Despite the rapid development of electric vehicles (EVs), the safety of lithium-ion (Li-ion) batteries remains an issue as they pose a risk of fire and explosion. Among the various approaches to solving this problem, Korean researchers have used semiconductor technology to improve the safety of Li-ion batteries. A research team from Korea Institute of Science and Technology (KIST) under the direction of Dr. Joong Kee Lee from the Center for Energy Storage Research has succeeded in inhibiting the growth of dendrites, crystals with multiple branches that cause fires in EV batteries, by forming protective semiconducting passivation layers on the surface of Li electrodes.
When charging Li-ion batteries, Li-ions are transported to the anode (the negative electrode) and deposited on the surface as Li-metal; At this point, tree-like dendrites form. These Li dendrites are responsible for the uncontrollable fluctuations in volume and lead to reactions between the solid electrode and the liquid electrolyte, which cause a fire. Unsurprisingly, this has a huge impact on battery performance.
To prevent the formation of dendrites, the research team exposed fullerene (C60), a highly electronically conductive semiconductor material, to a plasma, which led to the formation of semiconducting carbon-containing passivation layers between the Li electrode and the electrolyte. The semiconducting carbonaceous passivation layers allow the passage of Li ions while blocking electrons due to the creation of a Schottky barrier, and by preventing the interaction of electrons and ions on the electrode surface and inside, they stop the formation of Li crystals and the resulting growth of dendrites.
* Fullerene: a special physical form of carbon in which 60 carbon atoms are linked by single and double bonds in a pentagonal shape to form a soccer ball-like shape
The stability of the electrodes with the semiconducting carbon-containing passivation layers was tested using symmetrical Li / Li cells in extreme electrochemical environments, in which typical Li electrodes remain stable for up to 20 charge / discharge cycles. The newly developed electrodes showed a significantly improved stability, with the growth of Li dendrites being suppressed for up to 1,200 cycles. In addition, when using a lithium cobalt oxide (LiCoO2) cathode in addition to the developed electrode, about 81% of the original battery capacity was maintained after 500 cycles, which corresponds to an improvement of about 60% over conventional Li electrodes.
Lead researcher Dr. Joong Kee Lee said, “Effectively suppressing dendrite growth on Li electrodes is critical to improving battery safety. The technology proposed in this study for developing highly safe Li-metal electrodes provides a blueprint for developing next generation batteries that do not pose a fire risk. “As Dr. Lee explains, his team’s next goal is to make this technology commercially viable to improve: “We want to make the production of the semiconducting carbon-containing passivation layers more cost-effective by replacing fullerene with more cost-effective materials.”
This research was carried out as part of an institutional R&D project of the KIST and a mid-career researcher project. It has also been recognized as an outstanding new overseas research project by the National Research Foundation of Korea with support from Ministry of Science and ICT (MSIT). The results of this study are in the current issue of ‘ACS energy letters‘(IF: 19.003, Top 1,852% in JCR), a highly regarded international journal in the field of materials science.
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