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Ⅲ-2
Material characterization of LIB anode
for root causes of resistivity increase
In order to investigate root causes of resistivity increase in anode after degradation test, we provide surface analysis (XPS + TOF‐SIMS), compositional analysis of water extract from whole anode mixture
(1H NMR + IC) and analysis of paramagnetic defects in graphite (ESR).
Surface analysis of anode
Composition and thickness of SEI on anode surface
2000
N=1
Degradation of electrolyte (P2p)
N=2
1000
500
0
Prisitine
Cycled
Stored
Laminate cells (1100 mAh)
‐ Cathode: LiNi1‐x‐yCoxAlyO2(NCA)
‐ Anode: graphite
‐ Electrolyte: 1M LiPF6 + EC/DEC(3/7) + VC
1. Pristine (Electrochemically activated)
2. Cycle‐tested (0.5C x 200cycles at RT)
3. Stored (4.1V for 2 months at RT)
Resistivity of anode: Cycled>Stored≒Pristine
C‐C, CHx
POx, PFxOy
(degraded components)
P‐F
Pristine
Cycled
Stored
144
140
136 132 128
Binding Energy (eV)
Thickness of SEI (C1s)
Normalized intensity
1500
Normalized intensity
Resistivity of anode (Ω・cm)
Samples
Oxygen containing functional groups
Active material, Conductive assistant
Pristine
Cycled
Stored
296
124
292 288 284 280
Binding Energy (eV)
XPS spectra of anode surface
LiF, Li3PO4, LiPF6, alkyl lithium phosphate, etc. were detected by TOF‐SIMS in a separate analysis.
Cycled vs. Stored
SEI composition: similar (degraded electrolyte and solvent)
SEI thickness: similar (thin as ca. 10nm, if homogeneous,
estimated from lowest energy peak height of C1s)
Analysis of extract from anode mixture layer
Degradation in active material Amount of paramagnetic defects in mixture rinsed with DEC
Qualitative and quantitative analysis results of organics, anions and organic acids of extract by water from anode mixture whole layer
Narrow component
(g=2.002)
3
Localized spin density (spins/g) Pristine
Carrier conc.
(carriers/g)
3.00E+18
3E18
1.50E+19
1.5E19
2.00E+18
2E18
1.00E+19
1E19
1E18
5.00E+18
5E18
Intensity (a.u.)
1.0E+02
2.5
Cycled
Stored
Content (weight %)
0.0E+00
2
‐1.0E+02
3277
1.5
1.00E+18
Broad component
3377
3427
3477
Magnetic field(G)
ESR spectra of anode mixture
(at 280K)
1
0.5
0
Pristine Cycled
Stored
Content measured by 1H NMR and Ion‐Chromatography
Cycled vs. Stored
SEI composition: similar
Amount of SEI: Cycled > Stored
0E0
0.00E+00
0E0
0.00E+00
3327
Pristine
Cycled
Stored
Localized spin and carrier (Mainly contributed from broad component)
‐Narrow component: caused by dangling bond in graphite
with lower crystallinity or SEI formation
Cycled >> Stored > Pristine
‐Broad component: dominantly from carrier in graphite
Cycled > Stored ≒ Pristine
・Composition and amount of SEI can be measured both at anode surface and inside mixture layer of tested cells using XPS, NMR and IC.
・Degradation in graphite can be analyzed by ESR.
・In this experiment we saw clear increase in dangling bond
in graphite after cycle‐test.
2016年6月TRCポスターセッション2016 No. Ⅲ-2
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