Charging methods of the future

By on Nov 9, 2011 in Editorial |

We’ve all watched with trepidation as increasingly wider smartphone displays require more and more battery power to sustain themselves; even with 2000 mAh batteries you’d be lucky to get more than a day’s full use out of a top-of-the-line smartphone these days.

Surely this can’t go on forever — even with power saving technologies, eventually our processing power on these mobile devices will be bound by the electrical charge that they depend on. Without significant advances in battery and charging technologies, we’ll hit an uncomfortable dead end. So what’s next for charging and energy storage?

So we all have a fairly good grasp on this kind of charging: there’s a lithium polymer or lithium ion battery inside the case that stores electrical charge in a lithium-salt electrolyte in a solid polymer compound or organic solvent, respectively. As the phone is used, the charge is depleted. When you plug in your phone via USB or an AC adapter, the electrical charge is restored.

Not very interesting, so let’s move onto fresher fare: wireless charging and (later) micro-supercapacitors.

Wireless charging

Wireless charging is a rather interesting proposition that’s received some main-stream attention, thanks to a few well publicised TED talks and even some real products.

The first thing to know about wireless charging is that it generally comes in one of two forms: close-range induction charging and long-range near field magnetic resonance (NFMR).

A commerically available wireless phone charger.

Induction charging requires two pieces, a charger station and a device to be charged. The charger station (typically a charging mat) contains a large coil of wire, which produces a small magnetic field when a current is passed through it. When the second coil, found in the smartphone, comes into contact with the field, it induces a current to pass through the second coil. It’s essentially the same idea as a normal power transformer, except the two coils act as a transformer with an air ‘core’.

The problem with induction charging is that it’s quite inefficient – only a fraction of the power used makes it to the device being charged. It also only works in very close proximity, when the two coils are almost touching. Because of this, the second form of near field magnetic resonance has the potential to be much better.

NFMR is powered by a low power magnetic resonator, which produces a much stronger magnetic field than an induction charger but only on a given frequency. Then the device to be charged has to tune in to the frequency of the magnetic field in order to be charged. This grants much higher efficiency (roughly 90%), making it comparable to wired charging methods. It also increases the size of the magnetic field, meaning you could have a charging zone the size of a desktop instead of the size of a mouse pad.

As you can see in the video above, it works quite well. The big down side to NFMR is that it’s still relatively expensive to produce the apparatus required. One major player that’s looking into magnetic resonance charging is Apple, who published a patent in May entitled ‘Wireless Power Utilization in a Local Computer Environment.’

It envisions a laptop or desktop with a built-in resonator or USB resonator, which produces a field large enough to cover the whole desk. The field could charge phones as well as wireless peripherals like the the Bluetooth keyboards and mice that Apple are so very fond of. The system also allows the devices to automatically tune themselves into the field when they enter it, then detune when they’re fully charged.

A diagram showing how NFMR charging works. A magnetic coil is housed in a box (1), and resonates at a certain frequency (2). The electromagnetic waves produced (3) travel to another magnetic coil (4) fitted into a laptop resonates at the same frquency and absorbs energy, charging the device (5).

Micro-supercapacitors

Supercapacitors are electrochemical capacitors that sit between traditional capacitors and traditional batteries in terms of the trade-off between energy density and power density, as they store energy as an electrical charge instead of in chemical reactants.

They typically offer lower charge capacity than traditional batteries, but can transfer that charge much faster, giving a greater power density overall. They do tend to suffer from dielectric absorption (i.e. an incomplete discharge) and high rates of self-discharge (i.e. discharging when not in use). The voltage also drops significantly as the supercapacitor discharges. They’re also quite expensive, although of course this is a common feature of most all new technologies.

The tradeoffs between energy density and power density for supercapacitors (labelled as 'ultracapacitors' on the graph).

These challenges which must be overcome to allow mainstream use. Micro-supercapacitors are one evolution of the supercapacitor concept which do look to minimise these disadvantages. They are essentially supercapacitors that have been constructed with micro-fabrication methods, which are more commonly used to construct microchips.

They can be constructed with monolithic carbon film electrodes etched into conduction titanium carbide, ultimately resulting in a micro-supercapacitor that has twice as much energy density as a normal supercapacitor. This brings the balance between energy density and power density more towards a traditional battery, minimising the traditional disadvantages of a supercapacitor.

Due to their smaller size, they could also potentially be integrated into the subsystems of devices they power, making them a kind of specialised battery delivering power at the specific voltages required, without having to spend energy converting. They also have a much longer cycle life, meaning they’d last dramatically longer than typical Lithium batteries.

Drexel University's Dr. Yury Gogotsi (right), part of the team responsible for developing micro-supercapacitors.

Still, this kind of technology is still quite far away from mainstream use. While micro-supercapacitors could be combined with micro-batteries to produce a more viable technology in the short term, full micro-supercapacitors with enough energy storage to operate effectively may be some decades away.

It’s an exciting future ahead of us — even in the outwardly mundane field of energy storage and transfer, there are big things afoot.

Personally, I’m looking forward to a future where my wirelessly charged game controllers work seamlessly with my portable micro-supercapacitor-powered HDTV in my back garden. That’d make writing articles quite difficult, but I bet that fresh air would improve my kill-death ratio in Call of Duty 26.

This article was written by William Judd. William is a writer for Mobile Fun, the UK’s leading online retailer of the kindle cover, including the new kindle cover and the kindle cover with light.