Project ID #: es025

Advanced Electrolyte Additives for PHEV/EV Lithium-ion Battery

Zhengcheng Zhang, Lu Zhang, Khalil Amine

Argonne National Laboratory

Vehicle Technologies Program Annual Merit Review and Peer Evaluation Meeting

Washington, D.C.June 9-13, 2011

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

2

Project start date: FY09 Project end date: FY14 Percent complete: 20%

Timeline

Budget

Barriers

Partners

Project Overview

Total project funding- 100% DOE funding

Funding received in FY10: $200K Funding for FY11: $200K

Electrolyte/electrode surface reactivity

Battery cycle life & calendar life Battery abuse tolerance

US Army Research Lab Northwestern University Center of Nanoscale Materials (ANL) Industrial Partners: EnerDel, Quallion,

Central Glass Inc. Project Lead - Zhengcheng Zhang

33

To develop an efficient, inexpensive functional electrolyte ADDITIVE technology to address the barriers existing in the current lithium ion battery system such as poor cycle life, calendar life and battery abuse tolerance;

To establish the ADDITIVE structure-property relationship by screening a variety of existing chemical compounds and develop (design, synthesize and evaluate) brand new electrolyte additives having superior performance with the aid of the theoretical modeling;

FY10’s objective is to evaluate and categorize the existing chemical compounds as possible SEI ADDITIVE to stabilize the carbonaceous anode/electrolyte interphase and improve battery performance.

Main Objectives

4

Technical Approach

Screen, identify various functional compounds including oxalic, carboxylic anhydride, vinyl, heterocyclic containing compounds based on the empirical rule of Degree of Unsaturation (DU) as potential electrolyte ADDITIVEs;

Evaluate the battery performance of the best ADDITIVE screened using LiNi1/3Co1/3Mn1/3O2/MCMB full cell testing vehicle: the capacity retention with cycling at various temperatures, storage property at elevated temperature, impedance growth with cycling, and cell power capability;

Propose the mechanisms of the SEI formation by the new ADDITIVE with aid of theoretical calculation method and provide insights for future research of advanced additives.

5

Achievements and ProgressPrevious Achievement (FY10) Current Work and Achievement (FY11)

Three categories of existing compoundswere screened and tested as lithium ionbattery electrolyte additives for prolonged cycle life and improved safety:

Oxalato phosphates:

Succinic, methyl succinic anhydride:

Maleic and methyl maleic anhydride:

PF

F

F

O

O

O

O

F

Li PO

OO

O

O

OO

OO

OO

O

Li

OO

O OO

O

OO

O OO

O

As a continuation of FY10’s work, this year we have investigated the following additives:

3-oxabicyclo[3.1.0]hexane-2,4-dione:

Disubstituted maleic anhydride:

Heterocyclic compounds:

OO

O

OO

O O

O

O

F

F

OO

O

N

N

O

OON

N

N

O

OO

6

Formation of Solid Electrolyte Interphase

Electrochemical process of graphite based anode

Pristine Llithium uptake Lithium removal

Lithiated graphite (LiC6) is thermodynamically unstable in contact with the electrolyte component including electrolyte solvent, lithium salt, impurities…

Lithiated graphite (LiC6) is dynamically stable in contact with the electrolyte due to the existence of solid electrolyte interphase (SEI) layer formed at the electrolyte/electrode interphase during the first charging process.

7

1. SEI Additive to enable cell operation (cell enabler):For new electrolytes (i.e. PC based electrolyte), the SEI additive is mandatory and indispensible for cell performance. SEI is formed on graphite anode surface to prevent the electrolyte solvent co-intercalation and carbon exfoliation with gas evolution.

2. SEI Additive to improve cell performance (cell improver):For conventional electrolyte (for example 1.2M LiPF6 EC/EMC), the SEI additive is the performance improver.

2-1. Artificial SEI forms prior the regular SEI and suppress the formation of the regular SEI. A brand new artificial SEI is formed: (A-SEI) 2-2. New SEI forms in addition to the formation of regular SEI by EC decomposition: A dual SEI is formed: (D-SEI)

SEI Additive Categories and Functions

ADDITIVE

8

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

1.7V 2.1V

LTFOP (1.7V vs Li+/Li)

LTOP (2.1V 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

Artificial SEI Formation(SEI additive suppresses the regular SEI formation)

Traditional SEIFormation was suppressed

9

In MCMB/Li half cell, additive reduction occurs at 1.6V, prior to the conventional SEI formationWhich take place at a potential between 0.6~0.8V vs Li+/LiElectrolyte: 1.2M LiPF6 EC/EMC 3/7 +2% LiDfOB

NMC/MCMB Full Cell

0.0 0.5 1.0 1.5 2.0-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

1.2 M LiPF6

1.2 M LiPF6 + 0.5% LiDFOB 1.0 M LiDFOB

dQ/d

V, m

Ah/V

Cell potential, V

New SEI

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.20.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0% LiDFOB 0.5% LiDFOB 2% LiDFOB 3% LiDFOB 5% LiDFOB

dQ/d

V, m

Ah/V

Cell voltage, V

New SEI

MCMB/Li Half Cell

Dual SEI Formation(SEI additive reduced prior the conventional SEI formation on Graphite)

Conventional SEI

In full cell, the peak at 2.1V is proportional to the concentration of additive, indicating the the new SEI formation by the additiveprior to the formation of conventional SEIat a potential ~3.0V.

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Empirical Rules for SEI Additive Screening

Degree of unsaturation (DU) should be more than two; The higher degree of unsaturation, the better SEI additive?

Rings count as one degree of unsaturation; Double bonds count as one degree of unsaturation; Triple bonds count as two degrees of unsaturation.

DU* Formula DU* Formula

*

OO

O

OO

O

O

O O

O

OB

OO

O

O

O O

O

O

BOO

O

F

F

2

3

4

6O O

O

OO

O

O O

ON5

O

OOLi

7Li O O

ON

O

O

PO

OO

O

O

OO

OO

OO

O

Li9

11

Proposed SEI Formation Additive Candidates

SS

O

S

S

17

O

O

O

O

18 22

O

O

O

OO

O

F

F

OO

O

Cl

Cl

23

OO

O

O O

O

O

24

OO

O

OO

25

O

O

O

26

OOO

27

O

28

OO

P

OCl

14

NH

HN

O

O

O

15

N

HN

O

O

16

Potential Compounds with multiple unsaturation degrees as Electrolyte Additives

O

O

OO

O

O

O

O

1 23

O

O

O O

O

O4

5 6

O

O

O

O

O

O

O

N

N

O

OO

N

N

N

O

OO

7

NO O

O

O

ON

N

N

O

OO

89 10

1211 13

NN

O

S

O

O

12

1st Group: Succinic Anhydride (SA) and Its Derivatives

SA as basic additive structure:Evaluate how the electronic structure and stereo hindrance affects the performance

O

O

O

O

O

O

O

24

O

O

O

O

O

25

OO

O

26

O

O

O

27

O

O

O1 2 3

O

O

OO

O

O

4

O

O

O

O

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Differential Capacity Profiles of Additive 3

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0-6-4-202468

dQ/d

V

Voltage (V)

1 wt% Additive 3 Pristine (Gen 2 electrolyte)

OO O

Diff. capacity vs voltage of MCMB-1028/Li1.1(Ni1/3Co1/3Mn1/3)0.9O2 coin cells in 3E7EMC/PF12 with or without 1 wt% Additive 3. The charge and discharge rate was C/10 with cut-off voltage 3 ~ 4 V.Peak at 2.25V is due to the new SEI formation through the decomposition of Additive 3, and the traditional SEI is not formed, indicating a brand new artificial SEI.

3-oxabicyclohexane-2,4-dione

1.0 1.5 2.0 2.5 3.0-0.2-0.10.00.10.20.30.40.50.6

dQ/d

VVoltage (V)

1 wt% Additive 3 Pristine (Gen 2 electrolyte)

2.25V

Traditional SEI by EC

14

Cycling Performance of Additive 3

Fig. (Left): Two cycle capacity retention of MCMB/NMC cell at 25°C; The first and second cycle charge and discharge capacities are comparable to that of the pristine electrolyte. Fig. (Right): Capacity improvement for cells in 3E7EMC/PF12 with Additive 3. 0.2% Additive 3 addition to the pristine electrolyte showed the most improvement. (cycled at 55 ◦C with 1C rate; cut-off voltage is 2.7 ~ 4.2 V).

0 50 100 150 2000.00.51.01.52.02.53.0

Dchg

cap

. (m

Ah)

Cycle number

Pristine (Gen 2 electrolyte) With 0.1 wt% Additive 3 With 0.2 wt% Additive 3

1 21.0

1.5

2.0

2.5

3.0

Capa

city

(mAh

)

Cycling number

With 0.2% Additive 3-charge With 0.2% Additive 3-discharge Pristine electrolyte-charge Pristine electrolyte-discharge

0.2% Add. 3

0.1% Add. 3

Without additive

15

AC Impedance of Cells with Additive 3

0 4 8 12 160

-2

-4

-6

-8

Z''

Z'

Pristine (Gen 2 electrolyte) With 0.2 wt % Additive 3

After formation (before cycling)

Fig. Impedance profiles of MCMB/NMC cell before cycling at 25°C; The Rb is smaller for the additive cell indicating the more conductive SEI layer formed compared to that of the pristine electrolyte. Unlike most of the existing commercial additives that show high initial interfacial impedance, ANL-Additive 3 shows similar initial interfacial impedance as the one without additive (stable and thin SEI).

Rb

AC impedance profile of MCMB/NMC cells in 3E7EMC/PF12 with or without 0.2 wt% additive 3. The cells were charged to 3.8 V with a charge rate of 1C.

16

Chemical Structure Effect on AC Impedance

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

2

O

O

O

Additive 3 showed very low initial impedance, however Additives 1, 2 showed a much larger initial impedance than the electrolyte without additive. Although good capacity retention was achieved with Additive 1 & 2, the power of the cell based on these additives is jeopardized.

After Formation

0 4 8 12 160

-2

-4

-6

-8

Z''

Z'

Pristine (Gen 2 electrolyte) With 0.2 wt % Additive 3

OO O

3

17

FT-IR Identification of SEI Formed by Additive 1

2000 1500 1000 50035

40

45

50

55

Tran

smitt

ancy

Wavenumber(cm-1)

Pristine MCMB SEI Additive 1

-C=O vibration

IR spectrum of new SEI( MCMB anode after formation)

Wavenumber (cm-1)

IR spectrum of Additive 1

-C=O vibration

18

O

O

OO

O

O

5 6

O

O

O

7

22

O

O

O

F

F

O

O

O

Cl

Cl

23

2nd Group: Maleic Anhydride (MA) and Its Derivatives

Evaluate how the electronic structure and the effect of stereo substitution group on MA basic additive on the cell performance

19

Differential Capacity and Initial Capacity of Additive 7

1 21.5

2.0

2.5

3.0

3.5

4.0

Capa

city

(mAh

)

Cycling number

with Additive 5-charge with Additive 5-discharge with Additive 6-charge with Additive 6-discharge with Additive 7-charge with Additive 7-discharge Pristine -charge Pristine -discharge

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

dQ/d

V

Voltage (V)

with Additive 5 with Additive 6 with Additive 7 Pristine electrolyte

Additive 7

O

O

OO

O

O

5 6

O

O

O

7

20

Capacity Retention, Impedance Profiles of Additive 5-7

O

O

OO

O

O

5 6

O

O

O

7

The cells were cycled at 55 ◦C with and without 1wt% of Additives. The charge rate was 1C. The cut-off voltages were 2.7 ~ 4.2 V. AC impedance profile of MCMB/NMC cells in 3E7EMC/PF12 with or without 1 wt% additives. The cells were charged to 3.8 V with a charge current of 1C.

0 50 100 150 2000.0

0.5

1.0

1.5

2.0

2.5

3.0

Capa

city

(mAh

)

Cycle number

With Additive 5 with Additive 6 with Additive 7 Pristine electrolyte

0 10 20 30 400

-5

-10

-15

Z''

Z'

with Additive 5 with Additive 6 with Additive 7 Pristine electrolyte

21

3rd Group: Heterocyclic Compounds (Ongoing)

N

N

O

OO

NO O

N

N

N

O

OO

8 9 10

11

NN

O

NH

HN

O

O

O

15

N

HN

O

O

16

22

Collaborations/Interactions

US Army Research Laboratory- Dr. Richard Jow and Dr. Kang Xu for technical and information exchanges; Argonne National Laboratory

- Dr. Larry Curtiss for calculation of reduction/oxidation potentials of additives by quantum chemical methods; Northwest University

- Professor Harold Kung for SEI characterization XPS and SEM; EnerDel

- Dr. Yumoto for the electrode and technical discussions.

23

Proposed Future Work

For the rest of this fiscal year of 2011 and FY12, we are proposing the following research work:

Continue the quantum chemical and electrochemical screening of the remaining compounds in the 1st, 2nd and 3rd groups outlined in the slides 12, 18 and 21 and expand the potential additive database;

Perform a study on the thermal stability of SEI formed by the best additives using differential scanning calorimetric and ARC method;

Investigate the lithium-ion cell self-discharge property at elevated temperature and evaluate the effect of new SEI additives on the cell power capability using HPPC test profile;

Characterize SEI morphology by SEM, TEM, XPS, IR, Raman et al. analytical methods;

Initiate the design and synthesis of the new advanced electrolyte additives.

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Summary New organic compounds containing oxalic, carboxylic anhydride, vinyl,

heterocyclic groups were proposed and identified based on the empirical rule of Degree of Unsaturation (DU) as potential electrolyte ADDITIVEs;

Electrochemical experiments (Li/graphite half cell) were performed and the succinic anhydride based additives, maleic anhydride based additives can be reductively decomposed forming a brand new SEI on surface of the graphite surface prior to the formation of conventional SEI layer at 0.5~0.8V vs Li/Li+;

The cell containing 3-oxabicyclohexane-2,4-dione (ANL-Additive 3) as an additive shows very low initial impedance and excellent capacity retention at both room temperature and at 55oC. This additive is very promising for extending the cycle and calendar life of lithium battery for automotive applications;

New additives with heterocyclic groups were proposed and will be investigated further in FY12.