Fraunhofer stabilises aluminium anodes for lithium-ion batteries
The Fraunhofer IPA and the University of Stuttgart have developed a new cell and electrode technology for aluminum anodes. It is intended to make the previously problematic volume changes during charging and discharging manageable, thereby enabling the use of aluminum as an anode material for practical battery applications.
The aluminum foil is active material and current collector.
Image: Fraunhofer IPA/Rainer Bez
Aluminium has long been considered a potential replacement for graphite or silicon in lithium-ion batteries. The material is relatively inexpensive, widely available, and offers high capacities. However, in practice, this approach has so far failed due to mechanical stress on the electrode: during charging and discharging, aluminium undergoes volume changes that can lead to cracks, pores, and ultimately pulverisation of the electrode material. The result is capacity loss and a limited lifespan.
The Fraunhofer Institute for Manufacturing Engineering and Automation IPA, together with the Institute for Photovoltaics at the University of Stuttgart, has now developed and patented a cell and electrode technology that addresses these ageing processes. According to the researchers, the approach stabilises the materials during operation and maintains electrical contact within the electrode over many charge and discharge cycles.
“We are making a battery technology that has been known for a long time but has been difficult to control practically usable,” said Kai Peter Birke, Scientific Director for Battery and Hydrogen Systems and Storage at Fraunhofer IPA, in a German-language press release.
The approach completely eliminates graphite and silicon from the anode. This could not only reduce the demand for graphite, which is considered a critical raw material for the European battery industry; it would also eliminate the problems associated with significant volume changes in highly silicon-based anodes. Another difference lies in the structure of the electrode. The starting material is a commercially available alloyed aluminium foil, which serves as both the active material and the current collector. This eliminates the need for the copper foil typically used in conventional anodes.
Aluminium foil serves as active material and current collector
A separate coating process, used to apply the active material to the current collector, is also eliminated. This is expected to reduce both process costs and energy consumption during electrode manufacturing. The researchers cite lithium manganese oxide (LMO) as a possible cathode. In combination with the aluminium anode, a competitive energy density could be achieved. At the same time, the cell chemistry would be phosphate-free and could thus represent a cost-effective alternative to lithium iron phosphate cells.
The aluminium anode could also be combined with electrolyte solvents with a high flash point. Together with a fluorine-free LMO cathode, Fraunhofer states that a completely fluorine- and thus PFAS-free cell structure would even be possible. This would also avoid the risk of hydrogen fluoride formation in the event of a battery fire.
Fraunhofer sees initial applications primarily in areas where safety, robustness, and compact installation space are particularly important. These include, among others, air freight applications, tracking systems for transport containers, and specialised medical devices.
For later industrial use, it is relevant that the cell chemistry could be produced on existing production facilities. According to the institute, a complete rebuild of the manufacturing infrastructure would therefore not be necessary. Several prototypes have already been built and are currently being tested at the Fraunhofer IPA’s Centre for Digitalised Battery Cell Production. The institute has not yet provided details on specific cycle numbers, gravimetric or volumetric energy density in its current announcement.
In parallel, Fraunhofer is working on further approaches to improve battery cells at the material and architecture levels. In September, the Fraunhofer ISE presented a cell architecture with significantly thicker electrodes. By reducing the proportion of current collectors, the energy density could be increased by ten to 15 per cent, depending on the battery type and design. This approach is still at the research stage and must first prove its industrial scalability.