Understanding ionic structure and dynamics in novel electrolytes ; Paving the way to improved energy storage.

Maria Forsyth

Typical electrolyte materials for electrochemical devices

• Batteries• Solar Cells• Fuel Cells• Actuators• Capacitors• Sensors

• Solvent based electrolytes.• Ionic Liquids• Gels and Polymer Electrolytes• Ceramic Conductors eg Li3N.• Plastic crystal fast-ion

conductors.

Electrolyte Families Devices

How to optimise electrolytes for target device?• Need to characterise ion transport and its relationship to structure / speciation – NMR perfect tool • Use Chemical shift, wide line, relaxation measurements, diffusion, imaging…multinuclear, variable temperature

Dr.Luke O’DellDeakin NMR Facility Co-director

NMR imaging of Zn/air battery

AnodeZn + 4OH- Zn(OH)4

-2 + 2e-

CathodeO2 + 2H2O + 4e- 4OH-

??

~1 M OH- conc.

~5 M OH- conc.

~10 M OH- conc.

+ =

Ti mesh Zn ribbon High pH KOH(aq)

Collaboration with Dr. Melanie Britton, Uni. Birmingham

- METAL/AIR BATTERIES- FLOW BATTERIES

ACES (I) PROJECTS• Zinc• Magnesium• Air electrodes for energy generation and storage

ACES (II) PROJECTS• Zinc Flow batteries• Reversible Metal Air batteries• Microfluidics and batteries for soft robotics

J. Sunarso, A. A. J. Torriero, W. Zhou, P. C. Howlett and M. Forsyth, Journal of Physical Chemistry C, 2012,

116, 5827-5834.

T. Khoo, P. C. Howlett, M. Tsagouria, D. R. MacFarlane and M. Forsyth, Electrochimica Acta, 2011, 58,

583-588.

T. J. Simons, A. A. J. Torriero, P. C. Howlett, D. R. MacFarlane and M. Forsyth, Electrochemistry

Communications, 2012, 18, 119-122.

Reversible Air cathode catalysisProton ConductorsElectrode 3D structuring

Approaches to Zn2+ IL based electrolytes

NTf2

Inclusion of Oxygen Decreases Viscosity

Decrease likelihood of Metal-AnionComplexation i.e. -

Zn2+ + 4[A-] [Zn(A)4]2-

Ether oxygen coordination Positively charged Zinc Complexes

Mega Kar, D.R. MacFarlane, B.J. Winther-Jensen and M. Forsyth PCCP 2013Mega Kar, etal PCCP (submitted)

Mega Kar

Metal deposition/cycling from ILsNovel ILs for Zn2+ Complexation – the affect of the cation

Mega Kar

4

• Novel ILs with ether containing cations, designed to chelate Zn2+.

• When paired with NTf2 anion, Zn2+ can be deposited and stripped.

• Increase in ether oxygen leads to more negative Zn2+ reduction current, suggesting stronger chelation.

M.Kar etal PCCP (2013)

8

Effect of Anions on Zn2+ Voltammetry

Zn(dca)2 displays:

• Lower OPD

• High Current Density

• High Solubility

Scan Rate – 100 mVs-1

WE – 1 mm GCCE – Pt wireRE – 100 mM AgOTf in [emim][dca]Contains 3 wt% H2O

T.J. Simons, A.A.J. Torriero, P.C. Howlett, D.R. MacFarlane, M. Forsyth, Electrochem. Commun., 18 (2012) 119-122.

Tristan Simons

Effect of Cation on Zn plating/stripping - pyrrolidinum vs immidazolium

T. J.Simons, D.R. MacFarlane, M. Forsyth & P.C.Howlett, ChemElectroChem, 2014.

Modelling the Electrode/Electrolyte interface to understand

electrochemical behaviour

Confidential 10Early results suggest layering is preferred for pyrrolidinum cation at

Carbon electrode corresponding to poorer echem for Zn2+ Zn

Erlendur Jonsson

O2 Redox chemistry - Phosphonium based IL/water

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

Cur

rent

den

sity

/ m

A c

m-2

1.5 % wt. water 4.5 % wt. water

Potential / V vs Ag/Ag+

-1.50 -1.25 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

Cur

rent

den

sity

/ m

A cm

-2

Potential / V vs. Ag/Ag+

Reversible O2/ O2●- process in

the presence of high quantities of water due to ion paring interactions

Improved performance toward the ORR upon addition of water

Cristina Pozo-Gonzalo et al. The Journal of Physical Chemistry Letters, 2013, 1834-1837.

O2/ O2●-

1.5 wt% H2O

P

C6H13C6H13C6H13

C14H29

Cl+Dr. Cristina Pozo-

Gonzalo

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

-0.3

-0.2

-0.1

0.0

0.1

0.2

Curr

ent d

ensi

ty /

mA

cm

-2

Potential / V vs Ag/Ag+

c)

N2-saturated

O1

R1

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

Potential / V vs Ag/Ag+

Curr

ent d

ensi

ty /

mA

cm

-2

b)

N2-saturated

O1

R1

Role of anion on reversibility of the 1 e- process

P

C6H13C6H13C6H13

C14H29

anion+

Anion: Cl, TFSI, dca-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

-0.2

-0.1

0.0

0.1

Cur

rent

den

sity

/ m

A c

m-2

Potential / V vs Ag/Ag+

N2-saturated

a)

R1

O1

[P66614]Cl

[P66614][TFSI][P66614]dca

• Kinetics

• Current density

Cristina Pozo-Gonzalo et al. The Journal of Physical C, 2014

N

N N

N-SS

CF3F3C

OO O

O

Other energy storage technologies under investigation include – Lithium, Sodium, Magnesium and Supercaps.

Fast Charge/Discharge of Li Metal Batteries Using An Ionic Liquid Electrolyte

S S

N-propyl-N-methylpyrrolidinium (C3mpyr+) Bis(fluorosulfonyl)imide (FSI)

H Yoon, PC Howlett, AS Best, M Forsyth, DR MacFarlane, Journal of The Electrochemical Society 160 (10), A1629-A1637

Dr Hyun (Martin) Yoon

Typical IL electrolyte for a Li cell

Much higher Li content- Equimolar mixture of salts

0 20 40 60 80 100 120 140

3.95

4.00

4.05

4.10

4.15

4.204.2V constant current (CC) charging cut off

4C, 5C, FSI only

3C

2C

Vo

lta

ge

(V

)

Capacity (mAh.g-1)

1C

Phosphonium FSI ILs – Fluid and High Electrochemical Stability in ‘mixed salts’

Gaetan Girard

Trimethyl isobutyl phosphonium bis(fluorosulfonyl)imide

3.2 mol/kg LiFSI

High stability and cycling efficiency even at 4.3V

Li cycled at eq. 0.5C x 50 cycles (0.5 Ccm-2)

3.8 molkg-1 LiFSI

Deposition morphology improved at high LiFSI

Advanced Characterisation of the interface-In collaboration with Nante University - Director IMN, Prof. D. Guyomard

And Cambridge Uni ( NMR) - Dr. P. Bayley)

Sodium Batteries – cheaper alternatives to Li- Need low temperature electrolytese.g. IL electrolytes, Na Ionomers (polymers)

In collaboration with Prof. Michel Armand and Teofilo Rojo, CIC Energinieu, Spain

Na+

ARC DP grant

S S

N-propyl-N-methylpyrrolidinium (C3mpyr+) Bis(fluorosulfonyl)imide (FSI)

50 mol% or 3.24 mol.kg-1

W: Ni, C: Ag, R: 10 mmol.kg-1 AgNTf2 in C4mpyrNTf2, 20 mV.s-1

25 oC 50 oC

75 oC 100 oC-4 -3 -2 -1 0

-12

-6

0

I (m

A.c

m-2)

E (V vs. Ag | AgNTf2)

1st 2nd 3rd 4th 5th

-4 -3 -2 -1 0-40

-30

-20

-10

0

10

I (m

A.c

m-2)

E (V vs. Ag | AgNTf2)

1st 2nd 3rd 4th 5th

-4 -3 -2 -1 0-10

-5

0

5

I (m

A.c

m-2)

E (V vs. Ag | AgNTf2)

1st 2nd 3rd 4th 5th

-4 -3 -2 -1 0-40

-30

-20

-10

0

10

20

30

I (m

A.c

m-2)

E (V vs. Ag | AgNTf2)

1st 2nd 3rd 4th 5th

Eg. Mixed NaFSI/Ionic Liquid electrolytes

Na | Na symmetric cells show improved stability with highest NaFSI in C3mpyrFSI

Highest NaFSI concentration gives BEST cycling performance M.Forsyth , P. Howlett, M.Yoon, M.Hilder D.Macfarlane, M.Armand Prov. Patent submitted (2015)

0.57 mol/kg (15 mol%) NaFSI 2.16 mol/kg (40 mol%) NaFSI

3.24 mol/kg (50 mol%) NaFSI

Interfacial resistance significantly decreased with highest NaFSI

0 5000 10000 15000

0

5000

10000

15000 0.17 mol.kg-1

0.36 mol.kg-1

0.57 mol.kg-1

0.81 mol.kg-1

1.08 mol.kg-1

1.39 mol.kg-1

2.16 mol.kg-1

3.24 mol.kg-1

-Z'' (

)

Z' ()

0 1000 2000 3000

0

1000

2000

3000 0.17 mol.kg-1

0.36 mol.kg-1

0.57 mol.kg-1

0.81 mol.kg-1

1.08 mol.kg-1

1.39 mol.kg-1

2.16 mol.kg-1

3.24 mol.kg-1

-Z'' (

)

Z' ()

GEIS 10 uA, 100 KHz – 300mHz, R.T.

R1 R2

CPE1

R3

CPE2

Element Freedom Value Error Error %R1 Fixed(X) 0 N/A N/AR2 Fixed(X) 0 N/A N/ACPE1-T Fixed(X) 0 N/A N/ACPE1-P Fixed(X) 1 N/A N/AR3 Fixed(X) 0 N/A N/ACPE2-T Fixed(X) 0 N/A N/ACPE2-P Fixed(X) 1 N/A N/A

Data File:Circuit Model File:Mode: Run Simulation / Freq. Range (0.001 - 1000000)Maximum Iterations: 100Optimization Iterations: 0Type of Fitting: ComplexType of Weighting: Calc-Modulus

Dot points : real data, Line: fitting data with the model

Can we understand this concentration phenomenon?

What is the effect of ion speciation?

What is the effect on electrochemistry, SEI?

[Na][TFSI]3-2 , CN=5-6 [Na][FSI]4

-3 , CN=4 [Na][FSI]5-4 , CN=5

Summary• Electrolyte chemistry crucial for optimised

electrochemical performance (rate and stability) of energy storage devices

• Ionic liquids can be designed for different battery systems– Imidazolium Dicyanamide seems optimal for Zn cycling– FSI or TFSI preferred for Li and Na – Phosphonium gives enhanced echem stability– Mixed IL/inorganic salts have been discovered to give best

Na performance

• Using simulations and NMR to understand behaviors

Acknowledgements – ARC, ACES and DU for funding, Deakin and Monash research teams.

PLASTIC CRYSTALS

31P

19F

31P

1H

NMR perfect tool

NMR SPRITE Imaging of Plastic Crystal Electrolyte- Effect of cooling rate

Slow Cool leads to oriented domains and higher ionic diffusion higher conductivity