Fluorinated Electrolyte for 5-V Li-Ion Chemistry

DOE Annual Merit Review MeetingWashington D.C.

June 8-12, 2015

Project ID #: ES218

Zhengcheng(John) Zhang (PI)Kang Xu (Co-PI), Xiao-Qing Yang (Co-PI)

Argonne National Laboratory

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

Project Overview

Timeline Barriers

Budget Partners

o Project start date: Oct. 1, 2013 o Project end date: Sept. 30, 2015 o Percent complete: 50%

o Low oxidation stability of electrolyte o High, low temperature performanceo Poor cycling life due to the instability of

electrode/electrolyte interfaceo Safety concern associated with high

flammability and reactivity

o Total project funding- 100% DOE funding

o Funding received in FY14: $500 Ko Funding for FY15: $500 K

o U.S. ARL (collaborator)o BNL (collaborator)o LBL (collaborator)o Prof. Brett Lucht (XPS)o Dr. Marshall Smart (JPL)o Dr. Larry Curtiss (DFT)

2

3

Project Objective

To develop advanced electrolyte materials that can significantly improve the electrochemical performance without sacrificing the safety of lithium-ion battery of high voltage high energy cathode materials to enable large-scale, cost competitive production of the next generation of electric-drive vehicles.

To develop electrolyte materials that can tolerate high charging voltage (>5.0 V vs Li+/Li) with high compatibility with anode material providing stable cycling performance for high voltage cathodes including 5-V LiNi0.5Mn1.5O4(LNMO) cathode and high energy LMR-NMC cathode recently developed for high energy high power lithium-ion battery for PHEV/EV applications.

3

Technical Approach/Strategy

LUMO

HOMO

µa

µc

Ecell

Anode

Cathode

LUMO

HOMO

µa (Li, C or Si)

Ecell = 4.3 ev

SEI

Ideal Unknown Electrolytes

LUMO

HOMOµc

SEI

Ecell = 4.7 ev

Anode

Cathode µc (LiMO2)

Anode

Cathode

µa (Li, C or Si)

Cathode Passivation Additive

LUMO

HOMOµc (LiNi0.5Mn1.5O4)

SEI

Ecell = > 4.7 ev

Anode

Cathode

µa (Li, C or Si)

SEI

New Solvents with Intrinsic Stability

SOA Carbonate Electrolytes

µa (LTO)

Ecell = 3.2 ev Ecell = 3.2 ev

µa (LTO)

Ewindow Ewindow

EwindowEwindow

Expand the electrochemical window of electrolyte solvents by molecular engineering to enhancethe oxidation stability of the electrolyte (5.0 V vs Li+/Li) without compromising the salt solubility,ionic conductivity, fast ion transportation, wide temperature range and safety.

High compatibility with cell component (separator, electrode, binder et al.) SEI formation capability on carbonaceous anode surface.

4

The Challenges for High Voltage LiNi0.5Mn1.5O4 Cells1. Variations in performance depending on the synthesis process/sintering conditions

SEM images of LiMn1.5Ni0.5O4 samples prepared by employing various precursors: (a) and (b); Crystallographic planes of (c) octahedral and (d) truncated octahedral spinel synthesized by different synthesis techniques;

Cycling performance of LNMO cell with various particle morphologies

1) Manthiram et al., Energy Environ. Sci., 2014, 7, 1339; K. Zaghib et al., RSC Adv., 2014, 4, 154-167.

(c) (d)

2. Instability of the cathode surface in contact with electrolyte at 4.7 V, especially at high T

charge

55oC

Heterogeneous charging voltage profile and heavy deposition observed on LNMO electrode surface (SEM), indicating the instability of SOA electrolyte at high charging voltage at high temperature.

OO

O

O O

O

P

F

FF

F

FFLi

+

Hu et al., J. Power Sources, 236, (2013), 175-180.

Technical Accomplishments and Progress

5

Molecular StructureOxidation Potential (Pox/V)

Anion EffectPotential (Pox/V)

Reduction Potential (Pred/V)

Stretch Bond Potentials (Pred/V)

7.10 (6.62, EMC)6.26 (PF6: HF forms)5.79 (TFSI: H transfer) 0.03

1.40 (CF3CH2-O)1.49 (CH3-O)

7.70 (6.46)6.28 (PF6)5.83 (TFSI) 0.30

7.96 (6.46)7.69 (PF6)5.76 (TFSI) 1.29

1.54 (CF3CH2-O)2.39 ((CF3)2CH-O1.47 (CF3-O)

7.25 (6.51, DEC)7.35 (PF6)- 0.22 1.65 (CF3CH2-O)

7.30 (6.80, PC)6.21 (PF6)5.33, 5.44, 5.87 (TFSI)

1.54 (spontaneous C-O bond opening)

7.24 (6.95, EC)6.44 (PF6)5.80 (TFSI) 0.33 1.56 (CHF-O)

6.97

6.246.05 (PF6)5.90, 5.19, 5.22 (TFSI) 0.01 1.50

Electron-withdrawing groups of -F and -Rf groups lower the energy level of the HOMO, thus increasethe theoretical oxidation stability of the F-compounds.

The electron-withdrawing effect varies with the structure and the position of the substitution groups.

OO

O

CF3

OO

O

F

CO

O

O

CF3

CF3

F

OF2C

CHF2

OO

O

OO

O

CF3

OO

O

CF3

CF3

OOF3C

O

CF3

CF3

OO

O

CF3F3C

Electron-Withdrawing Effect of F- and F-alkyl by DFT

6

7  

Synthesis of Fluorinated Carbonates

F-EMC

TF-DEC

FMiPC

HF-DEC

TFPC

TFP-PC-E

OF2C

CHF2

OO

O

ab,cd,e

f

g,h

af

g,h

b,c

d,e

145 (m/z)

87 (m/z)

OO

O

H2CO

F2C

CHF2

S.M. (0.02%)

Ukn. 1 (0.06%) Ukn. 2 (0.12%)

TFP-PC-E(Tetrafluoropropyl-Propylene Carbonate-Ether)

OO

F2C

CF2HO

F2C

CHF2

OCO

O

H HH

Spectroscopic Characterization and Identification

1H-NMR Spectrum GC-MS Spectrum

8

0.5M LiPF6 in F-cyclic carbonate/F-EMC=1:1 (v/v); LNMO/Li half cell, fully charged at 4.9, 5.0, 5.1 and 5.2V

Oxidation Stability of Cyclic F-Carbonates

F-cyclic carbonate FEC > TFPC > EC > TFE-PC-Eoxidation stability:

OO

O

F

OO

O

CF3

OO

O

OF2C

CHF2

OO

O

> > >

0 10 20 30 400.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20 EC/F-EMC TFPC/F-EMC FEC/F-EMC TFE-PC-E/F-EMC

Time (h)

Cur

rent

(mA

)

RT

5.2V5.1V5.0V4.9V

0 10 20 30 400.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20 EC/F-EMC TFPC/F-EMC FEC/F-EMC TFE-PC-E/F-EMC

Time (h)

Cur

rent

(mA

)

55 C

5.2V

5.1V5.0V4.9V55oC

F-electrolyte showed small difference in leakage current at RT; at 55oC, the current increases significantly Due to the catalytic reaction at the interface of LNMO/electrolyte at high temperature, EC and TFE-PC-E is

extremely unstable.

CO

O

O

CF3

CF3

F

9

HF-DEC > TF-DEC ≈ F-EMC > DMC

O O

O

OO

O

CF3OO

O

CF3F3C OO

O

CF3

* Oxidation stability at room temperature; high temperature data deviates from the RT data due to the thermal decomposition.

0.5 M LiPF6 in FEC/F-linear carbonate = 1:1 (v/v); LNMO/Li half cell, fully charged at 4.9, 5.0, 5.1 and 5.2 V at RT and 55oC.

0 10 20 30 400.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

Time (h)

Cur

rent

(mA

)

RT FEC/F-EMC FEC/TF-DEC FEC/DMC FEC/HF-DEC

5.2V5.1V5.0V4.9V

0 10 20 30 400.000.020.040.060.080.100.120.140.160.180.200.220.24

Time (h)C

urre

nt (m

A)

55C FEC/F-EMC FEC/TF-DEC FEC/DMC FEC/HF-DEC

5.2V5.1V5.0V4.9V

> ≈ >

55oC ?

Oxidation Stability of Linear F-Carbonates

10

Mixed Solvent Ratio and Salt Concentration on Oxidation

0 10 20 30 40 50 60 70 80 90

4

6

8

10

12

14

16

18

20

22

245.2 V

5.1 V

5.0 V

Cur

rent

(uA

)

FEC content (%)

4.9 V

0.5 M LiPF6 in FEC:DMC (from 1:9 to 9:1) FEC:DMC = 5:5 with LiPF6 from 0.5 M to 1.25 M

FEC content affects the voltage stability at high charge voltages, but less significant at lower voltages (4.9 and 5.0V)

0.00 0.25 0.50 0.75 1.00 1.25 1.50

4

6

8

10

12

14

5.2 V

5.1 V

5.0 V

Cur

rent

(uA

)

FEC content (%)

4.9 V

No significant effect of LiPF6 salt concentration on voltage stability, especially at charge voltages below 5 V.

11

0 1 2 3 4 50.0

0.5

1.0

1.5 1st cycle

Volta

ge (V

)

Capacity (mAh)

OF2C

CHF2

OO

O

OO

O

CF3

00.5

11.5

22.5

33.5

44.5

5

0 1 2 3 4 5

Volta

ge/ V

Capacity/ mAh

FEC_Full cellFEC_Anode

A12 anode

F

OO

O

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

0 1 2 3 4

Vol

tage

(V)

Capacity (mAh)

Gen 2

CO

O

O

CF3

CF3

F

0 50 100 150 200 250 300 350 400 450

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Gen 2 TFPC-3

Volta

ge (V

)

Capacity (mAh/g)

Compatibility of Electrolytes with Graphite Anode

12

Fluorinated Electrolyte for LNMO/Graphite Full Cell

F-EC(3) F-EMC(5) F-EPE(2) LiPF6 (1.0 M) LiDFOB (1%)

HVE 3 shows great compatibility with graphite surface as indicated by the improvement in LNMO/graphite cells comparedwith Gen 2 electrolyte, especially at 55 ºC.

0 20 40 60 80 1000

20

40

60

80

100

120

140

160

180

Capa

city

(mAh

g-1

)

Cycle Number

HVE 3 Charge HVE 3 Discharge Gen 2 Charge Gen 2 Discharge

(a)95

96

97

98

99

100

101

HVE 3 Coulombic efficiency Gen 2 Coulombic efficiency Co

ulom

bic

Effic

ienc

y (%

)

25 oC

0 20 40 60 80 1000

20

40

60

80

100

120

140

Capa

city

(mAh

g-1

)

Cycle Number

HVE 3 Charge HVE 3 Discharge Gen 2 Charge Gen 2 Discharge

55 oC

86

88

90

92

94

96

98

100

HVE 3 Coulombic efficiency Gen 2 Coulombic efficiency

Coul

ombi

c Ef

ficie

ncy

(%)

(b)LNMO/graphite, 3.5-4.9 V

Hu, Zhang et al. Electrochem. Commun., 2013, 35, 76.

HVE3HVE3

OO

O

F

O

OO CF3F2HC

CF2

O

F2C

CF2H P

F

FF

F

FFLi

OB

O F

F

O

O

Li+ ++ +

13

0 5 10 15 200

1

2

3

4

5

HVE-3 electrolyte @ RT HVE-3 electrolyte @ 55 oC Gen 2 electrolyte @ RT Gen 2 electrolyte @ 55 oC

Volta

ge (V

)

Time (day)

Cathode: LiNi0.5Mn1.5O4Anode: Graphite A12Formation condition: 3.5-4.9 V for 3 cycles, C/10 rate at RT

Self-discharge Test: fully charge to 4.9 V at C/10 (RT or 55 oC), then rest and monitor the voltage change. Data points are taken every 5 minutes.

Gen 2: SOA electrolyte (1.2M LiPF6 EC/EMC 3/7 in weight ratio)

HVE-3*: 3rd Generation high voltage F-electrolyte(1.0M LiPF6 FEC/FEMC/F-EFE 3/5/2 in volume ratio

* Ref: Hu & Zhang Electrochem. Commun. 35 (2013) 76-79.

Improved Self-Discharge of LNMO/Graphite Cells

14

Gen 2 HVE 3

1.2M LiPF6 EC/EMC 3/7 weight 1.0M LiPF6 FEC/F-EMC/F-EPE 3/5/2 in volume

Fluorinated Electrolytes are Not Flammable

Video Here Video Here

15

TEM Characterization of Cycled LNMO Cathode

Etching of LNMO particles is pronounced in baseline cell due to the oxidative decompositionof EC-EMC solvents and the generation of HF leading to Mn and Ni dissolution.

Mn and Ni exist in the cycled baseline electrolyte with much higher concentration (ICP-MSdata, not shown).

LNMO surface is intact with HVE electrolyte, and more integrated when LiDFOB additive wasemployed, indicating the improved chemical and electrochemical stability of F-electrolyte.

Gen 2 HVE 3 HVE 3+ Additive

16

0 1 2 3 4 5 6 7 8 9 10-50

0

50

100

150

200

250

300

350

400

450

500

550

600

Cu Kβ

F KαP Kα

Cu LαNi Kα

Mn Kα

Cu Kα

O Kα

Cou

nts

E/ KeV

C Kα

0 1 2 3 4 5 6 7 8 9 10-200

0

200

400

600

800

1000

1200

1400

Cu Kβ

Cu Lα

F Kα

P Kα

Ni KαMn Kα

Cu Kα

O Kα

Co

un

ts

E/ KeV

C Kα

0 1 2 3 4 5 6 7 8 9 10

0

1000

2000

3000

4000

5000

6000

Cu KβCu Lα

P Kα

Ni KαMn Kα

Cu Kα

O Kα

Cou

nts

E/ KeV

C Kα

Anode of Gen2 cell showed significant amount of nanoparticles (a few nm) of transitional M species in thecarbon black region, which might catalyze the parasitic reactions.

However, anode of HVE3 + Additive cell showed quite different morphology of the transition M: less amountand deposition/agglomeration (~10nm), less catalytic effect leading to less reductive decomposition ofelectrolyte.

Gen 2 HVE 3 HVE 3 + Additive

pristine

TEM Characterization of Graphite Anode

17

Charging

Li+

Lithiated graphite

Discharge

Partially lithiated graphite

Lithiated LNMO

Li+

Li metal will discharge first

Graphite LNMO

Li

DelithiatedLNMO

Li metal or SLMP

Press and contact with electrolyte

Lithiated graphite

Li metallithiation

Anode Graphite

Lithiated graphite

Graphite anode

Spacer

LNMO cathode

Separator

Spacer

PP gasketWave washer & cap

Case

LiLiLi Li

(a) (b)

(c) (d)

Hu & Zhang et al., Electrochem. Commun., 2014, 44, 34-37.

(a) LNMO/graphite cell assembly with incorporated lithium metal; (b) lithium metal working mechanism at the formation cycles; (c) electrochemical prelithiation of graphite anode; (d) direct shorting of graphite anode and Li.

0 20 40 60 80 1000

20406080

100120140160

Capa

city

(mAh

g-1

)

Cycle Number

HVE with Li metal HVE 4.9 V control Gen 2 4.9 V control

(a)

0 10 20 30 40 50 60 70 80 90 1008687888990919293949596979899

100

Cou

lom

bic

effic

ienc

y / %

Cycle number

55oC

HVE-3 + Li reservoir

HVE3

Gen2

HVE-3 + Li reservoir

Gen2HVE-3

Compensation of Lithium Loss by a Lithium Reservoir

18

Thermal Stability of FEC-Based Electrolytes: An NMR Study

FEC+LiPF6

FEC+LiTFSI

FEC

5 days @ 50oC

1H-NMR

HaHb,c

HaHb,c

FEC+LiPF6

O O

O

F@ 50oC

19F-NMRP

F

FF

F

FFLi

O O

O

FHbHc

Ha

5 days

2 days

O O

O

H H

OO

O

* *H

P

F

FF

F

FFLi

FEC+LiPF6

FEC+LiTFSI

FEC

19

31P-NMR

0.5 M LiPF6in FEC

P

F

FF

F

FFLi

5 days @ 50oC

2 days @ 50oC

Initial state

O O

O

P

F

FF

F

FFLi

F

-HF O O

O

+ HF radical

polymerization O O

O

OO

O

O O

O

OO

O

O O

O

OO

O

O O

O

OO

O

PF

FF

FF+ LiF

H2O or ROHP

FFF

O+ HF or RF

Heating

in solution

PF5

Proposed FEC Thermal Decomposition Pathway:

Thermal Stability of FEC-Based Electrolytes

20

15 days @ 50oC

2 days @ 50oC

2 days @ RT

Pure TFPC (no LiPF6)

Method: 1 M LiPF6 in TFPC, heated @ 50 °C for 15 days

a b c

1H NMR spectra of TFPC-3 electrolyte from harvested LNMO/graphite cells; TFPC remained stable during cycling at high temperature.

Thermal Stability of TF-PC Based Electrolytes

21  

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100

120

140

160

180

200

Spe

cific

Cap

acity

(mA

h/g)

Cycle number

50

60

70

80

90

100

Gen 2

TFPC-3

Coulom

bic Efficiency (%

)

0 20 40 60 80 100 120 140 1603.0

3.5

4.0

4.5

5.0

Volta

ge (V

)

Specific Capacity (mAh/g)

3.9 4.2 4.5 4.8-60

-30

0

30

60

90

Voltage (V)

dQ/d

V (m

Ah/

V)

1st cycle, C/10 C/3 @ RT

LNMO/Li half-cell with TFPC-3 electrolyte performs much better than the baseline cell Improved oxidation stability on LNMO Passivation of Li metal anode due to the thermodynamic instability

Cell Performance of TF-PC Based Electrolyte TFPC-3

TFPC-3OO

O

CF3

O

OO CF3P

F

FF

F

FFLi+ + 1.0 M

22

0 10 20 30 40 500

20

40

60

80

100

120

140

160

Spe

cific

Cap

acity

(mA

h/g)

Cycle number

50

60

70

80

90

100

TFPC-3

TFPC-3 + 10 wt% FEC

Coulom

bic Efficiency (%

)

0 20 40 60 80 100 120 140 1600.00.51.01.52.02.53.03.54.04.55.05.5

TFPC-3 TFPC-3 + 10 wt% FEC

Volta

ge (V

)

Specific Capacity (mAh/g)

1st cycle, C/10 C/3 @ RT

2.0 2.2 2.4 2.6 2.8 3.00.0

0.1

0.2

Voltage (V)

dQ/d

V (m

Ah/

V)

Presence of FEC as an additive in the TFPC electrolyte may promote the formation of a more stable SEI on graphite

OO

O

CF3

O

OO CF3P

F

FF

F

FFLi+ + 1.0 M OO

O

F

+ Additive

RT Cell Performance of TF-PC Based Electrolyte TFPC-3

23

0 10 20 30 40 500

20

40

60

80

100

120

140

160

Spe

cific

Cap

acity

(mA

h/g)

Cycle number

50

60

70

80

90

100

Gen 2

TFPC-3

TFPC-3 + 2 wt% LiDFOB

Coulom

bic Efficiency (%

)

C/3 @ 55 oC

0 20 40 60 80 100 1200

-20

-40

-60

-80

-100

-120

TFPC-3 + 2 wt% LiDFOB Gen 2TFPC-3

Z''(b

)

Z'(a)

EIS after 50 cycles @ 55 oC

LNMO/A12 cells with TFPC-based electrolyte exhibits improved capacity retention at 55 oC, which is attributed to the superior oxidation stability of TFPC during high-temperature cycling.

New formulations and additives for TFPC-based electrolyte is ongoing.

TF-PC Based Electrolyte for LNMO/Graphite Cell at HT

OO

O

CF3

O

OO CF3P

F

FF

F

FFLi+ + 1.0 M + LiDFOB Additive

24

ARL Tasks: Novel Additives

A. v. Cresce, S. M. Russell, O. Borodin, D. Tran, K. XuElectrochemistry Branch, Army Research Lab, Adelphi, MD 20783

• Design of new additive/co-solvent structures

• Synthesis, purification and structural characterizations

• Electrochemical characterizations• Fundamental understanding of

interphasial process

DOE BATT ARLFR 14 $100K $100KFR 15 $100K $100K

The fate of phosphate in electrolyte• Phosphate ends up on cathode and anode• Fluorinated alkyls substructure on cathode

HR-XPS conducted on both cathode and anode cycled in baseline and HFiP-containing electrolytes• P 2p absent in control samples• P2p on test samples

• 5~10 X more on cathode than anode

• C1s for CF3 only found on cathode

Philosophy for New Additives Structure

Design Concept:• Additives interact with both cathode and anode in the cell• Conventional approach: cathode-specific or anode-specific;

cocktail • Hollistic approach: key structural elements that are effective

in forming either cathode or anode SEIs are synthetically-integrated in the same molecule• Both high HOMO and low LUMO

A CA C

Computational Aid (Borodin):• QC prediction of HOMO/LUMO can be both very accurate• Reduction and oxidation potentials cannot predict the consequent

interphase chemistry and properties

• Organic synthesis/electrochemical testing/surface characterization/organic re-synthesis (Xu, Cresce, Russell)

B3LYP/6-31+G** optimization, gas-phase not PCM eV eVO V HOMO LUMO SMILES

112/CCO3CCC-B3LYP-631xGss.out -0.29624 0.00664 -8.06 0.18 COc(=O)OCCC (MePrCO3)22/CCO3Ccc-B3LYP-631xGss.out -0.28179 -0.01912 -7.67 -0.52 COc(=O)Occc

314/CCO3Cctc-B3LYP-631xGss.out -0.28822 -0.00968 -7.84 -0.26 COc(=O)OCc#c

423/C4F6H3CO3Cctc-B3LYP-631xGss.out -0.29754 -0.02028 -8.10 -0.55 C(C)(C(F)(F)(F))(C(F)(F)(F))Oc(=O)OCc#c

55/C4F6H3CO3Ccc-B3LYP-631xGss.out -0.29177 -0.02851 -7.94 -0.78 C(C)(C(F)(F)(F))(C(F)(F)(F))Oc(=O)Occc

611/C3F6HCO3Cctc-B3LYP-631xGss.out -0.30199 -0.0261 -8.22 -0.71 C(C(F)(F)(F))(C(F)(F)(F))Oc(=O)OCc#c

COc(=O)OCCC (MePrCO3)

Design Strategy for New Additives

From Computer to Glassware…

Synthesis of the new concept compounds:

• 9 successes, >15 failures(1) (2)

(3)

(4)

All new compounds• No hits in SciFinder

• New molecules never existed before• Patent in process

• Complete ARL IP• Ready for scale-up at ANL MERF

Key sub-structures synthetically integrated into a single molecule

O

O OCH

H2C

CHC

CF3

CF3

Functional Carbonates

Functional Silanes Phosphite

* structure and purity both confirmed * structural confirmation on-going * purity still an issue to

resolve

OO

O

CF3

CF3

OO

O

CF3

CF3

OO

O

CF3

CF3

CH3SiCH3

H3C O

Summary of New AdditivesMade in FY2014

PO O

O

C

C

C

F3C CF3

CH3

CF3

CF3

CH3

CF3

F3C

CF3

CH3SiCH3

H3C O

O

O

OO

O

CF3

CF3 CH3SiCH3

O CF3

CH3SiCH3

O CF3

CF3

CH3SiCH3

O CF3

CF3

Multi-functional Units integrated into a Single Molecule

Electrochemical characterization on-going in FY 15Cycling, floating test, etc:• cathode: high V LMNO, S/C composite…• anode: Si/C, graphite

• Effect of additives on Fluorinated Baseline• Similar but smaller effects as compared with Gen 2

0

0.005

0.01

0.015

0.02

0 5 10 15 20 25 30 35 40 45

Cur

rent

(mA)

Time (h)

DK control 2DK 1% HFiPP 2DK 1% DMVS-TFE 1DK 1% TMSHFIP 2DK 1% MHC 1

4.9V 5.0V 5.1V 5.2V

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 5 10 15 20 25 30 35 40 45

Gen 2 vs fluorinated electrolyteGen 2 electrolyte(1.2 M LiPF6/EC/EMC 3:7)

Fluorinated electrolyt(1.0 M LiPF6/FEC/FEMC/

4.9V 5.2V5.1V5.0V

Two baseline electrolytes selected as baseline• Aggressive floating tests were performed as rapid screening tool

• full Li-ion cells after initial cycling/forming• Advantage of fluorinated electrolyte against oxidation is apparent

Preliminary Characterization

Effect of TMSHFiP on Impedance

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100 120 140Rea

l im

peda

nce

, oh

ms

Test time, hours

1 kHz single-pulse impedance Control fluoro-electrolyteControl + 1v% TMSHFiP

Fully charged

Fully discharged

Fluoro-electrolyte with 1 vol% TMSHFiP additive

cycles with lower

impedance in bothcharged and discharged states.

1. TMSHFiP silane effective in Gen 2 carbonate and fluorinated electrolyte system.• Significantly reduces charge consumed by oxidation of Gen 2 carbonates• Observed decreased 1 kHz cycling impedance in fluorinated electrolyte

TMSHFiP additive: a descendant of the HFiPP phosphate-based electrolyte additive;MHC: a fluorinated carbonate

2. None of the propargyl-containing additives works• Too reactive for any electrolyte/LNMO combination• Stable radical may form shuttling species• DMVS-TFE very promising for Gen 2 carbonate systemC

oncl

usio

ns

Collaboration:

U.S. Army Research Laboratory (Dr. Kang Xu, Project team member) Brookhaven National Laboratory (Dr. Xiao-Qing Yang, Project team member) University of Texas - Austin (Prof. Arumugam Manthiram) Center of Nano-Materials, Argonne National Laboratory (Dr. Larry Curtiss)

Interactions:

• University of Rhode Island (Prof. Brett Lucht)• Jet Propulsion Laboratory (Dr. Marshall Smart)• Lawrence Berkeley National Laboratory (Dr. Vincent Battaglia)• Cell Analysis, Modeling, and Prototyping Facility (CAMP) (Dr. Andrew Jansen) • Material Engineering and Research Facility (MERF) (Dr. Gregory Krumdick)• Arkema (Dr. Ryan Dirkx)• NEI (Dr. Ganesh Skandan, Dr. Nader Hagh)

Collaboration and Coordination with Other Institutions

32

Argonne took a combined approach to tackle the voltage instability of electrolyte by developing the fluorinated carbonate-based electrolytes with intrinsic stability and the passivating cathode additive to afford a stable electrode/electrolyte interphase.

An effective probing tool was established for electrolyte oxidation stability by electrochemical floating test.

Fluorinated cyclic carbonates and fluorinated linear carbonates were synthesized and characterized and their electrochemical performance were evaluated in LNMO/graphite cells.

FEC and TF-PC based electrolyte have achieved superior capacity retention especially at elevated temperatures in 5-V LNMO/graphite cells. Post-test analysis showed that the fluorinated electrolytes are much more stable in both the liquid electrolyte phase and on the electrolyte/cathode interface.

Lithium compensation provides an efficient way to further improve the LNMO/graphite cells with a more stable fluorinated electrolytes.

LNMO/graphite cells with fluorinated electrolytes showed improved self-discharge at elevated temperature at fully charged state.

New electrolyte additives were synthesized and characterized; Live-formation of SEI by F-solvent was observed by in-situ electrochemical AFM.

New fluorinated sulfone-based electrolyte is in process.

Summary

33

For the rest of the FY15, we will continue to explore the fluorinated carbonate-based electrolytes to enable the high voltage high energy cells.

Synthesis and development of new additives tailored to stabilize the thermally stable fluorinated electrolyte TF-PC3.

Investigate the Li+ solvation in the fluorinated electrolytes by 2D-DOSY NMR. Electrode surface analysis using XPS and HR-TEM. Scientific write-up for publication in peer-reviewed journals.

For the rest of the FY15, we will initiate the fluorinated sulfone-based electrolyte study for high voltage high energy Li-ion cells.

DFT modeling of the electrochemical window of fluorinated sulfone. Synthesis and characterization of new fluorinated sulfone solvents. Evaluation of electrochemical performance.

Proposed Future Work

34

Technical Back-Up Slides

35

Other Benefits of Fluorinated ElectrolytesImproved wetting (contact angle measurement)

0

10

20

30

40

50

60

PolypropylenePlateCelgard 2325

Graphite

LNMO

OO

O

OO

O

OO

O

F

OO

O

CF3

HF2CCF2

OF2C

CF2H

OO

O

F

OO

O

CF3

OO

O

F

OO

O

CF3F3C

HF2CCF2

OF2C

CF2H

OO

O

F

OO

O

CF3F3C

HF2CCF2

OF2C

CF2H

Improves wetting!

Con

tact

Ang

le θ

(o) HVE-3

Gen 2

36

Conductivity:

> ~ >

0 10 20 30 40 50 60 7002468

101214161820

Gen 2 FEC/F-EMC=1/1 FEC/F-MiPC/F-EMC=2/1/1 EC/F-EMC=1/1 FEC/HF-DEC=1/1 FEC/TF-DEC=1/1 EC/EMC=1/1

Cond

uctiv

ity ( x

10-3 S

/cm

)

Temperature (OC)

Conductivity for New Linear Carbonate formulations

2.9 3.0 3.1 3.2 3.3 3.4 3.5 3.6-4.0

-3.5

-3.0

-2.5

-2.0

-1.5

Gen 2 FEC/F-EMC=1/1 FEC/F-MiPC/F-EMC=2/1/1 EC/F-EMC=1/1 FEC/HF-DEC=1/1 FEC/TF-DEC=1/1 EC/EMC=1/1

Log

(α)

1000/T (K-1)

O O

O

CF3 O O

O

CF3

CF3

O O

O

CF3 O O

O

CF3F3C

37