The transition from fossil fuels to renewable energy sources requires economic and sustainable electrochemical energy storage solutions with high energy and power density. The current lithium-ion battery technology employs an intercalation anode. The lithium-ion technology enabled substantial progress in electric vehicles and consumer electronics. However, due to the inherent technological limitations, it cannot meet all future requirements. The voluminous intercalation anode represents a central drawback. A promising alternative that we want to pursue in this project is anode-free cells with alkali-metal anodes paired with solid electrolytes. Such cells do not require any intercalation material in the anode and no addition of alkali metal during cell assembly. Thereby, the energy density is increased by up to 35%, while production costs are reduced.

Alkali-metal anodes can be either solid or liquid, depending on the operating temperature and employed materials. Solid alkali-metal anodes suffer from dendrite formation and limited power capabilities. In contrast, liquid alkali-metal anodes paired with solid electrolytes enable high-power charging and discharging, as well as high areal capacities. However, a major challenge of liquid anodes is alkali-metal management. This challenge includes achieving complete storage and release of the liquid alkali metal within the anode compartment during cell cycling, handling the volumetric changes within the anode, and ensuring good electrical contact between the alkali metal and solid electrolyte. Only effective alkali-metal management enables sufficient cycling stability and efficient use of the entire active material at low overpotentials and low operating temperatures. To date, the fundamental wetting and phase change interactions of alkali metals under battery-relevant conditions are not sufficiently understood to inform the design of coatings and capillary structures for effective alkali-metal management. Therefore, in this project, we want to first lay these important foundations in the area of interfacial phenomena, so that in next steps we can build on this fundamental understanding to develop functional coatings and structures which can be integrated into next-generation anode designs to enable high-performance batteries.

To ensure that an energy storage technology is sustainable, the employed raw materials are of primary importance. The selected materials should cause minimal adverse effects on the environment through their entire life cycle from material sourcing to recycling and be globally available in sufficient quantities and thereby reduce societal risks and dependencies in times of collapsing supply chains and geopolitical tension. These are important criteria when exploring potential beyond-lithium-ion technologies. Therefore, in this project, we will set a focus on sodium (Na) and potassium (K) as active materials, since these represent sustainable, economic and little explored alternatives to the less abundant and unevenly distributed lithium (Li). However, not only the employed alkali metals determine sustainability and viability of a technology, also the remaining components of the battery need to be considered. Especially promising for future electrochemical energy storage are sodium-metal chloride and metal-sulfur batteries, since these rely on abundant raw materials and promise competitive energy densities and cycle life. For this reason, we are initially targeting sodium-metal chloride and metal-sulfur batteries as primary cell chemistries for the integration of the high-performance anodes that we want to develop in this project. However, the remaining components of the battery, beyond the employed alkali metals, need to also be considered for sustainability and viability of the technology.

It is envisioned that developing sustainable, economic solutions for the realization of alkali-metal anodes will critically advance stationary energy storage capabilities to allow us to effectively decarbonize our society and gain independence from fossil fuels, thereby overcoming the associated environmental and geopolitical risks. For mobile applications, economic, compact, high-power batteries translate into long-range, fast-charging and affordable electric vehicles. Such drastic performance improvements as targeted in the present project also represent a key requirement for more demanding future applications such as electrified aviation.