A research team at the Paul Scherrer Institute (PSI) in Switzerland has developed a new sustainable process and cathode surface coating that can be used to improve the electrochemical performance of lithium-ion batteries.
Initial tests of high-voltage batteries using this method indicate it could be used to make lithium-ion batteries for EVs more efficient.
At operating voltages above 4.3 V, 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, Mario El Kazzi and his team have developed a new method to stabilize the surface of the cathode by coating it with a thin, uniform protective layer. The researchers report on their discovery in a study published in the scientific journal ChemSusChem (Wiley).
The process centers on a gas that is produced as a by-product during the manufacture of plastics such as PTFE, PVDF, and foam: trifluoromethane (CHF3). In the laboratory, El Kazzi and his team initiated a reaction at 300° C 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). The lithium atoms of the cathode material remain as ions, which must be able to move back and forth between the cathode and the anode to maintain the battery capacity.
The researchers tested the effectiveness of the protective coating by carrying out electrochemical tests at high operating voltages. The protective coating remained stable even at high voltages, allowing it to operate at voltages of 4.5 V and up to 4.8 V.
The coated batteries outperformed batteries with unprotected cathodes. For example, the impedance—the resistance for the lithium ions at the cathode interface—was around 30% lower after 100 charging and discharging cycles than in the batteries with untreated cathodes. The capacity retention was more than 94% after 100 charging and discharging cycles without a decrease in charging speed, while the untreated battery achieved 80%.
“We can assume that our lithium fluoride protective coating is universal and can be used with most cathode materials,” said Mario El Kazzi from the Center for Energy and Environmental Sciences at PSI. “For example, it also works with nickel- and lithium-rich high-voltage batteries.”
Source: Paul Scherrer Institute
