(English) The complex nature of electrode/electrolyte interfaces explored with improved methodology

tisdag, april 29, 2014

Katarzyna Ciosek Högström has been the first to apply an improved photoelectron spectroscopy methodology to study the electrode/electrolyte interface layers in Li-ion batteries. The goal of her research has been to understand the aging processes at Li-ion battery interfaces and to use electrolyte additives in order to improve safety and lifetime of the cells.

Batteries for vehicles need to maintain a stable performance for many years. However, the commercial Li-ion batteries of today still degrade despite improved reliability. Understanding the processes taking place at the interface between the electrode and the electrolyte is of vital importance for the development of safer and more reliable Li-ion batteries.

A schematic picture of a Li-ion battery and interface layers between graphite negative electrode/electrolyte and LiFePO4 positive electrode/electrolyte.

Until recently, the attempts to perform depth characterization of Li-ion battery interfaces with photoelectron spectroscopy have led to destruction of the surface, which compromises the results and limit the range of processes that can be studied. Now, doctoral student Katarzyna Ciosek Högström along with a team of researchers at the Department of Chemistry – Ångström Laboratory, Uppsala University, has been the first to apply a method for non-destructive depth profiling of Li-ion battery interfaces. It allows the researchers to study the different layers from the outermost surface into the electrode bulk, without causing damage to the surface.

– Since the interface remains intact, we can obtain much more reliable results and study processes which lead to Li-ion battery aging, says Katarzyna Ciosek Högström, who recently defended her doctoral thesis.

Another part of Katarzyna´s work focused on electrolyte additives.

– Additives are one of the most efficient ways to improve battery performance, she explains. They have different functionality and in commercial batteries a combination of various additives is used. However, many additives lead to a trade-off between the effectiveness of an additive and cell performance.

Of the additives in the project, one turned out to improve Li-ion battery performance over time, due to formation of an interface layer with higher stability. Another additive was studied to improve safety of Li-ion batteries; however it had small influence on flammability and lead to lower energy efficiency of the cell.

In her thesis, Katarzyna Ciosek Högström shows that reliable measurements on such sensitive systems as the electrode/electrolyte interfaces formed in Li-ion batteries can be obtained as long as careful sample handling and measurements are maintained.

– Although the additives I have studied may not be the final solution to improve lifetime and safety of commercial batteries, I have achieved better understanding of the mechanisms that degrade the Li-ion battery, says Katarzyna. I hope my research will bring us one step closer to safer and more reliable Li-ion batteries in the future.

The doctoral research project “Designed, controlled and safer lithium-ion cells – Electrode materials” is part of the Swedish Hybrid Vehicle Centre (SHC) and was carried out at Uppsala University.

Read Katarzyna Ciosek Högström´s doctoral thesis >>