R.G.A. Wills

A Dynamic Unit Cell Model for the All-Vanadium Flow Battery

In this paper, a mathematical model for the all-vanadium battery is presented and analytical solutions are derived. The model is based on the principles of mass and charge conservation, incorporating the major resistances, the electrochemical reactions and recirculation of the electrolyte through external reservoirs. Comparisons between the model results and experimental data show good agreement over practical ranges of the vanadium concentrations and the flow rate. The model is designed to provide accurate, rapid solutions at the unit-cell scale, which can be used for control and monitoring purposes. Crucially, the model relates the process time and process conditions to the state of charge via vanadium concentrations.

A Mathematical Model for the Soluble Lead-Acid Flow Battery

The soluble lead-acid battery is a redox flow cell that uses a single reservoir to store the electrolyte and does not require a microporous separator or membrane, allowing a simpler design and a substantial reduction in cost. In this paper, a transient model for a reversible, lead-acid flow battery incorporating mass and charge transport and surface electrode reactions is developed. The charge–discharge behavior is complicated by the formation and subsequent oxidation of a complex oxide layer on the positive electrode surface, which is accounted for in the model. The full charge/discharge behavior over two cycles is simulated for many cases. Experiments measuring the cell voltage during repeated charge–discharge cycles are described, and the simulation results are compared to the laboratory data, demonstrating good agreement. The model is then employed to investigate the effects of variations in the current density on the performance of the battery.

Effect of slot configuration and airgap and magnet thicknesses on rotor electromagnetic loss in surface PM synchronous machines

This paper presents a systematic study of the effect of slotting, i.e. number of slots and slot opening; and airgap and magnet thicknesses on rotor electromagnetic losses in surface magnet synchronous generators. All machines have the same overall diameter, stator bore diameter and active length. They were all designed to have approximately the same emf; the magnet thickness was adjusted to achieve this. All machines were also assumed to output the same sinusoidal current, at the same power factor. Rotor losses were calculated using both analytical and transient rotating mesh finite element analysis methods. The results are presented in the paper in a normalised fashion showing losses per unit surface area of the rotor surface versus s /λ and g /λ, where s, g, λ denote slot-opening, total gap between hub and stator bore, and slot pitch. In addition to providing an insight into the effect of slotting and gap geometry on losses, such graphs may be used to make quick estimates of rotor losses. The validity of this approach is investigated by comparison of estimates of losses from the normalised data with those calculated using FEA for machines of different sizes and number of slots.

Rotor Eddy Current Power Loss in Permanent Magnet Synchronous Generators Feeding Uncontrolled Rectifier Loads

Analytical methods and transient finite element analysis (FEA) with rotating mesh are used to calculate rotor eddy current power loss in a permanent magnet synchronous generator connected to an uncontrolled bridge rectifier. Two winding and rectifier topologies are considered: a three-phase winding with a three-phase bridge rectifier and a double three-phase winding with a three-phase rectifier each, connected in series. Both magnet flux tooth ripple and stator magneto-motive force harmonics are considered in the calculation of rotor loss; the harmonics are added vectorially. Good agreement is observed between analytical and FEA for constant dc link current and constant voltage loads. The machine with double three-phase windings was found to have considerably lower rotor losses than the machine with one single three-phase winding.

Calculation of no-load rotor eddy current power loss in PM synchronous machines

Three analytical methods, and finite-element analysis (FEA), are used to calculate no-load flux harmonics traveling with respect to the rotor of a surface permanent magnet machine. Rotor eddy-current losses caused by each harmonic are calculated analytically using a multilayer eddy-current model of the machine, in which each harmonic is represented by an equivalent current sheet on the bore of a slotless stator. Losses are also calculated using transient time-stepping FEA coupled with the equation of motion of the rotor. Significant discrepancies are observed between the results obtained from the different methods and FEA, especially when the level of saturation in the stator core is significant.

Zinc-based flow batteries for medium- and large-scale energy storage

This chapter reviews three types of redox flow batteries using zinc negative electrodes, namely, the zinc-bromine flow battery, zinc-cerium flow battery, and zinc-air flow battery. It provides a summary of the overall development of these batteries, including proposed chemistry, performance of the positive electrode and negative electrode, and cell developments. It also discusses remaining challenges and directions for future development of redox flow batteries using zinc electrodes.

The 3D Printing of a Polymeric Electrochemical Cell Body and its Characterisation

An undivided flow cell was designed and constructed using additive manufacturing technology and its mass transport characteristics were evaluated using the reduction of ferricyanide, hexacyanoferrate (III) ions at a nickel surface. The dimensionless mass transfer correlation Sh = aRebScdLee was obtained using the convective-diffusion limiting current observed in linear sweep voltammetry; this correlation compared closely with that reported in the literature from traditionally machined plane parallel rectangular flow channel reactors. The ability of 3D printer technology, aided by computational graphics, to rapidly and conveniently design, manufacture and re-design the geometrical characteristics of the flow cell is highlighted.

SECONDARY BATTERIES – FLOW SYSTEMS | Overview

Redox flow batteries provide a possible solution to energy storage requirements by improving power transmission/distribution together with the integration of renewable energy sources. Such batteries can provide large-scale storage at competitive operational costs, while remaining environmentally acceptable. Several systems, for example, vanadium–vanadium, zinc–bromine, zinc–cerium, iron–chromium, bromine–polysulfide, and soluble lead, are currently under development worldwide. The principles of redox flow battery technology and the characteristics of several systems are considered. Applications are being developed, for example, in load leveling, uninterrupted power supplies, and strategic energy storage in remote sites; applications in the power conditioning of sustainable energy generators (including wind and solar devices) are anticipated.

Environmental Screening of Electrode Materials for a Rechargeable Aluminum Battery with an AlCl3/EMIMCl Electrolyte

Recently, rechargeable aluminum batteries have received much attention due to their low cost, easy operation, and high safety. As the research into rechargeable aluminum batteries with a room-temperature ionic liquid electrolyte is relatively new, research efforts have focused on finding suitable electrode materials. An understanding of the environmental aspects of electrode materials is essential to make informed and conscious decisions in aluminum battery development. The purpose of this study was to evaluate and compare the relative environmental performance of electrode material candidates for rechargeable aluminum batteries with an AlCl3/EMIMCl (1-ethyl-3-methylimidazolium chloride) room-temperature ionic liquid electrolyte. To this end, we used a lifecycle environmental screening framework to evaluate 12 candidate electrode materials. We found that all of the studied materials are associated with one or more drawbacks and therefore do not represent a “silver bullet” for the aluminum battery. Even so, some materials appeared more promising than others did. We also found that aluminum battery technology is likely to face some of the same environmental challenges as Li-ion technology but also offers an opportunity to avoid others. The insights provided here can aid aluminum battery development in an environmentally sustainable direction.

Electrochemically Treated TiO2 for Enhanced Performance in Aqueous Al-Ion Batteries

The potential for low cost, environmentally friendly and high rate energy storage has led to the study of anatase-TiO2 as an electrode material in aqueous Al3+ electrolytes. This paper describes the improved performance from an electrochemically treated composite TiO2 electrode for use in aqueous Al-ion batteries. After application of the cathodic electrochemical treatment in 1 mol/dm3 KOH, Mott–Schottky analysis showed the treated electrode as having an increased electron density and an altered open circuit potential, which remained stable throughout cycling. The cathodic treatment also resulted in a change in colour of TiO2. Treated-TiO2 demonstrated improved capacity, coulombic efficiency and stability when galvanostatically cycled in 1 mol·dm−3AlCl3/1 mol·dm−3 KCl. A treated-TiO2 electrode produced a capacity of 15.3 mA·h·g−1 with 99.95% coulombic efficiency at the high specific current of 10 A/g. Additionally, X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy were employed to elucidate the origin of this improved performance.