Battery Basics

A lithium-ion battery stores and releases energy by moving lithium ions between two electrodes: the anode and the cathode. To do this, the battery also needs an electrolyte, a separator, and current collectors.

How It Works

When the battery discharges, lithium ions move from the anode to the cathode through the electrolyte. At the same time, electrons flow through the external circuit from the anode to the cathode.

This separation of ion flow inside the battery and electron flow through the external circuit is what allows the battery to deliver electrical energy.

During discharge:

• The anode releases lithium ions into the electrolyte
• The lithium ions move through the electrolyte to the cathode
• Electrons flow through the external circuit, where they can power an electric motor or other electrical systems
• The cathode receives the lithium ions and electrons

During charging, the process is reversed. The charger pushes electrons back toward the anode, and lithium ions move from the cathode back to the anode.

The voltage of a battery cell comes from the difference in electrochemical potential between the anode and cathode materials. That voltage depends on the cell chemistry and the state of charge. A typical lithium-ion cell operates in a range of roughly 3.2 to 4.2 volts, depending on chemistry.

External Circuit

In an EV, electrons flowing through the external circuit power the vehicle's motor and other electronic systems. The battery therefore works as an energy source that converts stored chemical energy into electrical energy.

Current Collectors

Current collectors are conductive materials connected to the electrodes. Their role is to carry electrons between the anode and cathode materials and the external circuit, while adding as little resistance and weight as possible.

For readers who want a deeper explanation of how lithium-ion batteries work, this video from The Limiting Factor provides a useful technical walkthrough.