Battery technology gets a fresh charge

Where batteries are used most in our lives reveals a lot about their pros and cons.

Stick a regular battery in a torch or a home fire alarm and you’ve got power for months. You might get eight or nine hours of use out of your laptop or smartphone battery while you’re on the move – not fantastic, but decent enough for a day’s use.

But the more work they need to do, the more impractical using batteries gets. Try and run a car exclusively on battery power rather than gasoline or diesel and you’re unlikely to go much further than 100 miles before you need to stop and recharge. That makes them pretty useless for long journeys – especially because it can take hours to top up a car battery. And while the fuel costs are much lower than in conventional cars, electric vehicles are more expensive to buy – precisely because of that pricey battery.

And if you wanted to be able to power your home using batteries – to store solar energy for night-time use, for example, or to protect yourself from the vagaries of an unreliable power grid – the batteries would set you back thousands of dollars and you’d probably need to dedicate a whole room in your house to battery storage.

Small is better

So batteries work well for relatively small devices with light energy consumption, but they haven’t proved too practical at the other end of the scale. That hasn’t mattered too much in the past, but it does now because batteries are playing an increasingly important role in reducing dependence on fossil fuels in power generation and on the road.

By 2020, the global investment in stored energy for use in electricity grids is expected to be $5.1 billion a year, over 17 times higher than the figure for 2013, according Bloomberg New Energy Finance, a consultancy. Meanwhile, a recent report by Cambridge Econometrics, another consultancy, estimated that the UK could slash carbon emissions from vehicles by 47% by 2030 by 80% by 2050 if measures were put in place to replace the existing vehicle fleet using low-carbon technologies, including electric cars.

The prize is, therefore, a big one. And if the batteries in electric cars could be made cheaper and more powerful, thus extending their driving range, then car buyers would think more seriously about making the switch. Meanwhile, if power utility companies could afford to use massive battery arrays to store power for use when the sun isn’t shining or the wind isn’t blowing, then that would put paid to the biggest argument against renewable energy sources like solar and wind power – that they are intermittent.

The billions of dollars now being poured into research around the world, aimed at making batteries more effective and cheaper, are starting to pay off. Several models of electric cars can now match the performance and approach the range of conventional vehicles, and while most of them still cost more, their price is gradually coming down. The Tesla company – co-founded by PayPal billionaire Elon Musk – has shown what can be done by developing a lithium-ion battery-powered sports car, the Model S, whose speediest version puts some of the world’s fastest conventionally fuelled supercars to shame. It’s able to accelerate from zero to 60 miles an hour in as little as 3.1 seconds, can achieve a range of up to 270 miles on one charge, and can get 170 miles-worth of charge in 30 minutes – if you have a high-power electrical socket handy and the right kit inside the car, the company says. A new Model S costs the best part of $100,000, so it’s not for everyone. Yet Tesla has proved that batteries don’t have to be the second-best option to power a car, even a highly specified one, and that potentially paves the way for greater acceptance of the technology.

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Going the distance

Tesla’s success has prompted big manufacturers, such as BMW and Audi, to come up with improved high-end electric sports cars of their own. At the same time – more practically for most consumers – vehicle makers continue to improve the performance and reduce the cost of electric models aimed at people without $100,000 to spend on a car; Nissan, which makes the world’s biggest-selling all-electric car, hopes the next version of its Leaf model (which currently costs around $30,000) will be able to travel considerably further than the 84 miles or so the current model can achieve – in part because of a bigger, better battery assembly. Nissan’s rivals, such as GM, are pushing for greater ranges too.

Musk is now aiming to drive down the cost of the high-spec lithium-ion batteries used in electric-only vehicles by building a 10 million-square-foot battery plant in the US, known as the “gigafactory”, at a cost of some $5 billion. The factory will also make batteries for another growth area – large-scale storage that can supply buildings or even grid-scale power.

Doing this involves installing a series of high-efficiency batteries in housings that can range from the size of a larger refrigerator to that of an entire warehouse – depending on how much stored power is needed. California’s 32 megawatt-hours Tehachapi Energy Storage Project is an example of a battery on the warehouse-end of the scale: a public-private venture, it is North America’s largest battery energy-storage project, consisting of 608,832 individual battery cells and 604 battery racks, housed in a 6,300 square-foot facility.

Until now, lithium-ion batteries, while powerful, have generally been considered too expensive to interest power-generation companies. But if Tesla achieves its aim of cutting their costs by around a third through economies of scale and technological wizardry, they could become much more appealing to power firms seeking to harness solar and wind power. The idea certainly makes sense: being able to store energy generated during off-peak hours (energy that would otherwise have been lost) means renewables developers don’t need to install lots of spare solar panels or windmills to ensure they can meet demand at peak times. In 2014, IHS, a consultancy, said the global grid-connected energy storage market would increase from 340 megawatts in 2013 to over 6 gigawatts in 2017 and to more than 40 gigawatts by 2022. To put that into context, 6 gigawatts would be enough to supply almost half the peak power demand in New York City for as long as battery output lasts.

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Two-way flow

Falling battery costs would make having your own solar panels and battery combination at home look a lot more affordable too. And the economics of that set-up could be improved still further by allowing energy from home storage – and indeed vehicle batteries – to be fed into the local power network for a fee, when it’s not needed at home. Some enterprising people have even shown it is possible to bring down costs still further, “hacking” the technology by taking discarded batteries from old electric cars and adapting them for home power storage.

Lithium-ion, meanwhile, is not the only game in town. There are several other promising battery types for both transport and power generation. And Tesla is far from alone in the push to improve battery storage. Renewable energy providers, power generators and battery firms around the world are teaming up to meet the technological challenges, driven not least by the prospect that a power-packed, long-lasting, affordable and safe battery will be a highly lucrative product.

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Leaders of the (battery) pack

Lithium-ion batteries have become increasingly popular in response to growing demand for rechargeable portable consumer products, such as mobile phones. Lithium ions move from a negative electrode to a positive one during discharge and back when charging. Lithium-ion batteries have a high energy density, hold their charge well and are much lighter than, say, lead acid batteries, which have traditionally been used for some higher-power uses. Their lightness makes them suitable for vehicles as well as small appliances.

Liquid-metal batteries use molten salts as the electrolyte (so do sodium sulfur batteries). But unlike in other molten-salt batteries, the electrodes in liquid-metal batteries are also liquid and the constituents’ different densities keep them apart, floating in separate layers. These can potentially be scaled up to hold more energy at a cheaper cost than solid-state batteries, while the liquid electrodes won’t degrade as rapidly as the solid electrodes in other types of battery. Cheap, powerful and reliable, these batteries are ideal for electricity grid-scale storage. A US company called Ambri, backed by French oil firm Total and Bill Gates, among others, plans to test grid-connected prototypes in 2015 and is looking for a location to build a full-scale plant. The prototypes can produce 200 kilowatt-hours of electricity each, enough to power 10-15 homes per day, Ambri says.

Flow batteries generate electricity by ion exchange, a process in which ions pass through a membrane between two tanks of liquids in which different chemicals are dissolved. This arrangement can keep the battery working much longer than is possible with other rechargeable batteries and the potential for power output is high, if the tanks are large enough, so flow batteries could be an attractive technology for grid-scale power storage and generation. US pioneer Imergy says the working lifetime of its latest vanadium flow battery (20 years or more) is likely to be at least three times as long as that of lithium ion batteries, without loss of performance.

Touted as the replacement for lithium-ion, lithium-sulfur batteries have higher energy densities and are even lighter. They will also probably last longer and are less likely to overheat. Developers claim lithium-sulfur batteries could be nearly five times as powerful as their lithium-ion counterparts. Use of low-cost sulfur instead of some of the lithium could also make them cheaper.

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