Post on 16-Mar-2018
A New Vanadium Redox Flow BatteryUsing Mixed Acid Electrolytes
November 2, 2010
US DOE Energy Storage Systems (ESS) Program Review
Washington DC
Liyu Li, Soowhan Kim, Wei Wang, M. Vijayakumar, Zimin Nie, Baowei Chen, Jianlu Zhang, Jianzhi Hu, Gordon Graff, Jun Liu, Gary Yang*
Funded by the Energy Storage Systems Program of the U.S. Department Of Energy through Pacific Northwest National Laboratories
Redox Flow Battery (RFB)
A redox flow battery is a promising technology for large scale energy storage .
Potential RFB Systems
-1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Standard potential (V) of redox couples
H2 evolution O2 evolution V3+/V2+ VO2+/VO2+
VO2+/V3+
Fe3+/Fe2+
Mn3+/Mn2+
MnO4-/MnO2
Ce4+/Ce3+
Co3+/Co2+
Cu2+/Cu+
TiOH3+/Ti3+
Ti3+/Ti2+
Cr3+/Cr2+
Zn2+/Zn
S/S2-
Br2/Br-
BrCl2-/Br-
Cr5+/Cr4+
Cl2/Cl-
All V Redox Flow Battery
The use of vanadium in both the anolyte and catholyte effectively eliminate the cross-contamination between the electrolytes through the ion-exchange membrane.
Challenges for All Vanadium Sulfate RFBV specie Vn+, M H+, M SO4
2-, M Temp, oC Time for p.p.
V2+
2 6 5 -5 419 hr2 6 5 25 Stable (>30 d)2 6 5 40 Stable (>30 d)
V3+
2 4 5 -5 634 hr2 4 5 25 Stable (>30 d)2 4 5 40 Stable (>30 d)
V4+ (VO2+)2 6 5 -5 18 hr2 6 5 25 95 hr2 6 5 40 Stable (>30 d)
V5+ (VO2+)
2 8 5 -5 Stable (>30 d)2 8 5 25 Stable (>30 d)
2.2 7.8 5 40 95 hr1.8 8.4 5 40 358 hr
Low energy density: Vn+ concentration <1.7M, decided by the low solubility of V4+ at low temperatures and the poor stability of V5+ at high temperatures.
Limited operation temperature window: 10 to 40oC, requiring active electrolytes temperature management during hot/cold weathers.
Stability of Vn+ Cations in HCl Solution
Vn+ specie Vn+, M H+, M Cl-, M T, oC Time for precipitationV2+ 2.3 5.4 10 -5 Stable (>10 d)
2.3 5.4 10 25 Stable (>10 d)2.3 5.4 10 40 Stable (>10 d)
V3+ 1.5 3.0 7.5 -5 Stable (>10 d)1.8 3.0 8.4 -5 124 hr2.3 3.1 10 -5 96 hr2.3 3.1 10 25 Stable (>10 d)2.3 3.1 10 40 Stable (>10 d)
V4+ (VO2+) 2.3 5.4 10 -5 Stable (>10 d)2.3 5.4 10 25 Stable (>10 d)2.3 5.4 10 40 Stable (>10 d)
V5+ (VO2+) 2.3 7.7 10 -5 Stable (>10 d)
2.3 7.7 10 25 Stable (>10 d)2.3 7.7 10 40 Stable (>10 d)
Cl- anions can effectively stabilize V5+, V4+, and V2+.
It is likely that high concentration of V2+, V3+, V4+, and V5+ cations can be stabilized in a mixed sulfate and chloride electrolyte solution.
Vn+ Stability in SO42—Cl- Mixed Solutions
Vn+
specieVn+, M T, oC Time for
precipitationV2+ 3 -5 Stable (>10 d)
2.5 -5 Stable (>10 d)2.5 25 Stable (>10 d)2.5 40 Stable (>10 d)3 40 Stable (>10 d)
V3+ 3 -5 192 hr (8 d)2.5 -5 Stable (>10 d)2.5 25 Stable (>10 d)2.5 40 Stable (>10 d)3 40 Stable (>10 d)
Vn+
specieVn+, M T, oC Time for
precipitationV4+
(VO2+)3 -5 Stable (>10 d)
2.5 -5 Stable (>10 d)2.5 25 Stable (>10 d)2.5 40 Stable (>10 d)3 40 Stable (>10 d)
V5+
(VO2+)
3 -5 Stable (>10 d)2.5 -5 Stable (>10 d)2.5 25 Stable (>10 d)2.5 40 Stable (>10 d)3 40 Stable (>10 d)
2.7 V5+
0.3 V4+50 Stable (>10 d)
2.7 V5+
0.3 V4+60 Stable (>10 d)
SO42-/Cl- mixtures can effectively stabilize >2.5M V5+, V4+, V3+ and V2+.
Much broad operation temperature window (-5 to 60 oC) can be achieved using SO42-/Cl- mixed electrolytes.
The overall stability of vanadium is decided by V3+ at low temperatures.
V
O
O
O
O
O
O
O
O
O
Cl
In sulfate solution, V5+ exists as [VO2(H2O)3]+, which tends to convert to V2O5-3H2O precipitation via:
[VO2(H2O)3]+ → VO(OH)3 + [H3O]+
2VO(OH)3 → V2O5-3H2O ↓
Solution Chemistry of the Mixed Electrolytes-DFT Study
V
51V in mixed acid
51V in sulfuric acid
51V in VOCl3standard
35Cl in mixed acid
35Cl in VOCl3
35Cl in HCl
Solution Chemistry of the Mixed Electrolytes-
NMR Study
Temperature Dependence of VO2Cl(H2O)2 Formation
-570
-565
-560
-555
-550
-545
-540
-30 -20 -10 0 10 20 30 40 50 60Temperature, oC
51V
Che
mic
al S
hift
(ppm
)
0
10
20
30
40
50
60
70
80
51V
Line
Wid
th (k
Hz)
Chemical Shift-Sulfuric AcidChemical Shift Mixed AcidLine Width Sulfuric AcidLine Width Mixed Acid
VO2Cl(H2O)2 complex starts to form in the mixed solutions when temperatures reaching ~20oC.
Solution Chemistry of the Mixed Electrolytes-
DFT and Stability Studies
Same V2+, V3+ and V4+ -containing structures was predictedin both electrolyte solutions: [V(H2O)6]2+, [V(H2O)6]3+ and[VO(H2O)5]2+.
According to SEM-EDS, and XRD analysis, in the mixedsystems, the stability of V4+ is controlled by the solubility ofVOSO4, the stability of V3+ is controlled by the solubility ofV2(SO4)3 and VOCl, the stability of V2+ is controlled by thesolubility of VSO4.
The improvement of stability of V2+, V3+, and V4+ in the mixedsystem over the current sulfate systems is due to thedecrease of SO4
2- concentration in the solutions.
Electrochemical Properties of Mixed Solutions
-0.8 -0.4 0.0 0.4 0.8 1.2 1.6-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3
2.5 M V4+ + 2.5 M SO2-4 + 6 M Cl-
1.5 M V4+ + 5 M SO2-4
Curr
ent D
ensi
ty (A
/cm
2 )
Potential (V vs. SHE)
V5+V4+
V4+ V5+
V2+ V3+
V3+V2+
No chlorine gas evolution.
Electrode and Cell Reactions (T<10oC)
Cathode: VO2+ + H2O – e VO2+ + 2H+ E° = 1.00V
Anode: V3+ + e V2+ E°=-0.25V
Cell: VO2+ + H2O + V3+ VO2+ + 2H+ + V2+ E°=1.25V
Charge Discharge
Charge Discharge
Charge Discharge
Cathode: VO2+ + Cl- + H2O – e VO2Cl + 2H+
Anode: V3+ + e V2+
Cell: VO2+ + Cl- + H2O + V3+ VO2Cl + 2H+ + V2+
Charge Discharge
Charge Discharge
Charge Discharge
Electrode and Cell Reactions (T>10oC)
- Cell and reservoirs are inside the environmental chamber.
- Circulating pump is out side of the chamber.
- Pressure monitoring.
Cell Testing and RFB Evaluation
0 10 20 30 40 50 60 70 80 90 1000.6
0.8
1.0
1.2
1.4
1.6
1.8
Charging
Volta
ge (V
)
Capacity / Charging Capacity (Ah%)
Discharging
10 15 20 25 30 35 40 45 50 5570
75
80
85
90
95
100
Coulomb Energy Voltage
Ef
ficie
ncy
(%)
Cycle Number
Stable performance with 88% energy efficiency at 50 mA.cm-2
Cell Performance at Ambient Temperature
70
75
80
85
90
95
100
0 10 20 30 40 50 60 70 80 90
Cycle number
Effic
ienc
y, %
Coulombic Efficiency
Voltage Efficiency
Energy Efficiency
40oC 0oC5oC50oC
A VFB with 2.5 M V mixed acid electrolyte can be operated under a broad temperature range of 0 to 50 oC.
Redox reactions are temperature dependent.
No noticeable gas evolution over 25 days.
Cell Performance at Varied Temperatures
Cell Performance at Varied Current Densities
Cell operation conditions: 10 cm2 flow cell, Charged to 1.7V by 50 mA/cm2 current.
Discharge Current,
(mA.cm-2)
Energy Density(Wh.L-1)
Columbic Efficiency
Energy Efficiency
Mixed sulfate Mixed sulfate Mixed sulfate2.5MV 3MV 1.6MV 2.5MV 3MV 1.6MV 2.5MV 3MV 1.6MV
100 36.2 39.5 22.3 0.95 0.95 0.94 0.81 0.76 0.83
75 37.5 40.8 22.4 0.96 0.96 0.94 0.84 0.81 0.85
50 38.5 41.8 22.6 0.96 0.97 0.94 0.87 0.85 0.87
25 39.2 43.1 22.6 0.96 0.97 0.94 0.90 0.89 0.88
The VRBs using mixed sulafte-chloride electrolytes were able to deliver 70 to 80% more energy than the
sulfate system, while still being highly efficient.
A new vanadium redox flow battery with a significant improvement over the current technology was developed.
This battery utilizes sulfate-chloride mixed electrolytes, which are capable of dissolving 2.5 M vanadium, representing about 70% increase in energy density over the current sulfate system.
More importantly, the new electrolyte remains stable over a wide temperature range of -5 to 60oC, potentially eliminating the need of energy-consuming solution temperature management.
Battery tests indicated no concern of chlorine gas evolution during the battery operation.
Summary
Further Work
Optimize the mixed electrolyte for further improvement in energy density and stability.
Demonstrate a 2.0 kWh (0.3 kW) bench-top prototype FRB with the newly developed mixed electrolyte.
Build up strong collaborations with industry, university, and other national laboratory partners.
Prepare for larger systems demonstration within 2-3 years.
AcknowledgementsFinancial support :1. DOE Office of Electricity Delivery and Energy Reliability
Energy Storage Program (Manager: Dr. Imre Gyuk)
2. PNNL LDRD program for NMR and DFT-related work.
The NMR work was carried out at the Environmental and MolecularScience Laboratory, a national scientific user facility sponsored bythe DOE’s Office of Biological and Environmental Research (BER).