U.S. patent application number 14/987859 was filed with the patent office on 2019-08-08 for process for manufacturing electrode for secondary battery.
The applicant listed for this patent is ARAKAWA CHEMICAL INDUSTRIES, LTD., KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. Invention is credited to Kyoichi KINOSHITA, Manabu MIYOSHI, Hitotoshi MURASE, Toshio OTAGIRI, Katsufumi TANAKA.
Application Number | 20190245208 14/987859 |
Document ID | / |
Family ID | 40350568 |
Filed Date | 2019-08-08 |
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United States Patent
Application |
20190245208 |
Kind Code |
A9 |
MURASE; Hitotoshi ; et
al. |
August 8, 2019 |
PROCESS FOR MANUFACTURING ELECTRODE FOR SECONDARY BATTERY
Abstract
It is an assignment to be solved to provide an electrode for
secondary battery, electrode in which the active material is
suppressed from coming off or falling down from the electricity
collector, and that has excellent cyclic performance. It is
characterized in that, in an electrode for secondary battery, the
electrode being manufactured via an application step of applying a
binder resin and an active material onto a surface of electricity
collector, said binder resin is an alkoxysilyl group-containing
resin that has a structure being specified by formula (I):
##STR00001## wherein "R.sub.1" is an alkyl group whose number of
carbon atoms is from 1 to 8; "R.sub.2" is an alkyl group or alkoxyl
group whose number of carbon atoms is from 1 to 8; and "q" is an
integer of from 1 to 100.
Inventors: |
MURASE; Hitotoshi; (Obu-shi,
JP) ; OTAGIRI; Toshio; (Obu-shi, JP) ;
KINOSHITA; Kyoichi; (Obu-shi, JP) ; TANAKA;
Katsufumi; (Obu-shi, JP) ; MIYOSHI; Manabu;
(Obu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOYOTA JIDOSHOKKI
ARAKAWA CHEMICAL INDUSTRIES, LTD. |
Aichi
Osaka |
|
JP
JP |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20170194646 A1 |
July 6, 2017 |
|
|
Family ID: |
40350568 |
Appl. No.: |
14/987859 |
Filed: |
January 5, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12672887 |
Jun 10, 2011 |
|
|
|
PCT/JP2008/062713 |
Jul 14, 2008 |
|
|
|
14987859 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 2004/027 20130101;
H01M 10/0525 20130101; Y10T 29/49115 20150115; H01M 4/0404
20130101; H01M 4/622 20130101; H01M 4/386 20130101; H01M 4/1395
20130101 |
International
Class: |
H01M 4/62 20060101
H01M004/62; H01M 10/0525 20060101 H01M010/0525; H01M 4/38 20060101
H01M004/38; H01M 4/04 20060101 H01M004/04; H01M 4/1395 20060101
H01M004/1395 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2007 |
JP |
2007-210228 |
Claims
1. A manufacturing process for electrode for secondary battery, the
manufacturing process comprising: an application step of applying a
binder resin and an active material onto a surface of electricity
collector; and a curing step of curing said binder resin and then
binding said active material on said electricity-collector surface,
the manufacturing process for electrode for secondary battery being
characterized in that said binder resin is an alkoxysilyl
group-containing resin that has a structure being specified by
formula (I): ##STR00005## wherein "R.sub.1" is an alkyl group whose
number of carbon atoms is from 1 to 8; "R.sub.2" is an alkyl group
or alkoxyl group whose number of carbon atoms is from 1 to 8; and
"q" is an integer of from 1 to 100.
Description
[0001] This is a divisional of co-pending application Ser. No.
12/672,887, filed Feb. 9, 2010.
TECHNICAL FIELD
[0002] The present invention is one which relates to an electrode
for secondary battery, and to a manufacturing process for the
same.
BACKGROUND ART
[0003] Since downsizing and weight saving of electronic devices
have been advancing, secondary batteries whose energy density is
high have been desired for their power source. A secondary battery
is one that takes out chemical energy, which the positive-electrode
active material and negative-electrode material possess, as
electric energy by means of chemical reaction through electrolyte.
In such secondary batteries, lithium-ion secondary batteries are
secondary batteries, which possess a higher energy density, among
those that have been put in practical use. Even among those, the
spreading of organic-electrolyte-system lithium-ion secondary
batteries (hereinafter being recited simply as "lithium-ion
secondary batteries") has been progressing.
[0004] For lithium-ion secondary battery, lithium-containing
metallic composite oxides, such as lithium-cobalt composite oxides,
have been used mainly as an active material for the positive
electrode; and carbonaceous materials, which have a multi-layered
structure that enables the insertion of lithium ions between the
layers (i.e., the formation of lithium intercalation complex) and
the discharge of lithium ions out from between the layers, have
been used mainly as an active material for the negative electrode.
The positive-electrode and negative-electrode polar plates are made
in the following manner: these active materials, and a binder resin
are dispersed in a solvent to make a slurry, respectively; then the
resulting slurries are applied onto opposite faces of a metallic
foil, namely, an electricity collector, respectively; and then the
solvent is dry removed to form mixture-agent layers; and thereafter
the resulting mixture-agent layers and electricity collector are
compression molded with a roller pressing machine.
[0005] In the other secondary batteries as well, although the types
of respective active materials, electricity collectors, and the
like, differ, such secondary batteries have been available as those
in which the active materials are bound or immobilized to the
electricity collector by means of a binder resin similarly.
[0006] As for the binder resin on this occasion, polyvinylidene
fluoride (hereinafter being abbreviated to as "PVdf") has been used
often for both of the electrodes. Since this binder resin is a
fluorinated resin, the adhesiveness to electricity collectors is
poor, and accordingly it is probable that the falling down of
active materials might occur.
[0007] Moreover, as the negative-electrode active material for
lithium secondary battery, the development of next-generation
negative-electrode active materials, which possess a
charge/discharge capacity that exceeds the theoretical capacity of
carbonaceous material, has been advanced recently. For example,
materials that include a metal, such as Si or Sn, which is capable
of alloying with lithium, are regarded prospective. In the case of
using Si or Sn, and so forth, for an active material, it is
difficult to maintain the bonded state to electricity collector
satisfactorily even when the aforementioned fluorinated resin is
used for the binder, because the volumetric change of the
aforementioned active material that is accompanied by the
occlusion/release of Li at the time of charging/discharging is
great. These materials exhibit a large rate of volumetric change
that is accompanied by the insertion and elimination of lithium;
and accordingly they are associated with such a drawback that the
cyclic degradation is great considerably, because they are expanded
and contracted repeatedly so that their active-material particles
have been pulverized finely or have come to be detached.
[0008] In Patent Literature No. 1, there is a recitation on a
negative electrode for secondary battery that has excellent cyclic
performance, and in which the battery reliability at high
temperatures is improved by means of binding the following together
with a binder, such as polyimide or polyamide-imide, which has been
known as a heat-resistant polymer: an active material containing an
element that is capable of alloying with lithium; a catalytic
element for promoting the growth of carbon nano-fibers; and
composite particles containing carbon nano-fibers that have been
grown from the active material's surface.
[0009] Moreover, in Patent Literature No. 2, a binder resinous
composition for battery is disclosed, binder resinous composition
in which a block copolymer is used, block copolymer in which
nonpolar molecular species that do not have any ring on the
principal-chain framework, and polar molecular species that have a
ring on the principal-chain framework are bonded to each other. In
the examples, it indicates that the cyclic life of
nonaqueous-electrolytic-solution secondary batteries, which were
made by using the binder resinous composition that included the
block copolymer, was improved.
[0010] Patent Literature No. 1: Japanese Unexamined Patent
Publication (KOKAI) Gazette No. 2006-339,092; and
[0011] Patent Literature No. 2: Japanese Unexamined Patent
Publication (KOKAI) Gazette No. 2004-221,014.
DISCLOSURE OF THE INVENTION
Assignment to be Solved by the Invention
[0012] Although binder resins that bind active materials together
as set forth in Patent Literature No. 1 and Patent Literature No. 2
have been investigated, a binder resin with furthermore improved
performance has been sought in the process of investigating
next-generation active materials.
[0013] The present invention is one which has been done in view of
such circumstances, and it is an object to provide an electrode for
secondary battery, electrode in which the active material is
suppressed from coming off or falling down from the electricity
collector, and which has excellent cyclic performance.
Means for Solving the Assignment
[0014] As a result of earnest studies being made by the present
inventors, they found out that it is possible to provide an
electrode for secondary battery, electrode in which the active
material is suppressed from coming off or falling down from the
electricity collector and which has good cyclic performance, by
means of utilizing a specific resin that has not been utilized so
far as a binder resin for secondary-battery electrode, that is, an
alkoxysilyl group-containing resin that has a structure being
specified by formula (I), as a binder resin for electrode.
[0015] Specifically, an electrode for secondary battery according
to the present invention is characterized in that, in an electrode
for secondary battery, the electrode being manufactured via an
application step of applying a binder resin and an active material
onto a surface of electricity collector, said binder resin is an
alkoxysilyl group-containing resin that has a structure being
specified by formula (I).
##STR00002##
[0016] wherein "R.sub.1" is an alkyl group whose number of carbon
atoms is from 1 to 8;
[0017] "R.sub.2" is an alkyl group or alkoxyl group whose number of
carbon atoms is from 1 to 8; and
[0018] "q" is an integer of from 1 to 100.
[0019] The alkoxysilyl group-containing resin that has a structure
being specified by formula (I) is a hybrid composite of resin and
silica. The thermal stability becomes higher than that of the
resinous simple substance by means of turning into a hybrid
composite of resin and silica.
[0020] Moreover, said alkoxysilyl group-containing resin has a
structure that is specified by formula (I). The structure that is
specified by formula (I) is a structure that is made of parts
having undergone sol-gel reaction, and accordingly indicates that
unreacted parts that undergo a sol-gel reaction remain.
Consequently, the sol-gel reaction also occurs when the binder
resin cures, and thereby not only the parts having undergone
sol-gel reaction react with each other but also react with the
resin's OH groups. Moreover, they are believed to react with the
electricity collector's surface as well. Therefore, it is possible
to retain the electricity collector and the active material firmly
to each other.
[0021] As said alkoxysilyl group-containing resin, it is possible
the following can be used: an alkoxy group-containing
silane-modified bisphenol type-A epoxy resin, an alkoxy
group-containing silane-modified novolac-type epoxy resin, an
alkoxy group-containing silane-modified acrylic resin, an alkoxy
group-containing silane-modified phenolic resin, an alkoxy
group-containing silane-modified polyamic acid resin, an alkoxy
group-containing silane-modified soluble polyimide resin, an alkoxy
group-containing silane-modified polyurethane resin, or an alkoxy
group-containing silane-modified polyamide-imide resin.
[0022] In particular, it is more preferable that said alkoxysilyl
group-containing resin can be adapted into an alkoxy
group-containing silane-modified polyamic acid resin or an alkoxy
group-containing silane-modified polyamide-imide resin. Since the
aforementioned alkoxysilyl group-containing resins not only exhibit
good workability but also can be handled simply and easily, the
workability improves furthermore.
[0023] Moreover, an electrode for secondary battery according to
the present invention is characterized in that, in an electrode for
secondary battery, electrode in which an active material is bound
on a surface of electricity collector by way of a binder, said
binder is an alkoxysilyl group-containing resinous cured substance
that has a structure being specified by formula (II):
R.sup.1.sub.mSi0(4-m)/2 (II)
[0024] wherein "m"=an integer of from 0 to 2; and
[0025] "R.sup.1" designates an alkyl group or aryl group whose
number of carbon atoms is 8 or less.
[0026] The adhesiveness between the electricity collector and the
active material, namely, inorganic substrates, is improved by means
of the setting in which said binder is an alkoxysilyl
group-containing resinous cured substance that has a structure
being specified by formula (II): R.sup.1niSi0(4-n)n wherein "m"=an
integer of from 0 to 2; and "R.sup.1" designates an alkyl group or
aryl group whose number of carbon atoms is 8 or less.
[0027] As said alkoxysilyl group-containing resinous cured
substance, it is possible to use the following: an alkoxy
group-containing silane-modified bisphenol type-A epoxy resinous
cured substance, an alkoxy group-containing silane-modified
novolac-type epoxy resinous cured substance, an alkoxy
group-containing silane-modified acrylic resinous cured substance,
an alkoxy group-containing silane-modified phenolic resinous cured
substance, an alkoxy group-containing silane-modified polyimide
resinous cured substance, an alkoxy group-containing
silane-modified soluble polyimide resinous cured substance, an
alkoxy group-containing silane-modified polyurethane resinous cured
substance, or an alkoxy group-containing silane-modified
polyamide-imide resinous cured substance.
[0028] By means of adapting said alkoxysilyl group-containing
resinous cured substance into one of the aforementioned cured
substances, it is possible to turn the binder into a binder
resinous cured substance that is excellent in terms of
adhesiveness, and which is good in terms of heat resistance.
[0029] Moreover, it is preferable that the electrode for secondary
battery can be an electrode for lithium-ion secondary battery. In
particular, when being an electrode for negative electrode, the
effect is high. It is allowable that the active material can also
be one which includes carbon. Moreover, it is permissible that the
electricity collector can comprise copper or aluminum, and that the
active material can even be one which includes metal or metallic
oxide that is capable of alloying with lithium. When using an
electrode for lithium-ion secondary battery, electrode which has
such a construction, the resulting electrode makes an electrode for
secondary battery, electrode in which the active material is
suppressed from coming off or falling down from the electricity
collector, and which has excellent cyclic performance.
[0030] In particular, in the case where the metal or metallic oxide
that is capable of alloying with lithium includes Si and/or Sn, by
means of using the aforementioned binder resin, it is possible to
inhibit the active-material particles from pulverizing finely or
detaching, namely, the drawback that results from the following
fact: the active material exhibits a considerably great rate of
volumetric change being accompanied by the insertion and
elimination of lithium so that it expands and contracts repeatedly
by means of charge/discharge cycle.
[0031] Moreover, a manufacturing process for electrode for
secondary battery according to the present invention is a
manufacturing process for electrode for secondary battery, the
manufacturing process comprising: an application step of applying a
binder resin and an active material onto a surface of electricity
collector; and a curing step of curing said binder resin and then
binding said active material on said electricity-collector surface,
and it is characterized in that said binder resin is an alkoxysilyl
group-containing resin that has a structure being specified by
formula (I).
[0032] By adapting the manufacturing process into one which uses
such a binder resin, it is possible to manufacture an electrode for
secondary battery, electrode in which the active material is less
likely to come off from the electricity collector's surface.
Effect of the Invention
[0033] In the electrode for secondary battery according to the
present invention, the active material is suppressed from coming
off or falling down from the electricity collector by means of
utilizing an alkoxysilyl group-containing resin, which has a
structure being specified by formula (I), as the binder resin for
electrode, and thereby it is possible for the present electrode to
exhibit excellent cyclic performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 illustrates a partial schematic explanatory diagram
of an electrode for secondary battery;
[0035] FIG. 2 illustrates a graph for comparing cyclic
characteristics regarding batteries, in which negative electrodes
according to Example Nos. 1 and 2 were used, with those regarding
batteries, in which negative electrodes according to Comparative
Example Nos. 1 and 2 were used; and
[0036] FIG. 3 illustrates a graph for comparing a first-cycle
charge/discharge curb regarding the battery, in which the negative
electrode according Example No. 1 was used, in a cyclic test, with
that regarding the battery, in which the negative electrode
according
to Comparative Example No. 2 was used, in that test.
EXPLANATION ON REFERENCE NUMERALS
[0037] 1: Electricity Collector; [0038] 2: Active Materials; [0039]
3: Conductive Additives; and [0040] 4: Binder Resins
BEST MODE FOR CARRYING OUT THE INVENTION
[0041] An electrode for secondary battery according to the present
invention is one which is manufactured via an application step of
applying a binder resin and an active material onto a surface of
electricity collector. As for a secondary battery that has such a
construction, the following can be given: nickel-zinc secondary
batteries; lithium-ion secondary batteries; silver oxide secondary
batteries; and nickel-hydrogen secondary batteries.
[0042] The "applying" means that it is allowable that a binder
resin, and an active material can be put onto an electricity
collector. As for an application method, it is possible to use the
following application methods that have been used generally when
making electrodes for secondary battery: roll coating methods; dip
coating methods; doctor blade methods; spray coating methods; and
curtain coating methods.
[0043] The "electricity collector" refers to a chemically-inactive
highly-electron-conductive body for keeping electric current
flowing to electrodes during discharging or charging. The
electricity collector is formed as a configuration, such as a foil
or plate that is formed of said highly-electron-conductive body.
The configuration is not limited to above especially as far as it
is a configuration that fits for the objective. As for the
electricity collector, it is possible to name copper foils,
aluminum foils, and the like, for instance.
[0044] The "active material" refers to a substance that contributes
directly to electrode reactions, such as charging reactions and
discharging reactions. Although the substance that makes the active
material differs depending on the types of secondary battery, it is
not limited especially as far as being one into which substances
that fit the objective of that secondary battery are inserted and
from which those substances are released reversibly by means of
charging/discharging. The active material that is used in the
present invention has a powdery configuration, and is applied and
then bound on the electricity collector's surface by way of the
binder resin. Although the powder differs depending on batteries
that are aimed for, it is preferable that the particle diameter can
be 10 ktm or less.
[0045] For example, in the case of lithium-ion secondary battery,
lithium-containing metallic composite oxides, such as
lithium-cobalt composite oxides, lithium-nickel composite oxides
and lithium-manganese composite oxides, can be used as for an
active material for the positive electrode. For an active material
for the negative electrode, the following can be used: carbonaceous
materials that are capable of occluding and releasing lithium; and
metals, which are capable of turning lithium into alloy, or oxides
of these, and the like. It is possible to use these active
materials independently, or it is possible to combine two or more
species of them to use. As for the metals that are capable of
turning lithium into alloy, the following can be given: Al, Si, Zn,
Ge, Cd, Sn, Pb, and so forth. In particular, Si and Sn are
effective. A theoretical capacity of carbon is 372 mAhg.sup.-1,
whereas theoretical capacities of Si, Ge and Sn, which are the
metals that are capable of alloying with lithium, are 4,200
mAhg.sup.-1, 1,620 mAhg.sup.-1 and 994 mAhg.sup.-1, respectively.
However, the alloyable metals, or oxides of these, exhibit
considerably great rates of volumetric change that is accompanied
by the insertion and elimination of lithium, compared with those of
the carbonaceous materials.
[0046] A composite powder of metals that are capable of turning
lithium into alloy, or oxides thereof, and the like, can be
produced by mean of mechanical alloying method. In this method, it
is feasible to form fine primary particles whose particle diameters
are from 10 to 200 nm approximately with ease. As for a specific
method, it is possible to obtain a composite powder, namely, an
active material that is aimed at, by means of setting the primary
particle diameter to from 10 to 200 nm approximately by the
following: mixing a raw-material substance comprising a plurality
of components; and then carrying out a mechanical alloying
treatment. It is preferable that a centrifugal acceleration (or
input energy) in the mechanical alloying treatment can be from 5 to
20 G approximately, and it is more preferable that it can be from 7
to 15 G approximately.
[0047] It is allowable to apply conventionally-known methods as
they are to the mechanical alloying treatment per se. For example,
it is possible to obtain a composite powder, namely, an active
material that is aimed at, by means of compositing a raw-material
mixture (or alloying it partially) by repeating mixing and adhering
by means of mechanical joining force. As for an apparatus to be
made use of for the mechanical alloying treatment, it is possible
to make use of the following as they are mixing machines,
dispersing machines, pulverizing machines, and the like, which have
been made use of generally in the field of powder. To be concrete,
the following can be exemplified: kneading machines, ball mills,
vibration mills, agitator mills, and so forth. In particular, it is
desirable to use a mixing machine that can give shearing force to
the raw-material mixture, because it is necessary to efficiently
disperse particles, which have been overlapped or agglomerated
during the compositing operation, one particle by one particle in
order to make the overlapping powder, whose major component is made
of a battery active material that exists between networks, less.
Operational conditions for these apparatuses are not those which
are limited in particular.
[0048] It is also possible to bind a conductive additive onto a
surface of the electricity collector together with the active
material. The conductive additive is one which is added in order to
enhance electric conductivity when the active material is bound on
the electricity collector by way of the binder resin. As for the
conductive additive, it is allowable to add the following, namely,
carbonaceous fine particles: carbon black, graphite, acetylene
black, KETJENBLACK, carbon fibers, and the like, independently; or
to combine two or more species of them to add.
[0049] The binder resin is used as a binding agent when applying
these active material and conductive additive to the electricity
collector. It is required for the binding resin to bind the active
material and conductive additive together in an amount as less as
possible, and it is desirable that that amount can be from 0.5% by
weight to 50% by weight of a summed total of the active material,
the conductive additive, and the binder resin. The binder resin
according to the present invention is an alkoxysilyl
group-containing resin that has a structure being specified by
formula (I).
[0050] The structure that is specified by formula (I) includes a
structure that is made of parts having undergone sol-gel reaction,
and the alkoxysilyl group-containing resin makes a hybrid composite
of resin and silica.
[0051] The "structure that is made of parts having undergone
sol-gel reaction" is a structure that contributes to reactions in
carrying out sol-gel process. The "sol-gel process" is process in
which a solution of inorganic or organic metallic salt is adapted
into a starting solution; and the resultant solution is turned into
a colloid solution (Sol) by means of hydrolysis and condensation
polymerization reactions; and then a solid (Gel) that has lost
flowability is formed by facilitating the reactions furthermore.
Generally speaking, metallic alkoxides (i.e., compounds that are
expressed by WOR)x where "M" is a metal and "R" is an alkyl group)
are adapted into a raw material in the sol-gel process.
[0052] The compounds that are expressed by M(OR).sub.x react like
following equation (A) by means of hydrolysis.
nM(OR).sub.x+nH.sub.2O--->nM(OH)(OR).sub.x.sub._.sub.1+nROH
(A)
[0053] The compounds turn into M(OH).sub.x, eventually when the
reaction being shown herein is facilitated furthermore, and then
react like following equation (B) when a condensation
polymerization reaction occurs between two molecules being
generated herein, that is, between two hydroxides.
M(OH).sub.x+M(OH).sub.x--->(OH)x-.sub.1M-0-M(OH).sub.x-1+H.sub.2O-.
(B)
[0054] On this occasion, it is feasible for all the OH groups to
undergo polycondensation; and moreover it is feasible for them to
undergo dehydration/condensation polymerization reaction with
organic polymers that possess an OH group at the terminal ends.
[0055] The binder resin can react not only between parts having
undergone sol-gel reaction but also with the resin's OH groups at
the time of curing binder resin, because of having a structure,
which is made of parts that have undergone sol-gel reaction, as
indicated by formula (I). Moreover, the binder resin exhibits good
adhesiveness to the electricity collector, active material and
conductive additive, namely, inorganic components, because of being
a hybrid composite of resin and silica, and consequently it is
possible to retain the active material and conductive additive on
the electricity collector firmly.
[0056] On this occasion, as for the resin that makes a hybrid
composite with silica, the following can be given: bisphenol type-A
epoxy resins, novolac-type epoxy resins, acrylic resins, phenolic
resins, polyamic acid resins, soluble polyimide resins,
polyurethane resins, or polyamide-imide resins. It is possible to
adapt these resins and silica into hybrid composites, which have a
structure that is specified by formula (I), by means of sol-gel
process, thereby turning into the following, respectively: alkoxy
group-containing silane-modified bisphenol type-A epoxy resins,
alkoxy group-containing silane-modified novolac-type epoxy resins,
alkoxy group-containing silane-modified acrylic resins, alkoxy
group-containing silane-modified phenolic resins, alkoxy
group-containing silane-modified polyamic acid resins, alkoxy
group-containing silane-modified soluble polyimide resins, alkoxy
group-containing silane-modified polyurethane resins, or alkoxy
group-containing silane-modified polyamide-imide resins. In this
instance, the binder resin has a structure that is specified by
formula (I), and this indicates such a state that parts that have
undergone sol-gel reaction still remain therein. Therefore, it is
possible for the binder resin to react not only between the parts
that have undergone sol-gel reaction but also with the resin's OH
groups at the time of curing binder resin by adapting the binder
resin into an alkoxysilyl group-containing resin that has a
structure being specified by formula (I).
[0057] It is possible to synthesize the aforementioned binder
resins by means of publicly-known technique, respectively. For
example, in the case of using an alkoxy group-containing
silane-modified polyamic acid resin as the binder resin, the binder
resin can be formed by reacting precursors, namely, a polyamic acid
comprising a carboxylic-acid-anhydride component and a diamine
component, and an alkoxysilane partial condensate. As for the
alkoxysilane partial condensate, it is possible to use those which
are obtained by condensing hydrolysable alkoxysilane monomers
partially in the presence of acid or base catalyst and water. On
this occasion, it is also permissible that the alkoxy
group-containing silane-modified polyamic acid resin can be formed
as follows: the alkoxysilane partial condensate is reacted with an
epoxy compound in advance to turn it into an epoxy group-containing
alkoxysilane partial condensate; and the resulting epoxy
group-containing alkoxysilane partial condensate is then reacted
with the polyamic acid.
[0058] Moreover, as for the aforementioned binder resin, it is
possible to use commercial products suitably. For example, various
commercial products are available as follows: "COMPOCERAN E
(product name)" (produced by ARAKAWA CHEMICAL INDUSTRIES, LTD.),
namely, an alkoxy group-containing silane-modified bisphenol type-A
epoxy resin or alkoxy group-containing silane-modified novolac-type
epoxy resin; "COMPOCERAN AC (product name)" (produced by ARAKAWA
CHEMICAL INDUSTRIES, LTD.), namely, an alkoxy group-containing
silane-modified acrylic resin; "COMPOCERAN P (product name)"
(produced by ARAKAWA CHEMICAL INDUSTRIES, LTD.), namely, an alkoxy
group-containing silane-modified phenolic resin; "COMPOCERAN H800
(product name)" (produced by ARAKAWA CHEMICAL INDUSTRIES, LTD.),
namely, an alkoxy group-containing silane-modified polyamic acid
resin; "COMPOCERAN H700 (product name)" (produced by ARAKAWA
CHEMICAL INDUSTRIES, LTD.), namely, an alkoxy group-containing
silane-modified soluble polyimide resin; "UREANO U (product name)"
(produced by ARAKAWA CHEMICAL INDUSTRIES, LTD.), namely, an alkoxy
group-containing siiane-modifiedpolyurethane resin; or "COMPOCERAN
H900 (product name)" (produced by ARAKAWA CHEMICAL INDUSTRIES,
LTD.), namely, an alkoxy group-containing silane-modified
polyamide-imide resin.
[0059] Shown below is a chemical formula of the basic framework for
each of the aforementioned following ones: "COMPOCERAN E (product
name)" (produced by ARAKAWA CHEMICAL INDUSTRIES, LTD.); "COMPOCERAN
AC (product name)" (produced by ARAKAWA CHEMICAL INDUSTRIES, LTD.);
"COMPOCERAN P (product name)" (produced by ARAKAWA CHEMICAL
INDUSTRIES, LTD.); "COMPOCERAN H800 (product name)" (produced by
ARAKAWA CHEMICAL INDUSTRIES, LTD.); and "COMPOCERAN H900 (product
name)" (produced by ARAKAWA CHEMICAL INDUSTRIES, LTD.)
##STR00003## ##STR00004##
[0060] Moreover, an electrode for secondary battery according to
the present invention is an electrode for secondary battery,
electrode in which an active material is bound on a surface of
electricity collector. It is allowable that a conductive additive
can also be bound on the surface of electricity collector together
with the active material. The electricity collector, active
material and conductive additive are those which are the same as
those being aforementioned. Said binder is an alkoxysilyl
group-containing resinous cured substance that has a structure
being specified by formula (II): R.sup.i.sub.mSiO (4-m)/2 wherein
"m"=an integer of from 0 to 2; and "R.sup.1" designates an alkyl
group or aryl group whose number of carbon atoms is 8 or less. The
structure that is specified by formula (II) is a structure that is
made of gelated fine silica parts (or a high-order network
structure with siloxane bonds). This structure is a structure of
organic silicone polymer that comprises siloxane bonds, and is a
structure that is obtainable by means of the polycondensation of
silanol according to following equation (C).
nR.sub.mSi(OH).sub.4-m--->(R.sub.mSiO.sub.(4-m)/2)n Equation
(C)
[0061] where "R": Organic Group, "m"=from 1 to 3, and n>1 For
the alkoxysilyl group-containing resinous cured substance, it is
possible to use the following: alkoxy group-containing
silane-modified bisphenol type-A epoxy resinous cured substances,
alkoxy group-containing silane-modified novolac-type epoxy resinous
cured substances, alkoxy group-containing silane-modified acrylic
resinous cured substances, alkoxy group-containing silane-modified
phenolic resinous cured substances, alkoxy group-containing
silane-modified polyimide resinous cured substances, alkoxy
group-containing silane-modified polyurethane resinous cured
substances, or alkoxy group-containing silane-modified
polyamide-imide resinous cured substances. This binder corresponds
to cured substances of the above-explained binder resins.
[0062] Moreover, a manufacturing process according to the present
invention for electrode for secondary battery comprises an
application step, and a curing step.
[0063] The application step is a step of applying a binder resin
and an active material onto a surface of electricity collector.
Moreover, it is also permissible to apply a conductive additive
together with them at the application step.
[0064] The curing step is a step of curing said binder resin and
then binding said active material on said electricity-collector
surface. Said binder resin is characterized in that it is an
alkoxysilyl group-containing resin that has a structure being
specified by formula (I).
[0065] At the application step, it is possible to apply the binder
resin and active material onto the electricity collector after
mixing them in advance and then turning them into a slurry by
adding a solvent, or the like, to the resulting mixture. It is
permissible that a conductive additive can also be turned into a
slurry together with them and can then be applied to the
electricity collector. It is preferable that an applied thickness
can be from 10 .mu.m to 300 .mu.m. Moreover, it is preferable that
a mixing proportion of the binder resin and active material can be
the active material: the binder resin=from 99:1 to 70:30 by parts
by weight. In the case of including a conductive additive, it is
preferable that a mixing proportion of the binder resin, active
material and conductive additive can be the active material: the
conductive additive: the binder resin =from 98:1:1 to 60:20:20 by
parts by weight.
[0066] The curing step is a step of curing the binder resin,
namely, an alkoxysilyl group-containing resin. The active material
is bound on the electricity-collector surface by means of curing
the binder resin. In the case of including a conductive additive,
the conductive additive is also bound thereon similarly. It is
permissible that the curing of the binder resin can be done in
conformity to the curing condition of a binder resin to be made use
of. Moreover, in the curing of the binder resin, a sol-gel curing
reaction also occurs, sol-gel reaction which results from the
structure being specified by formula (I) that the binder resin has.
An alkoxysilyl group-containing resin in which the sol-gel curing
reaction has occurred exhibits good adhesiveness to the active
material, conductive additive and electricity collector, because it
has a structure that is made of gelated fine silica parts (or a
high-order network structure with siloxane bonds)
EXAMPLES
[0067] Hereinafter, the present invention will be explained in more
detail while giving examples. A partial schematic explanatory
diagram of an electrode for secondary battery according to the
present invention is illustrated in FIG. 1. An example of the
electrode for secondary battery according to the present invention
is one in which active materials 2, and conductive additives 3 are
bound on a surface of electricity collector 1 by way of binder
resins 4. The binder resins 4 are dispersed between the dispersed
active materials 2 and the dispersed conductive additives 3, and
make such a state that they join the active materials 2, conductive
additives 3 and electricity collector 1 one another to put them
together. Since FIG. 1 is a schematic drawing, the drawn
configurations are not correct ones. Although the binder resins 4
are depicted as a powdery configuration in FIG. 1, they have
indeterminate forms. Moreover, as shown in FIG. 1, the entire
surface of the electricity collector 1 is not covered with the
binder resins 4, the active materials 2 and/or the conductive
additives 3 completely, but minute pores exist between the
respective substances and the surface of the electricity collector
1 here and there.
[0068] The electrode for secondary battery according to the present
invention was made as follows, and then a discharging cyclic test
was carried out using a model battery for evaluation. In the test,
the negative electrode of lithium-ion secondary battery was adapted
into an electrode to be evaluated, and a coin-shaped lithium-ion
secondary battery was used.
(Making of Electrodes for Evaluation)
Example No. 1, Example No. 2, Comparative Example No. 1, and
Comparative Example No. 2
[0069] As an active material, an Si powder was used, Si powder
whose discharge capacity was large, and whose particle diameters
were about 4, um or less. Although Si powder is good in terms of
the discharge capacity compared with that of the other active
materials, it is likely to come off from electricity collectors
because of the expansion of its own particles; moreover, it has
fallen down from them because the active materials are pulverized
finely due to volumetric expansion that results from
charging/discharging, and thereby the discharge capacity declines
sharply at the time of cyclic test.
[0070] As the Si powder, Si particles (produced by KO-JUNDO KAGAKU)
with 4-, .mu.m-or-less particle diameters were made use of as they
were.
[0071] 10 parts by weight of a paste in which a binder resin was
dissolved in N-methylpyrrolidone (or NMP), and 5 parts by weight of
KETJENBLACK (or KB) were added to 85 parts by weight of the Si
powder, and were then mixed to prepare a slurry.
[0072] For the binder resin, those being specified in Table 1 were
used. In Example No. 1, an alkoxy group-containing silane-modified
polyamide-imide resin was used, alkoxy group-containing
silane-modified polyamide-imide resin which was produced by ARAKAWA
CHEMICAL INDUSTRIES, LTD.; whose product name was COMPOCERAN; whose
product number was H901-2; whose solvent composition was NMP/xylene
(or Xyl); which had cured residuals in an amount of 30%; which
exhibited a viscosity of 8,000 mPas; and which had silica in an
amount of 2% by weight in the cured residuals (note herein that the
"cured residuals" means solid contents after removing the volatile
components by curing the resinous components). The alkoxy
group-containing silane-modified polyamide-imide resin that was
used in Example No. 1 was one of aforementioned COMPOCERAN (product
name) H900-series products, and had a structure that is specified
in above (Chemical Formula 7).
[0073] In Example No. 2, an alkoxy group-containing silane-modified
polyamic acid resin was used, alkoxy group-containing
silane-modified polyamic acid resin which was produced by ARAKAWA
CHEMICAL INDUSTRIES, LTD.; whose product name was COMPOCERAN; whose
product number was H850D; whose solvent composition was N,
N-dimethylacetamide (DMAc); which had cured residuals in an amount
of 15%; which exhibited a viscosity of 5,000 mPas; and which had
silica in an amount of 2% by weight in the cured residuals. The
alkoxy group-containing silane-modified polyamic acid resin that
was used in Example No. 2 was one of aforementioned COMPOCERAN
(product name) H800-series products, and had a structure that is
specified in above (Chemical Formula 6).
[0074] In Comparative Example No. 1, PVdF (produced by KUREHA) was
used. In Comparative Example No. 2, a polyamide-imide resin
(produced by ARAKAWA CHEMICAL INDUSTRIES, LTD.) was used.
[0075] After preparing the aforementioned slurries, the slurries
are put on an electrolytic copper foil with 20.sub.Th um thickness,
and were then formed as a film on the copper foil, respectively,
using a doctor blade.
[0076] After drying the thus obtained sheets at 80.degree. C. for
20 minutes and then removing NMP by evaporation, an electricity
collector, which comprised the electrolytic copper foil, and
negative-electrode layers, which comprised the aforementioned
complex powders, were joined together firmly by means of adhesion
with a roller pressing machine. These were punched out with a
1-cm.sup.2 circular punch, and were then adapted into an electrode
with 100-, um-or-less thickness by vacuum drying them as follows,
respectively: at 200.degree. C. for 3 hours in Example No. 1 and
Example No. 2; at 140.degree. C. for 3 hours in Comparative Example
No. 1; and at 200.degree. C. for 3 hours in Comparative Example No.
2.
TABLE-US-00001 TABLE 1 Binder Resin Example No. 1 Alkoxy
Group-containing Silane-modified Polyamide-imide Resin Example No.
2 Alkoxy Group-containing Silane-modified Polyamic Acid Resin
Comparative PVdF (Polyvinylidene Example No. 1 Fluoride)
Comparative Polyamide-imide Resin Example No. 2
(Making of Coin-Shaped Batteries)
[0077] Coin-shaped model batteries (type "CR2032") were made within
a dry room while adapting the aforementioned electrodes into the
negative electrode, adapting metallic lithium into the positive
electrode, and adapting a solution, namely, 1-mol
LiPF.sub.6/ethylene carbonate (or EC)+diethyl carbonate (or DEC)
where EC:DEC=1:1 (by volume ratio), into the electrolyte. The
coin-shaped model batteries were made by overlapping a spacer, an
Li foil with 500p, m thickness making a counter electrode, a
separator ("Celgard #2400" (trademark name) produced by CELGARD,
LLC), and the evaluation electrodes in this order, and then
subjecting them to a crimping process.
(Evaluation for Coin-Shaped Batteries)
[0078] An evaluation of each of the electrodes to be evaluated in
these model batteries were carried out by the following method.
[0079] First of all, model batteries were discharged at a constant
electric current of 0.2 mA until reaching 0 V, and were then
charged at a constant electric current of 0.2 mA until reaching 2.0
V after having a 5-minute intermission. These were considered 1
cycle, and the charging/discharging was carried out repeatedly to
examine their discharge capacities.
[0080] FIG. 2 illustrates a graph that shows the number of the
cycles and the discharge capacities which are relevant to the model
batteries according to the respective examples and comparative
examples. It is apparent from FIG. 2 that the decrease magnitudes
of the initial discharge capacity were small in the batteries in
which the respective examples were adapted into the evaluation
electrode, compared with those of the batteries in which the
respective comparative examples were adapted into the evaluation
electrode.
[0081] As specified by Comparative Example No. 1, in the electrode
that used PVdF, namely, a conventional binder resin, the discharge
capacity dropped sharply to almost 10% approximately after being
subjected to the cyclic test once, whereas the discharge capacities
were maintained as much as from 70% to 80% approximately in Example
No. 1 and Example No. 2. Besides, it is understood that the
after-20-cycle discharge capacities of Comparative Example No. 1
and Comparative Example No. 2 were 0, whereas the after-20-cycle
discharge capacity was also maintained as much as 10% or more in
Example No. 2.
[0082] In the case of adapting the Si particles into the active
material, the first-round discharge capacity exceeded 3,000 mAh/g.
It is remarkable that the discharge capacity remained as much as
375 mAh/g approximately after 20 cycles in Example No. 2, because
the first-round discharge capacity was 400 mAh/g or less usually in
the case of using graphite as the active material.
[0083] Moreover, Example No. 1 and Comparative Example No. 2 made
one which comprised the polyamide-imide resin into which silica was
incorporated, and another one which comprised the polyamide-imide
resin into which no silica was incorporated, respectively. As
illustrated in FIG. 2, it is possible to see that the discharge
characteristic of Example No. 1 was superior to the discharge
characteristic of Comparative Example No. 2.
[0084] FIG. 3 illustrates a comparison between the charge/discharge
curves at the first cycle in the cyclic test. Example No. 1
comprised the binder resin into which silica was incorporated in an
amount of 2%, whereas Comparative Example No. 2 comprised the
binder resin into which no silica was incorporated. As can be
viewed in FIG. 3, when comparing the first-cycle discharge
characteristic of Example No. 1 with that of Comparative Example
No. 2, it is possible to see that the former was superior to the
latter almost doubly.
* * * * *