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Revealing Aging Mechanisms in Lithium-Ion Cells
Daniel Abraham
Interna�onal Ba�ery Seminar − 2017
March 22, 2017
Fort Lauderdale, FL
AcknowledgmentDOE-EERE
James Gilbert
Kaushik Kalaga
Pierre Yao
Ilya Shkrob
Javier Bareno
CAMP, APS, CMM
UIC, UIUC, ANL
2
ACCESS - Argonne Collaborative Center for Energy Storage Science
Core competency in energy storage research spans discovery to pilot scale
ACCESS matrixes these capabilities to solve S&T problems
Phenomena and Prediction Synthesis
Scale Up Engineering
Cell Fabrication
Battery TestingPost-test Analysis
Grid System Modeling
Vehicle Testing
http://access.anl.gov/
Computational Modeling
3
4
Diagnostics Overview
� Use of characterization tools (electrochemical, physicochemical,
mechanical, acoustic) to explain the electrochemical behavior of
materials, electrodes, and cells
– Every part of the cell is examined – electrodes (active and inactive
components in coating, current collector, tabs), electrolyte, separator, etc.
� To identify constituents and mechanisms responsible for cell performance and performance degradation
– To recommend solutions that improve performance and minimize performance degradation of materials, electrodes, and cells
5
Current Projects
Relating Electrode Architecture to Electrochemical Performance
6
3-D reconstructions
from FIB-SEM
cross-sections
Electrode architecture examined by X-ray tomography and FIB-SEM imaging
� Provides information on material
distribution, porosity, tortuosity, etc.
� How are these parameters affected by
electrode calendering? Drying?
� How do these parameters affect
electrode performance?
Goal is to use computational methods to design high-performance electrodes
7
Improving Performance of Si-bearing electrodes
Pristine Gr-15 wt% Si (50 – 70 nm)
Aged Gr-15 wt% Si
Aged Graphite
5 µm
SEM images
Diagnostic studies on NCM/SiGr full cell show
� Extensive SEI on the nanoSi component. Capacity
fade arises from Li-trapping in SEI.
� Impedance rise at the NCM electrode
To improve performance use
� Electrolyte additives
� Electrode pre-lithiation
8
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
3.0
3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6Increasing x in Li1-x(Ni0.5Co0.2Mn0.3)O2
Increasing x in LixGraphite
Net
ReductionV
olt
age
vs. L
i/Li
+ , V
� Li-trapping in negative SEI is main contributor to capacity fade
– Positive electrode is main contributor to impedance rise
� Electrode potential window shifts observed on aging
– Reduces utilization of electrode active material
– Causes positive electrode to cycle at higher SOCs
� Electrolyte additives and/or coatings can improve cell cycle life
High energy, high voltage studies – NCM/Gr cells
Recent Publications
9
� J.A. Gilbert, I.A. Shkrob, D.P. Abraham, "Transition Metal Dissolution, Ion Migration, Electrocatalytic Reduction and Capacity Loss in Lithium-Ion Full Cells”, J. Electrochem. Soc. 164 (2017) A389.
� M. Klett, J.A. Gilbert, K.Z. Pupek, S.E. Trask, D.P. Abraham, “Layered Oxide, Graphite and Silicon-Graphite Electrodes for Lithium-ion Cells: Effect of Electrolyte Composition and Cycling Windows”, J. Electrochem. Soc. 164 (2017) A6095.
� J.A. Gilbert, J. Bareño, T. Spila, S.E. Trask, D.J. Miller, B.J. Polzin, A.N. Jansen, D.P. Abraham, “Cycling behavior of NCM523//Graphite lithium-ion cells in the 3-4.4 V Range – Diagnostic studies of Full Cells and Harvested Electrodes”, J. Electrochem. Soc. 164 (2017) A6054.
� I.A. Shkrob, D.P. Abraham, “Electrocatalysis Paradigm for Protection of Cathode Materials in High-Voltage Lithium-Ion Batteries”, J. Phys. Chem. C 120 (2016) 15119.
� M. Klett, J.A. Gilbert, S.E. Trask, B.J. Polzin, A.N. Jansen, D.W. Dees, D.P. Abraham, “Electrode Behavior RE-Visited: Monitoring Potential Windows, Capacity Loss, and Impedance Changes in Li1.03(Ni0.5Co0.2Mn0.3)0.97O2/Silicon-Graphite Full Cells”, J. Electrochem. Soc. 163 (2016) A875.
� S.E. Trask, K.Z. Pupek, J.A. Gilbert, M. Klett, B.J. Polzin, A.N. Jansen, D.P. Abraham, “Performance of Full Cells Containing Carbonate-Based LiFSI Electrolytes and Silicon-Graphite Negative Electrodes” J. Electrochem. Soc. 163 (2016) A345.
� I.A. Shkrob, J.F. Wishart, D.P. Abraham, “What Makes Fluoroethylene Carbonate Different?”, J. Phys. Chem. C 119 (2015) 14954.
10
Present Focus
NCM oxides – effect of exposure to moisture
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Positive Electrode contains� 90 wt% NCM523 Oxide� 5 wt% C45 carbon� 5 wt% PVdF binder
� Water-based binders are being considered for positive electrode fabrication
� Oxide coatings are often applied in aqueous media
� Newer methods of electrode fabrication, such as electrophoretic deposition in aqueous media, are being developed.
� How are the oxides affected by exposure to moisture/water?
Experimental Procedure
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� Electrode samples are sealed in a container, adjacent to an open beaker of water– Placed inside in a 30 °C constant-temperature chamber
– 100% humidity
– Moisture droplets formed on samples
– Samples removed periodically for characterization
� Control samples – Samples in a container with no water (ambient-air exposure)
– Samples stored in a dry-room (extremely low humidity)
� All electrodes dried at 120°C for 24h, in vacuum oven
Effect of moisture exposure 1st cycle – NCM523/Li cell
13
4.5
4.0
3.5
3.0
Po
ten
tial vs. L
i/L
i+, V
20015010050
Specific capacity, mAh/goxide
exposure
cell E1 E2 E3
3-4.5 V, ~C/10, 30°C
Cell E1 E2 E3
Months 0 1 2
C, V 3.68 4.12 4.26
C, mAh/g 219 191 179
D, V 4.48 4.43 4.3
D, mAh/g 198 166 155
Significant effect on electrochemical performance
O1s XPS spectrum shows significant changesE1: Pristine electrode; E2: 1-month exposure
14
Li+ + H2O → H+ + LiOHLiOH + CO2 → LiHCO3
LiOH + LiHCO3 → H2O + Li2CO3
4x103
2
0XP
S s
ign
al,
arb
. u
.
295 290 285
E1 E2
C-C
PVdFbinder
(a) C 1s 4x10
3
2
0XP
S s
ign
al,
arb
. u
.
536 532 528
NMC oxide
surface impurity
LiOH, LiHCO3, Li2CO3(c) O 1s
Small decreases in peak intensities indicate surface coverage
15
STEM images near particle surfaces E3: 2-month moisture exposure
A
In addition to amorphous regions new crystal structure(s) are seen at the basal plane edges. These structures appear to have transition metal ions in Li-planes
LAADF image
All moisture-exposed samples showed unusual sensitivity to electron beam
Synchrotron XRD data indicate structure changesE1: Pristine; E3: 2-month exposure; E4: Relithiated (3-4.5 V, 4 cycles)
16
Compared to pristine sampleE3 shows c-axis contraction (0.06%) and a-axis dilation (0.03%)Re-lithiation appears to restore crystal structure
λλλλ=0.459268 Å
17
Replacing some Li+ ions with protons can lead to c-axis contraction
AOur computations indicate that ~5-8% of Li+ ion substitution by protons can explain data for the 2-month exposure sample
Decreasing energy per H+ suggests that H+/Li+ substitution becomes easier as H+ content increases
3
2
1
0
- ∆∆ ∆∆c
/co , %
20100
H+/Li
+ substitution, %
190
180
170
160
en
erg
y p
er H
+, kc
al/m
ol.e
q
Synchrotron XRD data indicates a new cubic phase after moisture exposure. E1: Pristine; E3: 2-month exposure
18
Structure factor analyses shows that the cubic phase is rock-salt with some H+ substitution
λλλλ=0.459268 Å
a=4.049722 Å
Summary and Conclusions
19
Experimental data on moisture-exposed samples� Electrochemistry shows 1st cycle charge voltage polarization
� XPS spectra show surface coverage of the oxide
� STEM images show that oxide bulk maintains layered nature, whereas edge areas show new crystal structures
� XRD data of oxides show c-axis contraction and a-axis dilation
Exchange of Li+ by H+ can explain experimental data� Exposure to typical laboratory environments also induces (smaller) changes
Article, under review, 2017