13 elements: Lanthanum and Cerium

Lanthanum and Cerium

Rare earth elements
Atomic numbers: 57; 58
Used in: Batteries
Criticality ratings: near-critical; near-critical
When it comes to batteries, lithium is the true Olympian. Lithium-ion batteries are unsurpassed in energy density, and dominate the market in laptops, cellphones and other devices where a slimline figure is all-important.
Yet they are also rather explosive characters: computer manufacturer Dell recalled four million lithium laptop batteries in 2006 amid fears they might burst into flames if overheated. That risk makes them unsuitable for use in electric and hybrid electric cars, leaving the market to the less explosion-prone nickel-metal-hydride batteries.
This is where lanthanum and cerium come in. They are the main components of a “mischmetal” mixture of rare earth elements that makes up the nickel-metal-hydride battery's negative electrode. The increased demand for electric cars, and the elements' subsidiary roles as phosphorescents in energy-saving light bulbs, place lanthanum and cerium on the US DoE's short-term “near-critical” list for green technologies – a position also assumed by lithium in the medium term.
Meanwhile, a mischmetal mixture is not totally inert: strike one and it produces a spark. This property has seen it being widely adopted as the ignition element in cigarette lighters – clearly no skill for would-be Olympians.