How new battery tech will make your gadgets last longer

True Capacity

An important characteristic of a battery is its energy density, that is how much electrical energy can be produced per gram or per cubic millimetre of battery. Things aren’t that simple though because, in many cases, it’s just not possible to extract all the energy that is, at least in theory, trapped inside a battery.

First, manufacturers usually quote an ideal case scenario which involves extracting the energy at a given rate. If you have a power-hungry device that has a greater rate of energy use, you’ll end up with less energy out of the battery. Alkaline cells are particularly bad in this respect which means that, while they are quoted as having a higher energy density than common rechargeable batteries, in practice it can be lower. An AA cell, for example, might provide 3W hours of energy if you draw just 25mA of current, but at 500mW you might get less than half as much.

Second, the capacity often depends on the temperature so, if you’re using kit outside in cold weather, you could find battery to be disappointing. In fact, the capacity of an alkaline cell can drop five-fold in going from +10°C to -20°C. Something we’ve experienced with smartphones in very cold conditions.

Finally, while some battery technologies maintain their voltage until they’re almost flat, with others, and again alkaline batteries are especially poor, the voltage gradually drops as they’re discharged. This was particularly noticeable with old style torches that used filament bulbs, as they got progressively dimmer as the battery became exhausted. Modern electronic gear can better cope with this because today’s power supplies can operate over a broad range of voltages but, even so, they’ll eventually come to a point at which energy still remains in the battery but the voltage is too low to do anything useful with it. Batteries that maintain their voltage as they’re discharged, only dropping when they’re almost flat, will allow better use to be made of their energy.

^The amount of energy you get out of a battery depends on how you use it

Better Batteries

It seems likely that batteries based in lithium-ion technology will continue as the dominant force in portable power for many years to come. That isn’t preventing far-sighted scientists from looking for its successor, though.

Intriguingly, one hot area of research for portable power of the future isn’t a battery at all, although most people will probably view it as such. Instead of storing chemical energy which is converted to electrical energy when power is required, in this solution the energy is genuinely stored as an electrical charge. Electronic components that do exactly this have been around for over a century, in fact your smartphone and PC motherboard will contain loads of them.

The component in question is of course a capacitor but, for ordinary electronic applications, the amount of charge they can store is minute. An up-and-coming breed of super-capacitor, otherwise known as the electrochemical capacitor, promises to provide much greater levels of storage than ordinary capacitors. Even so, that energy density suffers by comparison to the best batteries on offer but they do have other advantages as Dr. Pooja M. Panchmatia of the Department of Chemical Sciences at the University of Huddersfield described.

“Electrochemical capacitors have unusually high energy densities when compared to common capacitors as well as very high specific short duration peak power (i.e., rapid energy delivery). Batteries have significantly higher energy densities than electrochemical capacitors with lower short duration peak power.

“For example, Li-ion batteries have specific energy densities of hundreds of Watt hours per kg, with electrochemical capacitors having specific energy densities ranging from several to tens of Watt hours per kg. However, the short duration peak power of an electrochemical capacitor exceeds 1,000 Watts per kg, which is an order of magnitude better than that of typical Li-ion batteries.”

When we bear in mind that it’s also possible to charge super-capacitors much more quickly than batteries, perhaps in seconds, we can see another reason for the intense research interest in this technology.

This level of interest in super-capacitors doesn’t mean that true batteries, the ones that rely on electro-chemical reactions, have come to the end of the line except for incremental improvements to lithium-ion technology. Dr Panchmatia outlined several technologies that might just provide that much sought-after combination of high energy and power densities, low cost and safety.

“In recent years, metal-air and metal-sulphur batteries have generated great interest in the research community”, she said. “For example, Zinc-air batteries combine atmospheric oxygen and zinc metal in a liquid alkaline electrolyte to generate electricity with a by-product of zinc oxide. When the process is reversed during recharging, oxygen and zinc metal are regenerated. Zinc-air batteries are attractive because of the abundance and low cost of zinc metal, as well as the non-flammable nature of aqueous electrolytes which makes the batteries inherently safe to operate.”

However, it appears we’re not going to be seeing this technology in our smarthpones anytime soon. “It remains a grand challenge to develop electrically rechargeable batteries, with the stumbling blocks being the lack of efficient and robust air catalysts, as well as the limited cycle life of the zinc electrodes”, she warned. “Zinc-air batteries have been commercialized only for small medical and telecommunication applications”, she said. “Similar constraints remain with the Li-sulphur and the Li-air batteries, which have not yet been commercialized.”

^Zinc Air batteries might be used mostly in hearing aids today but all that could change

Intriguingly, Dr Panchmatia even suggested that something as simple as making batteries a different shape could reap major benefits. “Further research into the redesign of the batteries has also gained momentum. Researchers from the Pacific Northwest National Laboratory claim to increase battery power by 30% by simply changing the shape of the battery from cylindrical to planar. Additionally new materials using elements of the periodic table that are readily available such as sodium and nickel are also being sought and even commercialized by General Electric”.