Electrochemical properties of titanium fluoride with high rate capability for lithium-ion batteries

• Published in: Journal of power sources Vol. 419; pp. 1 - 5
• Main Authors: Kitajou, Ayuko, Eguchi, Katsuya, Ishado, Yuji, Setoyama, Hiroyuki, Okajima, Toshihiro, Okada, Shigeto
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2019
• Subjects: Conversion-type material; Lithium-ion battery; Titanium fluoride; Lithium-ion battery; Titanium fluoride; Conversion-type material
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2019.02.056

As a conversion-type active material, we investigated the electrochemical properties and the discharge-charge reaction mechanisms of a TiF3 having the same symmetry as FeF3. First, the insertion reaction of TiF3 proceeded at an average voltage of 2.0 V. Once the voltage of the conversion reaction declined to 0.5 V, the generated metallic Ti was indexed to a cubic system with the Im-3m space group, which is different from the stable structure of metallic Ti with the P63/mmc space group. Moreover, upon recharging to 4.0 V after the conversion reaction, the structure had an amorphous phase of LixTiF3. It is known that, on the first discharge, FeF3 first shows a reversible insertion reaction with 1 Li and then a conversion reaction with the other 2 Li. These results demonstrated that TiF3 had the following overall discharge-charge reaction, which was distinct from that of FeF3: TiF3 + 3Li → 3LiF + Ti ⇄ (3-x)Li+ + LixTiF3 (amorphous phase). •TiF3 showed large discharge capacity of 730 mAh g−1 corresponding to 2.9 Li reaction.•TiF3 has excellent rate capability and good cyclability even in a conversion reaction.•The reaction mechanism of TiF3 and Li is investigated by XRD and XANES.