Two studies by teams at the University of Geneva (UNIGE) may have resolved the issue of poor movement of sodium ions in solid electrolyte batteries.
The teams modified the structure of the crystals in the solid electrolyte to allow for the more efficient transportation of sodium ions.
Due to sodium being heavier than lithium, the movement of its ions through liquid electrolyte is hindered, which makes it unable to achieve the performance of lithium batteries — to date.
Previous studies using a solid electrolyte composed of hydridoborates (boron and hydrogen) did not solve the issue.
Now, two studies conducted by the UNIGE crystallography laboratory has led to the development of sodium carbo-hydridoborate (NaCB11H12).
The research projects were headed by professor Radovan Cerny.
The first project, published in peer-reviewed scientific journal ACS Applied Materials & Interfaces, subjected the NaCB11H12 compound to high shocks, generating high temperatures, inside a ball mill.
The second research project, published in peer-reviewed scientific journal Advanced Materials Interfaces, consisted of putting this material in situation (in contact with the positive and negative electrodes of the battery).
To contain the material firmly within the battery pressure must be applied by means of screws or springs, said Matteo Brighi, former postdoctoral scholar in the crystallography laboratory.
The team found the ideal ‘force’ to exert on solid electrolytes was around 400 atmospheres.
The discoveries could pave the way for easier production of sodium batteries, especially in the automotive industry.
Fabrizio Murgia, a researcher in the crystallography laboratory of the UNIGE Faculty of Science, told BEST: “The results have been paving the way for further studies on full cells.
“However, at present, we’re not directly testing our new electrolyte in full cells, since we’re carrying out some preliminary tests in half-cells, in order to check the interaction with both negative and positive electrodes, separately, as well as other tests in order to evaluate the opportune stack pressure to maximize the contact area between components.
“We expect good results in terms of wide voltage window, thanks to the superior (electro)chemical stability of such material, but the overall capacity will strongly be affected by the electrodes that will show the highest chemical and mechanical compatibility with our new electrolyte.”
Murgia believes that because of the slightly heavier weight of the batteries, they could be used primarily to power cars.
The cost-effectiveness of manufacturing them has to be assessed, as the production of this type of battery involves a different technology from that used for lithium-based ones.
As an alternative to lithium-ion, sodium is being explored because the element is abundant, cheaper than lithium, and easier to recycle.
The solid electrolyte developed by the UNIGE team lets the ions move efficiently within the sodium batteries. (c) Xavier Ravinet / Olivier Gaumer – UNIGE