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

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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

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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

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Current Projects

Relating Electrode Architecture to Electrochemical Performance

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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

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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

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� 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.

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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

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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

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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

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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)

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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

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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

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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

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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