The team of KIT researchers: (from left to right) Michael Knapp, Sylvio Indris, Weibo Hua and Björn Schwarz. Photo: Amadeus Bramsiepe, KIT.
The team of KIT researchers: (from left to right) Michael Knapp, Sylvio Indris, Weibo Hua and Björn Schwarz. Photo: Amadeus Bramsiepe, KIT.

By studying structural changes during the synthesis of cathode materials for future high-energy lithium-ion batteries, researchers at Karlsruhe Institute of Technology (KIT) in Germany, together with colleagues at various other institutions, have uncovered new findings about degradation mechanisms. These findings might contribute to the development of batteries with a far higher capacity, which could increase the range of electric vehicles. The researchers report their findings in a paper in Nature Communications.

So far, breakthroughs in electric mobility have been impeded by insufficient vehicle ranges, among other issues. Increasing the charge capacity of lithium-ion batteries will help to increase these ranges.

“We are in the process of developing such high-energy systems,” says Helmut Ehrenberg, head of the Institute for Applied Materials – Energy Storage Systems (IAM-ESS) at KIT. “Based on fundamental understanding of electrochemical processes in batteries and by the innovative use of new materials, storage capacity of lithium-ion batteries may be increased by up to 30% in our opinion.” At KIT, this research is conducted at the Center for Electrochemical Energy Storage Ulm & Karlsruhe (CELEST), the biggest German research platform for electrochemical energy storage.

High-energy lithium-ion technology differs from conventional lithium-ion battery technology by its cathode material. Instead of layered oxides with varying ratios of nickel, manganese and cobalt, it uses manganese-rich materials with lithium excess, which offer considerably enhanced energy storage capacity.

Up to now, however, there has been a problem with these materials, in that inserting and extracting lithium ions causes them to degrade. After a certain time, the layered oxide transforms into a crystal structure with highly unfavorable electrochemical properties. This means the average charge and discharge voltage decreases from the very beginning of the charging and discharging process, which has prevented the development of suitable high-energy lithium-ion batteries. Now, however, the KIT researchers and their colleagues have managed to determine the basic mechanism behind the degradation.

“Based on detailed studies of the high-energy cathode material, we found that degradation does not take place directly, but indirectly via the formation of a – so far hardly noticed – lithium-containing rock-salt structure,” explains Weibo Hua at IAM-ESS and one of the main authors of the paper. “In addition, oxygen plays an important role in the reactions.”

Surprisingly, these findings didn’t come directly from investigations into the degradation process. Instead, Weibo and his colleagues made their discovery while synthesizing the cathode material. Nevertheless, the findings mark an important milestone in the development of high-energy lithium-ion batteries for electric cars, by potentially pointing the way to new approaches for minimizing degradation in layered oxides.

This story is adapted from material from Karlsruhe Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.