Researchers at the University of Tokyo have developed a battery based on the concept of a combination of a perovskite-type cathode and a low-electrode-potential anode that can achieve high energy densities through the use of organic rather than aqueous electrolytes. The work is derivative of their earlier investigation into a “oxygen-rocking batteries” reported in 2012. (Earlier post.)
Batteries based on this system allow the use of various anode materials, such as lithium and sodium, without the requirement to develop new cathode intercalation materials. In the new study reported in the Journal of the American Chemical Society, they used the concept and demonstrated a new battery based on a CaFeO3 cathode with a sodium anode, in conjunction with a NaClO4/triglyme electrolyte.
We have recently both proposed and demonstrated an oxygen rocking battery in which oxygen atoms are shuttled between a cathode and an anode composed of iron-based perovskite oxides Ca0.5La0.5FeOz, with 2.58 ≤ z ≤ 2.63 for the anode and 2.75 ≤ z ≤ 2.863 for the cathode. These materials have been found to allow topotactic [transformation within a crystal lattice] and reversible extraction/insertion of oxygen atoms.
…During discharge, the CaFeO3 cathode undergoes topotactic extraction of oxygen atoms and changes to CaFeO2.5, and the extracted oxygen atoms react with sodium ions to form sodium oxides. This cathode has a theoretical specific capacity of 187 mAh g-1 if the final discharge product is NaO2.—Hibino et al.
The team developed a process that allows the oxidation of CaFeO2.5 under milder conditions than usual. They mixed CaCO3 (>99.99%, 4.00 g) and α-Fe2O3 (99.9%, 3.19 g) were mixed together and ground in an agate mortar for 5 h, following which the mixture was heated to 1000 °C at 20 °C min−1, held at 1000 °C for 5 h, and then cooled to room temperature in air.
The resulting powder was ground again with an agate mortar and pressed into a thin disk, which was subsequently heated to 1100 °C at 20 °C min−1, held at 1100 °C for 24 h, and cooled to room temperature in air to obtain CaFeO2.5.
For electrochemical measurements they used a three-electrode beaker cell employing metallic sodium as the counter and reference electrodes and a 1 M NaClO4/triglyme electrolyte solution.
They also reported that it was also possible to prepare an iron-based perovskite-type material SrFeO3 according to the same method as used to synthesize CaFeO3, and these materials could be reversibly reduced and reoxidized in an organic electrolyte using not only a sodium anode but also lithium and magnesium anodes.
This research was supported by the Japan Society for the Promotion of Science (JSPS) through its “Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program)”. A part of this work was supported by “Nanotechnology Platform” (Project 12024046) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
Mitsuhiro Hibino, Ryuji Harimoto, Yoshiyuki Ogasawara, Ryota Kido, Akira Sugahara, Tetsuichi Kudo, Eita Tochigi, Naoya Shibata, Yuichi Ikuhara, and Noritaka Mizuno (2013) “A New Rechargeable Sodium Battery Utilizing Reversible Topotactic Oxygen Extraction/Insertion of CaFeOz (2.5 ≤ z ≤ 3) in an Organic Electrolyte.” Journal of the American Chemical Society doi: 10.1021/ja411365z