First principles design of lithium superionic conductors

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Solid-state electrolytes exhibit good safety and stability, and are promising to replace current organic liquid electrolytes in rechargeable battery applications. In this talk, we will present our efforts at developing scalable first principles techniques to design novel solid-state electrolytes. Using the recently discovered Li10GeP2S12 lithium super ionic conductor as an example, we will discuss how various properties of interest in a solid-state electrolyte can be predicted using first principles calculations. We will show how the application of these first principles techniques has suggested two chemical modifications, Li10SiP2S12 and Li10SnP2S12, that retains the excellent Li+ conductivity of Li10GeP2S12 at a significantly reduced cost. These modifications have recently been synthesized, and the measured Li+ conductivities are in excellent agreement with our first principles predictions. We will conclude with a demonstration of how relatively expensive first principles calculations can be intelligently scaled and combined with topological analysis to be a useful screening tool for novel solid-state electrolytes.

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First principles design of lithium superionic conductors

  1. 1. materiaIs virtuaLab First Principles Design of Lithium Superionic Conductors Shyue Ping Ong,Yifei Mo, William Davidson Richards, Lincoln Miara, Hyo Sug Lee, Gerbrand Ceder Aug 12, 2014 ACS 248th National Meeting
  2. 2. Outline Introduction to Lithium Superionic Conductors First Principles Optimization of State of the Art Superionic conductor • Li10GeP2S12 • Li7La3Zr2O12 Concept for High-throughput Superionic Conductor Design Aug 12, 2014 ACS 248th National Meeting
  3. 3. Current organic electrolytes have two severe limitations Ethylene carbonate Dimethyl carbonate Two key limitations 1) Flammability 2) Electrochemical windows < 4.5V •  Limits choice of electrode and achievable energy densities A lithium superionic conductor solid electrolyte can potentially address both issues. NTSB report, March 7 2013 Aug 12, 2014 ACS 248th National Meeting
  4. 4. State-of-the-art lithium superionic conductors Garnet Li7La3Zr2O12 (LLZO)Thio-lisicon Li10GeP2S12 (LGPS) N. Kamaya et al., Nat. Mater. 2011, 10, 682-686 R. Murugan, et al.,Angew. Chem., Int. Ed. 2007, 46, 7778−81. Aug 12, 2014 ACS 248th National Meeting
  5. 5. State-of-the-art lithium superionic conductors N. Kamaya et al., Nat. Mater. 2011, 10, 682-686 R. Murugan, et al.,Angew. Chem., Int. Ed. 2007, 46, 7778−81. LGPS One of the highest Li+ cond. of 12 mS/cm Reported electrochemical window of > 5V Ge is expensive Sulfide chemistry is air and moisture sensitive LLZO Oxide chemistry is air stable Stable against Li? Low grain boundary resistance Lower Li+ cond. of ~0.1 mS/ cm Aug 12, 2014 ACS 248th National Meeting
  6. 6. First principles materials property prediction What makes a good ionic conductor? Stability •  Phase stability •  Electrochemical stability Diffusivity •  High conductivity @ 300K Materials •  Handling / air sensitivity •  Cost Phase diagrams MD simulations Element substitutions Aug 12, 2014 ACS 248th National Meeting
  7. 7. Ab initio modeling of LGPS diffusivity DFT molecular dynamics simulation Self-diffusivity calculated from simulated Li+ ion motion Y. Mo, S. P. Ong, G. Ceder, First principles study of the Li10GeP2S12 lithium super ionic conductor material. Chem. Mater. 2012, 24 15-17 Lithium motion in LGPS (P/GeS4 tetrahedra frozen for clarity) Aug 12, 2014 ACS 248th National Meeting
  8. 8. Excellent agreement between ab initio diffusivity and experiments 1 S. P. OngY. Mo,W. Richards, L. Miara, H. S. Lee, G. Ceder. Phase stability, electrochemical stability and ionic conductivity of the Li10±1MP2X12 (M = Ge, Si, Sn,Al or P, and X = O, S or Se) family of superionic conductors. Energy & Environ. Sci., 2012. doi:10.1039/c2ee23355j 2 N. Kamaya et al.,A lithium superionic conductor. Nat. Mater. 2011, 10, 682-686 activation energy (meV) conductivity @ 300 K (mS/cm) computed1 210 13 experiment2 240 12 Temperature range: 600 K to 1200 K Computed diffusivities Aug 12, 2014 ACS 248th National Meeting
  9. 9. Ab initio molecular dynamics predict 3D conduction pathway Y. Mo, S. P. Ong, G. Ceder, First principles study of the Li10GeP2S12 lithium super ionic conductor material. Chem. Mater. 2012, 24 15-17. Lithium trace in MD simulation at 900K a! c! a! b! Important because 1D conductors would be highly sensitive to blocking defects! Aug 12, 2014 ACS 248th National Meeting
  10. 10. Bandgap is upper bound on electrochemical window DOS calculated with HSE06 3.6 eV This is how people have estimated electrochemical windows in the past. But is it relevant? Aug 12, 2014 ACS 248th National Meeting
  11. 11. A thought experiment Anode CathodeLGPS Li sinkLi source High μLi Low μLi Aug 12, 2014 ACS 248th National Meeting
  12. 12. Now let us imagine what it is like at the electrode-electrolyte interface Anode CathodeLGPS High μLi Low μLi Li source Li sink Systems open wrt Li Aug 12, 2014 ACS 248th National Meeting
  13. 13. A new way of assessing electrochemical stability Relevant thermodynamic potential at electrode- electrolyte interface is the Li grand potential1: Construct phase diagrams at extrema of corresponding to the cathode and anode: φ = E −µLiNLi µLi Voltage = −(µLi −µLi 0 ) 1S. P. Ong, L.Wang, B. Kang, & G. Ceder. Li-Fe-P-O2 Phase Diagram from First Principles Calculations. Chemistry of Materials, 2008, 20(5), 1798–1807. doi:10.1021/cm702327g Aug 12, 2014 ACS 248th National Meeting
  14. 14. Ge P GeS GeS 2 P 4 S 3 P4 S7 S P2 S5 P 4 S 9 LGPS is unstable against electrodes Li15 Ge4 Li3 P Li2 S Y. Mo, S. P. Ong, G. Ceder, First principles study of the Li10GeP2S12 lithium super ionic conductor material. Chem. Mater. 2012, 24 15-17 E = 0V E = 5V Aug 12, 2014 ACS 248th National Meeting
  15. 15. LGPS achieves electrochemical stability by passivation Li2S + Li15Ge4 + Li3P S + GeS2 + P2S5 Anode CathodeLGPS High μLi Low μLi Well-known glassy conductors! Aug 12, 2014 ACS 248th National Meeting
  16. 16. Summary on Li10GeP2S12 Kamaya et al. (Experiments) 1D conductor σ=12 mS/cm Stable over 5V First principles calculations 3D conductor σ=13 mS/cm SEI formation ✗ ✔ ? Aug 12, 2014 ACS 248th National Meeting
  17. 17. The LGPS scooter, but why is it so small? Aug 12, 2014 ACS 248th National Meeting
  18. 18. Modifying Li10GeP2S12 Two critical problems with LGPS • Ge is expensive ($1600-1800 per kg) • S chemistry likely reactive with H2O and air S Se, OAnion Ge Si, Sn,Al, PCation Substitutions Aug 12, 2014 ACS 248th National Meeting
  19. 19. Phase stability of nine Li10MP2X12 derived from substitution S. P. Ong,Y. Mo,W. D. Richards, L. Miara, H. S. Lee, G. Ceder, Phase stability, electrochemical stability and ionic conductivity in the Li10±1MP2X12 family of superionic conductors. Energy Environ. Sci. 2012, doi: 10.1039/C2EE23355J > 90 meV, oxides unstable! < 25 meV, S & Se compounds may be entropically stabilized Edecomp of Li10MP2X12 (meV/atom) Aug 12, 2014 ACS 248th National Meeting
  20. 20. Chemical compatibility with electrodes Possibly passivating ionic conductors S. P. Ong,Y. Mo,W. D. Richards, L. Miara, H. S. Lee, G. Ceder, Phase stability, electrochemical stability and ionic conductivity in the Li10±1MP2X12 family of superionic conductors. Energy Environ. Sci. 2012, doi: 10.1039/C2EE23355J O2 evolution! Li10MP2X12 Aug 12, 2014 ACS 248th National Meeting
  21. 21. Anion has a large effect on diffusivity of Li10GeP2X12 σ @ 300 K (mS/Cm) Ea (meV) O 0.03 360 S 13 210 Se 24 190 Causes: •  Lattice parameter •  Anion polarizability Se S O S. P. Ong,Y. Mo,W. D. Richards, L. Miara, H. S. Lee, G. Ceder, Phase stability, electrochemical stability and ionic conductivity in the Li10±1MP2X12 family of superionic conductors. Energy Environ. Sci., 2012, doi: 10.1039/C2EE23355J Aug 12, 2014 ACS 248th National Meeting
  22. 22. Cation has a small effect on diffusivity of Li10MP2S12 Isovalent Aliovalent Ge Si Sn P Al σ @ 300 K (mS/Cm) 13 23 6 4 33 Ea (meV) 210 200 240 260 180 (Aliovalent substitutions are Li+ compensated) S. P. Ong,Y. Mo,W. D. Richards, L. Miara, H. S. Lee, G. Ceder, Phase stability, electrochemical stability and ionic conductivity in the Li10±1MP2X12 family of superionic conductors. Energy Environ. Sci., 2012, doi: 10.1039/C2EE23355J Aug 12, 2014 ACS 248th National Meeting
  23. 23. Recent experiments validate first principles predictions! A. Kuhn et al., 2014, arxiv:1402.4586P. Bron, JACS, 2013, 135, 15694–7. Aug 12, 2014 ACS 248th National Meeting
  24. 24. Voronoi topological analysis of LGPS Aug 12, 2014 ACS 248th National Meeting Using Zeo++ code (R. L. Martin, B. Smit, M. Haranczyk,. Journal of Chemical Information and Modeling, 2012, 52(2), 308–18. Y. Mo, S. P. Ong, G. Ceder, First principles study of the Li10GeP2S12 lithium super ionic conductor material. Chem. Mater. 2012, 24 15-17.
  25. 25. 1.2 1.4 1.6 1.8 2 O O O S S S S S Se Se Se Si Ge Sn Si Ge Sn Al P Si Ge Sn ~20% ~7% Bottleneck size as a descriptor for diffusivity Li±1 Ge4+:Al3+, Si4+, Sn4+, P5+ P5+ S2-: O2-, Se2- Substitution Scheme 1.0E-3 1.0E-1 1.0E+1 O O O S S S S S Se Se Se Si Ge Sn Si Ge Sn Al P Si Ge Sn Conductivity σ (mS/cm)     Bottleneck size (Å) Aug 12, 2014 ACS 248th National Meeting Generally, bottleneck size seems to be a pretty good initial screening descriptor for diffusivity.
  26. 26. State-of-the-art lithium superionic conductors N. Kamaya et al., Nat. Mater. 2011, 10, 682-686 R. Murugan, et al.,Angew. Chem., Int. Ed. 2007, 46, 7778−81. LGPS One of the highest Li+ cond. of 12 mS/cm Reported electrochemical window of > 5V Ge is expensive Sulfide chemistry is air and moisture sensitive LLZO Oxide chemistry is air stable Stable against Li? Low grain boundary resistance Lower Li+ cond. of ~0.1 mS/ cm Aug 12, 2014 ACS 248th National Meeting
  27. 27. First principles optimization of garnet

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