Sodium-Manganese Oxide Electrode Materials for Aqueous Electrochemical Energy Storage copy

© 2014 University of New Hampshire. All rights reserved.

Sodium-Manganese Oxide Electrode Materials for Aqueous Electrochemical Energy Storage

Xin Jin12/04/2015

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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)


Na0.257(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)


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)


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)


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)


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)


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


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)


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)


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)


Raw data K1V K2V (̂1/2) K1V+K2V (̂1/2)


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)



5 mVs-1

HER Range

-1.0 -0.5 0.0 0.5 1.0-8

-4

0

4

8

Curre

nt (u

A)



5 mVs-1

0.8 1.0 1.2 1.4-8

-4

0

4

8

Curre

nt (u

A)



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?

Sodium-Manganese Oxide Electrode Materials for Aqueous Electrochemical Energy Storage copy

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