The best battery you’ve probably never heard of

There is no doubt that Lithium-ion batteries have changed the world. From mobile phones to reasonably cost-effective electric cars, they have proven a path to CO2 reduction, not to mention cleaner air, and localised energy self-sufficiency.

Of course, Li-Ion batteries are not without problems. First proposed by British chemist M. Stanley Whittingham while working for Exxon in the 1970s, it took almost another two decades before Li-ion batteries as we know them were commercialised by Sony. Despite a reasonable energy density and recharge life, Li-ion batteries based on lithium cobalt oxide (LiCoO) contain a flammable electrolyte that can catch fire or even explode, especially when damaged…or when there is a manufacturing fault, as Samsung found with the ill-fated Galaxy Note 7.

Lithium is quite a useful element to hold electric charge, and there are many compounds that can partner with it to make a battery, each of which provides different performance characteristics. NMC batteries–Lithium Nickel Manganese Cobalt Oxide–are often used in power tools but also EVs because while they offer lower energy density than LiCoO, they last longer and are less likely to burn or explode in general use. Lithium–sulfur batteries have a high specific energy and are relatively light, so are ideal for aviation uses, but are not in widespread use because sulfer is non-conductive, complicating design and manufacturing. It is an obvious requirement of a battery that the compounds have to allow electron mobility, otherwise electric currents cannot flow. Sulfur definitely makes that a challenge.

Shaving off the whiskers

While powerful, Li-ion batteries have a downside: the dreaded dendrite! Lithium-ion batteries store and release energy by moving electrons and lithium ions from one side of the battery to the other. The problem is that doing this causes electroplating, which is where the electric current causes a thin metal coating on an electrode. It is very useful in manufacturing…and not at all useful inside your batteries. Electroplating creates miniscule dendrites, or tiny lithium whiskers, that can grow sufficiently long to cause short circuits within the battery itself. If you’ve ever held a device with a short circuit, you’ve likely been surprised by how hot it was. A short within a Li-ion battery similarly heats it up, which can trigger a catastrophic collapse of the separator between the two sides of the battery. Temperatures can exceed 500° C, and that is high enough for the flammable electrolyte to ignite or explode when exposed to the air.

Solving the dendrite problem is the subject of intense and ongoing research, with potential solutions including solid-state batteries, in which dendrites cannot grow, and different liquid electrolytes that supress dendrite growth. Chinese battery startup, Qing Tao Energy Development Co, announced recently that they have started production of solid-state Li-ion batteries, beating an array of better known innovators and established players. The head of Qing Tao Energy Development, Nan Cewen, claims they have achieved an energy density of over 400 Wh/kg compared to 250 to 300 Wh/kg for conventional Li-ion batteries.

While their production claims are for a modest 100 MWh capacity per year, Qing Tao Energy Development has flagged a significant breakthrough. Initial reaction to this announcement is probably best described as cautious scepticism. As chemical process development expert, Paul Martin, succulently put it, “I'll believe it 3 months after I've seen one in a commercial cellphone”, and that’s a reasonable response. The startup comes out of Tsinghua University, which has been conducting energy research for a couple of decades and have revealed various breakthroughs in battery design during that time, so it’s not unreasonable that a solid-start Li-ion battery might have been kept under wraps but it is still an unexpected claim.

Irrespective of this announcement, solid-state Li-ion will revolutionise batteries by significantly improving safety, slashing recharge times, increasing recharge life, and packing more energy into the same space. What they might cost is an open question but given how Li-ion battery costs fallen, it is unlikely that solid-state Li-ion batteries would stay expensive for long, assuming that they are expensive to start with.

A moral dilemma

There is another problem with Li-ion batteries, but it is moral, not technical. Recall that most of our batteries are made of lithium and cobalt. Some two-thirds of the world's cobalt is mined in the Democratic Republic of Congo, and some of those mines use child labour. Mining is a dirty business at the best of times and mines no place for children. Unlike blood diamonds or Nike’s alleged sweatshop workers, Li-ion batteries are so widely used it is hard for consumers to effectively boycott them. Still, consumer concern is putting pressure on the Li-ion supply chain to clean up the mines, plus, manufacturers are working to reduce the amount of cobalt used in batteries. Both solutions will take time to implement, but child labour is an unintended consequence of the skyrocketing demand.

First mover advantage

So, Li-ion is changing the world by providing cost-effective, high power density, high energy density, rechargeable batteries that are generally safe. They are the powerhouse of the low carbon economy, and only gaining more traction month-by-month. Bloomberg New Energy Finance analyst Logan Goldie-Scot told a conference in Perth recently that the world’s lithium battery-making capacity will more than triple from 175 gigawatt hours to 630GwH by 2022. By 2025, Li-ion battery pack prices should hit US $100 / kWh, which is seen as the sweet spot for EVs to reach price parity with petrol engine vehicles. Given how Li-ion battery prices dropped faster than expected over the last decade and taking Tesla as the market-leading battery price indicator, price parity might be reached even sooner.

From an innovation perspective, those plummeting prices actually form a strong barrier-to-entry for new technologies. Li-ion is not ideal for all use cases, yet it is being deployed as such, essentially because it is the only game in town. I’ve posted about NantEnergy on LinkedIn before. The US company, which recently changed its name from Fluidic Energy, provides zinc-air flow batteries that are ideal for fixed installations, and particularly grid-scale backup connected to renewable energy plants. Other companies are also playing around the edges of the industry, deploying alternatives to Li-ion for specialist requirements.

I introduced NantEnergy because the ‘air’ in their zinc-air battery highlights one of the issues of Li-ion batteries. As with most batteries, Li-ion is self-contained. That is a very useful trait, but it adds to their weight. A Tesla Model S weighs about 750kg more than a petrol-engine Mercedes C Class, and the batteries comprise some 500kg of that. Given that an EV does not need nearly as many mechanical parts as a petrol or diesel car, the battery weight is even more pronounced. A zinc-air battery, by contrast, uses the oxygen in the atmosphere so it does not need to carry some of the ‘fuel’, which provides a significant weight saving. Alternatively, more electrolyte can be stored for the same weight, increasing energy density.

As Aviv Tzidon, co-Founder and CEO of Phinergy, a developer of clean and high energy-density systems based on metal-air technology, neatly describes it, “Simply put, it's like the difference between a scuba diver and a fish. While the diver carries oxygen tanks in order to breathe, the fish simply breathes through its gills.”

The big reveal

Comparing the weight of Li-ion and zinc-air is apples for oranges, of course, but it brings us, finally, to the battery that you’ve likely never heard of. It is metal based, like lithium, and it uses air, like NantEnergy’s units. Unlike lithium, it is based on the most abundant metal in the earth’s crust. And it does not need to be partnered with cobalt to operate. This wonder element is aluminium, and being honest, you’ve likely not heard of it because this technology is still on the cusp of commercialisation. But bear with me, because aluminium-air is seen to have considerable upside as a battery technology.

One of the main advantages of aluminium as a battery comes from its atomic structure, which allows the exchange of three electrons where lithium can only exchange one. Compared to lithium–and pretty much everything else–aluminium tops the charts on energy density. Which accounts for the interest in making batteries from it, obviously.

A battery is a battery is a battery

If you google “aluminium-air batteries” you will find numerous articles and posts extolling its superior characteristics over Li-ion. What you might also see are references to the fact that aluminium-air batteries are not rechargeable. They are what’s known as ‘primary cells’, and you’ve likely been using those your entire life in the form of AAA, AA, C, D, and the like. Eveready’s Energizer Bunny is the archetypal primary cell consumer, and pretty much every parent will experience the horror of missing the “batteries not included” disclaimer on a Christmas toy and having no primary cells to hand to fire that present up.

Unless they can be cost-effectively and conveniently recycled, primary cells are ultimately wasteful, and despite their massive energy density, that’s an obvious problem. It also undermines the decentralisation of electricity generation that is upending the industry. This is not a solar battery contender, it’s more like “aluminium as fuel”.

Another problem is the somewhat-joke that aluminium is “congealed electricity.” This highlights the difficulty of extracting it from bauxite and the energy input needed to reduce it to metallic form. Aluminium production represented around 14% of Australia’s entire electrical consumption in 2017. If that sounds like a huge amount, it is. In actual terms, it is about 27 terawatt hours, about as much electricity as Ireland uses annually.

It is a frustrating situation because compared to lithium, we’re pretty much tripping over aluminium. It sits at Number 3 on the ‘The abundance of elements in Earth's crust’ list while lithium is way down at Number 33. Still, as difficult as aluminium is to refine, the abundance imbalance is reflected in the costs, with aluminium selling for around US $1,900 per metric ton and lithium selling for around US $16,500 per metric ton. Demand for lithium is trending its price up, with an almost four-fold rise over the last decade, while aluminium prices have barely changed.

A third problem is that oxygen is so reactive that it not only corrodes battery components but accelerates discharge. An inactive aluminium-air battery can lose 80% of its charge in a month, which is wholly unacceptable. MIT researchers recently found that introducing an oil barrier between the aluminium electrode and the electrolyte slashes energy loss to 0.02% a month. That is an impressive improvement, though the need for oil to lubricate a battery inside your EV is ironic. Aside from the oil, this aggressive oxidisation is a problem for all metal-air batteries, and is focus of intense research to figure out how to selectively utilise oxygens reactive properties.

Is aluminium-air just a pipe dream?

There is an obvious question into why researchers are persisting with aluminium-air given it has such obvious problems.

One reason is the view that “aluminium as fuel” actually just might work. At least for mobile transport, like EVs. An aluminium-air battery can be ‘recharged’ by replacing the aluminium. This is the scenario that Phinergy is promoting. There is a cute little animation of a car travelling 1,000 km then refuelling in 3 minutes on their website, but honestly, precious little else regarding their tech. A sperate YouTube clip has a city car purportedly driving 300 km using their aluminium-air batteries, noting that it needs to take on water every “few hundred kilometres”, but thus far, Phinergy is not obviously delivering anything in volume.

Other research suggests that primary cell aluminium-air batteries could be less expensive than rechargeable Li-ion but I put this entire concept in the same bucket as hydrogen-powered EVS…nice idea, but not so practical in practice. You can’t make aluminium at home, and it’s not a liquid so aluminium as fuel requires significant–think $000B–retooling of our service-station infrastructure, not to mention vehicle manufacturing. Aluminium as fuel is not just another battery pack, it is an entirely different technology. This means that the business case vis-à-vis Li-ion EVs probably does not stack up sufficiently to overcome the chicken-and-egg startup hurdle. Phinergy, for example, was founded a decade ago and while there are numerous joint-venture announcements regarding aluminium-air initiatives, there does not seem to be much in the way of ready to use production-line output.

What is more interesting for me is a rechargeable aluminium battery, Al-ion. That higher electron transfer rate I mentioned previously suggests that Al-ion will pack a larger energy punch than Li-ion, but just as researchers are only starting to really understand what happens at the nanoscale within a Li-ion battery, we are a long way from building a robust, consumer-ready, Al-ion battery. But even as there is a frantic effort to crack this tech, a lot more research dollars are being spent on improvements to Li-ion, including a near-mythical lithium-air.

Lithium is dead, long live lithium

Even if Qing Tao Energy Development Co’s solid-state battery announcement is premature, there is so much momentum behind solid-state Li-ion that a battery of this kind will emerge within the next few years. Cracking this will spur ‘extension’ research into using other metals–such as aluminium–instead of lithium. We may never see a practical, cost-effective metal-air battery in our EVs, but we will definitely see dramatic improvements in metal-ion batteries. And that’s a battery I can definitely buy into.