Progress in Fine Structure Characterization of Carbon Materials … · 2010. 4. 19. · 10 002 11...
Transcript of Progress in Fine Structure Characterization of Carbon Materials … · 2010. 4. 19. · 10 002 11...
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Progress in Fine Structure Characterization of Carbon Materials with TEM- 2D and 3D characterization of nanocarbons -
Noriko Yoshizawa, Ph.D.National Institute of Advanced Industrial
Science and Technology (AIST)
Turkish-Japanese Joint Carbon SymposiumMarch 19, 2010 (Istanbul, Turkey)
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agenda
1. about AIST
2. basics of TEM(transmission electron microscope) and its advantage in characterization of carbon structure
3. 2D and 3D characterization of carbon nanosphere for Li-ion batteries
4. summary
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1. about AIST
15 research institute under MITI (Ministry of International Trade and Industry )
National Institute of Advanced Industrial Science and Technology(AIST)
April, 2001
amalgamation
Tsukuba
TokyoTsukuba Center
JapanTurkey
1882~
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facts and figures in AIST
Number of Employees
Post-docs 500
From Private companies 1,100
From Universities 2,000
From other corporations 850
From overseas 750
Number of Visiting researchers (approx.)
Research Staff(tenured/fixed-term)
2,370
Administrative Staff 696
Total 3,066
Exectives 13
Life science and bio-technology 17%
Metrology and measurement science
16%
Information technology and electronics 18%
Geological survey and applied geoscience 10%
Environment and energy23%
Nanotechnology, Materials and Manufacturing 16%
Composition of research staff by research field
as of August, 2009,
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agenda
1. about AIST
2. basics of TEM(transmission electron microscope) and its advantage in characterization of carbon structure
3. 2D and 3D characterization of carbon nanosphere for Li-ion batteries
4. summary
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-basics of TEM (1)-Different from scanning electron microscope (SEM) or optical microscope(OP)
Visible light
Electron beam(101kV)
Electron beam(102 kV)
Optical Microscope
SEMTEM
transmitted/reflected lightoptic lenses(mag:101-103x)
reflected/secondary electron (beam) magnetic lenses(mag: 102-104x, resolution: 0.5-4nm)
transmitted electron (beam)magnetic lenses(mag: 102-105x, resolution: 0.1-0.3nm)
Surface structure Inside/crystallographicstructure
e-
e-
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basics of TEM (2)
High resolution by using electron beam with high energy (i.e., accelerating voltage)
De Broglie’s equation
λ: wavelength, h: Plank constant, m: mass of electron, ν: velocity of electron
Wavelength of electron beam is therefore calculated as
100kV:0.0039nm200kV:0.0025nm300kV:0.0022nm
mvh
=λ
2
2mvVe =mVev 2
=
VVemh 150
2==λ
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Often observed with TEM
TEM observation of carbon materials- what is observed in graphitic structure ? -
c/2=0.3354nm
c=0.6708nm
a0=0.2456nm
Structure of graphite crystal
top view
side view
Unit cell
a0
c/2c
Representative lattice plane
(002)
(100) (110)
Regularity in stacking structure of aromatic (graphene) layers
Regularity of in-plane structure
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TEM observation of graphitic and non-graphitic carbons
Carbon 002 lattice image of graphitic (above: graphite) and non-graphitic (bottom: phenol resin heat-treated at 2800 oC)carbon materials.
002004006
002
00410
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agenda
1. about AIST
2. basics of TEM(transmission electron microscope) and its advantage in characterization of carbon structure
3. 2D and 3D characterization of carbon nanosphere for Li-ion batteries
4. summary
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Basic structure of Li-ion batteries
Positive electrode Negative electrode
charge
discharge
GraphiteLiCoO2 etc.
Carbon materials for negative electrode
Intercalation of Li+(LiC6 at maximum)
capacity - graphization degree
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High-rate charge-discharge performance in Li-ion batteries
Applications: electric vehicles, grid-connection of new energy(solar, wind power)Design of negative electrode is a key technique
Many types of materials, including carbon materials, have been studied.So far, carbon materials are good options because of their high capacity
One of the ideal texture is…・concentric orientation of aromatic layers ・moderate number of defects to insert Li+ smoothly・small particle size
aromatic carbon layers
Rate-capacity curve of CNSin 1M LiClO4/(EC+DEC) (1:1)Wang et al. Advanced Materials 17 (2005)
Standard carbon materials (MCMB)
Graphitized CNS
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Structure model of CNS
Objective: Detailed characterization of CNS structure with TEM2D-imaging: projection
outline of a particle, crystallographic information (lattice image, diffraction pattern, etc.)
3D-imaging: rotation and reconstruction outline of a particle, inside texture
In the outside region • development of graphitic texture • distribution of structural defects as pathway of Li+
TEM-BF image of CNS20-28and ED pattern from whole particle
Center regionConcentric orientationThin carbon layers (10-20nm)
with nesting texture
outside regionConcentric orientationgraphitic structure along
surface
mechanism of efficient charge-discharge behavior of CNS
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00210
11
Edges of aromatic layers were often exposed
Pristine
Stacking structure was much developedLayers with extended sizeSome curved layers at ridgelines
2000℃
Stacking structure was more developed with large layers (~20 nm)
2800℃
-2D characterization: carbon 002 lattice image of CNS-
Graphitization process of CNS (200nm)
Rate-capacity curve of CNSin 1M LiClO4/(EC+DEC) (1:1)
Wang et al. Advanced Materials 17 (2005)
Standard carbon materials (MCMB)
Graphitized CNS
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White area (domain) in DF: continuous crystalline area
2D characterization: Bright- and dark-field image of graphitized CNS(defects as pathways of Li+)
Column-like domains(Lc >> La) at ridges: defective
Large Lc and LaIn polyhedron face region
Lines parallel to stacking layers(polygonization wall)
Bright-field image Dark-field image
concentration of structural defects (edges in aromatic layers) on ridgelines
Development of graphitic structure In polyhedron faces
Paths of Li ions Intercalation of Li
Advantage of graphitized CNS from the crystallographic viewpoint
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- 2D characterization: TEM observation of larger CNS (1μm-class) -
CNS100-26 CNS100-29
CNS100-26:stacking structure developed in polyhedron faces/ridges CNS100-29:ordered stacking structure in polyhedron faces
frequently collapses (exfoliation, crack) at ridges
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In general,Graphitization texture in carbon particles is likely to be
developedin larger particlesin particles heat-treated at higher temperature
Graphitization process under a morphologically-constrained condition
The formation of such structural defects at ridges in larger CNSheat-treated at higher temp. is not an usual phenomena.
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CNS particle size vs. number of collapsed ridges in CNS100‐29 ?
(1) number of collapsed (exfoliated or cracked) and non-damaged ridges in an arbitrary particle(2) size of that particle by TEM observation (2D-image) for CNS100-29 (same lot)
Ratio of ridge with collapse to a total number of ridges: obviously higher in CNS particles with larger diameter
0
0.2
0.4
0.6
0.8
1
0 1000 2000 3000
ratio
diameter /nm
collapse(total)/ridgecollapse(exfoliation)/ridge
Crystallinity in face region(degree of graphitization)
Shrinkage by the heat-treatment --- thermal stress can be focused at ridges with these structural defects --- collapses especially at ridges at 2900oC
Mechanism of defects at ridges
Focused tension at ridges
larger CNS
smaller CNS
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Electron tomography (3D‐TEM) ‐basics‐
“electron tomography”• continuous recording of 2D‐projection images by tilting sample holder
(max. ‐75 ‐> +75 deg, 1‐2 deg. step)• series of position‐aligned projection images = “rotation image”• Reconstruction of rotation image based on the scattering contrast = “slice image”
similar to CT scanning in medical examinationThe slice images in this study were reconstructed as if the particles were virtually cut by a plane parallel to the grid
Sample particle &Recognizable small particles (as marks for position tracking)
Sample holder (tip)
Electron beam
sample holder
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electron tomography- rotation image of carbon nanosphere -
Au colloids were dispersed on the grid as markers
-70o - +70o, x34000
ca. 2o step(step-rotation by Saxton scheme)
‐70˚ ‐35˚
‐10˚ 0˚
35˚ 70˚
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z=180nm z=120nm z=80nm z=10nm
Electron tomography‐ Series of sliced model and 3D‐models of CNS20‐28‐
x
y
z
Inner texture can be represented at any height(central core, boarder between particles, connectivity of voids, etc. )
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-Pt‐supporting carbon nanosphere-
Pt-supporting CNS, rotation image
・CNS20-p(pristine):fine Pt particles are homogeneously dispersed on the surface of CNS
・CNS20-28(HTT=2800oC):Pt particles are aggregated along the
polyhedron ridgelines or between CNS particles
CNS20-p CNS20-28
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- Pt‐supporting carbon nanosphere: slice image-
Dispersion of Pt vs. surface structure, morphology of aggregate
z=95nm
z=80nmz=110nm
z=220nm
z
x
y0
Pt‐CNS20p Pt‐CNS20‐28
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agenda
1. about AIST
2. basics of TEM(transmission electron microscope) and its advantage in characterization of carbon structure
3. 2D and 3D characterization of carbon nanosphere for Li-ion batteries
4. summary
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summary
• TEM (transmission electron microscope) seems to be one of the most powerful techniques to characterize microtexture of carbon materials.
• Basics of 2D- and 3D-imagings with TEM were explained.
• Some examples of TEM observation were reviewed for carbon nanospheres as superior negative electrodes in Li-ion batteries.
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acknowledgementPart of this research was financially supported by a grant from New Energy and Industrial Technology Develop Organization (NEDO) (PJ code: P06004), as a collaborative work with Tokai Carbon Co. Ltd. and Kyoto University.
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Thank you very much.
Sagol
ありがとうございました。