Computational search of anion redox Li-ion battery composition space

MRS Fall Meeting 2019, EN02.

Transcript

1. Computational search of anion redox Li-ion battery composition space Dan Davies MRS Fall Meeting EN02 2nd December 2019 @danwdavies
2. Redox processes in metal oxides M O M redox: Mn à Mn+1 Most battery cathodes O redox: O2- à O1- 2p6 à 2p5 Localised “oxygen hole”
3. Oxygen redox Proc. Roy. Soc. A, 231, 404 (1955)
4. Oxygen redox Proc. Roy. Soc. A, 231, 404 (1955) S = ½ hole on O R. Schnadt, J. Schneider, Phys. Kondens. Materie, 11, 19 (1970)
5. Anion redox processes M redox: O redox: Mn à Mn+1 O2- à O1- “Anion redox”
6. High-throughput materials screening LOW COST HIGH COST Band gap Electron energies Likely crystal structure Sustainability … Thermodynamic stability Dynamic stability Electronic structure New energy materials Chemical heuristics Data-driven models Automated calculations (DFT, hybrid DFT and beyond)
7. Anion redox cathodes 1. Electrostatic environment of O From Madelung potentials 2. Orbital overlap From electronic density of states analysis
8. LiMO2 and Li2 MO3 systems Li O E.g: LiCoO2 LiNiO2 E.g: Li2 RuO3 Li2 MnO3
9. Electrostatic environment of O Madelung site potential: In practice calculated using Ewald method:
10. O Madelung potentials Oxygen is very sensitive to its crystal environment: High variation in potential within the same crystal structure type 1st row 2nd row 3rd row
11. Madelung potentials: local O environment In a disordered supercell: Madelung site potential decreases when changing the local O coordination environment from TM à Li
12. Madelung potentials: local O environment In a disordered supercell: Madelung site potential decreases when changing the local O coordination environment from TM à Li
13. Hole localization: the ionic picture Atomic contributions Structural contributions d0 Strongly favour O holes Increasing d-electrons disfavours M holes (in line with M ionisation energy) J. B. Torrance, R. M. Metzger, Role of the Madelung energy in hole conductivity of copper oxides, Phys. Rev. Lett. 1989
14. Orbital overlap from DFT calculations E M O U Δ Generate possible spin orderings Full relaxation DOS calculation for lowest energy structure 1M. K. Horton et al., High-throughput prediction of the ground-state collinear magnetic order of inorganic materials using Density Functional Theory, npj Comp. Mater. 2019 , , … Magnetic ordering1 Hybrid DFT • HSE06 (25% screened HF exact exchange) • 64 Å3 K-point density • 600 eV energy cut off
15. Orbital overlap −4 −2 0 2 4 (nergy (eV) ArE. unitV TotDO D2S 0g (V) 2 (S) −4 −2 0 2 4 (nergy (eV) ArE. unitV TotDO D2S Cu (d) 2 (S) MgO VBM is ~100% O p-states Cu2 O VBM is ~90% Cu d-states At the two extremes for binary oxides, the VBM can be dominated by O p-states or M d-states
16. At the two extremes for binary oxides, the VBM can be dominated by O p-states or M d-states −4 −2 0 2 4 (nergy (eV) ArE. unitV TotDO D2S 0g (V) 2 (S) −4 −2 0 2 4 (nergy (eV) ArE. unitV TotDO D2S Cu (d) 2 (S) LiCoO2 VBM is ~40% O p-states, ~60% Co d-states −4 −2 0 2 4 (nergy (eV) ArE. unitV TotDO D2S Co (d) 2 (S) Orbital overlap
17. p-DOS analysis: LiMO2 vs Li2 MO3 LiWO2 Li2 WO3 −2 −1 0 1 2 (nergy (eV) ArE. uniWV ToWDO D2S W (d) 2 (S) −2 −1 0 1 2 (nergy (eV) ArE. unitV LiRuO2 Li2 RuO3 −2 −1 0 1 2 (nergy (eV) ArE. unitV −2 −1 0 1 2 (nergy (eV) ArE. unitV
18. p-DOS analysis: LiMO2 vs Li2 MO3 20%-90% range Increase in p-character across each TM row (Large JT effect for Fe and reorganisation to square planar for Pt) Fraction of O p-states in upper 1 eV of VBM 1st row 2nd row 3rd row
19. Summary and ongoing work • Structural and electronic factors influence anion redox processes in metal oxides • Qualitative trends can be extracted from electrostatic considerations • The fraction of O p-character can vary from 20% – 90% • The materials design challenge is to tune the fraction deterministically
20. Acknowledgements • Aron Walsh • David Scanlon (UCL) • Keith Butler (Sci-ML, STFC) • Benjamin Morgan (Bath) • Alex Squires (Bath)
21. Extra: Hole localization: the ionic picture