Zinc-Iron Flow Batteries with Common Electrolyte · total • Store solar energy during day, use at...
Transcript of Zinc-Iron Flow Batteries with Common Electrolyte · total • Store solar energy during day, use at...
Zinc-Iron Flow Batterieswith Common Electrolyte
Steven Selverston231st ECS Meeting, May 30, 2017
Electrochemical Engineering and Energy Laboratory
Department of Chemical and Biomolecular Engineering
Case Western Reserve University, Cleveland, Ohio
Principal Investigators:Robert Savinell, Ph.D.Jesse Wainright, Ph.D.
Motivation: Grid-Scale Energy Storage
30
20
10
12 24
net
load
(GW
)
time of day (h)
solar surplus
energy deficit
batte
ries
0
0.5
1
1.5
2
2.5
3
3.5
4
2014 2016 2018 2020 2022 2024 2026
globa
lmar
kets
ize(b
illion
s) lead acidli-ionflow
sodiumothertotal
• Store solar energy during day, use at night 1
• Replace peaker plants, enable micro-grids• Need improvements in cost and safety
1Adapted from California Association of Independent System Operators (CAISO)
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“Zinc-Iron” Flow Batteries
• Abundant, low-cost, readily-available materials• Challenges include solids/slurry handling, ion-exchange membranes
ferri/ferrostorage
50 % solids
filter
sump
HEX
H2-Fe(CN)6recomb
cell stackT=60◦ C
ZnOslurry
20 % solid
O2
CEM AEM
negativeelectrolyte
positiveelectrolyte
Zn
Zn(OH)2−4
2Fe2+
2Fe3+
Na+ Cl−
middleelectrolyte
(a) (b)(a) Alkaline zinc-ferricyanide battery, adapted from Magnani et al.1, and(b) a 2-membrane, 3-electrolyte battery, adapted from Gong et al.2
1N. Magnani et al., Sandia Report, SAND86-1266, (1987)2K. Gong et al., Energy Environ. Sci. 8, 2941 (2015)
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Zinc-Iron Chloride: A New Approach1
• Fe3+ is safer than Br2 (positive redox electrode)• Zn has higher performance than Fe (negative plating electrode)• No ion-exchange membranes, no solids handling, no oil phase, no CN
1.84 V 1.53 V 1.21 V
Zn2+/0
Fe2+/3+
Fe2+/0
Fe2+/3+
zinc all-iron
negative:
positive:
Zn2+/0
Br−/Br2
cell:
name: bromine ironzinc --
FeCl2ZnCl2
FeCl2FeCl3ZnCl2
Zn0
Zn2+
Fe3+
Fe2+
(−) (+)porous
separator
1S. Selverston et al., J. Electrochem. Soc. 164, 1069 (2017)
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Can We Use a Mixed ZnCl2-FeCl2 Electrolyte?
H+/H2 Fe2+/Fe3+Fe2+/Fe0Zn2+/Zn0
0 0.77-0.44-0.77
• Thermodynamics would predict iron should be electroplated beforezinc
• “Hydrogen evolution [on zinc] is greatly enhanced in the presence ofimpurities such as Fe...” (McBreen, 1984)
• “it is infeasible to use mixed electrolyte containing Zn and Fe as boththe negative electrolyte and positive electrolyte” (Xie et al., 2016)
• Does Zn2+ affect the Fe2+/3+ reaction?
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Effect of Zinc on Fe2+/3+
• Iron redox kinetics not strongly affected1 by Zn2+
−30
−20
−10
0
10
20
30
0 0.2 0.4 0.6 0.8 1
(a)(b)
204060
3 4 5 6 7 8
(a)(b)
i/mA
cm−
2
E/VAg/AgCl
i p,a/
mA
cm−
2
ν1/2/mV1/2s−1/2
Effect of ZnCl2 on Fe (II)/(III) redox reaction on graphite electrode with1 M NH4Cl at pH=1 at ν = 10 mV s−1. Initial electrolyte (a) contained0.2 M Fe(II) and 0.2 M Fe(III), and the modified electrolyte (b)contained 0.8 M Zn(II).1S. Selverston et al., J. Electrochem. Soc. 164, 1069 (2017)
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Using “Anomalous Codeposition (ACD)” to our Advantage
• Iron electrodeposition is strongly inhibited in the mixed electrolyte• Deposition and stripping from mixed ZnCl2-FeCl2 almost the same
as ZnCl2-only electrolyte 1
−1.2 −1 −0.8 −0.6 −0.4 −0.2 0
0.5 M ZnCl2
0.5 M ZnCl2 +0.5 M FeCl2
0.5 M FeCl2140 mA cm−2
E / VAg/AgCl
−1
−0.6
−0.2
0.2
0.6
1
−1.2 −1 −0.8 −0.6 −0.4
i ii iiii iv v
i/ip,
a
E/VAg/AgCl
1S. Selverston et al., J. Electrochem. Soc. 164 1069 (2017)
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Hydroxide Suppression Mechanism (HSM)
• Proposed in 1965 for Ni-Fe 1,2
cathode(Zn)
Zn(OH)2
Zn2+
H+
Fe2+
[OH −]
Zn2+
OH−
Fe
Ni
-600 -700 -800
2
4
6
8
10
2
4
6
8
pH
atelectrodesurface
dep
ositionrate
/mA
cm−2
electrode potential / mV vs NHE
Zn(OH)2 + 2e −→ Zn + 2OH−
1H. Dahms, I. Croll, J. Electrochem. Soc. 112 (1965)2H. Yan, et al., J. Electrochem. Soc. 43, 1577 (1996)
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Competitive Adsorption
• Emphasis on kinetics rather than thermodynamics1
M(II) + e− k1,M−−→ M(I)ads (1)
M(I) + e− k2,M−−→ M (2)k1,M = ko
1,M exp(b1,MV) (3)
1.0
0.5
0.0
−E/V
θ
θZn
θFe
1M. Matlosz, J. Electrochem. Soc. 140, 2272 (1993)
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Negative Scan Limit and RPM on Glassy Carbon
• Increasing rotation rate enhances ACD, contrary to HSM1
• 0.5 M ZnCl2, 0.5 M FeCl2, 1 M NH4Cl, ν = 50 mV s−1, bulk pH=1
−40−30−20−10
010203040
−1.2 −1.1 −1 −0.9 −0.8 −0.7 −0.6 −0.5
300 rpm9001500
i/mAc
m−
2
E/VAg/AgCl
−150
−100
−50
0
50
100
150
−1.3 −1.2 −1.1 −1 −0.9 −0.8 −0.7 −0.6 −0.5
300 rpm900 rpm1500 rpm
i/mAc
m−
2
E/VAg/AgCl
-1150 mV -1250 mV
−250−200−150−100−50
050
100150200250300
−1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0
300 rpm900 rpm1500 rpm
i/mAc
m−
2
E/VAg/AgCl
−300
−200
−100
0
100
200
300
400
−1.6 −1.4 −1.2 −1 −0.8 −0.6 −0.4 −0.2 0
300 rpm
900 rpm1500 rpm
i/mAc
m−
2
E/VAg/AgCl
-1350 mV -1450 mV1S. Selverston et al., J. Electrochem. Soc. 164 1069 (2017)
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Battery Proof-of-Concept
• 42 % relative gain in discharge voltage, 26 % relative gain in voltaicefficiency compared to all-iron at ± 25 mA cm−2
• Consistent with selective zinc plating via anomalous codeposition(ACD)
end
plate
graphite
plate
plastic
ribs
teflon
gasket
thickness = 2 mm
Daramic
separator
carbon
felt
A=6.25 cm2
current
collector
1/8” tubing 0
0.3
0.6
0.9
1.2
1.5
1.8
0 1 2
All-Iron ChlorideDischarge: 0.95 VV.E.: 66 %
Zinc-Iron ChlorideDischarge: 1.35 VV.E.: 83 %
cell
pote
ntial
/V
time / h
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Accelerated Lifetime Testing
• 30-days, 175 continuous cycles achieved without replacing electrolyte• Room-temperature, no flow fields, no dendrite suppressors used• Two-hour charges at 25 mA cm−2 (loading = 50 mAh cm−2)
00.20.40.60.8
11.21.41.6
0 1 2 3 4
E/V
t/h
0
20
40
60
80
100
0 20 40 60 80 100 120 140 160 180
averages:VE: 82 %CE: 87 %EE: 71 %
efficie
ncy
/%
cycle number
V.E.C.E.E.E.
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Conclusions
• First demonstration of a zinc-iron hybrid flow battery based usingmixed electrolytes, microporous separators
• Based on anomalous codeposition of zinc; probably not HSM• Demonstrated 30 days of cycling with over 70 % energy efficiency• Extraordinary balance between cost, safety and performance
I would like to thank:
• My advisors: Prof. Robert Savinell and Prof. Jesse Wainright• My colleagues in the EEEL Lab• The project sponsors: US DOE-OE, PNNL
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Thank you!
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Supplementary Material
All-Fe Losses
0.100.050.22
0.080.050.20
12
3
12
3
OCV = 1.21 V
discharge 0.87 Vcharge 1.57 V
1 Positive electrode2 Separator IR3 Negative electrode
• Adapted from 1981 study1
1Hruska and Savinell, J. Electrochem. Soc. 128, 18 (1981)
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Zinc-Iron Chloride Conductivity
• Sufficiently high conductivity, similar to all-iron chloride battery
platinized Pt
leads
50
100
150
200
250
300
0 0.5 1 1.5 2 2.5 3
κ/m
Scm
−1
support concentration / M
NH4ClKCl
NaCl
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XPS Analysis
0
20000
40000
60000
80000
100000
120000
140000
02004006008001000
1100
1500
1900
2300
304050607080
fe3p (Zn/Fe = 0.5)co
unts
binding energy / eV
coun
ts
binding energy / eV
XPS analysis of three samples deposited at pH=2. The sample withZn/Fe=0.5 showed a pronounced Fe3p peak and an estimated 10 %atiron.
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Supporting Electrolyte Effects
−100
−50
0
50
100
150
−1.2 −1.1 −1 −0.9 −0.8 −0.7 −0.6 −0.5 −0.4
5 M NH4Cl
3 M NH4Cl1 M NH4Cl
i/mAc
m−
2
E/VAg/AgCl
−100
−50
0
50
100
150
−1.2 −1.1 −1 −0.9 −0.8 −0.7 −0.6 −0.5 −0.4
1 M KCl3 M KCl
Sat’d KCl
i/mA
cm−
2
E/VAg/AgCl
Effect of supporting electrolyte cations on the deposition and dissolution(Zn/Fe=4, pH=1). Total metal ion concentration CMe2+ = 1 M.Titanium sheet substrate. Room-temp, unstirred.
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EIS during Lifetime Testing
• Color shows number of days• Oscillating resistance- not linearly increasing with time
0
0.5
1
1.5
2
2.5
3
0 0.5 1 1.5 2 2.5 3
-Im(Z
)/Oh
m
Re(Z)/Ohm
0
5
10
15
20
25
30
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
-Im(Z
)/Oh
m
Re(Z)/Ohm
0
5
10
15
20
25
30
Electrochemical impedance spectroscopy (EIS) of zinc-iron chloride cellover 30 days of operation. Scans were carried out from 10 kHz to 10 Hzafter charging.
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