CIC energiGUNE, the Basque research center of reference in electrochemical energy storage, thermal energy storage and conversion and hydrogen technologies, has succeeded in manufacturing for the first time a sodium metal anode with a thickness of only 7 microns through an innovative physical evaporation process. This scientific-technological breakthrough, which is part of the TOPSIDES project funded by the State Innovation Agency, opens the door to the manufacture of flexible solid-state batteries, with the thin sodium anode as a key element to provide a safer, cheaper and smaller alternative to current liquid electrolyte batteries that use graphite.
"Sodium, although it represents a more sustainable alternative to lithium, is a much more complex material to handle, as it cannot be easily laminated due to its sticky texture, similar to plasticine," said Montse Galcerán, Principal Investigator of the project at CIC energiGUNE. "To date, the most common method used to laminate a block of sodium was as basic as processing it with a hammer, but this meant that a thin, homogeneous sheet could not be obtained, and therefore there was a large excess of unused sodium in the batteries. Thanks to evaporation, we have managed to overcome this obstacle," he said.
Specifically, the system used at CIC energiGUNE to achieve this 7-micron sodium thin metal anode is based on a precise technique that consists of evaporating the sodium and then condensing it directly on the current collector of the battery inside a high-vacuum chamber. In this way, the sodium is deposited on the current collector atom by atom and exactly the thickness needed for the battery to function is achieved, without excess sodium.
"To get an idea of what this breakthrough means, it is enough to say that conventional sodium metal anodes usually look like a 5-cent coin (with a thickness of around 500 microns), to give a simple example. At CIC energiGUNE we have achieved to make this anode measure only 7 microns, some 70 times thinner", explained Lorenzo Fallarino and Rosalía Cid, researchers at the Surface Analysis Unit, a state-of-the-art laboratory located at the Basque center´s facilities, which has enabled such a breakthrough to be made, together with researchers from the sodium battery line.
The immediate benefits of this development are cost reduction - especially in the amount of sodium used - an increase in energy density - reducing the weight and dimensions of the battery - and improved safety. For future battery applications, the evaporation-grown metal thin anode is a milestone for the manufacture of flexible and micro sodium batteries. This development offers the possibility of increasing the efficiency and safety of solid-state batteries, since the sodium metal anode is the element used in these solid-state batteries, instead of the hard carbon used in conventional organic liquid electrolyte batteries.
The work carried out at CIC energiGUNE will also be key to progress in the final development of the TOPSIDES project, coordinated by the Basque center and in which POLYMAT-UPV/EHU and the Catalan company CROMOGENIA-UNITS also participate with the aim of developing solid state sodium-metal batteries, with a coin cell configuration, which allows its evaluation in terms of electrochemical performance, the investigation of the aging process and the analysis of its technological feasibility. In this sense, the next step of the project will be to develop the solid electrolytes, a work package that POLYMAT-UPV/EHU is in charge of together with the polymer line of CIC energiGUNE.
