Vehicle Technologies Program
Screen Electrode Materials & Cell Chemistriesand
Streamlining Optimization of Electrode
Wenquan Lu
Electrochemical Energy StorageChemical Sciences and Engineering DivisionArgonne National Laboratory
This presentation does not contain any proprietary, confidential, or otherwise restricted information
Vehicle Technologies Annual Merit Review and Peer EvaluationWashington, D.C.May 9th – 13th , 2011
Project ID: ES028
Vehicle Technologies ProgramVehicle Technologies Program 2
Overview
Start – Oct. 2008 Finish – Sep. 2014 ~45% Complete
An overwhelming number of materials are being marketed by vendors for Lithium-ion batteries.
No commercially available high energy material to meet the 40 mile PHEV application established by the FreedomCAR and Fuels Partnership.
The impact of formulation and fabrication on performance of electrode materials with a broad variation of chemical and physical properties.
Timeline
Budget
Barriers
Total project funding in FY2010
–Screening: $350K
–Streamlining: $300K
Partners and Collaborators Andrew Jansen (Argonne National Laboratory)
Sun-Ho Kang (Argonne National Laboratory)
Dennis Dees (Argonne National Laboratory)
Jai Prakash and Aadil Benmayza (Illinois Institute of Technology)
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Project I: Objectives of Material Screening
To identify and evaluate low-cost cell chemistries that can simultaneously meet the life, performance, abuse tolerance, and cost goals for Plug-in HEV application.
To enhance the understandingof advanced cell components on the electrochemical performance and safety of lithium-ion batteries.
Identification of high energy density electrode materials is the key for this project.
100 Wh/kg145 Wh/L
145 Wh/kg207 Wh/L
70%
PHEV
Battery System Level
Material Requirements
150 160 170 180 190 200 210 220 230300
350
400
450
500BOL 40 mile PHEV
130kg
Assumption:Fix material density (Gen2)
Norminal Voltage, V 3.6ASI, ohm-cm2 50Range(CD:70%), mile 40Battery power, kW 50.0Capacity at C/3, Ah 60.0Number of modules 7Cells per module 12Cells per battery 84
Cathode Capacity, mAh/g
Anod
e C
apac
ity, m
Ah/g
95.00
100.0
105.0
110.0
115.0
120.0
125.0
130.0
135.0Tota
l Bat
tery
Wei
ght,
kg
120kg
100kg
Calculated using ANL’sBattery Design ModelCalculated using ANL’sBattery Design Model
Vehicle Technologies ProgramVehicle Technologies Program 4
Approach: Test Protocol Development
Test protocol has been defined in “Battery Test Manual for Plug-in Hybrid Electric Vehicles” by INL 2010.
Accordingly, test procedure and method have been translated to fit the material screening purpose.
Characteristics at EOL (End of Life)
High Power/Energy Ratio
High Energy/Power Ratio
Reference Equivalent Electric Range miles 10 40Peak Pulse Discharge Power (10 sec) kW 45 38Peak Regen Pulse Power (10 sec) kW 30 25Available Energy for CD (Charge Depleting) Mode, 10 kW Rate kWh 3.4 11.6Available Energy for CS (Charge Sustaining) Mode kWh 0.5 0.3Maximum System Weight kg 60 120Maximum System Volume Liter 40 80
USABC Requirements of Energy Storage Systems for PHEV
Material Identification
Material Characterization
(XRD, SEM, BET, Particle size, etc.)
ElectrochemicalEvaluation
Specific Capacity (energy)
IrreversibleCapacity
Loss
HybridPulsePower
Characterization
RateCapability
Thermal Investigation
CapacityRetention
Vehicle Technologies ProgramVehicle Technologies Program 5
Technical Accomplishments Several high energy electrode couples, surface treated natural graphite and composite
cathode materials, have been identified and studied. – Test results have been reported to suppliers.– Information is also delivered to cell fabrication team under ABR program (A. Jansen)
Other cell components, such as electrolyte, redox shuttle, conductive additive, binders, etc., are also investigated.
Fluorinated electrolyte (Daikin)
Conductiveadditive
Composite cathode
High voltage spinel
Surface coated graphite (ConocoPhillips)
Surface modified graphite(Hitachi Chemical)
Redox shuttle (ANL)
Carbon black (Cabot)
Copper (Somer Thin Strip)
Carbon coated Aluminum (Showa Denko)
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Highlight 1: Composite Cathode Materials
0 50 100 150 200 250 300
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Volta
ge, V
Capacity, mAh
charg-1 charg-2 charg-3 disch-1 disch-2 disch-3
327
Li/NCM cell4.6V~2.0V0.343mA1st charg: 300mAh/g1st disch: 249mAh/gICL: 17%
Toda Kogyo0.5Li2MnO3 • 0.5LiNi0.37Co0.24Mn0.39O2
C/10 C/3Average voltage V 3.64 3.58Specific capacity mAh/g 246 222ICL % 17Energy density mWh/g
full cycle 4.6~2.0 897 790Capacity retention % (50 cyc) 90
(1-x)Li2MnO3 xLiMO2 cathode materials, where M is a collection of transition metals and the average oxidation state of M is trivalent, have been used to increase the energy density for advanced batteries.
The boost in energy density is due to the electrochemical activation of Li2MnO3domains in the composite material.
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Rate Performance of Composite Cathode Material
Excellent rate performance up to 1C with 194 mAh/g.
Small impedance during HPPC between 10% and 70% DOD.
0 1 2 3 4
2
3
4
5
Li/NCM Cell4.6V~2.0V
Volta
ge, V
Capacity, mAh
C/5 C/3 C/2 1C
327
230220210194
3.2 3.4 3.6 3.8 4.0 4.2 4.40
20
40
60
80
100
120
140
pulse regen
ASI,
ohm
-cm
2
Voltage, V
nl327
Li/Toda cellHPPC3C/2C
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Voltage Depression of Composite Cathode Material
2.0 2.5 3.0 3.5 4.0 4.5 5.0-6
-4
-2
0
2
4
6 Li/composite Cell4.6V~2.0Vformation: 20mAh/gcycling: 67mAh/g
dQ/d
V, m
Ah/V
Voltage, V
7 17 27 37
nl330
0 1 2 3 4 5
2
3
4
5
Li/NCM Cell4.6V~2.0Vcycling: 67mAh/g
Volta
ge, V
Capacity, mAh
7 17 27 37
nl330
voltage depression
Composite cathode material shows very good capacity retention during cycling.
However, voltage depression during cycling was observed, which may affect the energy density.
0 10 20 30 400
1
2
3
4
5
6
Ca
pacit
y, m
Ah
Cycle number
Li/composite Cell4.6V~2.0Vformation: 20mAh/gcycling: 67mAh/g
91%
nl330
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Thermal Property of Composite Cathode
DSC results indicates that the on-set temperature of exothermic reaction of the fully charge composite is 215oC, same as LiNi0.8Co0.15Al0.05O2 at 4.2V.
The total heat generation of fully charged composite is about 1184J/g, which is less than LiNi0.8Co0.15Al0.05O2 at 4.2V.
50 100 150 200 250 300 350-5
0
5
10
15
20
25
30
35
40
Heat
, µJ/
sec
Temperature, oC
NCA composite
4.2V4.6V
1184J/g
1878J/g
Scan rate: 10oC/min
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Highlight 2: Fluorinated Electrolyte from Daikin
Electrolyte=Solvent + Salt
LiNi0.8Co0.15Al0.05O2•High Current Overcharge•High Temperature
Fluorinated electrolyte may address safety concerns caused byheat and pressure build-up within the cell and the flammable electrolyte, since it has:
Higher operational voltage window Lower reactivity to anode and cathode Thermally stable
10Illinois Institute of Technology
Vehicle Technologies ProgramVehicle Technologies Program 11
-10
-8
-6
-4
-2
0
250 100 150 200 250 300 350 400
Nor
mal
ized
Hea
t Flo
w (W
/g)
Temperature (oC)
FE1Gen2
Pros and Cons of Fluorinated Electrolyte
-300
-250
-200
-150
-100
-50
0
503 3.5 4 4.5 5 5.5 6
Voltage, V vs Li/Li+
Cur
rent
Den
sity
(µA
/cm
2)
GenII
FE
FE1
WE: Glassy Carbon
RE: Li
CE: Li
Scan Rate: 0.5 mv/s
-300
-250
-200
-150
-100
-50
0
503 3.5 4 4.5 5 5.5 6
Voltage, V vs Li/Li+
Cur
rent
Den
sity
(µA
/cm
2)
GenII
FE
FE1
WE: Glassy Carbon
RE: Li
CE: Li
Scan Rate: 0.5 mv/s
Electrolyte composition:Gen II: 1.2 M LiPF6 EC/EMC (3/7)FE1: 1.2M LiPF6 FEC/EMC (3/7)
Electrolyte conductivity
[Fluorinated Materials for Energy ConversionT Nakajima and H. Groult, 2005]
C-H : Binding energy: 417kJ/molC-F : Binding energy: 486kJ/molElectron negativity: H /2.1; F/4.0
Fluorinated Solvent
Safer Electrolyte Conductivity (mS/cm)
GenII 1.2M LiPF6 in EC/EMC (3:7) 8.2
FE 1.2M LiPF6 FEC/EMC/D2 (2:4:4) 7.2
Electrolyte Conductivity (mS/cm)
GenII 1.2M LiPF6 in EC/EMC (3:7) 8.2
FE 1.2M LiPF6 FEC/EMC/D2 (2:4:4) 7.2
FE1 1.2M LiPF6 FEC/EMC(3:7) 4.8
FE1 1.2M LiPF6 FEC/EMC(3:7) 4.8
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Comparable performance at lower rates.
At high rates especially at 1C and 2C the cathode with Gen2 electrolyte shows better performance than FE1.
100
110
120
130
140
150
160
170
180
0 4 8 12 16 20
Spec
ific
Dis
char
ge C
apac
ity (m
Ah/
g)
Cycle_Index
Gen2 FE1
C/10 C/5 C/3 C/2 1C 2C
Rate Performance of Fluorinated Electrolytes
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Onset Temperature (˚C) ΔH(J/g)
State of charge (%) Gen2 FE1 Gen2 FE1
100 206 220 1183 1009
80 209 232 1100 788
40 238 273 624 243
20 252 280 394 240
DSC Results of Fluorinated Electrolyte
-14
-12
-10
-8
-6
-4
-2
0
250 100 150 200 250 300 350 400
Nor
mal
ized
Hea
t Flo
w (W
/g)
Temperature (oC)
Gen2_20%SOCGen2_40%SOCGen2_80%SOCGen2_100%SOC
-14
-12
-10
-8
-6
-4
-2
0
250 100 150 200 250 300 350 400
Nor
mal
ized
Hea
t Flo
w (W
/g)
Temperature (oC)
FE1_20%SOCFE1_40%SOCFE1_80%SOCFE1_100%SOC
Gen2
FE1 Higher on-set temperature
and less total heat generation were observed to FE1 electrolyte at various state of charge compared to Gen2 electrolyte.
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Summary Composite cathode materials
0.5Li2MnO3 0.5LiNi0.37Co0.24Mn0.29O2– Deliver 897Wh/kg, more than 70% of
conventional LiCoO2. – Good rate performance: 210mAh/g @ C/2.– Area specific impedance is about 40 ohm-cm2
at 50% DOD.– 91% capacity retention within 40 cycles.– Less heat generation at fully charged state
compared to NCA.
Daikin’s Fluorinated ethylene carbonate (FEC)
– Less capacity is delivered @ 1C due to low conductivity of FEC.
– DSC results indicate better thermal stability at various state of charge.
Surface modified graphites from various vendors have been investigated. They all show high capacity, good rate capability and thermal stability and will be used for cell build at ANL.
Other cell components, such as redox shuttle, binder, separator, carbon additive, current collector have been studied.
To continue to search and evaluate the high energy density electrode couples to meet the performance and cost goal for PHEV applications.
– (1-x)Li2MnO3 xLiMO2 – Surface modified graphite– Silicon and its composite– Hard carbon (Kureha)
Other available cell chemistries for lithium battery
– Electrolyte, additives, redox shuttles– Separators – Current collector– Binder– Conductive additives
Support electrode and cell build project under ABR program
– Electrode thickness Support material scale up
program at ANL
Future Plans
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Project II: Objectives and Approach of Streamlining the Optimization of Electrode
To establish the scientific basis needed to streamline the lithium-ion electrode optimization process.
– To identify and characterize the physical properties relevant to the electrode performance at the particle level.
– To quantify the impact of fundamental phenomena associated with electrode formulation and fabrication (process) on lithium ion electrode performance.
Particlesize
Pore structure
Surface area
Particle morphology
material
Power
Energy
outputConductive
additive
Porosity
laminate
Binder
Thickness
Currentcollector
Separator
cell
Tab
General approachNew approach
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Technical Accomplishments
Single particle conductivity was found to be higher than powder conductivity in general. The contact resistance between particles should be addressed for electrode optimization.
Composite electrode made of 0%, 1% and 3% carbon coated Li1+xNi1/3Co1/3Mn1/3O2 (NCM) was intensively investigated. Interfacial resistance was found to be dominant for the composite electrode using aluminum substrate.
Nano electrical imaging was carried out on composite electrode to better understand the conductive network. It was found that the full utilization of conductive carbon additives is necessary to reduce the content of carbon and improve conductivity.
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Impact of Electrode Electronic Conductivity– Impedance Simulation of Gen 3 (NCM) Positive Electrode 5C HPPC
>0.01 (ohm cm)-1: electronic conductivity is much greater than the ionic conductivity and does not impact electrode impedance
0.001-0.01 (ohm cm)-1: electronic conductivity is comparable to the ionic conductivity
<0.001 (ohm cm)-1: electronic conductivity is much less than the ionic conductivity and significantly impacts electrode impedance
18
20
22
24
26
28
30
0.0001 0.001 0.01 0.1 1
Electrode Electronic Conductivity, (ohm cm)-1
Posi
tive
Elec
trod
e A
SI10
s, oh
m c
m2 low
conductivity
medium conductivity
high conductivity
Together with the electrolyte conductivity, the composition of the conductive additive should be tailored to meet the power and energy requirements of lithium ion batteries.
From Dennis Dees’ model (Argonne)
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Electronic Conductivity Investigation
Single particle and powder conductivity measurements demonstrate that contact resistance is the key for conductivity of composite electrode.
In order to address the interfacial resistance between the particle, and current collector, carbon coated Li1+xNi1/3Co1/3Mn1/3O2 has been studied.
Pressure
Pow
der c
ondu
ctiv
itycurrent
resistance
Schematic diagram of powder conductivity measurement
apparatus
Cu
HDPE
PVDF film
PVDF
Single particle conductivity Powder conductivity Binder conductivity
NCAPart5-13
1
4 32
Single particle conductivity by Nano-probe SEM
pristine
> >
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Effects of Carbon Coating on Morphology of Li1+xNi1/3Co1/3Mn1/3O2 (NCM)
0 200 400 600 800
97.0
97.5
98.0
98.5
99.0
99.5
100.0
Wei
ght l
oss,
%
Temperature, oC
NCM NCM2-1 NCM2-2 NCM1-1 NCM1-2
Carbon coated NCM10oC/min250 ml/min air
y = 0.7264x + 0.5514
0
0.5
1
1.5
2
2.5
3
0 1 2 3Carbon, %
BE
T, m
2/g
Series1
Linear (Series1)
y = 1E-05e2.0855x
R2 = 0.997
0.00001
0.0001
0.001
0.01
0.1
0 1 2 3 4
Carbon, wt.%
Con
duct
ivity
, S/c
m
TGA
pristine
3wt% carbon
Conductivity
BETpristine
3% carbon
1% carbon
The powders are subjected to a centrifugal force and are securely pressed against the inner wall of rotating casing.
The powders are further subjected to various mechanical forces, such as compression and shear forces, as they pass through a narrow gap between the casing wall and the press head.
As a result, smaller guest particles are dispersed and bonded onto the surface of larger host particles without using binder of any kind.
SEM
NCM
NCM1
NCM3
Hosokawa
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Cross Section of NCM Electrode
Continuous carbon pathway was observed for NCM0 with 4% carbon additive.
But, little or longer pathway for NCM3 electrode with only 1wt% additional carbon additives.
NCM0-24 NCM3-04Al Al
surface surface
Cross section Cross section
NCM/CB/PVDF84/ 4 /4
NCM3(w/3%cb)/CB/PVDF87/ 1 /4
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Electrode Conductivity by 4 Probe Method
Electrode composition*:– Active: 84%, – SFG-6: 4% – Carbon: 4% (*including coated
carbon); – PVDF: 8%
Aluminum
0
0.02
0.04
0.06
0.08
Before 40% 30%
R, o
hm
NCMNCM 3%
Polyester
0
100
200
300
400
500
600
Before 40% 30%
R, o
hm
NCM PENCM 3% PE
The resistance of the NCM3 electrode with 1wt% additional carbon on aluminum foil shows less resistance before calendering. Resistances of both electrodes NCM0 and NCM3 on aluminum decreases after calendering.
For the electrode on polyester substrate, the sheet resistance of the NCM3 electrode is higher. The electrode sheet resistance increases after calendering for both NCM0 and NCM3.
Therefore, interfacial resistance is dominant for the composite electrode using aluminum substrate. The contact resistance between the particles and substrate was small for carbon coated sample.
substrateinterfacesample
iV
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4 Probe Modeling of Composite Electrode
The conductivity calculated from modeling is consistent to the 4 probe measurement.
The validated model will be used to determine the interfacial resistance between the composite layer and substrate.
0.0
0.1
0.2
0.3
65 70 75 80 85Thickness, µm
Con
duct
ivity
, S/c
m
4probemodel
i1
V1
V2 i2
Errlim = 0.00001Rcontact = 0.5 ohm-cm2Rinterface = 10000 ohm-cm2conductivity = 0.221 S/cm
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Nano-Electrical Imaging of Electrode using AFM
3% carbon coated NCM + 4% carbon + 7% PVDF
Higher current indicates higher conductivity.
There are two distinct regions in the image: isolated blue rocky-like (NCM) and continuous patches (CB + PVDF).
The conductivity various with CB/PVDF region, which should be further studied.
Current: purple/pink < green < yellow < red
AFM by Bruker (Veeco)
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Future Plans
The electronic conductivity of composite electrode made of carbon coated NCM was intensively investigated.
– The composite electrode with carbon coated particles has better interfacial conductivity between composite layer and substrate, but higher sheet resistance compared with uncoated particles.
– The electrode with uncoated particles has lower interfacial conductivity but higher conductivity within the composite sheet.
– The 4 probe model was validated and the interfacial resistance will be studied.
Nano electrical image indicates that the carbon additive is not fully utilized to form the conductive matrix.
Carbon coating impact on the cathode performance will be continued.
– The amount of coating, additional carbon additive, and binder effect will be investigated.
– This 4 probe modeling will be utilized to study the interfacial resistance.
Electrode optimization on electronic conductivity will be address through
– Percolation theory
– Optimization of composite electrode conductivity
Summary
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Contributors and Acknowledgments
Argonne National Laboratory Nathan Liu Huiming Wu Bryant Polzin Jack Vaughey Daniel Abraham Khalil Amine Kevin Gallagher Gary Henriksen Electron Microscopy Center (EMC) Center for Nanoscale Materials (CNM)
ConocoPhillips Toda Kogyo Hitachi Chemicals, Japan Solvay Daikin Inc., Japan Hirose Paper North America, GA Somer Thin Strip, CT Pred Materials International, Inc., NY Hosokawa Micron Corporation, NJ Leica Microsystems Bruker (Veeco)
Support from David Howell and Peter Faguy of the U.S. Department of Energy’s Office of Vehicle Technologies Program is gratefully acknowledged.