Thermal synthesis of conversion-type bismuth fluoride cathodes for high-energy-density Li-ion batteries

Julian F Baumgärtner; Frank Krumeich; Michael Wörle; Kostiantyn V Kravchyk; Maksym V Kovalenko

doi:10.1038/s42004-021-00622-y

Thermal synthesis of conversion-type bismuth fluoride cathodes for high-energy-density Li-ion batteries

Commun Chem. 2022 Jan 11;5(1):6. doi: 10.1038/s42004-021-00622-y.

Authors

Julian F Baumgärtner^{1

2}, Frank Krumeich¹, Michael Wörle¹, Kostiantyn V Kravchyk^{3

4}, Maksym V Kovalenko^{5

6}

Affiliations

¹ Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1, CH-8093, Zürich, Switzerland.
² Laboratory for Thin Films and Photovoltaics, Empa - Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600, Dübendorf, Switzerland.
³ Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1, CH-8093, Zürich, Switzerland. kravchyk@inorg.chem.ethz.ch.
⁴ Laboratory for Thin Films and Photovoltaics, Empa - Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600, Dübendorf, Switzerland. kravchyk@inorg.chem.ethz.ch.
⁵ Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 1, CH-8093, Zürich, Switzerland. mvkovalenko@ethz.ch.
⁶ Laboratory for Thin Films and Photovoltaics, Empa - Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, CH-8600, Dübendorf, Switzerland. mvkovalenko@ethz.ch.

Abstract

Towards enhancement of the energy density of Li-ion batteries, BiF₃ has recently attracted considerable attention as a compelling conversion-type cathode material due to its high theoretical capacity of 302 mAh g^-1, average discharge voltage of ca. 3.0 V vs. Li⁺/Li, the low theoretical volume change of ca. 1.7% upon lithiation, and an intrinsically high oxidative stability. Here we report a facile and scalable synthesis of phase-pure and highly crystalline orthorhombic BiF₃ via thermal decomposition of bismuth(III) trifluoroacetate at T = 300 °C under inert atmosphere. The electrochemical measurements of BiF₃ in both carbonate (LiPF₆-EC/DMC)- and ionic liquid-based (LiFSI-Pyr_1,4TFSI) Li-ion electrolytes demonstrated that ionic liquids improve the cyclic stability of BiF₃. In particular, BiF₃ in 4.3 M LiFSI-Pyr_1,4TFSI shows a high initial capacity of 208 mA g^-1 and capacity retention of ca. 50% over at least 80 cycles at a current density of 30 mA g^-1.