Novel Electrolytes and Additives

Project Id: ES023

D.P. AbrahamGang Cheng, Steve Trask

Vehicle Technologies Program Annual Merit Review 

Washington DC, June 7 ‐ 11, 2010

This presentation does not contain any proprietary or confidential information

2

Overview

Timeline• Start date: FY09

• End date: On‐going

• Percent complete: 

‐ project on‐going

Budget• Total project funding

‐ 100% DOE

• FY09:  $200K

• FY10:  $300K

Barriers• Performance

• Calendar/Cycle Life

• Abuse tolerance

Partners• Argonne colleagues

• University of Rhode Island

• CSIRO, Australia

• Kevin Gering, Idaho NL

• Industrial collaborators

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Objectives

Performance, calendar-life, and safety characteristics of Li-ion cells are dictated by the nature and stability of the electrolyte and the electrode-electrolyte interfaces.

Our goal is to develop novel electrolytes and electrolyte additives for PHEV batteries.An ideal electrolyte would display the following characteristics:– Low Cost, non‐toxic, non‐flammable – Non‐reactivity with other cell components– Wide electrochemical stability window, 0 to >5 V– Wide temperature stability range, ‐30 to +50 °C– Excellent ionic conductivity to enable rapid ion transport– Negligible electronic conductivity to minimize self‐discharge– Stability over the 10y battery life

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Approach

Investigate novel electrolytes that include glycerol carbonate, and modifications thereof. The modified glycerol carbonates will include methyl ethers, ethyl ethers, and oligoethylene oxide ethers.

Investigate electrolyte additives designed to react and stabilize the cathode surface to improve cell calendar life.  The additives may  include unsaturated ethers, vinyl silanes, and other compounds.

Examine room‐temperature ionic‐liquids (RTIL), and mixtures of RTIL and organic electrolytes, to enable high‐safety, high‐performance batteries.

Recommend promising electrolytes and electrolyte additives for use in ABRT cells (calendar life and safety studies)

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MilestonesYear 2Year 1 Year 3

GC acquisition/developing purification techniques

Electrolyte Additive synthesis/preparation

Ionic liquids acquisition and electrolyte preparation

Property (voltage window, ionic conductivity, etc.) measurement

Data documentation

Current status

Performance examination (cycling behavior, etc.)

“GC derivatives” synthesis

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Technical Accomplishments

Investigation of GC‐based electrolytesExamined performance/cycling behavior of electrolyte mixtures containing various Li‐salts

Developed techniques to replace the H (in the OH of GC) with other species, and conducted experiments with these  “GC‐derivative” solvents

Examined performance/cycling behavior of electrolyte mixtures

Identified new electrolyte solvents and electrolyte additives that can enhance cell life

Effects on cell performance, life, and safety are being determined

Electrochemical studies with ionic liquids Examined electrode performance/cycling behavior

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Point of Reference - Electrode and Electrolyte Chemistries

Gen 2 electrolyteEC:EMC (3:7 by wt.) + 1.2M LiPF6

Cu(-)

Al(+)

Mag-10 graphiteParticle size ~5 μm

Celgard separator25 μm thk

LiNi0.8Co0.15Al0.05O2Particle size ~ 5 μm

Gen2 Cathode35μm thick coating

Gen2 Anode35μm thick coating

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Glycerol Carbonate from a commercial manufacturer was dried and purified before use in cells

Impure GC+

Molecular sieves(vacuum dried)

Decanted GC+

Molecular sieves(vacuum dried)

o o

OH

decant vacuum filtration

12h 12h Pure

GC drying/purification was conducted in an Ar-atmosphere glove box

FT-IR spectrum of glycerol carbonate

OO

O

OH

O-H stretching: 3446 cm-1

C=O stretching: 1777 cm-1

C-O stretching: 1171 cm-1, 1049 cm-1

o

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Graphite Electrode – 1.2M LiPF6 in GC:DMC (2:8)

0.2 0.6 1 1.4 1.8 2.2

dQ/d

V

SEI formation peaks

lithiation

delithiation

0 0.05 0.1 0.15 0.2 0.25 0.3

Voltage, V

dQ/d

VLi-ion Intercalation-

deintercalation peaks

delithiation

lithiation

0

0.4

0.8

1.2

1.6

2

0 100 200 300 400Capacity, mAh/g

Volta

ge, V

Graphite vs. Li/Li+C/15 rate, 2-0 V

lithiation

Graphite electrodes can be cycled in GC-based electrolytes. The SEI that forms apparently protects the graphite from solvent intercalation.

1st cycle2nd cycle

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0 0.1 0.2 0.3 0.4

1st Cycle2nd Cycle

0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

1st Cycle2nd Cycle

0

0.4

0.8

1.2

1.6

2

0 100 200 300 400

Graphite Electrode – 1M LiBF4 in GC:DMC (2:8)

dQ/d

V

SEI formation peaks

lithiation

delithiation

Voltage, V

dQ/d

VLi-ion Intercalation-

deintercalation peaks

delithiation

lithiation

Capacity, mAh/g

Volta

ge, V

Graphite vs. Li/Li+C/15 rate, 2-0 V

lithiation

Graphite electrodes can be cycled in LiBF4-based electrolytes. The SEI that forms apparently protects the graphite from solvent intercalation.

1st cycle2nd cycle

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3 3.2 3.4 3.6 3.8 4 4.2 4.4

Oxide Electrode – 1.2M LiPF6 in GC:DMC (2:8)

dQ/d

V

lithiation

delithiation

Lithium is consumed during the first charge cycle to form a surface film on the oxide electrodes. (Significant Li consumption is not observed for EC-based electrolytes.) The GC apparently oxidizes during the first cycle, but not in subsequent cycles.

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

0 100 200 300 400Capacity, mAh/g

Volta

ge, V

Gen2 oxide vs. Li/Li+C/30 rate, 3-4.3 V

1st cycle2nd cycle

Surface filmformation

Voltage, V

1st cycle2nd cycle

Oxide electrodes can be cycled in GC-based electrolytes. But, significant lithium consumption occurs during the first cycle. Later cycles show reasonable data.

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3 3.2 3.4 3.6 3.8 4 4.2 4.4

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

0 40 80 120 160 200

Oxide Electrode – 1M LiBF4 in GC:DMC (2:8)

dQ/d

V

lithiation

delithiation

Lithium is consumed during the first charge cycle to form a surface film on the oxide electrodes. (Significant Li consumption is not observed for EC-based electrolytes.) The GC apparently oxidizes during the first cycle, but not in subsequent cycles.

Capacity, mAh/g

Volta

ge, V

Gen2 oxide vs. Li/Li+5mA/g, 3-4.3V, 55C

1st cycle2nd cycle

Surface filmformation

Voltage, V

1st cycle2nd cycle

Oxide electrodes can be cycled in GC-based electrolytes. Lithium consumption during the first cycle is smaller than that for LiPF6electrolytes. Later cycles show reasonable data.

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1

1.5

2

2.5

3

3.5

4

4.5

0 50 100 150 200 250

Oxide/Graphite Cell – 1.2M LiPF6 in GC:DMC (2:8)

Capacity, mAh/g

Volta

ge, V

Oxide(+) vs. Graphite (-) 3-4.1 V

1st cycle2nd cycle

Lithium consumption during GC oxidation depletes Li‐inventory in full cell. Therefore, full cell cycling behavior is not good 

Li consumption during surface film formation

Similar results for LiBF4 electrolyte

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Preparing the methyl ester version of GC (aka GCAc)

4000 3500 3000 2500 2000 1500 1000

70

75

80

85

90

95

100

Tran

smitt

ance

(%)

wavenumber (cm-1)

Glycerin Carbonate devirvative

1792 1742

1387

1233

11681052

772

FTIR Spectrum of GCAc

3000 cm‐1 , ‐CH31792 and 1742 cm‐1 C=O stretching1233 cm‐1, 1168 cm‐1, and 1052   C‐O stretching

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3 3.2 3.4 3.6 3.8 4 4.2 4.4

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

0 50 100 150 200 250

Oxide Electrode – 1.2M LiPF6 in GCAc:DMC (2:8)

dQ/d

V

lithiation

delithiation

The lithium consumption observed for GC-based electrolytes is NOT seen in GCAc-based electrolytes.

Capacity, mAh/g

Volta

ge, V

Gen2 oxide vs. Li/Li+C/30 rate, 3-4.3 V

1st cycle3rd cycle

Voltage, V

1st cycle3rd cycle

Oxide electrodes can be cycled in GCAc-based electrolytes

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0.2 0.6 1 1.4 1.8 2.2

Graphite Electrode – 1.2M LiPF6 in GCAc:DMC (2:8)

Graphite electrodes can be cycled in GC-based electrolytes. The SEI that forms apparently protects the graphite from solvent intercalation.

0.0

0.4

0.8

1.2

1.6

2.0

2.4

0 50 100 150 200 250 300 350 400Capacity, mAh/g

Volta

ge, V

Graphite vs. Li/Li+2-0 V

lithiation

2nd cycle

30th cycle10th cycle

0.0

0.5

1.0

1.5

2.0

2.5

0 100 200 300 400

Volta

ge, V

Capacity, mAh/g

1st cycle 1st cycle

dQ/d

V

SEI formation peaks

lithiation

delithiation

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Oxide/Graphite Cell – 1.2M LiPF6 in GCAc:DMC (2:8)

3.0

3.2

3.4

3.6

3.8

4.0

4.2

4.4

0 40 80 120 160

Charge 1Discharge 1Charge 5Discharge 5Charge 10Discharge 10Charge 15Discharge 15Charge 20Discharge 20Charge 25Discharge 25

Capacity, mAh/g

Volta

ge, V

3 3.2 3.4 3.6 3.8 4 4.2 4.4

Charge 1Discharge 1Charge 5Discharge 5Charge 10Discharge 10Charge 15Discharge 15Charge 20Discharge 20Charge 25Discharge 25

dQ/d

V

Voltage, V

Capacity retention is better when upper voltage is limited to 4V. This observation suggests that the electrolyte oxidizes at higher voltages (> 4V).

12mA/g, 3-4.3V, 55°C

Oxide/Graphite (Full) cells show reasonable cycling behavior in GCAc-based electrolytes

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2,5 DHF showed promise as an electrolyte additive in early tests

Baseline electrolyte: stable to 5.2V vs. Li2%DHF‐added electrolyte: 4.75V vs. Li peak2,5 DHF is oxidized at high voltagesAdditive could form passivation layer on positive electrode

3-4.1V, 2X @ 0.16mA, 50X @ 0.5mA,2X @0.16mA0.16 mA (or 12.5 mAh/g), 0.5 mA (or 39 mAh/g)Cycling at 55degC

Capacity data from the cells are similar. 2,5DHF addition to Gen2 electrolyte does 

not seem to have a beneficial effect on cell capacity retention.

Conclusions from tests conducted in NMC(+)//Gr(‐) were similar.

Glassy carbon vs. Li

19

A new family of electrolyte solvents/additives has been identified – performance and life tests are in progress

0

20

40

60

80

100

120

140

160

180

0 10 20 30 40 50

Cycle Number

Dis

char

ge C

apac

ity, m

Ah/

g

Gen2Gen2+0.3wt%A1Gen2+0.3wt%A2Gen2+0.3wt%A3Gen2+0.3wt%A4

Small additive concentrations (0.3 wt%) improve capacity retention. Cells containing higher concentration (3 wt%) show lower capacity and poorer capacity retention. Of the above, A3 appears to be the best candidate.

Compounds A1, A2, A3 and A4 are derived from the same family of compounds. They are also being evaluated as solvents 

1st 2 cycles at C/12 rateNext 50 cycles at C/4 rate

Oxide//Graphite cell 30°C, 3-4.1 V

This behavior is not observed when formation is conducted at 55°C. Related to electrode wetting

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1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2

Voltage, V

dQ

/dV

1.8 2 2.2 2.4 2.6 2.8 3 3.2

dQ/dV

Voltage

dQ/dV data – Effect of Additives (see previous slide)

Additives induce significant changes in dQ/dV data Peaks between 1.8 and 3V associated with reactions at graphite.

Gen2Gen2+0.3wt%A1Gen2+0.3wt%A2Gen2+0.3wt%A3Gen2+0.3wt%A4

1st cycle at C/12 rate

Oxide//Graphite cell 30°C, 3-4.1 V

21

0

40

80

120

160

200

0 50 100 150 200 250 300

Cycle Number

Dis

char

ge C

apac

ity, m

Ah/

g

0

2

4

6

8

10

12

0 5 10 15 20Z (Re), ASI

-Z (I

mg)

, ASI

Effect of additives on cell impedance and long-term cycling behavior

Gen2+0.3wt%A1Gen2+0.3wt%A2Gen2+0.3wt%A3Gen2+0.3wt%A4

Impedance of cells containing additives are comparable or better than that of cells with Gen2 electrolyte.

Oxide//Graphite cell after 50 cycles, 30°C

Gen2+0.3wt%A3

Long‐term cycling behavior of cells, both at RT and at higher 

temperatures is currently being evaluated. 

Oxide//Graphite cell 30°C, 3-4.1V

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Ionic Liquid Electrolytes

P14TFSI = N‐butyl‐N‐methylpyrrolidinium bis(trifluoromethanesulfonyl)imide 

P13FSI = N‐propyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide 

Salt

LiTFSI

LiFSI 

Electrolytes were dried at 50°C for 48h (in a vacuum oven located inside a glovebox) before use.

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Oxide(+)//Li cell with P14 electrolyte, tested at 55°C

3.03.13.23.33.43.53.63.73.83.94.0

0 50 100 150 200Capacity, mAh/g

Vol

tage

, V

-0.008

-0.006

-0.004

-0.002

0.000

0.002

0.004

0.006

0.008

3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4Voltage, V

dQ/d

V, A

h/V

0

40

80

120

160

200

0 5 10 15 20 25Cycle Number

mA

h/g

0

20

40

60

80

100

Effi

cien

cy, %Disch Cap

Ch Cap

Eff iciency, %

Voltage: 3 – 4 VCurrent: 6.25 mA/g (~C/24)

‐ The NCA electrode cycled well in the 3‐4V range; the  capacity values and dQ/dV plots are as expected.

‐ The cells retained their original capacity after 20 cycles at 55°C.

‐ We did not test cells at higher voltages, i.e., >4V vs. Li.

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Graphite(-)//Li cell with P13 electrolyte, tested at 55°C

1. Cell delithiation capacities increased during the early cycles and steadied around 300 mAh/g.  These cells can be  cycled more than a hundred times.

2. Electrochemical eff. during first cycle is ~52%, 2nd cycle is ~90% and >99% after 10 cycles. SEI formation during early cycles consumes significant amounts of Li. 

-0.0020

-0.0015

-0.0010

-0.0005

0.0000

0.0005

0.0010

0.0015

0.0020

0 0.5 1 1.5 2

Voltage, V

dQ

/dV

, A

h/V

Charge 1Discharge 1Charge 2Discharge 2

Electrolyte Reduction

-0.2000

-0.1500

-0.1000

-0.0500

0.0000

0.0500

0.1000

0.1500

0.2000

0 0.1 0.2 0.3 0.4 0.5

Voltage, VdQ

/dV

, A

h/V

Charge 1Discharge 1Charge 2Discharge 2

Lithiation-Delithiation

0.0

0.5

1.0

1.5

2.0

2.5

0 100 200 300 400 500 600Capacity, mAh/g

Vol

tage

, V

Charge 1 Discharge 1Charge 2 Discharge 2Charge 8 Discharge 8Charge 20 Discharge 20

0

50

100

150

200

250

300

350

0 5 10 15 20 25Cycle Number

Delithiation capacityvs.

Cycle Number

Voltage Range: 2 – 0 VApplied Current: 10.2 mA/g (~C/20)

Graphite staging behavior is as expected.

Electrolyte reduction starts ≈1.5V.  Seen only in 1st cycle.

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Ionic Liquids Study Summary

P14_TFsi ‐ worked well in NCA(+)/Li cell, 3‐4V, gave expected capacity

P14_TFsi ‐ cell worked, in Graphite/Li cell, 1.5‐0V, but capacity less than half of expected value

P14_TFsi ‐ NCA(+)/Gr cell, poor electrochemical behavior

P13_Fsi ‐ worked well in Graphite/Li cell, 1.5‐0V, 3‐4V, gave expected capacity, cell can be cycled more than a hundred times

P13_Fsi ‐ NCA(+)/Li cell did not work – electrolyte apparently degrades >3.5V

P13_TFsi ‐ NCA(+)/Gr cell, poor electrochemical behavior

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Summary and Future Work

Novel electrolytes need to be developed to meet the cost, calendar life and safety requirements of batteries for PHEV applications– These batteries may be deep‐discharged > 5000 times during the lifetime of 

the automobile and should have a calendar life of more than 10 years

We will continue our investigations of novel solvents that include  glycerol carbonate (GC), and modifications thereof, which includes– Preparation of compounds derived from GC

– Performance/cycling behavior of various solvent‐salt electrolyte mixtures

– Properties (electrochemical stability window, temperature stability, etc.) of “promising” electrolytes

Develop criteria to identify new electrolyte additives that can enhance cell life by protecting electrode surfaces from reactions with the electrolyte– Examine multifunctional additives that can simultaneously affect both positive 

and negative electrodes

Continue studies on ionic liquids and on mixtures of ionic liquids and conventional electrolytes– Examine electrode performance/cycling behavior under PHEV conditions

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Related Publications and Presentations

1. Electrolytes For Lithium And Lithium‐Ion BatteriesArgonne Invention Report, ANL‐IN‐10‐003

2. Electrolytes For Lithium And Lithium‐Ion BatteriesArgonne Invention Report, ANL‐IN‐08‐071

3. Electrochemical Behavior of electrolytes based on glycerol carbonate and related solvents

Abraham et al., manuscript in preparation