Evaluating Electrical Properties, Band Gaps and Rate Capability of Li2MSiO4 (M= Mn, Fe, Co, Ni) Cathode Materials Using DOS Diagrams

In this study, theoretical investigations of Li2MSiO4 family cathode materials, including Li2MnSiO4, Li2FeSiO4, Li2CoSiO4, and Li2NiSiO4 are performed using density functional theory (DFT), by GGA and GGA+U methods. The materials properties including electrical conductivity and rate capability were investigated. To evaluate electrical conductivity, we use here a noble approach in DFT established in our previous work, which is related to intrinsic/extrinsic band gap concepts in solid state physics. Also, using lithiated-delithiated junction, aligning Fermi levels, and the difference between conduction bands value is the basis of the comparison of                      rate-capability, which is also a noble approach. To perform a quantitative investigation of electrical rate-capability, Fermi levels of obtained DOS diagrams of lithiated and delithiated structures were aligned. The difference between maximum of valance band (MVB) of lithiated and delithiated structures was considered as the criteria of rate-capability. The obtained values for the considered materials were fairly close. It was concluded that electron conductivity and rate-capability of this family of Li-ion cathode material is in the same range and do not strictly relate to the transition metal.