High-Performance Sulfide-based Solid-state

Electrolytes and Interfaces for All-solid-

state Li Batteries

Presenter: Dr. Feipeng Zhao

Advisor: Prof. Andy Xueliang Sun

Western University, Canada

October, 2021

1

240th ECS meeting

Conclusions

Advanced electrolyte and derived anode interface

Acknowledgements

Introduction: Sulfide-based ASSLMBs

Outline

• Fluorinating Li6PS5Cl (LPSI) SSEs

• Sn-substituted Li6PS5I (LPSI) and Li3PS4 (LPS)SSEs

• Solid-state batteries and sulfide SSEs

• Challenges and strategies

2

S. HessJ, et al. J. Electrochm. Soc. 2015, 162, A3084 H. Li, et al. Chem. Rev. 2020, 120, 6820–6877

Introduction: why solid state?

3

Commercial Li-ion batteries

(LIBs)

fire

degassing

explosion

Flash points (FPs) and self-extinguishing

times (SETs) of electrolytes

Anode: graphite

Cathode: LCO, LFP, NMC, LMO, etc.

Electrolytes: flammable organic liquid

ASSLMBs are much safer and can improve the performance:• SSEs: non-flammable, cannot leak• Cells: Improved energy density

(packing techniques, avoiding using inactive separators)

F. Zhao, Y. Li, X. Sun. 2021, to be submitted; R. Kanno, et al. Nat. Energy 2016, 1, 16030; J. Schnell, et al. J. Power Sources 2018, 382, 160

All-solid-state Li metal batteries(ASSLMBs)

Introduction: why solid state?

4

Toyota’s battery road map

Packing of ASSLMBs

Li metal

Solid-state electrolytes (SSEs)

5

Introduction: sulfide SSEs

BY News from Tokyo Institute of Technology, 2016H. Zhu, et al. Adv. Mater. 2019, 31, 1901131

Advantages of sulfide SSEs:• High σ (10-2 S cm-1, comparable to

Liquid electrolyte) • Decent mechanical properties• Low grain-boundary resistance

Upgrade trend of solid-state electrolytes (SSEs):• Improved ionic conductivity (σ)• From oxides/chlorides to sulfides• Accompanied by polymer-based

Ion

ic c

on

ductivity,

6

Challenge I and stretagies: Air sensitivity

H2S derived from degradation of sulfide-based electrolytes

M. Tatsumisago, et al. Solid State Ionics 2011, 182, 116-119; A. Hayashi, et al. J. Mater. Chem. A, 2013, 1, 6320-6326Y

Inte

nsi

ty (

a.u

.)

H2S gas Chromatogram

P2S64-

Adding MxOy (M = Fe, Zn, and Bi) nanoparticles as absorbents

Replacing S with O in the Li2S-P2S5 system

1

3 Replacing P with As or Sn in the LixMSx system

2

Strategy H2Sgeneration

Ionic conductivity

Note

1 Suppressed Reduced CANNOT avoid H2S generation

fundamentally

2 Suppressed Reduced -

3 Suppressed Dramaticallyreduced

As substitution can improve σ, but NOT

practical

Improving the air stability of sulfide SSEs while keeping the ionic conductivity is very important!

7

Challenge II: electrode/sulfide interface issues

Sulfide SSEs(Li-P-S

Li-P-S-M,Li-P-S-halogen,

…)

Li anode

Li3P, Li2S,

Li halides,Li-M,

…

Li dendrites propagation2

Oxide-based

cathode (LCO, NMC, NCA)

Interfacial side reactions1 Interfacial side reactions

2 Space-charge layer (SCL) effect

1

TMs: Transition metal elements of cathode active materials; LCO: LiCoO2; NMC: LiNixMnyCozO2; NCA: LiNi0.8Co0.15Al0.05O2

Y. Mo, et al. ACS Appl. Mater. Interfaces 2015, 7, 23685; H. Zhu, et al. Matter 2020, 3, 57-94;K. Takata. Acta Mater. 2013, 61, 759-770

POx,

SOx,

Reduced TMs,

…

SEI (solid-electrolyte interphase) CEI (cathode-electrolyte interphase)

High reduction potential of sulfide SSEs Low oxidation potential of sulfide SSEs

Growth and propagation of Li dendrites

SCL formation

Interface stability (anode and cathode) can determine battery performance!

Li-deficient layer

Li metal

8

Strategies for Li/sulfide interface

Placing interlayer (electro)chemically1

Main requirements:

Smooth and robust surface

(Electro-)Chemically inert

Only Li-ion conductive interface

Self-terminating side reaction

Simple fabrication

Without losing energy density

√√Only Li-ion conductive

√×Li-ion & electron conductive

× ×Only electron conductive

J. Janek, et al. Solid State Ionics 2015, 278, 98-105

Constructing Li-M alloy (Ag, In, Al)2

Modifying sulfide SEs with LiI doping 3

Ideal model:

Reported strategies:

Modifying sulfide SSEs is the most straightforward and feasible method!

9

Objectives and organization

Modifying SSEs

Sulfide SSEs

Li anode

SEI

High ionic conductivity

Air stability

Li anode interface

Part 1Fluorinating sulfide SSEs for improved Li/sulfide interface stability

Part 2 Sn-substituted Li6PS5I and glass-ceramic Li3PS4 to realize high ionic conductivity, Li compatibility, and air stability

10

Background: Argyrodite-type Li6PS5X

The item Argyrodite is named from one natural mineral ‘Ag8GeS6‘. LGPS: Li10GeP2S12C. Yu, F. Zhao, X. Sun, et al. Nano Energy 2021, 83, 105858W. Zeier, et al. J. Am. Chem. Soc. 2017, 139, 10909-10918

• High popularity of LPSCl (synthesis, understanding, battery performance)• Ionic conductivity: σ (LGPS) > σ (LPSCl) > σ (LPS) (LPSCl, > 10-3 S cm-1 at RT)• Cheaper precursors (Li2S + P2S5 + LiCl) compared with preparing LGPS

Li6PS5X: LPSX, X = Cl or Br or I

Choosing LPSC as the base sulfide SEs:

High crystallinity (cubic)

Can fluorinated LPSCl derive LiF at the Li/sulfide interface and improve the stability?

11

Motivations

LiF-rich SEI is an essential component to suppress Li dendrites and prevent interfacial reactions:

1. Low electronic conductivity 2. High bulk modulus3. High interface energy with Li metal

4. High Li-ion diffusivity derived from LiF in SEI

C. Wang, et al. Science Advances 2018, 4, 9245; F. Mashayek, et al. J. Phys. Chem. C 2019, 123, 10237−10245B. Gallant, et al. Proc. Nati. Acad. Sci. U.S.A. 2020, 117, 73-79;

Benefit of fluorinating electrolytes

Heterogeneous interface: Higher Li-ion diffusivity

Calculation on the Li+ diffusion at LiF-related GB

Synthesis and structure

Li2SP2S5

LiClLiF

Ball milling Sealing in quartz tube Annealing in muffle oven

Synthesis route (solid reaction method) towards Li6PS5Cl1-xFx (x = 0, 0.05,0.3, 0.5, 0.7, 0.8, 1)

Pelleting

XRD results

Interaction between F and PS43- molecules was confirmed by Raman.

Raman results

Fluorinating Li6PS5Cl can induce formation of a mixture of distorted Li6PS5Cl and β-Li3PS4.

Stretching P-S in PS4

12F. Zhao, et al. ACS Energy Lett. 2020, 5, 4, 1035-1043

13

Improved Li/Li6PS5Cl1-xFx interface

Li-Li symmetric cell test: to evaluate the Li/electrolyte interface stabilityLi metal

Li metal

cyclerSSEs

Excellent high rate performance can be obtained for Li6PS5Cl0.3F0.7 SSEs. It was the best in solid-state cells and comparable to the liquid electrolyte system.

14

Characterizations of LiF-rich interface

Li/Li6PS5Cl0.3F0.7 interface after symmetric cell cycling 0.1 mA cm-2/ 0.1 mAh cm-2 for ~200 h

SEM ToF-SIMS

XPS depth profiling

X-ray electrons

Ar etching

Interface

Smooth and sheet-like (dense) interface was formed in-situ.

High F concentration was found at the Li/SSEs interface.

Rich-LiF (sub-micro thick) containing interface was confirmed by XPS (684.8 eV).

15

Objectives and organization

Modifying SSEs

High ionic conductivity

Air stability

Li anode interface

Part 1Fluorinating sulfide SSEs for improved Li/sulfide interface stability

Part 2 Sn-substituted Li6PS5I and glass-ceramic Li3PS4 to realize high ionic conductivity, Li compatibility, and air stability

16

Hard base: O

Soft base: S

Hard acid: P

Soft acid: Sn

√×√

Sn-S bonding stabilize the structure (HSAB)

Chem. Mater. 2012, 24, 2211−2219

Nat. Energy 2018, 3, 310

With LiSnprotective layer

Pristine Li

In-situ triggered Li-Sn alloy regulate Li deposition

Low-valence element substitution P (V) Sn (IV) to improve the structure

J. Mater. Chem. A, 2018, 6, 645

2.4×10-3 S/cmLi6+xP1-xSixSBr

P (V) Si (IV)

0.7×10-3 S/cm

• Expansion of unit cell• Increase of Li+ number

Motivations: why Sn substitution

16

Compound LPSI-20Sn LPSI

a, Å 10.218 10.145

b, Å 10.218 10.145

c, Å 10.218 10.145

V, Å3 1066.711 1,044.134

17

Structure of Sn-substituted LPSI

Li6+xP1-xSnxS5I (LPSI-xSn, x= 0, 10, 20, 30, 50, 80, 100%)

Li2SP2S5

LiISnS2

Synthesis

Ball milling +

annealing in Vac.

XRD XRD refinement

Reaction equation: (5+x) Li2S + (1-x) P2S5 + (2x) SnS2 + 2 LiI = 2 Li6+xP1−xSnxS5I

The Argyrodite phase is pure when the substitution percentage is less than 20%;

The aliovalent Sn (IV) substitution leads to a expanded unit cell and increase Li+ contents.

Li6.24P0.823Sn0.177S4.58I0.9

F. Zhao, et al. Adv. Energy Mater. 2020, 10, 1903422

18

Ionic conduction of Sn-substituted LPSI

Sn substitution can improve the σ significantly. 20% is the optimized value, LPSI-20Sn: 125-time increase in the RT ionic conductivity Variable-Temp 7Li-NMR indicate a ultralow activation energy (Ea).

Derived from EIS measurements

LPSI LPSI-20Sn

σ at RT (S/cm)

2.8 × 10-6 3.5 × 10-4

Ea(eV)

0.424 0.304

19

Motivations

Clarifying the ‘three-in-one’ effect of Sn-substitution strategy

• Ruling out the effect of LiI formation on the stability of Li metal interface• Studying the possibility of generating Li-Sn alloys and its influence on performance• Obtaining high RT σ over 10-3 S cm-1 for sole applications (rather than as interlayer)

Crystal structure of β-Li3PS4

Sulfide prototype Most air-stable in Li2S-P2S5 system Wider electrochemical window Low cost

o Metastable at RT (need to be embedded as ceramic in glass)

o Insufficient σ: 1-3.8 ×10-4 S/cmo Zn, Si can replace P, BUT only Li

dynamic was studied.

Pros.

Cons.

Li3+xSixP1-xS4 x=0.4 σ = 0.64 mS/cm

x=0.25 σ = 1.2 mS/cm

Li1-2xZnxP1-xS4 x=0.6 σ = 0.57 mS/cm

Y. Mo, et al. ACS Appl. Mater. Interfaces 2015, 7, 23685; G. Ceder, et al. Energy Environ. Sci. 2016, 9, 3272-3278; N. Suzuki, et al. Chem. Mater. 2018, 30, 2236-2244; Linda Nazar, et al. Chem. Mater. 2019, 31, 7801-7811.

20

Synthesis and structure

Li2SP2S5

SnS2

High-energy ball milling

Glassy precursors(g)

Glass-ceramicsamples (gc)

Annealing in vacuumed quartz tube

Using DSC to determine the heating temperature

Synthesis route (solid reaction)

XRD results

Compound Li3.2P0.8Sn0.2S4 Li3PS4

a, Å 13.159 13.066

b, Å 8.025 8.015

c, Å 6.135 6.101

V, Å3 647.885 638.92

At the substitution percentage of 20%, gc-Li3.2P0.8Sn0.2S4

showed only β-phase Li3PS4, but with an expanded unit cell.

F. Zhao, et al. Adv. Mater. 2021, 33, 8, 2006577

21

Ionic conduction of Sn-substituted gc-Li3PS4

6.5-times increase after the 20% (optimized) Sn substitution (gc-Li3.2P0.8Sn0.2S4), reaching 1.22 × 10-3

S/cm with Ea = 0.311 eV at RT (gc-Li3PS4: 1.94 × 10-4 S/cm, Ea = 0.381 eV). Dynamic 7Li-NMR revel the improved local Li-ion transport after Sn substitution.

22

Air stability of gc-Li3.2P0.8Sn0.2S4

Exposing to 5%-humidity air overnight

gc-Li3.2P0.8Sn0.2S4 gc-Li3PS4

1.21 × 10-3 S/cm 1.94 × 10-4 S/cm

1.03 × 10-3 S/cm 0.25 × 10-4 S/cm

Unobservable change of XRD and XANES (before and after 5%-humidity exposure) indicate the robust structure consisting of (P/Sn)S4 tetrahedra;

High σ over 10-3 S cm-1 can be obtained after exposing to 5%-humidity air overnight, which is important for applications.

(simulating dry-room environment)

23

Li compatibility of gc-Li3.2P0.8Sn0.2S4

gc-Li3.2P0.8Sn0.2S4

gc-Li3PS4

Li symmetric cell

XPS results

Simulation (finite element method)

Uniform Li+ flux through the entire interface and towards the Li metal electrode

Li-Sn alloys were embedded in the insulating matrix (Li2S + Li3P), serving as the stabilized Li/sulfide interface (the interfacial reaction is self-terminating).

24

Li/gc-Li3.2P0.8Sn0.2S4 /LCO full cells

0.05

@RTUnit: C

0.1

0.20. 5

0.1

0.81

0 5 10 15 20 25 30 350

30

60

90

120

150

180

Sp

ec

ific

Ca

pa

cit

y (

mA

h g

-1)

Cycle Number

0 20 40 60 80 100 120 1402.7

3.0

3.3

3.6

3.9

4.2

Vo

lta

ge

(V

vs

. L

i/L

i+)

Specific Capacity (mAh g-1)

Li//gc-Li3PS

4//LCO full cell

1st Charging

1st Disharging

Li//gc-Li3.2

P0.8

Sn0.2

S4//LCO full cell

1st Charging

1st Disharging 0.05C@RT

0 10 20 30 40 50 600

30

60

90

120

150

180

gc-Li3.2

P0.8

Sn0.2

S4

gc-Li3PS

4

Sp

ec

ific

Ca

pa

cit

y (

mA

h g

-1)

Cycle Number

0

20

40

60

80

100

Co

ulo

mb

ic E

ffic

ien

cy

(%

)

@RT

0.1 C

0.05 C

0.1 C

96% 1st CE

125 mAh g-1@ 0.05C91 mAh g-1@ 1C

118 mAh g-1@ 0.1C77% retention after 60 cycles

0.1 C

25

Conclusions

Fluorinated sulfide SSEs could derive LiF-rich interface in-situ and improve the stability of Li metal/sulfide interface.

Sn-substituted LPSI sulfide SSEs showed significantly improved ionic conductivity and ‘three-in-one’ strategy of the Sn substitution was studied systematically in Sn-substituted Li3PS4 glass-ceramic.

Acknowledgement

26

Supervisor:

Dr. Xueliang Andy Sun

Group photo 2019

Collaborators:

Prof. Yining Huang, NMR, Western University

Prof. T.K. Sham, Synchrotron, Western University

Dr. Jian Wang, Beamline Scientist, CLS

Dr. Yongfeng Hu, Beamline Scientist, CLS

Dr. Renfei Feng, Beamline Scientist, CLS

Dr. Rana Sodhi, XPS, University of Toronto

27

Thanks for your attention!

Supporting information

29

Full cell performance

Full cell test: to demonstrate applicable capability

Very similar electrochemical behavior to the liquid electrolyte full batteries. Excellent cycling stability and rate capability in full cells: 95% capacity

retention after 50 cycles and 85.7 mAh/g at 1 C (1.3 mA cm-2) at RT.

30

Background

Argyrodite-type Li6PS5X (LPSX, X = Cl, Br, I)

Li interface stability of iodine (I)-containing sulfide SSEs

W. Zeier, et al. J. Am. Chem. Soc. 2017, 139, 10909-10918;C. Wang, et al. Nano Energy 2018, 53, 958-966; C. Wang, et al. Adv. Energy Mater. 2018, 8, 1703644.

vs.

The derived LiI-containing interface is compatible with Li metal.

Disorder of S (4d)/X (4a) correlate the σ σ (LPSCl) > σ (LPSBr) >> σ (LPSI) (10-3 vs. 10-6 S/cm)

LPS: Li3PS4

LPS30I: 70Li3PS4·30LiI

31

Li metal/LPSI-20Sn interface stability

Symmetric cell testing Interface characterizations

Stable Li plating/stripping happened to the Li/LPSI-20Sn interface, even at high rate (1 mA cm-2); High ionic conductivity is also important for stable Li plating/stripping assuming LiI formed at Li/LPSI; LiI at the interface was confirmed by XPS, and distributed uniformly.

(The sample after symmetric cell cycling ~60h)

32

LPSI-20Sn as interlayer for full cells

Highly reversible charge and discharge curves; 123.7 mAh/g@0.05C, 93.8 mAh/g@1C, the 1st coulombic efficiency is up to 91%; Negligible decay in the initial 20 cycle at 1C, 88.5% capacity retention after 50 cycles.

33

Synthesis and structure

ss-NMR results

Existence of (P/Sn)S4 tetrahedral; Deconvolution of the 31P NMR spectra indicates the amorphous content is ~12.4%.

Raman results SEM image

Nanozised primary particles

Uniform Sn doping

8 µm