Structural, Electronic, and Electrochemical Properties of Cathode Materials Li2MSiO4 (M = Mn, Fe, and Co): Density Functional Calculations

For Li2FeSiO4, its P2(1) Space group makes it possibly perfect as a new Cathode material for Li-ion batteries (Nishimura et al. J. Am. Chem. Soc. 2008, 130, 13212). For this type of Li2AlSiO4 (M = Mn, Fe, and Co), the structural, electronic, and electrochemical properties have been investigated, using the density functional theory with the exchange-correlation energy treated as the generalized gradient approximation (GGA) plus oil-site coulomb energy correction (+U). Within the GGA+U framework, the fully lithiated Li2MSiO4 as well as the delithiated LiMSiO4 and MSiO4 are all semiconducting, and the band gap lowers with the extraction of lithium ions. The fully lithiated compounds are all stabilized at their ferromagnetic phase, while the delithiated compounds are all stabilized when antiferromagnetic. Starting from the P2(1) structure, the fully delithiated MSiO4 has better stability than that obtained from Pmn2(1) structure. In Li2FeSiO4, the possibility of reversibly extracting more than one lithium ion is enhanced because of the lower stability of the intermediate phase LiFeSiO4 comparing with the Pmn2(1) symmetry Situation Li2MnSiO4 with the P2(1) symmetry has higher electronic conductivity, and Li2CoSiO4 has the suitable second-step voltage of less than 5.0 V. All Li2FeSiO4, Li2MnSiO4, and Li2CoSiO4 are predicted is promising cathode materials.