New protective coating for more powerful batteries
A research team at the Paul Scherrer Institute PSI has developed a new sustainable process that can be used to improve the electrochemical performance of lithium-ion batteries.
Lithium-ion batteries are considered a key technology for decarbonisation. Therefore, researchers around the world are working to continuously improve their performance, for example by increasing their energy density. “One way to achieve this is to increase the operating voltage,” says Mario El Kazzi from the Center for Energy and Environmental Sciences at Paul Scherrer Institute PSI. “If the voltage increases, the energy density also increases.”
However, there is a problem: At operating voltages above 4.3 volts, strong chemical and electrochemical degradation processes take place at the transition between the cathode, the positive pole, and the electrolyte, the conductive medium. To solve this problem, El Kazzi and his team have developed a new method to stabilise the surface of the cathode by coating it with a thin, uniform protective layer.
Effective protective coating
The process centres on a gas that is produced as a by-product during the manufacture of plastics such as PTFE, PVDF, and foam: trifluoromethane, with the chemical formula CHF3. In the laboratory, El Kazzi and his team initiated a reaction at 300 degrees Celsius between the CHF3 and the thin layer of lithium carbonate that covers the surface of the cathodes. This converts the lithium at the interface into lithium fluoride (LiF). It is important to note that the lithium atoms of the cathode material remain as ions, that is, as positively charged particles. These lithium ions must be able to move back and forth between the cathode and the anode, the negative pole, during charging and discharging so that the battery capacity is not impaired during subsequent operation.
In a further step, the researchers tested the effectiveness of the protective coating by carrying out electrochemical tests at high operating voltages. The gratifying result: The protective coating remained stable even at high voltages. It protects the cathode material so well that it is possible to operate at voltages of 4.5 and even 4.8 volts.
Further information can be found on the website of the Paul Scherrer Institute PSI.
Reading tip:
Learn more about current approaches to produce coatings in a more environmentally friendly way and to give coated products a longer service life in the EC Tech Report Sustainability. In addition, its handpicked content dives deeply into the European Green Deal, its key points and main purpose as well as consequences for the coatings industry.
