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

Abstract

For Li 2 FeSiO 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 2 MSiO 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 2 MSiO 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 2 FeSiO 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. Li 2 MnSiO 4 with the P2 1 symmetry has higher electronic conductivity, and Li 2 CoSiO 4 has the suitable second-step voltage of less than 5.0 V. All Li 2 FeSiO 4 , Li 2 MnSiO 4 , and Li 2 CoSiO 4 are predicted as promising cathode materials.

Insights into Changes in Voltage and Structure of Li2FeSiO4 Polymorphs for Lithium-Ion Batteries

“…The LINDOS program was then used to sum the band occupancies at each energy and produce the density of states presented in Figure 5. As found in previous work, 16,17,20 4 states there are no significant differences between the DOS, and these will not make a large contribution to the cell voltage trends.…”

“…The calculated and experimental structural parameters for the as-prepared polymorphs (β II , γ s , and γ II ) are compared in Table 1 and show general good agreement, as found in other DFT studies. [15][16][17][18]20,21 As noted, the cycled structure has been derived recently from neutron diffraction by Armstrong et al 10 We have taken this experimentally derived structure as the starting point for our structure optimizations. It was first necessary to consider how the Li/Fe ions that share a site in the cycled structure (inverse-β II ) might order.…”

Looking beyond single electron extraction in cathode materials for lithium ion batteries

“…Although Li 2 FeSiO 4 in Pmn2 1 symmetry offers good electronic properties, their relative theoretical conductivity is somewhat lower and reversibility along with cycling performance is not good [8]. In 2008 Nishimura et al proposed a different structure with the P2 1 symmetry using high-resolution synchrotron XRD [17] which shows much better properties [21].…”

Polar Surface Energies of Iono‐Covalent Materials: Implications of a Charge‐Transfer Model Tested on Li2FeSiO4 Surfaces

“…This material is especially interesting as a possible electrode material of Li-ion batteries. [25][26][27][28][29][30][31][32] We use our model to estimate electrostatic contributions to polar surface energies in this compound. The separation of surface energy into local bond-cutting and longrange polar contributions provides a general explanation for observed stability trends.…”