Electronics continue to shrink to ever smaller sizes, but researchers are having a tough time miniaturising the batteries powering today’s mobile gadgets. Step forward, bicontinuous nanoporous electrodes.
Smartphones use smaller power packs than they did five years ago, it’s true, but that’s because their chips and radios are more power efficient, not because of any major new battery technology.
Now boffins from the University of Illinois at Urbana-Champaign reckon they have come up with a new pocket-friendly electricity supply.
Enter the “microbattery”, a compact power cell constructed from many three-dimensional nanoporous electrodes capable, its developers claim, of delivering both high power and a large energy capacity.
The negative cathode was devised by another team at the university, but graduate student James Pikul, working under Bliss Professor of mechanical science and engineering William King, figured out how to create a compatible anode and put the two into a battery.
Their approach, outlined in Nature Communications, involves assembling a matrix of microscopic polythene balls placed on a glass substrate. The particles are used to hold electrically desposited coverings of nickel onto which the anode and cathode materials can be deposited once the remaining polythene particles have been chemically washed away.
Each discrete electrode is essentially a three-dimension array of tiny electrodes - or “bicontinuous interdigitated microelectrodes”, as the researchers put it.
The anode is based on a nickel-tin alloy, the cathode on Lithium-Magnesium-Oxide. Embedded Gold-Chromium connectors link each anode and cathode to their respective terminals.
The result is a microbattery with a power density of 7.4mW cm−2 μm−1 which, say the boffins, “equals or exceeds that of the best supercapacitors” and is “2000 times higher than that of other microbatteries”.
The upshot is that the battery’s design can be scaled to deliver high power level units or shrunk to deliver very, very small but capacious power units that can be embedded in mobile devices. Think of a battery a few millimetres in size, able to “jump-start a dead car battery”.
“Now the power source is as high-performance as the rest of [the device],” King claimed.
“If you want high energy you can’t get high power. If you want high power it’s very difficult to get high energy,” said Pikul. “But for very interesting applications, especially modern applications, you really need both. That’s what our batteries are starting to do.
“It’s a new enabling technology. It’s not a progressive improvement over previous technologies.”
The cathode design, devised by a team led by the University’s Professor Paul Braun, is fast charging. Pikul reckons building a battery out of it yields a rechargeable that can be filled up in a thousandth of the time it takes to charge a comparably sized regular rechargeable cell.
Building a battery in a lab is one thing. Working out how to manufacture it commercially at a price that makes it a realistic power source for future devices is another thing altogether. Pikul and King will be working on that next. ®