Advanced Materials for Lithium-Sulfur...

Managed by UT-Battelle for the Department of Energy

Chengdu Liang

Staff Scientist

June 8, 2011

Advanced Materials for Lithium-Sulfur Batteries

Nancy Dudney, Jane Howe, Wujun Fu,

Zhan Lin, and Zengcai Liu

Beyond Lithium-Ion Batteries

Symposium IV

2 Managed by UT-Battelle for the Department of Energy

Battery Chemistry: Essential for Innovative Breakthrough for Li-Batteries

heavy compounds with O, P

light elements

Cathode material

Theoretical capacity [mAh/g]

Relative price

LiCoO2 275 1

LiNiO2 274 0.86

LiMn2O4 148 0.17

LiFePO4 170 0.15

S8 1675 0.017

O2 1675 or 3350

free

Ideal battery system: pure elements with every atom contributing to charge

transfer and energy exchange. Li-S/ Li-O will be the systems of choice!

Intercalation vs Conversion


Li/S:

2600 Wh/kg

Theoretical

Specific Energy

Li-S Batteries Hold the Promise for Next Generation of Battery Technology.

Source: Sion Power

• High Capacity

• High energy density

• Moderate Voltage

• Safe

• Compatibility

• Low Cost

• High abundance

Features of Li-S


Migration of S Poses the Major Challenge for Li-S Batteries.

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


S82- S4

2-

S Li

Polysulfide Shuttle •Self-discharge

•Capacity fading

•Cell resistance increase

•Poor cyclability

1) Cheon, S. E.; Choi, S. S.; Han, J. S.; Choi, Y. S.; Jung, B. H.; Lim, H. S. Journal of the Electrochemical Society 2004,

151, A2067-A2073. 2)Mikhaylik, Y. V.; Akridge, J. R. Journal of the Electrochemical Society 2004, 151, A1969-A1976.

•Passivate Li anode

•Decrease the diffusivity

of ions

•Gel electrolytes

•Solid electrolytes

•Physically absorb S

•High surface area

carbons

•Conducting

polymers

•Chemically immobilize

S

•S-polymers

•S-salts

Why Li-S Cannot Cycle Long?

S62-

S22-

Li2S


0 10 20 30 40 50 601.0

1.5

2.0

2.5

3.0

3.5

4.0

Vo

lta

ge

(V

)

Time (min)

Li-S Cell Has a Short Cycle-Life.

0 5 10 15 20 25 30 35 40 45 500.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

Dis

ch

arg

e C

ap

ac

ity

(m

Ah

)

Cycle Number

Increase of cycle #

Detrimental deposition of Li2S :

• Increase of cell resistance

• Decrease of cell capacity

Charge/discharge curves

charge

discharge

Cycle performance


1000 Cycle-Life is Possible.

0 200 400 600 800 1000

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800S

pe

cif

ic C

ap

ac

ity

(m

Ah

/g)

Cycle Number

Theoretical Max. 1675 mAh/g

Traditional Li/S cell

ORNL discovery


Approach to Improve Performance is Three-fold.

longevity of

cycle-life

C/S composites

electrolytes

& additives Li-metal anode

Enablers:

• Advanced synthesis

• In situ SEM

• Electrochemical

characterization

Goal: Understand and overcome the obstacles of cycling the Li-S battery

Retain S at the cathode

Reverse Li2S formation Heal the damaged Li anode


Activated Templated Carbon Gives Well Controlled Porosity for Sulfur Host.

C/S composites by using bimodal porous carbon

– Physical confinement of S in < 2nm pores

– Electronic contact of S

– Adsorption of polysulfides

– Ionic path through mesoporous

Sx2- Sx

2-

Sx2-

Sx2-

Sx2- Sx

2-

Sx2-

MPC Activated MPC

KOH

S8

discharge

charge

Micropores (<2nm): host sites for S

Mesopores (2-50 nm): path for Li+ transport


Simple Synthesis Procedure Eases the Preparation.

0.0 0.2 0.4 0.6 0.8 1.00

200

400

600

800

1000

MPC

a-MPC

Vo

lum

e A

ds

orb

ed

(c

c/g

ST

P)

Relative Pressure (P/P0)

0.0 0.2 0.4 0.6 0.8 1.00

200

400

600

800

1000 a-MPC

S_C01

S_C02

S_C03

S_C04

S_C05

S_C06

S_C07V

olu

me

Ad

so

rbe

d (

cc

/g S

TP

)

Relative Pressure (P/P0)

1. Soft-template synthesis of

mesoporous carbon

2. KOH activation

3. Sulfur infiltration

Three-step Synthesis of

Carbon/Sulfur Composite

Activ

atio

n

S L

oad

ing


Composite is Tailored with Sulfur Loading.

0 2 4 6 8 10 12 14 16 18 200.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

V

D

Pore Diameter (nm)

a-MPC

S_C01

S_C02

S_C03

S_C04

S_C05

S_C06

S_C07

0 5 10 15 200.0

0.2

0.4

0.6

0.8

1.0

Cu

mu

lati

ve

Po

re V

olu

me

(c

c/g

)

Pore Diameter (nm)

a-MPC

S_C01

S_C02

S_C03

S_C04

S_C05

S_C06

S_C07

0 10 20 30 40 50

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0

200

400

600

800

1000

1200

1400

1600

Po

re V

olu

me

(c

c/g

)

Sulfur Content (wt.%)

micropore volume

mesopore volume

total pore volume

surface area

Pore Volume VS Sulfur Loading

Pore size distribution Cumulated pore volume

• S preferentially fills the

micropores

• Pore Volume is the key

parameter for S loading

• Mesopores impart high surface

area to the composite


Sulfur Loading is Precisely Positioned.

Business Sensitive

TGA analysis of Sulfur Loading SEM and Elemental Maps

Elemental S is precisely

controlled within the

micropores


Cycling Performance (without Electrolytes Additives) is Greatly Improved by Nano-engineered Carbon Host which Retains Sulfur.

0 10 20 30 40 500

200

400

600

800

1000

1200

1400

1600

1800

bimodal porous carbon

mesoporous carbon

microporous carbon

Sp

ec

ific

Ca

pa

cit

y (

mA

h/g

)

Cycle Number

Note: specific capacity is per gram sulfur. Theoretical is 1675 mAh/g.

0 10 20 30 40 50

0

200

400

600

800

1000

1200

1400

1600

1800

Sp

ecif

ic C

ap

acit

y (

mA

h/g

)

Cycle Number

25%

40%

50%

60%

Pore size effect Loading effect


Electrolyte Additives Can Reverse Li2S Formation, Improving Cycle Life of Li/S Half-cells.

0 20 40 60 80 100 120 140 160 180 200

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

LiBr 0.05

LiBr 0.1m

LiBr 0.5 m

LiCl 0.05m

no additive

Sp

ecif

ic C

ap

acit

y (

mA

h/g

)

Cycle Number

Theoretical Max. 1675 mAh/g

Polymerization of electrolytes after 10 cycles

• Additives improve the

reversibility of Li2S

formation

• The polymerization of the

electrolytes plays an

important role on the

cyclability of Li-S cells

Traditional approach:

Avoid the formation of Li2S

Our approach:

Allow the formation of Li2S

and make it reversible

through a catalytic process


Catalyzed Reversibility of Li2S Formation Drives S back to Cycling.

S82-

S22-

S Li Reverse Shuttle

Ad

S62-

S42-

Li2S

Speculation on how the additives function?

1. React with Li2S and free the sulfur back to cycling.

2. Regenerate electrochemically at the charge cycle.


LiBr Additive Alters and Stabilizes Shape of Voltage Curves.

V of TESTER_SC34-01.009

I of TESTER_SC34-01.009

Time/min

403020100

Vo

lta

ge

/V

3.5

3

2.5

2

1.5

1

Cu

rre

nt/m

A

0.5

0.4

0.3

0.2

0.1

0



Time/min

100500

Vo

lta

ge

/V

3.5

3

2.5

2

1.5

1

Cu

rre

nt/m

A

0.5

0.4

0.3

0.2

0.1

0

Discharge Charge



Time/min

2520151050

Vo

lta

ge

/V

3.5

3

2.5

2

1.5

1

Cu

rre

nt/m

A

0.5

0.4

0.3

0.2

0.1

0



Time/min

35302520151050

Vo

lta

ge

/V

3.5

3

2.5

2

1.5

1

Cu

rre

nt/m

A

0.5

0.4

0.3

0.2

0.1

0

LiBr LiBr


Possible Mechanism for Reverse Shuttle Reaction

S8

e+SHx

2-SLx

-

Br-

Br

SLx- +

Lx=2,3,4

SLx2-

+ Br

e+Br-

SLx- + Br

BrSLx-

BrSLx-

+ Br

BrSLxBr

BrSLxBr Br-+

S1,22- Br-+

e+

e+

SLx- e+ SLx

2- e+ S1,22-

Hx=6,8

BrSLx- S1,2

2- Br-+e+

Discharging Charging

S8

e-

SHx2-

SLx-

Lx=2,3,4

SLx- + Br

BrSLx-

BrSLx-

+ Br BrSLxBr Br-+

e

SLx- e

SLx2-

e

S1,22-

Hx=6,8

-

- -

Br- e-Br

S1,22-

+ Br SLx- Br-+

BrSLx- S1,2

2-+ SHx2- Br-+

BrSLxBr S1,22-+ Br-+S8

Additives create additional reactions that reverse the formations of Li2S.


Bench-top Demonstration Gives Further Evidence that LiBr Catalyzes Reversibility of Li2S Formation.

Br2 (liquid) + Li2S (solid)

Li2Sx (solution) + LiBr (solution)

Images of Li2S in organic solvents:

Left, without Br2; right, with Br2

LiBr

In the charging cycle:

Br2 (cathode) + Li (anode)

Electrochemically generated Br2

proceeds to the following chemical

reaction

This reaction returns the Li2S solid back to

solution and accelerates the

electrochemical reaction, therefore

catalyzing the reversibility of Li2S

formation


Shuttles could Possible Heal Damaged Li Anode.

Br2 S2-x SxBr2

Over charging at the Cathode produces:

Migration through the electrolyte

Dendrite

dissolution

Over charging at the anode rebuilds:

Thick lithium metal anode

Li+

Re-deposition of lithium

Self-healing


A Major Drawback of LiBr Additive is Severe Corrosion of Cell Parts.

Corrosion of stainless steel parts

Corrosion of aluminum

current collector

Use carbon to replace all metal parts could be the solution.


Emerging Concerns of Electrolyte Compatibility Need to be Addressed

Polymerization and the carbonization of electrolyte

could cause problems for long-term cyclability .

Need further investigation of electrolyte composition.


Conclusions

Li-S chemistry is promising for next generation of batteries

– High energy density

– Low cost

– Environmental benignity

Advances in material development are essential

– Enhance electronic and ionic conductivities

– Inhibit the migration of sulfur species

– Reverse the formation of Li2S

Key challenges still remain

– Block the polysulfide shuttle completely

– Improve the compatibility of electrolytes with cell components


Acknowledgements

Funding support

LDRD

BES

VT program

User Facilities

Date post:	09-Oct-2020
Category:	Documents
Upload:	others
View:	0 times
Download:	0 times

Advanced Materials for Lithium-Sulfur...

Documents