Sounding Off on Battery Technology

Speaking with Frank Harris of AER Energy Resources

Ask IT managers what they would most like to see improved in handheld and tablet computers, and they’re likely to answer battery technology. While most other mobile components follow Moore’s Law to varying degrees, battery technology has proved to be a stubborn challenge.

The fundamental issue is chemistry and materials science, according to Frank Harris, vice president of marketing at Zinc-Air battery developer AER Energy Resources. It’s simply getting tougher to coax more energy from the known elements and alloys. Instead, designers are looking at increasing the efficiency of known processes, and developing innovative ways to package the batteries to meet the needs of a new generation of devices.

Zinc-Air technology offers one option worth considering for certain mobile applications. But as with any technology, there are trade-offs to consider.

Why is battery technology developing at a seemingly slower rate than other aspects of mobile computing?

“Basically a battery is an electro-chemical device, taking chemical energy and converting it to electrical energy. And because of that, batteries utilize a combination of metals, or metal compounds.”

“The reason that it appears to the electronics world that batteries are a slowly evolving technology is because when you develop a new rechargeable battery, in order to test and verify that it actually works, say over something like 300 cycles, you literally have to put it through 300 charge and discharge cycles.”

“In the case of Zinc Air, where a cycle may be one day, that would result in a 300 day test. That explains one aspect of the issue. Another issue arises since we’re dealing with metals. If you look at the periodic table, over the 150 years of battery technology every single one of those metals, and most combinations, have been tried.”

“So what happens these days is that advances typically come in materials science. There’s a finite number of metals that are known to be able to be used safely in battery combinations. And the advances in batteries come in the mechanical packaging of those metals in order to improve existing technologies such as Nickel Metal Hydride, and others. And that’s a process that can go on for decades.”

“To better understand the process, it’s useful to separate batteries into two classes: primary (meaning disposable), and secondary (rechargeable). It’s inherently easier to develop a primary system because you don’t have to worry about the reaction during recharge. So, in the case of alkaline, this technology is only picking up mild improvements as the companies that manufacture them try to make the chemical process more efficient.”

“Safety concerns also contributes to the length of time it takes to develop a rechargeable battery, especially during the recharge mode. Where Lithium Ion tends to have its failure is during recharge. There has to be a lot of overhead, from the aspect of safety, in that technology.”

Describe some of the history of Zinc-Air technology?

“Zinc-Air has been around for about 50 years, and was typically made into large battery systems serving applications such as harbor buoy lights and railroad switching, where people could go out and replace the zinc in a maintenance cycle.”

“Then, in the early 1970’s, with some of the advances in miniaturization and materials, we got the button cell battery, which is a primary (disposable) technology using Zinc-Air. These are chiefly used in hearing aids today. The reason that it’s used in hearing aids is because Zinc-Air, by weight, has the highest energy of the commercial technologies.”

“In the case of button cells, it has four times the energy of an equivalent alkaline cell, and two times the energy of the lithium button cells.”

How does Zinc-Air technology work?

“It’s a very simple process. Oxygen moves from the air and directly into the cell through a membrane, which is the cathode.”

“That reacts with the zinc, which is the anode. This converts zinc to zinc oxide, and in that oxidation, or rusting process, the electrons are thrown off. The electrolyte in Zinc-Air is potassium hydroxide, which is the same electrolyte used in alkaline, Nickel Cadmium, and Nickel Metal Hydride batteries.”

How is this different from the process in a Lithium Ion battery?

“Because we’re able to absorb oxygen directly from the atmosphere, we don’t have to carry around the reactant agent in the cell. In the case of Lithium Ion, they employ a self-contained unit with however much oxidizing agent or lithium they have—it all has to be contained within.”

“Because we’re able to absorb oxygen directly from the atmosphere, we don’t have to carry around the reactant agent in the cell.”

“We don’t have to contain half of it, allowing us to drive up the energy density with the addition of more zinc. The issue with Zinc-Air is that you have to use a flat shape in most cases enabling you to get the air to the air electrode.”

What are the discharge characteristics of Zinc-Air batteries?

“Nickel Cadmium, Nickel Metal Hydride, and Zinc-Air have a very flat discharge profile, which means that they operate at the running voltage pretty much for their entire capacity, and then they kneel over and drop off. Lithium Ion is more of a sloping curve—it’s not as flat.”

How many times can you recharge a Zinc-Air battery?

“Because Zinc Air is a different technology, and because it’s a high energy technology, we look at it from the point of view of total hours of usage. In the case of other technologies, such as Lithium Ion and Nickel Metal Hydride, because they have lower capacities, they tend to run for a couple of hours in a typical electronic product application. We’re designing batteries that run 8, 10, and maybe even 30 hours in those applications.”

“So if you look at the results, Zinc Air will offer you about 400 hours of usage, which translates to something like 20 cycles, assuming full discharges. Shorter discharges will allow you to get about 100 to 300 cycles. So it’s not so much cycle dependent, as total energy delivered.”

“Comparing this to Lithium Ion, the typical battery in an application such as a portable computer is going to give you somewhere between 300 and 500 cycles, and somewhere between two to three hours of run-time per cycle. So you’re going to end up somewhere between 500 to 600 hours of usage, perhaps all the way up to about 1000 hours.”

“So Zinc-Air has an inherently lower cycle life than other technologies, and that’s the nature of being air-breathing. But it gives you the benefit of longer run time between charges. And if you ask users, they typically say that one of their main concerns is maximizing the time between recharges.”

How is Zinc Air being used in mobile applications today?

“The main application that we’ve been able to latch on to is satellite phones for geostationary satellites. For that application, we offer a 180 watt-hour battery, which would be the equivalent of about five or six typical mobile computer batteries.”

“The main application that we’ve been able to latch on to is satellite phones for geostationary satellites.”

“This will run the satellite phone for about 50 hours on standby, and eight hours of transmit time. In comparison, the internal battery, whether it’s Lithium Ion or Nickel Metal Hydride, will give a user about two and a half to three hours in that mode.”

“But here’s something you have to keep in mind when you turn your attention to products like computers, pen tablets, and even devices like the color HPC. These are devices that draw wattages of one to five watts, depending on the configuration.”

“In the case of a satellite phone, it runs on average at about 10-12 watts, and when it transmits, it’s up to perhaps as high as 21 watts. And in the case of a notebook computer, average usage consumption is about 20 watts, and up to 30 watts during peak power consumption.”

“So the application that Zinc-Air has in electronic products is in devices that need long run time, and are in a power band that ranges from one to ten watts. That’s an ideal application for a battery that can fit either in, or under, the device, and will run the devices for eight or tens hours between charges.”

“Here’s how we’ve been taking the technology forward. In December, we announced that we received a patent for our diffusion air manager. Here’s why this is important. When you buy a button cell for your hearing aid, it comes with the air hole taped up with mylar, so no air can get into the cell.”

“When you put it into your hearing aid, you pull the mylar tape off and, at this point, the battery starts being exposed to air.”

“But for cases when you’re going to use Zinc-Air in an intermittent device, or a device that requires long shelf life, we’ve developed an air management system as part of our base technology.

We’ve just now come up with something we call a diffusion air manager which doesn’t require you to remove tape or open some sort of small door.”

“Instead we use a very clever method employing a long diffusion tube, sort of like a straw. When the battery is not on, our air moving device is not operating, therefore acting just like a door.”

“That diffusion air manager has opened up new opportunities that we didn’t have before for smaller cell sizes and smaller applications. And that’s where we’re spending the majority of our R&D effort right now.”

Are there any hazards related to Zinc-Air, perhaps during the more volatile recharging process? How does it compare to a technology such as Lithium Ion?

“Zinc Air is inherently one of the safest battery technologies available, including during the recharging mode. Since it absorbs oxygen from the atmosphere, the system is at atmospheric pressure. This contrasts with systems such as Nickel Cadmium or Lithium Ion, which are high pressure cell technologies.”

“Since it absorbs oxygen from the atmosphere, the system is at atmospheric pressure. So even if there is an abuse, we’re not going to rapidly disassemble, or in layman terms, explode.”

“So even if there is an abuse, we’re not going to rapidly disassemble, or in layman terms, explode. When we’re abused by short circuit, for example, the system cannot absorb oxygen fast enough to sustain the short circuit condition. So the reaction basically shuts itself down. This means that you fail safe in an abuse mode.”

“In addition, Zinc-Air does not employ toxic material such as mercury, which is also true for alkaline batteries nowadays. We’ve worked hard to get the mercury out of our cell, so all that remains are trace amounts that can’t effectively be processed out. Overall, it’s a very safe technology.”

We hear a lot about the application of technologies such as fuel cells for electric cars and the like. Is there any chance that this technology will be scaled down for consumer electronics applications?

“There are people who think that there can be ways to scale it down. But it is decades away from practicality, in my opinion, especially for small devices. It’s clearly an area that people will work on during the coming years, but I think that you’ll find battery technologies are inexpensive relative to fuel cell technology.”

“Batteries are also considered to be comparatively safe next to fuel cells. The hydrogen used in today’s fuel cells is, as we all know, a very volatile substance. There are issues related to containing the hydrogen, and so on.”

“So to answer the question of whether it’s a short term threat, the answer is not at all. Over the longer term, perhaps ten to fifteen years down the road, yes. And this is mostly because who knows what’s going to happen in the field of materials technology.”

Are you examining relatively exotic substances in your search for a better battery? In this case, I’m thinking about something like Buckminsterfullerenes, a.k.a Buckyballs, the 60 atom carbon structure.

“We’ve looked at it because our air electrode is basically a carbon membrane. However, it’s quite an expensive material right now. And that’s another side of this. Zinc-Air, relative to the other technologies, can be a very low cost technology.”

“It’s not as capital intensive from a manufacturing point of view, and it also uses comparatively low cost materials such as carbon and zinc. Both are readily available and are inexpensive relative to something like lithium or cadmium.”

What’s in store for battery technology over the next twelve months? Also, what about three to ten years?

“I think that Lithium Ion will be a technology that will continue to be applied in small cell applications for electronic products. The advantage of Lithium Ion polymers, over current Lithium Ion however, is not readily apparent. It’s probably no better than existing Lithium Ion, other than in the form factor area.”

“But from a performance standpoint, it might even be a step back a little bit. The existing batteries, such as Nickel Cadmium and Nickel Metal Hydride, will continue to push forward at a slower pace, as measured by increases in watt-hours per kilogram and watt-hours per litre.”

“Lithium technologies will remain expensive relative to the other technologies, so you’ll start getting some trade-offs in terms of cost versus performance, especially since it’s not radically better than Nickel Metal Hydride on an energy density basis or a power basis.”

“As far as new battery technologies, we feel that some of the work we’ve done on the air management system for Zinc-Air, and the ability to apply these advances to both primary and secondary (rechargeable) cells, makes the application of Zinc-Air more promising.”

“This means that you can indeed build low cost, long run-time batteries. And this could have an impact on certain product categories. Certainly we intend to continue forward in that direction.”

“Basically, we don’t see any other primary technologies out there—alkaline is pretty much it when it comes to performance in non-rechargeable systems. There is some work being done around lead acid, but this is really geared more towards the power tools market.”

AER Energy Resources
www.aern.com