Energy Storage, 2nd Edition

Chapter 9Design Considerations

9.1 Examination of Diffusion and Reaction Rates and Cell Design

When embarking on the design of a new electrochemical cell, there are numerous factors to consider at the initial stages. After deciding on the chemistry and electrolyte to be employed, perhaps the most important factor to be reviewed is that of electrodes. What electrode materials will be used as the basic structure upon which the energy storing reactions will occur?

In most electrochemical cells, the electrode participates directly in the processes. Examples of this are the lead-acid, nickel-cadmium, lithium-ion, and metal hydride cells. In the case of redox-type cells, whether they are of the full flow chemical couple devices or the static electrolyte concentration cells, the electrodes are designed to be electronically conductive but chemically inert. This property is chosen so that the system will have a relatively long life with chemically reversible reactions such that there are essentially no inherent chemical changes with a cell even after a very large number of cycles. There are very few systems that truly offer this distinctly desirable advantage. In almost all energy processes that employ chemical reactions, there are some irreversible processes that take an eventual toll on the device life.

The concentration cells offer the opportunity of circumventing most problems that beset conventional “batteries.” Electrodes are of great concern in these new types of cells because ...