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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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materiaIsvirtuaLab
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
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
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
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
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
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
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
Excellent agreement between ab initio diffusivity and experiments
1 S. P. Ong Y. 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
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
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
A thought experiment
Anode
Cathode
LGPS
Li sink Li source
High μLi Low μLi
Aug 12, 2014 ACS 248th National Meeting
Now let us imagine what it is like at the electrode-electrolyte interface
Anode
Cathode
LGPS
High μLi Low μLi
Li source Li sink
Systems open wrt Li
Aug 12, 2014 ACS 248th National Meeting
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 −µLi0 )
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
Ge
P
GeSGeS2
P4S3
P4S7
SP2S5P4S9
LGPS is unstable against electrodes
Li15Ge4
Li3P
Li2S
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 = 0 V E = 5 V
Aug 12, 2014 ACS 248th National Meeting
LGPS achieves electrochemical stability by passivation
Li2S + Li15Ge4 + Li3P S + GeS2 + P2S5
Anode
Cathode
LGPS
High μLi Low μLi
Well-known glassy conductors!
Aug 12, 2014 ACS 248th National Meeting
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
The LGPS scooter, but why is it so small?
Aug 12, 2014 ACS 248th National Meeting
Modifying Li10GeP2S12
Two critical problems with LGPS • Ge is expensive ($1600-1800 per kg) • S chemistry likely reactive with H2O and air
S Se, O Anion
Ge Si, Sn, Al, P Cation
Substitutions
Aug 12, 2014 ACS 248th National Meeting
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
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
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
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
Recent experiments validate first principles predictions!
A. Kuhn et al., 2014, arxiv:1402.4586 P. Bron, JACS, 2013, 135, 15694–7.
Aug 12, 2014 ACS 248th National Meeting
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.
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.
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
First principles optimization of garnet ���Li7+2x−y(La3−xRbx)(Zr2−yTay)O12
0.00 0.10 0.20 0.30 0.40 0.50
6 6.5 7 7.5
Act
ivat
ion
Ene
rgy
(eV
)
1.0E-07
1.0E-05
1.0E-03
1.0E-01
σ 300
(S/
cm) Rb Doped Ta Doped
Max conductivity and min Ea at Li = 6.75
Miara, L. J.; Ong, S. P.; Mo, Y.; Richards, W. D.; Park, Y.; Lee, J.-M.; Lee, H. S.; Ceder, G. Chem. Mater., 2013, 25, 3048–3055.
Aug 12, 2014 ACS 248th National Meeting
Voronoi topological analysis of LLZO
Aug 12, 2014 ACS 248th National Meeting
Miara, L. J.; Ong, S. P.; Mo, Y.; Richards, W. D.; Park, Y.; Lee, J.-M.; Lee, H. S.; Ceder, G. Chem. Mater., 2013, 25, 3048–3055.
Pathway to High-throughput First Principles Design of Lithium Superionic Conductors
Aug 12, 2014 ACS 248th National Meeting
Starting candidates
Topological Screening (augmented by DFT)
Stability (phase & EW) screening
Diffusivity
Optimized candidates
Automated “one-click” MD workflow based on pymatgen, custodian and fireworks
AIMD SDSC
Multi-week AIMD simulation
Statistical exclusionary screening
Y. Mo, S. P. Ong, G. Ceder, “Insights into Diffusion Mechanisms in P2 Layered Oxide Materials by First-Principles Calculations”, submitted
Automated pathway extraction + NEB
Summary
• Developed sophisticated AIMD automation and workflow infrastructure for rapid kinetic studies.
• Developed Li-grand potential PD as a powerful new way of studying electrode-electrolyte interfacial phase equilibria.
Technical Advances
• Li10SiP2S12 and Li10SnP2S12, earth-abundant variants of LGPS, were predicted and confirmed to have similar performance.
• Suggested doping strategies to further enhance conductivity of LLZO.
Materials Design
Aug 12, 2014 ACS 248th National Meeting
Acknowledgements and Publications
Funding
Computing resources from
Y. Mo, S. P. Ong, G. Ceder, First principles study of the Li10GeP2S12 lithium super ionic conductor material. Chem. Mater. 24 15-17 (2012) 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 Miara, L. J.; Ong, S. P.; Mo, Y.; Richards, W. D.; Park, Y.; Lee, J.-M.; Lee, H. S.; Ceder, G. Effect of Rb and Ta Doping on the Ionic Conductivity and Stability of the Garnet Li7+2 x – y (La3–
xRbx)(Zr2– yTay)O12 (0 ≤ x ≤ 0.375, 0 ≤ y ≤ 1) Superionic Conductor: A First Principles Investigation, Chem. Mater., 2013, 25, 3048–3055, doi:10.1021/cm401232r.
Aug 12, 2014 ACS 248th National Meeting
materiaIsvirtuaLab
Thank you.
Aug 12, 2014
ACS 248th National Meeting