Power stores of the future

Ambri's prototype liquid metal battery

Ambri's liquid metal battery

Ambri is one of those tiny start-ups with a potentially dazzling future.  It's the brainchild of two MIT researchers, Donald Sadoway and David Bradwell.  They're looking to address one of the major issues with the power industry - inadequate ways to store electricity once it has been generated.

On their website Ambri talks about electricity being "the largest supply chain in the world with no warehouse". Typically, electricity is generated as it is needed - we don't have the capacity to store it en masse for later like we do with water, gas, oil or anything else that we pipe to a destination.

Batteries intended for storage of generated power are not bound by the same physical and practical constraints as those harnessed for mobile use.  We don't need to make them light or small.  Indeed, the Ambri batteries are likely to be as big as a 40-foot shipping container and weigh many tons.  The bigger they are, the more energy they are able to store.  Given that Ambri intends these their batteries for in situ placement at power generation facilities stations, their storage capacity rather than their physical dimensions is the more important consideration.

Sadoway has a background in metallurgy and he hit on the idea of his battery whilst observing how an aluminium smelter works.  He marvelled at the huge amount of power in the liquid metal smelter and he started thinking how he could use this principle for making a large battery.

Like many practical processes this one is pretty straightforward.  Ambri recognises that if industry is going to embrace their product, it needs to be cost effective.  Consequently they have settled on using materials that are cheap, abundant and reliable.

Even though this liquid metal colossus is massive, it is at heart just a battery.  There are electrodes - an anode (positive) and a cathode (negative) kept apart by an electrolyte.  Ambri uses magnesium for the anode, antimony for the cathode and a pile of liquid salts for the electrolyte.

However, unlike a traditional battery where the electrodes are solid, these melt when the battery is heated to its operating temperature of 500 degrees centigrade.  As the battery charges, the liquid magnesium flows through the electrolyte to be re-deposited on the anode.

The battery is actually a whole load of smaller units stacked like ice hockey pucks and wired together in series.  The team hope to have a fully working prototype by 2014, capable of storing 2 megawatt hours of electricity (or enough to power 70 homes for a whole day).

Ambri attracted the attention of some big players and obtained seed money from Bill Gates and the energy giant, Total.  That's a great start for a small company.

They have high hopes that these massive batteries will find a home storing energy produced via renewable options, such as wind and solar farms.  As long as they can get the pricing right for the batteries that future looks very bright indeed.

Links to Ambri liquid metal battery technology

Magnesium, liquid salts and antimony in the Ambri battery

Ambri home

Ambri's grid battery (Technology Review)

Renamed Liquid Metal Battery (GigaOm)

Liquid metal battery is on its way