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Can Aluminum Take Us beyond Lithium?

Money is a big driving force when it comes to batteries. Lithium is today’s primary ingredient for laptop, electric vehicle, and grid storage batteries. But the price of lithium has more than tripled in the…

Editor 4 min read
Can Aluminum Take Us beyond Lithium?
Can Aluminum Take Us beyond Lithium?

From the Lithium News archive. This article dates from May 18, 2018 and is preserved as first published.

Money is a big driving force when it comes to batteries. Lithium is today’s primary ingredient for laptop, electric vehicle, and grid storage batteries. But the price of lithium has more than tripled in the past year. The ultra-light metal hovers around $20,000 per metric ton. By contrast, aluminum—much more abundant and available—costs around $2,200 per metric ton. Is it any wonder that researchers are looking to replace lithium with aluminum?

Beyond Lithium?

Lithium has other challenges beyond cost in rechargeable battery usage. Ideally, for example, the anode of the battery could be made from a thin lithium metal foil. This provides a maximum number of lithium ions during discharge, increasing battery power and capacity. When the battery is charged, however, the lithium ions form on the metal foil as spiky crystalline structures called dendrites. These dendrites can grow large enough to short out the battery—potentially causing a fire. To avoid dendrite growth, the anode is made from carbon graphite that can hold lithium ions between its layers (a process called intercalation). A graphite anode can’t release as many lithium ions as the metal foil can. It reduces the battery performance, but it is safer.

So what about aluminum? It is the most abundant metal in the Earth’s crust. When used as an anode in a battery, aluminum can release three electrons when discharging, compared to the single electron that lithium releases. Aluminum also does not form dendritic crystals during charging. Of course, it isn’t as easy as simply substituting one metal for the other.

More Pluses

In a lithium ion battery, the mobile ion is simply a positively charged lithium (Li+). In an aluminum ion battery, aluminum forms a complex with chlorine from the electrolyte to create two mobile ionic charge carriers, AlCl4– and Al2Cl7–. During discharging, these chloroaluminate anions travel from the aluminum metal anode, through the electrolyte, to the graphite cathode. At the cathode, the anions fit between the graphite layers by intercalation. When the battery is charged, the anions travel back through the electrolyte and are deposited onto the metallic aluminum.

In a lithium ion battery, the mobile ion is simply a positively charged lithium (Li+).

The electrolyte used in an aluminum ion battery provides challenges. It is an ionic liquid formed by mixing organic and inorganic chlorides. The resulting electrolyte fluid is extremely aggressive and will corrode all metals, including stainless steel, gold, and platinum. This corrosive property makes the conductive parts of the aluminum ion battery, which are used to carry electrons away from and back to the battery, extremely vulnerable.

Enhanced Protection

Researchers at the Eidgenössische Technische Hochschule (ETH) Zürich in Switzerland have developed a corrosion-resistant coating material that can be used in aluminum ion batteries. The ceramic material is a titanium nitride ceramic. According to an ETH press release, the material has high enough conductivity to be used as the battery’s conductive parts. Or, it can be produced in a thin film to create a protective coating on other materials.

In the ETH release, Maksym Kovalenko, professor of functional inorganic materials, stated, “The potential applications of titanium nitride are not limited to aluminum batteries. The material could also be used in other types of batteries; for example, in those based on magnesium or sodium, or in high-voltage lithium-ion batteries.”

Swiss Banking

Protection from the corrosive nature is not the only aspect of aluminum ion batteries on which ETH Zürich is working. Batteries made with aluminum typically use a cathode made from graphite. But banking large numbers of chloroaluminate anions in the layers of graphite can cause a distortion of the anion structure. This has prompted a search for other cathode materials.

ETH has found that a conductive polymer, called polypyrene, stores at least the same amount of energy as does a graphite cathode in an aluminum ion battery. The ETH researchers also discovered that the disorderly arrangement of hydrocarbon polymer chains in polypyrene provided what was needed for a better battery. “A lot of space remains between the molecular chains,” explained Kovalenko. “This allows the relatively large ions of the electrolyte fluid to penetrate and charge the electrode material easily,” he added. Electrodes of polypyrene are both flexible and adaptable. Scientists can influence polypyrene’s material properties, such as porosity, much easier than can be done with solid graphite.

Future aluminum ion batteries are expected to have a specific energy of around 1,000 watt-hours per kilogram (Wh/kg)—significantly more than the 400 Wh/kg of a lithium ion battery. This means aluminum ion batteries can either be smaller and lighter at the same capacity, or offer more power and longer duration at the same size as present lithium ion batteries. There is still significant work to be done, but the effort by ETH Zürich is a promising start on what might come after lithium.

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Minnesota utilities hope surge of big-scale batteries helps transition to clean energyJared Newton remembers panicking at times when launching three first-of-their-kind battery projects in Minnesota for Connexus Energy in 2019. Would lithium technology — paired with solar farms — charge fast enough in the morning to meet afternoon electric needs? "Until I saw it in action, we didn't know if we'd be able to get them charged in time," said Newton, who leads engineering and system operations for the electric cooperative in Ramsey. Newton and Connexus are local trailblazers in the fledgling world of utility batteries. Now, Minnesota is on the brink of a large-scale rollout of the mega batteries over the next six years, putting the state on pace for a relative boom in battery infrastructure. On Thursday, state utility regulators approved a certificate of need for a $450 million project by Invenergy near Lake Wilson that would be by far the largest storage system in the state. Utilities — plus state planners here and across the country — are counting on utility-scale batteries to help with the shift from coal to wind and solar energy in the next two decades. However, many forms of the promising technology are still mostly untested beyond pilot projects and the batteries, while they have dropped in price, are still expensive. Xcel Energy, Minnesota's largest electricity provider, has no batteries in the state so far but released plans in February for a sizable fleet to help as it works toward closing its coal plants by 2030. A study commissioned by the state Legislature released this month also said a battery influx is needed for utilities to meet a state target for carbon-free electricity by 2040. "I feel like we've been talking about [energy storage] a long time," said Julie Pierce, vice president of planning and strategy for Duluth-based Minnesota Power. "Now we're really seeing the fit and form come into fruition here." What batteries can be used for The biggest challenge of shifting energy sources from fossil fuels to wind and solar power is 24-hour reliability. If there's no wind or it's a cloudy day, it can interfere with power generation. Especially during spikes in need, utilities need a backup. Xcel has two large nuclear plants, some hydropower and will use natural gas "peaking" plants for many years. But batteries can be used instead of gas for extra juice when demand is at its highest, like a hot summer day when people are running air-conditioning. "We're losing over two gigawatts of round-the-clock potential baseload power," said Justin Tomljanovic, Xcel's vice president of corporate development. "We're replacing it with generally intermittent resources." Two gigawatts can supply enough power for up to 2 million homes. Astrid Atkinson, CEO of California-based Camus Energy, said batteries also will play many smaller and more specific roles in a modern electric grid that has become more complex because of things like increased use of electric vehicles. Her company is working with Connexus and pitches software that acts as an air-traffic controller and helps cooperatives better use batteries. Pilot projects and 'baby steps' Connexus has 15 megawatts of batteries at three sites and plans for more. It uses a form of common lithium batteries that has a short battery life but is trusted and already widely available. Not only was the cooperative an early adopter of batteries, it still stands out. Outside of Connexus, there was only one other utility-scale battery facility in Minnesota as of December, a state study released this month found, and it is small. The study, commissioned by the Legislature and conducted by Siemens Industry, suggested Minnesota could need between 1.35 and 2.8 gigawatts of energy storage to hit the 2040 carbon-free target. Siemens pegged the optimal amount at 1.7 gigawatts, a little more than the capacity of Xcel's largest Minnesota coal plant in Sherburne County. So far, Xcel has state approval for an experimental 10 megawatt, 100-hour long-duration battery with Form Energy that uses iron and the process of rusting to store power. Great River Energy has a smaller pilot project with Form in the works, too. Cole Funseth, Great River's manager of generation engineering, said the battery is so promising and desired by the industry because it could help over long stretches, like a polar vortex that hampers natural gas production. Minnesota Power is a partner on the state's other battery facility, a small lithium ion project in Grand Rapids, but the company is eyeing grant funding after unsuccessfully applying for federal help to test another long-lasting technology known as a flow battery. "The utilities are still very much calling these pilot projects," said Beth Soholt, executive director of Clean Grid Alliance, a trade group that represents wind, solar and battery developers. "Until they have operating experience — they can touch it, kick it, see what it does — they don't know." Meanwhile, Soholt said the 15-state regional grid operator is still taking "baby steps" on batteries, writing rules for the open energy market that will be critical for developers and the future of the technology. In this early phase, utilities also say grant money is crucial. Ryan Long, Xcel's president in Minnesota, said in general the economics for batteries have improved. But Pierce of Minnesota Power said costs are still high, especially for technology that hasn't been fully commercialized. "It's probably on the higher end of some of the [carbon-free] alternatives right now, though we do have a lot of hope for the industry," Pierce said. Xcel, while refusing to divulge the overall cost, got a $70 million grant to use on the Form pilot project in Minnesota and another in Colorado, as well as $20 million from a Bill Gates-founded platform. Power surge ahead Xcel's new long-range plan calls for 600 megawatts of storage by 2030, which is large but less than half the power output of the large coal-fired plant in Sherburne County. Great River plans to add 200 megawatts in 2030. The state Public Utilities Commission (PUC) approved a plan for Minnesota Power to incorporate up to 500 megawatt hours — a measure that accounts for output and duration — of storage, likely by 2030. That is in the ballpark for how much battery storage Siemens found each utility might need. Smaller cooperatives and municipal utilities also will have to build hundreds of megawatts of batteries in total, Siemens said. Still, the question of exactly what kind of technology the utilities will build is unresolved. Connexus seems likely to keep its focus on lithium, the proverbial meat and potatoes of the battery world. Newton said long-duration batteries are likely critical in a carbon-free grid, but he said the highly anticipated technology such as Form seems "sort of like vaporware" until it's actually operating. Xcel isn't solely focused on the Form battery either. Tomljanovic said the utility is planning on also using lots of the readily available lithium ion units. And because long-range technology is still under development, the Siemens projection was based on four-hour lithium ion. Great River initially said its Form battery would be in operation by the end of 2023, though now the company expects late 2024 or early 2025. Funseth said the delay is because GRE is waiting to get batteries produced at Form's factory under construction in West Virginia rather than get custom infrastructure. "I wish the Form Energy pilot projects could go faster," Soholt said. "Because I think that we need to understand if they're going to pan out or not." Minnesota Power also is looking at a combination of technologies, Pierce said. The utility needs energy storage systems that can last for 10 to 12 hours that would better serve the company's customer base, which includes heavy industry like taconite mines. Right now, along with state regulators, Xcel is taking bids for a large amount of what is called "dispatchable" energy — power sources like gas plants or batteries that can be called on quickly for fast power that isn't dependent on weather. The Invenergy project near Lake Wilson in front of the PUC Thursday was for a 95 MW lithium ion battery project — the largest in the state if built — and solar farm. Then there are more novel ideas. California-based Rondo Energy bid what it calls a thermal battery, which would operate by storing heat in refractory bricks that could be released as steam heat or electricity. Connexus, Newton said, is confident now in both the economics and operation of its batteries. "It had to save money for the members," he said. "But then we're also really excited because we now have had a team of engineers and operators that have five years of battery experience under their belt."