Energy storage in liquid metals and molten salts
Energy systems with a dominant share of volatile sources, such as photovoltaics and wind power, require storage to balance the time difference between supply and demand.
As part of the Horizon 2020 SOLSTICE project, innovative Na-ZnCl2 high-temperature cells are being developed that are tailored from the outset to the requirements of stationary storage. SOLSTICE aims to produce storage systems that are as cost-effective and environmentally friendly as possible, do not contain conflict minerals, and are easily recyclable in order to meet the requirements of the circular economy pursued by the EU.
Schematic diagram of the Na-ZnCl2 cells developed by SOLSTICE. (Grafic: HZDR/Blaurock)
How is it researched?
Twelve European partners are collaborating on the SOLSTICE research project. Developing the cells requires knowledge of the electrochemistry of molten salts and liquid metals, as well as expertise in battery manufacturing and management and techno-economic evaluation. SOLSTICE is developing and testing Na-ZnCl2 cells in the laboratory with the aim of demonstrating that they can be used as storage devices over long periods of time under realistic operating conditions. The behavior of the cells is being investigated electrochemically. For a deeper understanding, some cells are X-rayed and neutron-scanned during operation to gain insights into their inner workings. The experiments are accompanied by numerical simulations that help to understand and optimize cell behavior. Economic feasibility studies and life cycle analyses are used to evaluate the results achieved.
Setup of a test cell (left) and X-ray image during operation at 600 °C (right).
What is the benefit for society?
The transition of energy supply to predominantly volatile sources (wind power and photovoltaics) leads to differences between supply and demand. Balancing these differences requires high-capacity stationary storage systems that should be manufactured at low cost and with as little environmental impact as possible. The storage systems developed by SOLSTICE use NaCl and Zn, raw materials that are readily available in the European Union, inexpensive, and whose extraction has a comparatively low environmental impact. The structure of the cells, with macroscopically separated layers of materials, greatly facilitates reuse and thus contributes to a favorable overall balance.