How Battery Materials Work: Visualizing Ion Migration Mette Ø. Filsø, Aarhus University, Denmark

Transcription

1 How Battery Materials Work: Visualizing Ion Migration Mette Ø. Filsø, Aarhus University, Denmark

2 BATTERY RESEARCH AT UNIVERSITY Synthesis and characterization of electrode materials Li 4 Ti 5 O 12, LiFePO 4, LiCoO 2, LiMn 2 O 4, TiO 2, SnO 2 SYNTHESIS Na x Mn y Co z Ni 1-y-z O 4 Nanostructuring Performance testing of half-cells In operando X-ray diffraction In situ X-ray diffraction Visualization of ion migration MOFs In situ MATERIAL STRUCTURE In operando PROPERTIES Laumann et al., Solid State Ionics 181 (2010), Laumann et al., J. Inorg. Chem. 14 (2011), Jensen et al., JACS 134 (2012), Laumann et al., J. Electrochem. Soc. 159 (2012), A166 Lock et al. Dalton T. 42 (2013), Jensen et al., Chem. Mater. 25 (2013), Shen et al., Chem. Mater. 25 (2013), Shen et al., Chem. Mater. 26 (2014), Birgisson et al., Dalton T. 43 (2014), Eikeland et al. Inorg. Chem. 53 (2014), Shen et al. Rev. Sci. Inst. 85 (2014), Søndergard et al. Chem. Mater. 27 (2015),

3 INTRODUCTION Stable Environmentally friendly High capacity Important properties of battery electrode materials Cheap Rapid intercalation and migration of ions High energy density

4 THE PROCRYSTAL ANALYSIS The Procrystal Analysis is performed with the software CrystalExplorer. Procrystal Unit cell dimensions Space group Atomic positions pro ( r ) ( r) A Acrystal Ball-and-stick model Continuous landscape of electron density Spackman and McKinnon, CrystEngComm. 11 (2009), 19-32

5 THE PROCRYSTAL ANALYSIS LiFePO 4 When the ion moves through the crystal structure, it is affected by the electron density Li Fe P O The ion will choose the path of lower electron density. ρ pro Ion migration a c b

6 THE PROCRYSTAL ANALYSIS Electron density = Potential energy? For dense lattices there is a clear similarity between curves! Dense lattices ρ Popelier Atoms in molecules: an introduction, Prentice Hall, PTR (2000), R

7 THE PROCRYSTAL ANALYSIS Limitations: 1) Does not directly account for Li Li interactions, or Li framework interactions 2) Static lattice 3) Analysis depends on the CIF used 4) Relies on the electron density = potential energy assumption 5) Neutral atoms!

8 RESULTS Li Fe P O LiFePO 4 a c b MEM Atomistic modeling Procrystal calculation ρ pro = au ρ pro (migration) = au Islam et al., Chem. Mater. 17 (2005), Nishimura et al., Nature mat, 7 (2008),

9 RESULTS LiTiS 2 LiCoO 2 LiMn 2 O 4 ρ pro = au ρ pro (migration) = au ρ pro = au ρ pro (migration) = au ρ pro = au ρ pro (migration) = au

10 RESULTS Dimensionality Compounds 1D LiAlPO 4 F LiFePO 4 LiFeBO 3 2D LiTiS 2 LiCoO 2 LiMnO 2 LiFeP 2 O 7 3D Li 4 Ti 5 O 12 LiTi 2 O 4 LiMn 2 O 4 Li 2 Mn 2 O 4 Procrystal value for rapid Li-ion migration: ρ pro (migration) = (7) au Li 6 Si 2 O 7 Li 6 PS 5 I LiFeSO 4 F Li 5 AlO 4 -α Li 2 SiO 3 Li 1.8 SnO 3 Li 4 GeS 4 Li 3 Fe 2 (PO 4 ) 3 Li 2 Ge 2 O 5 Li 4 P 2 O 7 Li 2 TiO 3 Li 3 V 2 (PO 4 ) 3 NB: for layered materials: ρ pro (migration) = (9) au Li 3 AuO 3 Li 3 BO 3

11 APPLICATIONS 1) Educational tool 2) Visual addition to scientific communication 3) first approximation tool First approximation - Experiments - Theoretical calculations First approximation tool: - Quick - Simple - Cheap - Accurate Introduce new material Test properties Results? Good Test for applications Poor

12 TREATING ATOMIC DISORDER Li 4 Ti 5 O 12 densest framework actual stoichiometry 8a site: Li 32e site: O 16d site: 1/6 Li, 5/6 Ti ρ pro (migration) = au ρ pro (migration) = au

13 TREATING ATOMIC DISORDER Li 4 Ti 5 O 12 densest framework actual stoichiometry (16d Li stationary) 8a site: Li 32e site: O 16d site: 1/6 Li, 5/6 Ti ρ pro (migration) = au ρ pro (migration) = au

14 COMPARISON WITH BOND VALENCE THEORY Li 3 AuO 3 LiFePO 4 (1) = 0.50 ev (2) = 1.20 ev (3) = 1.50 ev ρ pro (1) = au ρ pro (2) = au ρ pro (3) = au b a (1) = 0.35 ev (dark pink) (2) = 0.64 ev (light pink) ρ pro (1) = au (dark blue) ρ pro (2) = au (light blue) b a Made in collaboration with assoc. Prof. Stefan Adams, Department of Materials Science & Engineering National University of Singapore

15 COMPARISON WITH BOND VALENCE THEORY Li 6 Si 2 O 7 Li 1.8 SnO 3 (1) = 0.10 ev (2) = 0.40 ev (3) = 0.48 ev b ρ pro (1) = au ρ pro (2) = au ρ pro (3) = au a (1) = 0.05 ev (2) = 0.30 ev (3) = 0.80 ev ρ pro (1) = au ρ pro (2) = au ρ pro (3) = au b a Made in collaboration with assoc. Prof. Stefan Adams, Department of Materials Science & Engineering National University of Singapore

16 ACKNOWLEDGEMENTS Prof. Bo Brummerstedt Iversen Prof. Mark Arthur Spackman Assoc. Prof. Stefan Adams The Aarhus Battery Group CMC/iNANO Danish National Research Fondation