Electrochemical Cells: Automobile Batteries
The automobile battery, or lead storage battery, consists of six electrochemical cells connected in series. The anode of each cell is lead, while the cathode is lead dioxide.
Lead dioxide is represented as:
The electrodes are immersed in a sulfuric acid solution. Sulfuric acid is represented as:
When you start your car, the following cell reactions take place:
When this reaction takes place, both electrodes become coated with solid lead (II) sulfate, and the sulfuric acid is used up.
After the automobile has been started, the alternator or generator takes over the job of producing electricity (for spark plugs, lights, and so on) and also recharges the battery. The alternator reverses both the flow of electrons into the battery and the original redox reactions, and regenerates the lead and lead dioxide:
The lead storage battery can be discharged and charged many times. But the shock of running over bumps in the road or into the curb flakes off a little of the lead (II) sulfate and eventually causes the battery to fail.
During charging, the automobile battery acts like a second type of electrochemical cell, an electrolytic cell, which uses electricity to produce a desired redox reaction.