The Li-ion awakens

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Laptop computers, mobile phones and iPods all rely on lithium-ion batteries. They are light, hold their charge well and are able to store two to three times more energy for their weight than their nickel-cadmium rivals. They are also easier to recycle; cadmium, in particular, is a very nasty ingredient.

But Li-ion batteries, as they are known in the trade, are sensitive souls. They last only a few years, even if they are not used. And they fade even faster when used in harsh conditions, such as high temperatures. They need special protective circuits to manage the charging and discharging. And they may react to abuse by bursting into flames.

However, the chances of Toshiba’s new Super Charge ion Battery (SCiB) catching fire are “extremely low”, according to Toshiharu Watanabe, the head of the company’s industrial systems group. “And it will not explode even if it ruptures,” he adds reassuringly. Just as important, the battery can be recharged to 90% of its capacity in less than five minutes, instead of the hour or so required by most Li-ion batteries. And it will last for more than ten years.

The SCiB is one member of a new generation of Li-ion batteries. They are being made safer after the recall of millions of laptop batteries in 2006, when some caught fire. But they are also being made better. And that should allow them to move out of the gadget market and into electric bicycles and motorcycles, fork-lift trucks and construction machinery. According to Donald Saxman, who studies the battery industry for BCC Research, they should be powerful enough for cars, too, within five years or so. Indeed, they are already being used in some experimental and exotic electric vehicles, such as the 210 kph Sports car developed in California by Tesla Motors.

Like other batteries, those that use lithium work by shuttling ions (electrically charged atoms or groups of atoms) between their electrodes. When they are charging, the ions go in one direction. When they are discharging, they go in the other. The most widely used lithium-ion batteries have a positive electrode made from cobalt oxide and a negative electrode made from graphite. The electrolyte (the material through which the ions pass from one electrode to the other) is a lithium-based gel or polymer.

Cobalt oxide gives this class of battery its high energy density. The downside is that cobalt oxide batteries easily overheat, especially if a battery is damaged or assembled wrongly in a way that causes an internal short-circuit. Such an overheating cell can ignite, causing its neighbours to catch fire in a ‘thermal runaway’—as happened to the faulty batches in 2006. To stop that occurring, and also to enhance performance, new electrode materials are being tried out. The most promising are phosphates of manganese and iron—made more promising still by being manufactured as particles whose dimensions are measured in nanometres (billionths of a metre). Making an electrode out of such nanoparticles increases its surface area. That, in turn, decreases the battery’s internal resistance and improves its ability to store and deliver energy.

One of the leaders in this field is A123 Systems of Watertown, Massachusetts. The phosphate particles in its electrodes are less than 100 nanometres across—about a hundredth of the size of the oxide particles used in existing Li-ion batteries. The new generation of Li-ion batteries are hardy enough for A123 Systems to make batteries for DeWalt, a supplier of industrial power tools. DeWalt is now confident enough in the ability of Li-ion batteries to withstand the rigours of construction sites that it recently began offering them as an option for its cordless hammerdrills and other heavy-duty machines. A123 Systems is now developing a Li-ion system for the Chevvy Volt, an electric car planned by General Motors.

The prize for machismo in this area, however, goes to Saft, a French firm. In November it unveiled a Li-ion cell capable of withstanding extreme vibration, high pressure and temperatures of up to 125°C. This will be used to power the measuring equipment incorporated into drill heads used by the oil and gas industry. If Li-ion can withstand that sort of punishment, electric cars should be a breeze.