Electrochemical Reactions of Perovskite-Type SrCoO3−δvia Topotactic Oxygen Extraction/Insertion in Aprotic Li+Electrolyte Solutions

Electrochemical redox reactions with extraction/insertion of ions in solid materials are often used for electrode reactions of rechargeable batteries. Here we show electrochemical redox behaviors of perovskite-type SrCoO x (2.5 ≤ x ≤ 2.92) in aprotic Li + electrolyte solutions by measurements of open circuit potentials (OCPs) and X-ray diffraction (XRD) patterns. Changes in OCPs and XRD patterns suggest that SrCoO 2.92 is electrochemically reduced to SrCoO 2.5 as follows: First, oxygen atoms are extracted from SrCoO 2.92 to form Li 2 O 2 by reacting with Li + . Then both the reduction of the Li 2 O 2 and the further extraction of oxygen atoms from SrCoO x proceed to form Li 2 O and SrCoO 2.5 . In the subsequent re-oxidation, oxygen atoms of Li 2 O are re-inserted into SrCoO 2.5 and the oxygen composition reach SrCoO 2.67 , followed by evolution of gaseous molecular oxygen and carbon dioxide by decomposition of the Li 2 O and side reactions of the electrolyte, respectively. The cycling test shows the 1st discharge capacity is 75 mAh g −1 and the 10th one is still 41 mAh g −1 . These results indicate the viability of a rechargeable battery utilizing the topotactic oxygen extraction/insertion of cathode materials such as SrCoO x in aprotic Li + electrolyte solutions.