Crystal structure, phase relations and electrochemical properties of monoclinic Li2MnSiO4

Phase relations in the MnO–SiO2–Li4SiO4 subsystem have been investigated by X-ray diffraction after solid-state reactions in hydrogen at 950–1150 °C. Both cation-deficient and cation-excess solid solutions Li2+2xMn1−xSiO4 (−0.2⩽x⩽0.2) based on Li2MnSiO4 have been found. According to Rietveld analysis, Li2MnSiO4 (monoclinic, P21/n, a=6.3368(1), b=10.9146(2), c=5.0730(1) Å, β=90.987(1)°) is isostructural with γII-Li2ZnSiO4 and low-temperature Li2MgSiO4. All components are in tetrahedral environment, (MnSiO4)2− framework is built of four-, six- and eight-member rings of tetrahedra. Testing Li2MnSiO4 in an electrochemical cell showed that only 4% Li could be extracted between 3.5 and 5 V against Li metal. These results are discussed in comparison with those for recently reported orthorhombic layered Li2MnSiO4 and other tetrahedral Li2MXO4 phases.