U.S. patent application number 12/133000 was filed with the patent office on 2008-12-11 for anode and secondary battery.
This patent application is currently assigned to Sony Corporation. Invention is credited to Takakazu Hirose, Masayuki Iwama, Kenichi Kawase, Isamu Konishiike, Shunsuke Kurasawa, Koichi Matsumoto.
Application Number | 20080305395 12/133000 |
Document ID | / |
Family ID | 40096175 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080305395 |
Kind Code |
A1 |
Hirose; Takakazu ; et
al. |
December 11, 2008 |
ANODE AND SECONDARY BATTERY
Abstract
A battery capable of improving cycle characteristics is
provided. An anode includes: an anode current collector, and an
anode active material layer arranged on the anode current
collector, in which the anode active material layer includes an
anode active material including silicon (Si), and including a pore
group with a diameter ranging from 3 nm to 50 nm both inclusive,
and the volumetric capacity per unit weight of silicon of the pore
group with a diameter ranging from 3 nm to 50 nm both inclusive is
0.2 cm.sup.3/g or less, the volumetric capacity being measured by
mercury porosimetry using a mercury porosimeter.
Inventors: |
Hirose; Takakazu;
(Fukushima, JP) ; Kawase; Kenichi; (Fukushima,
JP) ; Konishiike; Isamu; (Fukushima, JP) ;
Kurasawa; Shunsuke; (Fukushima, JP) ; Iwama;
Masayuki; (Fukushima, JP) ; Matsumoto; Koichi;
(Fukushima, JP) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL LLP
P.O. BOX 061080, WACKER DRIVE STATION, SEARS TOWER
CHICAGO
IL
60606-1080
US
|
Assignee: |
Sony Corporation
Tokyo
JP
|
Family ID: |
40096175 |
Appl. No.: |
12/133000 |
Filed: |
June 4, 2008 |
Current U.S.
Class: |
429/218.1 ;
429/220; 429/221; 429/223; 429/229; 429/231.5 |
Current CPC
Class: |
H01M 4/0404 20130101;
H01M 4/045 20130101; H01M 2300/0034 20130101; H01M 4/049 20130101;
H01M 4/362 20130101; H01M 4/38 20130101; H01M 6/164 20130101; H01M
2004/021 20130101; H01M 50/107 20210101; H01M 4/483 20130101; H01M
50/103 20210101; H01M 10/0569 20130101; H01M 2220/30 20130101; H01M
4/1395 20130101; H01M 50/116 20210101; H01M 10/0525 20130101; H01M
10/0568 20130101; H01M 2004/027 20130101; Y02E 60/10 20130101; H01M
4/366 20130101; H01M 4/386 20130101; H01M 4/134 20130101 |
Class at
Publication: |
429/218.1 ;
429/220; 429/221; 429/223; 429/229; 429/231.5 |
International
Class: |
H01M 4/42 20060101
H01M004/42; H01M 4/58 20060101 H01M004/58; H01M 4/52 20060101
H01M004/52 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 5, 2007 |
JP |
2007-149253 |
Jan 25, 2008 |
JP |
2008-015256 |
Claims
1. An anode comprising: an anode current collector; and an anode
active material layer arranged on the anode current collector,
wherein the anode active material layer includes an anode active
material including silicon (Si), and including a pore group with a
diameter ranging from 3 nm to 50 nm both inclusive, and the
volumetric capacity per unit weight of silicon of the pore group
with a diameter ranging from 3 nm to 50 nm both inclusive is 0.2
cm.sup.3/g or less, the volumetric capacity being measured by
mercury porosimetry using a mercury porosimeter.
2. The anode according to claim 1, wherein the volumetric capacity
per unit weight of silicon of the pore group with a diameter
ranging from 3 nm to 50 nm both inclusive is 0.05 cm.sup.3/g or
less.
3. The anode according to claim 1, wherein the volumetric capacity
per unit weight of silicon of the pore group with a diameter
ranging from 3 nm to 50 nm both inclusive is 0 cm.sup.3/g.
4. The anode according to claim 1, wherein the volumetric capacity
per unit weight of silicon of a pore group with a diameter ranging
from 3 nm to 20 nm both inclusive is 0.2 cm.sup.3/g or less, the
volumetric capacity being measured by mercury porosimetry using a
mercury porosimeter.
5. The anode according to claim 4, wherein the volumetric capacity
per unit weight of silicon of the pore group with a diameter
ranging from 3 nm to 20 nm both inclusive is 0.05 cm.sup.3/g or
less.
6. The anode according to claim 4, wherein the volumetric capacity
per unit weight of silicon of the pore group with a diameter
ranging from 3 nm to 20 nm both inclusive is 0 cm.sup.3/g.
7. The anode according to claim 1, wherein the anode active
material layer includes an oxide-containing film in pores.
8. The anode according to claim 7, wherein the oxide-containing
film includes at least one kind of oxide selected from the group
consisting of an oxide of silicon, an oxide of germanium (Ge) and
an oxide of tin (Sn).
9. The anode according to claim 7, wherein the oxide-containing
film is formed by a liquid-phase deposition method, a sol-gel
method, a coating method or a dip coating method.
10. The anode according to claim 1, wherein the anode active
material layer includes a metal material which is not alloyed with
an electrode reactant in pores.
11. The anode according to claim 10, wherein the metal material
includes at least one kind selected from the group consisting of
iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn) and copper (Cu).
12. The anode according to claim 10, wherein the metal material is
formed by an electrolytic plating method or an electroless plating
method.
13. The anode according to claim 1, wherein the anode active
material is in the form of a plurality of particles.
14. The anode according to claim 13, wherein the anode active
material has a multilayer configuration in its particles.
15. The anode according to claim 1, wherein the anode active
material is formed by a vapor-phase method.
16. The anode according to claim 1, wherein the anode active
material includes oxygen (O), and the oxygen content in the anode
active material is within a range from 3 at % to 40 at % both
inclusive.
17. The anode according to claim 1, wherein the anode active
material includes at least one kind of metal element selected from
the group consisting of iron, cobalt, nickel, chromium (Cr),
titanium (Ti) and molybdenum (Mo).
18. The anode according to claim 1, wherein the anode active
material includes an oxygen-containing region including oxygen in
its thickness direction, and the oxygen content in the
oxygen-containing region is higher than the oxygen content in a
region other than the oxygen-containing region.
19. The anode according to claim 1, wherein the ten-point height of
roughness profile Rz of the surface of the anode current collector
is within a range from 1.5 .mu.m to 6.5 .mu.m both inclusive.
20. A secondary battery comprising a cathode, an anode and an
electrolytic solution, wherein the anode includes an anode current
collector and an anode active material layer arranged on the anode
current collector, the anode active material layer includes an
anode active material including silicon, and including a pore group
with a diameter ranging from 3 nm to 50 nm both inclusive, and the
volumetric capacity per unit weight of silicon of the pore group
with a diameter ranging from 3 nm to 50 nm both inclusive is 0.2
cm.sup.3/g or less, the volumetric capacity being measured by
mercury porosimetry using a mercury porosimeter.
21. The secondary battery according to claim 20, wherein the
volumetric capacity per unit weight of silicon of the pore group
with a diameter ranging from 3 nm to 50 nm both inclusive is 0.05
cm.sup.3/g or less.
22. The secondary battery according to claim 20, wherein the
volumetric capacity per unit weight of silicon of the pore group
with a diameter ranging from 3 nm to 50 nm both inclusive is 0
cm.sup.3/g.
23. The secondary battery according to claim 20, wherein the
volumetric capacity per unit weight of silicon of a pore group with
a diameter ranging from 3 nm to 20 nm both inclusive is 0.2
cm.sup.3/g or less, the volumetric capacity being measured by
mercury porosimetry using a mercury porosimeter.
24. The secondary battery according to claim 23, wherein the
volumetric capacity per unit weight of silicon of the pore group
with a diameter ranging from 3 nm to 20 nm both inclusive is 0.05
cm.sup.3/g or less.
25. The secondary battery according to claim 23, wherein the
volumetric capacity per unit weight of silicon of the pore group
with a diameter ranging from 3 nm to 20 nm both inclusive is 0
cm.sup.3/g.
26. The secondary battery according to claim 20, wherein the anode
active material layer includes an oxide-containing film in
pores.
27. The secondary battery according to claim 26, wherein the
oxide-containing film includes at least one kind of oxide selected
from the group consisting of an oxide of silicon, an oxide of
germanium and an oxide of tin.
28. The secondary battery according to claim 26, wherein the
oxide-containing film is formed by a liquid-phase deposition
method, a sol-gel method, a coating method or a dip coating
method.
29. The secondary battery according to claim 20, wherein the anode
active material layer includes a metal material which is not
alloyed with an electrode reactant in pores.
30. The secondary battery according to claim 29, wherein the metal
material includes at least one kind selected from the group
consisting of iron, cobalt, nickel, zinc and copper.
31. The secondary battery according to claim 29, wherein the metal
material is formed by an electrolytic plating method or an
electroless plating method.
32. The secondary battery according to claim 20, wherein the anode
active material is in the form of a plurality of particles.
33. The secondary battery according to claim 32, wherein the anode
active material has a multilayer configuration in its
particles.
34. The secondary battery according to claim 20, wherein the anode
active material is formed by a vapor-phase method.
35. The secondary battery according to claim 20, wherein the anode
active material includes oxygen, and the oxygen content in the
anode active material is within a range from 3 at % to 40 at % both
inclusive.
36. The secondary battery according to claim 20, wherein the anode
active material includes at least one kind of metal element
selected from the group consisting of iron, cobalt, nickel,
chromium, titanium and molybdenum.
37. The secondary battery according to claim 20, wherein the anode
active material includes an oxygen-containing region including
oxygen in its thickness direction, and the oxygen content in the
oxygen-containing region is higher than the oxygen content in a
region other than the oxygen-containing region.
38. The secondary battery according to claim 20, wherein the
ten-point height of roughness profile Rz of the surface of the
anode current collector is within a range from 1.5 .mu.m to 6.5
.mu.m both inclusive.
39. The secondary battery according to claim 20, wherein the
electrolytic solution includes a solvent including a sultone.
40. The secondary battery according to claim 39, wherein the
sultone is 1,3-propene sultone.
41. The secondary battery according to claim 20, wherein the
electrolytic solution includes a solvent including a cyclic
carbonate including an unsaturated bond.
42. The secondary battery according to claim 41, wherein the cyclic
carbonate including an unsaturated bond is vinylene carbonate or
vinyl ethylene carbonate.
43. The secondary battery according to claim 20, wherein the
electrolytic solution includes a solvent including a fluorinated
carbonate.
44. The secondary battery according to claim 43, wherein the
fluorinated carbonate is difluoroethylene carbonate.
45. The secondary battery according to claim 20, wherein the
electrolytic solution includes an electrolyte salt including boron
(B) and fluorine (F).
46. The secondary battery according to claim 45, the electrolyte
salt is lithium tetrafluoroborate (LiBF.sub.4).
47. The secondary battery according to claim 20, wherein the
cathode, the anode and the electrolytic solution are contained in a
cylindrical or prismatic package member.
48. The secondary battery according to claim 47, wherein the
package member includes iron or an iron alloy.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] The present invention contains subject matter related to
Japanese Patent Application JP 2007-149253 filed in the Japanese
Patent Office on Jun. 5, 2007 and Japanese Patent Application JP
2008-015253 filed in the Japanese Patent Office on Jan. 25, 2008,
the entire contents of which being incorporated herein by
references.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an anode including an anode
current collector and an anode active material layer arranged on
the anode current collector, and a secondary battery including the
anode.
[0004] 2. Description of the Related Art
[0005] In recent years, portable electronic devices such as
camera-integrated VTRs (videotape recorders), cellular phones, or
laptop computers are widely used, and size and weight reduction in
the portable electronic devices and an increase in longevity of the
portable electronic devices have been strongly demanded.
Accordingly, as power sources for the portable electronic devices,
the development of batteries, specifically lightweight secondary
batteries capable of obtaining a high energy density have been
promoted. Among them, a secondary battery (a so-called lithium-ion
secondary battery) using insertion and extraction of lithium for
charge-discharge reaction holds greater promise, because the
secondary battery is capable of obtaining a larger energy density,
compared to a lead-acid battery or a nickel-cadmium battery.
[0006] The lithium-ion secondary battery includes a cathode, an
anode and an electrolytic solution, and the anode has a
configuration in which an anode active material layer including an
anode active material is arranged on an anode current collector. As
the anode active material, a carbon material is widely used;
however, recently with enhancement of performance and expansion of
functions in portable electronic devices, a further improvement in
battery capacity is desired, so it is considered to use silicon
instead of a carbon material. It is because the theoretical
capacity of silicon (4199 mAh/g) is much larger than the
theoretical capacity of graphite (372 mAh/g), so an increase in
battery capacity is expected.
[0007] However, when silicon is deposited as the anode active
material by a vapor-phase method, a large number of pores are
formed in the anode active material to increase the surface area of
the anode active material. In this case, the anode active material
has high activity, so an electrolytic solution is easily decomposed
during charge and discharge, and lithium is easily inactivated.
Thereby, while the secondary battery obtains a higher capacity,
cycle characteristics which are important characteristics of the
secondary battery easily decline.
[0008] Therefore, to improve cycle characteristics even in the case
where silicon is used as the anode active material, various ideas
have been made.
[0009] More specifically, a technique in which in the case where
the deposition of a silicon thin film is performed a plurality of
times by a vapor-phase method, ions are applied to a surface of the
silicon thin film before the second or later deposition steps (for
example, refer to Japanese Unexamined Patent Application
Publication No. 2005-293899), a technique in which an anode current
collector having a three-dimensional configuration such as foam
metal or a sintered fiber metal body is used (for example, refer to
Japanese Unexamined Patent Application Publication No.
2004-071305), or a technique in which silicon is sintered to be
integrated with an anode current collector (for example, refer to
Japanese Unexamined Patent Application Publication Nos. H11-339777
and H11-339778) or the like has been proposed.
[0010] Moreover, a technique in which silicon particles are coated
with a fired body (ceramic) such as a metal oxide (for example,
refer to Japanese Unexamined Patent Application Publication Nos.
2004-335334 and 2004-335335), a technique in which an oxide layer
such as silicon oxide is formed on a surface of a silicon alloy
layer (for example, refer to Japanese Unexamined Patent Application
Publication No. 2004-319469), a technique in which a conductive
metal is reductively deposited on silicon powder (for example,
refer to Japanese Unexamined Patent Application Publication No.
H11-297311), a technique in which silicon compound particles are
coated with a metal (for example, refer to Japanese Unexamined
Patent Application Publication No. 2000-036323), a technique in
which a metal element not alloyed with lithium is dispersed in
silicon particles (for example, refer to Japanese Unexamined Patent
Application Publication No. 2001-273892), a technique in which
copper is dissolved into a silicon thin film (for example, refer to
Japanese Unexamined Patent Application Publication No. 2002-289177)
or the like has been proposed.
SUMMARY OF THE INVENTION
[0011] As recent portable electronic devices have a smaller size,
higher performance and more functions, secondary batteries tend to
be frequently charged and discharged accordingly, thereby cycle
characteristics easily decline. In particular, in a lithium-ion
secondary battery using silicon as an anode active material to
increase the capacity, cycle characteristics are noticeably prone
to decline due to the above-described increase in surface area.
Therefore, further improvement in cycle characteristics of the
secondary battery is desired.
[0012] In view of the foregoing, it is desirable to provide an
anode and a secondary battery which are capable of improving cycle
characteristics.
[0013] According to an embodiment of the invention, there is
provided an anode including: an anode current collector; and an
anode active material layer arranged on the anode current
collector, in which the anode active material layer includes an
anode active material including silicon, and including a pore group
with a diameter ranging from 3 nm to 50 nm both inclusive, and the
volumetric capacity per unit weight of silicon of the pore group
with a diameter ranging from 3 nm to 50 nm both inclusive is 0.2
cm.sup.3/g or less, the volumetric capacity being measured by
mercury porosimetry using a mercury porosimeter.
[0014] According to an embodiment of the invention, there is
provided a secondary battery including a cathode, an anode and an
electrolytic solution, in which the anode includes an anode current
collector and an anode active material layer arranged on the anode
current collector, the anode active material layer includes an
anode active material including silicon, and including a pore group
with a diameter ranging from 3 nm to 50 nm both inclusive, and the
volumetric capacity per unit weight of silicon of the pore group
with a diameter ranging from 3 nm to 50 nm both inclusive is 0.2
cm.sup.3/g or less, the volumetric capacity being measured by
mercury porosimetry using a mercury porosimeter.
[0015] The above-described "volumetric capacity of a pore group" is
determined by replacing the amount of mercury intruded which is
measured by mercury porosimetry using a mercury porosimeter with
the volumetric capacity of the small pore group. Thereby, "the
capacity of a pore group with a diameter ranging from 3 nm to 50 nm
both inclusive" is determined by replacing the measured total
amount of mercury intruded into pores with a diameter ranging from
3 nm to 50 nm both inclusive with the volumetric capacity of a pore
group with a diameter of the same range. Moreover, "the capacity of
a pore group with a diameter ranging from 3 nm to 20 nm both
inclusive" is determined by replacing the measured total amount of
mercury intruded into pores with a diameter ranging from 3 nm to 20
nm both inclusive with the volumetric capacity of a pore group with
a diameter of the same range. The amount of mercury intruded is a
value measured under conditions that the surface tension and the
contact angle of mercury are 485 mN/m and 130.degree.,
respectively, and a relationship between the diameter of a pore and
pressure is approximate to 180/pressure=diameter. The volumetric
capacity (cm.sup.3/g) of a pore group per unit weight of silicon is
able to be calculated from the weight (g) of silicon and the amount
of mercury intruded (=the capacity of a pore group: cm.sup.3).
[0016] In the anode according to the embodiment of the invention,
the anode active material includes silicon, and includes a pore
group with a diameter ranging from 3 nm to 50 nm both inclusive,
and the volumetric capacity of the pore group with a diameter
ranging from 3 nm to 50 nm per unit weight of silicon which is
measured by mercury porosimetry using a mercury porosimeter is 0.2
cm.sup.3/g or less, so compared to the case where the volumetric
capacity is out of the range, even if the anode active material
includes silicon with high reactivity, the anode active material is
resistant to reacting with another material. Thereby, in the
secondary battery according to the embodiment of the invention, the
electrolytic solution is resistant to decomposition during charge
and discharge, so cycle characteristics may be improved. In this
case, when the volumetric capacity of the pore group with a
diameter ranging from 3 nm to 50 nm both inclusive per unit weight
of silicon is 0.05 cm.sup.3/g or less, more specifically 0
cm.sup.3/g, a higher effect may be obtained.
[0017] Moreover, when the volumetric capacity of a pore group with
a diameter ranging from 3 nm to 20 nm both inclusive per unit
weight of silicon which is measured by mercury porosimetry using a
mercury porosimeter is 0.2 cm.sup.3/g or less, a higher effect may
be obtained. In this case, the volumetric capacity of the pore
group with a diameter ranging from 3 nm to 20 nm both inclusive per
unit weight of silicon is 0.05 cm.sup.3/g or less, or more
specifically 0 cm.sup.3/g, a higher effect may be obtained.
[0018] Further, when an oxide-containing film or a metal material
which is not alloyed with an electrode reactant is included in
pores, even in the case where the volumetric capacity of a pore
group per unit weight of silicon is inherently out of the
above-described range, the volumetric capacity of the pore group
per unit weight of silicon may be easily controlled within the
range. In this case, when the oxide-containing film is formed by a
liquid-phase method such as a liquid-phase deposition method, or
the metal material is formed by a liquid-phase method such as an
electrolytic plating method, the oxide-containing film or the metal
material is easily intruded into the pores, so a higher effect may
be obtained.
[0019] When the anode active material includes oxygen, and the
oxygen content in the anode active material is within a range from
3 at % to 40 at % both inclusive, or when the anode active material
includes at least one kind of metal element selected from the group
consisting of iron, cobalt, nickel, titanium, chromium and
molybdenum, or when anode active material particles include an
oxygen-containing region (a region in which oxygen is included and
the oxygen content is higher than that in a region other than the
region) in its thickness direction, a higher effect may be
obtained.
[0020] When the ten-point height of roughness profile Rz of the
surface of the anode current collector is within a range from 1.5
.mu.m to 6.5 .mu.m both inclusive, a higher effect may be
obtained.
[0021] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a sectional view showing the configuration of an
anode according to an embodiment of the invention;
[0023] FIGS. 2A and 2B are an SEM photograph and a schematic view
showing a sectional configuration of the anode shown in FIG. 1;
[0024] FIG. 3 is a chart showing the distribution of the rate of
change in the amount of mercury intruded;
[0025] FIGS. 4A and 4B are an SEM photograph and a schematic view
showing another sectional configuration of the anode shown in FIG.
1;
[0026] FIG. 5 is a sectional view showing the configuration of a
first secondary battery including the anode according to the
embodiment of the invention;
[0027] FIG. 6 is a sectional view of the first secondary battery
taken along a line VI-VI of FIG. 5;
[0028] FIG. 7 is a sectional view showing a second secondary
battery including the anode according to the embodiment of the
invention;
[0029] FIG. 8 is an enlarged sectional view showing a part of a
spirally wound electrode body shown in FIG. 7;
[0030] FIG. 9 is a sectional view showing the configuration of a
third secondary battery including the anode according to the
embodiment of the invention;
[0031] FIG. 10 is a sectional view of a spirally wound electrode
body taken along a line X-X of FIG. 9;
[0032] FIG. 11 is a diagram showing a correlation between a
volumetric capacity and a discharge capacity retention ratio;
[0033] FIG. 12 is a diagram showing another correlation between a
volumetric capacity and a discharge capacity retention ratio;
[0034] FIG. 13 is a diagram showing a correlation between the
oxygen content and a discharge capacity retention ratio; and
[0035] FIG. 14 is a diagram showing a correlation between a
ten-point height of roughness profile and a discharge capacity
retention ratio.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] A preferred embodiment will be described in detail below
referring to the accompanying drawings.
[0037] FIG. 1 shows a sectional view of an anode according to an
embodiment of the invention. The anode is used in, for example, an
electrochemical device such as a secondary battery, and includes an
anode current collector 1 having a pair of surfaces, and an anode
active material layer 2 arranged on the anode current collector
1.
[0038] The anode current collector 1 is preferably made of a metal
material having good electrochemical stability, electrical
conductivity and mechanical strength. Examples of the metal
material include copper, nickel, stainless and the like. Among
them, copper is preferable, because high electrical conductivity is
obtained.
[0039] In particular, as the metal material of which the anode
current collector 1 is made, a metal material including one kind or
two or more kinds of metal elements which do not form an
intermetallic compound with an electrode reactant is preferable.
When the metal elements form an intermetallic compound with the
electrode reactant, the influence of a stress due to swelling and
shrinkage of the anode active material layer 2 during the operation
of an electrochemical device (for example, during charge and
discharge of a secondary battery) may cause a decline in the
current collecting property or peeling of the anode active material
layer 2 from the anode current collector 1. Examples of the metal
elements include copper, nickel, titanium, iron, chromium and the
like.
[0040] Moreover, the above-described metal material preferably
includes one kind or two or more kinds of metal elements which are
alloyed with the anode active material layer 2. It is because
adhesion between the anode current collector 1 and the anode active
material layer 2 is improved, so the anode active material layer 2
is less prone to being peeled from the anode current collector 1.
Examples of metal elements which do not form an intermetallic
compound with the electrode reactant and are alloyed with the anode
active material layer 2 include copper, nickel, iron and the like
in the case where the anode active material layer 2 includes
silicon as an anode active material. These metal elements are
preferable in terms of strength and electrical conductivity.
[0041] The anode current collector 1 may have a single-layer
configuration or a multilayer configuration. In the case where the
anode current collector 1 has a multilayer configuration, for
example, it is preferable that a layer adjacent to the anode active
material layer 2 is made of a metal material which is alloyed with
the anode active material layer 2, and a layer not adjacent to the
anode active material layer 2 is made of any other metal
material.
[0042] The surface of the anode current collector 1 is preferably
roughened. It is because adhesion between the anode current
collector 1 and the anode active material layer 2 is improved by a
so-called anchor effect. In this case, at least a surface facing
the anode active material layer 2 of the anode current collector 1
may be roughened. As a roughening method, for example, a method of
forming fine particles by electrolytic treatment or the like is
cited. The electrolytic treatment is a method of forming fine
particles on the surface of the anode current collector 1 in an
electrolytic bath by an electrolytic method to form a roughened
surface. Copper foil subjected to the electrolytic treatment is
generally called "electrolytic copper foil".
[0043] The ten-point height of roughness profile Rz of the surface
of the anode current collector 1 is preferably within a range from
1.5 .mu.m to 6.5 .mu.m both inclusive. It is because adhesion
between the anode current collector 1 and the anode active material
layer 2 is further improved. More specifically, when the ten-point
height of roughness profile Rz is smaller than 1.5 .mu.m,
sufficient adhesion may not be obtained, and when the ten-point
height of roughness profile Rz is larger than 6.5 .mu.m, the anode
active material may include a large number of holes to increase its
surface area.
[0044] The anode active material layer 2 includes an anode active
material capable of inserting and extracting an electrode reactant.
The anode active material includes silicon as an element. It is
because silicon has a high capability of inserting and extracting
an electrode reactant, so a high energy density is obtained.
Moreover, the anode active material includes a plurality of pores,
so the diameters of the plurality of pores are distributed over a
wide range from approximately a few nm to a few thousands nm. When
attention is given to a pore group having a small diameter ranging
from 3 nm to 50 nm both inclusive (hereinafter simply referred to
as "a small pore group") among them, the volumetric capacity of the
small pore group per unit weight of silicon, which is measured by
mercury porosimetry using a mercury porosimeter, is 0.2 cm.sup.3/g
or less. It is because the volumetric capacity of the small pore
group is reduced, and the surface area of the anode active material
is controlled to be small, so even in the case where the anode
active material has high activity, the anode active material is
less prone to reacting with another material. As another material,
for example, an electrolytic solution in the case where the anode
is used in a secondary battery is cited.
[0045] The volumetric capacity of the above-described small pore
group is determined by replacing the amount of mercury intruded
which is measured by mercury porosimetry using a mercury
porosimeter with the volumetric capacity of the small pore group,
and the amount of mercury intruded is a value measured under
conditions that the surface tension and the contact angle of
mercury are 485 mN/m and 130.degree., respectively, and a
relationship between the diameter of a pore and pressure is
approximate to 180/pressure=diameter. By this method, in the case
where the diameters of the plurality of pores are distributed over
a wide range, it is possible to measure the volumetric capacities
of pores (the amount of mercury intruded into pores) in each
specific diameter range, so it is possible to determine the
above-described volumetric capacity (cm.sup.3/g) of the small pore
group per unit weight of silicon from the total weight (g) of
silicon and the measured total amount of mercury intruded into
pores with a diameter ranging from 3 nm to 50 nm both inclusive
(the total volumetric capacity of the small pore group: cm.sup.3).
The reason why the pores with a diameter ranging from 3 nm to 50 nm
both inclusive are used when defining the range of the volumetric
capacity of the small pore group per unit weight of silicon is that
as the volumetric capacity of each pore is small, but the total
number of pores is extremely large, so the pores have a large
influence on the surface area of the anode active material.
[0046] In particular, the volumetric capacity of the small pore
group with a diameter ranging from 3 nm to 50 nm both inclusive per
unit weight of silicon is preferably 0.05 cm.sup.3/g or less, and
more preferably 0 cm.sup.3/g, because a higher effect is obtained.
As it is obvious that the volumetric capacity of the small pore
group is measured by a mercury porosimeter, the capacity of the
small pore group being 0 cm.sup.3/g means that the volumetric
capacity of the small pore group is 0 cm.sup.3/g as a result
measured by the mercury porosimeter (the volumetric capacity of the
small pore group is unmeasurable).
[0047] In this case, when attention is given to a very small pore
group with a diameter ranging from 3 nm to 20 nm both inclusive
(hereinafter simply referred to as "a very small pore group") in
the small pore group with a diameter ranging from 3 nm to 50 nm
both inclusive, the volumetric capacity of the very small pore
group per unit weight of silicon which is measured by mercury
porosimetry using a mercury porosimeter is preferably 0.2
cm.sup.3/g or less, and more preferably 0.05 cm.sup.3/g or less,
and more preferably 0 cm.sup.3/g. It is because the volumetric
capacity of the very small pore group in the small pore group has a
large influence on the surface area of the anode active material,
so a higher effect is obtained.
[0048] The anode active material layer 2 may include, if necessary,
an oxide-containing film or a metal material not alloyed with the
electrode reactant in small pores to set the volumetric capacity of
the small pore group per unit weight of silicon within the
above-described range. It is because when the oxide-containing film
or the metal material is intruded into the small pores, the
volumetric capacity of the small pore group is reduced. In this
case, when the small pores are completely filled with the
oxide-containing film or the metal material, the volumetric
capacity of the small pore group per unit weight of silicon may be
0 cm.sup.3/g.
[0049] The oxide-containing film includes, for example, at least
one kind of oxide selected from the group consisting of an oxide of
silicon, an oxide of germanium and an oxide of tin. The
oxide-containing film may include any other oxide except for them.
The oxide-containing film may be formed by any one of a vapor-phase
method and a liquid-phase method. Among them, the liquid-phase
method such as a liquid-phase deposition method, a sol-gel method a
coating method or a dip coating method is preferable, and among
them, the liquid-phase deposition method is more preferable,
because the oxide-containing film is easily intruded into the small
pores.
[0050] As the metal material intruded into the small pores, for
example, a metal material including a metal element not alloyed
with the electrode reactant as an element is cited, and, for
example, at least one kind selected from the group consisting of
iron, cobalt, nickel, zinc and copper is cited. The metal material
may include any other metal element except for them. The form of
the metal material is not limited to the simple substance, and the
metal material may be an alloy or a metal compound. The metal
material may be formed by any one of a vapor-phase method or a
liquid-phase method. Among them, the liquid-phase method such as an
electrolytic plating method or an electroless plating method is
preferable, and the electrolytic plating method is more preferable,
because the metal material is easily intruded into the small pores,
and only a short plating time is necessary. When the anode active
material layer 2 includes the metal material, the metal material
functions as a binder, so binding in the anode active material is
improved.
[0051] The anode active material layer 2 may include only one or
both of the oxide-containing film and the metal material. In the
case where only one of them is included, the oxide-containing film
is preferably included. It is because the oxide-containing film
formed by a liquid-phase method such as a liquid-phase deposition
method is intruded into small pores more easily than the metal
material formed by a liquid-phase method such as an electrolytic
plating method.
[0052] The anode active material may be the simple substance, an
alloy or a compound of silicon, or an anode active material
including a phase including one kind or two or more kinds selected
from them at least in part. Only one kind or mixture of a plurality
of kinds selected from them may be used.
[0053] In the invention, the alloy includes an alloy including one
or more kinds of metal elements and one or more kinds of metalloid
elements in addition to an alloy including two or more kinds of
metal elements. Further, in the invention, the alloy may include a
non-metal element. As the texture of the alloy, a solid solution, a
eutectic (eutectic mixture), an intermetallic compound or the
coexistence of two or more kinds selected from them is cited.
[0054] As an alloy of silicon, for example, an alloy including at
least one kind selected from the group consisting of tin (Sn),
nickel, copper, iron, cobalt, manganese (Mn), zinc, indium (In),
silver (Ag), titanium, germanium (Ge), bismuth (Bi), antimony (Sb)
and chromium as an element except for silicon is cited.
[0055] As a compound of silicon, for example, a compound including
oxygen or carbon (C) as an element except for silicon is cited. For
example, the compound of silicon may include one kind or two or
more kinds selected from elements described in the alloy of silicon
as elements except for silicon.
[0056] The anode active material is attached to the anode current
collector 1, and is grown from the surface of the anode current
collector 1 in the thickness direction of the anode active material
layer 2. In this case, the anode active material is formed by a
vapor-phase method, and as described above, the anode current
collector 1 and the anode active material layer 2 are preferably
alloyed at least in a part of an interface therebetween. More
specifically, the elements of the anode current collector 1 may be
diffused into the anode active material layer 2 in the interface,
or the elements of the anode active material layer 2 may be
diffused into the anode current collector 1 in the interface, or
they may be diffused into each other in the interface. It is
because it is difficult to cause a fracture in the anode active
material layer 2 due to swelling and shrinkage thereof during
electrode reaction, and electron conductivity between the anode
current collector 1 and the anode active material layer 2 is
improved.
[0057] As the above-described vapor-phase method, for example, a
physical deposition method or a chemical deposition method, more
specifically, a vacuum deposition method, a sputtering method, an
ion plating method, a laser ablation method, a thermal CVD
(Chemical Vapor Deposition) method, a plasma chemical vapor
deposition method or the like is cited.
[0058] Moreover, the anode active material may have the form of a
plurality of particles. The anode active material may be formed by
one deposition step to have a single-layer configuration, or may be
formed by a plurality of deposition steps to have a multilayer
configuration in particles. However, in the case where the anode
active material is formed by an evaporation method accompanied by
high heat during deposition, to prevent the anode current collector
1 from suffering heat damage, the anode active material preferably
has a multilayer configuration. It is because when the step of
depositing the anode active material is divided into several times
to be performed (the anode active material is successively formed
to be deposited), compared to the case where the deposition step is
performed only once, the time that the anode current collector 1 is
exposed to high heat is reduced.
[0059] In particular, the anode active material preferably includes
oxygen as an element. It is because swelling and shrinkage of the
anode active material layer 2 are prevented. In the anode active
material layer 2, at least a part of oxygen is bonded to a part of
silicon. In this case, bonding between oxygen and silicon may be in
the state of silicon monoxide or silicon dioxide, or in any other
metastable state.
[0060] The oxygen content in the anode active material is
preferably within a range from 3 at % to 40 at % both inclusive,
because a higher effect is obtained. More specifically, when the
oxygen content is smaller than 3 at %, there is a possibility that
swelling and shrinkage of the anode active material layer 2 are not
sufficiently prevented, and when the oxygen content is larger than
40 at %, there is a possibility that resistance is increased too
much. In the case where the anode is used with an electrolytic
solution in an electrochemical device, a coating formed by the
decomposition of the electrolytic solution is not included in the
anode active material. In other words, in the case where the oxygen
content in the anode active material is determined by calculation,
oxygen in the above-described coating is not included.
[0061] For example, in the case where the anode active material is
formed by a vapor-phase method, the anode active material including
oxygen may be formed by continuously introducing an oxygen gas into
a chamber. In particular, in the case where a desired oxygen
content is not obtained only by introducing the oxygen gas, a
liquid (for example, water vapor or the like) may be introduced
into the chamber as a supply source of oxygen.
[0062] Moreover, the anode active material preferably includes at
least one kind of metal element selected from the group consisting
of iron, cobalt, nickel, titanium, chromium and molybdenum. It is
because binding in the anode active material is improved, and
swelling and shrinkage of the anode active material layer 2 are
prevented, and the resistance of the anode active material is
reduced. The content of the metal element in the anode active
material is freely settable. However, in the case where the anode
is used in a secondary battery, when the content of the metal
element is too large, to obtain a desired battery capacity, it is
necessary to increase the thickness of the anode active material
layer 2, so the anode active material layer 2 may be peeled from
the anode current collector 1, or the anode active material layer 2
may be cracked.
[0063] The anode active material including the above-described
metal element may be formed by using an evaporation source in which
a metal element is mixed, or a multicomponent evaporation source
when the anode active material is formed by an evaporation method
as a vapor-phase method.
[0064] The anode active material includes an oxygen-containing
region including oxygen in its thickness direction, and the oxygen
content in the oxygen-containing region is preferably higher than
the oxygen content in a region other than the oxygen-containing
region. It is because swelling and shrinkage of the anode active
material layer 2 are prevented. The region other than the
oxygen-containing region may or may not include oxygen. In the case
where the region other than the oxygen-containing region includes
oxygen, the oxygen content in the region other than the
oxygen-containing region is lower than that in the
oxygen-containing region.
[0065] In this case, to prevent swelling and shrinkage of the anode
active material layer 2, it is preferable that the region other
than the oxygen-containing region includes oxygen, and the anode
active material includes a first oxygen-containing region (a region
having a lower oxygen content) and a second oxygen-containing
region having a higher oxygen content than the first
oxygen-containing region (a region having a higher oxygen content).
In this case, the second oxygen-containing region is preferably
sandwiched by the first oxygen-containing region, and more
preferably, the first oxygen-containing region and the second
oxygen-containing region are alternately laminated. It is because a
higher effect is obtained. The oxygen content in the first
oxygen-containing region is preferably as low as possible, and, for
example, the oxygen content in the second oxygen-containing region
is equal to the oxygen content in the case where the
above-described material includes oxygen.
[0066] The anode active material including the first and second
oxygen-containing regions may be formed by intermittently
introducing an oxygen gas into a chamber, or changing the amount of
the oxygen gas introduced into the chamber in the case where the
anode active material is formed by, for example, a vapor-phase
method. In the case where a desired oxygen content is not obtained
only by introducing the oxygen gas, a liquid (for example, a water
vapor or the like) may be introduced into the chamber.
[0067] The oxygen contents in the first and second
oxygen-containing regions may or may not be distinctly different
from each other. In particular, in the case where the amount of the
above-described oxygen gas introduced is continuously changed, the
oxygen content may be also continuously changed. In the case where
the amount of the oxygen gas introduced is intermittently changed,
the first and second oxygen-containing regions become so-called
"layers", and in the case where the amount of the oxygen gas
introduced is continuously changed, the first and second
oxygen-containing regions become "laminar" rather than "layers". In
the latter case, the oxygen content in the anode active material is
distributed while the oxygen content changed up and down
repeatedly. In this case, the oxygen content is preferably changed
step by step or continuously between the first and second
oxygen-containing regions. When the oxygen content is rapidly
changed, ion diffusion may decline or resistance may be
increased.
[0068] Referring to FIGS. 2A and 2B to 4A and 4B, a specific
configuration example of the anode in the case where a particulate
anode active material has a multilayer configuration in its
particles will be described below. FIGS. 2A, 2B, 4A and 4B show
enlarged sectional views of the anode, and FIGS. 2A and 4A show
scanning electron microscope (SEM) photographs (secondary electron
images), and FIGS. 2B and 4B show schematic views of the SEM images
shown in FIGS. 2A and 4A, respectively. FIG. 3 shows a distribution
of the rate of change in the amount of mercury intruded.
[0069] As shown in FIGS. 2A and 2B, in the case where the anode
active material includes a plurality of particles (anode active
material particles 201), the anode active material includes a
plurality of pores 202. More specifically, on the roughened surface
of the anode current collector 1, a plurality of projections (for
example, fine particles formed by electrolytic treatment) are
present. In this case, the anode active material is deposited and
laminated on the surface of the anode current collector 1 a
plurality of times by a vapor-phase method or the like so as to
grow the anode active material particles 201 step by step in a
thickness direction on each of the above-described projections.
Because of the closely packed configuration of the plurality of
anode active material particles 201, the multilayer configuration
and the surface configuration, a plurality of pores 202 are
formed.
[0070] The pores 202 include three kinds, that is, pores 202A, 202B
and 202C classified by causes of formation. The pores 202A are gaps
formed between the anode active material particles 201 growing on
each projection which is present on the surface of the anode
current collector 1. The pores 202B are gaps formed between small
stubble-shaped projections (not shown) which are formed on the
surfaces of the anode active material particles 201. The pores 202B
may be formed on the whole exposed surfaces of the anode active
material particles 201, or a part of the exposed surfaces of the
anode active material particles 201. The anode active material
particles 201 have a multilayer configuration, and the pores 202C
are gaps formed between layers of the multilayer configuration. The
above-described small stubble-shaped projections are formed on the
surfaces of the anode active material particles 201 in each
formation of the anode active material particles 201, so the pores
202B are formed not only on the exposed surfaces (the outer
surfaces) of the anode active material particles 201 but also
between layers. The pores 202 may include any other pores formed
because of any other cause of formation except for the
above-described causes of formation.
[0071] When the amount V of mercury intruded into the pores 202 is
measured while increasing a pressure P by a mercury porosimeter in
stages, the rate of change (AV/AP) in the amount of mercury
intruded is distributed as shown in FIG. 3. In FIG. 3, the
horizontal axis indicates the diameters (nm) of the pores 202, and
the vertical axis indicates the rate of change in the amount of
mercury intruded into the pores 202. The rate of change in the
amount of mercury intruded is distributed so that two peaks P1 and
P2 are shown in a diameter ranging from 3 nm to 3000 nm both
inclusive which is measurable by the mercury porosimeter. The peak
P1 on a wide diameter side is formed mainly due to the presence of
the pores 202A, and the distribution range of the diameter is from
50 nm to 3000 nm both inclusive. On the other hand, the peak P2 on
a narrow diameter side is formed mainly due to the presence of the
pores 202B and 202C, and the distribution range of the diameter is
3 nm to 50 nm both inclusive. The rate of change in the amount of
mercury intruded on the vertical axis of FIG. 3 is a normalized
value under the condition that the rate of change at the peak P1
(the maximum value of the rate of change in a diameter ranging from
50 nm to 3000 nm both inclusive) is 1.
[0072] As shown in FIGS. 4A and 4B, after a plurality of anode
active material particles 201 are formed, a metal material 203 is
formed by an electrolytic plating method or the like, thereby the
metal material 203 is intruded into the pores 202. In other words,
the metal material 203 is intruded into gaps (the pores 202A)
between adjacent anode active material particles 201, gaps (pores
202B) between small stubble-shaped projections formed on the
surfaces of the anode active material particles 201, and gaps (the
pores 202C) in the anode active material particles 201. In FIGS. 4A
and 4B, dotting the metal material 203 around the surfaces of the
anode active material particles 202 in the outermost layer means
that the above-described small projections are present in positions
where the metal material 203 is dotted.
[0073] As shown in FIGS. 2A and 2B to 4A and 4B, in the case where
the particulate anode active material has a multilayer
configuration in its particles, the above-described small pores
include both of the pores 202B and 202C. In this case, only to set
the volumetric capacity of the small pore group per unit weight of
silicon within the above-described range, the metal material 203
may include only pores 202B and 202C; however, in consideration of
the performance of the whole anode, the metal material 203 is
preferably intruded into the pores 202A, and the pores 202A is more
preferably filled with the metal material 203. It is because the
binding in the anode active material is improved by the metal
material 203, and swelling and shrinkage of the anode active
material layer 2 do not easily occur.
[0074] In the case where the particulate anode active material does
not have a multilayer configuration in its particles (has a
single-layer configuration), the pores 202C are not formed, so
small pores include only the pores 202B.
[0075] Although specific description is not given referring to
drawings here, in the case where instead of the metal material, the
oxide-containing film is formed by a liquid-phase deposition method
or the like, the oxide-containing film is grown along the surfaces
of the anode active material particles 201, so the oxide-containing
film is preferentially intruded into the pores 202B and 202C. In
this case, when the deposition time is increased, the
oxide-containing film is intruded into the pores 202A.
[0076] The anode is manufactured by the following steps, for
example.
[0077] At first, after the anode current collector 1 is prepared,
roughening treatment is subjected to the surface of the anode
current collector 1 if necessary. Next, silicon is deposited on the
anode current collector 1 by a vapor-phase method or the like to
form the anode active material. In the case where the anode active
material is formed, the anode active material may be formed by one
deposition step to have a single-layer configuration, or the anode
active material may be formed by a plurality of deposition steps to
have a multilayer configuration. In the case where the anode active
material is formed by a vapor-phase method to have a multilayer
configuration, silicon may be deposited a plurality of times while
the anode current collector 1 is moved back and forth relatively to
an evaporation source, or silicon may be deposited a plurality of
times while the anode current collector 1 is fixed relative to the
evaporation source, and a shutter is repeatedly opened and closed.
After that, an oxide-containing film or a metal material not
alloyed with an electrode reactant may be formed by a liquid-phase
method or the like. In the case where the oxide-containing film is
formed by a liquid-phase deposition method, after a dissolved
species which easily coordinates fluorine as an anion trapping
agent is added to and mixed with a solution of a fluoride complex
such as silicon to form a mixture, the anode current collector 1 on
which the anode active material is formed is immersed in the
mixture, and then a fluorine anion generated from the fluoride
complex is trapped by the dissolved species, thereby an oxide is
deposited on the surface of the anode active material. In this
case, instead of the fluoride complex, a compound of silicon or the
like generating other anions such as sulfate ions may be used.
Thereby, the anode active material layer 2 is formed, so the anode
is completed.
[0078] In the anode, the anode active material includes silicon,
and has the small pore group (a pore group with a diameter ranging
from 3 nm to 50 nm both inclusive), and the volumetric capacity of
the small pore group per unit weight of silicon which is measured
by mercury porosimetry using a mercury porosimeter is 0.2
cm.sup.3/g or less, so compared to the case where the volumetric
capacity is out of the range, even in the case where the anode
active material includes silicon having high activity, the anode
active material is resistant to reacting with another material.
Therefore, the anode active material is capable of contributing to
an improvement in cycle characteristics of an electrochemical
device using the anode. In this case, when the volumetric capacity
of the small pore group per unit weight of silicon is 0.05
cm.sup.3/g or less, or more specifically 0 cm.sup.3/g, a higher
effect may be obtained.
[0079] In particular, when the volumetric capacity of the very
small pore group (a pore group with a diameter ranging from 3 nm to
20 nm both inclusive) per unit weight of silicon which is measured
by mercury porosimetry using a mercury porosimeter is 0.2
cm.sup.3/g or less, a higher effect may be obtained. In this case,
when the volumetric capacity of the very small pore group per unit
weight of silicon is 0.05 cm.sup.3/g or less, or more specifically
0 cm.sup.3/g, a higher effect may be obtained.
[0080] Moreover, when the oxide-containing film or the metal
material not alloyed with an electrode reactant is included in
small pores, even in the case where the volumetric capacity of the
small pore group per unit weight of silicon is out of the
above-described range, the volumetric capacity of the small pore
group per unit weight of silicon may be easily controlled within
the range. In this case, when the oxide-containing film is formed
by a liquid-phase method such as a liquid-phase deposition method,
or the metal material is formed by a liquid-phase method such as an
electrolytic plating method is formed, the oxide-containing film or
the metal material is easily intruded into small pores, so a higher
effect may be obtained.
[0081] Further, when the anode active material includes oxygen, and
the oxygen content in the anode active material is within a range
from 3 at % to 40 at % both inclusive, or when the anode active
material includes at least one kind of metal element selected from
the group consisting of iron, cobalt, nickel, titanium, chromium
and molybdenum, or when the anode active material particles
includes an oxygen-containing region (a region including oxygen in
which the oxygen content is higher than that in a region other than
the region) in its thickness direction, a higher effect may be
obtained.
[0082] When the surface facing the anode active material layer 2 of
the anode current collector 1 is roughened by fine particles formed
by electrolytic treatment, adhesion between the anode current
collector 1 and the anode active material layer 2 may be improved.
In this case, when the ten-point height of roughness profile Rz of
the surface of the anode current collector 1 is within a range from
1.5 .mu.m to 6.5 .mu.m both inclusive, a higher effect may be
obtained.
[0083] Next, application examples of the above-described anode will
be described below. As an example of the electrochemical device, a
secondary battery is used, and the anode is used in the secondary
battery as below.
(First Secondary Battery)
[0084] FIGS. 5 and 6 show sectional views of a first secondary
battery, and FIG. 6 shows a sectional view taken along a line VI-VI
of FIG. 5. The secondary battery described here is, for example, a
lithium-ion secondary battery in which the capacity of an anode 22
is represented based on insertion and extraction of lithium as an
electrode reactant.
[0085] The secondary battery contains a battery element 20 having a
flat winding configuration in a battery can 11.
[0086] The battery can 11 is, for example, a prismatic package
member. As shown in FIG. 6, in the prismatic package member, a
sectional surface in a longitudinal direction has a rectangular
shape or a substantially rectangular shape (including a curve in
part), and the prismatic package member forms not only a prismatic
battery with a rectangular shape but also a prismatic battery with
an oval shape. In other words, the prismatic package member is a
vessel-shaped member having a rectangular closed end or a oval
closed end and an opening with a rectangular shape or a
substantially rectangular (an oval) shape formed by connecting arcs
with straight lines. In FIG. 6, the battery can 11 having a
rectangular sectional surface is shown. The battery configuration
including the battery can 11 is a so-called prismatic type.
[0087] The battery can 11 is made of, for example, a metal material
including iron or aluminum (Al), or an alloy thereof, and may have
a function as an electrode terminal. In this case, to prevent
swelling of the secondary battery through the use of the hardness
(resistance to deformation) of the battery can 11 during charge and
discharge, iron which is harder than aluminum is preferable. In the
case where the battery can 11 is made of iron, for example, iron
may be plated with nickel (Ni) or the like.
[0088] Moreover, the battery can 11 has a hollow configuration
having an open end and a closed end, and an insulating plate 12 and
a battery cover 13 are attached to the open end, and the battery
can 11 is sealed. The insulating plate 12 is arranged between the
battery element 20 and the battery cover 13 in a direction
perpendicular to a peripheral winding surface of the battery
element 20, and the insulating plate 12 is made of, for example,
polypropylene or the like. The battery cover 13 is made of, for
example, the same material as that of the battery can 11, and may
have a function as an electrode terminal in the same manner.
[0089] A terminal plate 14 which becomes a cathode terminal is
arranged outside of the battery cover 13, and the terminal plate 14
is electrically insulated from the battery cover 13 by an
insulating case 16. The insulating case 16 is made of, for example,
polybutylene terephthalate or the like. Moreover, a through hole is
arranged around the center of the battery cover 13, and a cathode
pin 15 is inserted into the through hole so as to be electrically
connected to the terminal plate 14 and to be electrically insulated
from the battery cover 13 by a gasket 17. The gasket 17 is made of,
for example, an insulating material, and its surface is coated with
asphalt.
[0090] A cleavage valve 18 and an injection hole 19 are arranged
around an edge of the battery cover 13. The cleavage valve 18 is
electrically connected to the battery cover 13, and when an
internal pressure in the secondary battery increases to a certain
extent or higher due to an internal short circuit or external
application of heat, the cleavage valve 18 is separated from the
battery cover 13 to release the internal pressure. The injection
hole 19 is filled with a sealing member 19A made of, for example, a
stainless steel ball.
[0091] The battery element 20 is formed by laminating a cathode 21
and an anode 22 with a separator 23 in between, and spirally
winding them, and has a flat shape according to the shape of the
battery can 11. A cathode lead 24 made of aluminum or the like is
attached to an end (for example, an inside end) of the cathode 21,
and an anode lead 25 made of nickel or the like is attached to an
end (for example, an outside end) of the anode 22. The cathode lead
24 is welded to an end of the cathode pin 15 to be electrically
connected to the terminal plate 14, and the anode lead 25 is welded
and electrically connected to the battery can 11.
[0092] The cathode 21 is formed by arranging a cathode active
material layer 21B on both sides of a strip-shaped cathode current
collector 21A. The cathode current collector 21A is made of, for
example, a metal material such as aluminum, nickel or stainless.
The cathode active material layer 21B includes a cathode active
material, and may include a binder, an electrical conductor or the
like, if necessary.
[0093] The cathode active material includes one kind or two or more
kinds of cathode materials capable of inserting and extracting
lithium as an electrode reactant. As the cathode material, for
example, lithium cobalt oxide, lithium nickel oxide, a solid
solution including lithium cobalt oxide and lithium nickel oxide
(Li(Ni.sub.xCo.sub.yMn.sub.z)O.sub.2; the values of x, y and z are
0<x<1, 0<y<1 and 0<z<1, and x+y+z=1), lithium
complex oxide such as lithium manganese oxide (LiMn.sub.2O.sub.4)
with a spinel structure or a solid solution thereof
(Li(Mn.sub.2-vNi.sub.v)O.sub.4; the value of v is v<2) or the
like is cited. Moreover, as the cathode material, for example, a
phosphate compound with an olivine structure such as lithium iron
phosphate (LiFePO.sub.4) is also cited. It is because a high energy
density is obtained. In addition to the above-described materials,
the cathode material may be, for example, an oxide such as titanium
oxide, vanadium oxide or manganese dioxide, a bisulfide such as
iron bisulfide, titanium bisulfide or molybdenum sulfide, sulfur,
or a conductive polymer such as polyaniline or polythiophene.
[0094] The anode 22 has the same configuration as that of the
above-described anode, and is formed by arranging an anode active
material layer 22B on both sides of a strip-shaped anode current
collector 22A. The configurations of the anode current collector
22A and the anode active material layer 22B are the same as those
of the anode current collector 1 and the anode active material
layer 2 in the above-described anode, respectively. The charge
capacity of the anode active material capable of inserting and
extracting lithium is preferably larger than the charge capacity of
the cathode 21.
[0095] The separator 23 isolates between the cathode 21 and the
anode 22 so that ions of an electrode reactant pass therethrough
while preventing a short circuit of a current due to contact
between the cathode 21 and the anode 22. The separator 23 is made
of, for example, a porous film of a synthetic resin such as
polytetrafluoroethylene, polypropylene or polyethylene, a porous
ceramic film or the like, and the separator 23 may have a
configuration in which two or more kinds of the porous films are
laminated.
[0096] The separator 23 is impregnated with an electrolytic
solution as a liquid electrolyte. The electrolytic solution
includes a solvent and an electrolyte salt dissolved in the
solvent.
[0097] The solvent includes, for example, one kind or two or more
kinds of nonaqueous solvents such as organic solvents. Examples of
the nonaqueous solvents include carbonate-based solvents such as
ethylene carbonate, propylene carbonate, butylene carbonate,
dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and
methyl propyl carbonate. It is because superior capacity
characteristics, storage characteristics and cycle characteristics
are obtained. Only one kind or a mixture of a plurality of kinds
selected from them may be used. Among them, as the solvent, a
mixture of a high-viscosity solvent such as ethylene carbonate or
propylene carbonate and a low-viscosity solvent such as dimethyl
carbonate, ethyl methyl carbonate or diethyl carbonate is
preferable. It is because the dissociation property of the
electrolyte salt and ion mobility are improved, so a higher effect
is obtained.
[0098] Moreover, the solvent preferably includes a halogenated
carbonate. It is because a stable coating is formed on a surface of
the anode 22 to prevent decomposition of the electrolytic solution,
thereby the cycle characteristics are improved. As the halogenated
carbonate, a fluorinated carbonate is preferable, and
difluoroethylene carbonate is more preferable, because a higher
effect is obtained. As the difluoroethylene carbonate, for example,
4,5-difluoro-1,3-dioxolane-2-one or the like is cited.
[0099] Further, the solvent preferably includes a cyclic carbonate
including an unsaturated bond, because the cycle characteristics
are improved. Examples of the cyclic carbonate including an
unsaturated bond include vinylene carbonate, vinyl ethylene
carbonate and the like, and a mixture of them may be used.
[0100] Moreover, the solvent preferably includes a sultone. It is
because the cycle characteristics are improved, and swelling of the
secondary battery is prevented. Examples of the sultone include
1,3-propene sultone and the like.
[0101] The electrolyte salt includes one kind or two or more kind
of light metal salts such as lithium salt. Examples of the lithium
salt include lithium hexafluorophosphate (LiPF.sub.6), lithium
perchlorate (LiClO.sub.4), lithium hexafluoroarsenate (LiAsF.sub.6)
and the like. It is because superior capacity characteristics,
storage characteristics and cycle characteristics are obtained.
Only one kind or a mixture of a plurality of kinds selected from
them may be used. Among them, as the electrolyte salt, lithium
hexafluorophosphate is preferable, because internal resistance is
reduced, so a higher effect is obtained.
[0102] Moreover, the electrolyte salt preferably includes a
compound including boron and fluorine, because cycle
characteristics are improved, and swelling of the secondary battery
is prevented. Examples of the compound including boron and fluorine
include lithium tetrafluoroborate and the like.
[0103] The content of the electrolyte salt in the solvent is, for
example, within a range from 0.3 mol/kg to 3.0 mol/kg both
inclusive, because superior capacity characteristics are
obtained.
[0104] The secondary battery is manufactured by the following
steps, for example.
[0105] At first, the cathode 21 is formed. At first, after the
cathode active material, a binder and an electrical conductor are
mixed to form a cathode mixture, the cathode mixture is dispersed
in an organic solvent to form a paste-form cathode mixture slurry.
Next, the cathode mixture slurry is uniformly applied to both sides
of the cathode current collector 21A through the use of a doctor
blade, a bar coater or the like, and the cathode mixture slurry is
dried. Finally, the cathode mixture slurry is compression molded by
a roller press while applying heat, if necessary, thereby the
cathode active material layer 21B is formed. In this case,
compression molding may be repeated a plurality of times.
[0106] Next, the anode active material layer 22B is formed on both
sides of the anode current collector 22A by the same steps as the
above-described steps of forming the anode so as to form the anode
22.
[0107] Then, the battery element 20 is formed through the use of
the cathode 21 and the anode 22. At first, the cathode lead 24 and
the anode lead 25 are attached to the cathode current collector 21A
and the anode current collector 22A, respectively. Next, the
cathode 21 and the anode 22 are laminated with the separator 23 in
between to form a laminate, and the laminate are spirally wound in
a longitudinal direction. Finally, the laminate is molded into a
flat shape to form the battery element 20.
[0108] Finally, the secondary battery is assembled. At first, after
the battery element 20 is contained in the battery can 11, the
insulating plate 12 is arranged on the battery element 20. Next,
after the cathode lead 24 and the anode lead 25 are connected to
the cathode pin 15 and the battery can 11, respectively, by welding
or the like, the battery cover 13 is fixed in an open end of the
battery can 11 by laser welding or the like. Finally, the
electrolytic solution is injected into the battery can 11 through
the injection hole 19 so that the separator 23 is impregnated with
the electrolytic solution, and then the injection hole 19 is filled
with the sealing member 19A. Thereby, the secondary battery shown
in FIGS. 5 and 6 is completed.
[0109] When the secondary battery is charged, for example, lithium
ions are extracted from the cathode 21, and are inserted into the
anode 22 through the electrolytic solution with which the separator
23 is impregnated. On the other hand, when the secondary battery is
discharged, the lithium ions are extracted from the anode 22 and
are inserted into the cathode 21 through the electrolytic solution
with which the separator 23 is impregnated.
[0110] In the prismatic secondary battery, the anode 22 has the
same configuration as that of the above-described anode, so even if
charge and discharge are repeated, the discharge capacity does not
easily decline. Therefore, the cycle characteristics may be
improved. In this case, in the case where the anode 22 includes
silicon which is advantageous to increase a capacity, the cycle
characteristics are improved, so a higher effect than that in the
case where the anode includes another anode material such as a
carbon material may be obtained. The effects of the secondary
battery except for the above-described effects are the same as
those of the above-described anode.
[0111] In particular, in the case where the battery can 11 is made
of a hard metal, compared to the case where the battery can 11 is
made of a soft film, the anode 22 is resistant to damage due to
swelling and shrinkage of the anode active material layer 22B.
Therefore, the cycle characteristics may be improved. In this case,
when the battery can 11 is made of iron which is harder than
aluminum, a higher effect may be obtained.
(Second Secondary Battery)
[0112] FIGS. 7 and 8 show sectional views of a second secondary
battery, and FIG. 8 shows an enlarged view of a part of a spirally
wound electrode body 40 shown in FIG. 7. The secondary battery is a
lithium-ion secondary battery as in the case of the first secondary
battery, and includes the spirally wound electrode body 40 which
includes a cathode 41 and an anode 42 spirally wound with a
separator 43 in between, and a pair of insulating plates 32 and 33
in a substantially hollow cylindrical-shaped battery can 31. The
battery configuration including the battery can 31 is called a
so-called cylindrical type.
[0113] The battery can 31 is made of, the same metal material as
that of the battery can 11 in the first secondary battery, and an
end of the battery can 31 is closed, and the other end thereof is
opened. The spirally wound electrode body 40 is sandwiched between
the pair of insulating plates 32 and 33, and the pair of insulating
plates 32 and 33 are arranged so as to extend in a direction
perpendicular to a peripheral winding surface.
[0114] In the open end of the battery can 31, a battery cover 34,
and a safety valve mechanism 35 and a positive temperature
coefficient device (PTC device) 36 arranged inside the battery
cover 34 are mounted by caulking by a gasket 37. Thereby, the
interior of the battery can 31 is sealed. The battery cover 34 is
made of, for example, the same material as that of the battery can
31. The safety valve mechanism 35 is electrically connected to the
battery cover 34 through the PTC device 36. In the safety valve
mechanism 35, when an internal pressure in the secondary battery
increases to a certain extent or higher due to an internal short
circuit or external application of heat, a disk plate 35A is
flipped so as to disconnect the electrical connection between the
battery cover 34 and the spirally wound electrode body 40. When a
temperature rises, the PTC device 36 limits a current by an
increased resistance to prevent abnormal heat generation caused by
a large current. The gasket 37 is made of, for example, an
insulating material, and its surface is coated with asphalt.
[0115] For example, a center pin 44 may be inserted into the center
of the spirally wound electrode body 40. In the spirally wound
electrode body 40, a cathode lead 45 made of aluminum or the like
is connected to the cathode 41, and an anode lead 46 made of nickel
or the like is connected to the anode 42. The cathode lead 45 is
welded to the safety valve mechanism 35 so as to be electrically
connected to the battery cover 34, and the anode lead 46 is welded
and electrically connected to the battery can 31.
[0116] The cathode 41 is formed by arranging a cathode active
material layer 41B on both sides of a strip-shaped cathode current
collector 41A. The anode 42 has the same configuration as that of
the above-described anode, and is formed, for example, by arranging
an anode active material layer 42B on both sides of a strip-shaped
anode current collector 42A. The configurations of the cathode
current collector 41A, the cathode active material layer 41B, the
anode current collector 42A, the anode active material layer 42B
and the separator 43, and the composition of the electrolytic
solution are the same as the configurations of the cathode current
collector 21A, the cathode active material layer 21B, the anode
current collector 22A, the anode active material layer 22B and the
separator 23, and the composition of the electrolytic solution in
the first secondary battery, respectively.
[0117] The secondary battery is manufactured by the following
steps, for example.
[0118] At first, the cathode 41 in which the cathode active
material layer 41B is arranged on both sides of the cathode current
collector 41A, and the anode 42 in which the anode active material
layer 42B is arranged on both sides of the anode current collector
42A are formed by the same steps as the above-described steps of
forming the cathode 21 and the anode 22 in the first secondary
battery. Next, the cathode lead 45 is attached to the cathode 41,
and the anode lead 46 is attached to the anode 42. Then, the
cathode 41 and the anode 42 are spirally wound with the separator
43 in between to form the spirally wound electrode body 40, and an
end of the cathode lead 45 is welded to the safety valve mechanism
35, and an end of the anode lead 46 is welded to eth battery can
31, and then the spirally wound electrode body 40 sandwiched
between the pair of insulating plates 32 and 33 is contained in the
battery can 31. Next, the electrolytic solution is injected into
the battery can 31 so that the separator 43 is impregnated with the
electrolytic solution. Finally, the battery cover 34, the safety
valve mechanism 35 and the PTC device 36 are fixed in an open end
of the battery can 31 by caulking by the gasket 37. Thereby, the
secondary battery shown in FIGS. 7 and 8 is completed.
[0119] When the secondary battery is charged, for example, lithium
ions are extracted from the cathode 41, and are inserted into the
anode 42 through the electrolytic solution. On the other hand, when
the secondary battery is discharged, for example, the lithium ions
are extracted from the anode 42 and are inserted into the cathode
41 through the electrolytic solution.
[0120] In the cylindrical secondary battery, the anode 42 has the
same configuration as that of the above-described anode, so the
cycle characteristics may be improved. The effects of the secondary
battery except for the above-described effects are the same as
those of the first secondary battery.
(Third Secondary Battery)
[0121] FIG. 9 shows an exploded perspective view of a third
secondary battery, and FIG. 10 shows an enlarged sectional view
taken along a line X-X of FIG. 9. In the secondary battery, a
spirally wound electrode body 50 to which a cathode lead 51 and an
anode lead 52 are attached is contained in film-shaped package
members 60, and the configuration of the battery including the
package members 60 is a so-called laminate film type.
[0122] The cathode lead 51 and the anode lead 52 are drawn, for
example, from the interiors of the package members 60 to outside in
the same direction. The cathode lead 51 is made of, for example, a
metal material such as aluminum, and the anode lead 52 are made of,
for example, a metal material such as copper, nickel or stainless.
The metal materials of which the cathode lead 51 and the anode lead
52 are made each have a sheet shape or a mesh shape.
[0123] The package members 60 are made of, for example, an aluminum
laminate film including a nylon film, aluminum foil and a
polyethylene film which are bonded in this order. The package
members 60 are arranged so that the polyethylene film of each of
the package members 60 faces the spirally wound electrode body 50,
and edge portions of two rectangular aluminum laminate films are
adhered to each other by fusion bonding or an adhesive.
[0124] An adhesive film 61 is inserted between the package members
60 and the cathode lead 51 and the anode lead 52 for preventing the
entry of outside air. The adhesive film 61 is made of, for example,
a material having adhesion to the cathode lead 51 and the anode
lead 52, for example, a polyolefin resin such as polyethylene,
polypropylene, modified polyethylene or modified polypropylene.
[0125] In addition, the package members 60 may be made of a
laminate film with any other configuration, a polymer film such as
polypropylene or a metal film instead of the above-described
aluminum laminate film.
[0126] The spirally wound electrode body 50 is formed by laminating
a cathode 53 and an anode 54 with a separator 55 and an electrolyte
56 in between, and then spirally winding them, and an outermost
portion of the spirally wound electrode body 50 is protected with a
protective tape 57.
[0127] The cathode 53 is formed by arranging a cathode active
material layer 53B on both sides of a cathode current collector 53A
having a pair of surfaces. The anode 54 has the same configuration
as that of the above-described anode, and the anode 54 is formed by
arranging an anode active material layer 54B on both sides of a
strip-shaped anode current collector 54A. The configurations of the
cathode current collector 53A, the cathode active material layer
53B, the anode current collector 54A, the anode active material
layer 54B and the separator 55 are the same as those of the cathode
current collector 21A, the cathode active material layer 21B, the
anode current collector 22A, the anode active material layer 22B
and the separator 23 in the first secondary battery.
[0128] The electrolyte 56 includes an electrolytic solution and a
polymer compound holding the electrolytic solution, and is a
so-called gel electrolyte. The gel electrolyte is preferable,
because the gel electrolyte is capable of obtaining high ionic
conductivity (for example, 1 mS/cm or over at room temperature),
and leakage of an electrolyte from the secondary battery is
prevented. The electrolyte 56 is arranged, for example, between the
cathode 53 and the separator 55 and between the anode 54 and the
separator 55.
[0129] Examples of the polymer compound include polyacrylonitrile,
polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and
polyhexafluoropyrene, polytetrafluoroethylene,
polyhexafluoropropylene, polyethylene oxide, polypropylene oxide,
polyphosphazene, polysiloxane, polyvinyl acetate, polyvinyl
alcohol, polymethyl methacrylate, polyacrylic acids,
polymethacrylic acids, styrene-butadiene rubber, nitrile-butadiene
rubber, polystyrene, polycarbonate and the like. Only one kind or a
mixture of a plurality of kinds selected from them may be used.
Among them, as the polymer compound, polyacrylonitrile,
polyvinylidene fluoride, polyhexafluoropropylene or polyethylene
oxide is preferable, because they are electrochemically stable.
[0130] The composition of the electrolytic solution is the same as
the composition of the electrolytic solution in the first secondary
battery. However, the solvent in this case means a wide concept
including not only a liquid solvent but also a solvent having ionic
conductivity capable of dissociating the electrolyte salt.
Therefore, in the case where a polymer compound having ionic
conductivity is used, the polymer compound is included in the
concept of the solvent.
[0131] In addition, instead of the gel electrolyte 56 in which the
polymer compound holds the electrolytic solution, the electrolytic
solution may be used as it is. In this case, the separator 55 is
impregnated with the electrolytic solution.
[0132] The secondary battery including the gel electrolyte 56 is
manufactured by the following steps, for example.
[0133] At first, the cathode 53 in which the cathode active
material layer 53B is arranged on both sides of the cathode current
collector 53A and the anode 54 in which the anode active material
layer 54B is arranged on both sides of the anode current collector
54A are formed by the same steps as the above-described steps of
forming the cathode 21 and the anode 22 in the first secondary
battery. Next, the gel electrolyte 56 is formed by preparing a
precursor solution including the electrolytic solution, the polymer
compound and a solvent, applying the precursor solution to the
cathode 53 and the anode 54, and volatilizing the solvent. Next,
the cathode lead 51 and the anode lead 52 are attached to the
cathode current collector 53A and the anode current collector 54A,
respectively. Next, after the cathode 53 on which the electrolyte
56 is formed and the anode 54 on which the electrolyte 56 is formed
are laminated with the separator 55 in between to form a laminate,
the laminate is spirally wound in a longitudinal direction, and the
protective tape 57 is bonded to an outermost portion of the
laminate so as to form the spirally wound electrode body 50. Then,
for example, the spirally wound electrode body 50 is sandwiched
between the package members 60, and edge portions of the package
members 60 are adhered to each other by thermal fusion bonding or
the like to seal the spirally wound electrode body 50 in the
package members 60. At this time, the adhesive film 61 is inserted
between the cathode lead 51 and the anode lead 52, and the package
members 60. Thereby, the secondary battery shown in FIGS. 9 and 10
is completed.
[0134] The above-described secondary battery may be manufactured by
the following steps. At first, after the cathode lead 51 and the
anode lead 52 are attached to the cathode 53 and the anode 54,
respectively, the cathode 53 and the anode 54 are laminated with
the separator 55 in between to form a laminate, and the laminate is
spirally wound, and the protective tape 57 is bonded to an
outermost portion of the spirally wound laminate so as to form a
spirally wound body as a precursor body of the spirally wound
electrode body 50. Next, the spirally wound body is sandwiched
between the package members 60, and the edge portions of the
package members 60 except for edge portions on one side are adhered
by thermal fusion bonding or the like to form a pouched package,
thereby the spirally wound body is contained in the package members
60. An electrolytic composition which includes the electrolytic
solution, monomers as materials of a polymer compound and a
polymerization initiator and, if necessary, any other material such
as a polymerization inhibitor is prepared, and the electrolytic
composition is injected into the package members 60, and then an
opened portion of the package members 60 are sealed by thermal
fusion bonding or the like. Finally, the monomers are polymerized
by applying heat to form the polymer compound, thereby the gel
electrolyte 56 is formed. Thus, the secondary battery shown in
FIGS. 9 and 10 is completed.
[0135] In the laminate film type secondary battery, the anode 54
has the same configuration as that of the above-described anode, so
the cycle characteristics may be improved. The effects of the
secondary battery except for the above-described effects are the
same as those of the first secondary battery.
EXAMPLES
[0136] Examples of the invention will be described in detail
below.
Example 1-1
[0137] A laminate film type secondary battery shown in FIGS. 9 and
10 was manufactured by the following steps. At that time, the
laminate film type secondary battery was a lithium-ion secondary
battery in which the capacity of the anode 54 is represented based
on insertion and extraction of lithium.
[0138] At first, the cathode 53 was formed. After lithium carbonate
(Li.sub.2CO.sub.3) and cobalt carbonate (CoCO.sub.3) were mixed at
a molar ratio of 0.5:1, the mixture was fired in air at 900.degree.
C. for 5 hours to obtain a lithium-cobalt complex oxide
(LiCoO.sub.2). Next, after 91 parts by weight of the lithium-cobalt
complex oxide as a cathode active material, 6 parts by weight of
graphite as an electrical conductor and 3 parts by weight of
polyvinylidene fluoride as a binder were mixed to form a cathode
mixture, the cathode mixture was dispersed in
N-methyl-2-pyrrolidone to form paste-form cathode mixture slurry.
Finally, after the cathode mixture slurry was uniformly applied to
both sides of the cathode current collector 53A made of
strip-shaped aluminum foil (with a thickness of 12 .mu.m), and was
dried, the cathode mixture slurry was compression molded by a
roller press to form the cathode active material layer 53B.
[0139] Next, the anode 54 was formed. At first, after the anode
current collector 54A made of electrolytic copper foil (with a
thickness of 18 .mu.m and a ten-point height of roughness profile
Rz of 3.5 .mu.m) was prepared, silicon was deposited on both sides
of the anode current collector 54A by an electron beam evaporation
method using a deflection electron beam evaporation source while
continuously introducing an oxygen gas and, if necessary, water
vapor into a chamber, thereby a plurality of anode active material
particles were formed so as to have a single-layer configuration
(with a thickness of 5.8 .mu.m). At that time, as the evaporation
source, silicon with a purity of 99% was used, and the deposition
rate was 10 nm/s, and the oxygen content in the anode active
material particles was 3 at %. Finally, silicon oxide (SiO.sub.2)
was deposited by a liquid-phase deposition method to form an
oxide-containing film, thereby the anode active material layer 54B
was formed. In the case where the oxide-containing film was formed,
after a dissolved species easily coordinating fluorine as an anion
trapping agent was added to and mixed with a solution of a fluoride
complex of silicon to form a mixture, the anode current collector
54A on which the anode active material was formed was immersed in
the mixture, and a fluorine anion generated from the fluoride
complex is trapped by the dissolved species, thereby an oxide was
deposited on the surface of the anode active material. At that
time, the deposition time of the oxide (the amount of the
oxide-containing film intruded into small pores) was adjusted so
that the volumetric capacity of the small pore group per unit
weight of silicon was 0.2 cm.sup.3/g. The volumetric capacity of
the small pore group per unit weight of silicon was determined by a
value (the weight of silicon as the anode active material)
determined by subtracting the weight of the anode current collector
54A from the total weight of the anode current collector 54A on
which the anode active material was formed, and the value (the
volumetric capacity of the small pore group) of the amount of
mercury intruded into pores with a diameter ranging from 3 nm to 50
nm both inclusive which was measured by a mercury porosimeter of
Micromeritics (AutoPore 9500 series).
[0140] Next, the cathode lead 51 made of aluminum was attached to
an end of the cathode current collector 53A by welding, and the
anode lead 52 made of nickel was attached to an end of the anode
current collector 54A by welding. Then, after the cathode 53, a
three-layer configuration polymer separator 55 (with a thickness of
23 .mu.m) formed by sandwiching a film made of porous polyethylene
as a main component between films made of porous polypropylene as a
main component, the anode 54, and the above-described polymer
separator 55 were laminated in this order to form a laminate, and
the laminate was spirally wound in a longitudinal direction, an
outermost portion of the laminate was fixed by the protective tape
57 made of an adhesive tape to form a spirally wound body as a
precursor body of the spirally wound electrode body 50. Next, after
the spirally wound body was sandwiched between package members 60
made of a laminate film (with a total thickness of 100 .mu.m) with
a three-layer configuration formed by laminating nylon (with a
thickness of 30 .mu.m), aluminum (with a thickness of 40 .mu.m) and
cast polypropylene (with a thickness of 30 .mu.m) in order from
outside, the edge portions of the package members 60 except for
edge portions on one side were adhered by thermal fusion bonding to
form a pouched package, thereby the spirally wound body was
contained in the package members 60. Next, the electrolytic
solution was injected into the package members 60 from an opened
portion of the package members 60, and the separator 55 was
impregnated with the electrolytic solution, thereby the spirally
wound electrode body 50 was formed.
[0141] To form the electrolytic solution, a mixture solvent formed
by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) was
used as the solvent, and lithium hexafluorophosphate (LiPF.sub.6)
was used as the electrolyte salt. At that time, the composition of
the mixture solvent (EC:DEC) had a weight ratio of 50:50, and the
concentration of the electrolyte salt was 1 mol/kg.
[0142] Finally, the opened portion of the package members 60 were
sealed by thermal fusion bonding in a vacuum atmosphere, thereby a
laminate film type secondary battery was completed. In the
secondary battery, the thickness of the cathode active material
layer 53B was adjusted so that the charge-discharge capacity of the
anode 54 was larger than the charge-discharge capacity of the
cathode 53, thereby the deposition of lithium metal on the anode 54
when the secondary battery was fully charged was prevented.
Examples 1-2 to 1-14
[0143] Secondary batteries were formed by the same steps as those
in Example 1-1, except that instead of 0.2 cm.sup.3/g, the
volumetric capacity of the small pore group per unit weight of
silicon was 0.1 cm.sup.3/g (Example 1-2), 0.09 cm.sup.3/g (Example
1-3), 0.08 cm.sup.3/g (Example 1-4), 0.07 cm.sup.3/g (Example 1-5),
0.06 cm.sup.3/g (Example 1-6), 0.05 cm.sup.3/g (Example 1-7), 0.04
cm.sup.3/g (Example 1-8), 0.03 cm.sup.3/g (Example 1-9), 0.02
cm.sup.3/g (Example 1-10), 0.01 cm.sup.3/g (Example 1-11), 0.005
cm.sup.3/g (Example 1-12), 0.001 cm.sup.3/g (Example 1-13), or 0
cm.sup.3/g (Example 1-14).
Comparative Example 1-1
[0144] A secondary battery was formed by the same steps as those in
Example 1-1, except that the oxide-containing film was not formed.
In this case, the volumetric capacity of the small pore group per
unit weight of silicon was 0.4 cm.sup.3/g.
Comparative Examples 1-2, 1-3
[0145] Secondary batteries were formed by the same steps as those
in Example 1-1, except that the volumetric capacity of the small
pore group per unit weight of silicon was 0.35 cm.sup.3/g
(Comparative Example 1-2) or 0.3 cm.sup.3/g (Comparative Example
1-3).
[0146] When the cycle characteristics of the secondary batteries of
Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-3 were
determined, results shown in Table 1 and FIG. 11 were obtained.
[0147] To determine the cycle characteristics, a cycle test was
performed by the following steps to determine the discharge
capacity retention ratio of each of the secondary batteries. At
first, to stabilize the battery state of the secondary battery,
after one cycle of charge and discharge was performed on the
secondary battery in an atmosphere of 23.degree. C., the secondary
battery was charged and discharged again to determine the discharge
capacity in the second cycle. Next, 99 cycles of charge and
discharge were performed on the secondary battery in the same
atmosphere to determine the discharge capacity in the 101st cycle.
Finally, the discharge capacity retention ratio (%)=(discharge
capacity in the 101st cycle/discharge capacity in the second
cycle).times.100 was determined by calculation. As the condition of
charge, after the secondary battery was charged at a constant
current density of 3 mA/cm.sup.2 until the battery voltage reached
4.2 V, the secondary battery was charged at a constant voltage of
4.2 V until the current density reached 0.3 mA/cm.sup.2. Moreover,
as the condition of discharge, the secondary battery was discharged
at a constant current density of 3 mA/cm.sup.2 until the battery
voltage reached 2.5 V.
[0148] In addition, the same steps and the same conditions as the
above-described steps and the above-described conditions were used
to determine the cycle characteristics of secondary batteries of
the following examples and the following comparative examples.
TABLE-US-00001 TABLE 1 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
DISCHARGE MATERIAL OXIDE-CONTAINING CAPACITY LAYER FILM VOLUMETRIC
RETENTION NUMBER FORMING CAPACITY RATIO (LAYER) KIND METHOD
(cm.sup.3/g) (%) EXAMPLE 1-1 1 SiO.sub.2 LIQUID-PHASE 0.2 80.3
EXAMPLE 1-2 DEPOSITION 0.1 80.6 EXAMPLE 1-3 0.09 82.5 EXAMPLE 1-4
0.08 84.2 EXAMPLE 1-5 0.07 85.5 EXAMPLE 1-6 0.06 86.2 EXAMPLE 1-7
0.05 87 EXAMPLE 1-8 0.04 87.4 EXAMPLE 1-9 0.03 88.5 EXAMPLE 1-10
0.02 89 EXAMPLE 1-11 0.01 90 EXAMPLE 1-12 0.005 90.1 EXAMPLE 1-13
0.001 90.5 EXAMPLE 1-14 0 91 COMPARATIVE 1 -- -- 0.4 25 EXAMPLE 1-1
COMPARATIVE SiO.sub.2 LIQUID-PHASE 0.35 31 EXAMPLE 1-2 DEPOSITION
COMPARATIVE 0.3 54 EXAMPLE 1-3
[0149] As shown in Table 1 and FIG. 11, in the case where silicon
oxide was formed as the oxide-containing film by a liquid-phase
deposition method, the smaller the volumetric capacity of the small
pore group per unit weight of silicon was, the higher the discharge
capacity retention ratio became. The result indicated that when the
oxide-containing film was intruded into pores, the surface area of
the anode active material was reduced, so the electrolytic solution
was resistant to decomposition during charge and discharge. In this
case, in Examples 1-1 to 1-14 in which the volumetric capacity was
0.2 cm.sup.3/g or less, the discharge capacity retention ratio was
much higher than that in Comparative Examples 1-1 to 1-3 in which
the volumetric capacity was out of the range. In particular, when
the volumetric capacity was 0.05 cm.sup.3/g or less, the discharge
capacity retention ratio was higher, and when the volumetric
capacity was 0 cm.sup.3/g, the discharge capacity retention ratio
was at maximum. Therefore, it was confirmed that in the secondary
battery according to the embodiment of the invention, in the case
where the oxide-containing film was formed together with the anode
active material including silicon, when the volumetric capacity of
the small pore group per unit weight of silicon was 0.2 cm.sup.3/g
or less, the cycle characteristics were improved. In this case, it
was confirmed that when the volumetric capacity was 0.05 cm.sup.3/g
or less, or more specifically 0 cm.sup.3/g, a higher effect was
obtained.
Examples 2-1 to 2-9
[0150] Secondary batteries were formed by the same steps as those
in Examples 1-1, 1-2, 1-4, 1-7 and 1-10 to 1-14, except that while
the anode current collector 54A was moved back and forth relatively
to an evaporation source, silicon was deposited six times to be
laminated, thereby the anode active material had a six-layer
configuration. At that time, the deposition rate was 100 nm/s.
Comparative Example 2
[0151] A secondary battery was formed by the same steps as those in
Comparative Example 1-3, except that as in the case of Examples 2-1
to 2-9, the anode active material had a six-layer
configuration.
[0152] When the cycle characteristics of the secondary batteries of
Examples 2-1 to 2-9 and Comparative Example 2 were determined,
results shown in Table 2 and FIG. 12 were obtained.
TABLE-US-00002 TABLE 2 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
DISCHARGE MATERIAL OXIDE-CONTAINING CAPACITY LAYER FILM VOLUMETRIC
RETENTION NUMBER FORMING CAPACITY RATIO (LAYER) KIND METHOD
(cm.sup.3/g) (%) EXAMPLE 2-1 6 SiO.sub.2 LIQUID-PHASE 0.2 82
EXAMPLE 2-2 DEPOSITION 0.1 82.1 EXAMPLE 2-3 0.08 85.9 EXAMPLE 2-4
0.05 88.2 EXAMPLE 2-5 0.02 90.9 EXAMPLE 2-6 0.01 91.1 EXAMPLE 2-7
0.005 91.9 EXAMPLE 2-8 0.001 92.1 EXAMPLE 2-9 0 92.3 COMPARATIVE 6
SiO.sub.2 LIQUID-PHASE 0.3 51 EXAMPLE 2 DEPOSITION
[0153] As shown in Table 2 and FIG. 12, in Examples 2-1 to 2-9 in
which the anode active material had a six-layer configuration, the
same results as those in Examples 1-1 to 1-14 in which the anode
active material had a single-layer configuration were obtained.
More specifically, in Examples 2-1 to 2-9 in which the volumetric
capacity of the small pore group per unit weight of silicon was 0.2
cm.sup.3/g or less, the discharge capacity retention ratio was much
higher than that in Comparative Example 2 in which the volumetric
capacity was out of the range, and when the volumetric capacity was
0.05 cm.sup.3/g or less, or more specifically 0 cm.sup.3/g, the
discharge capacity retention ratio become higher. Therefore, it was
confirmed that in the secondary battery according to the embodiment
of the invention, even if the number of layers of the anode active
material was changed, the cycle characteristics were improved.
Examples 3-1 to 3-6
[0154] Secondary batteries were formed by the same steps as those
in Examples 2-1, 2-2, 2-4, 2-5, 2-7 and 2-9, except that instead of
the solution of the fluoride complex of silicon, a solution of a
fluoride complex of germanium was used, and instead of silicon
oxide, germanium oxide (GeO.sub.2) was formed as the
oxide-containing film.
Comparative Example 3
[0155] A secondary battery was formed by the same steps as those in
Comparative Example 2, except that as in the case of Examples 3-1
to 3-6, germanium oxide was formed as the oxide-containing
film.
Examples 4-1 to 4-6
[0156] Secondary batteries were formed by the same steps as those
in Examples 2-1, 2-2, 2-4, 2-5, 2-7 and 2-9, except that instead of
the solution of the fluoride complex of silicon, a solution of a
fluoride complex of tin was used, and instead of silicon oxide, tin
oxide (SnO.sub.2) was formed as the oxide-containing film.
Comparative Example 4
[0157] A secondary battery was formed by the same steps as those in
Comparative Example 2, except that as in the case of Examples 4-1
to 4-6, tin oxide was formed as the oxide-containing film.
[0158] When the cycle characteristics of the secondary batteries of
Examples 3-1 to 3-6 and 4-1 to 5-6 and Comparative Examples 3 and 4
were determined, results shown in Tables 3 and 4 were obtained.
TABLE-US-00003 TABLE 3 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
OXIDE-CONTAINING DISCHARGE MATERIAL FILM VOLUMETRIC CAPACITY LAYER
FORMING CAPACITY RETENTION NUMBER (LAYER) KIND METHOD (cm.sup.3/g)
RATIO (%) EXAMPLE 3-1 6 GeO.sub.2 LIQUID-PHASE 0.2 80.1 EXAMPLE 3-2
DEPOSITION 0.1 80.5 EXAMPLE 3-3 0.05 84.6 EXAMPLE 3-4 0.02 86.1
EXAMPLE 3-5 0.005 88.5 EXAMPLE 3-6 0 88.9 COMPARATIVE 6 GeO.sub.2
LIQUID-PHASE 0.3 49.4 EXAMPLE 3 DEPOSITION
TABLE-US-00004 TABLE 4 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
OXIDE-CONTAINING DISCHARGE MATERIAL FILM VOLUMETRIC CAPACITY LAYER
FORMING CAPACITY RETENTION NUMBER (LAYER) KIND METHOD (cm.sup.3/g)
RATIO (%) EXAMPLE 4-1 6 SnO.sub.2 LIQUID-PHASE 0.2 80 EXAMPLE 4-2
DEPOSITION 0.1 80.2 EXAMPLE 4-3 0.05 84.2 EXAMPLE 4-4 0.02 85.9
EXAMPLE 4-5 0.005 88 EXAMPLE 4-6 0 88.6 COMPARATIVE 6 SnO.sub.2
LIQUID-PHASE 0.3 49.1 EXAMPLE 4 DEPOSITION
[0159] As shown in Tables 3 and 4, in Examples 3-1 to 3-6 and 4-1
to 4-6 in which germanium oxide or tin oxide was formed by a
liquid-phase deposition method as the oxide-containing film, the
same results as those in Examples 1-1 to 1-14 were obtained. More
specifically, in Examples 3-1 to 3-6 and 4-1 to 4-6 in which the
volumetric capacity of the small pore group per unit weight of
silicon was 0.2 cm.sup.3/g or less, the discharge capacity
retention ratio was much higher than that in Comparative Examples 3
and 4 in which the volumetric capacity was out of the range, and
when the volumetric capacity was 0.05 cm.sup.3/g or less, or more
specifically 0 cm.sup.3/g, the discharge capacity retention ratio
became higher. In this case, there was a tendency that in the case
where the silicon oxide was formed, the discharge capacity
retention ratio became higher. Therefore, it was confirmed that in
the secondary battery according to the embodiment of the invention,
even if the kind of the oxide-containing film was changed, the
cycle characteristics were improved, and when the silicon oxide was
used, a higher effect was obtained.
Examples 5-1 to 5-3
[0160] Secondary batteries were formed the same steps as those in
Example 2-5, except that instead of the liquid-phase deposition
method, a sol-gel method (Example 5-1), a coating method (Example
5-2) or a dip coating method (Example 5-3) was used as the method
of forming the oxide-containing film.
[0161] When the secondary batteries of Examples 5-1 to 5-3 were
determined, results shown in Table 5 were obtained. In Table 5, the
results of Example 2-5 and Comparative Example 2 are also
shown.
TABLE-US-00005 TABLE 5 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
OXIDE-CONTAINING DISCHARGE MATERIAL FILM VOLUMETRIC CAPACITY LAYER
FORMING CAPACITY RETENTION NUMBER (LAYER) KIND METHOD (cm.sup.3/g)
RATIO (%) EXAMPLE 2-5 6 SiO.sub.2 LIQUID-PHASE 0.02 90.9 DEPOSITION
EXAMPLE 5-1 SOL-GEL 89.1 EXAMPLE 5-2 COATING 88.2 EXAMPLE 5-3 DIP
COATING 86.5 COMPARATIVE 6 SiO.sub.2 LIQUID-PHASE 0.3 51 EXAMPLE 2
DEPOSITION
[0162] As shown in Table 5, in Examples 5-1 to 5-3 in which the
oxide-containing film was formed by a sol-gel method or the like,
as in the case of Example 2-5 in which the oxide-containing film
was formed by a liquid-phase deposition method, the discharge
capacity retention ratio was much higher than that in Comparative
Example 2. In this case, there was a tendency that in the case
where the liquid-phase deposition method was used, the discharge
capacity retention ratio became higher. Therefore, it was confirmed
that in the secondary battery according to the embodiment of the
invention, even if the method of forming the oxide-containing film
was changed, the cycle characteristics were improved, and when the
liquid-phase deposition method was used, a higher effect was
obtained.
Example 6-1
[0163] A secondary battery was formed by the same steps as those in
Examples 2-1 to 2-9, except that after the anode active material
was formed, instead of the oxide-containing film, a metal material
not alloyed with lithium was formed. In the case where the metal
material was formed, while air was supplied to a plating bath,
cobalt was deposited on both sides of the anode current collector
54A by an electrolytic plating method. At that time, a cobalt
plating solution of Japan Pure Chemical Co., Ltd. was used as a
plating solution, and the current density was 2 A/dm.sup.2 to 5
A/dm.sup.2, and the plating rate was 10 nm/s. Moreover, the plating
time was adjusted so that the volumetric capacity of the small pore
group per unit weight of silicon was 0.2 cm.sup.3/g.
Examples 6-2 to 6-6
[0164] Secondary batteries were formed by the same steps as those
in Example 6-1, except that instead of 0.2 cm.sup.3/g, the
volumetric capacity of the small pore group per unit weight of
silicon was 0.1 cm.sup.3/g (Example 6-2), 0.05 cm.sup.3/g (Example
6-3), 0.02 cm.sup.3/g (Example 6-4), 0.005 cm.sup.3/g (Example 6-5)
or 0 cm.sup.3/g (Example 6-6).
Comparative Example 6
[0165] A secondary battery was formed by the same steps as those in
Comparative Example 2, except that as in the case of Example 6-1,
the metal material was formed.
[0166] When the cycle characteristics of the secondary batteries of
Examples 6-1 to 6-6 and Comparative Example 6 were determined,
results shown in Table 6 were obtained.
TABLE-US-00006 TABLE 6 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
METAL DISCHARGE MATERIAL MATERIAL VOLUMETRIC CAPACITY LAYER FORMING
CAPACITY RETENTION NUMBER (LAYER) KIND METHOD (cm.sup.3/g) RATIO
(%) EXAMPLE 6-1 6 Co ELECTROLYTIC 0.2 80 EXAMPLE 6-2 PLATING 0.1
80.2 EXAMPLE 6-3 0.05 85.2 EXAMPLE 6-4 0.02 88.1 EXAMPLE 6-5 0.005
89.8 EXAMPLE 6-6 0 90.2 COMPARATIVE 6 Co ELECTROLYTIC 0.3 54
EXAMPLE 6 PLATING
[0167] As shown in Table 6, in the case where cobalt was formed as
the metal material by the electrolytic plating method, the same
results as those in Examples 2-1 to 2-9 in which the
oxide-containing film was formed were obtained. More specifically,
in Examples 6-1 to 6-6 in which the volumetric capacity of the
small pore group per unit weight of silicon was 0.2 cm.sup.3/g or
less, the discharge capacity retention ratio was much higher than
that in Comparative Example 6 in which the volumetric capacity was
out of the range, and when the volumetric capacity was 0.05
cm.sup.3/g or less, or more specifically 0 cm.sup.3/g, the
discharge capacity retention ratio became higher. Therefore, it was
confirmed that in the secondary battery according to the embodiment
of the invention, in the case where the metal material was formed
together with the anode active material including silicon, when the
volumetric capacity of the small pore group per unit weight of
silicon was 0.2 cm.sup.3/g or less, the cycle characteristics were
improved, and when the volumetric capacity was 0.05 cm.sup.3/g or
less, or more specifically 0 cm.sup.3/g, a higher effect was
obtained.
Examples 7-1 to 7-6
[0168] Secondary batteries were formed by the same steps as those
in Examples 6-1 to 6-6, except that instead of the electrolytic
plating method, the metal material was formed by an electroless
plating method. At that time, as the plating solution, an
electroless cobalt plating solution of Japan Pure Chemical Co.,
Ltd. was used, and the plating time was 60 minutes.
Comparative Example 7
[0169] A secondary battery was formed by the same steps as those in
Comparative Example 2, except that as in the case of Examples 7-1
to 7-6, the metal material was formed by an electroless plating
method.
[0170] When the cycle characteristics of the secondary batteries of
Examples 7-1 to 7-6 and Comparative Example 7 were determined,
results shown in Table 7 were obtained.
TABLE-US-00007 TABLE 7 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
METAL DISCHARGE MATERIAL MATERIAL VOLUMETRIC CAPACITY LAYER FORMING
CAPACITY RETENTION NUMBER (LAYER) KIND METHOD (cm.sup.3/g) RATIO
(%) EXAMPLE 7-1 6 Co ELECTROLESS 0.2 79.8 EXAMPLE 7-2 PLATING 0.1
80 EXAMPLE 7-3 0.05 84.8 EXAMPLE 7-4 0.02 87 EXAMPLE 7-5 0.005 88.5
EXAMPLE 7-6 0 88.9 COMPARATIVE 6 Co ELECTROLESS 0.3 50 EXAMPLE 7
PLATING
[0171] As shown in Table 7, in Examples 7-1 to 7-6 in which the
metal material was formed by the electroless plating method, the
same results as those in Examples 6-1 to 6-6 in which the metal
material was formed by the electrolytic plating method were
obtained. More specifically, in Examples 7-1 to 7-6 in which the
volumetric capacity of the small pore group per unit weight of
silicon was 0.2 cm.sup.3/g or less, the discharge capacity
retention ratio was much higher than that in Comparative Example 7
in which the volumetric capacity was out of the range, and when the
volumetric capacity was 0.05 cm.sup.3/g or less, or more
specifically 0 cm.sup.3/g, the discharge capacity retention ratio
became higher. Therefore, it was confirmed that in the secondary
battery according to the embodiment of the invention, even in the
case where the method of forming the metal material was changed,
the cycle characteristics were improved.
Examples 8-1 to 8-4
[0172] Secondary batteries were formed by the same steps as those
in Example 6-4, except that as the material for forming the metal
material, instead of the cobalt plating solution, a nickel plating
solution (Example 8-1), an iron plating solution (Example 8-2), a
zinc plating solution (Example 8-3) or a copper plating solution
(Example 8-4) was used. At that time, the current density was 2
A/dm.sup.2 to 10 A/dm.sup.2 in the case where the nickel plating
solution was used, 2 A/dm.sup.2 to 5 A/dm.sup.2 in the case where
the iron plating solution was used, 1 A/dm.sup.2 to 3 A/dm.sup.2 in
the case the zinc plating solution was used, and 2 A/dm.sup.2 to 8
A/dm.sup.2 in the case where the copper plating solution was used.
The above-described plating solutions were of Japan Pure Chemical
Co., Ltd.
[0173] When the cycle characteristics of the secondary batteries of
Examples 8-1 to 8-4 were determined, results shown in Table 8 were
obtained. In Table 8, the results of Example 6-4 and Comparative
Example 6 are also shown.
TABLE-US-00008 TABLE 8 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
METAL DISCHARGE MATERIAL MATERIAL VOLUMETRIC CAPACITY LAYER FORMING
CAPACITY RETENTION NUMBER (LAYER) KIND METHOD (cm.sup.3/g) RATIO
(%) EXAMPLE 6-4 6 Co ELECTROLYTIC 0.02 88.1 EXAMPLE 8-1 Ni PLATING
87.1 EXAMPLE 8-2 Fe 87.5 EXAMPLE 8-3 Zn 87.1 EXAMPLE 8-4 Cu 87.6
COMPARATIVE 6 Co ELECTROLYTIC 0.3 54 EXAMPLE 6 PLATING
[0174] As shown in Table 8, in Examples 8-1 to 8-4 in which nickel
or the like was formed as the metal material, a discharge capacity
retention ratio equivalent to that in Example 6-4 in which the
cobalt was formed was obtained, and the discharge capacity
retention ratio was much higher than that in Comparative Example 6.
In this case, there was a tendency that in the case where cobalt
was used as the metal material, the discharge capacity retention
ratio was higher. Therefore, it was confirmed that in the secondary
battery according to the embodiment of the invention, even in the
case where the kind of the metal material was changed, the cycle
characteristics were improved, and when cobalt was used as the
metal material, a higher effect was obtained.
Examples 9-1 to 9-6
[0175] Secondary batteries were formed by the same steps as those
in Example 2-5, except that instead of 3 at %, the oxygen content
in the anode active material was 2 at % (Example 9-1), 10 a t%
(Example 9-2), 20 at % (Example 9-3), 30 at % (Example 9-4), 40 at
% (Example 9-5), or 45 at % (Example 9-6).
[0176] When the cycle characteristics of the secondary batteries of
Examples 9-1 to 9-6 were determined, results shown in Table 9 and
FIG. 13 were obtained. In Table 9, the results of Example 2-5 and
Comparative Example 2 are also shown.
TABLE-US-00009 TABLE 9 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m ANODE ACTIVE OXIDE-CONTAINING DISCHARGE MATERIAL FILM
CAPACITY LAYER OXYGEN FORMING VOLUMETRIC RETENTION NUMBER (LAYER)
CONTENT (at %) KIND METHOD CAPACITY (cm.sup.3/g) RATIO (%) EXAMPLE
9-1 6 2 SiO.sub.2 LIQUID-PHASE 0.02 79.2 EXAMPLE 2-5 3 DEPOSITION
90.9 EXAMPLE 9-2 10 91 EXAMPLE 9-3 20 91.2 EXAMPLE 9-4 30 91.4
EXAMPLE 9-5 40 91 EXAMPLE 9-6 45 91 COMPARATIVE 6 3 SiO.sub.2
LIQUID-PHASE 0.3 51 EXAMPLE 2 DEPOSITION
[0177] As shown in Table 9, in Examples 9-1 to 9-6 in which the
oxygen content in the anode active material was different, as in
the case of Example 2-5, the discharge capacity retention ratio was
much higher than that in Comparative Example 2. In this case, as
shown in Table 9 and FIG. 13, there was a tendency that as the
oxygen content increased, the discharge capacity retention ratio
was increased, and then decreased, and when the content was smaller
than 3 at %, the discharge capacity retention ratio was largely
reduced. However, the content was larger than 40 at %, a sufficient
discharge capacity retention ratio was obtained, but the battery
capacity was reduced. Therefore, it was confirmed that in the
secondary battery according to the embodiment of the invention,
even in the case where the oxygen content in the anode active
material was changed, the cycle characteristics were improved, and
when the content was within a range from 3 at % to 40 at % both
inclusive, a higher effect was obtained.
Examples 10-1 to 10-3
[0178] Secondary batteries were formed by the same steps as those
in Example 2-5, except that instead of the case where silicon was
deposited while continuously introducing an oxygen gas or the like
into a chamber, thereby oxygen was included in the anode active
material, silicon was deposited while intermittently introducing an
oxygen gas or the like into a chamber, thereby the anode active
material was formed so that a first oxygen-containing region and a
second oxygen-containing region with a higher oxygen content than
that in the first oxygen-containing region were alternately
laminated. At that time, the oxygen content in the second
oxygen-containing region was 3 at %, and the number of the second
oxygen-containing regions was 2 (Example 10-1), 4 (Example 10-2) or
6 (Example 10-3).
[0179] When the cycle characteristics of the secondary batteries of
Examples 10-1 to 10-3 were determined, results shown in Table 10
were obtained. In Table 10, the results of Example 2-5 and
Comparative Example 2 are also shown.
TABLE-US-00010 TABLE 10 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m ANODE ACTIVE MATERIAL OXIDE-CONTAINING DISCHARGE NUMBER OF
FILM CAPACITY LAYER SECOND OXYGEN- FORMING VOLUMETRIC RETENTION
NUMBER (LAYER) CONTAINING REGIONS KIND METHOD CAPACITY (cm.sup.3/g)
RATIO (%) EXAMPLE 2-5 6 -- SiO.sub.2 LIQUID- 0.02 90.9 EXAMPLE 10-1
2 PHASE 91.2 EXAMPLE 10-2 4 DEPOSITION 91.6 EXAMPLE 10-3 6 91.8
COMPARATIVE 6 3 SiO.sub.2 LIQUID- 0.3 51 EXAMPLE 2 PHASE
DEPOSITION
[0180] As shown in Table 10, in Examples 10-1 to 10-3 in which the
anode active material included the first and second
oxygen-containing regions, as in the case of Example 2-5, the
discharge capacity retention ratio was much higher than that in
Comparative Example 2. In this case, there was a tendency that the
larger the number of the second oxygen-containing regions was, the
higher the discharge capacity retention ratio became. Therefore, it
was confirmed that in the secondary battery according to the
embodiment of the invention, even in the case where the anode
active material particles were formed so as to include the first
and second oxygen-containing regions, the cycle characteristics
were improved, and when the number of the second oxygen-containing
regions increased, a higher effect was obtained.
Examples 11-1 to 11-6
[0181] Secondary batteries were formed by the same steps as those
in Example 2-5, except that silicon with a purity of 99% and a
metal element with a purity of 99.9% were used as evaporation
sources to form the anode active material including silicon and the
metal element. At that time, as the metal element, iron (Example
11-1), nickel (Example 11-2), molybdenum (Example 11-3), titanium
(Example 11-4), chromium (example 11-5) or cobalt (Example 11-6)
was used. At that time, the amount of the metal element evaporated
was adjusted so that the content of the metal element in the anode
active material was 5 at %.
[0182] When the cycle characteristics of the secondary batteries of
Examples 11-1 to 11-6 were determined, results shown in Table 11
were obtained. In Table 11, the results of Example 2-5 and
Comparative Example 2 are also shown.
TABLE-US-00011 TABLE 11 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % Content of
metal element in anode active material = 5 at % ANODE ACTIVE
OXIDE-CONTAINING DISCHARGE MATERIAL FILM CAPACITY LAYER METAL
FORMING VOLUMETRIC RETENTION NUMBER (LAYER) ELEMENT KIND METHOD
CAPACITY (cm.sup.3/g) RATIO (%) EXAMPLE 2-5 6 -- SiO.sub.2 LIQUID-
0.02 90.9 EXAMPLE 11-1 Fe PHASE 91.8 EXAMPLE 11-2 Ni DEPOSITION
91.5 EXAMPLE 11-3 Mo 91.4 EXAMPLE 11-4 Ti 91.6 EXAMPLE 11-5 Cr 91.4
EXAMPLE 11-6 Co 91.9 COMPARATIVE 6 -- SiO.sub.2 LIQUID- 0.3 51
EXAMPLE 2 PHASE DEPOSITION
[0183] As shown in Table 11, in Examples 11-1 to 11-6 in which the
anode active material included both of silicon and the metal
element, as in the case of Example 2-5, the discharge capacity
retention ratio was much higher than that in Comparative Example 2.
In this case, there was a tendency that the discharge capacity
retention ratio was higher than that in Example 2-5. Therefore, it
was confirmed that in the secondary battery according to the
embodiment of the invention, even in the case where the anode
active material included the metal element, the cycle
characteristics were improved, and when the metal element was
included, a higher effect was obtained.
Example 12-1
[0184] A secondary battery was formed by the same steps as those in
Example 2-5, except that instead of the electron beam evaporation
method, the anode active material was formed by an RF magnetron
sputtering method. At that time, silicon with a purity of 99.99%
was used as a target, and the deposition rate was 0.5 nm/s.
Example 12-2
[0185] A secondary battery was formed by the same steps as those in
Example 2-5, except that instead of the electron beam evaporation
method, the anode active material was formed by a CVD method. At
that time, silane and argon were used as a material and an
excitation gas, respectively, and the deposition rate and the
substrate temperature were 1.5 nm/s and 200.degree. C.,
respectively.
[0186] When the cycle characteristics of the secondary batteries of
Examples 12-1 and 12-2 were determined, results shown in Table 12
were obtained. In Table 12, the results of Example 2-5 and
Comparative Example 2 are also shown.
TABLE-US-00012 TABLE 12 Anode active material: silicon Ten-point
height of roughness profile Rz = 3.5 .mu.m Oxygen content in anode
active material = 3 at % ANODE ACTIVE OXIDE-CONTAINING DISCHARGE
MATERIAL FILM CAPACITY LAYER FORMING FORMING VOLUMETRIC RETENTION
NUMBER (LAYER) METHOD KIND METHOD CAPACITY (cm.sup.3/g) RATIO (%)
EXAMPLE 2-5 6 ELECTRON SiO.sub.2 LIQUID- 0.02 90.9 BEAM PHASE
EVAPORATION DEPOSITION EXAMPLE 12-1 SPUTTERING 88.5 EXAMPLE 12-2
CVD 87.9 COMPARATIVE 6 ELECTRON SiO.sub.2 LIQUID- 0.3 51 EXAMPLE 2
BEAM PHASE EVAPORATION DEPOSITION
[0187] As shown in Table 12, in Examples 12-1 and 12-2 in which the
method of forming the anode active material was different, as in
the case of Example 2-5, the discharge capacity retention ratio was
much higher than that in Comparative Example 2. In this case, there
was a tendency that the discharge retention ratio was higher in
order of the CVD method, the sputtering method and the electron
beam evaporation method as the method of forming the anode active
material. Therefore, it was confirmed that in the secondary battery
according to the embodiment of the invention, even in the case
where the method of forming the anode active material was changed,
the cycle characteristics were improved, and when the evaporation
method was used, a higher effect was obtained.
Examples 13-1 to 13-7
[0188] Secondary batteries were formed by the same steps as those
in Example 2-5, except that instead of 3.5 .mu.m, the ten-point
height of roughness profile Rz of the surface of the anode current
collector 54A was 1 .mu.m (Example 13-1), 1.5 .mu.m (Example 13-2),
2.5 .mu.m (Example 13-3), 4.5 .mu.m (Example 13-4), 5.5 .mu.m
(Example 13-5), 6.5 .mu.m (Example 13-6) or 7 .mu.m (Example
13-7).
[0189] When the cycle characteristics of the secondary batteries of
Examples 13-1 to 13-7 were determined, results shown in Table 13
and FIG. 14 were obtained. In Table 13, the results of Example 2-5
and Comparative Example 2 are also shown.
TABLE-US-00013 TABLE 13 Anode active material: silicon (electron
beam evaporation) Oxygen content in anode active material = 3 at %
ANODE CURRENT ANODE COLLECTOR ACTIVE OXIDE- TEN-POINT DISCHARGE
MATERIAL CONTAINING HEIGHT OF CAPACITY LAYER FILM ROUGHNESS
VOLUMETRIC RETENTION NUMBER FORMING PROFILE Rz CAPACITY RATIO
(LAYER) KIND METHOD (.mu.m) (cm.sup.3/g) (%) EXAMPLE 13-1 6
SiO.sub.2 LIQUID-PHASE 1 0.02 61 EXAMPLE 13-2 DEPOSITION 1.5 80.1
EXAMPLE 13-3 2.5 85.6 EXAMPLE 2-5 3.5 90.9 EXAMPLE 13-4 4.5 90.5
EXAMPLE 13-5 5.5 90.4 EXAMPLE 13-6 6.5 90.2 EXAMPLE 13-7 7 71
COMPARATIVE 6 SiO.sub.2 LIQUID-PHASE 3.5 0.3 51 EXAMPLE 2
DEPOSITION
[0190] As shown in Table 13, in Examples 13-1 to 13-7 in which the
ten-point height of roughness profile Rz was different, as in the
case of Example 2-5, the discharge capacity retention ratio was
much higher than that in Comparative Example 2. In this case, as
shown in Table 13 and FIG. 14, there was a tendency that as the
ten-point height of roughness profile Rz increased, the discharge
capacity retention ratio was increased, and then decreased, and
when the ten-point height of roughness profile Rz was smaller than
1.5 .mu.m or larger than 6.5 .mu.m, the discharge capacity
retention ratio was largely reduced. Therefore, it was confirmed
that in the secondary battery according to the embodiment of the
invention, even in the case where the ten-point height of roughness
profile Rz of the surface of the anode current collector 54A was
changed, the cycle characteristics were improved, and when the
ten-point height of roughness profile Rz was within a range from
1.5 .mu.m to 6.5 .mu.m both inclusive, a higher effect was
obtained.
Example 14-1
[0191] A secondary battery was formed by the same steps as those in
Example 2-5, except that instead of EC,
4-fluoro-1,3-dioxolane-2-one (FEC) as a fluorinated carbonate
(monofluoroethylene carbonate) was used as the solvent.
Example 14-2
[0192] A secondary battery was formed by the same steps as those in
Example 2-5, except that as the solvent,
4,5-difluoro-1,3-dioxolane-2-one (DFEC) as a fluorinated carbonate
(difluoroethylene carbonate) was added, and the composition
(EC:DFEC:DEC) of a mixture solvent had a weight ratio of
25:5:70.
Examples 14-3, 14-4
[0193] Secondary batteries were formed by the same steps as those
in Example 14-1, except that vinylene carbonate (VC: Example 14-3)
or vinyl ethylene carbonate (VEC: Example 14-4) as a cyclic
carbonate including an unsaturated bond was added to the
electrolytic solution as the solvent. At that time, the content of
VC or VEC in the electrolytic solution was 10 wt %.
Example 14-5
[0194] A secondary battery was formed by the same steps as those in
Example 14-1, except that 1,3-propane sultone (PRS) as a sultone
was added to the electrolytic solution as the solvent. At that
time, the concentration of PRS in the electrolytic solution was 1
wt %.
Example 14-6
[0195] A secondary battery was formed by the same steps as those in
Example 14-1, except that lithium tetrafluoroborate (LiBF.sub.4)
was added to the electrolytic solution as an electrolyte salt. At
that time, the concentration of LiBF.sub.4 in the electrolytic
solution was 0.1 mol/kg.
[0196] When the cycle characteristics of the secondary batteries of
Examples 14-1 to 14-6 were determined, results shown in Table 14
were obtained. In Table 14, the results of Example 2-5 and
Comparative Example 2 are also shown.
[0197] At that time, in addition to the cycle characteristics, the
swelling characteristics of the secondary batteries of Examples 2-5
and 14-5 were also determined. To determine the swelling
characteristics, the secondary batteries were charged by the
following steps to determine the swelling characteristics. At
first, to stabilize the battery state of each of the secondary
battery, one cycle of charge and discharge was performed in an
atmosphere at 23.degree. C., and the thickness of the secondary
battery before the second cycle of charge was measured. Next, after
the secondary battery was charged in the same atmosphere, the
thickness of the secondary battery after the second cycle of charge
was measured. Finally, the swelling rate (%)=[(thickness after
charge-thickness before charge)/thickness before charge].times.100
was determined by calculation. At that time, charge conditions were
the same as those in the case where the cycle characteristics were
determined.
TABLE-US-00014 TABLE 14 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ANODE
ACTIVE ELECTROLYTIC DISCHARGE MATEIRAL OXIDE-CONTAINING SOLUTION
CAPACITY LAYER FILM VOLUMETRIC SOLVENT RETENTION SWELLING NUMBER
FORMING CAPACITY (wt %) RATION RATE (LAYER) KIND METHOD
(cm.sup.3/g) EC FEC DFEC DEC OTHERS (%) (%) EXAMPLE 2-5 6 SiO.sub.2
LIQUID- 0.02 50 -- -- 50 -- 90.9 2.95 EXAMPLE 14-1 PHASE -- 50 --
50 91.2 -- EXAMPLE 14-2 DEPOSITION 25 -- 5 70 91.8 -- EXAMPLE 14-3
-- 50 -- 50 VC 91.9 -- EXAMPLE 14-4 VEC 91.8 -- EXAMPLE 14-5 PRS 91
0.38 EXAMPLE 14-6 LiBF.sub.4 91 -- COMPARATIVE 6 SiO.sub.2 LIQUID-
0.3 50 -- -- 50 -- 51 -- EXAMPLE 2 PHASE DEPOSITION
[0198] As shown in Table 14, in Examples 14-1 to 14-6 in which the
composition of the solvent and the kind of the electrolyte salt
were different, as in the case of Example 2-5, the discharge
capacity retention ratio was much higher than that in Comparative
Example 2. Therefore, it was confirmed that in the secondary
battery according to the embodiment of the invention, even in the
case where the composition of the solvent or the kind of the
electrolyte salt was changed, the cycle characteristics were
improved.
[0199] In particular, in Examples 14-1 and 14-2, the discharge
capacity retention ratio was higher than that in Example 2-5. In
this case, there was a tendency that in the case where the solvent
included DFEC, the discharge capacity retention ratio was higher
that in the case the solvent included FEC. Therefore, it was
confirmed that when the solvent included a fluorinated carbonate,
the cycle characteristics were further improved, and when
difluoroethylene carbonate was used as the fluorinated carbonate, a
higher effect than that in the case where monofluoroethylene
carbonate was used was obtained.
[0200] Moreover, in Examples 14-3 to 14-6, the discharge capacity
retention ratio was higher than that in Example 2-5. In this case,
there was a tendency that when the solvent included VC or VEC, the
discharge capacity retention ratio was higher than that in the case
where the solvent included PRS or LiBF.sub.4. Therefore, it was
confirmed that when the cyclic carbonate including an unsaturated
bond, a sultone or the electrolyte salt including boron and
fluorine was included, the cycle characteristics were further
improved, and when the cyclic carbonate including an unsaturated
bond was used, a higher effect was obtained.
[0201] In Example 14-5 in which the solvent included PRS, the
swelling rate was largely reduced, compared to Example 2-5 in which
the solvent did not included PRS. Therefore, it was confirmed that
in the secondary battery according to the embodiment of the
invention, when the solvent included a sultone or the like, the
swelling characteristics were improved.
Example 15-1
[0202] A secondary battery was formed by the same steps as those in
Example 2-5, except that instead of the laminate film type
secondary battery, a prismatic secondary battery shown in FIGS. 5
and 6 was formed by the following steps.
[0203] At first, after the cathode 21 and the anode 22 were formed,
the cathode lead 24 made of aluminum and the anode lead 25 made of
nickel were attached to the cathode current collector 21A and the
anode current collector 22A by welding, respectively. Next, the
cathode 21, the separator 23 and the anode 22 were laminated in
this order, and were spirally wound in a longitudinal direction,
and then molded into a flat shape, thereby the battery element 20
was formed. Then, after the battery element 20 was contained in the
battery can 11 made of aluminum, the insulating plate 12 was
arranged on the battery element 20. Next, after the cathode lead 24
and the anode lead 25 were welded to the cathode pin 15 and the
battery can 11, respectively, the battery cover 13 was fixed in an
open end of the battery can 11 by laser welding. Finally, the
electrolytic solution was injected into the battery can 11 through
the injected hole 19, and the injection hole 19 was filled with the
sealing member 19A, thereby a prismatic battery was formed.
Example 15-2
[0204] A secondary battery was formed by the same steps as those in
Example 15-1, except that instead of the battery can 11 made of
aluminum, the battery can 11 made of iron was used.
[0205] When the cycle characteristics of the secondary batteries of
Examples 15-1 and 15-2 were determined, results shown in Table 15
were obtained. In Table 15, the results in Example 2-5 and
Comparative Example 2 are also shown.
TABLE-US-00015 TABLE 15 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
OXIDE-CONTAINING DISCHARGE MATERIAL FILM CAPACITY BATTERY LAYER
FORMING VOLUMETRIC RETENTION CONFIGURATION NUMBER (LAYER) KIND
METHOD CAPACITY (cm.sup.3/g) RATIO (%) EXAMPLE 2-5 LAMINATE FILM 6
SiO.sub.2 LIQUID- 0.02 90.9 EXAMPLE 15-1 PRISMATIC PHASE 91.9
(ALUMINUM) DEPOSITION EXAMPLE 15-2 PRISMATIC 92.5 (IRON)
COMPARATIVE LAMINATE FILM 6 SiO.sub.2 LIQUID- 0.3 51 EXAMPLE 2
PHASE DEPOSITION
[0206] As shown in Table 15, in Examples 15-1 and 15-2 in which the
battery configuration was different, as in the case of Example 2-5,
the discharge capacity retention ration was much higher than that
in Comparative Example 2. In this case, the discharge capacity
retention ratio was higher than that in Example 2-5, and there was
a tendency that in the case where the battery can 11 was made of
iron, the discharge capacity retention ratio was higher than that
in the case where the battery can 11 was made of aluminum.
Therefore, it was confirmed that in the secondary battery according
to the embodiment of the invention, even in the case where the
battery configuration was changed, the cycle characteristics were
improved, and when the battery configuration had a prismatic type,
the cycle characteristics were further improved, compared to the
case where the battery configuration had a laminate film type, and
in the case where the battery can 11 made of iron was used, a
higher effect was obtained. Although descriptions are not given
here referring to a specific example, in a prismatic secondary
battery in which the package member was made of a metal material,
the cycle characteristics and the swelling characteristics were
further improved, compared to the laminate film type secondary
battery, so it was obvious that in a cylindrical secondary battery
in which the package member is made of a metal material, the same
result was obtained.
Examples 16-1 to 16-4
[0207] Secondary batteries were formed by the same steps as those
in Examples 2-1 to 2-9, except that the back-and-forth movement
speed of the anode current collector 54A relative to the
evaporation source was changed so that the volumetric capacity of
the very small pore group per unit weight of silicon was 0.2
cm.sup.3/g (Example 16-1), 0.05 cm.sup.3/g (Example 16-2), 0.01
cm.sup.3/g (Example 16-3) or 0 cm.sup.3/g (Example 16-4). The
volumetric capacity of the very small pore group per unit weight of
silicon was determined by a value (the weight of silicon as the
anode active material) determined by subtracting the weight of the
anode current collector 54A from the total weight of the anode
current collector 54A on which the anode active material was
formed, and the value (the volumetric capacity of the very small
pore group) of the amount of mercury intruded into pores with a
diameter ranging from 3 nm to 20 nm both inclusive which was
measured by a mercury porosimeter of Micromeritics (AutoPore 9500
series).
Comparative Example 16
[0208] A secondary battery was formed by the same steps as those in
Comparative Example 2, except that the volumetric capacity of the
very small pore group unit weight of silicon was 0.3
cm.sup.3/g.
[0209] When the cycle characteristics of the secondary batteries of
Examples 16-1 to 16-4 and Comparative Example 16 were determined,
results shown in Table 16 were obtained.
TABLE-US-00016 TABLE 16 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
OXIDE-CONTAINING DISCHARGE MATERIAL FILM VOLUMETRIC CAPACITY LAYER
FORMING CAPACITY RETENTION NUMBER (LAYER) KIND METHOD (cm.sup.3/g)
RATIO (%) EXAMPLE 16-1 6 SiO.sub.2 LIQUID-PHASE 0.2 83.2 EXAMPLE
16-2 DEPOSITION 0.05 90.1 EXAMPLE 16-3 0.01 92.2 EXAMPLE 16-4 0
93.4 COMPARATIVE 6 SiO.sub.2 LIQUID-PHASE 0.3 57.1 EXAMPLE 16
DEPOSITION
[0210] As shown in Table 16, in the case where the oxide-containing
film was formed, in Examples 16-1 to 16-4 in which the volumetric
capacity of the very small pore group per unit weight of silicon
was 0.2 cm.sup.3/g or less, the discharge capacity retention ratio
was much higher than that in Comparative Example 16 in which the
capacity was out of the range, and when the capacity was 0.05
cm.sup.3/g or less, or 0 cm.sup.3/g, the discharge capacity
retention ratio became higher. In this case, in consideration of a
difference between pore groups (the small pore group and the very
small pore group), there was a tendency that in Examples 16-1 to
16-4 relating to the very small pore group, the discharge capacity
retention ratio was higher than that in Examples 2-1, 2-4, 2-6 and
2-9 relating to the small pore group. The results showed that to
reduce the surface area of the anode active material, the
volumetric capacity of the very small pore group had a larger
influence than the volumetric capacity of the small pore group.
Therefore, it was confirmed that in the secondary battery according
to the embodiment of the invention, in the case where the
oxide-containing film was formed, when the volumetric capacity of
the very small pore group per unit weight of silicon was 0.2
cm.sup.3/g or less, the cycle characteristics were further
improved. In this case, it was confirmed that when the volumetric
capacity was 0.05 cm.sup.3/g or less, or more specifically 0
cm.sup.3/g, a higher effect was obtained.
Examples 17-1 to 17-4
[0211] Secondary batteries were formed by the same steps as those
in Examples 6-1 to 6-6, except that the back-and-forth movement
speed of the anode current collector 54A relative to the
evaporation source was changed so that the volumetric capacity of
the very small pore group per unit weight of silicon was 0.2
cm.sup.3/g (Example 17-1), 0.05 cm.sup.3/g (Example 17-2), 0.01
cm.sup.3/g (Example 17-3) or 0 cm.sup.3/g (Example 17-4).
Comparative Example 17
[0212] A secondary battery was formed by the same steps as those in
Comparative Example 6, except that the volumetric capacity of the
very small pore group per unit weight of silicon was 0.3
cm.sup.3/g.
[0213] When the cycle characteristics of the secondary batteries of
Examples 17-1 to 17-4 and Comparative Example 17 were determined,
results shown in Table 17 were obtained.
TABLE-US-00017 TABLE 17 Anode active material: silicon (electron
beam evaporation) Ten-point height of roughness profile Rz = 3.5
.mu.m Oxygen content in anode active material = 3 at % ANODE ACTIVE
METAL DISCHARGE MATERIAL MATERIAL VOLUMETRIC CAPACITY LAYER FORMING
CAPACITY RETENTION NUMBER (LAYER) KIND METHOD (cm.sup.3/g) RATIO
(%) EXAMPLE 17-1 6 Co ELECTROLYTIC 0.2 83.3 EXAMPLE 17-2 PLATING
0.05 90 EXAMPLE 17-3 0.01 92.1 EXAMPLE 17-4 0 93.5 COMPARATIVE 6 Co
ELECTROLYTIC 0.3 57 EXAMPLE 17 PLATING
[0214] As shown in Table 17, in the case where the metal material
was formed, in Examples 17-1 to 17-4 in which the volumetric
capacity of the very small pore group per unit weight of silicon
was 0.2 cm.sup.3/g or less, the discharge capacity retention ration
was much higher than that in Comparative Example 17 in which the
capacity was out of the range, and when the volumetric capacity was
0.05 cm.sup.3/g or less, or 0 cm.sup.3/g, the discharge capacity
retention ratio became higher. In this case, as in the case of the
results shown in Table 16, there was a tendency that in Examples
17-1, 17-3 and 17-4 relating to the very small pore group, the
discharge capacity retention ratio was higher than that in Examples
6-1, 6-3 and 6-6 relating to the small pore group. Therefore, it
was confirmed that in the secondary battery according to the
embodiment of the invention, in the case where the metal material
was formed, when the volumetric capacity of the very small pore
group per unit weight of silicon was 0.2 cm.sup.3/g, the cycle
characteristics were further improved. In this case, it was
confirmed that when the volumetric capacity was 0.05 cm.sup.3/g or
less, or more specifically 0 cm.sup.3/g, a higher effect was
obtained.
[0215] It was obvious from the results shown in Tables 1 to 17 and
FIGS. 11 to 14 that in the case where the anode active material
included silicon and the small pore group (a pore group with a
diameter ranging from 3 nm to 50 nm both inclusive), when the
volumetric capacity of the small pore group per unit weight of
silicon was 0.2 cm.sup.3/g or less, independent of the conditions
such as the number of layers of the anode active material or the
composition of the anode active material, the cycle characteristics
were improved.
[0216] Although the present invention is described referring to the
embodiment and the examples, the invention is not limited to the
embodiment and the examples, and may be variously modified. For
example, in the above-described embodiment and the above-described
examples, to set the volumetric capacity of the small pore group
per unit weight of silicon within a range of 0.2 cm.sup.3/g or
less, the oxide-containing film or the metal material is included
in pores as necessary; however, the invention is not limited to
this. As long as the volumetric capacity of the small pore group
per unit weight of silicon is 0.2 cm.sup.3/g or less, any other
filling material may be included in the pores. It is preferable
that the filling material does not have a specific influence on the
performance of the secondary battery.
[0217] In the above-described embodiment and the above-described
materials, as the kind of the secondary battery, the lithium-ion
secondary battery in which the capacity of the anode is represented
based on the insertion and extraction of lithium is described;
however, the invention is not limited to the lithium-ion secondary
battery. The secondary battery of the invention is applicable to a
secondary battery in which the charge capacity of an anode material
capable of inserting and extracting lithium is smaller than the
charge capacity of a cathode, thereby the capacity of the anode
includes a capacity by insertion and extraction of lithium and a
capacity by precipitation and dissolution of lithium, and is
represented by the sum of them in the same manner.
[0218] In the above-described embodiment and the above-described
examples, the case where the battery has a prismatic type, a
cylindrical type or a laminate film type, and the case where the
battery element has a spirally wound configuration are described as
examples; however, the secondary battery of the invention is
applicable to the case where a secondary battery has any other
shape such as a coin type or a button type or the case where the
battery element has any other configuration such as a laminate
configuration in the same manner.
[0219] In the above-described embodiment and the above-described
examples, the case where lithium is used as an electrode reactant
is described; however, any other Group 1 element in the long form
of the periodic table of the elements such as sodium (Na) or
potassium (K), a Group 2 element in the long form of the periodic
table of the elements such as magnesium (Mg) or calcium (Ca), or
any other light metal such as aluminum may be used. The long form
of the periodic table of the elements is represented by Revised
Edition of IUPAC Inorganic Chemistry Nomenclature set forth by
IUPAC (International Union of Pure and Applied Chemistry). Also in
this case, as the anode active material, the anode material
described in the above-described embodiment may be used.
[0220] In the above-described embodiment and the above-described
examples, an appropriate range, which is derived from the results
of the examples, of the volumetric capacity of the small pore group
per unit weight of silicon in the anode or the secondary battery of
the invention is described; however, the description does not
exclude the possibility that the volumetric capacity of the small
pore group per unit weight of silicon is out of the above-described
range. More specifically, the above-described appropriate range is
specifically a preferable range to obtain the effects of the
invention, and as long as the effects of the invention are
obtained, the volumetric capacity may be deviated from the
above-described range to some extent. It is not limited to the
above-described volumetric capacity, and the same holds for the
volumetric capacity of the very small pore group per unit weight of
silicon, the oxygen content in the anode active material, the
ten-point height of roughness profile Rz of the surface of the
anode current collector, and the like.
[0221] It should be understood by those skilled in the art that
various modifications, combinations, sub-combinations and
alterations may occur depending on design requirements and other
factors insofar as they are within the scope of the appended claims
or the equivalents thereof.
* * * * *