Updated: When it comes to all things batteries, I’m a fanboy of Venkat Srinivasan, researcher at the Lawrence Berkeley National Lab‘s Batteries for Advanced Transportation Technologies (BATT) program, and rockin’ blogger for his site This Week In Batteries. Well, for his weekly update this week, he helps explain some of the technology he thinks is at the heart of Apple’s recent announcement that it has developed and is selling a battery charger with six Apple-optimized nickel metal hydride (Ni-MH) reusable batteries for its wireless Mac accessories.
As Srinivasan dryly puts it: “Trust Apple to make a Ni-MH battery with a charger sound cool. Will the magic never stop?” Traditionally, Ni-MH batteries are not a good fit for the kinds of Bluetooth-connected applications that Apple has designed it for, because Srinivasan says Ni-MH batteries commonly lose their charge (called self discharge) by as much as 20 percent to 50 percent, depending on the climate, after just two weeks. Ni-MH batteries can self-discharge quickly because of internal leaks
But Srinivasan speculates that Steve Jobs and Apple are using have placed an effective separator — a barrier between the anode and the cathode in the battery that lets ions pass but not electrons — that’s preventing the common internal leaking that plagues Ni-MH batteries. It’s like placing a 25-micron thick crossing guard in the guts to control the traffic. As a result, Jobs can say that Apple’s Ni-MH batteries, combined with the charger, will still be able to hold 80 percent of its charge after a year.
Update: Various bloggers are saying they think Apple is using Sanyo’s Eneloop Ni-MH batteries for its battery technology. The connection makes sense if you read the description of Eneloop’s reliance on a separator to beat back self discharge. Srinivasan responds on his blog in the comment section that the Apple battery “is probably similar to the Eneloop (or maybe the same?). It’s 5-10 years old in design.” No word yet from Apple on whether its using Sanyo’s Eneloops or not.
Srinivasan says that developments in separators in older battery chemistries like Ni-MH have only started happening in the last five years, but because separators can cost up to 20 percent of the cost of the battery, a lot of innovation is starting to happen there. He himself is working on designing separator technology for a “flow battery,” using a $1.6 million APRA-E grant from the Department of Energy. Flow batteries are similar to large fuel cells but generally use large storage tanks full of electrolytes and pumps that circulate the solution through the system.
For lithium ion batteries — the technology that is in most of our laptops and the first-generation of electric vehicles on the roads — the separator is also responsible for trying to stop thermal run away (the battery blows up). It can clamp down on the flow of electrodes when the temperature goes too high. Another reason why separator technology for lithium ion batteries needs more innovation.
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