Applications of Electrochemistry: Batteries and Fuel Cells

Vocabulary and key concepts regarding primary and secondary electrochemical cells, various battery types, and fuel cells.

Primary cell

A class of battery that cannot be recharged and must be discarded or recycled after the voltage drops to zero.

Secondary cell

A class of battery that can be recharged from an external power source after the voltage has dropped.

Dry Cell Batteries

Common non-rechargeable primary cells, such as those used in flashlights, which are sealed in stainless steel to reduce the risk of $KOH$ leaking.

Alkaline batteries

Batteries in which reactions occur in a basic (alkaline) medium, typically producing a voltage of about $1.5\,V$.

Lead-Acid Storage Batteries

A type of rechargeable battery used in automobiles consisting of 6 electrochemical cells wired in series, each producing $2\,V$ for a total of $12\,V$.

Sulfuric acid ($H_2SO_4$)

The substance known as "battery acid" in which both the anode and cathode of a lead-acid storage battery are immersed.

Nickel-Cadmium (NiCad) Batteries

Rechargeable batteries with a single cell voltage of $1.30\,V$ that use cadmium metal; they are considered environmental hazards due to the toxicity of cadmium.

Nickel-Metal Hydride Batteries (NiMH)

Rechargeable batteries created to replace NiCad batteries where cadmium is replaced by a $ZrNi_2$ alloy to carry a greater energy density.

Energy density

The amount of energy stored per unit mass.

Nominal voltage of second generation Toyota Prius battery pack

A total of $201.6\,volts$, produced by 28 modules each containing six $1.2\,volt$ cells connected in series.

Lithium Ion Batteries

The newest and most expensive type of rechargeable battery, featuring the greatest energy density of all rechargeables and a cell voltage of $3.7\,V$.

Memory effect

The requirement to completely discharge a battery before recharging; lithium ion batteries do not have this effect.

Fuel Cells

Electrochemical applications that are not self-contained and require fuel to be continuously supplied to convert energy into electricity.

Hydrogen Fuel Cell

A cell used in space missions that generates $1\,V$ and produces water as a product from the reaction of hydrogen gas and oxygen.

Maximum efficiency of combustion energy conversion

Typically a maximum of only $40\%$ of energy from combustion is converted to electricity, whereas fuel cells can be more efficient.