First principles design of lithium superionic conductors

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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


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.





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


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


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)


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


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!


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?


A thought experiment

Anode

Cathode

LGPS

Li sink Li source

High μLi Low μLi


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


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


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


LGPS achieves electrochemical stability by passivation

Li2S + Li15Ge4 + Li3P S + GeS2 + P2S5

Anode

Cathode

LGPS

High μLi Low μLi

Well-known glassy conductors!


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

✗ ✔ ?


The LGPS scooter, but why is it so small?


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


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)


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


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


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


Recent experiments validate first principles predictions!

A. Kuhn et al., 2014, arxiv:1402.4586 P. Bron, JACS, 2013, 135, 15694–7.


Voronoi topological analysis of LGPS


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)


Generally, bottleneck size seems to be a pretty good initial screening descriptor for

diffusivity.




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


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.


Voronoi topological analysis of LLZO


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


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


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.


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Thank you.

Aug 12, 2014

ACS 248th National Meeting

First principles design of lithium superionic conductors

Science

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