Researchers at ETH Zurich have now developed a type of battery that consists entirely of solid chemical compounds and is non-flammable, unlike today’s batteries.
In conventional lithium-ion batteries, the positive and negative poles (the two electrodes) are made of solid conductive compounds. The charges move between these electrodes in a liquid or gel electrolyte. This means that if the battery was to be charged improperly, also called overcharged, or left sitting out in the sun, the liquid could ignite or the gel could swell up.
This is not the case with solid-state batteries, which are currently in development in labs around the world, because in these batteries, both the electrodes and the intermediary electrolyte are made of solid material.
"Solid electrolytes do not catch fire even when heated to high temperatures or exposed to the air," said Jennifer Rupp, Professor of Electrochemical Materials at ETH Zurich, who is leading the development of this new type of battery.
When it comes to developing solid-state batteries, one of the challenges is connecting the electrodes and electrolyte in a way that the charges can circulate between them with as little resistance as possible.
The ETH researchers have now developed an improved electrode-electrolyte interface to overcome this challenge.
How They Did It
The ETH team constructed a sandwich-like battery featuring a layer of lithium-containing compound (lithium garnet), which acts as a solid electrolyte between the two electrodes. Lithium garnet is a material well known for its high conductivity properties for lithium ions. The researchers made sure that the solid electrolyte layer had an absorbent surface and then applied the material of the negative pole in a viscous form, allowing it to seep into the pores.
The researchers then ran the battery’s temperature up to 100° C, which would be impossible to do to a battery that had a liquid or gel electrolyte.
The porous surface was what allowed the researchers to significantly enlarge the contact area between the negative pole and the solid electrolyte—ultimately making a battery that could be charged faster.
“Batteries produced like this could theoretically operate at a normal ambient temperature,” said 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° C and above at the current development state. The lithium ions can then move around better in the battery.”
The team says that this battery quality could be useful in battery storage power plants, which store excess energy and deliver it later as needed. Currently the waste heat from industrial processes is left unused, but according to Afyon, coupling battery power plants with industrial facilities would allow for the use of waste heat to operate the storage power plant at optimal temperatures.
"These thin-film batteries could revolutionize the energy supply of portable electronic devices," said Rupp.
The team will now focus on supplying energy to electronics to further the work. ETH will also collaborate with industrial partners in its next steps. But for now, the immediate task will be to optimize the battery, with a particular focus on increasing the conductivity of the electrode-electrolyte interface.