Direct Energy, 2018a

9 BATTERIES AND FUEL CELLS 229
were used in the 1970s in militaryapplications [128, p. 14.1]. Both primary
and secondarylithium batteries are available today. Theyare popular due
to their high specic energyand energydensity. Theyare used in many
consumer goods including cellphones, laptops, portable electronics, hearing
aids, and other medical devices [149]. Manylithium batteries are designed
to output relativelylow current to prevent damage, and secondarylithium
batteries require controlled recharging to prevent damage [128, ch. 15].
Even with these limitations, over 250 million cells are produced each month
[128, ch. 15].
Figure 9.9: Naturallyoccurring lepidolite, an ore of lithium.
9.6 Fuel Cells
9.6.1 Components of Fuel Cells and Fuel Cell Systems
A fuel cell is a device which converts chemical energyto electrical energy
through the oxidation of a fuel. Like batteries, all fuel cells contain an
anode from which electrons and ions ow away, a cathode from which electrons
and ions ow towards, and an electrolyte. The electrodes are typically
porous which makes it easier for the fuel and oxidizer to get to the reaction
site, provides more surface area for the reaction to occur, allows for a
higher current through the electrode, and allows for less catalyst to be used
[60, ch. 5]. The electrolyte may be a liquid or a solid. Examples of liquid
electrolytes include potassium hydroxide solution and phosphoric acid solution
[128]. Examples of solid electrolytes include (ZrO 2
) 0.85 (CaO) 0.15
and
(ZrO 2
) 0.9 (Y 2
O 3 ) 0.1 [60]. Also like a battery, individual cells may be stacked
together in a package. A single fuel cell mayhave a cell voltage of a few
volts, but multiple cells maybe packaged together in series to produce tens
or hundreds of volts from the unit.