Lithium-ion battery

A lithium-ion battery stores energy by moving lithium ions, not by dissolving or plating a metal. Both electrodes are layered materials that can hold lithium ions between their atomic sheets like cards slid into a deck: a lithium cobalt-oxide cathode and a graphite anode. On charge, an outside current drives lithium ions out of the cathode, across a lithium-salt electrolyte, and in among the layers of the graphite; on discharge they flow back the other way, pushing electrons through the circuit as they go. Because the lithium always stays as ions tucked inside a host and never forms reactive lithium metal, the cell is far safer and longer-lived than earlier lithium batteries — engineers call the back-and-forth a "rocking-chair" cell.

Lithium is the lightest metal and gives up its electron eagerly, so a lithium cell packs more energy into less weight than any earlier rechargeable — several times the energy per kilogram of lead-acid, at about 3.6 to 3.7 volts per cell against lead-acid's 2. That combination of light weight and high energy is exactly what a device you carry needs. The mobile phone, the laptop, the cordless tool, and the electric car are all, in a real sense, applications waiting for this battery; none of them is practical on lead-acid or nickel chemistry at a tolerable weight.

The lithium-ion cell is the reason electronics went truly portable and untethered: the smartphone in a pocket, the laptop on a lap, and the power tool without a cord all ride on it. Scaled up into packs of thousands of cells, it made the modern electric car possible and now stores energy from wind and solar for the grid, letting renewable power be used after the sun sets or the wind drops. A chemistry commercialized in a 1991 camcorder has become the default way the world carries electricity with it.