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To kick start the debate we've invited a panel of well known experts to share their views on the proliferation of hybrid cars.

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  • Why a hybrid world would face big battery problems by Roger Kemp
  • Environment | 12:11 p.m. | Tue 9 Oct 2007

  • It’s difficult to imagine a future with a lot of hybrids in it without raising some difficult questions about batteries.

    For decades, milk floats and industrial fork-lift trucks have been propelled by tubular-plate lead-acid batteries. These have a life of more than a thousand charge-discharge cycles but are heavy, having an energy density of around 30 kWh/tonne. Lighter lead-acid batteries can be produced but with a lower cycle-life.

    Unless there’s a major breakthrough in battery technology, it seems clear that hybrids will have to rely on types such as nickel-metal-hydride and lithium-ion. These produce up to 150 kWh/tonne, allowing a 30 kWh battery to weigh only 200 kg. Their cycle-life is also better than lead-acids. However, it’s still not enough to supply a modern car for its entire lifetime.

    Another problem is where to find the raw materials needed to produce hybrid batteries on a large scale. The lithium-ion battery in a digital camera weighs 75 grams but the battery in a plug-in hybrid would weigh 2,000 times as much. So how does this compare with the known production and reserves of lithium? Current production worldwide is 25,000 tonnes a year - roughly equivalent to a million electric vehicle batteries. But last year 1.6 million cars were made in the UK alone. One estimate of global reserves of lithium is 6.3 million tonnes - sufficient to maintain the Japanese car industry for only 20 years, if every new car were a hybrid. Clearly, lithium is not the long-term solution.

    In addition to their base materials, batteries also use various alloying elements and compounds. One additive, palladium, is extracted from very low-grade ores where production of six grams of metal from a tonne of rock is considered good. The work involved in extracting these materials could greatly increase the embedded cost of a car, notwithstanding the environmental impact of the mining operation.

    So, in conclusion, even a relatively small country such as the UK could find it impossible to effect a large-scale shift to hybrids owing to a shortage of battery materials.

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