Ceramics UK 2019 presentation

1. Ionic transport in garnet
electrolytes: driving the
performance of solid state batteries
Rowena Brugge
Telford, 10th July 2019

2. Contents
• Introduction to all solid state batteries
– LLZO garnet-type electrolytes
– Challenges
• Research approach:
– Degradation and moisture reactivity
– Dendrite formation
• Summary and outlook

3. Energy storage and conversion Battery
during charge:
stores electrical energy as chemical
energy
Reduction at the positive terminal
(cathode)
discharge:
converts chemical energy to electricity
Oxidation at the negative terminal
(anode)
Electrolyte separates the electrodes
and is electronically insulating

4. Why all-solid-state batteries?
• Next generation batteries:
• Drive towards higher energy and power densities
• Safety requirements
Energy density (W ∙ h ∙ kg-1) – car autonomy/range
Power density (W ∙ kg-1) – charge/discharge rates

5. Why all-solid-state batteries?
• New chemistries –
– higher voltages (>4 V vs. Li+/Li)
– Li metal
P. Bruce et al. Nat. Mater., 11, 19, 2012
Long-term stable and high energy density batteries

6. Format of all-solid-state batteries
European Commission, European Battery Alliance, 2018 Report
MRS Bulletin: Frontiers of Solid State Batteries 2018
Lithium- air
Device integration
Improve areal
specific capacity
(mAh cm-2)
Composite
electrodes

7. Inorganic solid electrolytes
• Development of solid electrolytes
with high ionic mobility
(conductivity), electrochemical
stability and chemical stability
• Mitigate electrolyte
decomposition
• Possibility of miniaturization
Bachman, et al. Chem. Rev. 116, 140, 2016

8. Inorganic solid electrolytes
• Development of solid electrolytes
with high ionic mobility
(conductivity), electrochemical
stability and chemical stability
• Mitigate electrolyte
decomposition
• Possibility of miniaturization
• Garnet-type Li7La3Zr2O12 (LLZO)
Bachman, et al. Chem. Rev. 116, 140, 2016
1 mS cm-1

9. Garnet-type electrolytes (“LLZO”)
J. Awaka et al. Chem. Lett. 40, 1, 2011
C. Bernuy-Lopez et al. Chem. Mater. 26, 3610, 2014
Li6.55A0.15□0.3La3Zr2O12 (A: Ga, Al)
Li (Td)
Li (Oh)
vacancy
Ga(b)
x
OLiLi OVAOA 342 /
32 ++= ••
• Cubic symmetry
(space groups Ia̅3d, I4̅3d)
• 6.5 Li per formula unit disordered
between Td and Oh positions
• Flexible Li framework – donor
doping to create vacancies

10. Motivation - challenges
Janek, et al. Nature Energy, 16141, 2016
Jena et al. ACS Energy Lett. 3, 2775, 2018
Aguesse, et al. ACS Appl. Mater. Interfaces, 9, 2017
Surfaces and interfaces a bottleneck to performance
X Degradation issues:
• Moisture sensitive
• Lithium ‘dendrites’
X Dynamic interfaces
X Chemical and structural variation amongst grains, grain
boundaries and surfaces of polycrystalline pellets - dependent on
processing conditions
Need to optimise ion dynamics to improve power density and block degradation

11. Our approach
Investigate the local chemical environment in both the electrolyte and
Li metal/electrolyte interface in terms of its impact on the Li-ion
dynamics and cell degradation
0 20 40 60 80 100 120 140 160
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
C(7
Li)
sputter time (s)
6
Li-Ga0.15-LLZO short exchange
through-surface dp
1. Quantify ion transfer processes using trace elements
(2D, 18O, 6Li) and surface analysis
2. Visualise local chemical environments & correlate to
electrochemical performance and degradation
R. H. Brugge, unpublished

12. Garnet-type electrolytes - synthesis
• Sol-gel synthesis, doping with Ga(III), Al(III) at Li+
site to create V’Li
• 10-500 μm grain sizes
• Liquid phase sintering (Al2O3-Li2O eutectic)
• Thermal treatment in oven coupled to glove box
• Dry processing in Ar glove box <0.1 ppm H2O Fracture surfacePellet surface (thermally etched)

13. • Reaction with water
• H+/Li+ exchange in the lattice – maintain crystal structure
• LiOH and Li2CO3 formation at surface
➢ Shown to be detrimental to densification
➢ Increased interfacial R with electrodes
• Ionic transport properties of proton-rich LLZO in a cell setup??
(b)
LLTOLLTO
Aguesse et al. Adv. Mater. Interfaces 2014
Cheng, ACS Appl. Mater. Interfaces 2015, 7, 17649; Sharafi, J. Mater Chem. A 2017, 5, 13475; Cheng, Phys. Chem. Phys. Chem. 2014, 16, 18294
Degradation – proton/lithium exchange

14. Degradation – proton/lithium exchange
Direct relationship between degree of H-Li exchange and degradation of Li mobility:
Formation of a H-rich electrolyte in the surface up to 1.2 𝜇m thick.
Li metal
Brugge et al. Chem. Mater. 30, 3704, 2018
5 10 15 20 25 30
0.0
0.5
1.0
1.5
length(m)
H2
O immersion time (minutes)
H-Ga0.15-LLZO plateau length
H-LLZO
LLZO
Aim: study the role of H-LLZO on the performance, isolated from surface LiOH and Li2CO3 reaction products.
100 °C
5-30 minsH2O
“FIB” SIMS

15. Degradation – proton/lithium exchange
Brugge et al. Chem. Mater. 30, 3704, 2018
Bulk Grain boundary Li metal interface
1
10
100
1000
10000
100000
Pristine
15 min
30 min
Resistance
R increase > 3 orders
R increase > 3 orders
Li/LLZO/LiDirect relationship between degree of H-Li exchange and degradation of Li mobility:
Surfaces and grain boundaries most affected.
LLZO
Li metal
Li metal
Spacer
Spacer
Spring
Cell Bottom
Cell Cap

16. Dendritic cell failure
10 μm
X Formation of dendrites limits the practical use of solid electrolytes with Li metal electrodes
• Composition and mechanism of formation remains unclear
• Electrochemo-mechanical models
• Possible link to defects in bulk and at interface/ non-uniform kinetics
• Role of electronic conductivity of electrolyte?
Krauskopf, Joule 2019; Swamy, J. Electrochem. Soc 2018; Tian, J. Power Sources 2018; Xie, ACS Appl. Mater. Interfaces 2018

17. Dendritic cell failure
F. Pesci et al., J. Mater. Chem A, 2018
• Cell cycling – increasing current density until short circuit reached
(at the “critical current density”, CCD)
• 60% difference in CCD for same thickness, microstructure, cycling
regime
Short circuit CCD:
Ga-LLZO=0.16 mA/cm2
Al-LLZO=0.1 mA/cm2
0.01 to 0.5 mA/cm2
Step 0.01 mA/cm2
Charge/discharge 30 min
OCP 5 min intervals

18. Dendritic cell failure
After cycling: intra- and inter-grain features
F. Pesci et al., J. Mater. Chem A, 2018

19. Dendritic cell failure – chemical analysis
After cycling Before cycling
Al, Li- rich
Li- rich
F. Pesci et al., J. Mater. Chem A, 2018
Al-LLZO
Ga-LLZO
10 μm
10 μm
5 m
Al Zr La O
5 m 5 m 5 m 5 m
5 m
Al Zr La O
5 m 5 m 5 m 5 m
Al-LLZO

20. Grain boundaries
• Isolate grain and grain boundary
transport properties
0 1x105
2x105
3x105
4x105
0.0
-5.0x104
-1.0x105
-1.5x105
-2.0x105
-2.5x105
-3.0x105
Al-LLZO
Fit
Ga-LLZO
Fit
Z''(Ohm)
Z' (Ohm)
Bulk
Al-LLZO: 1.2x10-3 S/cm
Ga-LLZO: 2.3 x10-3 S/cm
Cavallaro et al. work in progress

21. Summary – tools and approach
Study of ion-dynamics in materials and their effect on performance and degradation in surfaces, bulk and buried
interfaces:
• Correlate chemical analysis of garnet electrolytes and their degradation products to ionic transport and cell
performance, as applied to:
– Li+/H+ exchange processes resulting from moisture degradation
• Bulk, grain boundary and interfacial resistance increases as a result
– Cycling behaviour: dendritic-driven cell failure with Li metal electrodes
• Effect of dopant/local chemistry on propensity for dendrite formation
– Further characterization of grain boundaries and e.g. SEI formation and interface properties in Li/LLZO and
other systems

22. Outlook
Next-generation batteries, a balance of:
• discharge capacity
• thermal stability
• capacity retention and
• lifespan
• Defects key to transport properties
– Vacancies, grain boundaries,
dislocations
Kim et al. J. Mater. Chem. A, 2019, 7, 2942–2964, Luo et al. Adv. Sci. 2017, 4, 1700104
Next-next-generation?
• Hybrid conversion-storage devices:
photorechargeable batteries?

23. Thank You
• Dr Ainara Aguadero
• Dr Andrea Cavallaro
• Dr Federico Pesci
• Dr Ola Hekselman
• Dr Richard Chater
• Electroceramic Materials Group
• Professor John Kilner
• Professor Stephen Skinner
EPSRC ICSF “Genesis: garnet electrolytes for new energy storage integrated solutions” EP/R024006/1
EPSRC Supergen Energy Storage Challenge “Next Generation solid state Lithium Batteries” EP/P003532/1