The mobile power challenge

Mobile devices are power-hungry and the fundamental need to continue to improve both power-to-weight and absolute capacity, as well as a desire to lower recharge times, have resulted in a number of advances in battery research.

There are two great challenges ahead of us in mobile computing and communications, and, no, one of them is not security. Security has always been viewed as showstopper No. 1 in mobility, but while we'll never be "done" when it comes to security, we now have very good solutions to the security problem, and I'll cover these in an upcoming column. The biggest problem is a little more mundane -- it's power.

Specifically, it's how to power mobile devices that are ever more power-hungry, due to a combination of higher performance and more on-board features. From a purely wireless communication perspective, we've been able to address this challenge via more power-conservative circuitry, improved radio technology (primarily packing more bits into a given amount of spectrum per unit of time, with improved reliability), and power-saving protocols used by essentially every wireless system today. These primarily involve synchronizing transmitter and receiver so that the receiving end can go to "sleep" for brief periods of time, and then wake up at predefined intervals to check for traffic.

All of this helps, but there's no substitute for more juice, and therein lays the problem. Batteries (and we're only considering rechargeable cells here) work primarily via electrochemical reactions involving metals and other chemicals that yield free electrons – that's where the current comes from. But metals are, well, metals, and usually heavy. Nickel-cadmium cells are really heavy and have a "memory' effect that limits their usefulness – apart from the fact that cadmium is toxic. Nickel-metal hydride was a great leap forward, but the ultimate to date is lithium-ion (LiON) and lithium-polymer (LiPo) cells. Lithium is a very light metal, with atomic number 3. The primary benefit, then, of using Lithium is a significant improvement in the power-to-weight ratio of the resulting battery – more bang for the gram, if you will.

But building reliable lithium cells can be challenging, as Sony found out when it had to recall hundreds of millions of dollars' worth of defective batteries original sold to a number of notebook computer vendors. Now, I have no idea what a smoldering lithium cell smells like; the occurrence of the "burst into flames" problem is very, very rare indeed. But this is something we can't fool around with; the defect in the Sony cells, resulting from small metal particles that could cause short circuits, could have devastating consequences if a fire occurred on an aircraft, near combustible substances, or, let's face it, almost anywhere. But keep in mind this situation is the result of a manufacturing defect and not a problem inherent in lithium technology.

That being said, though, the fundamental need to continue to improve both power-to-weight and absolute capacity, as well as a desire to lower recharge times, have resulted in a number of advances in battery research, as follows:

  • Fuel cells: Fuel cells work by combining hydrogen and oxygen, with the resulting being electricity and water. The problem is where to get the hydrogen, which (like lithium, oddly) doesn't exist in a pure state most of the time. Hydrogen is very explosive and its precursors (like methane) quite flammable, and I really don't have high hopes for fuel cell technology in mobile devices.
  • Plastic batteries: If I were just entering college today, I'd get a degree in material science. It is all about new materials, and one of those is the use of plastics in batteries, with the hope of increased capacity and shorter recharge cycles.
  • Supercapacitors: A capacitor is a basic electronic device capable of storing an electric charge. A supercapacitor is designed to hold a lot of charge, and progress has been made in developing these for mobile applications. The core advantage to this approach is that capacitors have a very short "recharge" time – no need to plug the device in overnight. For an approach using yet more exotic materials (in this case carbon nanotubes), see here

I'll go out on a limb here and say that I'm very optimistic that this mobile challenge will see good progress over the next few years. And the other big challenge? This one is truly insoluble, and may always remain so - it's safety, as in human health and safety. And that's a topic I'll cover in an upcoming column.



This was last published in October 2006

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