Introduction Literature Overview - NASA · Copyright© 2011 Underwriters Laboratories Inc. All rights reserved EXPERIMENTAL Technique Purpose Material Analysis SEM To observe the

Copyright© 2011 Underwriters Laboratories Inc. All rights reserved Copyright© 2011 Underwriters Laboratories Inc. All rights reserved.

STUDY OF AGING EFFECTS ON

SAFETY OF

18650-TYPE LICOOX CELLS

J. Thomas Chapin

Alvin Wu

Carl Wang

Corporate Research

Underwriters Laboratories Inc.

Copyright© 2011 Underwriters Laboratories Inc. All rights reserved

OUTLINE

Introduction

Literature Overview

Study of Aging Effects on LiB Safety

• Electrochemistry properties of the cell

• Thermal stability

• Others

Summary

2


ROOT CAUSES OF LiB SAFETY ISSUES

Construction Integrity

Material Properties

Safety Function Design

Uniformity of Product Quality

Contamination

Production Line Testing

Out-going Quality Control

Mechanical Abuse Electrical Abuse Environmental Condition

User Behaviors Aging Effects

The Safety Performance of a Lithium Ion

Battery could change over time !

3


AGING EFFECT SHOULD NOT BE IGNORED

• Most product defects can be detected by

safety testing, production line testing and QC

screening

• Many battery incidents occur after the battery

was in use for some time, even under normal

(anticipated) conditions.

4


AGING EFFECTS ON LIB SAFETY

Mechanical Integrity

Lithium Plating & Dendrite Formation

Source: Presentation Prof. T. Takamura “Carbon Material in Power Sources”. June 2005, ZSW Ulm

Observed by SEM and conventional optical microscopy

Source: O. Crowther et al.,

J. of The Electrochemical

Society, 155 (11) A806-

A811 (2008)

Source: M. Rosso et al., Electrochimica Acta

51 (2006) 5334-5340

Observed by a Carl Seiss Stemi 2000-C optical microscope

equipped with a Pix-eLink 623-C digital camera

5


HYPOTHESIS OF AGING EFFECTS

Attribute of Cell Fresh Cell Aged Cell

Mechanical Integrity Better Getting Worse

Activity of Material(s)/Component(s) More active Less active

Dendrite Formation & Lithium Plating Not an issue Potential concern

Thermal Stability of Material(s)/Component(s) Good Could be worse

Polarization Effect Less concern Potential concern

Risk of Electrolyte Leakage No Yes

Tolerance to Thermal Abusive Conditions Good Could be worse

Material

Degradation

(Construction

Integrity)

Lithium

Plating

Dendrite

Formation

Passivation

Capacity

Fading SEI

Degradation

6


HYPOTHESIS OF AGING EFFECTS TO BATTERY FAILURES

Path I

Path II?

Path III?

Likelihood

Severi

ty

Understand the Mechanism of Aging can help to understand the

Battery Safety Behavior

7


STUDY OF LIB AGING EFFECT(S)

Literature ＆Database

Correlation of

Aging and

Safety

Abnormal test

· IIISC

· Hot box

· Overcharge

· Vibration

Batteries

(18650 type cell)

Battery aging

· 25, 45 oC

· 50, 100, 200, 350, 500 cycles

Material analysis

· SEM/EDX

· XRD

· Raman

· DSC

· XPS

· FTIR

· Pyrolysis GC/MS

Non-

destructive

analysis

· EIS

· CT-scan

8


EXPERIMENTAL Technique Purpose

Material Analysis

SEM To observe the change of morphology of electrode surface, such as particle

size, distribution of active material, binder, conductive carbon, coating layer, thickness and etc.

EDX To analyze the elements of battery materials (electrodes, separator) to obtain the composition change of battery materials

XRD Observe the crystal structural change of electrode

FTIR Analysis the surface chemistry, mainly SEI layer, of electrode

DSC Evaluate the change of thermal stability of the electrode materials

Raman Observe the structural change of electrode material

XPS Analyze the surface chemistry, mainly SEI layer, of electrode

Pyrolysis

GC/MS

Analyze the thermal decomposition mechanism for active materials

Non-

destructive Test

EIS Analyze the internal resistance change CT-Scan Investigate the internal physical structure, such as valve, electrode packing and

alignment

Abnormal Test

IIISC Evaluate the battery behaviors when localized internal short circuit occurs.

Vibration Evaluate the battery behaviors change upon vibration after charging/discharging

cycles Hot box Evaluate thermal stability of battery with temperature

Overcharge Evaluate the battery behavior under overcharging condition

9


TEST SAMPLE – 18650 2800MAH CELL

Cathode: LiCoO2

(Particle Size~10µm)

Anode: Graphite (Particle

Size~10µm)

with Al2O3 coating

(Particle Size~1µm)

Separator: Polyethylene

(Single Layer - PE)

Electrolyte: EC:DEC(Volume

ratio1:6.2) with LiPF6

10


CAPACITY FADING & EIS

2.75

3.25

3.75

4.25

0.00 2,000.00

Cell V

olt

ag

e,

V

Time, sec

45-C Aged Cell (200 Cycles)

Fresh Sample

IR Drop at starting point

Polarization

Effect

Sample aged at 45oC ambient

0

0.005

0.01

0.015

0.02

0.025

0.03

0 0.05 0.1 0.15 0.2

Zim

(O

hm

s)

Zre (Ohms)

Fresh

50 Cycles

150 Cycles

250 Cycles

2.00

2.10

2.20

2.30

2.40

2.50

0 50 100 150 200 250

Ca

pa

cit

y, A

h

Cycle(s)

45-C Aging

25-C Aging

11

0

0.005

0.01

0.015

0.02

0.02 0.07 0.12 0.17

Zim

(O

hm

s)

Zre (Ohms)

EIS Profiles of Samples aged under different temperature

Fresh

150 Cycles (45oC)

150 Cycles (25oC)


OVERCHARGE TEST

12


ISC TRIGGERED WHILE OVERCHARGING

0

1000

2000

3000

4000

5000

Fresh Sample 25oC-100Cycles 45oC-100Cycles

Tim

e t

o t

rig

ger

ISC

, sec.

13


INDENTATION-INDUCED ISC (IIISC) TEST

Purpose:

• To investigate the “severity” of ISC event of the cell design

• To study how the “severity” changes on the identical cell design, but

under different aging conditions

Test Method Overview

Indenter (Crush at constant speed 0.1mm/s)

Thermocouple

applied to

sample casing

Cell Voltage

reading

sampled at

100Hz

Test Sample (100%SOC)

Test chamber

temperature

maintained at

60±2oC

14


IIISC TEST, CELL BEHAVIOR

Fresh Sample 100%,

Fails IIISC Test (N=3) 50 Cycle Aged Sample,

100% Fails IIISC Test

100 Cycle Aged Sample,

1 cell pass and 1 cell fail

Cell aged at 45oC

Fresh Sample, 100%

Fails IIISC Test (N=3)


fails IIISC Test, but in

different failure mode

(i.e.. no sustained fire )



Cell aged at room temperature



15


HOT BOX TESTING

Purpose:

• To investigate cell behavior under heating conditions.

• To study the thermal stability of cells after aging under different aging

conditions.

Test Method Overview:

• Test Sample: The test sample is charged to 4.25V using CC-CV

standard charging protocol.

• Experimental:

- Put test sample in oven with the thermal couple(s) attached

on the cell casing.

- Raise the temperature of the test sample at a rate of 5oC/min

from room ambient (ex.25oC) to 180oC. Maintain the

oven temperature at 180oC until the “final event” of the

cell. The final event is usually the thermal runaway for

LiCoO2-type cell.

- Monitor the cell voltage and cell casing temperature

while testing.

16


HOT BOX TESTING DATA

0

100

200

300

400

500

600

700

800

0

1

2

3

4

0 500 1000 1500 2000 2500 3000

Ce

ll T

em

pe

ratu

re,

oC

Ce

ll V

olt

ag

e, V

Test Time, sec.

Cell Voltage (Fresh Sample)

Cell Voltage (200Cycles under 45C)

Cell Temperature (Fresh Sample)

Cell Temperature (200 Cycles under 45C)

Melting of Separator, ISC occurs Venting

Thermal Runaway

1700

1800

1900

2000

2100

2200

2300

2400

2500

2600

2700

Fresh Sample 100 Cyclesunder 45C

200 Cyclesunder 45C

Tim

e t

o T

rig

ger

Ev

en

t, s

ec.

Time to Trigger ISC

Time to TriggerVenting

Time to TriggerThermal Runaway

Venting Thermal Runaway

Before Test After Test

17


SEM AND XRD ANALYSIS

45oC, 100 cycles

10 20 30 40 50 60 70 80

45C-100cyc

45C200cyc

45C-50cyc

Fresh

Inte

nsit

y (

a.u

.)

(006)

2 (degree)

(107)

(105)

(104)

(102)

(101)(0

03)

LiCoO2 (50-0653)

SG. R-3m

a:2.824

c:13.888

10 20 30 40 50 60 70 80 90

Inte

nsit

y (

a.u

.)

2 (degree)

Fresh

45C50cyc

45C100cyc

45C200cyc

Al2O3

Graphite

Anode Cathode

Fresh

18


FTIR AND RAMAN ANALYSIS

2000 1800 1600 1400 1200 1000 800 600

45oC, 100 cycles

Inte

ns

ity

(a

.u.)

Wavelength (cm-1)

Fresh

Cathode, 0% SOC

2000 1800 1600 1400 1200 1000 800

Anode, 0% SOC

45 oC, 100 cycles

Inte

ns

ity

(a

.u.)

Wavelength (cm-1)

Fresh

19


DSC ANALYSIS

20


VIBRATION TEST & CONSTRUCTION INTEGRITY

Fresh Sample 100 Cycles, 25oC 100 Cycles, 45oC 200 Cycles, 45oC

Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Sample 7 Sample 8

OCV/Mass OCV/Mass OCV/Mass OCV/Mass OCV/Mass OCV/Mass OCV/Mass OCV/Mass

Before 4.213/45.81 4.209/45.90 4.198/45.78 4.208/45.88 4.208/45.98 4.214/45.79 4.210/45.90 4.203/45.88

After 4.213/45.81 4.209/45.90 4.198/45.78 4.208/45.88 4.208/45.98 4.214/45.79 4.209/45.90 4.203/45.88

Before Aging After Aging (250 Cycles under 45oC)

21


AGING EFFECT SUMMARY

22

Hypothesis UL’s Investigation on 18650 Cell

Mechanical Integrity Getting worse on aged battery No different observed (from

vibration test and CT images)

Activity of

Material(s)/Component(s)

Aged battery become less

active


active (from IIISC test)

Dendrite Formation &

Lithium Plating

Potential issue in aged battery N/A (can not be observed

directly, and no voltage drop

observed from Vibration test)

Thermal Stability of

Material(s)/Component(s)

Aged battery becomes worse Aged battery become worse

(from DSC data)

Polarization Effect More apparent on aged battery More apparent on aged battery

(from EIS and overcharging

test)

Risk of Electrolyte Leakage More risk on aged battery No different observed (from

vibration test)

Tolerance to Thermal

Abusive Conditions


tolerant to thermal abuse


tolerant to thermal abuse (from

Hot Box test)


FOLLOW UP AND FURTHER STUDY

Extend the aging effect study to different material

design (ie. NMC, LPF) and different cell type (ie.

Prismatic, Pouch type)

Study the aging effects on batteries with abuse aging

conditions

Further study in Overcharging Test to single cell

Further study in Thermal Stability to the Component(s)

in single cell

23


ACKNOWLEDGEMENT

CR: Mahmood Tabaddor, Harry P. Jones, Michael Wu and Helena Chiang PDE: Laurie B. Florence, Alex Liang

Prof. BM Hwang, Shawn Cheng

Dr. GM Chen, Bill Chang, GL Huang

24

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Introduction Literature Overview - NASA · Copyright© 2011 Underwriters Laboratories Inc. All rights reserved EXPERIMENTAL Technique Purpose Material Analysis SEM To observe the