Solid State Formation Mechanism of Li 4 Ti 5 O 12 from an Anatase TiO 2 Source

Solid state synthesis of Li 4 Ti 5 O 12 anode material for Li ion batteries typically results in products containing rutile TiO 2 and Li 2 TiO 3 impurities, and subsequent high calcination temperatures lead to particle growth that reduces capacity and rate ability. Here, the formation and growth of Li 4 Ti 5 O 12 particles by a solid-state reaction using anatase TiO 2 with various crystallite sizes and Li 2 CO 3 is investigated by in situ high temperature powder X-ray diffraction (HT-PXRD) and thermal gravimetry-differential thermal analysis (TG-DTA). The combined data provide insight into the origin of the impurity phases and reveal that formation of Li 4 Ti 5 O 12 from anatase TiO 2 and Li 2 CO 3 is a two stage process. Initially, TiO 2 and Li 2 CO 3 react to form monoclinic Li 2 TiO 3, followed at higher temperature by a reaction with the remaining TiO 2 to yield Li 4 Ti 5 O 12 . Four anatase TiO 2 powders with different crystallite sizes (∼50 nm, ∼30 nm, ∼20 nm, and amorphous) were explored, and decreasing crystallite sizes causes a reduced initial reaction temperature. Using anatase with a crystallite size of ∼20 nm resulted in phase pure Li 4 Ti 5 O 12 at the lowest temperature (800 °C). PXRD and TG-DTA results also revealed that Li 4 Ti 5 O 12 decomposes to some Ti rich phases and probably Li 2 O when heated above 1000 °C.