Structural, electronic, and electrochemical properties of cathode materials Li 2MSiO 4 (M ) Mn, Fe, and Co): Density functional calculations

Abstract

For Li 2FeSiO 4, 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 Li 2MSiO 4 (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 on-site Coulomb energy correction (+U). Within the GGA+U framework, the fully lithiated Li 2MSiO 4 as well as the delithiated LiMSiO 4 and MSiO 4 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 MSiO 4 has better stability than that obtained from Pmn2 1 structure. In Li 2FeSiO 4, the possibility of reversibly extracting more than one lithium ion is enhanced because of the lower stability of the intermediate phase LiFeSiO 4 comparing with the Pmn2 1 symmetry situation. Li2MnSiO4 with the P21 symmetry has higher electronic conductivity, and Li 2CoSiO 4 has the suitable second-step voltage of less than 5.0 v. All Li 2FeSiO 4, Li 2MnSiO 4, and Li 2CoSiO 4 are predicted as promising cathode materials. © 2010 American Chemical Society.