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Sunday, February 3, 2013

The good and bad of lithium

A Dell laptop catches fire in an airport; see the video. A massive battery catches fire in an electricity network; read the story. The Boeing 787 fleet is grounded after a battery fire. What do these events, each worrisome, have in common? Lithium.

Without batteries our high-tech world would stop. Scientists and engineers have come a long way since the zinc-carbon batteries that we put into flashlights and transistor radios 50 years ago. Other batteries we used in those days were nickel-cadmium rechargables and Duracells, a brand name for alkaline dry cells. Batteries today have much better energy density, much more favorable recharge characteristics, and far less weight than those. Also, there are international regimes known as RoHS and WEEE to manage the use of problematic substances in batteries. That's important -- cadmium, mercury (originally used in Duracells), and lead and arsenic (found in automobile batteries) are highly toxic.

Back to lithium, which is ideal for many batteries because

  • lithium is lightweight,
  • is available throughout the world (although half of the known deposits are in Chile),
  • is affordable,
  • is sufficiently reactive chemically that it can release a prodigious amount of electricity,
  • is not toxic at low concentrations (some medications use lithium),
  • has a reversible chemistry for recharging, and
  • can be used at ordinary temperatures.
Not many materials have all those characteristics. But do you remember a demonstration in high school or university chemistry when someone dropped a chunk of an alkali metal into water? It probably looked like this. The very reactivity of lithium is both its promise and its curse. One can say the same about gasoline and about uranium, in a nuclear sense instead of a chemical sense. We depend on substances that are inherently dangerous. The challenge for scientists and engineers is to tame the dangers so that the benefit/risk and benefit/cost ratios are more than acceptable. This takes time and money, and inevitably there will be accidents. Meanwhile we keep looking for better materials. It's a vital field of research.

By the way, solar panels are either composed of toxic substances (e.g. cadmium again) or require toxic substances (e.g. pure or halogenated silane) in the manufacturing process.