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Next Generation Redox Flow Battery Development at PNNL
Vincent Sprenkle, Wei Wang, David Reed, Ed Thomsen, Zimin Nie, Bin Li, Xiaoliang Wei, Brian Koeppel, Baowei Chen, Alasdair Crawford, Vish Viswanathan. DOE Office of Electricity Energy Storage Program – Imre Gyuk Program Manager. MRES 2014 Boston, MA August 19th, 2014
2
PNNL Electrical Energy Storage (EES) R&D strategy
Crosscutting science Advanced diagnostic
study, NMR, TEM, etc. Electrochemical
study
• Mass/charge transport • Electrochemical • Flow, thermal, …
• Basic chemistry • Materials structure • Physical properties
• Electrochemical activity • Reaction kinetics • Performance
Computer Modeling
Technology Transfer
EES Technologies Novel redox flow batteries
Next gen Na-batteries Low cost, long life Li-ion,
New concepts, emerging technologies
Grid Analytics • Roles of storage in
US grids • Value, locations,
targets
Cost Analysis • Cost and
performance requirements
Academic/National Lab/Industrial Collaborations
Next Generation Redox Flow Batteries Goal: Developed next generation redox flow battery (RFB) that can demonstrate substantial improvement in performance and economics, to accelerate its commercialization and market penetration, via collaborations with industries and universities
Key Aspects
Ø Power and Energy are separate enabling greater flexibility and safety. Ø Suitable for wide range of applications 10’s MW to ~ 5 kw Ø Wide range of chemistries available. Ø Low energy density ~ 30 Whr/kg
Vanadium Mixed Acid Electrolyte
Charge Discharge
Charge Discharge
Charge Discharge
Catholyte: VO2+ + Cl- + H2O – e VO2Cl + 2H+ εco=1.0 V
Anolyte: V3+ + e V2+ εao=-0.25
Overall: VO2+ + Cl- + H2O + V3+ VO2Cl + 2H+ + V2+ Eo=1.25 V
Ø 70% increase in capacity § V2+, V3+, V4+, V5+ stable >2.8M,
in SO2- and Cl- mixed solutions
Ø 80% increase in operating temperature window. § -5 – 50°C
Redox Flow Battery Objectives Develop the technologies, tools, and system understanding required to move the mixed acid electrolyte chemistry from basic chemistry to cost effective system solution.
Cost Model Program Screenshot:
6
Outputs
Inputs
Executable file released at PNNL Energy and Environment website http://energyenvironment.pnnl.gov/highlights/9_13_redox.asp
C++ Source Code released in Github Repository
https://github.com/PNNL-OE-Redox-Flow-Battery-Cost-Tool/PNNL-OE-Redox-Flow-Battery-Cost-Tool
Gen 2 V-V 1 MW /4 MWh At 80 mA/cm2
Ø Separator for stack is one significant cost element.
Ø Lower system cost can be accomplished by:
• Lower cost separator
• Higher current density operation. (Same power for less stack)
kW mixed acid system
#
1kW Stack
1kW / 1kWh VRFB System Tank
Pump
Stack
1kW Stack
1kW / 1kWh VRFB System
1kW / 1kWh VRFB System
Initial kW stack performance
#
0 20 40 60 8016
18
20
22
24
26
2 L/min 4 L/min 80 mA/cm2
160 mA/cm2
Volta
ge (V
)
Capacity (Ah)
6 L/min
2 4 60.6
0.8
1.0
1.2
1.4
1.6
Disc
harg
e en
ergy
(kW
h)
Flow rate (L/min)
80 mA/cm2
160 mA/cm2
Test Conditions • Flow rates 2, 4, 6, and 7 slpm • 15-85 SOC @ 80 mA/cm2
0 20 40 60 80 1000
10
20
30
40
50 Positive tank Negative tank Ambient
246246
160 mA/cm2
Tem
pera
ture
(o C)
Cycle Number
80 mA/cm2
7 LPMFlow rate
0 20 40 60 80 10060
70
80
90
100
CE EE
246246
160 mA/cm2
Effic
ienc
ies
(%)
Cycle Number
80 mA/cm2
7 LPMFlow rate
(a) (b)
Temperature exceeds stability of
conventional vanadium electrolyte
FY14 Redox Objectives and Goal
Operate at 240 mA/cm2 with improved energy efficiency and lower stack pressure drop.
Greater stack efficiency
Use of 212 membrane compared with 115.
Greater system efficiency Use of interdigitated flow field for reduced pressure drop.
Novel Catalysts.
Typical VRFB Stack Test Parameters
VRFB System
Stack
• 780 cm2 ac)ve area/cell • 15 cell stacks • 10-‐90% SOC • Mixed acid electrolyte
• 2M V, 2M S, 5M Cl • Nafion® membrane
• 115 (5 mil) • 212 (2 mil) • 211 (1 mil)
• Current density A/cm2 • 80 • 160 • 240 • 320
• Flow Rates sccm/cell • 133 • 267 • 400 (6 lpm for 15 cell stack) • 800, 1200 for IDD.
3-cell stack performance with Nafion® 115, 212, and 211 membrane (no IDD)
Stack Efficiency
3 Cell Stack Columbic Voltage Energy Discharge Discharge Pressure (psi) Pressure (psi) Flow Rate/cell
80 mA/cm2 Efficiency
(%) Efficiency
(%) Efficiency
(%) Capacity (Ah/L) Temp (°C) negative positive (cc/min)
Nafion® 115 96.7 87.4 84.5 19.4 33.7 8.4 6.7 400 Nafion® 212 96.5 90.2 87.0 20.7 28.8 10.7 7.7 400 Nafion® 211 95.8 91.3 87.5 20.4 37.2 7.9 6.1 400 160 mA/cm² Nafion® 115 96.9 77.7 75.3 18.2 39.3 7.0 6.0 400 Nafion® 212 97.2 82.4 80.1 19.8 30.8 10.4 7.3 400 Nafion® 211 96.9 84.0 81.4 20.1 38.8 7.9 5.9 400 240 mA/cm² Nafion® 211 97.0 77.8 75.5 18.1 45.5 6.5 5.2 400
74 76 78 80 82 84 86 88 90
50 100 150 200 250
Stac
k En
ergy
Ef
ficie
ncy
(%)
Current Density (mA/cm²)
Nafion 115 Nafion 212
Ø Replacement of 212 (2 mil) Nafion® with 211(1 mil) improved overall EE by 1-2%.
72
74
76
78
80
82
115 212 211
Stac
k Ef
f. (%
)
Nafion®
160 mA/cm2
3-cell high current stack performance with Nafion® 212, and 211 membrane (IDD)
68
70
72
74
76
78
80
82
84
0 200 400 600 800 1000 1200 1400 1600 1800
Stac
k En
ergy
Effi
cien
cy (%
)
Flow Rate / Cell (cc/min)
212
240 mA/cm2
320 mA/cm2
160 mA/cm2 211
211
212
Ø EE improvement with Nafion® 211(1 mil) consistently 1-2% over multiple flow and current densities.
Capacity fade of 3-cell stack with Nafion® 115, 212, and 211 membrane
Capacity Fade
50%
55%
60%
65%
70%
75%
80%
85%
90%
95%
100%
0 10 20 30 40 50 60 70
Dis
char
ge C
apac
ity (%
)
Cycle
Nafion 115
Nafion 212
Nafion 211
• 3 cell stack • 780 cm2 ac)ve area/cell • 10-‐90% SOC • 160 mA/cm2
Ø No significant difference capacity fade as a function of thickness
15
Thickness (µm)
Water Uptake (%)
ConducKvity (mS·∙cm-‐1)
Area Resistance (mΩ·∙cm2)
Diffusion Coefficient of VO2+ (10-‐6 cm2·∙min-‐1)
VO2+ Ion Flux (*10-‐7 mol·∙cm-‐2·∙min-‐1)
SelecKvity between H+ and VO2+
NDM221 25 3.2 19 223 0.16 0.30 117 N115 127 17.8 78 179 1.20 0.89 65
Current density (mA cm-‐2)
NDM221 N115 CE (%) EE(%) VE (%) CE(%) EE(%) VE(%)
50 99.2 89.3 90.0 97.5 87.7 90.0 75 99.1 84.6 85.4 97.9 83.5 85.3 100 99.1 79.8 80.5 97.9 78.4 80.1
Table 1. Proper0es of the NDM221 and N115 membranes
Table 2. Cell performance of VRBs with NDM221 and N115 membranes
Highly selective DuPont Nafion® membrane
PTFE/SiO2 Composite separator delivers similar performance at ~5% of Nafion cost.
16 Xiaoliang Wei, et. al. Adv. Energy Mater.. doi: 10.1002/aenm.201201112
Ø Nanoporous structure with average pore size of 38 nm and a porosity of 48%.
Ø Pores function as the ion transport channels during operation
Current designs have switched from porous felt to interdigitated (IDD) flow field design for lower pressure drop
Inlet
Outlet
a) Standard porous flow field, b) interdigitated flow field.
Side view of IDD flow
Side view of IDD flow
3-cell IDD vs. standard flow configuration.
#
IDD design results in 2-3X decrease in pressure drop at equivalent flow
Standard IDD
15-cell stack performance
15 Cell Stack Columbic Voltage Energy Discharge Discharge Average Pressure (psi) Pressure (psi) System Flow Rate/cell
80 mA/cm2 Efficiency (%) Efficiency (%) Efficiency (%) Capacity (Ah/
L) Energy (Wh) Power (W) negative positive Efficiency (%) (cc/min) Nafion® 115 95.2 86.9 82.7 18.6 1476 1248 8.9 6.7 61.3 (est.) 400 Nafion® 212 95.6 89.9 86.0 21.1 1711 1263 9.3 7.0 61.4 400 Nafion® 212 (IDD) 94.8 88.6 84.0 18.2 1466 1256 3.1 2.5 76.1 400 Nafion® 212 (IDD) 94.4 89.7 84.7 19.7 1590 1261 7.2 6.4 56.9 800 160 mA/cm2
Nafion® 115 95.8 77.6 74.4 17.7 1305 2336
6.5 5.4 65.0 (est.) 400 Nafion® 212 96.5 82.2 79.4 20.7 1585 2407 7.4 6.0 68.6 400 Nafion® 212 (IDD) 95.8 80.2 76.9 15.9 1204 2369 3.0 2.0 74.4 400 Nafion® 212 (IDD) 95.6 82.5 78.8 19.9 1524 2401 6.3 5.5 66.1 800 240 mA/cm2 Nafion® 212 97.0 75.7 73.5 18.7 1368 3457 6.5 5.4 67.5 400 Nafion® 212 (IDD) 95.9 74.4 71.4 14.0 1003 3442 2.6 1.8 66.7 400 Nafion® 212 (IDD) 96.0 76.8 73.7 17.3 1257 3444 5.9 5.2 65.8 800
Baseline
212 and IDD
Ø Switching to Nafion 212 and IDD enabled doubling current density while maintaining ~ 80% stack efficiency and improved system efficiency.
§ System efficiency not reflective of loss on scale-up: pump power a greater % of loss for low kW systems.
Ø Current goal is to maintain 80% energy efficiency at 240 mA/cm2.
240 mA/cm2
Current Stack performance (212 and IDF)
#
VRFB voltage probe to determine cell losses.
NegaKve Electrode V2+/V3+
PosiKve Electrode V4+/V5+
Voltage Probe
Nafion 212
TOP VIEW
Ø Voltage measurement within laminated Nafion® membrane
§ Carbon paper electrode with gold contact
§ Simultaneous measurement of both half-cells and full cell EIS response
§ EIS performed with constant current bias for realistic conditions
AcKve area (10 cm2)
VRFB voltage probe measurements
Charging 50% SOC
Discharging 50% SOC
Ø Negative/Positive Resistance = 1-layer of 212, electrode felt, electrolyte.
Ø Ohmic resistance ~ 93% of total contribution at 50% SOC.
23 Bin Li, et. al. Submitted
~11% increase in efficiency
25% increase in vanadium utilization
W-doped Nb2O5 nanorods catalyst
High performance electrode Nb2O5 based powerful catalyst
Impact of catalyst on VRFB performance
Standard
Bi3+
Nb2O5 Cha
rgin
g (5
0% S
OC
)
Ø Bi3+ addition impacts anode - results in slight drop in negative electrode ohmic and polarization losses.
Ø Nb2O5 addition to impacts both anode and cathode and results in significant drop to overall cell resistance.
Ø Catalyst added to both anode and cathode.
VRFB Voltage Probe – Charge-discharge behavior with modified electrode.
Standard Bi3+
Nb2O5
Charging
Discharging
Summary/Conclusions PNNL focused on understanding technologies necessary to reduce overall system cost of redox flow batteries.
Substitution of Nafion® 212 for 115 in 15-cell stack leads to ~5% increase in Energy Efficiency 10% decrease in operating temperature
Use of variable flow rate results in similar discharge capacity (6 lpm) with increased system efficiency
IDD design results in 2-3X decrease in pressure drop at equivalent flow field
Next Steps for stack development Ø Higher current density
u reduced stack cost however ….. § lower energy efficiency § Lower discharge capacity § Higher discharge temperature
Acknowledgements q DOE-OE Energy Storage Program, Dr. Imre Gyuk
q Stationary Energy Storage Staff at PNNL: Wei Wang, David Reed, Ed Thomsen, Zimin Nie, Qingtao Luo, Baowei Chen,, Xiaoliang Wei, Bin Li, Alasdair Crawford, Jun Liu, Yuyan Shao, Yuliang Chao, M. Vijayakumar, Birgit Schwenzer, CuiJin Yong Kim, Xiaochun Lu, Guosheng Li, Kerry Meinhardt, Brent Kirby, Vish Viswanathan, Daiwon Choi, Xioalin Li.
