A Short History of Aluminum Batteries
Did you ever hear the tragedy of aluminum batteries? I thought not.
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"Did you ever hear the Tragedy of Darth Plagueis the Wise?"
"No."
"I thought not. It's not a story the Jedi would tell you. It's a Sith legend."―Chancellor Palpatine and Anakin Skywalker in Star Wars Episode III.
You have heard of lithium-ion batteries, and you have probably heard of sodium-ion batteries. There is a small chance that you have also heard of zinc-ion batteries. However, you may not have heard of aluminum batteries. Yet, aluminum batteries have a history that is longer than that of the batteries currently powering your phones and electric vehicles.1
"So what?" you may ask. Well, among post-lithium battery chemistries, aluminum is particularly attractive. It is the most abundant metal on Earth—three orders of magnitude more abundant than lithium—and it has the lowest price, being nine times less expensive than lithium among all considered chemistries. Aluminum is regarded as a "green metal," and its recycling is economically advantageous due to its low energy consumption, requiring only an estimated 5% of the energy needed to mine and process ores. Consequently, the aluminum processing and recycling industry is well established, thanks to the pervasive use of this metal in various technological applications, such as in the transportation and construction industries (Figure 1). Today, around 75% of all aluminum that has been mined is still in circulation, making aluminum a prime resource for building a circular economy.
Additionally, the trivalent nature and small radius of the aluminum cation (68 pm for Al³⁺ compared to 76 pm for Li⁺) contribute to its excellent electrochemical potency, which is reflected in a theoretical gravimetric capacity of 2980 mAh/g—second only to lithium—and the highest volumetric capacity of all battery elements (8046 mAh/cm³). Moreover, this characteristic enhances the intrinsically stable nature of aluminum metal, as its surface is passivated under normal atmospheric conditions. This stability alleviates safety concerns that may be present in other, more reactive battery chemistries, such as the flammability of lithium-ion batteries
History of aluminum batteries
The interest in aluminum batteries is a continuation of a long story that began in the 19th century, when pioneering studies on electrical energy were conducted. Since then, research on aluminum batteries has experienced varying levels of interest, much of which has focused on identifying suitable cathodes and electrolytes. Overall, these efforts can be broadly categorized into early, recent, and contemporary research.
Early attempts (1850s - 1960s)
The first use of aluminum as a battery electrode was reported as early as 1855 when Hulot described an assembly composed of a Zn-Hg alloy anode and an aluminum cathode. This was followed, in 1857, by Tommasi's use of an aluminum anode in his Treaty of Electric Batteries. In 1893, Brown disclosed a galvanic cell with an Al-Zn alloy anode and a carbon cathode. Then, in 1907, Barnes and Shearer described a hydrogen peroxide cell where aluminum and magnesium electrodes were employed. Serious efforts to develop aluminum batteries came only after World War II. In 1948, Heise reported using an aluminum anode in chlorine-depolarized reserve-type cells. This was followed, in 1951, by Sargent's dry cell with alkaline electrolyte using an aluminum anode and a carbon cathode. In 1957, Samuel disclosed the use of a halogen salt electrolyte in an Al/MnO2 cell. Later on, the 1960s saw an increased interest in aluminum-air batteries, with Zaromb reporting some of the first works for these systems.
Interestingly, these early reports were characterized by the pervasive failure in removing the passivating aluminum layer while, at the same time, stabilizing the underlying aluminum metal electrode. Hence, in the following period, the research focus shifted towards electrolyte solutions. The general expectation was that novel developments in this area would provide a stable environment for aluminum electrodeposition.
More recent efforts (1970s - 2000s)
Due to the industrial importance of aluminum, its electrodeposition at room temperature was pursued separately from battery research. The initial reports can be traced back to the 1950s, when Hurley and Brenner successfully reported the electrodeposition of aluminum from AlCl3-based baths. This approach was later adopted for aluminum battery research, with its use accelerating during the 1970s. At that time, the behavior of aluminum in high-temperature AlCl3-based melts was intensely studied for battery applications. This effort culminated in 1985 when Barberio reported the reversible electrodeposition of aluminum from an AlCl3:[EMIm]Cl melt and proposed its use in secondary aluminum batteries. Despite this progress, the field slowed down with the successful development of lithium-ion batteries in the 1980s and their subsequent commercialization a decade later. During the 1990s and 2000s, research results were sporadically reported. For instance, starting in 1993, Licht published several works on primary aqueous Al/S batteries. Other notable studies from the same period focused on different electrolyte-cathode pairs. This revision enhances the overall clarity and flow while correcting grammatical issues.
Contemporary attempts (2010s - ongoing)
It was not until 2011 that interest in aluminum batteries resurfaced. Following repeated confirmations of the reversible and straightforward electrodeposition of aluminum in AlCl3:[EMIm]Cl melts, the Archer group at Cornell disclosed a battery employing an aluminum metal anode, a V2O5 cathode, and an AlCl3:[EMIm]Cl electrolyte. This work proved instrumental in the new wave of research that followed, resulting in the seminal work of the Dai group at Standford, where graphite was used as an electrode. Their assembled cell showed excellent stability for thousands of cycles with a capacity of ~60 mAh/g, an unprecedented value in 2015.
Since then, the main focus has been on designing high-capacity cathodes. Different compound materials such as oxides and sulfides, along with various carbonaceous electrodes, have been reported. Nevertheless, stable, high-capacity cathodes proved elusive. Generally, non-carbon materials showed high capacities that rapidly decayed, while carbonaceous cathodes performed very stably but with a much lower capacity.
In addition to new cathode materials, recently, the research community started venturing into exploring novel electrolytes. Some success was achieved by modifying the cations present in the ionic liquid, including replacing the [EMIm]Cl with trimethylamine hydrochloride, 1-butyl-3-methylimidazolium chloride, or 1-methyl-1-propylpyrrolidinium chloride. Notable attempts to use aqueous electrolytes have been gaining increased interest, but research into alternatives remains shallow despite these efforts.
What’s the problem?
Despite recent efforts, it is clear that the development of a feasible aluminum battery system remains elusive. Most work has been quite one-dimensional, with most reports in the last decade delving into the design of new cathodes. However, a more integrated approach is needed to overcome the numerous challenges that linger, which can be broadly summarized as follows:
The energy density of aluminum batteries is bottlenecked by low capacity and unstable cathodes. Consequently, abundant and low-cost materials that can reversibly uptake a large number of aluminum ions are required.
Suitable electrolytes that can help realize the full potential of aluminum batteries are lacking. Such an electrolyte should allow reversible electrodeposition of aluminum at room temperature and preferably consist of trivalent aluminum ions while being safe, non-flammable, and low-cost.
These two areas are currently the focus of extensive research in academic laboratories worldwide. Although aluminum batteries have limited practical applications at this time, they possess significant potential as the world increasingly embraces electrification, which requires diverse battery chemistries for various applications. In fact, aluminum batteries may soon emerge as the optimal choice for specific uses in the near future.
That’s all for now. Until next time 🔋!
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