A first principles-based model has been developed to simulate the capacity fade of Li-ion batteries. Incorporation of a continuous occurrence of the solvent reduction reaction during constant current and constant voltage ͑CC-CV͒ charging explains the capacity fade of the battery. The effect of parameters such as end of charge voltage and depth of discharge, the film resistance, the exchange current density, and the over voltage of the parasitic reaction on the capacity fade and battery performance were studied qualitatively. The parameters that were updated for every cycle as a result of the side reaction were state-of-charge of the electrode materials and the film resistance, both estimated at the end of CC-CV charging. The effect of rate of solvent reduction reaction and the conductivity of the film formed were also studied.

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SUMMARYA literature review of electrochemical impedance spectroscopy (EIS) analysis of proton exchange membrane fuel cells (PEMFCs) is presented. Emphasis is placed on the papers that analyse the impedance response of the cathode and anode half-cells of the PEMFCs based on a continuum-mechanics approach. The other type of analysis, which is based on the equivalent-circuits approach, is addressed for comparison. The relative advantages and disadvantages of the two approaches are discussed. Papers dealing with continuum-mechanics-based EIS modelling of general electrochemical systems are briefly reviewed.

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A three-dimensional mathematical model is presented to describe volume changes in porous electrodes occurring during operation. Material conservation equations are used to derive governing relationships between electrode dimensions and porosity for deposition/precipitation, intercalation, and ionomer-based electrodes. By introducing a parameter, called the swelling coefficient, the relative magnitudes of the change in electrode dimensions and the change in porosity are determined. The swelling coefficient is design-dependent and measured experimentally for a given cell design. The model is general and forms a critical addition required to extend the existing porous electrode models to include volume change effects. For the special case of uniform reaction distribution, analytical solutions are presented and used to illustrate the effect of volume changes in porous electrodes.

A mathematical model is developed that predicts the voltage-capacity behavior of a primary lithium battery containing a hybrid cathode, which combines the high energy density of carbon monofluoride ͑CF x ͒ and the higher power density of silver vanadium oxide ͑SVO͒. The model is developed using material balances and kinetic expressions for each material, extracting kinetic and thermodynamic parameters from data collected on CF x and SVO batteries, and then integrating this information into a hybrid system. The full model is validated by comparing simulations to experimental data on Li/CF x -SVO hybrid-cathode batteries of various designs and for a range of discharge currents. The model closely agrees with the data up to moderate discharge rates, beyond which the model overpredicts voltage as ignored phenomena ͑mainly, ohmic resistance͒ become important.Modern implantable medical devices such as pacemakers and neurostimulators offer an ever-increasing array of therapies and features that improve the management of disease states. 1 These features ͑e.g., increased computational power, sensing and long-distance telemetry͒ demand the device batteries to be increasingly high-power capable, without compromising on the excellent energy density provided by traditional Li/I 2 batteries. One possible solution, the Li/ silver vanadium oxide ͑SVO͒ battery, has attractive attributes such as high power density and a stepped voltage-capacity curve with a plateau near the end of discharge. ͑The latter feature provides an ample and reliable end-of-service warning for device replacement prior to battery depletion. 2-6 ͒ Therefore, the Li/SVO battery is the present state-of-the-art power source for implantable cardioverter defibrillators, which demand peak power loads as high as 10 W from the battery. However, for devices in which such high power is not needed, the Li/SVO battery may be less attractive because its energy density is substantially lower than the Li/I 2 battery. Another possible solution is the Li/CF x battery, which has comparable energy density to the Li/I 2 battery, although lower power density than the Li/SVO battery. Further, an end-of-service warning is relatively more difficult with the Li/CF x battery because its voltage-capacity curve remains nearly flat for most of discharge and falls off steeply near the end.In recent years, Medtronic introduced a battery whose cathode contains a mixture of CF x and SVO, preserving the best properties of each ͑namely, high energy and power densities, respectively͒. This battery, known as the Li/CF x -SVO hybrid-cathode battery, has comparable energy density to Li/I 2 , but with about two orders of magnitude greater power density. 1,7 In addition, the hybrid-cathode battery exhibits the same voltage plateau near the end of discharge as the Li/SVO battery, allowing for a convenient and reliable endof-service warning. By modulating the mix ratio of CF x and SVO, one can tune the battery's power-energy characteristic as well as the time interval between end-of-service warning an...

A theoretical analysis is presented that allows in situ measurements of the physical properties of a composite electrode, namely, the electronic conductivity, the ionic conductivity, the exchange-current density, and the double-layer capacitance. Use is made of the current-voltage responses of the composite electrode to dc and ac polarizations under three different experimental configurations. This analysis allows the physical properties to be obtained even when the various resistances in the composite ͑e.g., ionic, electronic, and charge-transfer͒ are of comparable values.

A two-dimensional ͑2-D͒ energy balance ͑the 2D model͒ is reduced to a one-dimensioanl ͑1-D͒ energy balance ͑the 1D-radialspiral model͒ by a coordinate transformation approach. The 1D-radial-spiral model, even though 1-D, captures both radial and spiral heat conductions over a wide range of design parameters. By comparing the temperature predictions of the 1D-radial-spiral model and the 2D model, parameter ranges were identified where spiral conduction was important and where the 1D-radial-spiral model held. The 1D-radial-spiral model provided a sixtyfold savings in computation time over the 2D model. When coupled to electrochemistry, the 2D model took approximately 20 h to simulate a 2C discharge of a Li-ion battery, while the 1D-radial-spiral model took about 20 min.