Models for Li+ ion mobility were developed and investigated in the 'corrugated layer' orthorhombic phase of Li1-xFeO2, an attractive possible electrode material for reversible lithium ion batteries. The ground-state crystal energy was computed by first-principles DFT (Density-Functional-Theory) methods, based on the use of the hybrid B3LYP functional with localized Gaussian-type basis sets. Appropriate supercells were devised as needed, with full least-energy structure optimization. In the defect-free case (x = 0), ion diffusion was found to take place cooperatively inside a fraction of active lithium layers separated by inert ones, so as to reduce lattice strain; intermediate bottleneck states of Li are either in tetrahedral (energy barrier Delta E-a - 0.410 eV) or linear (Delta E-a - 0.468 eV) coordination. For the Li0.75FeO2 deintercalated material a number of low energy vacancy configurations were considered, investigating also the vacancy influence on electron density of states and atomic charge distribution. The most favourable ion transport mechanisms (Delta E-a = 0.292 and 0.304 eV) imply a linear Li bottleneck state, with all lithium layers active and a quite small lattice strain. Accordingly, in the defective material the predicted ionic conductivity at room temperature rises from 10(-5)-10(-6) (LiFeO2) to 4 x 10 (4) ohm (1) cm (1) (Li0.75FeO2).
Catti, M., Montero Campillo, M. (2011). Lithium diffusion pathways and vacancy formation in the Pmmn-Li1-xFeO2 electrode material. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 13(23), 11156-11164 [10.1039/C1CP20551J].
Lithium diffusion pathways and vacancy formation in the Pmmn-Li1-xFeO2 electrode material
CATTI, MICHELE;
2011
Abstract
Models for Li+ ion mobility were developed and investigated in the 'corrugated layer' orthorhombic phase of Li1-xFeO2, an attractive possible electrode material for reversible lithium ion batteries. The ground-state crystal energy was computed by first-principles DFT (Density-Functional-Theory) methods, based on the use of the hybrid B3LYP functional with localized Gaussian-type basis sets. Appropriate supercells were devised as needed, with full least-energy structure optimization. In the defect-free case (x = 0), ion diffusion was found to take place cooperatively inside a fraction of active lithium layers separated by inert ones, so as to reduce lattice strain; intermediate bottleneck states of Li are either in tetrahedral (energy barrier Delta E-a - 0.410 eV) or linear (Delta E-a - 0.468 eV) coordination. For the Li0.75FeO2 deintercalated material a number of low energy vacancy configurations were considered, investigating also the vacancy influence on electron density of states and atomic charge distribution. The most favourable ion transport mechanisms (Delta E-a = 0.292 and 0.304 eV) imply a linear Li bottleneck state, with all lithium layers active and a quite small lattice strain. Accordingly, in the defective material the predicted ionic conductivity at room temperature rises from 10(-5)-10(-6) (LiFeO2) to 4 x 10 (4) ohm (1) cm (1) (Li0.75FeO2).
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