Battery life

Features Mark Pickavance Dec 15, 2012

Mark Pickavance looks at the future of battery technology and asks why we're charging our phones every day?

If, like many people, you own a smartphone, then you’ll be familiar with the daily ritual of charging yours or putting it on charge when you get to work if you use it plenty. Even the earliest mobile phones lasted longer than that, so what’s happening to battery technology, and can we extend those charging sessions to more helpful timescales?

Demanding power

The transition from old phone technology to a modern smartphone can be somewhat jarring for the owner, with so many new concepts to grasp and outmoded thinking to dispel. However, if you ask the majority of owners what they weren’t really prepared for, it was the incredibly short battery life that most phones come with.

What’s most disturbing about this phenomena is that anyone who owns one of these devices just assumes now that it will need charging once a day, at a very minimum. The first mobile phone that I possessed was the classic Nokia 6000 series - a 6150 to be precise. It contained a 600mAh Li-pol battery, which, according to Nokia, gave a talk time of between 100 and 180 minutes, and a standby of up to 170 hours. Later in that product’s life, Nokia gave it a 900mAh Li-ion upgrade that extended talk time to a maximum of 270 minutes and standby to in excess of ten days!

Let’s compare that with the recently released Apple iPhone 5. It has a 1440mAh (5.45Wh) battery, which it considers will give you eight hours of talk time and a standby of 225 hours. On the face of it, that’s an improvement in all but standby life, although the battery is now significantly bigger in capacity terms. Some smartphone designs have batteries that are larger than 2000mAh, and the trend is for them to get even bigger.

So why is it that my old Nokia got charged once a week and the iPhone is likely to see the charger every single day?

Changing demands

Those that test these devices on a regular basis found that if you never use your phone, then it will last a remarkably long time without a charge. Play games or surf using 3G (or LTE) and that lifespan might well reduce to as little as four hours. The truth is that we ourselves as much of an issue as the phones, because we won’t put the damn things down, and the more we use and play with them, the greater the impact on the battery life.

It’s worth remembering that the Nokia was exclusively used to make calls and send and receive text messages using the old GSM network. In contrast, a modern phone will be moving between the 2/3G digital networks, communicating with wi-fi hotspots and potentially accessing LTE services in the future. All these advancements are power consumers, and according those who have tested the latest LTE service just launched by EE in the UK, it kills the battery on those phones that can access it.

The Nokia also only had a simple LCD panel, whereas a modern phone has a colour display that requires backlighting to be seen. That’s a major drain on battery life and so is the level of computing power that many phones have. It’s difficult to compare an ARM CPU with the Intel or AMD equivalent in a PC, because the ARM is a RISC (Reduced Instruction Set) design where the Core series and AMD Bulldozer designs are primarily CISC (Complex Instruction Set). However, the Cortex-A9 that’s in an iPhone 5 is at least as powerful as a Pentium 3 and possibly more powerful when you consider its integrated GPU features.

The bottom line is that a phone is no longer a phone; it’s a mobile digital data service hub, so it’s using power even when we’re not expressly asking that it do something for us.

Be more efficient

Moving to the world of the PC for a short spell, for a while it seemed that power supplies for computers were destined to get ever bigger. These days, a standard PC comes with a PSU that’s about 500W, maybe less and occasionally more. Supplies in excess of 1000W are available, but you only really need those if you intend to deploy multiple video cards or something equally outrageous.
The 400-500W typical supply has been with us for a while, even though computers today are substantially more powerful than those of five or ten years ago.

What’s happened is that computers have become more efficient, delivering more computing cycles for the same electrical power, so even though they use such a similar power profile, they do more with it. Most of the efficiency improvements have come through the shrinking of chip technology, as a thinner track reduces the resistance overhead of the chip to power and, as such, it heats up less and can run at a higher speed. However, that’s only one part of the power efficiency story: PC power management is another, and the throttling on the CPU/GPU clock speeds is another.

The latest efficiency thinking is being directed at phones, where the power constraints are more severe. Most phones these days have a page or app where you can see where your phone ate most of its electrical lunch, and there you can see that the screen and communicating with the outside world took the biggest slices.

Research engineers from Eta Devices in Cambridge, Massachusetts, recently released an analysis, which goes some way to helping us understand why the phone uses so much power to achieve what’s required. The biggest issue is small components in the phone called power amplifiers, which take the voltage that the battery provides and boosts it to deliver the power that specific parts need, most notably those that transmit wireless signals.

Converting the power is massively inefficient, and it’s been determined that of the power they consume, only 35% of that is actually delivered to the target component, and the rest is wasted as heat. When you consider that the latest phones, like the iPhone 5, have six independent power amps, the potential for flushing most of the battery life away achieving very little is substantial.

The critical problem is that the power system in the phone assumes that these devices will need the power profile that they use all the time, not just when they’re active, and having that power ready to use burns through the battery. With wireless communications having power ramps tends to distort the signal, rather ruining the purpose of what it is they’re used for.

The reason for the Eta Devices report is that it’s developed a whole new type of power amp, which samples the demands made on it 20 million times a second, allowing it to deliver high power when it’s needed, but to also chop it right back when it isn’t.

It plans to take its prototype device and use it in LTE base stations in the next year, with mobile friendly chips to follow that, if successful. It’s chosen base stations initially because they currently require air conditioning to operate, which is space that could be better used for longer battery life in the event of power outages. If they can deliver these promised efficiency improvements, then any phone or tablet using these power amps could see battery life improve by 60%, with little or no other modifications to the hardware.

Fuel cells

Batteries are fine, but what happens when you can’t charge them? That’s precisely the problem that faces expeditions to remote places or just those for whom a power socket isn’t readily available. The solution is a fuel cell, which, as the name suggests, converts chemical energy into electricity, allowing battery-based devices to be recharged or run directly from the fuel cell.

The conventional fuels for these devices are hydrogen, though other flammable gases and liquids like methanol have also been used successfully. Their technological origins go back to the Victorian era, but their value was demonstrated by Nasa, which has used fuel cells on its spacecraft from its earliest manned missions. 

So could a fuel cell extend your computing experience? Yes, and in fact there are a few products close to availability. An MIT spin-off, Lilliputian Systems of Wilmington Massachusetts, has designed a tiny USB portable charger that uses cartridges containing lighter fluid to deliver multiple charges to any compatible device. The prototype device is about the size of a thick phone, and can offer between ten and 14 full recharges to a typical iPhone. The price of the device is expected to be less than $200, and each fuel cartridge just a few dollars.

The fuel cell has impressed those that have used it, and Lilliputian Systems has not only been able to crack a deal with BrookStone to distribute its first product, but it also successfully attained $60m in equity finance from its investors. Brookstone and Lilliputian will make a formal product announcement in the coming months, so hopefully ts device will be another option to extend battery life in 2013.

Nanotubes to the rescue

Carbon nanotube (that odd organisation of carbon atoms into very useful structures) have many uses, it’s been discovered. Graphene, as it’s now being referred to, has some especially interesting electrical properties, some of which might be incredibly useful for battery technology.

The one that scientists at MIT first alighted to was to do with the huge surface area that graphene offers, which is much greater than the graphite that’s traditionally been used. The first prototype battery demonstrated in 2010 increased the charge by about 30% more in the same volume. That’s a modest increase but one that is certainly worth having. The graphene battery also showed some other unique properties to do with how rapidly charge could be stored and subsequently released.

That allows the batteries to output increased power, which could certainly be of use in automotive applications, but it also allows the batteries to charge must faster too. For problems that need fast charge and release, the solution has been to use electrochemical capacitors, but these new graphene batteries provide a whole new layer between conventional lithium-ion tech and those more extreme devices.

That begs the question: why aren’t we using this now? Unfortunately, developing commercial solutions working with tubes that are just one 50,000th of the thickness of a human hair isn’t a priority for Yang Shao-Horn, an associate professor of materials science and mechanical engineering. She’s more interested in understanding the chemistry that their prototypes use, which has yet to be fully understood.

While this work is interesting in the wider context of battery technology, it probably won’t be what powers a future phone or PC. Nevertheless, it might demonstrate a path to making recharging less of a chore and something that could reduce the impact of the limited carrying capacity we have now. However, this isn’t the only way that nanotubes can help our power needs.

Fatter and faster

It’s worth considering that part of the battery life issue is the time it takes to charge, because if it didn’t take so long, then we’d do it more regularly without much concern. The most common type of battery used in computing devices is the lithium-ion variety, which has ousted other chemistry in the past ten years. The technology of this material has some unusual properties, some that slow down how rapidly it can be charged.

What you might be unaware of when you’re charging your phone is that the battery grows, as a charged cell occupies more volume than a depleted one. Also, the battery is charged from the outside in, so if you make the battery fatter for greater capacity, it takes even longer to charge. You can break the cell into small pieces, but this only helps a little. A new approach by Korean scientists, working at the Ulsan National Institute of Science and Technology (UNIST), appears to have solved this problem.

Their solution is amazingly simple: they take the cathode material (lithium manganese oxide in this case) and soak it in a solution containing graphite. That creates fibrous conductive pathways throughout the cathode, allowing power to penetrate the battery much more easily. It’s then packaged with the graphite anode component as in a normal battery and you have a device that is identical in performance, other than it can charge between 30 and 120 times faster.

The catch? The battery is marginally bigger, which means that it might not be ideal for phones, but it could be used in laptops, and it’s perfect for traditionally long-charging technology, like electric vehicles.

More anode options

Using graphite as the anode in batteries goes back to the very earliest battery designs, because it’s cheap and plentiful, and it works well enough. Yet much of the research into new battery concepts has focused on this part of the battery as being the key to superior performance.

3M, for example, has spent many millions of dollars and 15 years exploring using silicon as the anode, another cheap and plentiful material. Why? Well, graphite doesn’t actually store much charge for its volume, giving a low charge density. The work that 3M has now completed using silicon boosts the energy density by around 20%, but another 20% extra power can be had by using new high-energy cathode technology that 3M has also developed. A total of 40% extra power for the same volume is a significant improvement and one that most mobile phone and computer users would be keen to see.

The problem for 3M is that if it doesn’t get this technology to market soon, it could be overtaken by other developments in both anode and cathode chemistry. One of these candidates has been developed by research company CalBattery, which also uses a silicon anode, but its design mixes that silicon with graphene.

Dubbed ‘GEN3’ by CalBattery, the anode substrate it’s developed is a silicon-graphene composite that solves the problem that many battery chemists have encountered when experimenting with silicon. Namely, that silicon absorbs lithium better than any other anode material, but the charge/discharge cycles causes the combination to chemically alter, providing a short life-span. CalBattery claims to have solved that problem and in the process delivered triple the power density for the same volume and mass.

With CalBattery aiming to get products to market in the next two years, this could be the battery revolution that could see electric cars become much more practical and phones that work much longer than a day between recharges. These are just two of the companies involved in this line of research, but numerous other companies are investing heavily in battery research, including General Motors and Envia Systems, who together are aiming to sell electric vehicles with 200-plus mile ranges in the next four years. Tesla Motors is also working with PolyPlus, and their lithium-air and lithium-water battery technology aiming to get 500 miles of charge in a car. With that level of power density, surely making a phone or laptop work for longer isn’t just a pipe-dream?

Batteries everywhere

The conventional thinking is that the battery is an object in the device that you can easily identify and, if the manufacturer agrees, even replace yourself. However, that’s far from what a team at Rice University have been developing using traditional battery chemistry.

In their concept, the battery is assembled by spraying the components onto any surface, allowing simple household objects to hold a charge. In one of their prototype designs they’ve taken a simple house tile, applied a photo-voltaic cell to one side and sprayed a battery to the other. The concept is that a house could be covered in these, providing both a means to capture power but also store it for future use.

What’s exciting about this concept is that it could remove the battery as a part for which space needs to be made in any device, but instead it could be a coating that’s made to any internal surface, irrespective of shape.

Final thoughts

As much as extended battery life seems both desirable and inevitable, there are some issues with this happening, which haven’t been addressed and might prove contentious. The definition of a future battery might be a compact object containing a chemical compound that can be rapidly altered to release a large amount of energy, which, oddly enough, is also the characterisation of a bomb.

With high explosives, the chemical change that occurs is generally very rapid oxidisation, and in the battery it’s the transfer of ions, but you can see the problem. With the restrictions already imposed on what items you’re allowed to take in your carry-on luggage for international flights, an energy cell that, if modified, released all its power in a split second would seem an obvious candidate for banning.

If it proves possible to contain the amperes that a car battery can hold in a laptop battery, then that’s a clearly viable weapon, however the power contained inside it might be used. For exactly the same reasons, fuel cell technology might also prove a difficult sell to airlines and the international travellers who use them. 

These difficulties also point to a major litigation source, should very high capacity batteries have a manufacturing-based failure, as laptop batteries have experienced in the past. In these incidents, electrical shorting inside the cells caused them to become very hot and act like an incendiary, destroying the device. Some similar incidents have occurred with phones, leaving the owners with minor burns.
It doesn’t take much imagination to consider how much worse the outcome of these failures might be if the batteries contained five or ten times the power. A fault that was determined to be design- or manufacturing-based could open the originating manufacturer to personal injury claims that would run into billions of dollars, depending how many customers were affected. So in our efforts to go further for longer, we might actually open up an entirely different Pandora’s box, where having to charge your smartphone each day is the least of our worries.

I’m not pouring cold water on the idea entirely; I’m just pointing out that making the technology work isn’t the final hurdle that super-batteries might need to overcome. The challenge for electronics designers is to create a technology where battery capacity is large but physical scale is small, that can recharge rapidly but discharge much less rapidly, and that isn’t environmentally harmful. If that sounds difficult, then it’s probably a good reflection of why we’ve waited so long for longer battery life and how getting all those opposing priorities to balance might prove almost impossible.

However it’s achieved, batteries will hold more charge, charge faster and deliver more efficient power. Unfortunately, history suggests we’ll come up with even more ways to use the devices they power and, as such, it might be that we’ve eaten that lunch before it even arrives at the table.