ETH Zurich researchers have developed a new solid state lithium-ion battery from lithium garnet that contains neither liquids nor gels.
Moreover, the battery is non-flammable – even at very high temperatures, giving it a safety advantage over conventional batteries, the researchers contend.
In conventional lithium-ion batteries as well in most other batteries, the positive and negative electrodes are made of solid conductive compounds; charges move between these electrodes in a liquid or gel electrolyte. If you charge such a battery improperly or leave it sitting out in the sun, the liquid can ignite or the gel swell up.
One of the challenges in developing solid-state batteries is to connect the electrodes and electrolyte in such a way that the charges can circulate between them with as little resistance as possible. ETH researchers have now developed an improved electrode-electrolyte interface to sort out this problem.
The researchers have successfully constructed a sandwich-like battery featuring a layer of lithium garnet, which acts as a solid electrolyte between the two electrodes. Lithium garnet is one of the materials with the highest known conductivity for lithium ions.
“During production, we made sure that the solid electrolyte layer obtained a porous surface,” says Jan van den Broek, a master’s student in professor Jennifer Rupp’s group and one of the authors of the study. The researchers then applied the material of the negative pole in a viscous form, allowing it to seep into the pores. Finally, the scientists tempered the battery at 100 degrees Celsius.
“With a liquid or gel electrolyte, it would never be possible to heat a battery to such high temperatures,” says van den Broek. Thanks to the trick with the pores, the researchers were able to significantly enlarge the contact area between the negative pole and the solid electrolyte, which ultimately means that the battery can be charged faster.
Batteries produced like this could theoretically operate at a normal ambient temperature, says Semih Afyon, a former research scientist in Rupp’s group, now a professor at the Izmir Institute of Technology in Turkey. But they work best at 95 degrees Celsius and above at the current development state:
“The lithium ions can then move around better in the battery,” says Afyon. This characteristic could be put to use in battery storage power plants, which store excess energy and deliver it later as needed.
Many of today’s solid-state battery research projects focus on improving the electrolytes. However according to Afyon, there are very few studies such as this one, in which the scientists assembled an entire solid-state battery – using methods also used in industrial production – and tested it.
Rupp, a Professor of Electrochemical Materials at ETH Zurich, opines that these thin-film batteries could end up revolutionizing the energy supply of portable electronic devices. She and her team will pursue this approach in further research. To this end, they have also collaborated with industrial partners as well as with the Paul Scherrer Institute and Empa.
Image credits: ETH Zurich/Fabio Bergamin
