U.S. patent application number 13/905389 was filed with the patent office on 2013-10-03 for preparation process for preventing deformation of jelly-roll type electrode assembly.
The applicant listed for this patent is LG CHEM, LTD.. Invention is credited to Byungjin CHOI, SooRyoung KIM, Hyang Mok LEE, Jinsoo LEE, Sangbaek RYU, Youngkwang YUN.
Application Number | 20130260200 13/905389 |
Document ID | / |
Family ID | 40549362 |
Filed Date | 2013-10-03 |
United States Patent
Application |
20130260200 |
Kind Code |
A1 |
YUN; Youngkwang ; et
al. |
October 3, 2013 |
PREPARATION PROCESS FOR PREVENTING DEFORMATION OF JELLY-ROLL TYPE
ELECTRODE ASSEMBLY
Abstract
Provided is a method for fabrication of a jelly-roll type
electrode assembly having a cathode/separation membrane/anode
laminate structure, including: (a) coating both sides of a porous
substrate with organic/inorganic composite layers, each of which
includes inorganic particles and an organic polymer as a binder, so
as to fabricate a composite membrane; and (b) inserting one end of
a sheet laminate comprising a cathode sheet and an anode sheet as
well as the composite membrane into a mandrel, winding the sheet
laminate around the mandrel, and then, removing the mandrel,
wherein the organic/inorganic composite layer includes microfine
pores capable of moderating a variation in volume during
charge/discharge of a secondary battery and an interfacial friction
coefficient between the composite membrane and the mandrel is not
more than 0.28.
Inventors: |
YUN; Youngkwang; (Daejeon,
KR) ; RYU; Sangbaek; (Daejeon, KR) ; LEE;
Jinsoo; (Daejeon, KR) ; KIM; SooRyoung;
(Daejeon, KR) ; CHOI; Byungjin; (Daejeon, KR)
; LEE; Hyang Mok; (Daejeon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LG CHEM, LTD. |
Seoul |
|
KR |
|
|
Family ID: |
40549362 |
Appl. No.: |
13/905389 |
Filed: |
May 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12682664 |
Jul 20, 2010 |
|
|
|
PCT/KR08/05911 |
Oct 8, 2008 |
|
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|
13905389 |
|
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Current U.S.
Class: |
429/94 ;
29/623.5; 427/58; 429/145 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 10/0587 20130101; Y10T 29/49115 20150115; Y10T 29/49108
20150115; H01M 2/166 20130101; H01M 2/0275 20130101; H01M 10/0525
20130101; H01M 10/4235 20130101; H01M 2/0287 20130101; H01M 2/1673
20130101; H01M 10/0409 20130101; H01M 10/0431 20130101; H01M
10/0565 20130101 |
Class at
Publication: |
429/94 ; 429/145;
29/623.5; 427/58 |
International
Class: |
H01M 10/04 20060101
H01M010/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 12, 2007 |
KR |
10-2007-0102909 |
Claims
1. An organic/inorganic composite membrane for a secondary battery
prepared by the method comprising: (i) dissolving an organic
polymer, which is capable of inducing a binding force between
inorganic particles and adhesion of the inorganic particles to a
surface of a substrate, in a solvent to prepare a solution; (ii)
adding the inorganic particles to the prepared solution to prepare
an organic/inorganic coating solution; (iii) immersing a porous
substrate in the coating solution through dip-coating, so as to
form coating layers on both sides of the porous substrate; and (iv)
removing the solvent to produce an organic/inorganic composite
membrane having microfine pores, wherein the organic/inorganic
composite membrane includes microfine pores capable of moderating a
variation in volume during charge/discharge of the secondary
battery, and the interfacial friction coefficient (.mu.) between
the composite membrane and a mandrel used for manufacturing a
jelly-roll type electrode assembly is not more than 0.28.
2. A jelly-roll type electrode assembly having a cathode/separation
membrane/anode laminate structure prepared by the method
comprising: (a) coating both sides of a porous substrate with
organic/inorganic composite layers, each of which includes
inorganic particles and an organic polymer as a binder, so as to
fabricate an organic/inorganic composite membrane; and (b)
inserting one end of a sheet laminate comprising a cathode sheet
and an anode sheet as well as the composite membrane into a
mandrel, winding the sheet laminate around the mandrel, and then,
removing the mandrel, wherein an organic/inorganic composite layer,
which includes microfine pores capable of moderating a variation in
volume during charge/discharge of a secondary battery, is formed on
both sides of the porous substrate and an interfacial friction
coefficient between the composite membrane and the mandrel is not
more than 0.28.
3. A secondary battery comprising the jelly-roll type electrode
assembly according to claim 2 built in a battery case.
4. The secondary battery according to claim 3, wherein the battery
case is a pouch type case consisting of a laminate sheet comprising
a resin layer and a metal layer.
Description
[0001] This application is a Divisional application of co-pending
U.S. application Ser. No. 12/682,664, filed Apr. 12, 2010, which is
the national stage application of PCT/KR2008/005911, filed Oct. 8,
2008, which claims priority to Korean Patent Application No.
10-2007-0102909, filed Oct. 12, 2007, the contents all of which in
their entirety are herein incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for fabrication
of a jelly-roll type electrode assembly having a lamination
structure of cathode/separation membrane/anode and, more
particularly, a process for fabrication of a jelly-roll type
electrode assembly, including (a) preparing a composite membrane in
which an organic/inorganic composite layer containing inorganic
particles and an organic polymer as a binder is applied to both
sides of a porous substrate; and (b) inserting one end of a sheet
laminate comprising the composite membrane, a cathode sheet and an
anode sheet into a mandrel, winding the sheet laminate around the
mandrel, and removing the mandrel, wherein the organic/inorganic
composite layer may have microfine pores capable of moderating (or
reducing) a variation in volume during charge/discharge of a
secondary battery and an interfacial friction coefficient (.mu.)
between the composite membrane and the mandrel may be 0.28 or less,
as well as a composite membrane fabricated by the same.
BACKGROUND OF THE INVENTION
[0003] With an increase in technical development and demand for
mobile devices, secondary batteries as an energy source are
increasingly in demand. Accordingly, a great deal of studies and
investigation into batteries to satisfy various consumers requests
has been recently conducted.
[0004] For instance, in terms of morphology of a battery, a demand
for an angular type secondary battery and/or a pouch type secondary
battery with a small thickness being applicable to electronic
products such as a cellular phone is increasing, while a secondary
lithium battery having high energy density, discharge voltage,
output stability, etc. such as a lithium ion battery, a lithium ion
polymer battery and the like is in relatively great demand in terms
of raw materials.
[0005] In addition, the secondary battery may be classified in
terms of structure of an electrode assembly having the
cathode/separation membrane/anode structure. For instance, a
jelly-roll (winding type) electrode assembly having a structure
wherein cathodes and anodes in extended sheet forms are wound by
interposing a separation membrane therebetween, a stack/folding
type (lamination type) electrode assembly having a structure
wherein cathodes and anodes are stacked by interposing a separation
membrane to fabricate a bi-cell or full cell in a laminate form and
a plurality of the bi-cells or full cells are wound, and the like
may be representative of the secondary batteries. Such a
stack/folding type electrode assembly was described in detail in
Korean Patent Laid-Open Publication Nos. 2001-0082058, 2001-0082059
and 2001-0082060 issued to the present applicant.
[0006] Among the techniques described above, the jelly-roll type
electrode assembly has merits of simple and easy production and
relatively high energy density per weight. However, since this
assembly is generally fabricated by winding a cathode and an anode
under a compact condition, which each has an extended sheet form,
to constitute a structure in a cylindrical or elliptical shape so
that stress generated by expansion and contraction of an electrode
during charge/discharge may be accumulated in the electrode
assembly and, if such stress accumulation exceeds a constant limit,
the electrode assembly may become deformed. For this reason, a gap
between adjacent electrodes is irregular so that performance of a
battery having the electrodes may be rapidly deteriorated and
internal short-circuit may occur, causing a problem of threatening
safety of the battery.
[0007] Accordingly, in order to prevent deformation of a jelly-roll
type electrode assembly, the present inventors proposed use of an
organic/inorganic composite membrane and a method for fabrication
of a jelly-roll assembly with excellent production workability
because of low friction coefficient between a mandrel and a
separation membrane.
[0008] In this regard, some of conventional technologies concerning
organic/inorganic composite porous separation membranes have been
disclosed. For instance, Korean Patent Laid-Open Publication Nos.
2007-0055979 and 2006-0050976 issued to the present applicant
described an organic/inorganic composite porous membrane which
includes inorganic particles on both sides of the membrane and
pores formed by the inorganic particles, so as to solve thermal
safety problems of a polymer separation membrane.
[0009] However, such an organic/inorganic composite porous membrane
fabricated according to any conventional technique described above
may cause the following problems when the membrane is adopted for a
jell-roll type electrode assembly, although the membrane may be
useful for a stack/folding type electrode assembly.
[0010] In general, as to manufacture of a jelly-roll type electrode
assembly, a process of inserting one end of an cathode/separation
membrane/anode laminate into a mandrel, winding the laminate around
the mandrel in a cylindrical form, and then, removing the mandrel
is involved. However, during removal of the mandrel, due to
friction between the membrane, which was positioned in the
innermost layer of the laminate, and the mandrel, a sheet including
the electrode or the membrane may partially escape the wound
electrode assembly ("tail out condition") or other failures may
occur, leading to lowered safety of the battery. More particularly,
using a separation membrane with an organic/inorganic coating film
may increase friction between the mandrel and the membrane, causing
significant problems such as pushing off of the membrane and/or
tail out condition thereof.
[0011] So as to overcome these problems, Korean Patent Laid-Open
Publication No. 2007-0000231 described a novel technique
characterized in that a coating layer is formed on one side of an
organic/inorganic composite porous separation membrane through
roll-coating, and then, the coating layer is wound to orient an
electrode rather than a mandrel. However, according to practical
experiments conducted by the inventors, it was determined that the
above technique may cause damage to inorganic particles or a porous
material due to pressure applied during the coating process through
roll-coating, entailing problems such as difficulties in management
and complicated production processes. In addition, an
organic/inorganic composite film is applied to only one side of the
membrane, which in turn exhibits lowered buffer effects on
contraction and expansion of a jelly-roll structure, thus not
desirably satisfying prevention of the jelly-roll structure.
[0012] Consequently, there is a strong need for development of
improved techniques for enhancing safety of a battery and for
inhibiting damage to a separation membrane and/or a decrease in
production efficiency during manufacture of a jelly-roll structure
while favorably preventing deformation of the jelly-roll structure,
thereby extending battery life.
SUMMARY OF THE INVENTION
[0013] Therefore, the present invention has been made to solve the
above problems and other technical problems that have yet to be
resolved.
[0014] The present inventors have undertaken extensive research and
studies and found that a composite separation membrane with
organic/inorganic composite layers applied to both sides of the
membrane so as to have microfine pores, wherein an interfacial
friction coefficient (.mu.) between the membrane and a mandrel is
not more than a desired level, may exhibit excellent winding
assembly characteristics and, in addition, a jelly-roll structure
including the composite membrane fabricated as described above may
moderate (or reduce) a variation in volume of an electrode because
of the microfine pores so as to prevent deformation of the
jelly-roll structure, thereby improving safety of a secondary
battery having the jelly-roll structure. Accordingly, the present
invention has been accomplished.
[0015] On the basis of this finding, it is an object of the present
invention to provide a method for fabrication of a jelly-roll type
electrode assembly, including: (a) fabricating a composite membrane
in which an organic/inorganic composite layer containing organic
polymer as a binder as well as inorganic particles is applied to
both sides of a porous substrate; and (b) inserting one end of a
sheet laminate, which comprises the composite membrane, a cathode
sheet and an anode sheet, into a mandrel, winding the sheet
laminate around the mandrel, and then, removing the mandrel,
wherein the organic/inorganic composite layer may include microfine
pores capable of moderating a variation in volume during
charge/discharge of a secondary battery, and the interfacial
friction coefficient (.mu.) between the composite membrane and the
mandrel may be 0.28 or less.
[0016] The method for fabrication of the jelly-roll type electrode
assembly according to the present invention has an advantage in
that the interfacial friction coefficient (.mu.) between the
composite membrane and the mandrel is sufficiently low to inhibit a
"tail out condition," which may occur during removal of the
mandrel. Therefore, the present inventive method may attain a
decrease in failure rate of products and improve productivity.
Additionally, since the organic/inorganic composite layer involving
microfine pores is attached to both sides of the membrane, a
jelly-roll structure fabricated using this membrane may exhibit
superior buffer effects on expansion and contraction of an
electrode during charge/discharge thereof, thereby inhibiting
deformation of the jelly-roll structure and internal accumulation
of a stress which may be induced by the expansion and contraction.
Furthermore, the composite layer in the membrane contains an
inorganic substance to increase strength of the membrane, thus
enhancing safety of a battery against external force.
[0017] In step (a), an organic/inorganic composite layer including
inorganic particles and an organic polymer as a binder may be
formed on both sides of a porous substrate.
[0018] Such organic/inorganic composite layer may be, for example,
fabricated by coating the porous substrate with a mixture of the
inorganic particles and the organic polymer. The coating process
may be conducted by any conventional method including, for example,
dip coating, die coating, roll coating, comma coating and/or a
combination of two or more thereof. Dip coating may be particularly
preferred.
[0019] The organic/inorganic composite layer includes microfine
pores to provide thickness flexibility, which in turn, exhibits
favorable buffer effects when the electrode is expanded. The
microfine pore may be generated by a space between the inorganic
particles and/or formed during solvent evaporation in forming the
organic/inorganic composite layer. For the latter, relatively small
inorganic particles may be added.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0021] FIG. 1 schematically depicts graphs illustrating measured
results of increases in charge/discharge capacity and thickness of
a battery having a membrane with a coating layer, compared to a
battery having a membrane without a coating layer, in accordance
with Experimental Example 1 of the present invention; and
[0022] FIG. 2 schematically depicts graphs illustrating results of
evaluating mechanical properties of a battery having a membrane in
accordance with Experimental Example 2 of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0023] An exemplary embodiment of a process for fabricating the
coated composite membrane as described in Step (a) includes:
[0024] (i) dissolving an organic polymer, which is capable of
inducing a binding force between inorganic particles and adhesion
of the inorganic particles to a surface of a substrate, in a
solvent (`first solvent`) to prepare a solution;
[0025] (ii) adding the inorganic particles to the prepared solution
to prepare an organic/inorganic coating solution;
[0026] (iii) immersing a porous substrate in the coating solution
through dip-coating, so as to form coating layers on both sides of
the porous substrate; and
[0027] (iv) removing the solvent to produce an organic/inorganic
composite layer having microfine pores.
[0028] The composite membrane fabricated by the above process has
the organic/inorganic composite layers coated on both sides of the
porous substrate so as to have enough microfine pores, thereby
buffering contraction and/or expansion of an electrode during
charge and discharge and inhibiting deformation of an electrode
assembly. In addition, since the organic/inorganic composite layer
is formed through dip-coating, this fabrication process is simpler
than a roll-coating process and has merits of decreased damage to
the inorganic particles and/or the porous substrate while forming a
uniform coating layer.
[0029] In step (i), the organic polymer is not particularly
restricted so long as it may facilitate binding of the inorganic
particles and combine the inorganic particles with the porous
substrate. For example, the organic polymer may include at least
one selected from a group consisting of: polyvinylidenefluoride
(PVdF); polyvinylidenefluoride-co-hexafluoropropylene;
polyvinylidenefluoride-co-trichloroethylene; polyvinylidenefluoride
chlorotrifluoroethylene (PVdF-CTFE); polymethyl methacrylate;
polyacrylonitrile; polyvinylpyrrolidone; polyvinylacetate;
polyethylene-co-vinylacetate copolymer; polyethyleneoxide;
cellulose acetate; cellulose acetate butyrate; cellulose acetate
propionate; cyanoethylpullulan; cyanoethyl polyvinylalcohol;
cyanoethyl cellulose; cyanoethyl sucrose; pullulan; carboxylmethyl
cellulose; acrylonitrile-styrene-butadiene copolymer; and
polyimide, which is used alone or in combination with two or more
thereof. The organic polymer may be PVdF or PVdF-CTFE. PVdF-CTFE
which has superior adhesiveness to inhibit swelling caused by
heating, short circuit and the like is more preferred.
[0030] The first solvent is not particularly restricted so long as
it has a solubility parameter similar to that of an organic polymer
to be dissolved therein and may include, for example, at least one
selected from a group consisting of acetone, tetrahydrofuran,
methylene chloride, chloroform, dimethylformamide (DMF),
N-methyl-2-pyrrolidone (NMP), cyclohexane, water, and mixtures
thereof. Acetone is more preferred.
[0031] Step (ii) is a process of adding the inorganic particles to
the prepared solution. For example, inorganic particles in a powder
form may be directly added to an organic polymer in the first
solvent, or the inorganic particles dispersed in an alternative
dispersant may be added thereto.
[0032] In an exemplary embodiment of the above process, the
inorganic particles in step (ii) may be dispersed in a second
solvent, and then, added to the organic polymer solution. In this
regard, since the inorganic particles are homogeneously dispersed
in the second solvent, pores may be readily formed through
evaporation of the solvent, resulting in formation of a separation
membrane with a high porosity.
[0033] The second solvent is not particularly restricted so long as
it may enable the inorganic particles to be homogeneously dispersed
therein. Preferably, the second solvent has polar properties
substantially similar to the first solvent.
[0034] The second solvent may be ketones or alcohols having an
evaporation rate different from that of the first solvent for
dissolving the organic polymer and may include, for example,
methanol, methylethylketone (MEK), isopropanol, ethyleneglycol,
dimethylacetate, methyl isobutanol, and the like. Methanol or
methylethylketone is more preferred.
[0035] The inorganic particle used herein is not particularly
restricted so long as it does not cause oxidation and/or reduction
(often, referred to as "redox reaction"), that is, electrochemical
reaction with a cathode collector or an anode collector at
operating voltages of a battery (for example, 0 to 5V for
Li/Li.sup.+) and may not affect electrically conductive properties
due to lowered mobility of lithium ions. The inorganic particle may
include, for example, at least one or two selected from a group
consisting of BaTiO.sub.3, Pb(Zr, Ti)O.sub.3 (PZT),
Pb.sub.1-xLa.sub.xZr.sub.1-yTi.sub.yO.sub.3 (PLZT),
PB(Mg.sub.3Nb.sub.2/3)O.sub.3--PbTiO.sub.3 (PMN--PT), hafnia
(HfO.sub.2)SrTiO.sub.3, SnO.sub.2, CeO.sub.2, MgO, NiO, CaO, ZnO,
ZrO.sub.2, Y.sub.2O.sub.3, Al.sub.2O.sub.3, TiO.sub.2 and mixtures
thereof.
[0036] The inorganic particle may also include an inorganic
particle capable of delivering lithium ions. Such an inorganic
particle may contain a lithium element and transport a lithium ion,
instead of storage thereof. Therefore, if this inorganic particle
is included in a battery, the battery may have improved lithium ion
conductance.
[0037] Defects present in a structure of the inorganic particle
capable of delivering lithium ions may facilitate delivery and/or
movement of the lithium ions and such inorganic particle may
include, for example: (LiAlTiP).sub.xO.sub.y (0<x<4,
0<y,13) based glass such as lithium phosphate
(Li.sub.3PO.sub.4), lithium titanium phosphate
(Li.sub.xTi.sub.y(PO.sub.4).sub.3, 0<x<2, 0<y<3),
lithium aluminum titanium phosphate
(Li.sub.xAl.sub.yTi.sub.z(PO.sub.4).sub.3, 0<x<2,
0<y<1, 0<z<3),
14Li.sub.2O-9Al.sub.2O.sub.3-38TiO.sub.2-39P.sub.2O.sub.5, etc.;
Lithium lanthanum titanate (Li.sub.xLa.sub.yTiO.sub.3, 0<x<2,
0<y<3); lithium germanium thiophosphate
(Li.sub.xGe.sub.yP.sub.zS.sub.w, 0<x<4, 0<y<1,
0<z<1, 0<w<5) such as
Li.sub.3.25Ge.sub.0.25P.sub.0.75S.sub.4; lithium nitride
(Li.sub.xN.sub.y, 0<x<4, 0<y<2) such as Li.sub.3N;
SiS.sub.2 based glass (Li.sub.xSi.sub.yS.sub.z, 0<x<3,
0<y<2, 0<z<4) such as
Li.sub.3PO.sub.4--Li.sub.2S--SiS.sub.2; P.sub.2S.sub.5 based glass
(Li.sub.xP.sub.yS.sub.z, 0<x<3, 0<y<3, 0<z<7)
such as LiI--Li.sub.2S--P.sub.2S.sub.5; or mixtures thereof.
[0038] The inorganic particle may have a particle diameter ranging
from 0.001 to 10 .mu.m. If the particle diameter is too small, a
desirable increase in porosities is not attained and a degree of
dispersion of the particles may be reduced and interrupt movement
of lithium ions. On the other hand, if the particle diameter is
excessively large, a thickness of the membrane may increase to
inversely reduce battery capacity, and may cause a considerable
increase in size of pores, leading to a problem of internal short
circuit.
[0039] Meanwhile, constitutional ratios of the inorganic particle
to the organic polymer are not particularly limited and may be
controlled in the range of 10:90 to 90:10 (% by weight) and,
preferably, 70:30 to 90:10. If a content of the organic polymer is
too high, an empty space formed between the inorganic particles is
reduced, which in turn, reduces pore size and porosity, thus not
attaining desired thickness flexibility. On the other hand, if the
content of the organic polymer is too low, binding force between
inorganic particles and/or adhesion of the inorganic particle to a
porous substrate may be reduced, causing a decrease in mechanical
properties of a final organic/inorganic composite membrane.
[0040] Step (iii) is a process of coating both sides of the porous
substrate with a mixture of organic/inorganic materials via
dip-coating. The dip-coating which immerses the porous substrate in
a coating solution is well known in the art and, therefore, further
detailed description thereof will be omitted hereinafter for
brevity and to prevent the present invention from being
unclear.
[0041] The porous substrate is not particularly restricted so long
as it has a number of pores through which lithium ions are moved,
and may include a polyolefin based membrane. Such a polyolefin
based membrane may include, for example, high density polyethylene,
linear low density polyethylene, low density polyethylene,
ultrahigh molecular weight polyethylene, polypropylene or
derivatives thereof. The porous substrate may also include fibrous
or membrane type substrates and, in case of the fibrous substrate,
it may include a spun-bond or melt-blown type substrate made of
filament fibers, which is a non-woven fabric useful for fabricating
a porous web.
[0042] Step (iv) is a process of removing the first solvent (or the
first and the second solvents). It is expected that microfine pores
may be formed by phase separation during evaporation of the
solvent.
[0043] Each of the microfine pores may have a diameter of 0.1 to 50
.mu.m and a permeability (or porosity) ranging from 100 to 1,000
sec/100 cc. As the diameter or the permeability increases, buffer
effects are higher, which in turn enhances prevention of
deformation of the jelly-roll structure. However, if the diameter
is too large or the permeability is too high, structural stability
may be deteriorated. On the other hand, if the diameter is too
small or the permeability is too low, desirable buffer effects may
not be attained and ion conductivity may be deteriorated, thus not
being preferred.
[0044] Controlling of buffer effects on contraction or expansion
during charge/discharge may be based on the diameter or the
permeability of the microfine pores. Such buffer effects may also
be controlled depending on a thickness of the organic/inorganic
composite layer. With regard to this aspect, the organic/inorganic
composite layer may be coated in a thickness ranging from 1 to 10
.mu.m.
[0045] Step (b) is a process that inserts one end of a sheet
laminate comprising a cathode sheet and an anode sheet as well as a
composite membrane fabricated in step (a) into a mandrel, winding
the sheet laminate around the mandrel, and removing the mandrel to
complete fabrication of a jelly-roll structure. When the mandrel is
removed, the interfacial friction coefficient (.mu.) between the
composite membrane and the mandrel is very low, especially, not
more than 0.28. Therefore, a "tail out condition" caused by high
friction generated during removal of the mandrel may be prevented,
thereby improving productivity. The interfacial friction may be
equal to or less than tension on the winding process.
[0046] The interfacial friction coefficient (.mu.) may be
calculated by friction force (F)/load (L), preferably, may be
0.25.mu. or less. Experimental results demonstrated that the tail
out condition is observed when the interfacial friction coefficient
is 0.30 or more.
[0047] In order to achieve such a low interfacial friction,
reduction of either the interfacial friction coefficient of the
composite membrane or the interfacial friction coefficient of the
mandrel may be considered.
[0048] As an exemplary embodiment of the former case, decreasing a
molecular weight of an organic polymer as a binder, the interfacial
friction coefficient of the composite membrane may be lowered. In
general, the organic polymer exhibits reduced viscosity with a
decrease in molecular weight thereof, thus lowering the interfacial
friction coefficient. However, since the organic polymer is
required to bind the inorganic particles together and/or bind the
inorganic particles to a substrate for the membrane, this must have
a molecular weight sufficient to exhibit desired adhesiveness.
Considering such aspects, the organic polymer, for example, PVdF
may have a molecular weight of 100,000 to 1,000,000.
[0049] As an exemplary embodiment of the latter case, coating a
surface of the mandrel with a low friction coating material, the
interfacial friction coefficient of the mandrel may be lowered.
Therefore, the coating material is not particularly restricted so
long as it may reduce surface roughness of an object to be coated,
that is, may maintain a low friction coefficient of the object. For
example, the coating material may include at least one selected
from: Group 4a, 5a and/or 6a elements in Periodic Table; aluminum;
carbides, nitrides, oxides and/or a solid solution of silicon;
diamond like carbon (DLC); diamond; and teflon. Teflon is more
preferred. Such a coating material may be applied to form a single
layer or two or more layers on the object.
[0050] The coating process is not particularly restricted and may
be conducted by vapor phase synthesis such as a physical vapor
deposition (PVD) method or a chemical vapor deposition (CVD)
method. The PVD method may be conducted by, for example, ion
plating, arc ion plating, sputtering deposition, and so forth. The
CVD method may be conducted by, for example, plasma CVD.
[0051] The present invention also provides a composite membrane for
a secondary battery fabricated by a process comprising:
[0052] (i) dissolving an organic polymer, which is capable of
inducing a binding force between inorganic particles and adhesion
of the inorganic particles to a surface of a substrate, in a
solvent to prepare a solution;
[0053] (ii) adding the inorganic particles to the prepared solution
to prepare an organic/inorganic coating solution;
[0054] (iii) immersing a porous substrate in the coating solution
through dip-coating, so as to form coating layers on both sides of
the porous substrate; and
[0055] (iv) removing the solvent to produce an organic/inorganic
composite layer having microfine pores, wherein the
organic/inorganic composite layer includes microfine pores for
moderating a variation in volume during charge/discharge of the
secondary battery and the interfacial friction coefficient (.mu.)
between the composite membrane and a mandrel used for manufacturing
a jelly-roll type electrode assembly is not more than 0.28.
[0056] The present invention also provides a jelly-roll type
electrode assembly fabricated by the method as described above,
wherein an organic/inorganic composite layer, which includes
microfine pores capable of moderating a variation in volume during
charge/discharge of a secondary battery, is formed on both sides of
a porous substrate for fabricating a membrane and the
organic/inorganic composite layer may be formed by interposing a
composite membrane therein wherein an interfacial friction
coefficient relative to a mandrel used for manufacturing the
jelly-roll electrode assembly may be not more than 0.28.
[0057] As is apparent from the above, a composite membrane for a
secondary battery fabricated according to the above processes and a
jelly-roll type electrode assembly including the same may exhibit
buffer effects on contraction and/or expansion of an electrode by
microfine pores included in an organic/inorganic coating layer so
as to inhibit deformation of the jelly-roll type electrode
assembly, thereby preventing performance and safety of a battery
having the jelly-roll type electrode from being deteriorated due to
the deformation. In addition, since inorganic particles are
homogeneously dispersed on both sides of the composite membrane,
the membrane may exhibit desired mechanical strength and excellent
dimensional stability, thus preventing contraction of the membrane
and internal short circuit damage due to the contraction.
Accordingly, the secondary battery having the jelly-roll type
electrode assembly described above may have superior thermal
stability and exhibit improved battery performance.
[0058] The electrode assembly may be fabricated by winding a
composite membrane, both sides of which are coated with
organic/inorganic coating layers while interposing the membrane
between a cathode and an anode.
[0059] The cathode may be fabricated by, for example, applying a
mixture comprising a cathode active material, a conductive material
and a binder to a cathode collector and drying the coated
collector. The mixture may optionally include a filler, a viscosity
controlling agent, a cross-linking promoter, a coupling agent, an
adhesion promoter and the like, alone or in combination with two or
more thereof.
[0060] The cathode active material may include, but is not limited
to, for example: a lamellar compound such as lithium cobalt oxide
(LiCoO.sub.2) or lithium nickel oxide (LiNiO.sub.2), or a compound
substituted by one or more of transitional metals; a lithium
manganese compound such as Li.sub.1+xMn.sub.2-xO.sub.2 (wherein x
ranges from 0 to 0.33), LiMnO.sub.3, LiMn.sub.2O.sub.3,
LiMnO.sub.2, etc.; a lithium copper oxide (Li.sub.2CuO.sub.2); a
vanadium oxide such as LiV.sub.3O.sub.8, LiFe.sub.3O.sub.4,
V.sub.2O.sub.5, Cu.sub.2V.sub.2O.sub.7, etc.; a Ni site type
lithium nickel oxide represented by LiNi.sub.1-xM.sub.xO.sub.2
(wherein M=Co, Mn, Al, Cu, Fe, Mg, B or Ga and x=0.01 to 0.3); a
lithium manganese composite oxide represented by
LiMn.sub.2-xM.sub.xO.sub.2 (wherein M=Co, Ni, Fe, Cr, Zn or Ta and
x=0.01 to 0.1) or Li.sub.2Mn.sub.3MO.sub.8 (wherein M=Fe, Co, Ni,
Cu or Zn); LiMn.sub.2O.sub.4 containing Li partially substituted by
alkali earth metal ions; a disulfide compound;
Fe.sub.2(MoO.sub.4).sub.3, and so forth.
[0061] The cathode collector may have a thickness ranging from 3 to
500 .mu.m. The cathode collector used herein is not particularly
restricted so long as it does not induce chemical modification of
the battery while having high conductivity. For example, the
cathode collector may include stainless steel, aluminum, nickel,
titanium, calcined carbon, or aluminum or stainless steel which is
surface-treated with carbon, nickel, titanium, silver and the like.
Forming a microfine relief on a surface of the collector, the
collector may enhance adhesive force of the cathode active material
and may be fabricated in various forms such as a film, a sheet, a
foil, a net, a porous material, a foamed material, a non-woven
fabric material, and the like.
[0062] The conductive material may be added in an amount of 1 to 50
wt. % of the total weight of a mixture containing the cathode
active material. Such conductive material is not particularly
restricted so long as it does not cause chemical modification of a
battery while having desired conductivity. For instance, the
conductive material may include: graphite such as natural graphite
or artificial graphite; carbon black such as carbon black,
acetylene black, kechen black, channel black, furnace black, lamp
black, summer black, etc.; conductive fiber such as carbon fiber,
metal fiber, etc.; metal powder such as carbon fluoride, aluminum,
nickel powder, etc.; conductive whiskers such as zinc oxide,
potassium titanate, etc.; conductive metal oxide such as titanium
oxide; polyphenylene derivatives, and so forth.
[0063] The binder may comprise a component for supporting
combination of an active material with the conductive material
and/or binding to the collector and, in general, may be added in an
amount of 1 to 50 wt. % of the total weight of a mixture comprising
a cathode active material. Such binder may include, for example,
polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose
(CMC), starch, hydroxypropyl cellulose, regenerated cellulose,
polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene,
polypropylene, ethylene-propylene-diene terpolymer (EPDM),
sulfonated EPDM, styrene butyrene rubber, fluorine rubber, various
copolymers, etc.
[0064] The filler may optionally be used to inhibit expansion of a
cathode and, is not particularly restricted so long as it is a
fibrous material which does not cause chemical modification of a
battery. For example, the filler may include an olefin based
polymer such as polyethylene, polypropylene, etc.; or a fibrous
material such as carbon fiber.
[0065] The viscosity controller may regulate viscosity of an
electrode composite material so as to readily conduct mixing of the
electrode composite material and application of the same to the
collector, and may be added in an amount of 0 to 30 wt. % relative
to the total weight of the composite material. For example, the
viscosity controller may include, but is not limited to,
carboxymethyl cellulose, polyvinylidene fluoride, polyvinyl
alcohol, and the like. Optionally, a solvent such as N-methyl
pyrrolidone (NMP) may be added in an amount of 0 to 30 wt. %
relative to the total weight of the electrode composite material so
as to regulate the viscosity of the electrode composite material.
After or before polymerization or curing, such a solvent is dried
to fabricate an anode.
[0066] The cross-linking promoter is a material for accelerating
cross-linkage of the binder and may be added in an amount of 0 to
50 wt. % relative to the total weight of the binder. The
cross-linking promoter may include, for example: amines such as
diethylene triamine, triethylene tetramine, diethylamino
propylamine, xylene diamine, isophorone diamine, etc.; acid
anhydrides such as dodecyl succinic anhydride, phthalic anhydride,
etc. Additionally, polyamide resin, polysulfite resin, phenol
resin, and the like may be used.
[0067] The coupling agent is a material to increase adhesion
between the active material and the binder, and may have at least
two functional groups. The coupling agent may be added in an amount
of 0 to 30 wt. % relative to the total weight of the binder. If one
of the functional groups in the coupling agent reacts with silicon,
tin, or with a hydroxyl group or a carboxyl group present on a
surface of a graphite based active material to form a chemical bond
while the other reacts with a nano composite in the present
invention to form another chemical bond, the coupling agent is not
particularly restricted. For instance, the coupling agent may
include silane based coupling agents such as triethoxysilylpropyl
tetrasulfide, mercaptopropyl triethoxysilane, aminopropyl
triethoxysilane, chloropropyl triethoxysilane, vinyl
triethoxysilane, methacryloxypropyl triethoxysilane,
glycidoxypropyl triethoxysilane, isocyanatopropyl triethoxysilane,
cyanatopropyl triethoxysilane, and the like.
[0068] The adhesion promoter may be added in an amount of 10 wt. %
relative to the binder and is not particularly restricted thereto
so long as it improves adhesion of an electrode active material to
the collector. For example, the adhesion promoter may include
oxalic acid, adipic acid, formic acid, acrylic acid derivatives,
itaconic acid derivatives, and so forth.
[0069] An anode is fabricated by applying an anode material to an
anode collector and drying the coated collector and, optionally,
may additionally include other components described above.
[0070] The anode collector generally has a thickness of 3 to 500
.mu.m. Such anode collector is not particularly restricted so long
as it does not induce chemical modification of a battery while
having conductive properties. For example, the anode collector may
include copper, stainless steel, aluminum, nickel, titanium,
calcined carbon, copper or stainless steel surface-treated with
carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, and
so forth. Similar to a cathode collector, the anode collector may
have microfine roughness on a surface thereof so as to reinforce
adhesion of the anode active material, and the anode collector may
be fabricated in various forms such as a film, a sheet, a foil, a
net, a porous material, a foamed material, a non-woven fabric
material, and the like.
[0071] The anode material may include, for example: carbon such as
graphite based carbon; metal composite oxides such as
Li.sub.xFe.sub.2O.sub.3 (0.ltoreq.x.ltoreq.1), Li.sub.xWO.sub.2
(0.ltoreq.x.ltoreq.1), Sn.sub.xMe.sub.1-xMe'.sub.yO.sub.z (Me:Mn,
Fe, Pb, Ge; and Me':Al, B, P, Si, Group 1, 2 or 3 elements;
0.ltoreq.x.ltoreq.1; 1.ltoreq.y.ltoreq.3; 1.ltoreq.z.ltoreq.8);
lithium metal; lithium alloy; silicon alloy; tin alloy; metal
oxides such as SnO, SnO.sub.2, PbO, PbO.sub.2, Pb.sub.2O.sub.3,
Pb.sub.3O.sub.4, Sb.sub.2O.sub.3, Sb.sub.2O.sub.4, Sb.sub.2O.sub.5,
GeO, GeO.sub.2, Bi.sub.2O.sub.3, Bi.sub.2O.sub.4, Bi.sub.2O.sub.5,
etc.; a conductive polymer such as polyacetylene; Li--Co--Ni based
materials, and the like.
[0072] The present invention further provides a secondary battery
having the jelly-roll type electrode assembly built in a battery
case. The secondary battery preferably has a structure of a
non-aqueous lithium electrolyte impregnated into the electrode
assembly.
[0073] The non-aqueous electrolyte containing lithium comprises a
non-aqueous electrolyte and a lithium salt. Such non-aqueous
electrolyte may include a non-aqueous liquid electrolyte, a solid
electrolyte, an inorganic solid electrolyte, etc.
[0074] The non-aqueous liquid electrolyte may include an aprotic
organic solvent such as N-methyl-2-pyrrolidinone, propylene
carbonate, ethylene carbonate, butylene carbonate, dimethyl
carbonate, diethyl carbonate, ethylmethyl carbonate,
.gamma.-butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane,
tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethylsulfoxide,
1,3-dioxolane, 4-methyl-1,3-dioxene, dimethylether, formamide,
dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl
formate, methyl acetate, phosphoric acid triester,
trimethoxymethane, dioxolane derivatives, sulpholane, methyl
sulpholane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate
derivatives, tetrahydrofuran derivatives, ether, methyl propionate,
ethyl propionate, and the like.
[0075] The organic solid electrolyte may include, for example,
polyethylene derivatives, polyethylene oxide derivatives,
polypropylene oxide derivatives, phosphoric acid ester polymer,
poly agitation lysine, polyester sulfide, polyvinyl alcohol,
polyvinylidene fluoride, a polymer containing an ionic dissociative
group, and the like.
[0076] The inorganic solid electrolyte may include, for example, Li
based nitrides, halides or sulfates such as Li.sub.3N, LiI,
Li.sub.5NI.sub.2, Li.sub.3N--LiI--LiOH, LiSiO.sub.4,
LiSiO.sub.4--LiI--LiOH, Li.sub.2SiS.sub.3, Li.sub.4SiO.sub.4,
Li.sub.4SiO.sub.4--LiI--LiOH,
Li.sub.3PO.sub.4--Li.sub.2S--SiS.sub.2, and so forth.
[0077] The lithium salts are readily dissolved in the non-aqueous
electrolyte and may include, for example, LiCl, LiBr LiI,
LiClO.sub.4, LiBF.sub.4, LiB.sub.10Cl.sub.10, LiPF.sub.6,
LiCF.sub.6SO.sub.3, LiCF.sub.3CO.sub.2, LiAsF.sub.6, LiSbF.sub.6,
LiAlCl.sub.4, CH.sub.4SO.sub.3Li, CF.sub.3SO.sub.3Li, LiSCN,
LiC(CF.sub.3SO.sub.2).sub.3, (CF.sub.3SO.sub.2).sub.2NLi,
chloroboran lithium, lower aliphatic carboxylic acid lithium,
lithium tetraphenyl borate, imide, etc.
[0078] In order to improve charge/discharge characteristics and/or
flame retardancy, the non-aqueous electrolyte may further include,
for example, pyridine, triethyl phosphite, triethanolamine, cyclic
ether, ethylenediamine, n-glyme, hexaphosphoric triamide,
nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted
oxazolidinone, N,N-substituted imidazolidine, ethyleneglycol
dialkylether, ammonium salts, pyrrol, 2-methoxy ethanol, aluminum
trichloride, etc. Optionally, halogen containing solvents such as
carbon tetrachloride or ethylene trifluoride may be added to obtain
flame resistance, or carbon dioxide gas may be added to enhance
high temperature retention properties.
[0079] In a preferred embodiment, the second battery may be a pouch
type battery having a laminate sheet wherein a jelly-roll type
electrode assembly comprises a resin layer and a metal layer.
[0080] A conventional pouch type battery has a case with relatively
reduced strength compared to a cylindrical battery or an angular
battery having a metal case. Therefore, if a jelly-roll type
electrode assembly with significant deformation caused by
charge/discharge is used, sealing effects may be deteriorated,
causing a decrease in battery life time and/or safety. However, the
jelly-roll type electrode assembly of the present invention has a
separation membrane coated with an organic/inorganic composite
layer including microfine pores so as to reduce pressure applied by
expansion of an electrode during charge/discharge, thereby
noticeably inhibiting deformation of the battery and having high
safety and excellent battery life time.
[0081] The laminate sheet described above may have a structure
comprising, for example, an inner resin layer, a shielding metal
layer and an outer resin layer. The outer resin layer must have
superior protective performance against external environments,
requiring at least a desired extent of tensile strength and
weatherproof properties. In this aspect, a polymer resin in the
outer resin layer may be polyethylene terephthalate (PET) and/or an
oriented nylon film. The shielding metal layer may be formed using
aluminum in order to prevent inflow of impurities such as gas or
moisture and/or leakage of materials out of the battery and, in
addition, to increase a strength of the battery case. On the other
hand, a polymer resin in the inner resin layer may include
polyolefin resin, which has favorable thermal adhesion and low
moisture absorption to inhibit penetration of an electrolyte, and
exhibits neither expansion nor erosion caused by the electrolyte.
More preferably, the polymer resin is polypropylene (CPP).
EXAMPLES
[0082] Now, the present invention will be described in more detail
in the following description with reference to exemplary
embodiments and examples of the present invention, which are given
for illustrative purposes only and should not be construed as
limiting the spirit and scope of the invention.
Example 1
1.1. Preparation of Electrode Sheet
[0083] A cathode sheet was fabricated by adding 95 wt. % of lithium
cobalt oxide (LiCoO.sub.2) as a cathode active material, 2.5 wt. %
of Super-P (a conductive material), 2.5 wt. % of PVdF (a binder) to
N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a cathode
mixture slurry, and then, applying the slurry to both sides of an
aluminum foil, drying and compressing the same.
[0084] An anode sheet was fabricated by adding 95 wt. % of graphite
as an anode active material, 1.5 wt. % of Super-P (a conductive
material), 3.5 wt. % of PVdF (a binder) to NMP to prepare an anode
mixture slurry, and then, applying the slurry to both sides of a
copper foil, drying and compressing the same.
1.2. Preparation of Organic/Inorganic Composite Porous Membrane
[0085] An organic/inorganic composite porous membrane was
fabricated by the following procedure. Firstly, 5 wt. % of
polyvinylidenefluoride-chlorotrifluoroethylene (PVdF-CTFE)
copolymer was added to acetone as a first solvent and dissolved at
60.degree. C. for about 3 hours to prepare a mixture solution.
Herein, a concentration of the polymer in the solution ranged from
4 to 6 wt. % relative to the total weight of the solution. After 3
hours, the polymer solution was cooled to room temperature and
BaTiO.sub.3 powder dispersed in methylethylketone as a second
solvent was added to the cooled solution in an amount of 8 to 12
wt. % relative to the total weight of the solution, followed by
agitating at room temperature for 1 hour. After a porous substrate
made of ethylene material was immersed in the prepared mixture
solution through dip-coating, the coated substrate was placed in a
convection oven and dried at 90.degree. C. A coating thickness was
controlled to about 5 .mu.m. As a result of measuring porosity with
a porosimeter, it was found that an active layer coated on the
polyethylene membrane had a pore size of 0.1 to 1 .mu.m and a
porosity of 30% (400 sec/100 cc).
1.3. Preparation of Jelly-Roll Structure
[0086] A cathode sheet, a separation membrane and an anode sheet
were sequentially stacked and wound using a mandrel to fabricate a
jelly-roll structure. The wound jelly-roll was fixed by attaching a
seal tape on one outer side of the jelly-roll, and then, compressed
to form a plate type product.
1.4. Preparation of Pouch Type Secondary Battery
[0087] After the fabricated jelly-roll structure was placed in a
pouch type battery case, a lithium electrolyte was introduced to
the same, followed by sealing to complete the secondary
battery.
Comparative Example 1
[0088] A secondary battery was fabricated by the same procedure as
described in Example 1 except that a porous membrane made of
polyethylene material, which has no organic/inorganic porous
coating layer, was used.
Experimental Example 1
[0089] In order to compare and determine differences in cycle
characteristics and swelling properties of two batteries fabricated
in Example 1 and Comparative Example 1, respectively, 500
charge/discharge cycles were conducted under charge/discharge
conditions shown in FIG. 1 and capacity ratios and swelling extents
were determined. The results are shown in FIG. 1.
[0090] As illustrated in FIG. 1, it was found that the battery
fabricated according to Example 1 has cycle characteristics
substantially corresponding to those of the battery fabricated
according to Comparative Example 1. More particularly, both of the
batteries of Example 1 and Comparative Example 1 substantially
maintained the same discharge capacity. Therefore, it may be
understood that the present inventive battery of Example 1
exhibited no decrease in discharge capacity, although it had a
separation membrane having an organic/inorganic composite
layer.
[0091] On the other hand, a swelling ratio of the battery of
Example 1 was only 30% relative to that of the battery of
Comparative Example 1, thus demonstrating noticeably inhibited
swelling. The reason behind these results may be that the
organic/inorganic composite membrane in the battery of Example 1
buffered thickness expansion and contraction of an electrode so as
to prevent deformation of the jelly-roll structure.
Experimental Example 2
[0092] In order to evaluate a mechanical strength of a battery, the
batteries fabricated in Example 1 and Comparative Example 1 were
subjected to bending strength measurement (using a texture
analyzer) so as to determine a piercing strength. The results are
shown in FIG. 2.
[0093] As illustrated in FIG. 2, the present inventive battery of
Example 1 exhibited greater than 30% higher strength than the
battery of Comparative Example 1. The reason behind these results
may be that the mechanical strength of the battery was improved by
inorganic particles in the organic/inorganic composite coating
layer.
[0094] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
INDUSTRIAL APPLICABILITY
[0095] As described above, the method for fabrication of a
jelly-roll type electrode assembly in accordance with the present
invention may maintain a low interfacial friction between a
composite membrane and a mandrel and, when the mandrel is removed,
may prevent the composite membrane from being released, thereby
exhibiting excellent winding assembly characteristics. In addition,
using the composite membrane coated with organic/inorganic
composite layers including microfine pores at both sides thereof,
the present invention may have various advantages in that a
mechanical strength of a battery is increased and deformation of
the electrode assembly is inhibited, thereby preventing
deterioration in performance of the battery while enhancing safety
of the battery.
* * * * *