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TitleDeterioration Analysis of Layered Lithium Nickel Oxide Based Cathode

s for High Energy Density Lithium-Ion Batteries

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Editor(s)

Citation

Issue Date 2014-02

URL http://hdl.handle.net/10466/14150

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Deterioration Analysis of

Layered Lithium Nickel Oxide Based Cathodes for High Energy Density Lithium-Ion Batteries

Shoichiro Watanabe

February 2014

Doctoral Thesis at Osaka Prefecture University

Deterioration Analysis of Layered Lithium Nickel Oxide Based Cathodes for

High Energy Density Lithium-Ion Batteries

Contents

1 General Introduction 1

1. 1 Introduction 1

1. 2 Background of This Study 5

1. 2. 1 Lithium-ion battery 5

1. 2. 1.1 Electrode reactions of lithium-ion battery 5

1. 2. 1. 2 Structure of lithium-ion battery 7

1. 2. 1. 3 Cathode material for lithium-ion battery 8

1. 2. 1.4 Other materials for lithium-ion battery 12

1. 2. 2 Deterioration analysis 13

1. 2. 2. 1 Typical deterioration mechanisms of lithium-ion battery 13

1. 2. 2. 2 Deterioration analysis of lithium-ion battery 16

1. 2. 2. 3 Acceleration test of lithium-ion batteries 17

1. 2. 2. 4 Impedance analysis method 19

1. 2. 2. 5 Spectroscopic analysis method 19

1. 3 Objectives of This Study 21

1. 4 Outline of This Thesis 21

References 23

2 Comparison analysis between LiNi1-x-yCoxAlyO2 and LiCoO2

cathodes in cylindrical lithium-ion cells during long-term

storage tests 27

2. 1 Introduction 27

2. 2 Experimental 28

2. 2. 1 Preparation of cylindrical 18650 cells 28

2. 2. 2 Accelerated calendar and cycle life tests for cylindrical 18650 cells 29

2. 2. 3 The model cell and impedance analysis 31

2. 2. 4 Surface and bulk analysis 31

2. 3 Results and Discussion 34

2. 3. 1 Performance of 18650 cells 34

2. 3. 2 Analysis of disassembled battery 40

2. 3. 3 Analysis of electrode/electrolyte interface 46

2. 3. 4 Analysis of local structure of cathode active material 56

2. 4 Conclusion 66

References 67

3 Effect of DOD in charge-discharge cycling on the suppression of

the micro-crack generation of LiNi1-x-yCoxAlyO2 particle 70



3. 2. 1 Cycle tests in different DOD conditions for cylindrical model cells 74

3. 2. 2 Impedance analysis of coin-type model cells 75

3. 2. 3 Surface and bulk analyses 76


3. 3. 1 Cycle performance of cylindrical model cells in the different DOD

conditions and characteristics of disassembled cathodes 77

3. 3. 2 Change in morphology and electrochemical properties of LiNi1-x-yCoxAlyO2

particles with charge- discharge cycling in different DOD conditions

and temperatures 83

3. 3. 3 Change in morphology and electrochemical properties of LiNi1-x-yCoxAlyO2

particles with charge-discharge cycling in restricted DODs 87

3. 4 Conclusion 95

References 96

4 Surface analysis of LiNi1-x-yCoxAlyO2 cathode after cycle tests

in restricted DOD ranges 98



4. 2. 1 Cycle tests in restricted DODs for cylindrical model cells 100

4. 2. 2 Surface and bulk analyses 100


4. 3. 1 Cycle performance of cylindrical model cells after cycle tests

in the controlled DODs and cross-sectional SEM images of

the NCA cathode 101

4. 3. 2 Surface and cross section analysis of Li1-x-yNixCoyAlO2 particle 103

4. 4 Conclusion 118

References 119

5 General Conclusions 121

Acknowledgement 123 List of Publication 125

Chapter 1 General Introduction

1. 1 Introduction

Lithium-ion battery is a rechargeable battery with light weight and high energy density.

The lithium-ion battery was commercialized in the 1990s and has widely been used in

portable devices such as notebook personal computers (PCs), cellular phones and digital still

cameras so far. The improvement of energy density has been requested for realizing smaller

size and longer operating time. Figure 1-1 shows the progress of gravimetric and volumetric

energy density of a standard 18650-size cylindrical lithium-ion battery.

Figure 1-1 The progress of gravimetric and volumetric energy density for a standard

18650-size cylindrical lithium-ion batteries.

100

125

150

175

200

225

250

275

250 300 350 400 450 500 550 600 650 700 750

Volumetric energy density (Wh l-1 )

Gra

vim

etric

ene

rgy

dens

ity (W

h kg

-1 )

LCo Type (4.1V charge)LCo Type (4.2V charge)LCo Type (4.3V Charge)NCA Type (4.2V Charge)

2600mAh

1260mAh

1900mAh

2200mAh

2000mAh

2400mAh

2900mAh2800mAh

3070mAh3000mAh

1998

20002001

2002

20042005

19941995

1996

20062009

2013

2011

3350mAh3550mAh

1370mAh1420mAh

1700mAh*Energy density is calculated with min. capacity and max. dimension

100

125

150

175

200

225

250

275

250 300 350 400 450 500 550 600 650 700 750

Volumetric energy density (Wh l-1 )

Gra

vim

etric

ene

rgy

dens

ity (W

h kg

-1 )

LCo Type (4.1V charge)LCo Type (4.2V charge)LCo Type (4.3V Charge)NCA Type (4.2V Charge)

2600mAh

1260mAh

1900mAh

2200mAh

2000mAh

2400mAh

2900mAh2800mAh

3070mAh3000mAh

1998

20002001

2002

20042005

19941995

1996

20062009

2013

2011

3350mAh3550mAh

1370mAh1420mAh

1700mAh*Energy density is calculated with min. capacity and max. dimension

The volumetric energy density of the initial model produced in 1994 was about 250 Wh l-1.

In 2012 it exceeds 700Wh l-1 because of various technical improvements. The achievement of

such high energy density is ascribed to the following technological factors.

(1) Increase in graphitization and initial charge-discharge efficiency of the graphite anode.

(2) Increase in charge voltage up to 4.1 - 4.35 V

(3) Increase in density of cathode and anode

(4) Introduction of thinner materials (current collector foil, separator, can thickness, etc.)

(5) Introduction of Ni-based cathode material

For the above (1) and (2), new electrolytes which could be tolerant to high voltages and

additives for electrolyte that could stabilize SEI (Solid Electrolyte Interface) formed at the

anode were developed in addition to the improvement of active material. For the above (3),

new electrode binders were developed and mass production equipment of electrode was

improved. For the above (4), for example, the thickness of separator which was 30 m in the

1990s was halved by continuous cooperation of battery makers and material makers.

Meanwhile, the uses of lithium-ion batteries are expanded to high-power applications and

electric energy storage use because environmental issues become more serious.

For instance, hybrid electric vehicles (HEVs) with an internal combustion engine and a

battery system have remarkably improved cost for gasoline consumption and are widespread.

Moreover, battery electric vehicles (BEVs) which are operated only by electric power and

plug-in hybrid electric vehicles (PHEVs) which are operated by electric power of lithium-ion

batteries with high energy density for short distance drives and by the HEV system for long

distance uses have been commercialized. In this way, performances required for lithium-ion

batteries is highly upgraded and diversified to fit expanded applications.

The requirement for rechargeable batteries of general portable equipments is as follows;

(1) High energy density (= discharge voltage capacity density)

(2) High power density

(3) Wide temperature range of usage

(4) Small self-discharge and good storage characteristics

(5) High energy conversion efficiency

(6) Easy handling, high safety and high reliability

(7) High cost performance

For EV and household electric energy storage applications, battery system units which

are composed of many batteries connected in parallels and series are used, and longer

calendar life than conventional usages is required. So the following requirements are added.

(8) Long-term storage characteristics more than 10 years

(9) Charge-discharge cycle performance more than several thousand cycles

(stable capacity and impedance)

(10) High safety and reliability as a total system

In various types of lithium-ion batteries, the 18650-type cylindrical lithium-ion battery

(diameter : 18 mm, total height : 65 mm), which is a standard size for notebook-type PC usage,

is widespread as a high cost performance battery which is produced with high-speed

production lines. The multi parallel-series system of 18650 batteries is used as accumulation

of electricity systems and a vehicle power supplies.

The general features of the multi parallel-series system of small batteries are as follows.

(1) High system redundancy because of a parallel system

(2) High reliability because of inspecting and controlling at a unit of a small capacity cell

(3) Small potential and the current distribution because of the use of small electrodes,

causing uniform cell reaction

(4) Use of technology for high energy density because incident events can be controlled

at a small unit

(5) No need for new investment because existing mass production lines can be used

For using the multi parallel-series system of small batteries as accumulation of electricity

systems and vehicle batteries, it is extremely important to precisely understand deterioration

mechanism of the batteries required for establishing the long-term reliability of the system.

I began research and development on lithium-ion batteries in 1990, and then have

developed a lot of batteries, improved their performance, and mass-produced them. Especially,

I have participated in the LEAD (Li-ion and Excellent Advanced Batteries Development)

program by NEDO (New Energy and Industrial Technology Development Organization)

since 2008, and focused on Ni-based LiNi1-x-yCoxAlyO2 (NCA) as the cathode material in R &

D on "High performance electricity system technology for the next generation cars".

In this thesis, I evaluated storage and cycle characteristics requiring long-term reliability

for a high capacity cylindrical lithium-ion battery with the LiNi1-x-yCoxAlyO2 cathode, and

clarified deterioration mechanism of the battery, in particular the cathode.

1. 2 Background of This Study

1. 2. 1 Lithium-ion battery

1. 2. 1. 1 Electrode reactions of lithium-ion battery

The lithium-ion battery is composed of lithium-included metal oxide compounds as a

cathode active material, graphite which can reversibly intercalate lithium as a anode active

material, organic electrolyte that contains the lithium salt, separator, aluminum foil as a

cathode current collector, copper foil as a anode current collector, can and several other parts.

Figure 1-2 indicates an electrochemical reaction scheme of a typical lithium-ion battery.

The lithium-ion batteries have a rocking chair charge-discharge reaction scheme.

Lithium-ions move between the cathode and anode active materials with different host

structures in charging and discharging. During the first charging, lithium-ions in the crystal

lattices of the cathode active material dissolve with solvation in an electrolyte solution, move

to the anode, and intercalate into the crystal lattices of the anode active material. It is

well-known that the SEI (solid electrolyte interface) film which lithium-ions can pass through

is also formed on the anode surface during the first charging, and suppresses the continuous

decomposition reaction of the solvent on the anode surface, leading to high charge-discharge

efficiency.

Figure 1-2 An electrochemical reaction scheme of a typical lithium-ion battery.

1. 2. 1. 2 Structure of lithium-ion battery

Figure 1-3 shows the schematic structure of a typical cylindrical lithium-ion battery.

Figure 1-3 Schematic structure of a typical cylindrical lithium-ion battery.

To prepare cathode or anode, the mixture paste of cathode or anode active material,

solvent, binder, and conductive compound (mainly carbon material) is thinly coated on an

aluminum foil (for cathode) or a copper foil (for anode) as current collector. The cathode,

anode and separator are cylindrically winded up. After the winding jerry roll is put into a

cylindrical can (nickel-plated iron can) and a tab is welded on the can, electrolyte is put into it.

A plastic gasket and a top cap are simultaneously cramped up to the can. Finally the battery is

completed by washing, charging-discharging and aging.

Top Cap Cathode TabGasket Safety vent

PTCInsulator Separator(Electrolyte)

Anode TabAnodeCathodeInsulator

Anode can

Top Cap Cathode TabGasket Safety Vent



Anode can

Top Cap Cathode TabGasket Safety vent



Anode can

Top Cap Cathode TabGasket Safety Vent



Anode can

The polyolefin porous thin film is used for a separator because the movement of lithium

ions is shut down as the battery is heated by short-circuit. Many safety devices such as a

Positive Temperature Coefficient (PTC) device which interrupts excessive current on

short-circuit, a Current Interrupter Device (CID) which operates automatically as the internal

pressure of the battery rises in overcharging and a safety vent which releases the pressurized

gas are introduced to lithium-ion batteries.

The long-term reliability tests in this study is performed with 18650 size (cylinder

diameter: 18 mm, total height: 65 mm) lithium-ion batteries.

1. 2. 1. 3 Cathode material for lithium-ion battery

Table 1-1 shows typical cathode materials for the lithium-ion batteries.

Table 1-1 Typical Cathode materials for lithium-ion batteries.

LiCoO2 (LCO) with a hexagonal crystal structure (Fig. 1-4) was widely used as the

cathode active material for lithium-ion batteries because of its simple preparation method,

high operation voltage of 3.9 V and flat discharge curve.

Materials Theoretical Exprimental rechargeable Average operating Density Energy Energycapacity capacity voltage density densityAh kg-1 Ah kg-1 V g cm-3 Wh kg-1 Wh cm-3

Li1-xCoO2 274 145 (Li0.5CoO2) 3.9 5.05 450 2273Li1-xNiO2 274 192 (Li0.7NiO2) 3.8 4.76 700 3332

Li1-xMn2O4 148 118 (Li0.2Mn2O4) 4 4.28 400 1712Li1-xFePO4 170 160 (Li0.06FePO4) 3.4 3.6 550 1980

Figure 1-4 Crystal structure of LiMO2 ( M = Co or Ni ).

As shown in Table 1-1, the theoretical capacity for LiCoO2 is 274 mAh g-1, while the

practical capacity is about only a half (145mAh g-1), which means low utilization of LiCoO2.

There are two possible approaches for enhancing energy density.

(1) Increase in the lithium utilization by increasing the upper limit of voltage in charging

(2) Use of LiNiO2 whose capacity is higher than that of LiCoO2

Recently, the increase in energy density by raising the charge voltage from 4.2 to 4.35V

has been realized in most of lithium-ion batteries for cellular phones and note PCs. However,

when the charge voltage is raised over 4.3 V, the battery storage characteristic and long-term

reliability at high temperatures are lowered due to oxidative dissolution of cathode material,

dry out of electrolyte solution and gas evolution which comes from electrolyte oxidation and

separator oxidation on the cathode surface. There are many researches on suppression of side

reactions, but they have been completely suppressed yet. [1-6]

Li

CoO

M: Co or Ni

Li

CoO

M: Co or Ni

Ni-based LiNiO2 has been expected as a promising next generation cathode material

because the Ni element has higher capacity, richer resource and lower and stabler price than

the Co element.

Lithium metal oxides (LiMO2 (M= Co, Ni)) are 4 V-class cathode active materials with

-NaFeO2 type R3_

m structure discovered by Goodenough [7]. Ohzuku et al. reported basic

structure and charge and discharge behaviors of LiNiO2 in 1993 [8]. LiNiO2 showed high

capacity more than 200mAh g-1 at the charge potential of 4.3 V vs. Li/Li+ , but it was unstable

because the change in crystal structure during charging and discharging was large [8]. The

synthesis conditions such as temperature, time and atmosphere strongly affected the capacity

of LiNiO2. The Ni2+ mixing into Li layer significantly decreased capacity [9-11]. The doping

of foreign metal elements such as Al, Co, Mn, Ti and Fe, etc. to stabilize the crystal structure

was investigated at the first stage of development [12-19]. Especially, in LiNi(1-x)CoxO2, Ni

could be substituted with Co over the whole Ni content (0x100), and therefore the cation

mixing of Ni2+ into Li layer and the large crystal structure change were effectively suppressed,

leading to the improvement of cycle characteristics [20-23].

A great deal of effort was put into mass production of LiNi1-x-yCoxAlzO2. Basically,

LiNiO2 is prepared by mixing nickel hydroxide with lithium hydroxide and then heat-treating

in oxygen atmosphere. On the other hand, LiNi1-x-yCoxAlzO2 was prepared by the

co-precipitation method. In this method, at first a sodium hydroxide solution is added in an

acidic solution containing Ni2+, Co2+ and Al3+ ions with controlling pH to have appropriate

particle configuration, resulting in the production of a co-precipitated precursor,

Ni1-x-yCoxAly(OH)2 [24-25]. After that, the precursor was mixed with lithium hydroxide and

heat-treated in oxygen atmosphere to prepare the final product LiNi1-x-yCoxAlyO2. The

resultant LiNi1-x-yCoxAlyO2 particles had a spherical configuration which was quite similar to

the configuration of the precursor particles. Each LiNi1-x-yCoxAlyO2 particle was an aggregate

of the primary particles with size of about 10 m, as shown in Fig. 1-5.

Figure 1-5 SEM photographs of Ni1-x-yCoxAly(OH)2 precursor and synthesized

LiNi1-x-yCoxAlyO2.

The thermal stability of charged cathode material is important to design batteries with

high safety. However, it was a serious problem that the thermal stability of charged LiNiO2

was lower than that of charged LiMn2O4 and LiCoO2 [26].

Since Al has the similar ionic radius to Ni and Co (Ni3+=0.0560 nm, Co3+=0.0545 nm,

Al3+=0.0535 nm), substitution of Ni and Co with Al does not change lattice constant. So Al

can be uniformly distributed in the Ni and the Co layer of LiNi1-x-yCoxAlyO2. It was reported

that the addition of Al in LiNi1-x-yCoxAlyO2 improved thermal stability at the charged states

and cycle characteristics, which accelerated the development of Ni-based cathode material

[27-31]. Madhavi et al. reported that since the Al-O bond was more ionic than the Co-O bond,

the substitution of Co with Al made the Ni-O bond more covalent, leading to the increase in

the ionicity of the Li-O bond or the mobility of lithium ions in the Li layer [32]. In 2006,

Panasonic Co Ltd. succeeded in mass-production of cylindrical lithium-ion batteries

NCR18650 in which NCA was used as a cathode material.

6m 6m

Ni1-x-yCoxAly(OH)2 LiNi1-x-yCoxAlyO2

6m6m 6m6m

Ni1-x-yCoxAly(OH)2 LiNi1-x-yCoxAlyO2

1. 2. 1. 4 Other materials for lithium-ion battery

Graphite is usually used as an anode of high-capacity lithium-ion batteries. In this thesis,

massive artificial graphite which can be filled with high density is used as an anode material.

Electrolyte for the lithium-ion battery is composed of lithium salt, organic solvent and

several kinds of functional additives. Lithium hexafluorophosphate (LiPF6) was widely used

because of its high tolerance for oxidation and reduction, high solubility and high degree of

ionization, and so it is used in the present study. Various solvents for lithium-ion batteries are

shown in Table 1-2 [33].

Table 1-2 Properties of solvents for lithium-ion batteries.

Since ethylene carbonate (EC) is known to be a solid at room temperature, low viscosity

solvents such as chain ester, dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), and

diethyl carbonate (DEC) are usually mixed with EC. In this study, a mixed solvent of

EC-EMC-DMC was used.

Coating of an inorganic material layer on the polyethylene micro-porous separator has

been used for maintaining its insulation properties and shape at high temperatures.

Solvent Chemial Melting Boiling Dielectric Viscosity EoxStructure point point constant

cP V vs.Li/Li+

Ethylene carbonate 37 238 90 1.9(40) 6.2(EC)

Propylene carbonate -49 242 65 2.5 6.6(PC)

-Butyrolactone -44 204 42 1.7 8.2(GBL)

Dimethyl carbonate 3 90 3.1 0.59 6.7(DMC)

Ethyl Methyl carbonate -55 108 2.9 0.65 6.7(EMC)

Diethyl carbonate -43 127 2.8 0.75 6.7(DEC)

O O

O

O O

O

O

O

O O

O

O O

O

O O

O

1.2.2 Deterioration analysis

1. 2. 2. 1 Typical deterioration mechanisms of lithium-ion battery

The capacity and charge-discharge performance of lithium-ion battery strongly depend on

its charge-discharge mechanism. The reaction of lithium-ion battery that is composed of the

carbon anode and lithium metal oxide cathode has the following characteristics;

(1) Li+ ions in the charge and discharge reactions are given from the cathode material.

(2) The amount of Li+ ions deintercalated from the cathode material is controlled by the

charging conditions (charge voltage, charging current and cut-off current).

(3) Side reactions at the anode influence capacity.

(4) Capacity decreases without deterioration of the battery material when the polarization

of the battery is increased.

(5) Electrolyte is a medium carrying lithium ions, and does not contribute to the charge and

discharge reactions except for side reactions.

The deterioration mechanism of the lithium-ion battery can be classified into three.

(1) The amount of Li+ ions which join in charge and discharge reactions is decreased due to

chemical changes.

(2) The amount of Li+ ions which join in charge and discharge reactions is decreased due to

physical changes.

(3) The power down and capacity decay occur due to an increase in impedance such as DC,

charge-transfer and diffusion resistances.

In practical lithium-ion battery, The above deterioration mechanisms (1) - (3)

concurrently proceed, and cause the decrease in capacity and discharge voltage. The proposed

mechanism of deterioration is shown in Table 1-4 and the schematic model is shown in Fig.

1-6 [34, 35].

Tabl

e 1-

4

The

cau

se o

f the

det

erio

ratio

n of

Lith

ium

-ion

batte

ries.

Oxi

datio

n of

sepa

rato

rD

ecom

posi

tion

of so

lven

tD

ecom

posi

tion

of so

lute

Blo

ckin

g th

e ho

le o

f sep

arat

orD

ry-o

ut o

f the

ele

ctro

lyte

Dec

reas

ing

the

Li io

n co

nduc

tivity

Ove

r C

harg

ing

Dec

ompo

sitio

n of

ele

ctro

lyte

Mic

ro sh

ort c

ircui

t by

depo

site

d m

etal

Ove

r D

ischa

rge

Dec

ompo

sitio

n of

SEI

Mic

ro sh

ort c

ircui

t by

depo

site

d m

etal

Shut

dow

n of

the

sepa

rato

r hol

eSh

ort c

ircui

t by

sepa

rato

r shr

inka

geD

ecom

posi

tion

of e

lect

roly

teD

ry-u

p of

the

elec

troly

te

Incr

easi

ng th

eim

peda

nce

Cha

ngin

g th

eC

hem

ical

s

Dec

ompo

sitio

n of

bin

der

Stru

ctur

al d

isor

derin

g

Dec

ompo

sitio

n of

SEI

Dec

ompo

sitio

n of

SEI

Ove

r H

eatin

g(s

hort

cir

cuit

orou

ter

heat

ing)

Isol

atio

n fr

om e

ach

othe

rIs

olat

ion

from

cur

rent

col

lect

or

Met

al d

epos

ition

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n

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mal

usag

e

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orm

alus

age

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n

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lect

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isso

lutio

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n/ni

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dep

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onC

an ir

on/n

icke

l dis

solu

tion

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n fr

om c

urre

nt c

olle

ctor

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rosi

on o

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urre

nt c

olle

ctor

Phas

e tra

nsiti

onEl

ectro

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dec

ompo

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al d

epos

ition

Elec

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te d

ecom

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al d

isso

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ium

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epos

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epos

ition

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ro c

rack

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yer f

orm

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n

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ace

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r for

mat

ion

Lith

ium

dep

ositi

on

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ompo

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n of

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deC

atho

de su

rfac

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node

surf

ace

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hode

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lect

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volu

tion

Figure 1-6 Schematic deterioration model of lithium ion battery.

thicker SEI formation

isolation from current collector

microcracking of graphite

Lithium metal deposition

generation of Li compounds

oxidation of separator decreasing the Gurley number by compressing the separator

blocking the hole by SEI compounds

deposition of dissolved metal and micro short circuit

dry-out of the electrolyte

isolation from current collector

isolation of graphiteisolation of LiMO2

structural disordering

phase transition

metal dissolutionmicrocracking

decomposition of binder

gas generation

Initial (Schematic modelof Li-ion Battery)

Initial (Schematic modelof Li-ion Battery)

After deteriorationAfter deterioration

Cathode current collector(Aluminum foil)

Cathode Anode Anode current collector(Copper foil)

Separator / Electrolyte

Anode material(Graphite)

Electrode material(Binder, electron conductor)

Cathode material(LiMO2)


Electrolyte(Solute:Li salt)(Solvent: mixture of cyclic carbonate and chain carbonate)

Separator(Polyolefin porous film)

Cathode current collector(Aluminum foil)

Cathode Anode Anode current collector(Copper foil)

Separator / Electrolyte

Anode material(Graphite)


Cathode material(LiMO2)


Electrolyte(Solute:Li salt)(Solvent: mixture of cyclic carbonate and chain carbonate)

Separator(Polyolefin porous film)

There are a lot of factors that cause the deterioration of the lithium-ion battery as shown

in Table 1-4 and Fig. 1-6.

It is very hard to understand the existence and the progress of side reactions because (1)

the charge and discharge efficiency of the lithium-ion battery is about 99.9% or more except

for initial several cycles, (2) the predominant factor changes with the progress of several

concurrent deterioration mechanisms and deterioration progress, and (3) the deterioration

mechanism changes when the same batteries are used under different conditions. Therefore,

the condition resembling the practical usage pattern should be set in the battery deterioration

analysis.

1. 2. 2. 2 Deterioration analysis of lithium-ion battery

The deterioration analysis method of the lithium-ion battery can be roughly classified as

follows.

(1) Battery performance is measured under various acceleration conditions to

mathematically predict the lifetime of the battery.

(2) The internal resistance and impedances of charge transfer and diffusion processes with

different relaxation times can be separated by AC impedance analysis.

(3) The battery components are taken out of the battery after the deterioration, and

analyzed by crystallographic, spectroscopic and chemical methods.

The deterioration behavior of the lithium-ion battery is complex as mentioned above.

If two batteries are operated under different acceleration conditions, they will deteriorate in

different mechanism. Therefore, it is important to combine the three analysis techniques

(1)-(3) to determine deterioration mechanism.

1. 2. 2. 3 Acceleration test of lithium-ion batteries

The acceleration condition for the lithium-ion battery needs to be set depending on

applications. For instance, the deterioration mode of lithium-ion batteries for cellular phone

and note PC applications in market is quite different. As shown in Fig. 1-7, for cellular phone

applications, the battery is charged in the night every day or once in a few days, whereas for

note PC application the battery is held in the full-charged and high temperature conditions for

a long time because the note PC is often used with connecting to an AC power supply. In the

latter, the deterioration mode is dominated by the storage deterioration at high temperature

and high state-of charge (SOC).

Figure 1-7 Usage pattern of cellar phone and note type personal computer batteries.

Even for on-vehicle use, the SOC range, charge-discharge pattern, and storage condition

of batteries for HEV, PHEV and BEV are so different that battery design and acceleration

conditions depending on applications need to be modified. The acceleration tests for high

capacity lithium-ion battery with Ni-based LiNi1-x-yCoxAlyO2 cathode are preceded. The

SAFT team developed lithium-ion batteries for backup and satellite applications.

Brossely et al. in the SAFT team carried out long-term storage tests at 15 60 C after

float charging at a certain voltage and periodically measured capacity at 100% DOD (Depth

Cellar phone usage pattern(1charge per day)

Note PC usage pattern(Continuous charged )

0 6 12 18

0~24oclock

AC-ON

100Storage

& Operating

AC-ON100

Storage

25 40 40 35

AC-ON100

Storage

100

0

SOC

/ %

010

0

Time (o'clock)0 6 12 18

0~6oclock

30 25

60%

99%

SOC

/ %

010

0

AC-off99

Storage

Mobile

Operating

Charging

(time of AC power supply) (time of AC power supply)

Cellar phone usage pattern(1charge per day)

Note PC usage pattern(Continuous charged )

0 6 12 18

0~24oclock

AC-ON

100Storage

& Operating

AC-ON100

Storage

25 40 40 35

AC-ON100

Storage

100

0

100

0

SOC

/ %

010

0


0~6oclock

30 25

60%

99%

SOC

/ %

010

0

AC-off99

Storage

Mobile

Operating

Charging

(time of AC power supply) (time of AC power supply)

of Discharge) during charge-discharge cycle tests of 80% DOD range. They found that the

corrosion of the SEI film on the anode surface was a predominant factor for deterioration in

the storage tests, and the corrosion rate followed the Arrhenius law [36-39].

Argonne National Laboratory (ANL), Sandia National Laboratory (SNL) and Idaho

National Engineering and Environmental Laboratory (INEEL) developed the life modeling of

lithium-ion batteries in Department of Energys Advanced Technology Development (ATD)

program for HEV application sponsored by US Department of Energy. In this program,

deterioration behavior after storage at several SOCs (40, 60 and 80 %) or charge-discharge

cycling at DODs (3, 6 %) at 40 70 C was mathematically discussed. Bloom et al.

showed that the increment in impedance depended on t1/2 because the rate of SEI formation

whose rate-determining step was diffusion was predominant, and the rate of fade in power

followed the Arrhenius law [40, 41]. Moreover, they indicated that in the 10% Al-doped cell

the time dependence of the impedance rise was composed of two distinct kinetic regimes; the

initial portion depended on t1/2 and the latter one depended on t [42].

In the lithium-ion battery, it is known that the reaction of the graphite anode with

electrolyte to cause the SEI formation is the most active, and the thicker SEI formation at the

anode surface is a predominant factor for deterioration.

However, after the carbon material and electrolyte were improved, the predominant

factor for deterioration was changed and the deterioration behavior did not follow the

conventional lifetime prediction. So the understanding of the predominant deterioration

mechanism is an urgent issue. There are a lot of deterioration factors for the lithium-ion

batteries as shown in Table 1-4. So it is important to understand the deterioration factors to

analyze the deterioration mechanism.

1. 2. 2. 4 Impedance analysis method

The deterioration analysis that uses ac impedance method is effective for to confirm the

deterioration factor because of its can divide the resistance element to the factor of electronic,

charge transfer and the diffusion resistance. In addition, it is easy to specify the rule factor of

deterioration because it is possible to measure by disassemble the deteriorated battery and

separating the cathode and anode.

Amine and Chen et al. showed that the impedance rise was dominantly contributed by the

increase of charge transfer resistance on the cathode by separating the cathode and anode from

disassembling the deteriorated battery. [43, 44] Moreover, Chen and Kondo et al. showed

that added Al and Mg, small amount of foreign metal doping in LiNi1-x-yCoxMyO2 cathodes

significantly stabilizes the cell impedance. [45, 46] Thus, the impedance analysis specifies the

factor of the impedance rise, and is important for judging to what to do focus a further

analysis.

1. 2. 2. 5 Spectroscopic analysis method

Recently, the deterioration analysis of the lithium-ion battery has dramatically been

improved by the progress of spectroscopic technique. Since the spectroscopic technique has

resolution of a nanometer level, it is possible to quantitatively analyze the modulations in

several nanometers on a specimen surface. Therefore microscopic monitoring of cathode

deterioration which was impossible to analyze qualitatively and quantitatively before became

possible. Thus the understanding for the deterioration mechanism of the cathode has

progressed rapidly.

XPS and FTIR-ATR spectroscopy are effective for the analysis of SEI which generated

on the cathode surface by reacting with the electrolyte. Andersson et al. showed in the analysis

of the LiNi1-xCoxO2 surface by XPS that lithium carbonate (Li2CO3) and lithium fluoride

(LiF) had been produced in the preparation of the active material, and they are converted to

the mixture of organic species including polycarbonates, LiF and LixPFy-type and

LixPFyOz-type compounds during storage in a battery [47].

From the late 1990s, the change in electrode structure with electrochemical reaction was

analyzed by X-ray Absorption Spectroscopy (XAS). Abraham et al. found that there were

oxygen deficiencies at the surface of LiNi0.8Co0.2O2 by comparing an oxygen K-edge

spectrum measured by the Total Electron Yield (TEY) method which could analyze from the

electrode material surface to a depth 5 nm with that measured by the Fluorescence Yield (FY)

method which could analyze the bulk of more than 300 nm in depth [48]. High Resolution

transmission Electron Microscopy (HR-TEM) indicated that a NiO-like rock salt (NaCl-type)

structure with 2 4 nm in depth was formed in the near-surface region of LiNi0.8Co0.2O2,

whereas its bulk had the expected -NaFeO2 type layered structure [48].

Ukyo et al. found that the valence of Ni in LiNi0.8Co0.15Al0.05O2 was converted from Ni3+

to Ni4+ during charging, whereas that of Co was hardly changed although only the local

structure around a Co atom was changed at 60 C [49]. They showed that Inactive Ni2+ atoms

existed on the surface and the average valence of Ni was increased by charge-discharge

cycling and aging. The EELS and HR-TEM revealed that a Ni-O layer with a rock salt

(NaCl)-type structure was formed at the surface of cathode particle during charge-discharge

cycling and aging, causing a rise in cathode impedance [50-52]. Tatsumi et al. proposed a

schematic degradation model of LiNi1-x-yCoxAlyO2 based on the above results and the data

obtained by neutron diffractometry and XPS [53-55].

1.3 Objectives of This Study

The main objective of this study was to elucidate the deterioration mechanism of the

lithium-ion battery with Lithium Nickel Cobalt Aluminum Oxide (LiNi1-x-yCoyAlzO2 , NCA)

cathode which has high capacity and high reliability under the acceleration test conditions for

charge discharge cycling and storage, and feed back to practical use.

First, two kinds of commercial lithium-ion batteries with NCA cathode (NCR18650) and

LCO cathode (CGR18650E) were compared in terms of long-term reliability, and the key

factor of battery deterioration was clarified.

Next, the difference in deterioration mechanism was clarified by testing under several

acceleration conditions which seriously influenced battery life using a model cell.

1. 4 Outline of This Thesis

This thesis consists of 5 chapters.

In Chapter 1, background on technical development of lithium-ion batteries and

analytical method for their deterioration mechanism was described. First, the history on the

improvement of energy density was summarized and then technical development of cathode

was described. Next, the development of analytical method for deterioration mechanism of

lithium-ion batteries was outlined.

In Chapter 2, for two cylindrical lithium-ion batteries, NCR18650 and CGR18650

whose long-term reliability was different, deterioration behavior was analyzed and compared.

The accelerated deterioration tests of these batteries were performed with various

electrochemical and spectroscopic technique under various conditions. Consequently, it was

found that the deterioration mainly came from the cathode and was ascribed to the difference

in production rate of a rock salt-type structure at the surface of active material between NCA

and LCO.

In Chapter 3, a model cell with the NCA cathode was fabricated, and the effect of DOD

condition on charge and discharge cycling characteristics was investigated. The cycle

characteristics in a specific potential region were evaluated. The deterioration of cathode was

not accelerated by the cycling in the specific potential region or DOD, but it was accelerated

by cycling in the wide DOD range because the generation of microcracks progressed.

In Chapter 4, it was clarified by electrochemical and spectroscopic analyses that

deterioration of cycle characteristics was ascribed to the generation of microcracks and the

following formation of rock salt-type layer at the surface of active material due to infiltration

of electrolyte. The generation of microcracks could be prevented by controlling DOD, and

the mechanism which could keep long-term reliability was demonstrated.

In Chapter 5, general conclusions of the results obtained in this study were described.

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Chapter 2 Comparison analysis between LiNi1-x-yCoxAlyO2 and LiCoO2 cathodes in cylindrical lithium-ion cells during long term storage test

2. 1 Introduction

Panasonic Co. launched the highest capacity and light weight lithium-ion battery series

with the nickel-based NCA cathode in 2006. The energy density of a cylindrical 18650-type

battery were 620 Wh l-1 and 230 Wh kg-1 or more. In the latest model in 2013, capacity is

3.55Ah and the volumetric energy density exceeds 750Wh l-1. These batteries are used as the

power supply for PC, power tools, in-vehicle, bicycle and electric energy storage. [1]

Battery packs inside notebook PCs were used under severe conditions like full charge

voltages and high temperatures of 40 C or more because many customers used PCs with

connecting the AC power supply as shown in Fig. 1-7. I found that the long term battery life

of the NCA-cathode batteries (NCR18650) was several times as long as that of the

LCO-cathode batteries (CGR18650E) [2-4]. Probably the difference in long-term reliability

between these two commercial lithium-ion batteries is caused by the difference of cathode

material.

In this chapter, the change of anode and cathode surface in the two 18650-type cells was

investigated by XPS, ICP and TEM-EELS during the long-term storage test simulating actual

usage conditions by PC users in the market, and the capacity fade was determined by the

reconstructed model cell method. Moreover, the mechanism of deterioration was proposed on

the basis of these results.

2. 2 Experimental

2.2.1 Preparation of cylindrical 18650 cells

Two cylindrical battery cells made by Panasonic Co. were used in this study. The NCA and

LCO cathode cells are NCR18650 (2900mAh) and CGR18650E (2600mAh).

Figure 2-1 The photograph of CGR18650E and NCR18650.

The nickel-based oxide cathode/graphite cell was composed of nickel-based oxide cathode,

graphite anode, electrolyte and micro-porous polyethylene separator. The nickel-based oxide

cathode was composed of a mixture of LiNi0.8Co0.15Al0.05O2, carbon black and

poly(vinylidene fluoride), and aluminum foil. The cobalt-based oxide cathode/graphite cell

was the same as the nickel-based oxide cathode/graphite cell except for the cathode active

material. Electrolyte was a mixture of ethylene carbonate (EC), ethylmethyl carbonate (EMC)

and dimethyl carbonate (DMC) containing 1 mol L-1 (= M) lithium hexafluorophosphate

(LiPF6).

2.2.2 Accelerated calendar and cycle life tests for cylindrical 18650 cells

The cycle tests, the storage tests and the interval storage and cycle tests were performed

according to protocols in Table 2-1.

Table 2-1 Cell materials, cell capacity and test conditions of cylindrical 18650 cells.

It is thought that the usage pattern that a lot of business uses PC mixed with the (a)

continuous charged (b) once a day mobility use as shown in figure 2-2. The protocols for the

interval storage and cycle tests imagine user's usage at office in note-type PC. The test

environment temperature was 45C and every charge rest time was 24 h.

NCR18650 CGR18650ELiNi0.8Co0.15Al0.05O2 LiCoO2

Graphite Graphite2.9Ah 2.6Ah

Charge 4.2V-cccv, 0.3It-max, 50mA-cutoff 4.2V-cccv, 0.7It-max, 50mA-cutoffCharge rest 20min 20minDischarge 1.0It-cc, 2.5V-cutoff 1.0It-cc, 3.0V-cutoffDischarge rest 20min 20mintemp. 45degC 45degCCharge 4.2V-cccv, 0.3It-max, 50mA-cutoff 4.2V-cccv, 0.7It-max, 50mA-cutoffCharge rest 24h 24hDischarge 1.0It-cc, 2.5V-cutoff 1.0It-cc, 3.0V-cutoffDischarge rest 20min 20mintemp. 45degC 45degCstorage temp. 45degC 45degCcharge before storage 4.1V-cccv, 0.3It-max, 50mA-cutoff 4.1V-cccv, 0.7It-max, 50mA-cutoffcharge for cap. Checking 4.2V-cccv, 0.3It-max, 50mA-cutoff 4.2V-cccv, 0.7It-max, 50mA-cutoffdischarge for cap. Checking 0.2It-cc, 2.5V-cutoff 0.2It-cc, 3.0V-cutoffcap. Checking periode 90 days 90days

Test conditionCathode materialAnode material

Storage test

Cell capacityCycletest

Interval storageand cycle test

Figure 2-2 The typical usage pattern of business uses PC.

(a) Note PC usage pattern(Continuous charged )

0 6 12 18

0~24oclock

AC-ON

100Storage

& Operating

AC-ON100

Storage

25 40 40 35

AC-ON100

Storage

100

0

SOC

/ %

010

0

Time (o'clock)

(time of AC power supply)

(a) Note PC usage pattern(Continuous charged )

0 6 12 18

0~24oclock

AC-ON

100Storage

& Operating

AC-ON100

Storage

25 40 40 35

AC-ON100

Storage

100

0

SOC

/ %

010

0


0~24oclock

AC-ON

100Storage

& Operating

AC-ON100

Storage

25 40 40 35

AC-ON100

Storage

100

0

100

0

SOC

/ %

010

0

Time (o'clock)

(time of AC power supply)

SOC

/ %

010

0

0 6 12 1824

0~10 oclock

AC-ON

99Storage

mobile

AC-off99

Storage

AC-off99

Storage

25 40 45 30

10%

99% AC-ON

99Storage

17~24 oclock(time of AC power supply)

(b) Note PC office usage pattern(once a day mobility use )

SOC

/ %

010

0

0 6 12 1824

0~10 oclock

AC-ON

99Storage

mobile

AC-off99

Storage

AC-off99

Storage

25 40 45 30

10%

99% AC-ON

99Storage

17~24 oclock(time of AC power supply)

(b) Note PC office usage pattern(once a day mobility use )

2.2.3 The model cell and impedance analysis

In order to determine which electrode was degraded, both the cathode and anode were

taken out of each 18650 cell and used for assembling a 2016 coin cell with the lithium metal

foil as a counter electrode under Ar atmosphere. An electrolyte and a separator of the coin cell

were the same as those of the 18650 cell. Impedance measurements were performed using a

Solartron 1260/1286 frequency response analyzer system. The amplitude of the ac signal was

10 mV over the frequency range between 1 MHz and 1 mHz in this study. All measurements

were carried out at 25 C. The capacity fade and impedance change of the cathode and anode

were compared with their initial conditions.

2.2.4 Surface and bulk analysis

XRD patterns were collected with a Panalytical XCelerator detector equipped with a Cu

target x-ray tube and a diffracted beam monochrometer. Each XRD measurement was

performed every 0.05 over a scattering angle range between 2= 10 and 90 and the

counting time was 10 s. SEM images were obtained with a Hitachi S-4500 scanning electron

microscope equipped with an energy-dispersive X-ray (EDX) analyzer.

Surface structure of each cathode material was characterized by XPS and scanning

transmission microscopy (STEM)-Selected Area Electron Diffraction (SAED)/EELS. XPS

analysis was performed with a PerkinElmer PHI 560/ESCA-SAM system. XPS spectra were

obtained after several times of Ar+-sputtering with 4 keV energy ions and a current beam of

0.36 A cm-2. A sample for the XPS analysis was excited with 1486.6 eV energy AlK

X-rays. Inductively coupled plasma atomic emission spectrometry (ICP-AES) measurement

was performed using ICPS-7500 in order to quantify the amount of metal deposited on the

anode surface. STEM-SAED/EELS analysis was conducted with a 200 kV JEOL JEM-2100F

equipped with a parallel electron energy loss spectrometer (Gatan 863). XRD and SEM were

used to study the phase change and microscopic morphology for each active material after

storage. For surface and bulk analyses, each cell was charged to a voltage of 4.1V at 0.2It rate

and then the voltage was kept until the current was reduced to 0.05It rate. After charging, the

cell was disassembled. The samples taken out of the disassembled cells were washed with dry

DMC and evaporated at room temperature.

Figure 2-3 Experimental flow chart of analysis for Lithium-ion batteries.

Cylindrical Lithium-ion battery

NCR18650 CGR18650E


NCR18650 CGR18650E

Accelerated calendar and cycle life test

Charge and discharge cycle test Storage test at high temperature Interval storage-cycle tests



Disassemble the cell Disassemble the cell

Electrochemical measurement

Capacity Impedance


Capacity Impedance

CathodeCathode AnodeAnode

Model cell X-ray analysis SEM XPS STEM-EELS HR-TEM


Model cell SEM XPS ICP-AES



NCR18650 CGR18650E


NCR18650 CGR18650E





Disassemble the cell Disassemble the cell


Capacity Impedance


Capacity Impedance

CathodeCathode AnodeAnode





2. 3 Results and Discussion

2.3.1 Performance of 18650 cells

Fig. 2-4 shows cycle performance for an NCR18650 (NCA cathode) and a CGR18650E

(LCO cathode) at 45C. This figure indicates there are only a few differences in cycle

performance between both cells. However, as for the interval storage and cycle test

performance, the NCR18650 was much superior to the CGR18650E as shown in Fig. 2-5.

The life time of the 70% capacity retention for the NCR18650 was twice longer than that for

the CGR18650E. These data showed a good correspondence to the difference of reliability in

an actual market.

Figure 2-4 Cycle performance of an NCR18650 (NCA cathode) and a CGR18650

(LCO cathode) at 45 C.

Figure 2-5 Interval storage and cycle test performance of an NCR18650 (NCA

cathode) and a CGR18650E (LCO cathode) at 45 C.

30

40

50

60

70

80

90

100

0 100 200 300 400 500

cycle number

NCR18650(NCA cathode)

CGR18650E(LCO cathode)

Rel

ativ

e C

apac

ity /

%

30

40

50

60

70

80

90

100

0 100 200 300 400 500

cycle number



Rel

ativ

e C

apac

ity /

%

30

40

50

60

70

80

90

100

0 100 200 300 400 500

cycle number



Rel

ativ

e C

apac

ity /

%

30

40

50

60

70

80

90

100

0 100 200 300 400 500

cycle number



Rel

ativ

e C

apac

ity /

%

In order to verify the difference, the capacity fade analysis during a long term storage test

was performed. Fig. 2-6 shows storage performance at 45C for the NCR18650 and

CGR18650E after they were charged to 4.1 V. The NCR18650 showed better storage

performance than the CGR18650E. The NCR18650 maintained about 90% of the initial

capacity even after storage for 2 years at 45 C.

Figure 2-6 Storage performance at 45 C of an NCR18650 (NCA cathode) and a

CGR18650 (LCO cathode) charged to 4.1V.

50

60

70

80

90

100

0 5 10 15 20 25Time / Month


CGR18650E(LCO cathode)Rela

tive

Cap

acity

/ %

50

60

70

80

90

100

0 5 10 15 20 25Time / Month


CGR18650E(LCO cathode)Rela

tive

Cap

acity

/ %

Fig. 2-7 shows rate performance for the NCR18650 and CGR18650E which were fresh

or stored for 2 years at 45 C after being charged to 4.1 V. As be seen from Fig. 2-7, capacity

fade and the polarization of the CGR18650E was remarkably increased during the storage

for 2 years.

Figure2-7 Rate performance of the (a) NCR18650 and (b) CGR18650E fresh and after 2

years storage at 45 C at 4.1V. Straight line and closed circles indicate the

() fresh cell and () stored cell, respectively. The cells were charged up to

4.2V by CVCC until the current reduced to 0.05It mA and discharged at (a)

0.2C, (b) 1C and (c) 2C rate at 25C.

2

2.5

3

3.5

4

4.5

0 500 1000 1500 2000 2500 3000Capacity / mAh

Volta

ge /

V

Stored Cell

Fresh Cell(a) NCR18650

(c) (b)(a) (b) (c) (a)

2

2.5

3

3.5

4

4.5

0 500 1000 1500 2000 2500 3000Capacity / mAh

Volta

ge /

V

(b) CGR18650

Stored Cell

Fresh Cell

(c)(b) (a) (c)(b)(a)

E

2

2.5

3

3.5

4

4.5

0 500 1000 1500 2000 2500 3000Capacity / mAh

Volta

ge /

V

(b) CGR18650

Stored Cell

Fresh Cell

(c)(b) (a) (c)(b)(a)

E

Fig. 2-8 shows ac impedance spectra of the NCR18650 and CGR18650E which were

fresh or stored for 2 years at 45C after being charged to 4.1 V. Each impedance

measurement was performed at 100% SOC and a temperature of 25 C. The charge transfer

resistance (Rct) was evaluated from the lower frequency semicircle in each Nyquist plot.

The Rct values for the fresh and stored NCR18650 were 0.0262 and 0.0356 , respectively,

while those for the fresh and stored CGR18650E were 0.0231 and 0.0407 , respectively.

The impedance of both cells was increased during storage, but its increment for the

CGR18650E was much larger than that for the NCR18650.

Figure 2-8 Nyquist plots of (a) NCR18650 and (b) CGR18650E which are () fresh or ()

stored at 45C for 2 years after being charged to 4.1 V. Each impedance

measurement was performed at 100% SOC and a temperature of 25 C.

10Hz

1Hz10Hz

100Hz

1kHz

-0.03

0

0.03

0.06

0.09

0 0.03 0.06 0.09 0.12Re / ohm

-Z /

ohm

1kHz

100Hz0.1Hz

(a) NCR18650 (NCA Cathode)

10Hz

1Hz10Hz

100Hz

1kHz

-0.03

0

0.03

0.06

0.09

0 0.03 0.06 0.09 0.12Re / ohm

-Z /

ohm

1kHz

100Hz0.1Hz

(a) NCR18650 (NCA Cathode)

0.1Hz

1Hz10Hz100Hz

1kHz

-0.03

0

0.03

0.06

0.09

0 0.03 0.06 0.09 0.12Re / ohm

-Z /

ohm

1kHz100Hz

(b) CGR18650E (LCO Cathode)

0.1Hz

1Hz10Hz100Hz

1kHz

-0.03

0

0.03

0.06

0.09

0 0.03 0.06 0.09 0.12Re / ohm

-Z /

ohm

1kHz100Hz

(b) CGR18650E (LCO Cathode)

2.3.2 Analysis of disassembled battery

To reassemble a 2016 coin cell, the cathode or anode active materials taken out of the

fresh and stored cells were used with a lithium metal counter electrode.

Fig. 2-9 shows discharge curves of each reassembled coin cell operated in the voltage

range of 2.5 4.3 V or 0.01 1.5 V at a constant current of 0.1It at 25 C. As be seen from

Fig. 2-9(a) and (b), in the discharge process no significant capacity fade was observed for the

NCA cathode after storage, while 30% capacity fade was observed for the LCO cathode after

storage. Moreover, as shown in Fig. 2-9(c) and (d), in the charge process the notable capacity

fade was not observed for the graphite anode in both NCR18650 and CGR18650E. These

results suggest that the difference in capacity fade of lithium-ion cells during high temperature

storage shown in Fig. 2-5 and Fig. 2-6 is ascribed to the degradation of cathode.

ICP analysis confirmed that the lithium composition, 1-x in Li1-xMO2, of both cathode

active materials, NCA and LCO, before and after the storage tests were equal when each cell

was charged to a voltage of 4.1V before every analysis below.

Figure 2-9 Discharge curves of (a) NCA cathode of NCR18650, (b) LCO cathode of

CGR18650E, (c) graphite anode of NCR18650, (d) graphite anode of

CGR18650E; the data of cathode obtained from the () fresh cell and ()

stored cell, respectively. Percentage of the initial value of discharge capacity

was shown.

2.5

3

3.5

4

4.5

0 20 40 60 80 100 120Capacity / %

Volta

ge /

V (v

s Li

)

2.5

3

3.5

4

4.5

0 20 40 60 80 100 120Capacity / %

Vol

tage

/ V

(vs

Li)

(a) NCR18650 cathode (b) CGR18650E cathode

Fresh Cell

Stored Cell

Fresh Cell

Stored Cell

0

0.5

1

1.5

2

0 20 40 60 80 100 120Capacity / %

Volta

ge /

V (v

s Li

)

0

0.5

1

1.5

2

0 20 40 60 80 100 120Capacity / %

Vol

tage

/ V

(vs

Li)

Fresh Cell

Stored Cell

Fresh Cell

Stored Cell

(c) NCR18650 anode (d) CGR18650E anode

Fig. 2-10 and Fig. 2-11 show XRD patterns of the fresh and stored NCA and LCO

cathode active materials, respectively. The samples for XRD were prepared by clipping from

4.1V charged cathode and then mixing with the standard reference material (NIST 640c Si).

All diffraction lines for fresh and stored cathode active materials were indexed by assuming a

hexagonal lattice. All XRD patterns of the fresh and stored NCA and LCO cathode active

materials were identical as -NaFeO2 having a space group of R3_

m. Ramadass et al. pointed

out that peak intensities of (003), (006), and (104) planes for the LCO changed during the

cycle tests at high temperatures [5, 6]. However, as can be seen from Fig. 2-10 and Fig. 2-11,

additional diffraction lines and line broadening of each diffraction line were not specifically

observed, indicating that the core structure of the cathode materials was not damaged during 2

year storage at 45 C. The integrated intensity ratio of (003) to (104) lines in each XRD

pattern indicates the amount of cobalt or nickel ion mixing into Li layer (cation mixing).

There was no significant difference in the intensity ratio between fresh and stored NCA

cathode active materials. On the other hand, the intensity ratio between fresh and stored LCO

cathode active materials showed a significant change.

Figure 2-10 X-ray diffraction patterns of NCA cathode taken out from the charged

NCR18650; (a) fresh cathode material and (b) stored cathode material.

Miller indexes and lattice parameters were given by assuming a hexagonal

lattice. The lattice parameters were obtained by a least-squares method

using nine diffraction lines depending on the number of well-defined

diffraction lines.

0

5000

10000

15000

20000

25000

30000

10 20 30 40 50 60 70 80 902? / ?

Inte

nsity

/ co

unts

(a)

(b)

(003

)

(101

)

Si

Si(102

)

(104

)

(105

)

(108

)(1

10)

2 / degree Cu (K)

(006

)

(107

)Si

(009

)

(113

)(b)

ah = 2,809, ch = 14.21in hexagonal setting

I(003)/I(104)=1.985


I(003)/I(104)=1.999

Assuming R3m

Inte

nsity

/ a

.u

0

5000

10000

15000

20000

25000

30000

10 20 30 40 50 60 70 80 902? / ?

Inte

nsity

/ co

unts

(a)

(b)

(003

)

(101

)

Si

Si(102

)

(104

)

(105

)

(108

)(1

10)

2 / degree Cu (K)

(006

)

(107

)Si

(009

)

(113

)(b)


I(003)/I(104)=1.985


I(003)/I(104)=1.999

Assuming R3m

Inte

nsity

/ a

.u

Figure 2-11 X-ray diffraction patterns of LCO cathode taken out from the charged

CGR18650E; (a) fresh cathode material and (b) stored cathode material.

Miller indexes and lattice parameters were given by assuming a hexagonal

lattice. The lattice parameters were obtained by a least-squares method

using nine diffraction lines depending on the number of well-defined

diffraction lines.

0

2000

4000

6000

8000

10000

12000

14000

16000

10 20 30 40 50 60 70 80 902? / ?

Inte

nsity

/ co

unts

Si

Si (a)

(b)

ah = 2,811, ch = 14.39in hexagonal settingI(003)/I(104)=2.430

Assuming R3m


Inte

nsity

/ a

.u

(003

)

(101

)(1

02) (1

04)

(105

)

(108

)

(006

)

(107

)Si

(009

)

(110

)(1

13)

2 / degree Cu (K)

0

2000

4000

6000

8000

10000

12000

14000

16000

10 20 30 40 50 60 70 80 902? / ?

Inte

nsity

/ co

unts

Si

Si (a)

(b)


Assuming R3m


Inte

nsity

/ a

.u

(003

)

(101

)(1

02) (1

04)

(105

)

(108

)

(006

)

(107

)Si

(009

)

(110

)(1

13)

2 / degree Cu (K)

SEM images of cathode active materials taken out of the disassembled cells are shown in Fig.

2-12. No notable difference in cathode particles morphology between the fresh and stored

samples was observed. In addition, we analyzed the electrolyte composition, SEM

morphology of the separator and Gurley number which indicated the air permeability of the

separator before and after the storage, but there was no substantial change. These results show

that the difference in degradation during high temperature long term storage between LCO

cathode and NCA cathode is due to the difference of cathode surface. Besides, the influence

of cathode surface on battery degradation has been pointed out [7-12].

Figure 2-12 Particles morphology of cathode materials observed by SEM; (a) Fresh

NCR18650 cathode, (b) Stored NCR18650 cathode, (c) Fresh CGR18650E

cathode and (d) Stored CGR18650E cathode.

(d)(c)

(b)(a)

10 m 10 m

10 m 10 m

2.3.3 Analysis of electrode/electrolyte interface

In order to obtain more information on the cathode/electrolyte interface, the surface of

the NCA and LCO cathodes was analyzed by XPS. Fig. 2-13 to 2-17 shows C1s, O1s, Li1s,

F1s and P2p core level spectra for the NCA and LCO cathodes before and after 2 year storage

at 45 C.

In the core level spectra of C1s, O1s and Li1s of Fig. 2-13 to 2-15, the peaks of the

lithium carbonate and lithium alkyl carbonate were observed before and after storage of NCA

and LCO. It is known that the lithium carbonate is generated on the cathode active material

surface by the reaction with CO2 in air as follows [13, 14].

Li(Ni,Co)O2 + x/2 CO2 + x/4 O2 Li1-x(Ni,Co)O2 + x/2 Li2CO3 (2-1)

The electrolyte solvents decompose on the cathode surface to form lithium alkyl

carbonates [15-16].

(2-2)

(2-3)

The lithium alkyl carbonates are decomposed to lithium carbonate [17].

(2-4)

(2-5)

O O

O

O O

O

2EC ( ) + 2e- + 2Li+ LiOCOCH2CH2OCOLi + C2H4O O

DEC ( ) + e- + 2Li+ CH3CH2OCOLi + CH3CH2O

Lithium alkyl carbonate

= =

=

LiOCOCH2CH2OCOLi Li2CO3 + CO2 + C2H4 + 0.5O2O O

= =LiOCOCH2CH2OCOLi Li2CO3 + CO2 + C2H4 + 0.5O2O O

= =

LiOCOCH2CH2OCOLi + 2Li+ + 2e- 2Li2CO3 + C2H4O O Lithium carbonate

= =LiOCOCH2CH2OCOLi + 2Li+ + 2e- 2Li2CO3 + C2H4

O O Lithium carbonate

= =

Figure 2-13 C1s core level XPS spectra for cathode surface (a) fresh cathode of

NCR18650 (b) fresh cathode of CGR18650 (c) stored cathode of

NCR18650 (d) stored cathode of CGR18650, the storage condition was

4.1V charged state at 45C for 2 years.

(a)

(b)

(c)

(d)

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3x 10

4

Binding Energy (eV)

c/s

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3x 10

4

Binding Energy (eV)

c/s

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3x 104

Binding Energy (eV)

c/s

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3x 10

4

Binding Energy (eV)

c/s

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3

Binding Energy (eV)

c/s

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

280290Binding Energy (eV)

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C


C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C


(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(a)

(b)

(c)

(d)

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3x 10

4

Binding Energy (eV)

c/s

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3x 10

4

Binding Energy (eV)

c/s

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3x 104

Binding Energy (eV)

c/s

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3x 10

4

Binding Energy (eV)

c/s

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C

2802900

0.5

1

1.5

2

2.5

3

Binding Energy (eV)

c/s

C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C


C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C


C1s

C-FPVDFLi2CO3

C-OC-H(PVDF

CHnO-C=O

C-C


(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

(nm)95503020105.01.00.2surface

Figure 2-14 O1s core level XPS spectra for cathode surface (a) fresh cathode of




(a)

(b)

(c)

(d)

O1s Li2OLi(NiCoAl)O2C-OO-C=OROCO2LiLi2CO3LiOHP-O

5305400

0.5

1

1.5

2

2.5

3

3.5

4x 104

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4x 104

Binding Energy (eV)

c/s

O1s Li2OLiCoO2C-OO-C=OROCO2LiLi2CO3LiOHP-O

5305400

0.5

1

1.5

2

2.5

3

3.5

4x 104

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4x 104

Binding Energy (eV)

c/s

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface


5305400

0.5

1

1.5

2

2.5

3

3.5

4

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4

Binding Energy (eV)

c/s

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(a)

(b)

(c)

(d)


5305400

0.5

1

1.5

2

2.5

3

3.5

4x 104

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4x 104

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4x 104

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4x 104

Binding Energy (eV)

c/s

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface


5305400

0.5

1

1.5

2

2.5

3

3.5

4

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4

Binding Energy (eV)

c/s


5305400

0.5

1

1.5

2

2.5

3

3.5

4

Binding Energy (eV)

c/s

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

(nm

95

50

30

20

10

5.0

1.0

0.2surface

Figure 2-15 Li1s core level XPS spectra for cathode surface (a) fresh cathode of




(a)

(b)

(c)

(d)

Li1sLi2CO3LiOHLi2O

Co3p LiFLi(NiCoAl)O2

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

c/s

Li1sLi2CO3LiOHLi2O

Co3p

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

c/s

LiFLi(NiCoAl)O2

Li2CO3LiOHLi2O

Co3p LiFLiCoO2

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

c/s

Li2CO3LiOHLi2O

Co3p LiFLiCoO2

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

c/s

Li1s Li1s

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

Li1sLi2CO3LiOHLi2O


45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

Li1sLi2CO3LiOHLi2O

Co3p

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

LiFLi(NiCoAl)O2

Li2CO3LiOHLi2O

Co3p LiFLiCoO2

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

Li2CO3LiOHLi2O

Co3p LiFLiCoO2

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

Li1s Li1s

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

(a)

(b)

(c)

(d)

Li1sLi2CO3LiOHLi2O


45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

c/s

Li1sLi2CO3LiOHLi2O

Co3p

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

c/s

LiFLi(NiCoAl)O2

Li2CO3LiOHLi2O

Co3p LiFLiCoO2

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

c/s

Li2CO3LiOHLi2O

Co3p LiFLiCoO2

45505560650

500

1000

1500

2000

2500

3000

Binding Energy (eV)

c/s

Li1s Li1s

(,nm

95

50

30

20

10

5.0

1.0

0.2

surface

Documents

Deterioration Analysis of Layered Lithium Nickel Oxide …repository.osakafu-u.ac.jp/dspace/bitstream/10466/14150/...Deterioration Analysis of Layered Lithium Nickel Oxide Based Cathodes