What electrolyte for non-aqueous Na-ion batteries?

Patrik Johansson

Patrik Johansson1,2, Ma Rosa Palacín2,3, Damien Monti1-3, Andrea Boschin1,2, Alexandre Ponrouch2,3, and Erlendur Jónsson1

1) Applied Physics, Chalmers University of Technology, SE-412 96 Göteborg, Sweden 2) Alistore-ERI

3) ICMAB-CSIC, Campus de la UAB, 08193 Bellaterra, Spain

1st Symposium on Na batteries by CIC EnergiGUNE Vitoria-Gasteiz Oct 16-17 2013

The Li-ion to Na-ion battery transition in materials

Patrik Johansson

New Electrode Mtrls: Anodes, Cathodes… !No Graphite Anodes! => No need to keep “the standard electrolyte” ≈1M LiPF6 in carbonates

New Electrolytes? Salts/Solvents/Additives/Concentrations etc possible… … but the basics stay the same

M. R. Palacin, Chem. Soc. Reviews 38 (2009) 2565

What electrolytes are being used for Na-ion? “Google research”

Patrik Johansson

Cathode studies Anode studies

Salts

NaClO4 > NaPF6 > NaTf

NaClO4 >> NaPF6 > NaFSI

Solvents PC, EC/DXC, TEGDME

EC/DXC, PC

Electrolytes 1M NaClO4 in PC 1M NaPF6 in EC/DXC

Notable new materials and concepts – arising from electrolyte focused groups: i) Not VC, but FEC as SEI forming additive (2 wt%) (FEC:DEC 1:1) ii) NaFSI/KFSI (56:44) eutectic - mp 61 °C iii) Tailoring conductivity and viscosity; single => binary => ternary solvent mix

What electrolyte should we pick?

Salt = NaClO4 !?

Na+-conducting organic electrolytes: single solvent to binary solvent mix

Patrik Johansson

A. Ponrouch et al., Energy Environ. Sci. (2012)

Macroscopic observations: i)Salt anion of minor importance for conductivity & viscosity (@ RT (20 °C) & 1M) Why not ση ≈ k? What about tNa

+? ii)Conductivities ≈ LP30 possible – other parameters decide choice (Tstab, ESW, etc) What electrolyte to pick? => NaPF6 in EC:PC

Solvent = PC Salt = NaClO4

Na+-conducting organic electrolytes: binary to ternary solvent mix

Patrik Johansson

A. Ponrouch et al., Energy Environ. Sci. 6 (2013) 2361. DOI:10.1039/c3ee41379a

Macroscopic & molecular observations: i)ση ≈ k ii)EC:PC:DMC (0.45:0.45:0.1) chosen based on s iii)DMC acts indirectly – very minor Na+ interaction iv)EC and TFSI both interact with Na+

0.1

Basics of Li+ vs. Na+ solvation in organic solvents

Patrik Johansson

+ +

Facts and beliefs about Na-salt vs. Li-salt solvation: i) Na+ is more weakly solvated than Li+ => Na-salts are less soluble (?) ii) Na-salts use same basic anions: weakly cation coordinating, delocalized iii) Na-salts have lower lattice energies => Na-salts are more soluble (?) iv) Na+ has more ligands and higher CN (?) v) Na+ has other ligand preferences (?)

Consequences of Li+ vs. Na+ solvation in organic solvents: Gedanken example of M+ in PC

Patrik Johansson

+ +

E. Jónsson et al., in manuscript (2013)

Solvation of Na-salts: Modelling by MC + DFT

Patrik Johansson

E. Jónsson et al., Phys. Chem. Chem. Phys. 14 (2012) 10774. E. Jónsson et al., in manuscript (2013)

NaAn Na+ + An- DEd

=> ΔEdNa ≈ ΔEdLi * 0.80-085

=> ΔEsolvNa ≈ ΔEsolvLi * 0.80-0.85

Status Quo !?

Lots of details to be discovered…

+ +

Na+ + xEC + yDMC [Na(EC)x(DMC)y]+

DEsolv

Ionic liquids for Li+ and Na+ solvation

Patrik Johansson

Promises: - thermally and el. chem. stable - low (no) volatility - ”high” conductivities - excellent salt solubilities - variety - 1012! - ...

Problems: - high viscosity => low conductivity - cost - manufacturing(?) - nature of charge carriers? - ...

Pyr14FSI

Use of ILs as matrices?!

Solvation of LiTFSI in Ionic Liquid matrices

Patrik Johansson

LiTFSI in XMITFSI: IR + Raman + DFT

J. C. Lassègues et al., J. Phys. Chem A 113 (2009) 305.

0

0.2

0.4

0.6

0.8

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

EMI 25C

EMI 80°CBMI 25CBMMI 25C

BMMI 80C

1 - A/A0

m/C0

520560600640680

Ab

sorb

ance

Wavenumber/cm-1

618

571

515

651

b

c

e

a

f

g

d

581

601

615

658 520

581

571

Exp. IR

DFT IR Wavenumbers [cm-1]

74X cm-1 Raman band

… and existing on a NMR time-scale… S. Duluard et al., J. Raman Spectrosc. (2008)

[Li(TFSI)2]- CN=4

Solvation of NaTFSI in Ionic Liquid matrices

Patrik Johansson

[Na(TFSI)3]2- CN= 5-6

(MD [Wipff] => CN=6.3)

D. Monti et al., J. Power Sources 245 (2014) 630.

Li+ vs. Na+ solvation in Ionic Liquid matrices

Patrik Johansson

A comparison of organic solvent vs. ILs for Li+ vs. Na+-salt solvation

Patrik Johansson

Org. Solv.

+ -

-

Li+An-

-

Charge of Carriers:

0 -2 -1 +1

Org. Solv.

IL (TFSI)

IL

(TFSI)

+

-

- +

+

Na+An-

- +

+ -

- +

+

+ +

Summary & Open Questions Remaining…

Patrik Johansson

- Changing Li+ to Na+ induce interaction & coordination changes = f(salt conc) => What is the optimal Na-salt concentration? => Are there safety implications by the coordination changes?

=> What solvent(s) should be chosen? => What is the Na+ coordination?

- Are there any especially promising Na-salt anions?

=> DFT studies give “No…” => New/old anions to (re-)discover?

- Matrices other than organic solvents: => IL-based electrolytes – profound changes – beneficial or not?

=> SPE-based electrolytes – minor changes – beneficial or not?

Patrik Johansson

Acknowledgements

Prof. Per Jacobsson Lic. Sc. Erlendur Jónsson MSc. Damien Monti MSc. Andrea Boschin - poster #5

International Collaborators Prof. Michel Armand CIC EnergiGUNE Prof. Jean-Claude Lassègues Univ. Bordeaux I Dr. Ma Rosa Palacin ICMAB – CSIC Dr. Alexandre Ponrouch ICMAB – CSIC

Funding

Thank you for your attention!