Crystal chemistry of the Pmnb polymorph of Li2MnSiO4

The crystal structure of the Pmnb polymorph of Li2MnSiO4 (prepared by solid-state synthesis in argon at 900 °C) is characterized by Rietveld refinement of structural models using high resolution synchrotron X-ray and neutron powder diffraction data. The crystal structure is confirmed to be isostructural with Li2CdSiO4 with lattice parameters a=6.30694(3), b=10.75355(4), and c=5.00863(2) Å, which are in good agreement with previously published data. No evidence was found for mixed lithium/manganese sites. Testing of the material as a cathode in a lithium cell shows that 1.3 lithium ions per formula unit can be extracted on the first charge cycle but very little lithium can be re-inserted. These results are compared with those of other phase-pure Li2MnSiO4 polymorphs.

Polyhedral representation of the crystal structure of Li2MnSiO4 in the Pmnb space group. LiO4, MnO4 and SiO4 tetrahedra are shown in green, purple and blue, respectively.Figure optionsDownload as PowerPoint slideHighlights
► A phase-pure sample of the Pmnb polymorph of Li2MnSiO4 was synthesized.
► Characterized by Rietveld refinement using high resolution synchrotron X-ray and neutron powder diffraction data.
► Results confirm the proposed Li2CdSiO4-type model with highly distorted Mn tetrahedra.