Polymorphism in Li-2(Fe,Mn)SiO4: A combined diffraction and NMR study

Li2MSiO4 compounds have been attracting significant attention as lithium intercalation compounds for the next generation of rechargeable lithium batteries. Their structures consist of slightly distorted close packed oxygen slabs between which cations occupy half the tetrahedral sites, leading to a range of polymorphs. In this paper we describe the rich polymorphism observed across the Li2FezMn(1-z)SiO4 solid solution, characterized by detailed powder neutron and X-ray diffraction studies, combined with solid state NMR. This polymorphism reflects that seen in the end-members, with a gradual transition from Fe-like behaviour for iron-rich compositions, to Mn-like behaviour with increasing manganese content.