joon ho shin, leanne beer and pratyay basak...-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 50 m v 500 mv 5000 mv...
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Interfacial Behavior of ElectrolytesJohn Kerr
Joon Ho Shin, Leanne Beer and Pratyay Basak
Lawrence Berkeley National Laboratory.
February 28, 2008.
This presentation does not contain any proprietary or confidential information
Outline• Purpose of work• Barriers • Previous Review Comments • Approach• Performance Measures and Accomplishments• Plans for Next Fiscal Year• Summary• Collaborations and Technology Transfer• Publications/Patents
Purpose of the Work• Investigate the Chemical and Electrochemical
reactivity of Li Ion electrolytes.– Effect of impurities and additives.– How are Calendar and Cycle Life affected?– Are 5V electrolytes at all feasible?
• How do the electrolyte components, reaction products and impurities affect the interfacial impedance at the electrodes.
Purpose of the Work.Impact of Interfacial vs. Bulk Impedance
0
50
100
150
200
250
300
350
400
0 20 40 60 80 100 120
PEGDME250-liTFSI(20) + 10% R805 SiO2
Bulk1 Interfacial 1 Bulk2 Interfacial2
R/oh
m.c
m2
Temperature(0C)
50
100
150
0 0.002 0.004 0.006 0.008 0.01 0.012
Peak
Pow
er, W
/kg
Anode Film resistance - Ohm-cm2Ohm.m2
Experimental Measurementson Li/Li symmetrical cells
Model of effect of Interfacial Impedance on Peak Power.(Karen Thomas-Alyea)
0.01 ohm.m2 = 100 ohm.cm2
Barriers Addressed• Poor Calendar Life – 2-3 yrs vs. 15 yr goal.• Poor Cycle Life – 3,000 -5,000 cycle goal.• Increase Power Density to 750 W/kg• Increase Energy Density to 100 Wh/kg• Low temperature (-30oC) performance• Increased Abuse Tolerance.
Electrolyte chemistry and interfacial behavior impacts these barriers.
Previous Review Comments
Recommendation:Reevaluate work on SPEs and ionic liquids (IL), as they may not meet low T or power requirements.
DOE Response:• LBNL/DOE will refocus some of the PIs’ who
are currently doing support work in these areas (Kerr and Doeff)
Previous Review Comments • The work on radical polymer electrolytes and ILs is the most
interesting project of those listed in future plans. • IL should be tested further. • Systematically determine water content vs. degradation
(various types) is very useful to industry, very relevant to next generation systems as well as to ameliorate effect of water in present electrolytes.
• Need to dig deeper than just running an experiment to validate or reject a one liner statement.
Reviewer Recommendations for Additional work:• This work should be continued, need polymer exploration.• Need to look carefully at the stability of ionic liquids (ILs) at
negative potentials.
Approach• Continue Chemical and Electrochemical
studies of carbonate-based electrolytes.– Better understand the role of water and alcohols– Understand the roles of acid and base components,
impurities and side products.– Improve correlation of chemical measurements
with electrochemical observations • Bring Ionic Liquid Work to some conclusions.• Exploratory work on Polymer-electrode/IL
systems
Radical Polymer Electrodesand Ionic Liquids
Li PTMA/C
Current collectorLi+ TFSI-
N
R1 R2NO
OO
n
NO
OO
n
PTMA
t / s
0 200 400 600 800 1000
Cel
l vol
tage
/ V
3.0
3.2
3.4
3.6
3.8
4.0First discharge10th 20th 30th 40th 50th 70th100th
Justin Salminen, Kentaro Nakahara (NEC, Japan) H. NishideWaseda Univ.Science, 2008,319(Feb 8), 737;Interface, 2005, 14, 32.
Remove the Li+
Both Electrodes are Redox Polymers.Ionic Liquid Electrolyte increases Safety
-0.001
-0.0005
0
0.0005
0.001
-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5
50 m V500 mV5000 mV
Cur
rent
(A)
Potential (V) vs. Ag+
CV: 5mM TEMPO, 0.1M TEAClO4 in acetonitrile on glassy carbon
NO
PTMA/CTFSI-N
R1 R2
PTMA/CNO
OO
n
NO
OO
n
NO
OO
n
NO
OO
n
TEMPO
Electrolyte water content 1000ppmCathode reaction not sensitive to water.Anode reaction sensitive andKinetically very slow.Replace anode polymer with polynitrostyrene(Miller, JACS 1980, 102, 3833)
NO
+NO
NO
+NO
+NONO
N
O
e N
O
Electrolyte System Studied
Ternary mixture electrolytes
PYR14TFSI + x LiTFSI + y PEGDME 250 (or 500)
x = LiTFSI mol/PYR14TFSI-kg, x = 0.5
y = PEGDME-kg/PYR14TFSI-kg, y = 1.0, 1.5 and 2.0
EO/Li ratio: 18 (y = 2.0), 13 (y = 1.5), 9 (y = 2.0)
N-methyl-N-butylpyrrolidinium bis(trifluoromethane sulfonyl)imide (PYR14TFSI)
Poly (ethylene glycol) dimethyl ether (PEGDME); n ~5 or 10
Ionic Liquid with Co-solvents Conductivity and Viscosity
10-5
10-4
10-3
10-2
10-1
2.6 2.8 3 3.2 3.4 3.6 3.8 4
PYR14TFSIy=0y=0.1y=0.3y=0.5y=1.0y=1.5y=2.0
Con
duct
ivity
(S/c
m)
1000/T (K-1)
0
20
40
60
80
100
120
20 30 40 50 60 70 80 90
Temperature (oC)
Visc
osity
(cP)
Pyr14T+0.5LiT+1.0P-500Pyr14T+0.5LiT+1.5P-500Pyr14T+0.5LiT+2.0P-500Pyr14T+0.5LiTPyr14T+0.5LiT+1.0P-250Pyr14T+0.5LiT+1.5P-250Pyr14T+0.5LiT+2.0P-250
Ionic conductivityPYR14TFSI + 0.5M LiTFSI
+ (y) PEGDME 250 mixtures.
ViscosityPYR14TFSI + 0.5M LiTFSI
+ PEGDME 250 and 500 mixtures.
PEGDME 250PEGDME 250
PEGDME 500PEGDME 500
Interfacial Impedance of Ionic Liquidswith co-solvents
Li/Li Graphite vs. Li reference
PEGDME 250PEGDME 250
PEGDME 500PEGDME 500
Exchange Current Density of Ionic Liquid Co-solvent Mixtures at Lithium and Graphite
Li/Li Graphite vs. Li Reference
Carbonate Based Electrolytes- Anode Formation Experiments
on Gen 2 Anode (ATD-ANL)
Schematic of three electrode cell
-15
-10
-5
0
5
10
0 0.5 1 1.5 2 2.5
CV_1mV_ECEMC+salt_RT_total
LiTFSILiPF6C
urre
nt (m
A/c
m2 )
Voltage (V)
Cyclic voltammetry of Li/EC/EMC (3/7 v/v) + 1.2M LiX/Graphite cell; 1mV/s, 25oC
0
100
200
300
400
500
600
0 100 200 300 400 500 600
Imp_ECEMC+salt_RT_before CV_total
LiTFSILiPF6LiTFSILiPF6
-ZIm
ag (O
hm c
m2 )
ZReal
(Ohm cm2)
before CV
after CV
LiPF6 soln.Water = 0 ppmbut pH low;LiTFSI soln.H2O = 30 ppm
Nyquist plot of ac impedance of Li/EC/EMC (3/7 v/v) + 1.2M LiX/Graphite cell at 25oC. 3-electrode measurement
Effect of Formation Potentialon Gen 2 Anode with LiTFSI
-4
-3
-2
-1
0
1
2
3
-0.5 0 0.5 1 1.5 2
LiC30_CV_RT_total
0.5mV/s,1st&2nd0.5mV/s,3rd&4th0.5mV/s,5th
Cur
rent
(mA
/cm
2 )
Voltage (V vs. Li/Li+)
0
200
400
600
800
1000
0 200 400 600 800 1000
LiC30_Imp_CV_0.5mV_RT_total
before CVafter 2nd scanafter 4th scanafter 5th scan
-ZIm
ag (O
hm c
m2 )
ZReal
(Ohm cm2)
Cyclic voltammograms(left) and Nyquist plots (right) of Li/EC/EMC(3/7v/v),1.2M LiTFSI/graphite, scan rate 0.5mV/s, 25oC
Nature of Surface Analysis of Products after formation cycling at Sputtered Mag-10 Anodes
Time/ min.0 10 20 30 40
Inte
nsity
a.u
.
(a)
DMC ECMeOH
*
*
(b)
Time/ min.0 10 20 30 40
Inte
nsity
a.u
.
(a)
DMC ECMeOH
*
*
(b)
Sputtered
Fresh
Gas Chromatography Analysis
O O
OO O O
OO
O
O O
O
O
O
O
OO
1 2 3 4
5 6
Mass Spectral analysis of GC peaks are consistent with structures 1-6 amongst othersincluding higher M.Wt. products (1500) that appear to contain fluorine. Compound 6 is consistent with base catalyzed ring opening of ECCE analysis also detects phosphates.
Ring-opening of EC initiated by Electrogenerated base.
O O
O
O O
OOR
O O
OOR
O O
O
O O
O
OO
O OR
RO OO O
O
O
O O
O
n
R'O
RO
n
PEO + CO2
• RO- anion is formed by reaction at the anode.•CO2 removed by reduction at anodes to form CO, carbonate, formate and Oxalate. Oxalate can act as a shuttle for reversible self-discharge or “Marching”
O O
OO
O
6 + CO2
Cathode Interfacial ImpedancePostulated that side reaction products
alter wetting characteristics.
0
200
400
600
800
1000
0 200 400 600 800 1000
LiG15_Imp_RT_072407_total
before testafter 1st chargeafter 1st discharge
-ZIm
ag (O
hm c
m2 )
ZReal
(Ohm cm2)
0
20
40
60
80
100
0 20 40 60 80 100
LiG15_Imp_RT_072407_total
before testafter 1st chargeafter 1st discharge
-ZIm
ag (O
hm c
m2 )
ZReal
(Ohm cm2)
Impedance of Gen 2 Cathode before and after cycling
Kinetic Measurements of Electrolyte Reactions
-10
-8
-6
-4
-2
0
20.0027 0.0028 0.0029 0.003 0.0031 0.0032
1/T (K)
Ln( r
ate
/ mg
uL-1
d -1
)-1
Ln (dDEC / dt)
Ln (d -EC / dt)
0oC•Previous measurements of Electrolytereactivity carried out under poorly controlled conditions
– e.g. variable moisture content.•Prepare solutions under better controland add known amounts of moisture, acids,bases and additives (LiF).
•EC/EMC-LiPF6+ 0.2mM H2O gelled at 43oC!-followed by thinning and coloring.
•EC/EMC-LiTFSI – no reaction at 85oC for 2 years!
- addition of 5mM HTFSI at 43oC results in no visible reaction.EC/EMC- LiPF6 heated
in glass vials
60oC84oC 4
Polymer Exploration Single-ion Conductors (NASA funded)
Possess adequate bulk transport but enormous interfacial impedance. What is the source of this?
2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4-9
-8
-7
-6
-5
-4
-3
-2
-12.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4
-9
-8
-7
-6
-5
-4
-3
-2
-1
Log σ
/ Scm
-1
1000 / T (K-1)
75 wt% PC/EMC (1/1, v/v) 50 wt% PC/EMC (1/1, v/v) 50 wt% PC/DMC (1/1, wt/wt) 50 wt% EC/DMC (1/1, wt/wt) Dry PAE8-g-E2SO3Li EO/Li = 118
25oC
0
5000
1 104
1.5 10 4
2 104
2.5 10 4
0 5000 1 104 1.5 10 4 2 104 2.5 10 4
Before cycling
After cycling
- Z"/Ω
Z'/Ω
Ionic Conductivity Interfacial Impedance at Lithium
Plans for Next Fiscal Year• Complete electrolyte degradation analysis under rigorously
controlled conditions– All operations in Glove-box or Schlenk-line.
• Continue to explore how electrolyte degradation affects impedance growth at both electrodes.
• Expand interfacial studies to cathodes.– Detailed analysis of cathode side reaction products and effects on
interfacial behavior– Study the effects of impurities (water, acids, additives) on interfacial
behavior.
• Use Single Ion Conductor polymers from DOE Hydrogen Program to investigate interfacial impedance.
Summary • Interfacial behavior of electrolytes is at least as
critical as bulk transport properties– Electrochemical kinetics.– Electrolyte mobility/wettability at surfaces.– Chemical/electrochemical degradation.
• Interfacial Impedance of Ionic Liquids precludes their use in high rate conventional cells.
• Ionic Liquids may find use in supercapacitors and hybrid polymer electrode batteries.
Collaborations and Technology Transfer
• ATD Program (Kostecki, Abraham)• BATT - Doeff, Battaglia, Kostecki, Creager,
HydroQuebec, Modeling Groups (Smith/Borodin, Newman/Srinivasan).
• CSIRO (Australia) Tony Hollenkamp. Adam Best
• Synergy with DOE Hydrogen program for Polymer materials.
• NASA
Publications/PatentsPapers:1. Saint, J., et al., Compatibility of LixTiyMn1-yO2 (y=0, 0.11) electrode
materials with pyrrolidinium-based ionic liquid electrolyte systems.Journal of the Electrochemical Society, 2008. 155(2): p. A172-A180.
2. Salminen, J., et al., Physicochemical properties and toxicities of hydrophobic piperidinium and pyrrolidinium ionic liquids. Fluid Phase Equilibria, 2007. 261(1-2): p. 421-426.
Patents: Shanger Wang, Jun Hou, Steve E. Sloop, Yong Bong Han and John B. Kerr.
Polymeric electrolytes based on hydrosilyation reactions USP 7,101,643, September 5, 2006.
Presentations:Joon Ho Shin, John B Kerr, Thermal Behavior and Interface Property of N-
methyl-n-butylpyrrolidinium Bis(trifluoromethanesulfonyl)imide-LiTFSI-PEGDME Mixtures. Presented at 212th ECS Meeting,Washington, DC, US October 7-12, 2007.