Molten Antimony Batteries – An Impending Deluge?

Battery technologies have been proliferating in recent years like mushrooms after the rain.. Despite this there are batteries and batteries. Many of the newly invented storage devices have specific usages and one new application is not necessarily a replacement for an existing type of battery. Unfortunately most parents still have reason to curse the ubiquitous Double A batteries that power Christmas gifts for children and never seem to have an up-to-date, cost-effective or long-lasting alternative. Once a rip-off, always a rip-off.

Most of the buzz in the mainstream media is about battery options that extend the life of cellphones or laptops and other PDAs or with regard to hybrid or electric vehicles. However the really great economic leap forward has to do with mass storage devices which mesh with energy grids to provide off-peak storage of electricity. Industrial or natural gas has been stored since its inception in the industrial revolution in massive tanks, caverns or gasometers, while a solution to massive electricity storage has been much more elusive. With conventional dry-cell battery using two electrodes separated by an electrolyte, it would require thousands of individual cells, the size of soft drink cans, to be strung together in a massive installation to create a mass storage battery of any usefulness to be attached the grid.

The relevance of this has been heightened with the burgeoning of alternative energy sources (wind and solar) that are irregular in their generating periods and do not always coincide with peak demand.

Mass Storage Devices

The important consideration is that mass storage devices do not even need to be connected to the grid and thus can be in the middle of nowhere bridging the infrastructure gap (and cost) that weighs on emerging economies (and isolated minesites).

Up until now the principal mass storage device we have concerned ourselves with has been the Vanadium Radox battery with its shipping container-sized housing. This is a very real and efficient alternative for those isolated locations we mentioned.

When one goes beyond the physical “battery”, the only widely used system for utility-scale storage of electricity is pumped hydro, in which water is pumped uphill to a storage reservoir when excess power is available, and then flows back down through a turbine to generate power when it is needed. Interestingly in the last week we met a miner, King Island Scheelite (KIS.ax) that has a Tungsten project on an isolated island between the Australian mainland and Tasmania. They had mentioned this storage method as a way they were considering of using the abundant (yet erratic) wind source at the location to make (from pumping seawater uphill to a dam) electricity and get their project liberated from dependence upon expensive imported diesel. The dam is essentially a big battery.

Therefore pumped hydro can be used to match the intermittent production of power from irregular sources, such as wind and solar power, with variations in demand. Because of inevitable losses from the friction in pumps and turbines, such systems return about 70% of the power that is put into them This “round-trip efficiency” may not be ideal but considering that the power source if “free” it is indeed a viable option.

And then there are liquid metal batteries…

The Latest Vibe

So the biggest remaining challenge is storing electricity that interacts with the grid. The latest technology to grapple with this issue is the liquid metal battery.

It seems most new battery innovations emerge from academia rather than commercial R&D. Researchers at MIT (led by Professor Donald Sadoway) have been working on a liquid battery system that could enable renewable energy sources to compete with conventional power plants. The research has been funded to the tune of $15m by the likes of Bill Gates, energy giant Total, the US Department of Energy’s Advanced Research Projects Agency and Khosla Ventures (run by Sun Microsystems co-founder Vinod Khosla).

The latest iteration involves a lithium/antimony/lead liquid metal battery comprising a liquid lithium negative electrode, a molten salt electrolyte, and a liquid antimony/lead alloy positive electrode, which self-segregate by density into three distinct layers owing to the immiscibility of the contiguous salt and metal phases. The difference in composition between the two liquid metals gives rise to a voltage. The music to our ears in all this is the use of Antimony, and seemingly in quantity.

The MIT battery design substitutes different metals (mainly lead and lithium) for the molten layers used in a battery previously developed by the team that had a strong Magnesium component. Here is a schematic of how the previous combination worked.

molten_antimony.jpg

Their latest formula replaces the Magnesium with lithium and allows the battery to work at a temperature more than 200 degrees Celsius lower than the previous formulation. The all-liquid construction confers the advantages of higher current density, longer cycle life and simpler manufacturing of large-scale storage systems (because no membranes or separators are involved) relative to those of conventional batteries.

The researchers found that while antimony could produce a high operating voltage, and lead gave a low melting point, a mixture of the two combined both advantages. In addition to the lower operating temperature, which should simplify the battery’s design and extend its working life, the new formulation will be less expensive to make. However when they make that comment it leaves me wondering whether they are factoring in how much antimony, which has a delicate supply/demand balance might rise if suddenly a new application that absorbs more metal starts to get traction.

Reports of the extensive testing indicate that even after 10 years of daily charging and discharging, the system should retain about 85% of its initial efficiency. This would be a major attraction for electric utilities, who have been largely watchers, rather than initiators, in new battery technologies. The MIT team has speculated that it may be possible to build giant batteries using 50-100 fewer individual cells this way, than would be possible with a conventional battery array, reducing cost and complexity.

Antimony – Let the Benefits Flow

I am well known as an unalloyed (pardon the pun) fan of Antimony but it must be admitted that while in a critical supply situation (which puts it near the top of most strategic metals rankings) the applications for Antimony are scarcely “high-tech” in the way Rare Earths are. The main traditional use was as a hardening alloy with lead in bullets and ammunition as lead batteries. The newer innovation was as a fire retardant, but there has been scarcely any new application of note for several decades. The liquid metal battery finds new uses for two of our favorite metals, antimony and lithium.

Conclusion

I suppose that technically pumped energy is just one gigantic “liquid battery” but that is obviously not what the scientists are proposing here. If Liquid Metal Batteries become the killer application in grid-linked storage (or non-grid linked) then it adds further feathers to the cap of lithium, adds a bit of spice to the eternally balanced and unpromising lead scene and potentially lights a fire under Antimony demand and pricing.

Have Your Say!