Doping with Boron Improves Electrochemical Properties of Cathode Materials

The performance of lithium ion batteries can be limited by the capacity of the cathode materials such as nickel-rich layered oxides. An effective strategy to enhance their electrochemical properties is to dope them and thus add impurity atoms. In an international study led by MEET Battery Research Center at the University of Münster, a scientific team has incorporated the semimetal boron into the tetrahedral site of nickel-rich layered oxides (NCM811). In this way, the researchers were able to significantly improve the capacity and cycle stability of the battery cells.

Direct Doping with Boron Instead of Surface Coating

To synthesize the cathode precursors precisely, the scientists used the coprecipitation method. They precisely controlled the temperature, pH value, concentration and stirring speed of the solution to achieve a uniform particle size and composition. “This process can be scaled up for industrial production in the future,” Dr Bixian Ying from MEET Battery Research Center explains the approach. The researchers incorporated the semimetal boron into the synthesized cathode material during coprecipitation – rather than by the subsequent surface coating. This led to an inductive effect on the bonds of transition metals, oxygen and boron contained in the layered oxides. This result in turn delayed their structural collapse and reduced oxygen release. The outcome: an improved cycling performance of the battery cells.

“We used Near Edge X-ray Absorption Finestructure Analysis Spectroscopy (NEXAFS) to precisely analyze the electronic structure and bonding characteristics of the individual materials to better understand their impact,” says Ying. The team was also able to precisely determine the exact crystallographic position of boron for the first time using advanced neutron powder diffraction with the boron isotope.

Detailed Results Online Available

The entire study has been published by the authors Bixian Ying, Zhenjie Teng and Karin Kleiner, MEET Battery Research Center, Anatoliy Senyshyn, Technical University of Munich, Maxim Avdeev, Australian Nuclear Science and Technology Organisation and the University of Sydney, Adrian Jonas, Physikalisch-Technische Bundesanstalt, Jiali Peng, Sylvio Indris, Oleksandr Dolotko, Helmut Ehrenberg, Michael Merz, Peter Nagel and Stefan Schuppler, Karlsruhe Institute of Technology (KIT), Søren Bredmose Simonsen, Technical University of Denmark, Richard Schmuch, Fraunhofer Research Institution for Battery Cell Production FFB, Peng Yan, Helmholtz Institute Münster of Forschungszentrum Jülich, as well as Martin Winter, MEET Battery Research Center and Helmholtz Institute Münster, in the journal “Small”.