Structure and lithium transport pathways in Li2FeSiO4 cathodes for lithium batteries.

The importance of exploring new low-cost and safe cathodes for large-scale lithium batteries has led to increasing interest in Li(2)FeSiO(4). The structure of Li(2)FeSiO(4) undergoes significant change on cycling, from the as-prepared γ(s) form to an inverse β(II) polymorph; therefore it is important to establish the structure of the cycled material. In γ(s) half the LiO(4), FeO(4), and SiO(4) tetrahedra point in opposite directions in an ordered manner and exhibit extensive edge sharing. Transformation to the inverse β(II) polymorph on cycling involves inversion of half the SiO(4), FeO(4), and LiO(4) tetrahedra, such that they all now point in the same direction, eliminating edge sharing between cation sites and flattening the oxygen layers. As a result of the structural changes, Li(+) transport paths and corresponding Li-Li separations in the cycled structure are quite different from the as-prepared material, as revealed here by computer modeling, and involve distinct zigzag paths between both Li sites and through intervening unoccupied octahedral sites that share faces with the LiO(4) tetrahedra.