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The New Battery That Could Power the Renewable Revolution by Mark Shwartz The Ecologist, April 26, 2015

A new high-performance 'aluminum-ion' battery could be the technical breakthrough needed to boost the renewable energy takeover. It's safe, uses abundant low-cost materials, recharges in one minute and withstands many thousands of recharge cycles.

If this new battery lives up to expectations, it could propel a whole new chapter in the renewable takeover of the world's energy supply. Stanford University scientists have invented the first high-performance aluminum battery that's fast-charging, long-lasting, inexpensive - and safe.

Its inventors including Hongjie Dai, professor of chemistry at Stanford, believe it could replace other battery technologies in a wide of applications from electic cars to storing power from solar panels to keep homes powered at night, and stabilising the power grid.

All these uses will help to drive the renewable energy revolution that's already under way, as variable power sources like wind and solar replace fossil fuel generation year by year.

As higher proportions of variable output renewables come onto the grid, it's increasingly imporant to store electricity surpluses efficiently so they can be used when needed to meet demand, and displace even more energy from fossil fuels.

"The grid needs a battery with a long cycle life that can rapidly store and release energy", explained Dai. "Our latest unpublished data suggest that an aluminum battery can be recharged tens of thousands of times. It's hard to imagine building a huge lithium-ion battery for grid storage."

Battery technology is currently the 'weak link' that's holding renewables back, owing to their high cost, environmental downsides, and reliance on scarce materials such as lithium. If this new battery lives up to expectations, it could propel a whole new chapter in the renewable takeover of the world's energy supply.

Finding the right materials

Aluminum has long been an attractive material for batteries, mainly because of its low cost, low flammability and high-charge storage capacity. For decades, researchers have tried unsuccessfully to develop a commercially viable aluminum-ion battery.

But the key challenge has been finding materials capable of producing sufficient voltage after repeated cycles of charging and discharging, the authors write:

"Research efforts over the past 30 years have encountered numerous problems, such as cathode material disintegration, low cell discharge voltage, capacitive behaviour without discharge voltage plateaus and insufficient cycle life (less than 100 cycles) with rapid capacity decay (by 26-85 per cent over 100 cycles)."

And a particular problem has been the cathode, says Dai: "People have tried different kinds of materials for the cathode. We accidentally discovered that a simple solution is to use graphite, which is basically carbon. In our study, we identified a few types of graphite material that give us very good performance."

For the experimental battery, the Stanford team placed the aluminum anode and graphitic foam cathode, along with a non-flammable ionic liquid electrolyte, inside a flexible polymer-coated pouch.

Dai and his colleagues describe their novel aluminum-ion battery in their article 'An ultrafast rechargeable aluminum-ion battery', published in the April 6 advance online edition of the journal Nature.

Safe and eco-friendly

The new aluminum batteries are safer than conventional lithium-ion batteries used in millions of laptops and cell phones today, Dai added.

"Lithium batteries can go off in an unpredictable manner - in the air, the car or in your pocket", he pointed out, and even "occasionally burst into flames." As an example, he pointed to recent decisions by United and Delta airlines to ban bulk lithium-battery shipments on passenger planes.

By contrast "Our new battery won't catch fire, even if you drill through it! In our study, we have videos showing that you can drill through the aluminum battery pouch, and it will continue working for a while longer without catching fire."

It's also environment friendly, compared to either disposable batteries, or nickel-cadmium or lead-acid rechargeables: both cadmium and lead are highly toxic heavy metals that can cause brain damage if ingested.

7,500 discharge-recharge cycles with no loss of capacity

The research team also claims "major breakthroughs in aluminum battery performance", with "unprecedented charging times" of down to one minute with the aluminum prototype. As Smartphone owners know, it can take hours to charge a lithium-ion battery.

Durability is another important factor. Aluminum batteries developed at other laboratories usually died after just 100 charge-discharge cycles. But the Stanford battery was able to withstand more than 7,500 cycles without any loss of capacity, a record number for aluminum batteries by a huge margin. By comparison, a typical lithium-ion battery lasts about 1,000 cycles.

The prototype also produced 2 volts of electrical potential - more than the standard 1.5 volts produced by standard AA and AAA battery types, and the highest ever produced from aluminium batteries. But it's still only half as much as typical lithium-ion batteries, and Dai says that more improvements will be needed to match their voltage:

"Improving the cathode material could eventually increase the voltage and energy density. Otherwise, our battery has everything else you'd dream that a battery should have: inexpensive electrodes, good safety, high-speed charging, flexibility and long cycle life. I see this as a new battery in its early days. It's quite exciting."

Another feature of the aluminum battery is its flexibility, added co-author Ming Gong: "You can bend it and fold it, so it has the potential for use in flexible electronic devices."

The paper: 'An ultrafast rechargeable aluminum-ion battery' by Meng-Chang Lin et al was published in the 6th April 2015 advance online edition of the journal Nature.