Battery cells are the smallest unit of every battery: the part that stores energy by chemical reaction. A lithium-ion cell has two electrodes, called the anode and the cathode, with a liquid between them. When the battery is charged, lithium ions move to the anode. When it is used, they move back and produce electric current. Cells are made in huge factories, and the mix of materials in them is called the chemistry.
Consider a cylindrical cell of the kind used in scooters. It is about the size of a thick finger. It supplies 3.6 volts and holds about 5 ampere-hours, which is about 18 watt-hours of energy. A scooter with a 3 kilowatt-hour battery therefore needs about 170 such cells. The cells are joined into modules and a pack, which is explained in battery cells, modules and packs. The battery pack and its management system then watches them.
Cells come in three shapes. A cylindrical cell is a metal can. A pouch cell is a flat bag. A prismatic cell is a flat box. The shape decides how the pack is built and how well it can be cooled. The chemistry decides the cost, the life and the energy stored for each kilogram. Cells are the most expensive part of an electric vehicle, and much of their cost is in materials such as lithium, nickel and graphite. India has imported most of its cells so far, and Indian companies are building cell factories.
New chemistries try to store more energy in the same space. For instance, a silicon anode, which replaces part of the usual graphite, can hold more lithium. Searching for such materials is now done partly by computer, in AI materials discovery. Cheaper chemistries without lithium, such as sodium-ion batteries, are also being developed for use in India.
A factory checks every cell before it ships. Leak testing checks that the seal does not leak. Industrial CT scanning looks inside a cell to see whether its layers are even. The finished cells go into packs for vehicles, and into large battery energy storage systems (BESS) for the power grid.