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© 2014 University of New Hampshire. All rights reserved.
Sodium-Manganese Oxide Electrode Materials for Aqueous Electrochemical Energy Storage
Xin Jin12/04/2015
2https://www.quizlife.com/sites/acquia_prod/files/quiz_icon/Lightning.jpghttp://www.ecmag.com/sites/default/files/bottled_lightning_think157166346.jpg
What is Energy Storage?
Can we store lightning?
3
Why We Need Energy Storage?Solar Energy
Wind Energy
http://www.saftbatteries.com/sites/default/files/styleshttp://assets.inhabitat.com/wp-content/blogs.dir/1/fileshttp://diydrones.com/forum/topics/ultra-capacitor-usagehttp://techcrunch.com/2016/01/09/tesla-model-s-can-now-drive-without-you/
Electric Energy
4Chem. Rev. 2014, 114, 11619−11635http://www.maxwell.com
Advantages:· High power performance· Environment-friendly· Long cycle life
How Fast VS How Much
Aqueous Electrochemical Energy Storage
5
Comparison of Na and Li metals
Characteristics Na Li
Price (for carbonates) 0.07-0.37a 4.11-4.49b
Capacity density 1.16 Ahg-1 3.86Ahg-1
Voltage Vs. S.H.Ec -2.7 V -3.0 V
Ionic radius 0.98 0.69
Melting point 97.7 oC 180.5 oC
a Purity: 98.8–99.2% b Battery grade: 99.9% c S.H.E.: Standard
Advantages: abundant and cheap environmental -fridendly
6
Synthesis of Electrode Materials
MnCl2 ∙4H2OInject NaOH(aq)
Mn3O4
Ground with NaOH(s) at different ratios
280 °C for 6h NaδMnOx (washed)
(a) (b)
Color changes during synthesis process
7
Na Ratio in NaδMnOx
Energy-dispersive X-ray Spectroscopy(EDS): elemental analysis technique.
0.0
0.2
0.4
0.6
Atom
ic ra
tio o
f Na
to M
n Theoretical Ratio Actual Ratio
0.103
0.2230.257 0.259
Na 0Mn 3
O 4
Na 0.5Mn 3
O 4
Na 1Mn 3
O 4
Na 1.5Mn 3
O 4
Na 2Mn 3
O 4
• The actual ratio of Na to Mn has no linear relationship due to the limitation of Na-ion in manganese oxide.
Chemical formula based on molar ratio of Na to Mn before thermal treatment
8
Phase Change upon Li+ De-intercalation
• Mn migrates to tetrahedral sites after alkali element (e.g. Li+) was removed
• Layered structure transformed to spinel manganese oxide
Phys. Chem. Chem. Phys., 2012, 14, 15571–15578 15571
9
X-Ray Diffraction Patterns
5 10 15 20 25 3031
2
116204
113112
11000
4
002
002
202
710132
71-1
33-2
62-1
003
40-3421
33-1
42-2
131
022
42-1
112
11-2002
22-1
31-202
1
31-1111
11-1
20-1
200
Norm
alize
d In
tens
ity
2 (Degree)
003 004 005001
Mn5O8
Mn5O8
Na0.223(Mn5O8)(MnO2)
Na0.103(Mn5O8)(MnO2)
Na0.257(Mn5O8)(MnO2)Na0.259(Mn5O8)(MnO2)MnO2
X-Ray diffraction technique: identifying the atomic and molecular crystalline structure.
10
Structure Transformation
Mn5O8
Na δ MnO2
280 °C , 6h
Mn3O4
280 °C , 6hNaOH ground with Mn3O4
Lattice system Lattice constants Lattice angles
Mn3O4 Tetragonal a =b c α=β=γ=90o
Mn5O8 Monoclinic a b c α=γ=90o, β90o
MnO2 Orthorhombic a b c α=β=γ=90o
11
Three-Electrode Half Cell
Glassy carbon working electrode
Platinum wire counter electrode
Ag/AgCl reference electrode Blank electrode
Ink containing electrode materials
3.5 mg Mn5O8
1.5 mg Carbon10 ml DI water
Electrode loaded with materials
0.1M Na2SO4 electrolyte
12
Cyclic Voltammetry
δMnOx MnOx + δNa+ +δe-
-1.0 -0.5 0.0 0.5 1.0
-0.04
-0.02
0.00
0.02
0.04
Cur
rent
(mA
)Potential vs. Ag/AgCl (V)
Forward
Backward50 mVs-1
Time
Time
PotentialCurrent
0
13
Cyclic Voltammetry of Na0.223(Mn5O8)(MnO2)
-1.0 -0.5 0.0 0.5 1.0
-40
0
40
80
Curre
nt D
ensit
y (A/
g)
Potential vs. Ag/AgCl (V)
5 mVs-1
10 mVs-1
50 mVs-1
100 mVs-1
200 mVs-1
500 mVs-1
1000 mVs-1
• Potential window: -1.25-1.25 V (vs Ag/AgCl) Oxidation peak: 0.97 V Reduction peak: -0.15 V
14
CV of Sodium-manganese Oxide
-1.0 -0.5 0.0 0.5 1.0
-40
0
40
80
Curre
nt D
ensit
y (A/
g)
Potential vs. Ag/AgCl (V)
5 mVs-1 10 mVs-1 50 mVs-1 100 mVs-1 200 mVs-1 500 mVs-1 1000 mVs-1
-1.0 -0.5 0.0 0.5 1.0
-40
0
40
80
Cur
rent
Den
sity (
A/g)
Potential vs. Ag/AgCl (V)
5 mVs-1
10 mVs-1
50 mVs-1
100 mVs-1
200 mVs-1
500 mVs-1
1000 mVs-1
-1.0 -0.5 0.0 0.5 1.0
-40
0
40
80
Curre
nt D
ensit
y (A/
g)
Potential vs. Ag/AgCl (V)
5 mVs-1
10 mVs-1
50 mVs-1
100 mVs-1
200 mVs-1
500 mVs-1
1000 mVs-1
-1.0 -0.5 0.0 0.5 1.0
-40
0
40
80
Curre
nt D
ensit
y (A/
g)
Potential vs. Ag/AgCl (V)
5 mVs-1
10 mVs-1
50 mVs-1
100 mVs-1
200 mVs-1
500 mVs-1
1000 mVs-1
-1.0 -0.5 0.0 0.5 1.0
-40
0
40
80
Curre
nt D
ensit
y (A/
g)
Potential vs. Ag/AgCl (V)
5 mVs-1
10 mVs-1
50 mVs-1
100 mVs-1
200 mVs-1
500 mVs-1
1000 mVs-1
Mn5O8 Na0.103(Mn5O8)(MnO2) Na0.223(Mn5O8)(MnO2)
Na0.257(Mn5O8)(MnO2) Na0.259(Mn5O8)(MnO2)
15
Capacitance of Sodium-manganese Oxide
10 100 1000
40
80
120
160
200 Mn5O8 Na0.103(Mn5O8)(MnO2) Na0.223(Mn5O8)(MnO2) Na0.257(Mn5O8)(MnO2) Na0.259(Mn5O8)(MnO2)
Spec
ific C
apac
itanc
e (F
g-1)
Potential vs. Ag/AgCl (v)-1.0 -0.5 0.0 0.5 1.0
-0.02
0.00
0.02
0.04
Curre
nt (m
A)
Mn5O8 Na0.115(Mn5O8)(MnO2) Na0.286(Mn5O8)(MnO2) Na0.344(Mn5O8)(MnO2) Na0.348(Mn5O8)(MnO2)
50 mVs-1
Potential vs. Ag/AgCl (V)
Peak current and specific capacitance become larger as the concentration of Na+ increases and structure changes.
16
Charge Storage Mechanism--Capacitive Current
_
_
_
_
_ElectrolyteElectrode
Charge adsorption at surface of the electrode
Double Layer Capacitance
++++++
Mn→Mn-1
ElectrolyteElectrode
Reversible redox reactions near electrode surface
Pseudocapacitance
𝑖1=𝑎1𝑣Capacitive/Pseudocapacitive Current :
Peak current
Constant
: Scan rate
17
In-depth Insertion of Na-ion into layered material
Insertion of Na-ion into an bulk electrode material
Na+
𝑖2=𝑎2𝑣0.5
Batteries
Diffusion-limited Redox Current:
Charge Storage Mechanism--Diffusion-limited Redox Current
Na+
Peak current
Constant
: Scan rate
18
Charge Storage Mechanism Analysis
0.8 0.9 1.0 1.1 1.20.0
0.3
0.6
0.9
Curre
nt (m
A)
Potential vs. Ag/AgCl (V)
5 mVs-1
10 mVs-1
50 mVs-1
100 mVs-1
200 mVs-1
-1.0 -0.5 0.0 0.5 1.0
-0.4
0.0
0.4
0.8
Curre
nt (m
A)
Potential (V)
5 mVs-1
10 mVs-1
50 mVs-1
100 mVs-1
200 mVs-1
𝑖1=𝑎1𝑣
𝑖2=𝑎2𝑣0.5 Diffusion-limited Redox Current:
Capacitive/Pseudocapacitive Current:
19
Redox Behavior of Sodium-manganese Oxide
b-valueAnodic Scan Cathodic
Scan
Na0Mn5O80.6699 0.7041
Na0.115(Mn5O8)(MnO2) 0.7457 0.7188
Na0.286(Mn5O8)(MnO2) 0.7765 0.7385
Na0.344(Mn5O8)(MnO2) 0.7964 0.7534
Na0.348(Mn5O8)(MnO2) 0.805 0.7513
b-value increases
Bigger b-value indicated stronger redox behavior as the concentration of Na+ increases, more capacitive reactions occur near the surface at the strongest redox potential.
0.65
0.70
0.75
0.80
0.85
b-va
lue
Anodic Scan Cathodic Scan
Na 0Mn 5
O 8
Na 0.103(M
n 5O 8
)(MnO 2
)
Na 0.223(M
n 5O 8
)(MnO 2
)
Na 0.257(M
n 5O 8
)(MnO 2
)
Na 0.259(M
n 5O 8
)(MnO 2
)
20
Capacitive and Diffusion-limited Redox Contribution
Capacitive contribution
Diffusion-limited redox contribution
0.1
0.2
0.3
Capacitive Contribution
0.16
0.230.25
0.260.28
Na 0Mn 5
O 8
Na 0.103(M
n 5O 8
)(MnO 2
)
Na 0.223(M
n 5O 8
)(MnO 2
)
Na 0.257(M
n 5O 8
)(MnO 2
)
Na 0.259(M
n 5O 8
)(MnO 2
)
𝑖=𝑘1𝑣+𝑘2𝑣1/2 𝑖/𝑣 1/2=𝑘1𝑣1 /2+𝑘2
𝑘1𝑣𝑘2𝑣1/2
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-2
-1
0
1
2
3
Curre
nt D
ensit
y (A/
g)
Potential vs. Ag/AgCl (V)
Raw data K1V K2V (̂1/2) K1V+K2V (̂1/2)
Na0Mn5O8
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5
-2
-1
0
1
2
3
Curre
nt D
ensit
y (A/
g)
Potential vs. Ag/AgCl (V)
Raw data K1V K2V (̂1/2) K1V+K2V (̂1/2)
Na0.259(Mn5O8)(MnO2)
21
Pourbaix Diagram• a: Hydrogen Evolution Reaction (HER)• b: Oxygen Evolution Reaction (OER)• Na2SO4 electrolyte: pH=7
0 2 4 6 8 10 12 14
-0.8
-0.4
0.0
0.4
0.8
1.2
Hydrogen Evolution
Pote
ntial
(V vs
. SHE
)
pH
Oxygen Evolution
a
b
E
E
22
𝜂=𝐴∗𝑙𝑛 𝑖𝑖0
· : overpotential, V· A : Tafel slope, V · i : current density, A/m2
· i0 : exchange current density, A/m2
Overpotential is the potential difference between experimentally observed potential and potential determined at equilibrium state.
Tafel Analysis
23
HER and OER Range for Tafel Analysis
-1.2 -1.0 -0.8-8
-4
0
4
8
Curre
nt (u
A)
Potential vs. Ag/AgCl (V)
Mn5O8 Na0.103(Mn5O8)(MnO2) Na0.223(Mn5O8)(MnO2) Na0.257(Mn5O8)(MnO2) Na0.259(Mn5O8)(MnO2)
5 mVs-1
HER Range
-1.0 -0.5 0.0 0.5 1.0-8
-4
0
4
8
Curre
nt (u
A)
Potential vs. Ag/AgCl (V)
Mn5O8 Na0.115(Mn5O8)(MnO2) Na0.286(Mn5O8)(MnO2) Na0.344(Mn5O8)(MnO2) Na0.348(Mn5O8)(MnO2)
5 mVs-1
0.8 1.0 1.2 1.4-8
-4
0
4
8
Curre
nt (u
A)
Potential vs. Ag/AgCl (V)
Mn5O8 Na0.103(Mn5O8)(MnO2) Na0.223(Mn5O8)(MnO2) Na0.257(Mn5O8)(MnO2) Na0.259(Mn5O8)(MnO2)
5 mVs-1
OER Range
• HER range: -1.249 V to -0.615 V (vs Ag/AgCl) Overpotential range: 0 V to 0.634 V
• OER range: 1.249 V to 0.616 V (vs Ag/AgCl) Overpotential range: 0 V to 0.633 V
24
HER &OER of Sodium-manganese Oxide
0.1
0.2
0.3
0.4
0.5 HER
Tafe
l Slop
e
0.4040.378
0.294
0.392 0.391
Mn 5O 8
Na 0.103(Mn 5
O 8)(M
nO 2)
Na 0.223(Mn 5
O 8)(M
nO 2)
Na 0.257(Mn 5
O 8)(M
nO 2)
Na 0.259(Mn 5
O 8)(M
nO 2)
0.1
0.2
0.3
Tafe
l Slop
e
OER
0.190
0.2140.232 0.228
0.263
Mn 5O 8
Na 0.103(Mn 5
O 8)(M
nO 2)
Na 0.223(Mn 5
O 8)(M
nO 2)
Na 0.257(Mn 5
O 8)(M
nO 2)
Na 0.259(Mn 5
O 8)(M
nO 2)
• Sodium-manganese oxide has a stable 2.5 V potential window, increasing energy density.
0.93 0.96 0.99 1.02 1.05 1.08
0.60
0.61
0.62
0.63
0.64
Over
pote
ntial
(V)
ln(i/i0)
5 mVs-1 Na0.223(Mn5O8)(MnO2) Liner fit of Tafel Equation
y=0.29x+0.33R2=0.9983
𝜂=𝐴∗𝑙𝑛 𝑖𝑖0
25
Conclusion
• X-ray diffraction showed the structural evolution from Mn5O8
phase to MnO2 phase when sodium concentration within manganese oxides increased.
• The specific capacitance of sodium-manganese materials increases and capacitive current behaviors become stronger as sodium concentration increases
• Sodium-manganese oxide can have a stable 2.5 V potential window without causing significant hydrogen and oxygen evolution reactions.
26
Acknowledgments
• UNH Chemical Engineering• Advisor: Dr. Xiaowei Teng • Colleague: Xiaoqiang Shan(XRD structure
analysis), Daniel S. Charles, Guangxing Yang
27
Thank you! Questions?