Project ID #: ES025

Development of Advanced Electrolytes and Electrolyte Additives

Zhengcheng Zhang (PI)Y. Qin, A. Abouimrane, L. Zhang, Z. Chen and K. Amine

Argonne National Laboratory

Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting

Washington, D.C.June 7-11, 2010

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

2

Start Date: FY09 (New project) End Date: September 2014 Percent complete: 20%

Total project funding- 100% DOE

FY10: $300K

Timeline

Budget

Barriers

K. Amine, A. AbouimraneY. Qin, Z. Chen, L. Zhang (CSE/ANL)

L. Curtiss ( MSD/CNM/ANL) H. Iddir (MSD/CNM/ANL)

Project Lead: Zhang & Amine

Partners

Overview

Insufficient voltage stability High flammability, low safety Poor Cycle & calendar life Surface reactivity with electrodes

33

Develop advanced electrolyte with high voltage stability, combined with high lithium ion conductivity, high thermal stability, non toxicity, non-flammability and enhanced safety.

Identify functional electrolyte additives that provide stable solid electrolyte interface (SEI) and investigate their formation mechanism and their effects on improving the cell performance.

Objectives

4

Develop novel electrolyte systems that include sulfone-based electrolytes, hybrid electrolytes of sulfone with other type of solvents, such as carbonate, ionic liquid to enable high power high energy lithium ion batteries with superior safety for PHEV applications.

Investigate compatibility of new electrolytes with different battery electrode chemistries.

Investigate electrolyte additives that stabilize the interface between the charged electrode and electrolyte and improve the cell performance. Electrolyte additives include compounds containing oxalic group, ester group, vinyl group et al..

Approaches

5

0 1 2 3 4 5 6

EVS

BS

FS

TMS

Cur

rent

, (a.

u.)

Voltage, V

EMS

Electrochemical Window stability

• EMS-Ethyl methyl sulfone: 5.5V• TMS-Tetramethylene sulfone: 5.0 V• FS-1-Fluoro-2-(methylsulfonyl)benzene: 4.7 V

• BS-Butyl sulfone: 4.5 V• EVS-Ethyl vinyl sulfone: 4.3 V

Fig.1 CV profiles of 1M LiTFSI in various sulfones.

ADVANTAGES: Large electrochemical windows

- Can enable high voltage cathodes High to medium ionic conductivityWide liquid-phase temperature Lower viscosity (vs. ionic-liquid) low cost (byproduct in petroleum industry)

S

O

O

CH2CH3H3CS

CH2

CH2H2C

H2C

O O

EMS TMS

Sulfones as High Voltage Electrolytes

6

0.4 0.8 1.2 1.6 2.00.01

0.1

1

σ

(mS/

cm)

X, Mol of LiTFSI in Sulfone

EVS EMS TMS BS FS

Solvent Melting Point

EVS: ethyl vinyl sulfone[C2H5SO2CH=CH2]

<-50ºC

EMS: ethyl methyl sulfone

[C2H5SO2CH3]

35ºC

TMS: tetramethylene sulfone

[C4H8O2S]

23ºC

BS: butyl sulfone {[CH3(CH2)3]2SO2}

44ºC

FS: 1-fluoro-2-(methyl-sulfonyl)benzene

[C7H7FO2S]

50ºC

3 x 10-3 S/cm at 1.2M LiTFSI with EVS

Ambient Ionic Conductivity of Various Sulfones

Physical Properties of Sulfones

7

020406080

100

020406080

100

0 20 40 60 80 1000

20406080

100

Current density = 33.2mA/g

ChargeDischarge(a)

EMS

Current density = 33.2mA/g

(b)

Capa

city

(mAh

g-1

)

Charge Discharge

TMS

Current density = 16.6mA/g

(c)

Cycle number

ChargeDischarge

FS

Excellent cycling performance for cells using EMS or TMS as electrolyte solvents. No capacity fade for 100 cycles.

Good performance was obtained using glass fiber separator (better wettability).

Poor cycleability for cells using FS as electrolyte, even at low current density- Low ionic conductivity (10-4 S/cm)- High reactivity.

Sulfone based electrolyte has an issue with wettability when using conventional separators. Ceramic coated separators will be preferable.

Performance of Sulfone Based Electrolyte Using Li1+xMn2-xO4 Based System

8

Capacity (mAh/g)

Performance of Sulfone Based Electrolyte Using LiMn1.5Ni0.5O4 (4.8V) Based System

0 20 40 60 80 1000

20

40

60

80

100

120

140

I =10 mA.g-1

Charge Discharge

Capa

city (

mAh

g-1

)

-20 0 20 40 60 80 100 120 140

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Volta

ge (V

)

1st cycle3th cycle10th cycle

I = 10 mA.g-1

TMS

0 200 400 600 800 10000

20

40

60

80

100

I = 240 mA.g-1 Ca

pacit

y (m

Ah g

-1)

Cycle number

Charge Discharge

-20 0 20 40 60 80 100 1200.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Volta

ge (V

)

1st cycle500th cycle1000th cycle

I = 240 mA.g-1

TMS/EMC

1M LiTFSI EMS 1M LiTFSI EMS

1.0M LiPF6 EMS/EMC 5/51.0M LiPF6 EMS/EMC 5/5

9

1M LiPF6 in (EC/EMC 3/7) need about 2 seconds to ignite.

1M LiPF6 in (TMS/EMC 5/5) need about 45 seconds to ignite.

Strong flame is observed for 1M LiPF6 EC/EMC 3/7 electrolyte.

Weak flame with self extinguishedcharacter is observed for 1M LiPF6TMS/EMC 5/5 electrolyte. Non-flammability is expected for pure sulfone electrolyte without EMC.

Flammability Test of Sulfone Based Electrolytes

1M LiPF6 in (EC/EMC 3/7)

1M LiPF6 in (TMS/EMC 5/5)

10

Background - Electrolyte Additives

Reduction occurs at 1.7V (LiBOB) and1.6V (LiDfOB) and form a new SEI beforethe formation of conventional SEI layerat a potential of 0.6~0.8V. Kang Xu, Chem. Rev. (2004)

Formation of Solid Electrolyte Interface (SEI)

11

SEI Modification: Additives to form polymerized artificial SEI film

LiDFOB

LTFOP LTOP

LiBOB

Lithium Tetrafluoro(oxalato) Phosphate Lithium Tris(oxalato) Phosphate

Lithium Bis(oxalato) Borate Lithium Difluoro(oxalato) Borate

PO

OO

O

O

OO

O

O

OO

O

LiPF

F

F

O

O

O

O

F

Li

B

O

OO

O

O

O

O

O

Li BF

F O

O

O

O

Li

SEI Additives Candidates

12

LTFOP (1.7V vs Li+/Li)

LTOP (2.1V vs Li+/Li)

0.0 0.4 0.8 1.2 1.6 2.0 2.4-1.0

-0.8

-0.6

-0.4

-0.2

0.0

Pristine LTOP LTFOP

dQ/d

V, m

Ah/V

Cell potential, V vs. Li+/Li

PO

OO

O

O

OO

O

O

OO

O

Li

PF

F

F

O

O

O

O

F

Li

Li/Graphite half cell differential capacity profilesElectrolyte: 1.2M LiPF6 EC/EMC 3/7+2% Additive

1.7V 2.1V

Reduction Voltage of Different Additives

13

Addition of 1~3 wt% LTFOP improves the cycle life, 3% shows the best result. More additive decreases the capacity due to thicker SEI layer formation. Addition of 1~3 wt% LTOP shows the similar improvement on the cycle life.

0 50 100 150 200406080

100

Pristine 1 wt% LTOP 2 wt% LTOP 3 wt% LTOP

Norm

alize

d Ca

paci

ty, %

Cycle Number

406080

100 Pristine 1 wt% LTFOP 2 wt% LTFOP 3 wt% LTFOP

LTFOP

LTOP

PO

OO

O

O

OO

O

O

OO

O

Li

PF

F

F

O

O

O

O

F

Li

1C rate

Cycling Performance at 55oC of NMC/MCMB W/O Additives

55oC

55oC

14

PF

F

F

O

O

O

O

F

Li

AC Impedance of NMC/MCMB Cells W/O Additives

LTFOP 1 Oxalic group, Low Impedance

LTOP3 Oxalic groups, High Impedance

0 20 40 60 800

4

8

12

16

Z"

Z'

0 20 40 60 800

4

8

12

16

Pristine 1 wt% LTFOP 2 wt% LTFOP 3 wt% LTFOP

Z"Z'

0 20 40 60 80

4

8

12

16

Pristine 1 wt% 2 wt% 3 wt%

Z"

Initial

0 20 40 60 80

4

8

12

16

Pristine 1 wt% LTOP 2 wt% LTOP 3 wt% LTOP

1M

Z"

After 200 cycles

PO

OO

O

O

OO

O

O

OO

O

Li

15

Li/Li1.1(Ni1/3Co1/3Mn1/3)0.9O2

Li/MCMB

0 20 40 60 800.0

0.5

1.0

1.5

2.0

2.5

3.0

Pristine 1% LTFOP 2% LTFOP 3% LTFOP

Capa

city

, mAh

Aging Time, days

Li/NCM

0 20 40 60 80 100

0

1

2

3

4

Pristine 1% LTFOP 2% LTFOP 3% LTFOP

Capa

city

, mAh

Aging Time, days

Li/MCMB

Effect of LTFOP Additive on NMC & MCMB Electrode During Aging at 55oC

PF

F

F

O

O

O

O

F

Li

LTFOP improves the calendar life of both MCMB & NMC cathode at high temperature.

55oC55oC

16

With addition of 1% LTFOP, the onset thermal decomposition temperature of SEI was pushed above 175oC (70oC increase compared with the conventional SEI).

PF

F

F

O

O

O

O

F

Li

50 100 150 200 2500.0

0.5

1.0

1.5

2.0

Heat

Flo

w, W

/g

Temperature, oC

100 200 300 4000

5

10

50 100 150 200 2500.0

0.5

1.0

Heat

Flo

w, W

/g

Temperature, oC

Heat

Flo

w, W

/g

Temperature, oC

Pristine 1 wt% LTFOP

5°C/min scan rate

Effect of LTFOP Additive on Cell Safety

17

CH2 CH

O

O O

O

CH CH2

0 100 200 300 4000.4

0.6

0.8

1.0

Capa

city

Ret

entio

n

Cycle Number

Pristine 0.25% 0.5% 0.75% 1% 2%

3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane (TOS)

TOS improves the cycle life of the lithium ion cell. 1 wt% can provide maximum improvement.

0.0 0.4 0.8 1.2 1.6 2.0 2.4-0.8

-0.4

0.0

Pristine TOS

dQ/d

V, m

Ah/V

Cell potential, V vs. Li+/Li

Reduction Peak is not observed, the reaction could be radical triggered instead of electrochemically induced.

New Additive Candidate TOS

18

0 20 40 60 800.0

0.2

0.4

0.6

0.8

1.0

Capa

city

Ret

entio

n

Pristine 0.25 % TOS 0.5 % TOS 0.75 % TOS 1 % TOS

55oC Aging

0 20 40 60 800.4

0.5

0.6

0.7

0.8

0.9

1.0

Capa

city

Ret

entio

n

Aging Time, Day

Pristine 0.25 % TOS 0.5 % TOS 0.75 % TOS 1 % TOS 2 % TOS

55oC Aging

TOS only provides very good protection for MCMB anode. No effect on cathode.

Impedance of cell with 1% TOS additive is initially very high.

NCM Li1.1(Ni1/3Co1/3Mn1/3)0.9O2

MCMB

Effect of TOS on Performance of MCMB & NMC Electrode During Aging at 55oC

48

0 20 40 60

0

8

16Pristine 1% TOS

Z"

a

Initial

19

0 5 10 15 20 25 30 35 40 450

-2

-4

-6

-8

-10

-12

-14

Z''

Z'

Gen 2 Additive 1 Additive 2

1

O

O

O

Additive 1 Additive 2 Gen 2

Succinic Anhydride as Potential Additive

0 50 100 150 2000.00.20.40.60.81.01.21.41.61.82.02.22.42.62.83.0

Disc

harg

e cap

acity

(mAh

)

Cycly number

Additive 1 Additive 2 Gen 2

1.5 2.0 2.5 3.0

0.0

0.5

dQ/d

V

Voltage (V)

Gen 2 additive 1 additive 2

EC reduction

2.23V for 1

2.25V for 2

2

O

O

O

LiNi1/3Co1/3Mn1/3O2 //1.2M LiPF6 EC/EMC 3/7+1% Add//MCMB

55oC cyclingNMC/MCMB cell

12

12

20

0.5 1.0 1.5 2.00

1

2

3

4

dQ/d

V

Voltage (V)

Additive 5 Additive 6 Gen 2

O

O

O

5

Maleic Anhydride as Potential Additive

0 50 100 150 2000.0

0.5

1.0

1.5

2.0

2.5

3.0

Cell C

apac

ity (m

Ah)

Cycle Number

Additive 5 Additive 6 Gen 2

0 10 20 30 400

-5

-10

-15

-20

Z''

Z'

additive 5 additive 6 Gen 2

LiNi1/3Co1/3Mn1/3O2 //1.2M LiPF6 EC/EMC 3/7+1% Add.//MCMB

O

O

O

6

55oC cyclingNMC/MCMB cell

5: 1.12V

6: 1.31V

56

5 6

21

Summary EMS and TMS were identified as solvents with high voltage stability (around 5.5V)

Wettability issues were identified when using sulfone based electrolytes. Need ceramic or ceramic coated separators for maximum performance.

Both TMS/ LiTFSI and EMS/LiTFSI electrolytes showed stable cycling using both Li1+xMn2-xO4 and LiMn1.5Ni0.5O4 systems (1000 cycles was achieved for the 4.8V spinel).

New compounds with oxalic group were identified as excellent SEI formation additives.

Using Lithium tetrafluoro(oxalato) phosphate (LTFOP) and lithium tris(oxalato) phosphate (LTOP) as additives has led to a significant improvement in cycling and aging performance of both NMC cathode and MCMB anode at 55°C.

Additives with unsaturated bonds (TOS) also exhibit positive effect on cell performance, however, initial impedance is large.

Succinic anhydride (SA) and maleic anhydride (MA) are reduced prior the decomposition of EC forming a unique SEI layer. This new SEI (without EC participation) provides excellent cycling stability and low impedance, which benefit both high power and high energy applications.

22

Work Plan for FY 11

Continue investigating sulfone-based electrolytes. - Examine how sulfone-based electrolyte performs in graphite system - Attempt enabling graphite cell by co-solvent approach- Develop new additives to enable graphite system with these solvents

Investigate ionic liquids as new electrolyte solvents. - Screen existing ionic liquids and evaluate potential candidates- Develop new ionic liquids with good compatibility with cell components- Synthesize new additives to enable ionic liquids for Li-ion cells

Continue the development of electrolyte additives.- Examine other performance of succinic/maleic anhydride additives including SEI thermal stability, cell self-discharge, and storage property

- Initiate the SEI morphology and SEI component study by SEM, TEM, XPS, FT-IR, Raman et al.