How Cars Work
The Big Battery
PART THREE — How an Electric Car Works
CHAPTER NINE
For the first eight chapters of this book, every car we have looked at has run on gasoline. That gasoline got mixed with air in either a carburetor (Part 1) or a fuel injector (Part 2), squeezed by a piston, lit by a spark, and burned. The hot expanding gas pushed the piston down, the piston turned the crankshaft, the crankshaft turned the wheels.
For an electric car, you can throw all of that out.
There is no gasoline. No cylinders. No pistons. No spark plugs. No transmission with gears. No long driveshaft. No exhaust pipe. No fuel pump.
What an electric car has, instead, is a giant battery (under the floor) and an electric motor (between the wheels), connected by wires.
That is it. Practically the whole car.
This part of the book is about how an electric car works. We start with the battery, because the battery is the heart of an electric car the same way the engine is the heart of a gasoline car. It is the biggest, heaviest, most expensive thing in the car. And it stores all the energy the car will ever use until somebody plugs it in again.
What a battery is
A battery stores energy as chemistry, and gives it back as electricity.
Inside a battery are two pieces of different material — usually two different metals, or chemicals containing metals — kept apart by something that conducts ions but not electrons. (Don’t worry too much about the words “ion” and “electron” yet. The point is that the separator lets parts of atoms move through it, but not the electricity itself.) When you connect the two pieces by an outside wire, a chemical reaction happens between them, and electricity flows through the wire while it is happening.
Run the reaction one way, and electricity comes out — that is discharging the battery, the way you do every time you use it. Run the reaction the other way (by pushing electricity in from outside), and the battery stores up energy again — that is charging.
Every battery, from a watch battery to a Tesla pack, works on this same principle. Two different materials, separated by something that lets ions through, hooked up by an outside wire that carries the actual electric current.
The materials and design have been refined over more than two hundred years. The materials in a modern car battery (or phone, or laptop) are lithium and a few cleverly chosen compounds. The basic idea is the same as the very first battery, invented in 1800. (See the sidebar.)