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

摘要

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 P6(3)/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 (sic) (3-x)Li+ + LixTiF3 (amorphous phase).