends x‐ray absorption spectroscopy to the study of a variety of unstable materials not amenable to ex situ techniques.

The electrochromic properties of sputtered nickel oxide films

Electrochromic nickel oxide films were prepared by reactive RF sputtering from a nickel target in an oxygen atmosphere. The films were deposited as a compact 40 nm layer of trivalent nickel oxide, Ni2O3. Reduction and oxidation of the films in 1 M KOH resulted in bleaching and coloration, respectively. Voltammetry indicated that the eventual electrochromic reaction involved the β-Ni(OH)2/β-NiOOH couple. In situ visible spectra showed electrochromic modulation of the transmittance throughout the visible range with a peak change in transmittance of about 60% at a wavelength of 500 nm. In situ spectra in the near-infrared region indicated improved electrochromic switching in this region; the sputtered nickel oxide film exhibited about a 30% change in transmittance in comparison to less than 10% for a similar electroprecipitated nickel hydroxide film. The sputtered nickel oxide films exhibited durable electrochromic switching for over 2500 coloration/bleaching cycles, a significant improvement over the less than 500 switching cycles exhibited by electroprecipitated nickel hydroxide films.

Electrolyte-free electrochromic device

A novel, solid‐state electrochromic device is described which utilizes a single film of Prussian blue as the only electrochemically active element. The device can be reversibly bleached by the application of a voltage across the film. Removal of the voltage results in immediate recoloration.