1. "Simulate, Know Materials"
Computational Studies on Advanced Lithium Batteries for Electronic Devices and Electric Vehicles.
MC Masedi, HM Sithole and PE Ngoepe
1. Materials Modelling Centre, School of Physical and Mineral Sciences
University of Limpopo, Private Bag x 1106, Sovenga, 0727, South Africa
2. CSIR, Meraka Institute, Meiring Naude, Brummeria, P. O. Box 395, Pretoria 0001
South Africa
CHPC Meeting 2013
06/12/2013

2. Introduction
The growing global energy demand of modern society is urging to find large-scale sources, which are more sustainable and environmentally friendly of the oil-based one.
The increase of CO2 emissions of oil , call for the search for sources of clean energy.
Rechargeable lithium batteries are expected to play a key role also in future energy storage, including both stationary [1] and automotive applications [2- 4].
Li-ion batteries have transformed portable electronic devices [5]. However, even when fully developed, the highest energy storage that this batteries can deliver is too low to meet the demands of key markets, such as transportation.

3. Reaching beyond the horizon of Li-ion batteries is a formidable challenge; it requires the exploration of new chemistry, especially electrochemistry and new materials [3].
Here we consider a study on: Lithium and Zinc – air batteries. All this batteries are potentially ultrahigh energy density chemical power sources, which could potentially offer higher specific energy and could address pressing environmental needs for energy storage systems .
In the current work we present a comparative study on stability, structural and electronic properties of discharge products formed in Lithium and Zinc – air batteries.
[1] B. Dunn, H. Kamath, J.-M. Tarascon, Science 334 (2011)
[2] P.G. Bruce, S.A. Frauberger, L.J. Hardwick, J.-M. Tarascon, Nat. Mater. 11
(2012)
[3] M. Armand, J.-M. Tarascon, Nature 451 (2008)
[4] J.-M. Tarascon, M. Armand, Nature 414 (2001)
[5] D. Linden (Ed.), Handbook of Batteries, McGraw-Hill, New York, 1984

4. Frontiers of Electrochemical Energy Storage
Product:
Li2O
Focus
US Advanced Battery Consortium USABC Goals for Advanced Batteries for Evs (2006)

5. Operations Model: Li-Air battery
Discharge phase e- e- e- e-
Lithium Oxide (Li2O) Li Li + –
Li+ e- O
Li+
O - O
O - Li e-
Li+
Li+
Li+
Li+ e-
Catalyst:
MnO2
O2+e -> O2-
O2- + Li+ ->LiO2
LiO2 + Li+ + e->Li2O2
Li+
Li -> Li++ e
Aprotic electrolyte
Lithium Anode
Nanostructured Cathode

6. Methodology
The calculations were carried out using ab initio Density Functional Theory (DFT) formalism as implemented in the VASP code [7] with the projector augmented wave (PAW) [8].
An energy cut-off of 500 eV was used, as it was sufficient to converge the total energy of all the systems and k-points of 8x8x8.
For the exchange-correlation functional, the generalized gradient approximation of Perdew, Burke and Ernzerhof (GGA-PBE) [9] was chosen.
Elastic properties were calculated with the strain of
Phonon dispersions calculations the interaction range of 10.0Å and displacement of atoms of +/- 0.02Å were used.
[7] P. E. Blöchl, Phys. Rev. B 50, (1994)
[8] H.J. Monkhorst and J.D. Pack, Phys. Rev. B 13, 5188 (1976).
[9] J.P. Perdew, K. Burke and M. Ernzerhof. Phys. Rev. Lett. 77 , 3865 (1996)

7. Structures O S Li Li
(b) Li2O
(a) Li2S
Li2O and Li2S have a cubic anti-fluorite structure with Fm-3m symmetry.

8. Active materials in lithium batteries
Discharge product of oxygen formed in Lithium- air battery
10. W. M. Haynes, ed., CRC Handbook of Chemistry and Physics, 91st edition (2010)

9. Results and Discussions
Structure and Heats of Formation
Elastic Properties
Li2O and Li2S satisfy the necessary conditions
for stability.
C11>0, C11-C12>0, C44>0
Hence Li2O and Li2S are mechanically stable.
[10] J.M Osollo-Guillen, B. Holm, R. Ahuja and B.A Johonsson. Journal 167, (2004)[14]
[11] Bertheville J Phys. Cond Matt 10, (1998) (Exp thermal exp)
[12] A. Golffon, J.C. Dumas and E. Phillippot. Journal 1, (2002)
[13] E. Zintl, A. Harder and B. Dauth, Z Elektorchem, (1934)

10. Phonon Dispersions Calculations
Phonon Dispersions, in condensed-matter physics, represents an excited state in the quantum mechanical quantization of the modes of vibrations of elastic structures of interacting particles.
They play a major role in determining a material's thermal conductivity, electrical conductivity and stability. Thus, the study of phonons is an important part of condensed-matter physics
Determining material’s stability.
Lattice Vibrations – Phonons in Solid State
Alex Mathew, University of Rochester

11. Phonon Dispersions of Li2O and Li2S
Phonon dispersion calculations for Li2O and Li2S structures, indicates that the structures are stable.

12. Phonon Dispersion for Li2SΓ X W L Γ X W L LA LA
Acoustic
Acoustic TA TA
Calculated
Experimental – Bill et al (1991)
Good agreement of calculated and experimental, especially on acoustic modes.

13. Phonon Dispersion for Li2O
Optical LA
Acoustic
Acoustic TA Г X Г
Calculated
Experimental-M Wilson et al (2004)
Good agreement of calculated and experimental, especially on acoustic modes and lower optical modes.

14. Problems with Li-air batteries: Dendrite Formation on Charge
In most lithium batteries, the anode is covered by a thin film called a Solid Electrolyte Interphase (SEI) [14].
As a result, on charge, lithium deposits through the SEI in the form of lithium dendrites and mossy (sponge) lithium.
This raises safety issues – the formation of internal short circuits by lithium dendrites.
[14]E. Peled. J. Electrochem. Soc. 126, (2011).

16. Sodium–air battery
We suggest here to replace the metallic lithium anode by liquid sodium and to operate the sodium–air (oxygen) battery.
The theoretical specific energy of the sodium–air cell, assuming Na2O as the discharge product, is expected to be 1690 Wh/kg.
The surface tension of the liquid sodium anode is expected to prevent the formation of sodium dendrites on charge.

17. Results and Discussions
Structure and Heats of Formation
Elastic Properties.
Na2O and Na2S satisfy the necessary conditions for
stability.
C11>0, C11-C12>0, C44>0
Hence Na2O and Na2S are mechanically stable.

18. Phonon Dispersions of Na2O and Na2S
Phonon dispersion calculations for Na2O and Na2S structures, indicates that the structures are stable.

19. Phonon Dispersion for Na2S
Brillouin Zone Direction
Experimental-M Wilson et al (2004)
Calculated

20. Phonon Dispersion for Na2O
Experimental-M Wilson et al (2004)
Calculated

22. Results and Discussion
Structure and Heats of Formation
Structure
Calc a
(Å)
Exp c
Volume
(Å3) ΔH
(kJ/mol)
ZnO
3.26
5.23
48.06
ZnS
5.45
162.06
Elastic Properties
Structure
ZnO
ZnS
C11
C12
C13
C16
C33
C44
C66
96.81
57.42
55.19
ZnO and ZnS satisfy the necessary conditions
for stability.
C11>0, C11-C12>0, C44>0
Hence ZnO and ZnS are mechanically stable.

23. Phonon Dispersions for ZnO and ZnS
Phonon dispersions calculations for ZnO and ZnS structures, indicates that the structures are stable.

24. Summary
All discharge products formed Li–O2 and Zn–O2 batteries are stable because of low values of the heats of formations.
Lattice parameters and elastic constants values are in good agreement with the experimental values especially for Li2O, Li2S, Na2O and Na2S structures.
The elastic constants suggest mechanical stability of all discharge products .
Our phonon dispersion calculations shows that all the discharge products are generally stable with the absence of vibrations in the negative frequency.
Phonon dispersions are in good agreement with the experimental studies especially for Li2O, Li2S, Na2O and Na2S structure.

25. Acknowledgements
"Simulate, Know Materials"

26. Nelson Rolihlahla Mandela 1918-2013
"Simulate, Know Materials"
THANK YOU
“Education is the most powerful weapon which you can use to change the world.”
Nelson Rolihlahla Mandela

27. Future Work

28. Battery Simulation using Battery Design Studio (BDS)

29. Require Improving Batteries Performances

30. The fundamental electrochemical reactions in Li-air batteries

31. MnO2 as a catalyst in Li-air batteries

32. Lithium-air Battery

33. Operations Model: Li-Air battery
Charging phase e- e- e- e- e- e- Li
O -
Li+ Li
Li+
Li+ e- e-
Li+ O
O - O
Catalyst Particle
MnO2 Li
Li+ e- e-
Li+
Li+ Li
Li2O2 –> LiO2- + Li+
LiO2- –> LiO2 + Li+ + e
Li+ + e –> Li 0
LiO2 –> O2 + Li+ + e
O -
Li+
Li+

34. All-electric – the BMW i3 Concept.
BMW i3 CONCEPT COUPE. ELECTRICITY MEETS INTELLIGENCE.

35. South African Nissan Leaf 2013
Launched by Department of Environmental Affairs

37. Thank you Research Success How does this study benefit us?
If we succeed in developing this technology, we are facing the ultimate breakthrough
for electric cars, because in practice, the energy density of Li-air batteries will be
comparable to that of petrol and diesel.
Thank you
"One of the reasons people don’t achieve their dreams is that they desire to change their results without changing their thinking“
(Maxwell 2003)