lithium-ion battery

A lithium-ion battery stores energy by ferrying tiny lithium ions back and forth between two host materials, like sand poured between two egg-cartons. On charge, lithium ions are pulled out of the cathode and slot into the graphite anode (a process called intercalation); on discharge they slide back, and each ion's journey pushes one electron through your circuit. Because lithium is the lightest metal and gives a high cell voltage (~3.7 V), Li-ion packs far more energy per kilogram (~250 Wh/kg) than lead-acid (~40 Wh/kg) — which is exactly why it powers your phone, laptop, and EV.

The magic is that nothing is plated or dissolved away — ions merely shuttle into and out of crystal lattices, so the cell survives hundreds to thousands of charge cycles. The trade-offs are real: a thin polymer separator keeps the electrodes apart, and if it is punctured or the cell is overcharged, a runaway exothermic reaction (thermal runaway) can ignite. That is why every Li-ion pack hides a battery management system policing voltage, current, and temperature cell by cell.