Electrochemical Properties of Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> as a Negative Electrode for Calcium Secondary Batteries in Ca(TFSI)<sub>2</sub>/THF Electrolyte

We investigated the electrochemical behavior and properties of lithium titanate oxide as the negative electrode for calcium ion batteries during charge/discharge tests in tetrahydrofuran (THF)-based electrolyte. The reversible charge and discharge capacities of ~150 and ~145 mAh g –1 were observed, respectively, in THF-based electrolyte. They are larger than those obtained in propylene carbonate-based electrolyte. Moreover, interesting charge/discharge curves were observed, which might be attributed to structural changes during the insertion/extraction of calcium ions. These results were confirmed by the charge/discharge curves and scanning electron microscopy images.