The Future Is Now for Rechargeable Laptop Batteries

A space-age battery is about to revolutionize portable computing.

You’re 35,000 feet up, a few hours into a cross-country airplane journey. Having dutifully worked on some office memos, you finally get around to watching the DVD of Murder on the Orient Express on your laptop. But just as Detective Poirot is revealing whodunit, the screen goes blank. Your laptop’s batteries have run out of juice.

It’s a common enough scenario because rechargeable battery technology has failed to keep pace with other improvements in computers. While the number of electricity-hungry transistors that can be squeezed onto a silicon chip has doubled about every two years over the past few decades, it took more than 20 years (from 1970 to 1990) to double the amount of energy that rechargeable batteries can store per pound.

Now portable-energy start-up ZPower aims to strike a blow for frustrated laptop owners everywhere with a rechargeable battery that the company claims will offer 20 to 40 percent more computer time per charge than do the current champs of rechargeable technology, lithium-ion batteries. ZPower’s batteries also offer the advantage of being immune to “exothermic decomposition” (also known as “bursting into flames”), a problem that has prompted the recall of millions of lithium-ion batteries worldwide, not to mention some spectacular YouTube videos.

ZPower’s batteries use silver- and zinc-based electrodes. Silver-zinc batteries are not technically new; because they are so good at storing electricity, they were used in NASA’s Apollo spacecraft of the 1960s and 1970s. The technology wasn’t widely adopted back then because those silver-zinc batteries could be charged only a few times before they stopped working—not a problem for a 10-day mission to the moon, but a real deal breaker for mobile electronics.

ZPower has made improvements that allow its silver-zinc batteries to be recharged as often as lithium-ion batteries. And when the batteries do reach the end of their useful life, the silver and zinc can easily be recovered and recycled into new batteries, reducing environmental impact. On the downside, the batteries operate at a voltage different from that of lithium-ion batteries, meaning that laptop makers have to tweak their computers to work with the new batteries. ZPower is collaborating with computer component suppliers to develop laptop power systems that can handle both lithium-ion and silver-zinc batteries and says the first silver-zinc battery–­powered laptop is due out in early 2009.

How It Works
One big problem with traditional silver-zinc batteries is that as each cell is drained and recharged, zinc dendrites (shown as irregular objects in the diagram above) can form within the zinc anode (shown in green). These dendrites can distort the shape of the anode and can migrate through it, eventually piercing the membrane (yellow) that separates the zinc anode from the silver cathode (not shown, for clarity). If the membrane is pierced, the cell will short-circuit and die. To solve this problem, ZPower introduced polymers (shown as red balls) into the zinc anode. The polymers inhibit dendrites from growing and block their migration inside the anode, reducing the likelihood that the membrane will be pierced.