Computational Studies on Advanced Lithium Batteries for Electronic Devices and Electric Vehicles.

1. Computational Studies on Advanced Lithium Batteries for Electronic Devices and Electric Vehicles. "Simulate, Know Materials" 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, MeiringNaude, Brummeria, P. O. Box 395, Pretoria 0001 South Africa CHPC Meeting2013 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 CO2emissions 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) 928-935. • [2] P.G. Bruce, S.A. Frauberger, L.J. Hardwick, J.-M. Tarascon, Nat. Mater. 11 • (2012) 19-29. • [3] M. Armand, J.-M. Tarascon, Nature 451 (2008) 652-657. • [4] J.-M. Tarascon, M. Armand, Nature 414 (2001) 359-367. • [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 O O - O - O O - O Discharge phase e- e- e- e- Lithium Oxide (Li2O) Li + Li – Li+ e- Li+ Li Li+ e- Li+ Li+ Li+ Catalyst: MnO2 e- O2+e -> O2- O2- + Li+ ->LiO2 LiO2 + Li+ + e->Li2O2 Li+ Li -> Li++ e Aprotic electrolyte Nanostructured Cathode Lithium Anode

6. Methodology The calculations were carried out using ab initioDensity Functional Theory (DFT) formalism as implemented in the VASPcode [7] with the projector augmented wave (PAW) [8]. An energy cut-off of 500 eVwas 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 0.003. 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, 17953 (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-3msymmetry.

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, 221-227 (2004)[14] [11] BerthevilleJ Phys. Cond Matt 10, 2155 -2169 (1998) (Exp thermal exp) [12] A. Golffon, J.C. Dumas and E. Phillippot. Journal 1, 1-123 (2002) [13] E. Zintl, A. Harder and B. Dauth, Z Elektorchem, 40 588 (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 Li2O Phonon dispersion calculations for Li2O and Li2Sstructures, indicates that the structures are stable.

12. Phonon Dispersion for Li2S Γ X W L Γ X W L LA LA Acoustic Acoustic TA TA Experimental – Bill et al (1991) Calculated 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, 2047-2051 (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 Na2S Na2O Phonon dispersion calculations for Na2O and Na2Sstructures, indicates that the structures are stable.

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

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

22. Results and Discussion Structure and Heats of Formation Elastic Properties ZnOand ZnSsatisfy the necessary conditions for stability. C11>0, C11-C12>0, C44>0 Hence ZnOand ZnSare 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 stablebecause 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 stablewith 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. "Simulate, Know Materials" THANK YOU “Education is the most powerful weapon which you can use to change the world.” Nelson Rolihlahla Mandela 1918-2013

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. O O e- e- e- e- e- e- O - O - O- Li+ O- Li+ Li+ O O- Operations Model: Li-Air battery Charging phase e- e- e- e- Li Li Li+ Li+ e- e- Li+ 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 Li+ + e –> Li 0 Li+

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37. How does this study benefit us? Research Success 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)