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Bo SONG Shanghai Institute of Applied Physics, CAS

北大新材料论坛. Intercalation and diffusion of lithium ions in a CNT bundle by ab initio molecular dynamics simulations. Bo SONG Shanghai Institute of Applied Physics, CAS. Dec., 2012. bosong@sinap.ac.cn. Outline. Motivations Molecular model and methods MD simulations and mechanism underlying

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Bo SONG Shanghai Institute of Applied Physics, CAS

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  1. 北大新材料论坛 Intercalation and diffusion of lithium ions in a CNT bundle byab initiomolecular dynamics simulations Bo SONG Shanghai Institute of Applied Physics, CAS Dec., 2012 bosong@sinap.ac.cn

  2. Outline • Motivations • Molecular model and methods • MD simulations and mechanism underlying • Conclusion and outlook

  3. Motivations Energy is the key challenge for human!

  4. Motivations • Energy!!! • Energy conversion? • Energy storage?

  5. Motivations Way to store energy with • A high charge-and-discharge rate • A high capacity • A high cyclability Century

  6. Motivations Nanotechnology, in the past two decades, provides a novel approach to improve energy storage device Energy Environ. Sci 2, 589 (2009)

  7. Motivations Li battery with nanotube-based anode is believed to be one of the most promising electrochemical energy storage systems Li-ions in nanotubes Nano Lett. 9, 3844 (2009)

  8. Motivations • Providing the visual of lithium intercalation and diffusion in the battery. • Understanding mechanism under the intercalation and diffusion. • Greatly promote the development and application of the Li battery.

  9. Intercalation and diffusion of lithium ions in a CNT bundle byab initiomolecular dynamics simulations Energy Environ. Sci. 4, 1379 (2011)

  10. Model and methods Molecular model by AIMD • Purple: lithium • Black: carbon • White: hydrogen Midpoint A among 3 CNTs Midpoint B between 2 CNTs (10, 0) zigzag, 15.61 Å x 7.97 Å

  11. MD results MD simulations • Conducting 10,000-fs simulation for each initial conformation A typical animation Li atom would lose 0.8 electrons

  12. All Li ions moving into the interior channel of the CNT or into the interstitial channel between CNTs

  13. 6.7 Å 2.0 Å • Axial and radial distributions of the 8 Li ions

  14. 6.7 Å 2.0 Å • Results of 16 Li ions in CNTs bundle ??? Uniformly,

  15. L • Snapshot of Li ions in CNTs bundle B 8 Li ions in CNTs bundle 16 Li ions in CNTs bundle

  16. Snapshot of Li ions in CNTs bundle B 8 Li ions in CNTs bundle 16 Li ions in CNTs bundle

  17. Distribution of Li ions in x-y plane 8 Li ions in CNTs bundle 16 Li ions in CNTs bundle

  18. Mechanism underlying r Z • Adsorption energy of one lithium atom with the nanotubes • Putting one Li atom in the interior or interstitial channels. • Moving it along the Z dirction. • Ead = E(Li + CNTs) – E(Li) – E(CNTs)

  19. Adsorption energy of a lithium atom with the nanotubes Interior channel of the nanotube r Z -■-:r = 0.0 Å -●-: r = 1.0 Å -▲-:r = 2.0 Å

  20. 1 3 2 • Adsorption energy of a lithium atom with the nanotubes Interstitial channel between the nanotubes A B ● ▲ -∆- : A position -○-: B position -■-:r = 0.0 Å -●-: r = 1.0 Å -▲-:r = 2.0 Å

  21. Third channel 8 Li ions in CNTs bundle • Snapshot of Li ions in CNTs bundle Two channels 16 Li ions in CNTs bundle

  22. 1 3 2 • Adsorption energy of a lithium atom with the nanotubes Interstitial channel between the nanotubes A B ● ▲ -∆- : A position -○-: B position -■-:r = 0.0 Å -●-: r = 1.0 Å -▲-:r = 2.0 Å A little large???

  23. Cation-pi interaction Li+ • Physics underlying: Cation-pi interaction Cation-induced re-arrangement of pi-electrons Ead = -1.67 eV

  24. Li+ • Cation-pi interaction for the interior channel of the nanotube Z r -■-:r = 0.0 Å -●-: r = 1.0 Å -▲-:r = 2.0 Å Ead = -1.67 eV

  25. 1 3 2 Li+ • Cation2pi for the interstitial channel between NTs B ● -○-: B position

  26. 1 3 2 Li+ • Cation3pi for the interstitial channel between NTs A ▲ -∆- : A position

  27. Third channel 8 Li ions in CNTs bundle • Snapshot of Li ions in CNTs bundle by Cationnpi Two channels 16 Li ions in CNTs bundle

  28. 1 3 2 Li+ Li+ • Cationnpi interaction for the interstitial channel between NTs ??? ● ▲

  29. Cationnpi interaction • Cation3pi interaction V.S. Cation2pi interaction J. Am. Chem. Soc. 134, 12104 (2012)

  30. Conclusion • Li ions intercalation and diffusion in a CNT bundle. • Interior and interstitial channels opened for Li ions. • For CNT with a small diameter, the adsorption energy at the site among three nanotubes is much higher than that in the interior channels. • Li ions located among three neighboring NTs would be very difficult to be removed from a bundle of nanotubes. • Irreversible storage capacity in a NT-based Li battery. • Keeping the nanotubes apart with an appropriate distance would hinder or promote the formation of irreversible intercalation and storage capacity. Control the irreversible intercalation

  31. Acknowledgement • Prof. David Tomanek • Profs. Haiping Fang, Jijun Zhao • My students

  32. Foundation

  33. thank you for your attention!

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