bosong@sinap.ac.cn bo song shanghai institute of applied physics, cas dec., 2012 intercalation and...

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Bo SONG

Shanghai Institute of Applied Physics, CAS

Dec., 2012

Intercalation and diffusion of Intercalation and diffusion of lithium ions in a CNT bundlelithium ions in a CNT bundle

byby ab initioab initio molecular dynamics simulationsmolecular dynamics simulations

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北大新材料论坛

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OutlineOutline

MotivationsMotivations Molecular model and methodsMolecular model and methods MD simulations and mechanism MD simulations and mechanism

underlyingunderlying

Conclusion and outlookConclusion and outlook

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Energy is the key challenge for human!

MotivationsMotivations

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Energy!!!Energy!!!

1.1. Energy conversion?Energy conversion?

2.2. Energy storage?Energy storage?

MotivationsMotivations

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A high charge-and-discharge rateA high charge-and-discharge rate A high capacityA high capacity A high A high cyclabilitycyclability

MotivationsMotivations

Way to store energy with

Century

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MotivationsMotivations

Nanotechnology, in the past two decades, provides a novel approach to improve energy storage device

Energy Environ. Sci 2, 589 (2009)

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MotivationsMotivations

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)

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MotivationsMotivations

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.

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Intercalation and diffusion Intercalation and diffusion of lithium ions in a CNT of lithium ions in a CNT bundlebundle

byby ab initioab initio molecular dynamics molecular dynamics simulationssimulations

Energy Environ. Sci. Energy Environ. Sci. 44, 1379 , 1379 (2011) (2011)

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Model and methodsModel and methods

Purple: lithiumPurple: lithium

Black: carbonBlack: carbon

White: White: hydrogenhydrogen

Midpoint A among 3 CNTs

Midpoint B between 2 CNTs

Molecular model by AIMD

(10, 0) zigzag, 15.61 Å x 7.97 Å

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MD simulations

Conducting 10,000-fs simulation for each initial conformation

MD resultsMD results

A typical animationA typical animation

Li atom would lose 0.8 electrons

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All Li ions moving into the interior channel of the the interior channel of the CNTCNT or into the interstitial channel between the interstitial channel between CNTsCNTs

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Axial and radial distributions of the 8 Li ions8 Li ions

2.0 Å

6.7 Å

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Results of 16 Li ions16 Li ions in CNTs bundle

Uniformly,

2.0 Å

6.7 Å

???

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LL

Snapshot of Li ions in CNTs bundle

16 Li ions16 Li ions in CNTs in CNTs

bundlebundle

8 Li ions8 Li ions in CNTs bundle in CNTs bundle

BB

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Snapshot of Li ions in CNTs bundle

16 Li ions16 Li ions in CNTs in CNTs

bundlebundle

8 Li ions8 Li ions in CNTs bundle in CNTs bundle

BB

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Distribution of Li ions in x-y plane

16 Li ions16 Li ions in CNTs in CNTs

bundlebundle

8 Li ions8 Li ions in CNTs bundle in CNTs bundle

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Adsorption energy of one lithium atom with the nanotubes

Mechanism underlyingMechanism underlying

Putting one Li atom in the interior or interstitial channels.

Moving it along the Z dirction.

rr

ZZ

EEadad = E(Li + CNTs) – E(Li) – = E(Li + CNTs) – E(Li) – E(CNTs)E(CNTs)

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Adsorption energy of a lithium atom with the nanotubes

-■-: r = 0.0 Å-●-: r = 1.0 Å -▲-: r = 2.0 Å

ZZrr

Interior channel of the Interior channel of the

nanotubenanotube

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▲●

Adsorption energy of a lithium atom with the nanotubes

--∆∆- : A - : A positionposition-○-: B -○-: B positionposition-■-: r = 0.0 Å-●-: r = 1.0 Å -▲-: r = 2.0 Å

Interstitial channel between the Interstitial channel between the

nanotubesnanotubes

33 22

11

AA

BB

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16 Li ions16 Li ions in CNTs bundle in CNTs bundle

Third channelThird channel

Snapshot of Li ions in CNTs bundle

8 Li ions8 Li ions in CNTs bundle in CNTs bundle

Two channelsTwo channels

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▲●

Adsorption energy of a lithium atom with the nanotubes

--∆∆- : A - : A positionposition-○-: B -○-: B positionposition-■-: r = 0.0 Å-●-: r = 1.0 Å -▲-: r = 2.0 Å

Interstitial channel between the Interstitial channel between the

nanotubesnanotubes

33 22

11

AA

BB

A little large???

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Physics underlying: Cation-pi interactionCation-pi interaction

Li+

Cation-induced re-arrangement of pi-

electrons

Ead = -1.67

eV

Cation-pi interactionCation-pi interaction

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Cation-pi interaction for the interior channel of the nanotube

-■-: r = 0.0 Å-●-: r = 1.0 Å -▲-: r = 2.0 Å

ZZrr

Li+

Ead = -1.67

eV

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-○-: B -○-: B positionposition

33 22

11 BB

Cation2pi for the interstitial channel between NTs

●

Li+

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33 22

11

-∆- : A -∆- : A positionposition

AA

Cation3pi for the interstitial channel between NTs

▲

Li+

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16 Li ions16 Li ions in CNTs bundle in CNTs bundle

Third channelThird channel

Snapshot of Li ions in CNTs bundle by Cationnpi

8 Li ions8 Li ions in CNTs bundle in CNTs bundle

Two channelsTwo channels

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33 22

11

CationCationnnpi interactionpi interaction

for the for the interstitial channelinterstitial channel between NTs between NTs

▲

Li+ Li

+

●???

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CationCation33pi interactionpi interaction V.S. V.S. CationCation2pi 2pi interactioninteraction

J. Am. Chem. Soc. 134, 12104 J. Am. Chem. Soc. 134, 12104 (2012)(2012)

CationCationnnpi interaction pi interaction

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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 Li ions located among three neighboring NTs would be very difficult to be removed from a would be very difficult to be removed from a bundle of nanotubes.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.

ConclusionConclusion

Control the irreversible

intercalation

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AcknowledgementAcknowledgement

Prof. David TomanekProf. David Tomanek

Profs. Haiping Fang, Jijun Profs. Haiping Fang, Jijun ZhaoZhao My studentsMy students

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FoundationFoundation

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thank you for your attention!