Computation Accelerated Design of Materials and Interfaces for All-Solid-State Li-ion Batteries

Transcription

1 Computation Accelerated Design of Materials and Interfaces for All-Solid-State Li-ion Batteries Yifei Mo Department of Materials Science and Engineering Maryland Energy Innovation Institute University of Maryland, College Park, MD Funding support: DOE, VTO, BMR program DOE-EERE DE-EE , DE-EE

2 Opportunities and Challenges: All-Solid-State Li-ion Batteries Opportunities and potentials: Improved safety : non-flammable ceramic electrolyte High energy density : Li metal anode and/or high-voltage cathode High power, long cycle life, wide temperature range Interfacial resistance Fast Li+ transport in solid electrolyte Interfacial resistance Challenges : Li solid electrolyte with high ionic conductivity, good stability, etc. Interfaces between electrolyte and electrodes. Our goal: Use first principles computation to achieve: fundamental understanding accelerated design of materials and interfaces. 2

3 What makes super-ionic conductor the key enabler? Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Crucial to understand universal features among super-ionic conductors and to rationally design new conductors Shao-horn et al. Chem. Rev. (2016) 3

4 Ion Diffusion in Solids Classical Model To achieve high ionic conductivity, needs low activation energy E a + high carrier concentration n Nernst-Einstein equation: Ionic conductivity! = #$ %& '( )* +( Atomistic diffusion in solid is mediated by vacancy or interstitial as carrier hopping among lattice sites. E a : Activation energy -. /0 ) n : mobile carrier concentration Energy landscape E a

5 Concerted migration mechanism dominates in super-ionic conductors Ab initio molecular dynamics (AIMD) simulations to observe real-time ion migration mechanism. Multiple Li ions hop simultaneously in a concerted migration mechanism Strong concerted migration is dominant in LGPS, garnet LLZO, NASICON LATP, as a general phenomena of super-ionic conductors. LGPS LLZO LATP 5

6 How concerted migration happens? LGPS LLZO LATP Barrier of concerted migration 0.20 ev 0.26 ev 0.27 ev Contradiction: How multiple ions migrating together can lead to a lower barrier? Energy landscape of single Li+ migration 0.47 ev 0.58 ev 0.49 ev

7 Why concerted migration has lower barrier? e.g. In LLZO Tet Oct Tet Li-Li Coulomb interaction High-energy sites occupancy Energy landscape of single Li + migration (ev) 0.58 ev Energy landscape of single Li + migration (ev) Position along migration path 0.0 Position along migration path (Å) During concerted migration, the down-hill migration of highenergy ions cancels out a part of hillclimbing migration barrier. Energy landscape 0.6 ev 0.3 ev Concerted migration barrier 0.3 ev Position along migration path (Å)

8 How to design super-ionic conductor? Single ion migration in typical solids X. He, Y. Zhu and Y. Mo, Nat. Commun., 2017, 8, Low-barrier concerted migration in super-ionic conductors Energy barrier Energy landscape Migration path Strong coulomb interaction Occupied high-energy site Flat landscape at high-energy site Mechanistic origin: High-energy site Li+ migrate downhill, canceling out a part of the energy barrier felt by other uphill-climbing ions. Design strategy for super-ionic conductor : Tailor mobile ion configuration to activate low-barrier concerted migration. 8

9 Design and discover new super-ionic conductor: Li 1+x Ta 1-x Zr x SiO 5 LiTaSiO 5 Not been studied for Li diffusion. TaO 6 Energy landscape (ev) C B A C SiO 4 Li A B A A Position along migration path Li 1.25 Ta 0.75 Zr 0.25 SiO 5 Zr4+ à Ta5+ Ea = 0.23 ev " (300 K) = 4.3 ms/cm Ea = 0.73 ev! (300 K) = ms/cm Demonstrated our design strategy in discover and design new super-ionic conductors 9 X. He, Y. Zhu and Y. Mo, Nat. Commun., 2017, 8,

10 Interfaces in All-Solid-State Li-ion Batteries Significant amount of solid-solid interfaces in solid-state batteries: Formation of SEI? Interface compatibility & stability. (coulombic efficiency, cycle life) Interfacial ionic transport. (Rate performance) Interfacial resistance Fast Li+ transport in solid electrolyte Interfacial resistance Thermodynamics indicate that the interface may degrade and an interphase layer may form due to: 1. The reduction / oxidation of the solid electrolyte materials at applied voltage. 2. Chemical reaction between solid electrolyte and electrodes. 3. Electrochemical reaction (during cycling voltage) between solid electrolyte and electrodes. What are the fundamental limitations at the interfaces in all-solid-state batteries? What are the general design principles for interfaces with good battery performance? 10

11 (Thermodynamic Intrinsic) Electrochemical window of solid electrolytes Li metal LGPS Li 3 PS 4 Li 6 PS 5 Cl Li 7 P 2 S 8 I LiPON LLZO LLTO LATP LAGP LISICON Li Solid electrolyte Phase equilibria with Li metal Li 15 Ge 4, Li 3 P, Li 2 S Li 3 P, Li 2 S Li 3 P, Li 2 S, LiCl Li 3 P, Li 2 S, LiI Li 3 P, Li 3 N, Li 2 O Zr (or Zr 3 O), La 2 O 3, Li 2 O Ti 6 O, La 2 O 3, Li 2 O Ti 3 P, TiAl, Li 3 P, Li 2 O Li 9 Al 4, Li 15 Ge 4, Li 3 P, Li 2 O Li 15 Ge 4, LiZn, Li 2 O Zhu, He, Mo, ACS Appl. Mater. Interfaces, 2015, 7 (42), LiF LiCl LiI Li2O Li2S Li3P Li3N LGPS Li3PS4 Li6PS5Cl Li7P2S8I LiPON LLZO LLTO LATP LAGP LISICON Potential Ref. to Li/Li + (V) Electrochemical window Li Chemical potential(ev)

12 Li-LGPS : Interphase layer formation and Incompatibility Li metal Lithiation Reduction Li 10 GeP 2 S 12 (LGPS) First principles calculations Li 10 GeP 2 S Li è12 Li 2 S + 2 Li 3 P Li 15 Ge 4 (ΔH = ev / kj/mol) Mixed Ionic & electronic conducting (MIEC) interphase layer formation: - Thick interphase layers - High interfacial resistance. - Incompatible! Wenzel, Randau, Leichtweiß, Weber, Sann, Zeier, Janek, Chemistry of Materials (2016)

13 Oxides have better stability than sulfides? Li metal LGPS Li 3 PS 4 Li 6 PS 5 Cl Li 7 P 2 S 8 I LiPON LLZO LLTO LATP LAGP LISICON Li Solid electrolyte Phase equilibria with Li metal Li 15 Ge 4, Li 3 P, Li 2 S Li 3 P, Li 2 S Li 3 P, Li 2 S, LiCl Li 3 P, Li 2 S, LiI Li 3 P, Li 3 N, Li 2 O Zr (or Zr 3 O), La 2 O 3, Li 2 O Ti 6 O, La 2 O 3, Li 2 O Ti 3 P, TiAl, Li 3 P, Li 2 O Li 9 Al 4, Li 15 Ge 4, Li 3 P, Li 2 O Li 15 Ge 4, LiZn, Li 2 O Zhu, He, Mo, ACS Appl. Mater. Interfaces, 2015, 7 (42), LiF LiCl LiI Li2O Li2S Li3P Li3N LGPS Li3PS4 Li6PS5Cl Li7P2S8I LiPON LLZO LLTO LATP LAGP LISICON Potential Ref. to Li/Li + (V) Electrochemical window Li Chemical potential(ev)

14 Formation of SEI enables compatible solid-solid interface Li Li 3 N,Li 3 P, Li 2 O LiPON x Li 2 O Li 3 N Thermodynamics also shows Li reduction is energetically favorable Li 3 P In-situ XPS also observed Li reduction of LiPON Schwobel et al. Solid State Ionic (2016) Li 2 O Li 3 N Li 3 P ² LiPON is well demonstrated for its Li metal compatibility in thin-film batteries. Why? ² Form SEI-like layer, Li 3 P, Li 3 N, Li 2 O, ion conducting but electronic insulating passivates the solid electrolytes. Lithiation pristine pristine

15 Formation of MIEC interphase layers in sulfide SE. Incompatible interface between sulfide SE-LiCoO 2 Solution: Converting to SEI interface by coating Sulfide electrolyte, e.g. LGPS Interphase Layer Co 9 S 8, etc. Oxide coating LiCoO 2 Sulfide electrolyte, LiCoO 2 e.g. LGPS Li 10 GeP 2 S 12 + LiCoO 2 è Co 9 S 8 + Li 2 S + Li 2 SO 4 + Li 3 PO 4 + Li 4 GeO 4 (ΔH = ev/atom) Li 10 GeP 2 S 12 + Li 0.5 CoO 2 è Co 9 S 8 + Li 2 S + Li 2 SO 4 + Li 3 PO 4 + Li 4 GeO 4 (ΔH = ev/atom) Origin of poor interfacial performance: Poor electrochemical/chemical stability Formation of MIEC interphase --> high resistive interphase layers Oxide coating layer, (e.g. LiNbO 3, Li 3 PO 4, etc. ) serves as artificial SEI Zhu, He, Mo, J. Mater. Chem. A, 2016,4,

16 Interface reactions for LiPON Cathode interface For LiPON-LiCoO 2 interface Y. S. Meng et al. Nano Letters (2016) LiPON LiCoO 2 Li 3 PO 4, Li 2 O, Li 2 O 2, CoN x, CoO x, Li x CoO y Electron energy loss (ev) LiPON+ LiCoO 2 è Li 3 PO 4 + Li 2 O + CoN (ΔH = -0.1 ev/atom) At applied voltage of 4.2V to 5.0V, ΔH = to ev/atom Electronic insulating but ion conducting interphase (like SEI) formed to stabilize the interface -> Self-Limiting decomposition -> Form SEI-like passivation -> Decent interfacial Li+ transport. Zhu, He, Mo, J. Mater. Chem. A, 2016,4,

17 Resolving interface compatibility in all-solid-state battery Current success cases: Li LiPON LCO / High-Voltage Cathode Carbon anode LPS Sulfide LCO Cathode Spontaneously formed stable SEI layer formed SEI layer Artificial coating layer Strategies for resolving interface issues: Optimize and design SE to form stable SEI (e.g. LiPON) good interfacial compatibility. Applying coating layer as artificial SEI (e.g. LiNbO 3 coating on sulfide SE) Novel interfacial engineering to spontaneously form stable SEI. 17

18 Can we have materials stable against Li metal? Electrochemical stability window of example Li-M-X compounds. M = Al, Zr, Si,Ge, P X = N, S, O, F Nitride Sulfide Oxide Fluoride General trend of cathode limit Cations lead to Li reduction and MIEC interphase (noncompatible! ) Nitride < Oxide ~ Sulfide < Fluoride Zhu, He, Mo, Advanced Science (2017) Nitrides like Li 3 AlN 2, Li 2 ZrN 2 are Li metal stable and electronic insulating. 18

19 Nitrides have unique thermodynamic stability against Li metal Li + Li x MF y -> Li z M + LiF Li + Li x MO y -> Li z M + Li 2 O Fluoride Oxide Sulfide Nitride Zhu, He, Mo, Advanced Science (2017)

20 Strategies using Nitride to stabilize Li metal Apply artificial SEI layer as coating Li+ Spontaneously formed stable SEI layer Li Solid Electrolyte Li Solid Electrolyte Li-stable nitride Coat Li-stable artificial SEI Li-stable nitride. N rich Form Li-stable SEI at interface High nitrogen doping at interfaces Li 3 N to react with SE to from stable SEI. N-rich salt doping Zhu, He, Mo, Advanced Science (2017)

21 Conclusions First principles Computation Methods Developed first principles computation techniques based on materials database to 1) design novel solid electrolytes and to 2) evaluate the thermodynamic equilibria of solid interfaces. The computation framework can be transferable to any materials and interfaces. Materials Design and Discovery Unique insights for super-ionic conductors obtained through atomistic modeling. First principles computation is demonstrated to discover and design new Li ion conductor materials. Implications for all-solid-state battery The interphase layers play a crucial role in the performance of solid-state batteries, and are likely an origin of high interfacial resistance. Interface engineering is the key to achieve good performance: 1) develop compatible electrolyte and electrode; 2) apply coating layer and novel interfacial engineering. He, Zhu, Mo, Nature Communications 2017, 8, Zhu, He, Mo, ACS Appl. Mater. Inter. 2015, 7 (42), Zhu, He, Mo, J. Mater. Chem. A 2016,4, Han, Zhu, He, Mo, Wang, Adv. Energy Mater. 2016, Zhu, He, Mo, Advanced Science 2017,

22 Acknowledgement Funding support: BMR program, VTO, EERE DOE-EERE DE-EE , DE-EE Collaborations at University of Maryland Prof. Chunsheng Wang Prof. Liangbing Hu Prof. Eric Wachsman Materials Project Computational resources: XSEDE: NSF TG-DMR130142, TG-DMR University of Maryland supercomputers Maryland Advanced Research Computing Center (MARCC) 22