Lithium-Ion Dominance

Nearly every rechargeable device you own uses a lithium-ion battery. The reason is energy density: lithium is the lightest metal and stores more energy per gram than the alternatives. During discharge, lithium ions move from the anode (usually graphite) through the electrolyte to the cathode (a metal oxide). Charging forces them back. This shuttling is called intercalation — ions slip between layers of the electrode like cards sliding into a deck. The structure never returns to quite the same state, which is why batteries degrade over time.