U.S. patent application number 17/411223 was filed with the patent office on 2021-12-09 for lithium secondary battery.
The applicant listed for this patent is SK INNOVATION CO., LTD.. Invention is credited to Sang Jin KIM, Jee Hee LEE, Dock Young YOON.
Application Number | 20210384546 17/411223 |
Document ID | / |
Family ID | 1000005798745 |
Filed Date | 2021-12-09 |
United States Patent
Application |
20210384546 |
Kind Code |
A1 |
YOON; Dock Young ; et
al. |
December 9, 2021 |
LITHIUM SECONDARY BATTERY
Abstract
A lithium secondary battery according to an embodiment of the
present disclosure includes a cathode, an anode and a non-aqueous
electrolyte. The anode includes an anode active material which
contains a mixture of an artificial graphite and a natural
graphite. A sphericity of the natural graphite is 0.96 or more. The
lithium secondary battery including the anode has improved
life-span and power properties.
Inventors: |
YOON; Dock Young; (Daejeon,
KR) ; LEE; Jee Hee; (Daejeon, KR) ; KIM; Sang
Jin; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SK INNOVATION CO., LTD. |
Seoul |
|
KR |
|
|
Family ID: |
1000005798745 |
Appl. No.: |
17/411223 |
Filed: |
August 25, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15991017 |
May 29, 2018 |
11145888 |
|
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17411223 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/661 20130101;
H01M 2004/028 20130101; H01M 4/1393 20130101; H01M 50/409 20210101;
H01M 4/583 20130101; H01M 2004/027 20130101; H01M 4/587 20130101;
H01M 10/0525 20130101; H01M 10/052 20130101; H01M 4/133
20130101 |
International
Class: |
H01M 10/052 20060101
H01M010/052; H01M 4/133 20060101 H01M004/133; H01M 4/66 20060101
H01M004/66; H01M 4/587 20060101 H01M004/587; H01M 10/0525 20060101
H01M010/0525 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2017 |
KR |
10-2017-0065943 |
Claims
1. A lithium secondary battery, comprising: a cathode; an anode
comprising an anode active material comprised of a mixture of an
artificial graphite and a natural graphite, wherein a sphericity of
the natural graphite is 0.96 or more; and a non-aqueous
electrolyte.
2. The lithium secondary battery of claim 1, wherein the sphericity
of the natural graphite is 0.98 or more.
3. The lithium secondary battery of claim 1, wherein an average
particle diameter (D.sub.50) of the natural graphite is in a range
from 9 .mu.m to 14 .mu.m.
4. The lithium secondary battery of claim 1, wherein a half value
width in a particle size distribution of the natural graphite is 10
.mu.m or less.
5. The lithium secondary battery of claim 1, wherein a half value
width in a particle size distribution of the natural graphite is 9
.mu.m or less.
6. The lithium secondary battery of claim 1, wherein a mixing
weight ratio of the natural graphite and the artificial graphite is
in a range from 10:1 to 1:1.
7. The lithium secondary battery of claim 1, wherein an anode
expansion rate represented by Equation 1 below is 20% or less:
Anode expansion rate (%)=100.times.(T.sub.2-T.sub.1)/(T.sub.1)
[Equation 1] wherein, in the Equation 1, T.sub.1 is a thickness of
the anode at 0% SOC (State Of Charge), and T.sub.2 is a thickness
of the anode at 100% SOC.
8. The lithium secondary battery of claim 1, wherein an average
particle diameter (D.sub.50) of the natural graphite is in a range
from 9 .mu.m to 14 .mu.m; a half value width in a particle size
distribution of the natural graphite is 10 .mu.m or less; a mixing
weight ratio of the natural graphite and the artificial graphite is
in a range from 10:1 to 1:1; and an anode expansion rate
represented by Equation 1 below is 20% or less: Anode expansion
rate (%)=100.times.(T.sub.2-T.sub.1)/(T.sub.1) [Equation 1]
wherein, in the Equation 1, T.sub.1 is a thickness of the anode at
0% SOC (State Of Charge), and T.sub.2 is a thickness of the anode
at 100% SOC.
Description
CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY
[0001] The present application is a continuation of U.S. patent
application Ser. No. 15/991,017, filed May 29, 2018, which claims
priority to the benefit of Korean Patent Application No.
10-2017-0065943 filed in the Korean Intellectual Property Office on
May 29, 2017, the entire contents of which is incorporated by
reference herein.
BACKGROUND
1. Field
[0002] The present invention relates to a lithium secondary battery
having improved power and life-span properties
2. Description of the Related Art
[0003] Demands for a lithium secondary battery are increasing as a
power source of a mobile electronic device such as a camcorder, a
mobile phone, a laptop computer, etc., according to developments of
information and display technologies.
[0004] Recently, the secondary battery is being developed and
applied as an eco-friendly power source of an electric automobile,
an uninterruptible power supply, an electrically-driven tool.
[0005] The lithium secondary battery may include a cathode and an
anode, each of which includes a current collector and an active
material coated thereon. A porous separation layer may be
interposed between the cathode and the anode to form an electrode
assembly. The electrode assembly may be impregnated by a
non-aqueous electrolyte including lithium salts. A transition metal
compound such as lithium cobalt oxide (LiCoO.sub.2), lithium nickel
oxide (LiNiO.sub.2), lithium manganese oxide (LiMnO.sub.2), etc.,
may be used as a cathode active material of the lithium secondary
battery. A crystalline carbon-based material such as a natural
graphite or an artificial graphite which may generally have a high
softening degree, or an amorphous or low crystalline carbon-based
material having a pseudo-graphite structure or a turbostratic
structure which may be obtained by a carbonization of a hydrocarbon
material or a polymer at a low temperature from about 1000.degree.
C. to about 1500.degree. C. may be used as an anode active material
of the lithium secondary battery.
[0006] However, the lithium secondary battery including the natural
graphite as the anode active material may have a high electrode
expansion rate to cause a poor life-span. If the artificial
graphite is introduced as the anode active material to overcome the
poor life-span, a power output of the battery may not be improved
and a resistance may be increased. If a high density active
material mixture is employed to an electrode for implementing a
lithium secondary battery of a high capacity, the life-span may be
also degraded and a high-performance battery may not be easily
implemented.
[0007] For example, Korean Registered Patent Publication No.
1057162 discloses a metal-carbon complex anode active material
which may not provide sufficient power output and life-span.
SUMMARY
[0008] According to an aspect of the present invention, there is
provided a lithium secondary battery having improved power output
and life-span.
[0009] According to exemplary embodiments, a lithium secondary
battery includes a cathode, an anode and a non-aqueous electrolyte.
The anode includes an anode active material which contains a
mixture of an artificial graphite and a natural graphite. A
sphericity of the natural graphite is 0.96 or more.
[0010] In some embodiments, the sphericity of the natural graphite
may be 0.98 or more.
[0011] In some embodiments, an average particle diameter (D.sub.50)
of the natural graphite may be in a range from 9 .mu.m to 14
.mu.m.
[0012] In some embodiments, a half value width in a particle size
distribution of the natural graphite may be 10 .mu.m or less.
[0013] In some embodiments, a half value width in a particle size
distribution of the natural graphite may be 9 .mu.m or less.
[0014] In some embodiments, a mixing weight ratio of the natural
graphite and the artificial graphite may be in a range from 10:1 to
1:1.
[0015] In some embodiments, an anode expansion rate represented by
Equation 1 below may be 20% or less.
Anode expansion rate (%)=100.times.(T.sub.2-T.sub.1)/(T.sub.1)
[Equation 1]
[0016] In the Equation 1, T.sub.1 is a thickness of the anode at 0%
SOC (State Of Charge), and T.sub.2 is a thickness of the anode at
100% SOC.
DETAILED DESCRIPTION
[0017] According to example embodiments of the present invention, a
lithium secondary battery including a cathode, an anode and a
non-aqueous electrolyte is provided. The anode includes an anode
active material which contains a mixture of an artificial graphite,
and a natural graphite having a sphericity of 0.96 or more so that
the lithium secondary battery may have improved power output and
life-span.
[0018] Hereinafter, the present invention will be described in
detail with reference to exemplary embodiments. However, those
skilled in the art will appreciate that such embodiments are
provided to further understand the spirit of the present invention
and do not limit subject matters to be protected as disclosed in
the detailed description and appended claims.
[0019] Anode Active Material and Anode
[0020] According to exemplary embodiments, an anode includes an
anode active material which contains a mixture of an artificial
graphite, and a natural graphite having a sphericity of 0.96 or
more.
[0021] The term "sphericity" used herein may be defined as
follow:
[0022] Sphericity=a circumference length of a circle having the
same area as a projection of a natural graphite particle/a real
circumference length of the projection of the natural graphite
particle
[0023] According to exemplary embodiments, the artificial graphite
may be mixed in the anode active material so that a filter clogging
or a poor slurry dispersion during a mixing process may be
prevented, and life-span and high temperature storage property may
be improved.
[0024] According to exemplary embodiments, the natural graphite
having the sphericity of 0.96 or more may be mixed in the anode
active material so that an electrode density may be enhanced, and
an electrode expansion may be suppressed. Thus, life-span and power
output of a lithium secondary battery may be improved. In an
embodiment, the sphericity of the natural graphite may be 0.98 or
more in consideration of the above mentioned aspects.
[0025] Further, the natural graphite having the sphericity of 0.96
or more may be used so that a change of an anode expansion rate
when a mixing weight ratio of the natural graphite and the
artificial graphite is changed may be suppressed. Thus, the mixing
weight ratio of the natural graphite and the artificial graphite
may be properly controlled in the lithium secondary battery
including the anode according to exemplary embodiments.
[0026] In an embodiment, an electrode expansion rate of the anode
may be about 20% or less, for example, about 17% or less. Thus, the
lithium secondary battery may have excellent long-term stability
and life-span. For example, a discharge capacity reduction rate may
be from about 1% to about 5% even after 500 cycles of charging and
discharging in the lithium secondary battery.
[0027] The electrode expansion rate of the anode may be calculated
by Equation 1 below.
Anode expansion rate (%)=100.times.(T.sub.2-T.sub.1)/(T.sub.1)
[Equation 1]
[0028] In the Equation 1, T.sub.1 is a thickness of the anode at 0%
SOC (State Of Charge), and T.sub.2 is a thickness of the anode at
100% SOC.
[0029] The thickness of the anode at 0% SOC is a thickness in a
state that the battery is substantially fully discharged. The fully
discharged state may include, e.g., a non-charged state after
fabrication of the anode, a theoretically fully discharged state or
a substantial fully discharged state (e.g., within .+-.0.5% from
the theoretically fully discharged state).
[0030] The thickness of the anode at 100% SOC is a thickness in a
state that the battery is substantially fully charged. The fully
charged state may indicate a maximally charged state with respect
to a battery capacity in a normal use, and may include a range of
.+-.0.5% from a theoretically fully charged state.
[0031] Charging and discharging conditions for 0% or 100% SOC may
be properly adjusted. For example, the charging condition may be
set as CC-CV 1.0 C 4.2V 0.1 C CUT-OFF, and the discharging
condition may be set as CC 1.0 C 2.5V CUT-OFF.
[0032] The anode expansion rate may be controlled by adjusting an
average diameter of a graphite particle, a pellet density, a
particle density change rate, a PSD half value width, a mixing
weight ratio of the natural graphite and the artificial graphite,
etc., as described below.
[0033] In some embodiments, an average particle diameter (D.sub.50)
may be in a range from about 9 .mu.m to about 14 .mu.m. The term
"D.sub.50" used herein indicate a particle diameter at 50% volume
fraction in a cumulative particle size distribution.
[0034] If the average particle diameter (D.sub.50) is less than
about 9 .mu.m, pores in the anode may not be easily controlled and
an impregnation uniformity may be degraded. If the average particle
diameter (D.sub.50) exceeds about 14 .mu.m, an electrode thickness
may be increased and the electrode expansion rate may not be easily
controlled.
[0035] A power output of a secondary battery including a natural
graphite as an anode active material may be influenced by the
particle diameter. According to exemplary embodiments, the power
output from the anode active material may be enhanced within the
D.sub.50 range from about 9 .mu.m to about 14 .mu.m, preferably
from about 10 .mu.m to about 12 .mu.m. Within this range, the
improved power output may be achieved while preventing an excessive
transformation of the electrode during repetitive charging and
discharging.
[0036] In an embodiment, the natural graphite having a pellet
density which is represented by Equation 2 below of 0.06 or less
may be used. In this case, the anode electrode expansion rate may
be effectively suppressed. Within this range, a packing of active
material particles may be efficiently implemented so that pores
between the particles of the natural graphite may be minimized. For
example, the pellet density change rate may be 0.04 or less so that
the packing of the active material particle may be enhanced to
suppress the anode expansion rate more efficiently.
Pellet density change rate=(Da-Db)/(a-b) [Equation 2]
[0037] In the Equation 2 above, Da represents a pellet density
(g/cc) measured by inputting 2.5 g of a natural graphite in a hole
with a 1 cm diameter and then applying a pressure of 8 kN for 5
seconds, Db represents a pellet density measured by applying a
pressure of 1 kN for 5 seconds, a represents 8 kN and b represents
1 kN.
[0038] The pellet density may be measured using a powder resistance
measuring device. Specifically, 2.5 g of a natural graphite may be
input in a hole with a 1 cm diameter, and then a predetermined
pressure may be applied for 5 seconds. A height of the hole in a
pressurized state may be measured using a micro gauge to obtain a
volume, and the pellet density may be calculated by Equation 3
below.
Pellet density (D)=m/V [Equation 3]
[0039] In the Equation 3 above, m represents a weight (g) of an
anode active material under a specific pressure, and V represents a
volume (cc) of the anode active material under the specific
pressure.
[0040] A method for obtaining the pellet density change rate is not
specifically limited. For example, a half value width in a particle
size distribution with respect to the natural graphite particle may
be set as 10 .mu.m or less to obtain the pellet density. In an
embodiment, the half value width may be set as 9 .mu.m or less to
obtain the natural graphite having improved packing of the active
material particle.
[0041] When a value of a longitudinal axis in a particle size
distribution graph of the natural graphite particle is a half of a
maximum value of the graph, a width of a lateral axis between the
two values may be determined as the half value width used
herein.
[0042] The natural graphite used herein may be a natural graphite
coated by a carbide layer on at least an edge portion thereof. The
carbide layer may be formed by coating a core carbon material with
a coal-based or a petroleum-based pitch, tar, or a mixture thereof,
and then carbonizing by firing to have a low crystallinity. The
term "low crystallinity" used herein may indicate that the
crystallinity of the carbide layer is less than that of the natural
graphite. The carbide layer may fill micro-pores in the natural
graphite to reduce a specific surface area, and thus sites at which
a decomposition reaction of an electrolyte occurs may be decreased
so that charging/discharging efficiency, cycle capacity retention
and life-span properties of the lithium secondary battery may be
enhanced.
[0043] For example, in a fabrication of the natural graphite coated
by the carbide layer, a particle-shaped natural graphite and a
carbon-based material derived from coal or petroleum may be mixed
by a wet or dry method to form a carbon coating layer on the
natural graphite. The natural graphite including the coating layer
thereon may be fired to form the carbide layer on at least an edge
portion of the natural graphite.
[0044] In an embodiment, a mixing weight ratio of the natural
graphite and the artificial graphite in the anode active material
may be in a range from 10:1 to 1:1, preferably, from 9:1 to 7:3.
Within this range, an anode density may be increased and the
electrode expansion rate may be remarkably decreased so that
life-span and power output properties of the lithium secondary
battery may be further improved.
[0045] In some embodiments, the anode active material may further
include ingredients commonly used in an anode of a lithium
secondary battery without departing from the spirit and concepts of
the present invention. For example, the anode active material may
further include at least one of lithium, a lithium alloy, lithium
titanate, silicon, a tin alloy, cokes, a combusted organic polymer
or a carbon fiber. An amount of the additional ingredient may be,
e.g., about 10 wt % or less. For example, the additional ingredient
may not be included in the anode active material.
[0046] Cathode Active Material
[0047] According to exemplary embodiments, a cathode active
material commonly used for a cathode of a conventional
electrochemical device may be used. For example, a lithium
intercalation compound such as a complex oxide including lithium
manganese oxide, lithium cobalt oxide, lithium nickel oxide or a
combination thereof may be used.
[0048] Lithium Secondary Battery
[0049] According to exemplary embodiments, a lithium secondary
battery using the cathode active material and the anode active
material as described above is also provided.
[0050] The lithium second battery may include a cathode, an anode
and a non-aqueous electrolyte.
[0051] Each of the cathode active material and the anode active
material may be mixed and stirred with a solvent and optionally
with a binder, a conductive agent, a dispersive agent, etc., to
form a mixture. The mixture may be coated on a metallic current
collector, and then pressed and dried to from the cathode and the
anode.
[0052] The binder may include, e.g., an organic binder such as a
copolymer of vinylidenefluoride and hexafluoropropylene
(PVDF-co-HFP), polyvinylidenefluoride (PVDF), polyacrylonitrile,
polymethylmethacrylate, etc., or an aqueous binder such as
styrene-butadiene rubber (SBR) that may be used with a thickening
agent such as carboxymethyl cellulose (CMC).
[0053] A conductive carbon-based material may be used as the
conductive agent.
[0054] The metal current collector may include a metal having a
high conductivity which may not be reactive within a voltage range
of the battery and may be easily coated with the mixture of the
anode active material or the cathode active material. A cathode
current collector may include, e.g., a foil prepared from aluminum,
nickel or a combination thereof. An anode current collector may
include, e.g., copper, gold, nickel, a copper alloy or a
combination thereof.
[0055] A separator may be interposed between the cathode and the
anode. The separator may include a porous polymer film. For
example, a polyolefin-based polymer including at least one of
ethylene homopolymer, propylene homopolymer, ethylene/butene
copolymer, ethylene/hexene copolymer or ethylene/methacrylate
copolymer may be used. A conventional porous non-woven fabric, a
glass having a high melting point, a polyethylene terephthalate
fiber may be also used in the separator. The separator may be
applied in the battery by winding, laminating, stacking, folding,
etc., with the electrodes.
[0056] A non-aqueous electrolyte may include a lithium salt and an
organic solvent. The lithium salt commonly used in an electrolyte
for a lithium secondary battery may be used. Non-limiting examples
of the organic solvent may include propylene carbonate (PC),
ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl
carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl
carbonate, dipropyl carbonate, fluoro ethylene carbonate (FEC),
dimethyl sulfoxide, acetonitrile, dimethoxy ethane, diethoxy
ethane, vinylene carbonate, sulfolane, gamma-butyrolactone,
propylene sulfite, tetrahydrofuran, etc. These may be used alone or
in a combination thereof.
[0057] The non-aqueous electrolyte may be injected to an electrode
assembly including the cathode, the anode and the separator
interposed therebetween to form the lithium secondary battery.
[0058] The lithium secondary battery may be fabricated as, e.g., a
cylindrical shape using a can, a pouch shape or a coin shape.
[0059] Hereinafter, exemplary embodiments are proposed to more
concretely describe the present invention. However, the following
examples are only given for illustrating the present invention and
those skilled in the related art will obviously understand that
various alterations and modifications are possible within the scope
and spirit of the present invention. Such alterations and
modifications are duly included in the appended claims.
Example 1
[0060] <Fabrication of Anode>
[0061] A natural graphite having a sphericity of 0.96, a D.sub.50
of 10 .mu.m, a half value width in PSD of 8.4 .mu.m, and an
artificial graphite having a D.sub.50 of 15 .mu.m were mixed by a
weight ratio of 7:3 to prepare an anode active material. An aqueous
binder was prepared by mixing styrene butadiene rubber (SBR) and
carboxy methyl cellulose (CMC) by a weight ratio of 5:5, and a
flake graphite was used as a conductive agent.
[0062] The anode active material, the conductive agent and the
binder were mixed by a weight ratio of 93:5:2, and then dispersed
in water to form an anode slurry. The anode slurry was coated on a
copper thin layer, dried and pressed by a pressure of 3.8 MPa to
form an anode for a lithium secondary battery.
[0063] The sphericity of the natural graphite was measured using
MORPHOLOGI G3 manufactured by Malvern Co., Ltd.
[0064] <Fabrication of Lithium Secondary Battery>
[0065] The anode as prepared above, a cathode including LiNiMnCoO2,
a separator (CELGARD 2400) and an aluminum case were used to form a
lithium secondary battery. A dimension of the prepared battery was
4.5 mm (thickness).times.64 mm (width).times.95 mm (length), and a
capacity of the prepared battery was 2,000 mAh.
Examples 2-12, and Comparative Examples 1-3
[0066] Lithium secondary batteries of Examples 2-12 and Comparative
Examples 1-3 were prepared by a method the same as that of Example
1 except that parameters or conditions were changed as listed in
Table 1 below.
Experimental Example
[0067] 1. Measuring Anode Expansion Rate
[0068] A thickness before charging of the anode in each Examples
and Comparative Examples was measured as T.sub.1, and a cell was
prepared after a vacuum drying for a day. The cell was charged
(CC-CV 1.0 C 4.2V 0.1 C CUT-OFF), and then disassembled in a dry
room. A thickness of the anode was measured as T.sub.2, and an
anode expansion rate was obtained based on Equation 1 below. The
results are shown in Table 1 below.
Anode expansion rate (%)=100.times.(T.sub.2-T.sub.1)/(T.sub.1)
[Equation 1]
[0069] 2. Evaluation of Power Output
[0070] A power output property at 50% SOC was measured using a
method of HPPC (Hybrid Pulse Power Characterization by Freedom Car
Battery Test Manual) in each battery of Examples and Comparative
Examples. The results are shown in Table 1 below.
[0071] 3. Evaluation of Life-Span Property
[0072] 1500 cycles of charging (CC-CV 1.0 C 4.2V 0.1 C CUT-OFF) and
discharging (CC 1.0 C 2.5V CUT-OFF) were repeated in each battery
of Examples and Comparative Examples. A ratio (%) of a discharging
capacity at 1500th cycle relative to a discharging capacity at a
first cycle was calculated to evaluate a life-span of each
battery.
[0073] The results are shown in Table 1 below.
TABLE-US-00001 TABLE 1 Mixing Weight Ratio Life- (natural Anode
span Half graphite/ Expansion Discharging (%) Value artificial Rate
Power (1500 Sphericity D.sub.50 Width graphite) (%) (W/kg) cycle)
Example 1 0.96 10 8.4 3:7 22.5 2374 93.1 Example 2 0.96 10 8.4 5:5
19.9 3220 93.8 Example 3 0.96 10 8.4 7:3 20.5 3433 93.3 Example 4
0.98 10 8.4 3:7 20.0 2611.4 93.5 Example 5 0.98 10 8.4 5:5 17.91
3542 93.7 Example 6 0.98 10 8.4 7:3 18.45 3776.3 94 Example 7 0.96
10 10.4 3:7 24.2 2320 92.2 Example 8 0.96 10 10.4 5:5 20.6 3014
92.7 Example 9 0.96 10 10.4 7:3 21.4 3364 92.5 Example 10 0.96 15.7
9.6 3:7 23.5 2302 92.5 Example 11 0.96 15.7 9.6 5:5 20.4 3029 92.9
Example 12 0.96 15.7 9.6 7:3 21.1 3230 93.0 Comparative 0.92 10 8.4
3:7 25.3 2281 91.5 Example 1 Comparative 0.92 10 8.4 5:5 23.4 2888
92.3 Example 2 Comparative 0.92 10 8.4 7:3 21.9 3214 92.1 Example
3
[0074] Referring to Table 1, the lithium secondary batteries of
Examples showed improved life-span properties and higher power
properties.
[0075] According to the mixing weight ratio of the natural graphite
and the artificial graphite, the batteries of Example 2 and 3
showed greater power and life-span properties than those of Example
1. The batteries of Example 5 and 6 showed greater power and
life-span properties than those of Example 4. The batteries of
Example 8 and 9 showed greater power and life-span properties than
those of Example 7. The batteries of Example 11 and 12 showed
greater power and life-span properties than those of Example
10.
[0076] When the half value width was 9 .mu.m or less, and an
average diameter was in a range from 9 .mu.m to 14 .mu.m as in
Examples 1-6, the life-span and power properties were further
enhanced.
[0077] However, the batteries of Comparative Examples showed
degraded life-span and power properties.
* * * * *