Li₂MTi₆O₁₄ (M = Sr, Ba): New anodes for lithium-ion batteries

Isostructural Li₂MTi₆O₁₄ (M = Sr, Ba) materials, prepared by a solid state reaction method, have been investigated as insertion electrodes for lithium battery applications. These titanate compounds have a structure that consists of a three-dimensional network of corner- and edge-shared[TiO₆] octahedra, 11-coordinate polyhedra for the alkali-earth ions, and [LiO₄] tetrahedra in tunnels that also contain vacant tetrahedral and octahedral sites. Electrochemical data show that these compounds are capable of reversibly intercalating four lithium atoms in a three-stage process between 1.4 and 0.5 V vs. metallic lithium. The electrodes provide a practical capacity of approximately 140 mAh/g; they are, therefore, possible alternative anode materials to the lithium titanate spinel, Li₄Ti₅O₁₂. The lithium intercalation mechanism and crystal structure of Li₂MTi₆O₁₄ (M = Sr, Ba) electrodes are discussed and compared with the electrochemical and structural properties of Li₄Ti₅O₁₂. The area-specific impedance (ASI) of Li/Li₂SrTi₆O₁₄ cells was found to be significantly lower than that of Li/Li₄Ti₅O₁₂ cells.