Additives and Cathode Materials for High-Energy Lithium ... · Li + Li + Li + P S S S S S-x-S. y z....

Managed by UT-Battelle for the Department of Energy

Chengdu Liang

Oak Ridge National Laboratory

Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting, May

2013

Additives and Cathode Materials for High-Energy Lithium Sulfur Batteries

“This presentation does not contain any proprietary, confidential, or otherwise restricted information”

Contributors: Zhan Lin, Nancy Dudney, and Jane Howe

Project ID: ES105

2 Managed by UT-Battelle for the Department of Energy

Overview

• Timeline – Start June, 2010

• Technical barriers for EV and PHEV – Very High Energy Li-S Battery

(500 Wh/kg) by 2020 – Poor cycling of Li metal anode

• Budget – $220k FY10 – $350k FY11 – $350k FY12 – $350k FY13

• Partners – Oak Ridge National Laboratory – Center for Nanophase Materials

Sciences, ORNL – High Temperature Materials Lab,

ORNL • In situ SEM


Objectives and Relevance

• Objectives: – Improve the electronic conductivity of sulfur cathode by using high surface area

mesoporous carbon materials – Block the polysulfide shuttle to extend the cycle-life of Li-S batteries – Explore novel battery structure of all-solid Li-S batteries – Develop enabling materials for all-solid Li-S batteries

• Relevance: – Enables high-energy Li-S battery chemistry for EV and PHEV batteries – Addresses the cycling problems of Li metal anode


Milestones

Milestones: Target: 1. Confirm the earlier observation of long cycle-life in half cells

and expand the synthesis of sulfur/carbon composite materials of various sulfur loadings

2. Compare the performance for different concentrations of additives to the electrolyte

3. Investigate additives to the cathode material, including catalysts and alternative sulfur compounds

4. Design new liquid electrolytes, considering both poor/good solvents for Li polysulfides

5. Synthesize novel composite cathodes to improve cyclability

6. Explore full cell configuration to minimize excess lithium at the anode

7. Develop all-solid battery architectures

8. Identify enabling materials for all-solid Li-S batteries

Sep, 2010 Jan, 2011 Sep, 2011 Sep, 2011 Sep, 2012

Sep, 2012 Sep, 2013 on schedule

Sep, 2013 on schedule


Approaches to Fundamental Research of Li-S Batteries

Goal: Enabling long cycle-life of Li-S batteries by the elimination of the polysulfide shuttle phenomenon

Enable solid-state Li-S batteries − Eliminate the polysulfide shuttle − Promote ionic conductivity

Liquid-Electrolyte Batteries All-Solid-State Batteries

Tailor electrolytes for Li-S batteries − Reduce the polysulfide shuttle − Protect metallic lithium anode

Li S Li+ Conducting Solid Electrolyte S8

2-

S42-

Li S62-

S22-

S

S2-n-Dissolving

Liquid Electrolyte


Progress #1: P2S5 Additive to Liquid Electrolytes Protects Lithium Anode

P2S5

P2S5 + S2-n + Li Li3PS4

Chemical reaction of P2S5 passivation

The passivation layer has a chemical composition of Li3PS4, which is a superionic conductor!

fresh protected protection layer revealed by micrographs

Z. Lin, Z. Liu, W. Fu, N.J. Dudney, and C.D. Liang; “Phosphorous Pentasulfide as a Novel Additive for High-Performance Lithium-Sulfur Batteries,” Advanced Functional Materials, 2013, 23, 1064-1069


Progress #1: P2S5 Additive Facilitates Electrochemical Reaction of Li2Sn

1.5 2.0 2.5 3.0 3.5 4.0-100

-50

0

50

100

150

200

I (µA

)

E (V)

Li2S/P2S5

Li2S2/P2S5

Li2S4/P2S5

Li2S6/P2S5

Li2S8/P2S5

Z. Lin, Z. Liu, W. Fu, N.J. Dudney, and C.D. Liang; “Phosphorous Pentasulfide as a Novel Additive for High-Performance Lithium-Sulfur Batteries,” Advanced Functional Materials, 2013, 23, 1064-1069

P2S5 forms soluble complexes with Li2Sn (n, 1-8) in Tetraglyme

P2S5/Li2Sn complexes are electrochemically active

Increase in sulfur number


0 5 10 15 20 25 30 35 400

200

400

600

800

1000

1200

1400

1600

0

20

40

60

80

100with P2S5

without P2S5

with P2S5

without P2S5

A

Cou

lom

bic

effic

ienc

y (%

)Cycle number

Dis

char

ge c

apac

ity (m

Ah

g-1)

Progress #1: Good Cycling Achieved but Challenges Remain

Li film

SEI SEI

dendrites

• Problematic cycling of Li anode – Dendritic growth of lithium – SEI formation – Safety

• Dissolution of sulfur cathode – Loss of active material – Self discharge – Low energy efficiency (polysulfide shuttle)

All-solid Li-S battery configuration eliminates these problems!

Highlighted as journal cover on

Feb. 25, 2013 issue of Advanced

Functional Materials


0 1 2 3 4 5-80-60-40-20

0204060

i / µ

Acm

-2

E / V vs Li/Li+

Challenges of All-Solid Li-S Batteries

Li S Li+ Conducting Solid Electrolyte

0 1000 2000 3000 4000 5000-0.10-0.08-0.06-0.04-0.020.000.020.040.060.080.10

Appl

ied

cell

volta

ge /

VTime / min

80oC 25oC

The development of Li3PS4 solid electrolyte is a collaboration with a BES project. Liu and Liang et al. JACS, 2013, 135, 975-978

Nanostructured Li3PS4 meets the requirements for a solid electrolyte.

Solid electrolyte: • > 10-4 S/cm Ionic

conductivity at RT • Compatible with

lithium and sulfur or sulfur compounds

• Low interfacial resistance

Sulfur cathode: • Ionic conductivity • Electronic conductivity • Electrochemical

reversibility • Fast kinetics • Compatibility with solid

electrolytes

A photo of solid cells

S/C cathode

Li metal anode


Progress #2: Li2S@Li3PS4 Core-Shell Nanoparticles Conducts Li+

Z. Lin, Z. Liu, N.J. Dudney, and C.D. Liang; “A Lithium Superionic Sulfide Cathode for All-Solid Lithium-Sulfur Batteries,” ACS Nano, 2013 web-published Feb. 22

10 20 30 40 50 60

In

tens

ity (a

.u.)

2θ (degree)

(222)(311)(220)

LSS

NanoLi2S

Bulk-Li2S (200)

(111)XRD patterns

150 200 250 300 350 400 450 500 550

Li3PS4

LSS

Wavelength (cm-1)

Inte

nsity

(a.u

.)

NanoLi2S

Raman spectra

2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5-13-12-11-10-9-8-7-6-5

0.66 eV

0.74 eV

LSS NanoLi2S Bulk Li2S

log

σ / S

cm-1

T -1 / 1000K -1

0.38 eV

110100 90 80 70 60 50 40 30 20t / oC

106 X higher conductivity!

10 wt.% coating

SEM image

Nano

Li2S nanoparticles mixed with P2S5 yields core-shell nanoparticles Li2S@Li3PS4 which are designated as LSS (lithium superionic sulfide). The LSS has an excellent ionic conductivity. The core-shell structure was confirmed by XRD, SEM and Raman.


Progress #2: LSS Enables All-Solid Li-S Battery Cycling at 60 ºC

0 20 40 60 80 1000

102030405060708090

100

Cycle number

Colo

umbi

c Ef

ficie

ncy

(%)

LSS NanoLi2S

no polysulfide shuttle!

0 20 40 60 80 1000

150

300

450

600

750

900

1050

Discharge Charge

NanoLi2S

LSS

Capa

city

(mAh

g-1, n

orm

aliz

ed to

Li 2S

)

Cycle number

Discharge Charge

0

200

400

600

800

1000

1200

1400

1600

Capacity (mAh g

-1, normalized to S)

good cyclability

0 5 10 15 20 25 30 35 40 450

150

300

450

600

750

900

1050

C/10

2C1CC/2.5

C/5C/10

Capa

city

(mAh

g-1, n

orm

aliz

ed to

Li 2S

)

Cycle number

Discharge Charge

0

200

400

600

800

1000

1200

1400

1600

Capacity (mAh g

-1, normalized to S)

excellent rate performance

Z. Lin, Z. Liu, N.J. Dudney, and C.D. Liang; “A Lithium Superionic Sulfide Cathode for All-Solid Lithium-Sulfur Batteries,” ACS Nano, 2013 web-published Feb. 22

• LSS functions as a pre-lithiated cathode: no lithium metal is required for battery assembly

• Good cyclability has been achieved in an all-solid Li-S battery configuration

• Excellent rate performance has been obtained at 60 ºC

• No polysulfide shuttle observed


Progress #3: Overcome the Poor Ionic Conductivity of S Cathode through Chemical Reactions

Li+

Li+Li+

P

S-

-S

S-

S + (x+y+z) SWet-Chemistry

Li+

Li+

Li+

P

S

S

S

S

Charge/DischargeLi

a

b

+ 2(x+y+z) (x+y+z)

Li+

P

S-

-S

S-

S + Li+Li+

S2-

Li+

Li+

S-

Li+

Li+

Li+

P

S

S

S

S

S-

x

-S y

S-z

S-

-S

x

y

z

x,y,z from 0 to 8

Key problem for S cathode: Poor ionic conductivities of S and its discharge products

(a) Lin and Liang patent pending (b) Z. Lin, Z. Liu, W. Fu, N.J. Dudney, and C.D. Liang, “Lithium Polysulfidophosphates: A Family of Lithium-Conducting Sulfur-Rich Compounds for Lithium-Sulfur Batteries,” Angew. Chem.-Int. Ed. (under review)

• Lithium polysulfidophosphates were discovered by reacting Li3PS4 with elemental sulfur

• This new family of sulfur rich compounds are able to be discharged and charged through reversible cession and formation of S-S single bond


Progress #3: XRD and Raman Spectra Confirm the Reaction of Sulfur with Li3PS4

Peaks related to S-S bond

125 130 135 140 145 150 155 160 165 170 175

Li3PS4+3

Li3PS4+5

SLi3PS4+6

Inte

nsity

(a.u

.)

Wavelength (cm-1)

460 465 470 475 480 485 490

S

Li3PS4+3

Li3PS4+5

Li3PS4+6

Inte

nsity

(a.u

.)

Wavelength (cm-1)

10 20 30 40 50 60 70 80

Inte

nsity

(a.u

.)

2θ (degree)

S

Li3PS4

Li3PS4+5

100 200 300 400 500 600

Li3PS4

Li3PS4+3

Li3PS4+5

Li3PS4+6Inte

nsity

(a.u

.)

S

Wavelength (cm-1)

• XRD confirms the formation of new materials

• Raman reveals the polysulfide chains of the lithium polysulfidophosphate


Progress #3: Ionic Conductivity of the Cathode is a Function of Sulfur to Li3PS4 Ratio

2 3 4 5 6 7 8-5.4

-5.1

-4.8

-4.5

-4.2

-3.9

-3.6

Li3PS4+n

n

Log

σ (S

cm-1)

2.8 2.9 3.0 3.1 3.2 3.3 3.4 3.5-5.0

-4.8

-4.6

-4.4

-4.2

-4.0

-3.8

-3.6

log

σ (S

cm-1)

1000/T (K-1)

Ea = 0.37 eV

Li3PS4+5

90 80 70 60 50 40 30 20t / oC

Room temperature conductivity as a function of sulfur in SE

Arrhenius plot

Room temperature ionic conductivity of Li3PS4+5 is 107 times higher than that of Li2S!


Progress #3: All-solid Li-S Batteries Have Excellent Cyclability and Rate Performance

0 50 100 150 200 250 3000

200

400

600

800

1000

1200

1400

1600

Discharge Charge Discharge Charge

Cycle number

RT

60 oC

0

100

200

300

400

500

600

700

Cap

acit

y (m

Ah

g-1, n

orm

aliz

ed t

o S

)

C

apacity (m

Ah

g-1, n

orm

alized to

Li3 P

S4+n )

0 10 20 30 40 50 600

200

400

600

800

1000

1200

1400

1600

Discharge Charge

Cap

acity

(mA

h g

-1, no

rmalize

d to

Li3 P

S4+

n )

Cap

acit

y (

mA

h g

-1, n

orm

alize

d t

o S

)

2CC

C/5

C/2.5

C/10C/10

Cycle number

0

100

200

300

400

500

600

700100% coulombic efficiency!

All-solid Li-S cells can be cycled at room temperature with better performance at elevated temperatures

Z. Lin, Z. Liu, W. Fu, N.J. Dudney, and C.D. Liang, “Lithium Polysulfidophosphates: A Family of Lithium-Conducting Sulfur-Rich Compounds for Lithium-Sulfur Batteries,” Angew. Chem.-Int. Ed. (under review)


Progress #3: All-solid Li-S Batteries Have a Different Electrochemical Reaction Path

0 300 600 900 1200 15000.0

0.5

1.0

1.5

2.0

2.5

3.0

Volta

ge (V

)

Capacity (mAh/g)

RT discharge RT charge 60C discharge 60C charge

60 °C RT

Solid electrolyte

0 200 400 600 800 100012000.0

0.51.0

1.52.0

2.53.0

Volta

ge (v

s. L

i/Li+ )

Capacity (mAh g-1)

Discharge

Charge

The two-plateau feature of the liquid electrolyte cell.

Liquid electrolyte

• No polysulfide plateau presents in the all-solid cell • Over 85% energy efficiency at 60 ºC


Cathode Structure Preserved after Intensive Cycling

SEM and elemental maps before cycling

SEM and elemental maps after 300 cycles at 60 °C

C

C

P

P S

S

Images prove the advantages of all-solid Li-S: • No structural change of the cathode after intensive cycling • No sulfur migration was observed


Future work • Develop new sulfur-rich compounds with ionic conductivity greater than 10-5 S/cm

– Reduce cell resistance – Boost room temperature performance – Enable high rate cycling

• Investigate charge-discharge mechanism of sulfur-rich compounds in the all-solid battery configuration

– Guide materials discovery

• Explore solid electrolytes of high ionic conductivity and low interfacial resistance – Increase energy efficiency

• Optimize the electrode structure to achieve homogeneous mixing of active materials with electronic conductors

– Reduce cell resistance

• Evaluate the full cell performance of Li-S batteries with optimized thickness of the solid electrolyte layer

– Develop practical batteries


Summary • Relevance: Exploratory research of Li-S battery chemistry leads to discoveries of advanced

materials for high-energy batteries with potential use in EVs and PHEVs

• Approach: – Electrolyte additives facilitate the electrochemical cycling of Li2S and protect the metallic lithium

anode – All-solid battery structure completely eliminates the polysulfide shuttle phenomenon – Solid electrolyte membrane prevents the migration of sulfur – Li+-conductive cathode materials enable the cycling of all-solid Li-S batteries

• Accomplishments and progress: – Discovered new electrolyte additive of P2S5 for conventional Li-S batteries with a liquid electrolyte – Demonstrated the success of cycling all-solid Li-S batteries – Developed Li2S@Li3PS4 Core-Shell nanoparticles as pre-lithiated cathode material for all-solid Li-S

batteries – Discovered a new family of sulfur-rich ionic conductors as the cathode materials for all-solid Li-S

batteries

• Future work: – Optimize the electrode structure to facilitate electrochemical cycling of all-solid Li2S batteries – Explore solid electrolyte with high ionic conductivity – Evaluate the full cell performance of all-solid Li-S batteries with optimized cell components


Technical Back-Up slides

Business Sensitive


Challenges for Li-S Battery with Liquid Electrolytes

• Intrinsic sulfur migration: liquid phase diffusion

• Irreversible Li2S formation: both cathode and anode

• Poor Li anode cyclability: corrosion/ Li2S deposition/ dendrites

S8 Li2S8 Li2S6 Li2S4 Li2S2 Cathode:

Anode: Li Li+

soluble/liquid form S migration through diffusion

Li2S

Li2S

insoluble solid /irreversible deposition

charge discharge

solid

solid

2.4 V 1.8 V

X

X

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Additives and Cathode Materials for High-Energy Lithium ... · Li + Li + Li + P S S S S S-x-S. y z....

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