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

Abstract As a conversion-type active material, we investigated the electrochemical properties and the discharge-charge reaction mechanisms of a TiF 3 having the same symmetry as FeF 3 . First, the insertion reaction of TiF 3 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 I m-3m space group, which is different from the stable structure of metallic Ti with the P 6 3 /mmc space group. Moreover, upon recharging to 4.0 V after the conversion reaction, the structure had an amorphous phase of Li x TiF 3 . It is known that, on the first discharge, FeF 3 first shows a reversible insertion reaction with 1 Li and then a conversion reaction with the other 2 Li. These results demonstrated that TiF 3 had the following overall discharge-charge reaction, which was distinct from that of FeF 3 : TiF 3 + 3Li → 3LiF + Ti ⇄ (3-x)Li +  + Li x TiF 3 (amorphous phase).