High temperature solid battery leads to ‘battery on a chip’

Technology News |
By Nick Flaherty

The team constructed a sandwich-like battery featuring a layer of lithium garnet which acts as a solid electrolyte between the two electrodes. This works best at high temperatures, and could also be used to build batteries in a silicon device.

In conventional lithium-ion batteries as well in most other batteries, the positive and negative electrodes are made of solid conductive compounds and charge moves between them in a liquid or gel electrolyte. Overcharging or overheating means the liquid can ignite or the gel can swell up. With the solid 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. However, one of the key challenges is to connect the electrodes and electrolyte in such 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.

“In this work we have for the first time built a whole lithium-ion battery with a solid lithium garnet electrolyte and a solid minus pole made of an oxide-based material. Thus, we have shown that it is possible to build whole batteries based on lithium garnet,” said Rupp. Thanks to this solid electrolyte one can not only operate batteries at higher temperatures, but also build thin-film batteries, that can even be directly placed on silicon chips. “These thin-film batteries could revolutionise the energy supply of portable electronic devices,” she said.

“During production, we made sure that the solid electrolyte layer obtained a porous surface,” said Jan van den Broek, a master’s student in Rupp’s group. The researchers then applied the material of the negative electrode in a viscous form, allowing it to seep into the pores. Finally, the scientists tempered the battery at 100 ºC. “With a liquid or gel electrolyte, it would never be possible to heat a battery to such high temperatures,” he said. The porous surface allows a significantly larger 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 ºC and above at the current development state. “The lithium ions can then move around better in the battery,” he said.

This characteristic could be put to use in battery storage power plants, which store excess energy and deliver it later as needed. “Today, the waste heat that results from many industrial processes vanishes unused,” he added. “By coupling battery power plants with industrial facilities, you could use the waste heat to operate the storage power plant at optimal temperatures.”

Rupp and her team will pursue this approach in further research with industrial partners as well as with the Paul Scherrer Institute and with Empa. The immediate next step is to optimise the battery, with a particular focus on further increasing the conductivity of the electrode-electrolyte interface.


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