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The beauty of bendable batteries :: The Guardian

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  • RemyC
    From: http://www.guardian.co.uk/life/feature/story/0,13026,1423451,00.html The beauty of bendable batteries Vastly thinner, lighter power sources are destined
    Message 1 of 1 , Mar 9, 2005

      The beauty of bendable batteries

      Vastly thinner, lighter power sources are destined to make all our electric
      dreams come true, writes Alok Jha

      Thursday February 24, 2005
      The Guardian

      Just over 10 years ago, Donald Sadoway went for a drive in his first
      electric car. It was an early, clunky design but the experience changed his
      world - ever since he has dedicated himself to doing his part in making
      electric cars a commercial reality.

      "For personal transportation, it's lunacy that we don't have electric
      vehicles," says Sadoway, a professor of materials science at the
      Massachusetts Institute of Technology. "It's crazy to be burning carbon to
      move around short distances. For congested urban environments, the future is
      now. The only thing that's missing is a viable battery."

      Our increasingly mobile world depends on the ability to store and move
      energy around with us in the form of batteries (there's no point in a
      top-of-the-range laptop if it needs a cell that costs more than a space
      station and is the size of Texas). But lack of academic and commercial
      interest in the field, and the concentration of what effort there is on
      developing fuel cells and hydrogen cars, means innovation has hit a wall.

      Which is why Sadoway is getting excited about crisp packets. Smoothing one
      out in front of him, he describes how the thin sandwich of metal and plastic
      is set to be the unwitting battering ram to that technological brick wall.
      His remarkable idea is a battery which is as thin as a crisp packet and is
      as cheap, well, as the crisps in them.

      The Slimcell, as Sadoway calls his invention, is a sandwich of lithium and a
      special type of Perspex. Because it is so light, it solves the problem that
      has kept batteries out of the running for electric cars: it can store a huge
      amount of energy per kilogram.

      Batteries work because chemical reactions inside them force electrons to
      collect at one of the two electrodes. Connect an appliance and the electrons
      travel through it to the other electrode, making an electrical circuit.

      A traditional lead acid battery (where one electrode is made of lead, the
      other of lead dioxide and sulphuric acid floats between the two) has a
      capacity of 35 watt hours per kilogram (Wh/kg). The nickel metal hydride
      batteries that became available in the early 1990s, and enabled laptop
      computing, are about 90Wh/kg. Newer lithium ion batteries, used in mobile
      phones and today's laptops, are 125 Wh/kg.

      "At 125Wh/kg, you can drive a car 125 miles on a single charge - that's not
      good enough," says Sadoway. "You need to go about 250 miles on a single
      charge before it's going to have widespread appeal. So you need a battery
      that's about 250Wh/kg. We've got batteries in my lab right now that are
      300Wh/kg and I can see the possibility of breaking 400Wh/kg."

      The Slimcell gets these big energy densities by ditching weight. Sadoway
      could take little off the electrodes in a lithium ion battery, because the
      metal is so light. Instead, he focused on a component that was crucial but
      which didn't contribute to the storage capacity, the liquid electrolyte.

      "An ideal battery is maximally electrode and minimally everything else,"
      says Sadoway. "The electrolyte doesn't contribute to storage capacity at all
      but you have to have it. What you would like is the thinnest electrolyte."

      Working with MIT colleague Anne Mayes, Sadoway set out to ditch the liquid.
      "The only way we were going to break the 200Wh/kg, I reasoned, was to ask
      was it possible to invent a solid polymer electrolyte that had the
      mechanical properties of a solid and the electrical properties of a liquid,"
      says Sadoway. Many blind avenues later, his team had found his wonder
      material and rethought battery design.

      "There are various companies that claim to have variants of a solid
      separator but, to the best of my knowledge, these companies are all relying
      upon infusing some kind of polymer host with something that's an organic
      liquid," says Sadoway.

      The Slimcell's sandwich of metal electrodes and plastic electrolyte not only
      means it is light and easy to make, it also makes it much safer. Because
      there is no liquid, the battery can't leak. If it is somehow punctured in
      one part, the rest of the battery can carry on working regardless.

      Sadoway and Mayes's team have been steadily improving their polymer
      electrolyte: by developing a way to evaporate the material on to the lithium
      electrodes, they have made it as thin (and light) as physically possible.
      The next step is industrial-scale manufacture, something that has yet to be
      worked out. Sadoway reckons that the Slimcell is at least five years from
      being commercially available.

      Remarkable as the battery is, the MIT team behind it see problems in finding
      a market, mainly due to resistance from battery manufacturers. In the mid
      1990s, just as a lot of companies had invested heavily in NiMH batteries,
      the more advanced lithium ion batteries came out of nowhere. Instead of
      embracing lithium ion, many producers tried to slow its introduction.

      "Until the late Nineties, you could buy laptops fitted with NiMH batteries
      and lithium ion was an option, even though it gave superior performance,
      because they were saying, 'we need to sell as many NiMH batteries as we can
      to try to pay back the capital costs of building these darn plants'," says

      "People would like better batteries but they are wary of making investments.
      What is required is both a technology push and a market pull. Right now
      there are cellphone batteries and the cellphone manufacturers are
      comfortable with them."

      It will take a specialised niche, then, to make the Slimcell viable. Sadoway
      says that whoever develops it commercially needs to find applications for
      which dedicated batteries don't yet exist - medical devices, for example.

      "In a wristwatch, imagine the battery is in the strap and there's a medical
      sensor in there connected to the internet," he says. "If someone is
      monitoring that, they could phone up if the user has forgotten to take some
      medication. This could save hundreds of dollars in medical fees later.
      What's missing? It's a stable battery."

      The Slimcell's big advantage is its versatility. "You can do something with
      this you can't do with any other battery - fold it up, make it conform to
      the shape," says Sadoway. "You can put the battery not in a compartment but
      behind the screen of a computer, or in the fender of a car, so you can have
      distributed power. You don't have it in one big block." After these
      applications, Sadoway's dream of powering electric cars will be a step
      closer. Which is quite a feat for something that is, basically, just like a
      crisp packet.
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