Breakthrough battery technology sparks global interest

Breakthrough battery technology sparks global interest

By Jack Ward, MD of Powermode

In South Africa, solar photovoltaic (PV) power is proven to be viable and a reliable energy source, thanks to the country’s sunny climate in which solar irradiation is both abundant and free.

Solar power is also one of the most desirable ways to boost efficiency, minimise energy waste and improve CO2 emissions at minimum cost. But without an effective means to store excess energy, solar power is only effective as long as the sun shines.

One new and promising storage option is a battery made with all-liquid active materials. Unlike conventional lead-acid or dry-cell batteries, liquid technology batteries are expected to be far better options – once they become commercially available - as they will cost less and last longer.

Invented by Donald Sadoway, Professor of Materials Chemistry at the Massachusetts Institute of Technology (MIT), his liquid metal battery (LMB) is unlike any other. The electrodes are molten metals, and the electrolyte that conducts current between them is a molten salt.

Inspired by the technique developed in the 19th century to produce aluminium at very low cost, Sadoway came up with the idea of using commonly available materials to create his battery.

Essentially, Sadoway’s LMB consists of a container surrounded by insulating material. To this is added raw molten antimony on the bottom, an electrolyte such as sodium sulphide in the middle, and magnesium at the top. Since each material has a different density, they naturally remain in distinct layers, which simplifies manufacturing. The difference in composition between the two liquid metals at the top and bottom gives rise to a voltage.

Technically speaking, the procedure is known as ‘reversible ambi-polar electrolysis’. A key benefit of the design is its avoidance of cycle-to-cycle capacity fade. This is because the electrodes are reconstituted with each charge through an alloying/de-alloying process, enabling the battery to exceed 70% round-trip efficiency without degradation.

Another advantage is that no thermal management or control is required, because the movement of the electrons through the cell generate enough heat to keep the battery at temperature - further ensuring the battery’s simplicity.

While commercial sensitivities mean that the exact chemistry used in Sadoway’s LMB remains secret, he says he can build giant batteries using 50 to 100 fewer individual cells than would be possible with a conventional battery array, reducing cost and complexity.

His efforts have resulted in an unusually resilient device that can quickly absorb large amounts of electricity. The electrodes can operate at electrical currents tens of times higher than any battery that's ever been measured. What's more, the materials are cheap, readily available and the design allows for ease of manufacture.

Still in the development stage, Sadoway is exploring various cell sizes to determine which will be most economical to manufacture. The battery (which consists of many cells) will be tailored to specific applications. For example, one variant will be the size of a 40-foot shipping container and hold enough electricity to meet the daily needs of more than 200 households.

The first commercial prototypes are currently being tested, with widespread production and adoption by consumers, ranging from large industrial companies to home owners, being planned and envisioned.

Sadoway’s idea has attracted around $15m investment from Bill Gates, Total and Khosla Ventures, run by Sun Microsystems co-founder Vinod Khosla.

From a marketing perspective, Sadoway intends to initially target applications where large amounts of energy need to be stored, the benefit being that the battery can respond in milliseconds. This will potentially open up markets for storing and delivering electricity to the grid to make up for fluctuations in supply and demand.

To reduce costs going forward, he has a LMB design variant that can be fabricated in existing factories using contract manufacturing and targeted at smaller commercial and even homeowner markets. Price will be key if renewable energy sources such as rooftop solar PV are to become mainstream forms of energy generation. The support of high performance storage technologies is going to be absolutely critical in future.

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