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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
北大新材料论坛
OutlineOutline
MotivationsMotivations Molecular model and methodsMolecular model and methods MD simulations and mechanism MD simulations and mechanism
underlyingunderlying
Conclusion and outlookConclusion and outlook
Energy!!!Energy!!!
1.1. Energy conversion?Energy conversion?
2.2. Energy storage?Energy storage?
MotivationsMotivations
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
MotivationsMotivations
Nanotechnology, in the past two decades, provides a novel approach to improve energy storage device
Energy Environ. Sci 2, 589 (2009)
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)
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.
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)
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
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
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
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
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
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
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)
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
▲●
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
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
▲●
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???
Physics underlying: Cation-pi interactionCation-pi interaction
Li+
Cation-induced re-arrangement of pi-
electrons
Ead = -1.67
eV
Cation-pi interactionCation-pi interaction
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
-○-: B -○-: B positionposition
33 22
11 BB
Cation2pi for the interstitial channel between NTs
●
Li+
33 22
11
-∆- : A -∆- : A positionposition
AA
Cation3pi for the interstitial channel between NTs
▲
Li+
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
33 22
11
CationCationnnpi interactionpi interaction
for the for the interstitial channelinterstitial channel between NTs between NTs
▲
Li+ Li
+
●???
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
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
AcknowledgementAcknowledgement
Prof. David TomanekProf. David Tomanek
Profs. Haiping Fang, Jijun Profs. Haiping Fang, Jijun ZhaoZhao My studentsMy students
