Hydrophobic cationic sieve enabling rechargeable aluminium-lignin batteries
In the quest for cleaner and sustainable energy, aluminium metal batteries are emerging as a promising alternative to the widely used lithium-ion batteries. Aluminium is abundant, affordable, and has the potential to store large amounts of energy. However, developing efficient aluminium batteries comes with challenges, such as instability when exposed to water-based solutions. By exploring innovative approaches, including advanced electrolytes such as water-in-salt electrolyte and sustainable materials such as lignin, this project aims to create a new generation of rechargeable batteries that are not only powerful and safe but also environmentally friendly.
In our pursuit of sustainable energy solutions, aluminium metal batteries are emerging as a strong contender, offering a potential leap beyond the limitations of conventional lithium-ion batteries. Lithium-ion technology, while revolutionary, faces challenges such as the limited availability of lithium, high costs, safety and significant environmental impacts from mining. Aluminium, however, presents an exciting alternative with its abundance, cost-effectiveness, safe and favorable electrochemical properties.
Why Aluminium?
Aluminium (Al) is the third most abundant element on Earth, constituting about 8.21% of the Earth's crust, far surpassing the mere 0.0065% that lithium occupies. This abundance makes aluminium not only cheaper (22 SEK per kilogram) but also more sustainable, with a significantly lower environmental footprint in terms of extraction and processing. Beyond its abundance, aluminium possesses a high redox potential (-1.66 V vs SHE), meaning it has the capacity to store and release large amounts of energy: an essential feature for high-performance batteries.
However, the path towards development of practical aluminium batteries is not without its challenges. The primary challenge is the instability of aluminium when exposed to aqueous (water-based) electrolytes, which are crucial for safe and efficient battery operation. When aluminium comes into contact with water, it triggers the hydrogen evolution reaction (HER), a side reaction that degrades the battery over time. Furthermore, aluminium tends to form a passive oxide layer on its surface, which impedes its electrochemical performance. Another significant issue is dendritic growth, where needle-like structures form on the aluminium surface during subsequent charging/discharging. These dendrites can penetrate through separator and cause short circuits, posing serious safety risks.
The Solution: Water-in-Salt Electrolytes (WiSE)
To overcome these challenges, the project aims to adopt an innovative solution which is the use of "water-in-salt electrolytes" (WiSE). In a typical battery, the electrolyte—a solution that conducts ions between the battery’s electrodes—is made up of water and dissolved salts. However, in a WiSE, the concentration of salt is so high that it greatly reduces the amount of free water molecules available for water electrolysis. This highly concentrated environment stabilizes the aluminium by minimizing the side reactions with water, which in turn suppresses the unwanted hydrogen evolution reaction and reduces the risk of dendrite formation.
A Glimpse into the Future: Aluminium-Lignin Batteries
The ultimate objective of the project is not only to prove the viability of aluminium batteries but to also demonstrate their application in a sustainable manner. Here, another fascinating development comes into play: the combination of aluminium with lignin. Lignin is a natural biopolymer found in plants, particularly in wood, and is very inexpensive (1-4 SEK per kilogram). It has electrochemical activity, meaning it can participate in storing and releasing energy. However, lignin is naturally an electrical insulator, which makes it challenging to use directly in a battery. To overcome this, lignin can be combined with materials that conduct electricity, such as carbon. In fact, our team and Ligna Energy AB, have already demonstrated that lignin-carbon composites can work as cathode materials in batteries. By pairing lignin with aluminium, we aim to develop a cost-effective, safe, and sustainable battery system suitable for large-scale energy storage.
A rechargeable aluminium-lignin battery could revolutionize energy storage by offering a green alternative to current technologies. Imagine a world where your smartphone, electric vehicle, or even the power grid is powered by batteries made from common, abundant materials like aluminium and lignin, rather than rare and environmentally taxing metals like lithium and cobalt. This technology holds the promise of reducing the ecological footprint of energy storage, making it a key component in the global shift towards renewable energy.
Involved in the project
Ziyauddin Khan, Reverant Crispin, C. Moyses Araujo, Anna Martinelli, Nicole Abdou, Leandro Franco, Anders Hägerström
Partners
Linköping University, Ligna Energy AB