-
http://repository.osakafu-u.ac.jp/dspace/
TitleDeterioration Analysis of Layered Lithium Nickel Oxide Based Cathode
s for High Energy Density Lithium-Ion Batteries
Author(s) ,
Editor(s)
Citation
Issue Date 2014-02
URL http://hdl.handle.net/10466/14150
Rights
-
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. 1 Introduction 70
3. 2 Experimental 74
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 Results and Discussion 77
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. 1 Introduction 98
4. 2 Experimental 100
4. 2. 1 Cycle tests in restricted DODs for cylindrical model cells 100
4. 2. 2 Surface and bulk analyses 100
4. 3 Results and Discussion 101
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
PTCInsulator Separator(Electrolyte)
Anode TabAnodeCathodeInsulator
Anode can
Top Cap Cathode TabGasket Safety vent
PTCInsulator Separator(Electrolyte)
Anode TabAnodeCathodeInsulator
Anode can
Top Cap Cathode TabGasket Safety Vent
PTCInsulator Separator(Electrolyte)
Anode TabAnodeCathodeInsulator
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
Gas
evo
lutio
n
Nor
mal
usag
e
Abn
orm
alus
age
Gas
evo
lutio
n
Cur
rent
col
lect
or d
isso
lutio
nIo
n/ni
ckel
dep
ositi
onC
an ir
on/n
icke
l dis
solu
tion
Isol
atio
n fr
om c
urre
nt c
olle
ctor
Cor
rosi
on o
f cur
rent
col
lect
orC
orro
sion
of c
urre
nt c
olle
ctor
Phas
e tra
nsiti
onEl
ectro
lyte
dec
ompo
sitio
n
Met
al d
epos
ition
Elec
troly
te d
ecom
posi
tion
Met
al d
isso
lutio
nG
as e
volu
tion
Lith
ium
dep
ositi
onG
as e
volu
tion
Cop
per d
epos
ition
Isol
atio
n fr
om e
ach
othe
rO
xida
tion
of e
lect
ro c
ondu
ctor
Surf
ace
diso
rder
ing
Met
al d
isso
lutio
nLi
thiu
m d
epos
ition
Mic
rocr
acki
ngM
etal
dep
ositi
on
Mic
ro c
rack
ing
Elec
troly
te d
ecom
posi
tion
Gas
evo
lutio
nSu
rfac
e la
yer f
orm
atio
n
Surf
ace
laye
r for
mat
ion
Lith
ium
dep
ositi
on
Dec
ompo
sitio
n of
bin
der
Ano
deC
atho
de su
rfac
eA
node
surf
ace
Cat
hode
sepa
rato
r / e
lect
roly
te
Elec
troly
te d
ecom
posi
tion
Gra
phite
exf
olia
tion
Phas
e tra
nsiti
onG
as e
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)
Electrode material(Binder, electron conductor)
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)
Electrode material(Binder, electron conductor)
Cathode material(LiMO2)
Electrode material(Binder, electron conductor)
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
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)
-
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.
-
References
[1] G. G. Amatucci, J. M. Trascon, L.C. Klein, Solid State Ionics 83 (1996) 167.
[2] D. Aurbach, B. Markovsky, M. D. Levi, E. Levi, A. Schechter, M. Moshkovich, Y.
Cohen, J. Power sources 81-82 (1999) 95.
[3] D. Aurbach, J. Power sources 89 (2000) 206.
[4] Y-I. Jang, N. J. Dudney, D. A. Blom and L. F. Allard, J. Power sources 119-121 (2003)
295.
[5] D. Aurbach, J. Power sources 119-121 (2003) 497.
[6] D. Aurbach, B. Markovsky, Y. Talyossef, G. Salitra, H-J. Kim, S. Choi, J. Power sources
162 (2006) 780.
[7] K. Mizushima, P. C. Jones, P. C. Wiseman, J.B. Goodenough, Mater. Res. Bull. 15
(1980) 783.
[8] T. Ohzuku, A. Ueda, M. Nagayama, J. Electrochem. Soc. 140 (1993) 1862.
[9] A. Rougier, P. Gravereau, C. Delmas, J. Electrochem. Soc. 143 (1996) 1168.
[10] L. Croguennec, C. Pouillerie, C. Delmas, J. Electrochem. Soc. 147 (2000) 1314.
[11] A. N. Mansour, X. Q. Yang, X. Sun, J. McBreen, L. Croguennec, C. Delmas, J.
Electrochem. Soc. 147 (2000) 2104.
[12] T. Ohzuku, A. Ueda, M. Kouguchi , J. Electrochem. Soc. 142 (1995) 4033.
[13] H. Arai, S. Okada, Y. Sakurai, J. Yamaki, J. Electrochem. Soc. 144 (1997) 3117.
[14] T. Ohzuku, T. Yanagawa, M. Kouguchi, A. Ueda, J. Power Sources 68 (1997) 131.
[15] C. Delmas, M. Mntrier, L. Croguennec, I. Saadoune, A. Rougier, C. Pouillerie, G.
Prado, M. Grne, L. Fourns, Electrochim. Acta 45 (1999) 243.
[16] C. Pouillerie, L. Croguennec, Ph. Biensan, P. Willmann, C. Delmas, J. Electrochem.
Soc. 147 (2000) 2061.
[17] G. Prado, A. Rougier, L. Fournes, C. Delmas, J. Electrochem. Soc. 147 (2000) 2880.
-
[18] M. Guilmard, L. Croguennec, C. Delmas, J. Electrochem. Soc. 150 (2003) A1287.
[19] N.Tran, L. Croguennec, C. Labrugere, C. Jordy, Ph. Biensan, C. Delmas, J.
Electrochem. Soc. 153 (2006) A261.
[20] A. Kinoshita, K. Yanagida, A. Yanai, Y. Kida, A. Funahashi, T. Nohma, I. Yonezu, J.
Power Sources 102 (2001) 283.
[21] R. V. Chebiam, F. Prado, A. Manthiram, J. Electrochem. Soc. 148 (2001) A49.
[22] S. Levasseur, M. Menetrier, C. Delmas, J. Electrochem. Soc. 149 (2002) A1533.
[23] A. N. Mansour, L. Croguennec, C. Delmas, Electrochemical and Solid-State Letters 8
(2005) A544.
[24] S. Watanabe, T. Fujiwara, S. Kobayashi, A. Ohta, in Abstract of the ECS Spring
Meeting, Montreal, 1997, Abstract
[25] T. Fujiwara, S. Watanabe, T. Kawano, S. Kobayashi, A. Ohta, in Abstract of the ISE
Meeting, Kita-kyushu, 1998, Abstract
[26] H. Arai, M. Tsuda, Y. Sakurai, J. Power Sources 90 (2000) 76.
[27] P. Biensan, J. P. Prs, F. Perton, in Abstract of the ECS fall Meeting, Hawaii, 1999,
Abstract #131.
[28] C. H. Chen, J. Liu, K. Amine, in Abstract of the ECS fall Meeting, San Francisco,
2001, Abstract #176.
[29] S. Madhavi, G. V. S. Rao, B. V. R. Chowdari, S. F. Y. Li, J. Power Sources 93 (2001)
156.
[30] K. K. Lee, W. S. Yoon, K. B. Kim, K. Y. Lee, S. T. Hong, J. Power Sources 97 (2001)
308.
[31] S. Albrecht, J. Kmpers, M. Kruft, S. Malcus, C. Vogler, M. Wahl, M.
Wohlhart-Mehrens, J. Power Sources 119-121 (2003) 178.
[32] S. Madhavi, G.V. Subba Rao, B.V.R. Chowdari, S.F.Y. Li, J. Power Sources 93 (2001)
156.
[33] M. Ue, Prog. Batteries Battery Materials 16 (1997) 332.
-
[34] P. Arona, R. E. White, M. Doyle, J. Electrochem. Soc. 145 (1998) 3647.
[35] J. Vetter, P. Novk, M.R. Wagner, C. Veit, K.-C. Mller, J.O. Besenhard, M. Winter,
M. Wohlfahrt-Mehrens, C. Vogler, A. Hammouche, J. Power Sources 147 (2005) 269.
[36] M. Broussely, S. Herreyre, P. Biensan, P. Kasztejna, K. Nechev, R.J. Staniewicz, J.
Power Sources 97-98 (2001) 13.
[37] M. Broussely, P. Blanchard, P. Biensan, J.P. Planchat, K. Nechev, R.J. Staniewicz, J.
Power Sources 119121 (2003) 859.
[38] M. Broussely, P. Biensan, F. Bonhomme, P. Blanchard, S. Herreyre , K. Nechev, R.J.
Staniewicz, J. Power Sources 146 (2005) 90.
[39] J. F. Cousseaua, C. Siret, P. Biensan, M. Broussely, J. Power Sources 162 (2006) 790.
[40] I. Bloom, B. W. Cole, J. J. Sohn, S. A. Jones, E. G. Polzin, V. S. Battaglia, G. L.
Henriksen, C. Motloch, R. Richardson, T. Unkelhaeuser, D. Ingersoll, H. L. Case, J.
Power Sources 101 (2001) 238.
[41] R. B. Wright, C. G. Motloch, J. R. Belt, J. P. Christophersen, C. D. Ho, R. A.
Richardson, I. Bloom, S. A. Jones, V. S. Battaglia, G. L. Henriksen, T. Unkelhaeuser,
D. Ingersoll, H. L. Case, S. A. Rogers, R. A. Sutula, J. Power Sources 110 (2002)
445.
[42] I. Bloom, S. A. Jones, V. S. Battaglia, G. L. Henriksen, J. P. Christophersen, R.B.
Wright, C.D. Ho, J. R. Belt, C.G. Motloch, J. Power Sources 124 (2003) 538.
[43] C. H. Chen, J. Liu, K. Amine, J. Power Sources 96 (2001) 321.
[44] K.Amine, C.H.Chen, J.Liu, M.H.Hammond, A.Jansen, D.Dees, I. Bloom, D.Vissers,
G.Henriksen, J. Power Sources 97 (2001) 684.
[45] C.H.Chen, J.Liu, M.E.Stoll, G.Henriksen, D.R.Vissers, K. Amine, J. Power Sources
128 (2004) 278.
[46] H. Kondo, Y. Takeuchi, T. Kawauchi, Y. Itou, O. Hiruta, C. Okuda, M. Yonemura, T.
Kamiyama, Y. Ukyo, J. Power Sources 174 (2007) 1131.
-
[47] A. M. Andersson, D. P. Abraham, R. Haasch, S. MacLaren, J. Liu, K. Amine, J.
Electrochem. Soc. 149 (2002) A1358.
[48] D.P.Abraham, R.D. Twesten, M. Balasubramanian, I. Petrov, J. McBreen, K. Amine,
Electrochem. Commun. 4 (2002) 620.
[49] Y.Itou, Y.Ukyo, J.Power Sources 146 (2005) 39.
[50] T. Nonaka, C. Okuda, Y. Seno, H. Nakano, K. Koumoto, Y. Ukyo, J. Power Sources
162 (2006) 1329.
[51] T. Nonaka, C. Okuda, Y. Seno, Y. Kondo, K. Koumoto, Y. Ukyo, J. Electrochem. Soc.
154 (2007) A353.
[52] T. Nonaka, C. Okuda, Y. Seno, K. Koumoto, Y. Ukyo, Ceramics International 34
(2008) 859.
[53] T. Sasaki, T. Nonaka, H. Oka, C. Okuda, Y. Itou, Y. Kondo, Y. Takeuchi, Y. Ukyo, K.
Tatsumi, S. Muto, J. Electrochem. Soc. 156 (2009) A289.
[54] H. Kobayashi, M. Shikano, S. Koike, H. Sakaebe, K. Tatsumi, J. Power Sources 174
(2007) 380.
[55] D. Mori, H. Kobayashi, M. Shikano, H. Nitani, H. Kageyama, S. Koike, H. Sakaebe, K.
Tatsumi, J.Power Sources 189 (2009) 676.
-
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
Time (o'clock)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
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
Cylindrical Lithium-ion battery
NCR18650 CGR18650E
Accelerated calendar and cycle life test
Charge and discharge cycle test Storage test at high temperature Interval storage-cycle tests
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
Electrochemical measurement
Capacity Impedance
CathodeCathode AnodeAnode
Model cell X-ray analysis SEM XPS STEM-EELS HR-TEM
Model cell X-ray analysis SEM XPS STEM-EELS HR-TEM
Model cell SEM XPS ICP-AES
Model cell SEM XPS ICP-AES
Cylindrical Lithium-ion battery
NCR18650 CGR18650E
Cylindrical Lithium-ion battery
NCR18650 CGR18650E
Accelerated calendar and cycle life test
Charge and discharge cycle test Storage test at high temperature Interval storage-cycle tests
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
Electrochemical measurement
Capacity Impedance
CathodeCathode AnodeAnode
Model cell X-ray analysis SEM XPS STEM-EELS HR-TEM
Model cell X-ray analysis SEM XPS STEM-EELS HR-TEM
Model cell SEM XPS ICP-AES
Model cell SEM XPS ICP-AES
-
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
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
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
NCR18650(NCA cathode)
CGR18650E(LCO cathode)
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
NCR18650(NCA cathode)
CGR18650E(LCO cathode)Rela
tive
Cap
acity
/ %
50
60
70
80
90
100
0 5 10 15 20 25Time / Month
NCR18650(NCA cathode)
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
ah = 2,807, ch = 14.18in hexagonal setting
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)
ah = 2,809, ch = 14.21in hexagonal setting
I(003)/I(104)=1.985
ah = 2,807, ch = 14.18in hexagonal setting
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
ah = 2,809, ch = 14.43in hexagonal settingI(003)/I(104)=2.813
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)
ah = 2,811, ch = 14.39in hexagonal settingI(003)/I(104)=2.430
Assuming R3m
ah = 2,809, ch = 14.43in hexagonal settingI(003)/I(104)=2.813
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
280290Binding Energy (eV)
C1s
C-FPVDFLi2CO3
C-OC-H(PVDF
CHnO-C=O
C-C
280290Binding Energy (eV)
(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
280290Binding Energy (eV)
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
280290Binding Energy (eV)
(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
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)
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
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
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
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
(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
O1s Li2OLi(NiCoAl)O2C-OO-C=OROCO2LiLi2CO3LiOHP-O
5305400
0.5
1
1.5
2
2.5
3
3.5
4
Binding Energy (eV)
c/s
O1s Li2OLi(NiCoAl)O2C-OO-C=OROCO2LiLi2CO3LiOHP-O
5305400
0.5
1
1.5
2
2.5
3
3.5
4
Binding Energy (eV)
c/s
O1s Li2OLiCoO2C-OO-C=OROCO2LiLi2CO3LiOHP-O
5305400
0.5
1
1.5
2
2.5
3
3.5
4
Binding Energy (eV)
c/s
O1s Li2OLiCoO2C-OO-C=OROCO2LiLi2CO3LiOHP-O
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)
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
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
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
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
(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
O1s Li2OLi(NiCoAl)O2C-OO-C=OROCO2LiLi2CO3LiOHP-O
5305400
0.5
1
1.5
2
2.5
3
3.5
4
Binding Energy (eV)
c/s
O1s Li2OLi(NiCoAl)O2C-OO-C=OROCO2LiLi2CO3LiOHP-O
5305400
0.5
1
1.5
2
2.5
3
3.5
4
Binding Energy (eV)
c/s
O1s Li2OLiCoO2C-OO-C=OROCO2LiLi2CO3LiOHP-O
5305400
0.5
1
1.5
2
2.5
3
3.5
4
Binding Energy (eV)
c/s
O1s Li2OLiCoO2C-OO-C=OROCO2LiLi2CO3LiOHP-O
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
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)
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
Co3p LiFLi(NiCoAl)O2
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
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