Rechargeable batteries is one of the key technologies in the future energy system based on a high share of renewable energy. Over the past years, battery technologies have gained increasing attention for stationary applications, both as energy storage units (in the power system, as well as in so-called stand-alone systems), and for flexibility and frequency support in the power system. The dominating technology is Li-ion batteries, which have reached a high production volume over the last years, and thereby a significant cost reduction. This technology is very material intensive, and materials constitute a high share of the total costs (ca 50%). Current Li-ion technology is based on materials like lithum, cobolt, nickel and copper, which all have challenges related to abundancy, energy consumption and ethics during production (in particular for copper). Furthermore, there is a lack of processes for recycling of Li-ion batteries, which again is related to the complex materials used for this technology.
With respect to the near exponential growth currently experienced by the global battery industry, a key factor to success is to control the value chain of the production, in particular by securing access to raw materials. Within the framework of the ALCBATT project, we perform research related to an up to now relatively unexplored battery concept, based on an aluminium anodes, and a cathode made from a carbon material, most typically graphite or exfoliated graphite. This type of battery could potentially be a low cost battery, and will also be very easy to recycle. The concept has been demonstrated in laboratory scale cells, and most studies have used an electrolyte rich in chlorine based on a mixture of AlCl3 and EmimCl. The latter component is a socalled ionic liquid, which means it is a salt which is a liquid at room temperature. This electrolyte has a very high conductivity, around 2-3 times higher than electrolytes that are typically used in conventional Li-ion batteries.
There are still a number of challenges that needs to be solved before such batteries can be introduced for commercial use. Up to now, laboratory scale cells have been made from aluminium of a high purity. This is however costly, and in addition highly pure aluminium is very sensitive towards moist. Regarding the carbon cathode, there is still a need for optimization. In addition, the currently most used electrolyte is problematic due to the high content of chlorine, which means it is aggressive towards most materials. This poses a challenge also for future scale-up.
In the research project, which is conducted in collaboration between NTNU, SINTEF and industrial partners, we study different types of carbon, new electrolytes as well as different aluminium alloys and current collectors. In laboratory scale cells, we have demonstrated up to 1000 charge/discharge cycles. Synthetic graphite from a Norwegian industrial partner has so far given the best performance. We have shown that the current collector on the cathode side, which up to now has been based on Molybdenum in most studies, can successfully be replaced with carbon paper, which even contributes to increased performance for the cathode. Various aluminium alloys appear to give very similar performance, which is good news with respect to reducing costs. Another main activity of the project is to try to find alternative electrolytes based on less aggressive salts and solvents. For this activity, a Post Doc affiliated to the project use atomistic modelling techniques (primarily molecular dynamics simulations) as a tool, combined with machine learning algorithms. One challenge is the optimization of electrolyte to comply with both anode and cathode, which has turned out to be very challenging. We have identified a set of electrolytes for testing against both electrodes, after failure of the two initial attempts.
In view of the predicted exponential growth of the global battery industry, the key to success is the presence along the entire value chain, in particular securing the supply of raw materials. The research proposed within the ALCBATT proposal aims to demonstrate a nearly unexplored battery concept based on abundant, low cost, and recyclable materials, namely aluminum and carbon. The goal is further to demonstrate the improved performance of this battery on the laboratory scale. The research is thus perfectly aligned towards the societal challenges related to the climate crisis and reduction of fossil fuels, as well as the shift towards a circular economy. Key to the successful development of aluminum carbon batteries is identifying appropriate electrolytes, with an optimized solvation structure of the salt in a non-aqueous electrolyte. To identify electrolytes, a combination of fundamental modelling studies, utilizing machine learning algorithms, and advanced characterization and testing in small-scale batteries will be used. Furthermore, the studies of the charge and discharge reactions at the electrodes, particularly the aluminum anode, will be aided by the fabrication of controlled surface and grain boundary structures to gain the necessary knowledge on the quality of the materials. For all the components, Al anode, electrolyte, and carbon cathode, research will be aided by advanced characterization techniques, like XPS, TEM, and in-operando synchrotron techniques. Thus, the development will rely on enabling technologies like ICT and nanotechnology.
