Shining a light on a metal used in nearly all today's economic sectors

Used in everything from beer cans to spacecraft, aluminum is a metal most people interact with nearly every day. What many people don't know is this lightweight metal is also a candidate for next-generation rechargeable batteries with the potential to outperform the lithium-ion cells in use today.

The major uses for aluminum metal are generally found in:

• Transportation – automobiles, aircraft, trucks, railway cars, marine vessels, bicycles, spacecraft, etc., often chosen for its low density.

• Packaging – canning, foils, frame, etc., because it is non-toxic.

• Building and construction – windows, doors, siding, building wire, sheathing, roofing, etc. Although steel is cheaper, aluminum is chosen when lightness, corrosion resistance, or engineering features are important.

• Electricity-related uses – conductor alloys, motors, generators, transformers, capacitors, etc. Aluminum is relatively cheap, highly conductive, has adequate mechanical strength and low density, and is resistant to corrosion.

• A plethora of household items – from cooking utensils to furniture. Low density, appealing appearance, ease of fabrication, unlikeliness to spontaneously combust, and mechanical strength make it ideal in many consumer goods.

• Machinery and equipment – processing equipment, pipes, tools, etc., for many of the same reasons as above.

Despite global production of aluminum reaching almost 70 million metric tons in 2021, making it one of the highest produced metals in the world, this versatile metal has a place as one of the United States' 50 critical minerals due to its importance in the aerospace, defense, energy, and transportation industries.

"The United States is a deficit market for aluminum, meaning it consumes more of the metal than it is able to produce domestically. Consequently, most of U.S. aluminum industry jobs rely in some way on reliable international supply chains," Aluminum Association President and CEO Charles Johnson testified before the U.S. International Trade Commission in July. "I'm happy to report that the U.S. aluminum industry is globally competitive and growing. However, the industry has faced a distorted global market in recent years driven primarily by massive growth in government-subsidized and state-owned aluminum production in China."

A brief history of aluminum

The history of aluminum has been shaped by the usage of alum – a type of chemical compound, usually a hydrated double sulfate salt of aluminum and potassium used in medicinal solutions as well as dyeing and tanning – with the first written record of alum being made by Greek historian Herodotus dating back to the 5th century BCE.

The ancients were known to have used alum as a dyeing mordant, basically an adhesive to set color into fabric, as well as for city defenses.

After the crusades, alum had become an indispensable good in the European fabric industry and was the subject of international commerce, generally imported from the eastern Mediterranean until the mid-15th century.

While early chemists were eventually able to classify alum as its own substance – as it was often mistaken with other astringents like green vitriol or ferrous sulfate, attempts to produce aluminum metal would not occur until 1760, with the first successful attempt being completed over 50 years later in 1824 by Danish physicist and chemist Hans Christian Ørsted-by combining aluminum chloride and potassium amalgam, it yielded a lump of metal similar in appearance to tin.

Three years later, a German chemist named Friedrich Wöhler attempted to repeat Ørsted's experiments but was unable to produce or identify aluminum.

However, he did not give up and today is credited with being the first to thoroughly describe the metallic element aluminum as well as the discoverer of aluminum itself.

As Wöhler's method could not yield great quantities of aluminum, the metal remained rare, with its cost even exceeding that of gold. Thus, the first industrial large-scale production method would not come into inception until 1886; something called the Hall-Héroult process after French engineer Paul Héroult and American engineer Charles Martin Hall.

It was roughly 10 years later that Austrian chemist Carl Joseph Bayer discovered a way of purifying bauxite to yield alumina, now known as the Bayer process.

Both methods are still predominately used, with many aluminum producers transforming bauxite to alumina and then alumina to aluminum.

From bauxite to aluminum

Before being transformed into its well-known and lightweight metallic form, the Bayer process of making aluminum starts by drying crushed or washed bauxite which is then dissolved in caustic soda to form a slurry and then heated. This mixture is then filtered to remove the residue or what is commonly referred to as red mud.

The filtered solution is then transferred or pumped into precipitator tanks, where it cools and starts to seed. These seeds stimulate a precipitation process allowing solid aluminum hydroxide crystals to form.

After completion, all the aluminum hydroxide that settles at the bottom of the tanks is removed.

The remaining caustic soda is washed away from the aluminum hydroxide, which undergoes further levels of filtering and then finally heated once more to remove any excess water. After passing through a cooling stage, a fine white powder remains – aluminum oxide or alumina.

Bauxite residue, commonly referred to as red mud due to its color and consistency, is a waste material produced during the aluminum-making process that is typically stored in large containment facilities. This discarded waste material, however, has emerged as a potential alternative source of critical minerals.

More information on recovering critical minerals from bauxite residue and other alternative sources can be read at Outside-the-box critical mineral sources in this edition of Critical Minerals Alliances.

While a great majority of aluminum oxide produced with the Bayer process is converted to metal, aluminum compounds have many niche applications such as:

• Aluminum acetate in solution is used as an astringent to treat wounds.

• Aluminum phosphate is used in the manufacture of glass, ceramic, pulp and paper products, cosmetics, paints, varnishes and even dental cement.

• Aluminum hydroxide by itself is used as an antacid, as well as a dyeing binder, more specifically called a mordant. Aluminum hydroxide is also used in water purification, as well as other glass and ceramic products and the waterproofing of fabrics.

• Lithium aluminum hydride is a powerful reducing agent used in organic chemistry.

• Aqueous aluminum sulfate is used to treat against fish parasites commonly known as salmon fluke.

• Certain aluminum salts serve as an immune adjuvant or immune response booster in vaccinations.

• And many more uses, generally in advanced chemistry processes.

With such widespread usage, it is no small wonder it has become critical to the U.S. While concerns over supply chains being vulnerable to disruption are currently at the forefront of headlines everywhere, as the second-highest produced metal in the world, aluminum is not going anywhere, anytime soon.

Aluminum-graphene batteries

While aluminum is an excellent electric conductor, it is generally passed over for more resilient metals that require less preparation and provide better longevity in electricity-using industries.

One function, however, that is not well known is that aluminum has the potential to be a better base material for rechargeable batteries than lithium. This is due to aluminum's ability to exchange three electrons for every ion, compared to a single ion for lithium – enabling up to three times more energy density.

While scientists have long been searching for an alternative to the expensive and limiting lithium battery, previous iterations continue to use graphite as the primary cathode material, "which has too low an energy content to create battery cells with enough performance to be useful," according to some researchers.

That is until graphene entered the equation.

As graphene manufacturing has seen explosive growth in recent years – production facilities being able to scale up production of this 2D form of carbon and new and exciting innovations contributing to its widespread use – researchers and manufacturers have taken to the miracle material like bees to honey.

Graphene Manufacturing Group, an Australian-based clean-tech company that produces graphene and hydrogen by cracking methane instead of mining graphite, is incorporating a technology devised by the University of Queensland's Australian Institute of Bioengineering and Nanotechnology (AIBN) and the university's commercialization company Uniquest, to unlock the potential of graphene aluminum-ion batteries.

At the latter end of 2021, GMG announced that its pilot production and testing plant for its graphene aluminum-ion batteries is now operational, with the first coin cells being manufactured.

According to GMG, laboratory testing and experiments have shown so far that the graphene-aluminum-ion battery energy storage technology has high energy densities and higher power densities compared to current leading marketplace lithium-ion battery technology.

Specifications detailed by the company include a power density of up to 7,000 watts per kilogram, with testing confirming a cycle rate with minimal reduction over a 3,000-cycle experiment period – which included charging up to full charge and discharging down to near full discharge – at variable charging rates.

The company also said these results showed a very high cycling rate for the duration, with negligible reduction in performance and at a very high charging rate of up to 66 coulombs (amperes per second), which is comparable to lithium-ion batteries between 600 to 1,000 cycles at much lower charging rates of one-fifth coulombs, where performance typically reduces to 60% of original capacity.

In layman, this means a much longer battery charge, immensely shorter recharge time, and a significantly longer life span.

"Testing showed rechargeable graphene aluminium-ion batteries had a battery life of up to three times that of current leading lithium-ion batteries, and higher power density meant they charged up to 70 times faster," said University of Queensland AIBN Director Alan Rowan. "The batteries are rechargeable for a larger number of cycles without deteriorating performance and are easier to recycle, reducing potential for harmful metals to leak into the environment."

With the possibilities that graphene presents, aluminum may see a monumental jump in its critical status, and according to GMG CEO Craig Nicol, "It is the technology the industry has been waiting for."