The road to longer lasting batteries

Researchers from the Norwegian University of Science and Technology are working on improving battery life by changing the electrolyte composition.

When the battery is first charged up, a thin film called an SEI (solid electrolyte interphase) forms on the surface of the carbon anode. This film has a complex chemical structure containing both organic and inorganic lithium compounds.

“This film is an essential part of the battery,” said Professor Ann Mari Svensson, from the Norwegian University of Science and Engineering’s (NTNU) Department of Materials Science and Engineering.

The SEI film forms the first time the battery is charged, from the reaction between the electrolyte and the anode. This protective coating is key in determining a battery’s lifetime, thermal stability and capacity, especially at high rates.

Lithium that is bound in the film doesn’t participate in charging the electrodes, which results in reduced capacity.

“Once the battery is assembled, we cannot add more lithium to the cell, and therefore limiting the loss of available lithium in the cell is of prime importance for long-lasting batteries,” said Ahmet Oguz Tezel, a PhD candidate at the Department of Materials Science and Engineering.

If you can’t add more lithium to the solution, you have to do a better job of preserving the lithium that is already there. Tezel has recently handed in his PhD on the formation of SEI films, and how this is influenced by the composition of the electrolyte that is used.

Tezel’s work has focused on modifying the electrolyte to achieve higher battery capacity and life span, especially at low temperatures.

He has also had promising results with his work with developing a preparatory treatment that prevents too much lithium loss in the formation of the SEI film. This allows more of the lithium in the electrolyte solution to participate in charging the electrodes.

State-of-the-art electrolytes that consist of ethylene carbonate (EC), in principle, cannot operate when the temperature is at about -10°C, due to the high melting temperature of the EC. On the other hand, batteries containing the organic compound propylene carbonate (PC) can work at temperatures as low as -50°C.

“We think that we found a way to substitute EC for PC; however, we haven’t confirmed this yet,” Tezel said of the use of PC in batteries. “But our research suggests how it might be realised.”

Tezel’s supervisors are Professor Ann Mari Svensson and Professor Svein Sunde, also at the Department of Materials Science and Engineering. Tezel also works for Graphene Batteries AS in Oslo.

Image caption: Ahmet Oguz Tezel, Ann Mari Svensson and Svein Sunde. Photo: Steinar Brandslet, NTNU.