novel electrolytes and additives - energy.gov...graphite vs. li/li + c/15 rate, 2-0 v. lithiation....
TRANSCRIPT
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
3
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
4
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
6
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
8
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
9
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
10
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.
13
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
14
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
16
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
17
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
18
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
20
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
22
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.
23
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.
24
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.
25
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
26
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
27
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