U.S. patent application number 12/676963 was filed with the patent office on 2010-08-05 for non-woven material with particle filling.
This patent application is currently assigned to CARL FREUDENBERG KG. Invention is credited to Peter Kritzer, Michael Roth, Gunter Scharfenberger, Rudolf Wagner, Christoph Weber.
Application Number | 20100196688 12/676963 |
Document ID | / |
Family ID | 39846619 |
Filed Date | 2010-08-05 |
United States Patent
Application |
20100196688 |
Kind Code |
A1 |
Kritzer; Peter ; et
al. |
August 5, 2010 |
NON-WOVEN MATERIAL WITH PARTICLE FILLING
Abstract
A ply includes a fibrous nonwoven web fabric forming a
foundational structure, wherein the foundational structure includes
fibers forming first pores and is partially filled with particles,
wherein the particles at least partially fill the first pores so as
to form regions filled with particles, wherein the particles in the
filled regions form second pores such that an average diameter of
the particles is greater than an average pore size of more than 50%
of the second pores.
Inventors: |
Kritzer; Peter; (Forst,
DE) ; Weber; Christoph; (Laudenbach, DE) ;
Wagner; Rudolf; (Muellheim, DE) ; Scharfenberger;
Gunter; (Frankenthal, DE) ; Roth; Michael;
(Mainz, DE) |
Correspondence
Address: |
LEYDIG, VOIT AND MAYER
TWO PRUDENTIAL PLAZA, SUITE 4900, 180 NORTH STETSON AVENUE
CHICAGO
IL
60601
US
|
Assignee: |
CARL FREUDENBERG KG
Weinheim
DE
|
Family ID: |
39846619 |
Appl. No.: |
12/676963 |
Filed: |
June 16, 2008 |
PCT Filed: |
June 16, 2008 |
PCT NO: |
PCT/EP2008/004824 |
371 Date: |
March 8, 2010 |
Current U.S.
Class: |
428/220 ; 442/59;
442/60 |
Current CPC
Class: |
H01M 50/411 20210101;
Y10T 442/2885 20150401; Y10T 442/2008 20150401; H01M 50/44
20210101; Y02E 60/50 20130101; Y10T 442/20 20150401; H01M 2008/1095
20130101; Y02E 60/10 20130101; Y10T 442/2893 20150401; Y10T
442/2918 20150401; Y10T 442/291 20150401 |
Class at
Publication: |
428/220 ; 442/59;
442/60 |
International
Class: |
B32B 5/00 20060101
B32B005/00; B32B 5/02 20060101 B32B005/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 2007 |
DE |
10 2007 042 554.8 |
Claims
1-18. (canceled)
19. A ply comprising: a fibrous nonwoven web fabric forming a
foundational structure, wherein the foundational structure includes
fibers forming first pores and is partially filled with particles,
wherein the particles at least partially fill the first pores so as
to form regions filled with particles, wherein the particles in the
filled regions form second pores such that an average diameter of
the particles is greater than an average pore size of more than 50%
of the second pores.
20. The ply as recited in claim 19, wherein the particles are
spherical.
21. The ply as recited in claim 19, wherein the particles form a
sheet-like homogeneous distribution in the foundational
structure.
22. The ply as recited in claim 19, wherein at least a portion of
the filled regions forms a coating of the foundational
structure.
23. The ply as recited in claim 19, wherein the particles are
united with the fibrous nonwoven web fabric via a binder composed
of organic polymers selected from the group consisting of
polyvinylpyrrolidone, polyacrylic acid, polyacrylate,
polymethacrylic acid, polymethacrylate, polystyrene, polyvinyl
alcohol, polyvinyl acetate, polyacrylamide and copolymers thereof,
cellulose and its derivatives, polyethers, phenolic resin, melamine
resin, polyurethane, nitrile rubber (NBR), styrene-butadiene rubber
(SBR) and latex.
24. The ply as recited in claim 23, wherein a melting point of the
binder is below a melting point of at least one of the particles
and the fibers.
25. The ply as recited in claim 19, wherein the particles have an
average diameter between 0.01 and 10 .mu.m.
26. The ply as recited in claim 19, wherein the particles are
fabricated from organic polymers selected from the group consisting
of polypropylene, polyvinylpyrrolidone, polyvinylidene fluoride,
polyester, polytetrafluoroethylene, perfluoro-ethylene-propylene
(FEP), polystyrene, styrene-butadiene copolymers, polyacrylate and
nitrile-butadiene polymers and copolymers thereof.
27. The ply as recited in claim 19, wherein the fibers of the
fibrous nonwoven web fabric are fabricated from organic polymers
selected from the group consisting of polybutylene terephthalate,
polyethylene terephthalate, polyacrylonitrile, polyvinylidene
fluoride, polyether ether ketone, polyethylene naphthalate,
polysulfone, polyimide, polyester, polypropylene, polyoxymethylene,
polyamide and polyvinylpyrrolidone.
28. The ply as recited in claim 19, wherein an average length of
the fibers exceeds an average diameter of the fibers by at least a
factor of two.
29. The ply as recited in claim 19, wherein at least 90% of the
fibers have an average diameter of not more than 12 .mu.m.
30. The ply as recited in claim 19, wherein at least 40% of the
fibers have an average diameter of not more than 8 .mu.m.
31. The ply as recited in claim 19, wherein a thickness of the ply
is not more than 100 .mu.m.
32. The ply as recited in claim 19, wherein a porosity of the ply
is at least 25%.
33. The ply as recited in claim 19, wherein the first and second
pores form a labyrinthine microstructure.
34. The ply as recited in claim 19, wherein the first and second
pores have a pore size of not more than 3 .mu.m.
35. The ply as recited in claim 19, wherein an ultimate tensile
strength force of the ply is at least 15 N/5 cm in a longitudinal
direction.
36. The ply as recited in claim 19, wherein the foundational
structure is calendered.
Description
[0001] This application is a U.S. National Phase Application under
35 U.S.C. .sctn.371 of International Application No.
PCT/EP2008/004824, filed on Jun. 16, 2008, and claiming priority to
German Application No. DE 10 2007 042 554.8, filed on Sep. 7, 2007.
The International Application was published in German on Mar. 19,
2009 as WO 2009/033514 under PCT article 21 (2).
[0002] This invention relates to a ply having a foundational
structure composed of a fibrous nonwoven web fabric, the
foundational structure consisting of fibers and having first pores
formed by the fibers, the foundational structure being at least
partially filled with particles, which particles at least partially
fill the first pores and form regions filled with particles.
BACKGROUND
[0003] Plies of the type mentioned are already known from the prior
art. Such plies are used as separators in batteries and capacitors
in energy storage duty. Charge storage in batteries and capacitors
takes place chemically, physically or in a mixed form, for example
by chemisorption.
[0004] To avoid an internal discharge within the battery or
capacitor, oppositely charged electrodes are separated from each
other mechanically by means of materials which do not conduct
electrons and are known as separators or spacers. At the same time,
by virtue of their porosity being conformed to the energy storage
system and its use, the separators or spacers make it possible for
ionic charge-carriers of an electrolyte to move between the
electrodes.
[0005] The separators known from the prior art have small,
interlinked openings in the micrometer range. These openings are
said to be as large as possible in order that electrolyte
conductivity in the drenched separator be as high as possible and
the battery thus have a high power density. However, if the
openings are too large, then metal dendrites can lead to a short
circuit between the two electrodes which are actually to be
electrically separated from each other. The metal dendrites consist
either of lithium or of other metals which can be present in the
battery as impurities.
[0006] Furthermore, particles of electrically conductive electrode
materials can migrate through the openings. These processes can
give rise to a short circuit between the electrodes and greatly
speed the self-discharging of the battery or capacitor.
[0007] A short circuit can result in the local flow of very high
currents, which releases heat. This heat can cause the separator to
melt, which in turn can lead to a distinct decrease in the
insulating/isolating effect of the separator. A very rapidly
self-discharging battery consequently constitutes a high safety
risk because of its high energy content and also the combustibility
of the electrolyte and of other constituents.
[0008] A further disadvantage with separators known from the prior
art is their lack of stability in the event of rising temperatures.
The melting point is around 130.degree. C. when polyethylene is
used and around 150.degree. C. when polypropylene is used.
[0009] Causes of short circuits include shrinkage of the separator
due to excessive high temperature in the battery, metal dendrite
growth due to reduction of metal ions (lithium, iron, manganese or
other metallic impurities), debris from electrode particles,
cutting debris or broken covering on electrodes, and direct contact
between the two flat electrodes under pressure.
[0010] EP 0 892 448 A2 discloses the shutdown mechanism. The
shutdown mechanism responds to local heating, for example due to a
short circuit, by counteracting the aerial spreading of the short
circuit by prohibiting ion migration in the vicinity of the initial
short circuit. The heat loss due to the short circuit causes
polyethylene to heat up to such an extent that it will melt and
blind the pores of the separator. Polypropylene, which has a higher
melting point, stays mechanically intact.
[0011] US 2002/0168569 A1 describes the construction of a separator
consisting of polyvinyl difluoride which, in the manufacturing
operation, is incipiently solubilized with a solvent, mixed with
silica particles and applied as a thin film. Removing the solvent
leaves a porous membrane.
[0012] WO 2006/068428 A1 describes the production of separators for
lithium ion batteries by using a polyolefin separator which is
additionally filled with gellike polymers and inorganic
particles.
[0013] WO 2004/021475 A1 describes the use of ceramic particles
which are combined with organosilicon adhesion promoters and
inorganic binders from oxides of the elements silicon, aluminum
and/or zirconium to form a thin sheet material.
[0014] To achieve adequate mechanical flexibility, the ceramic
particles are incorporated into a supporting material, for example
a fibrous nonwoven web fabric. This is disclosed by WO 2005/038959
A1.
[0015] To prevent short circuits in the initial stages of metal
dendrite formation, WO 2005/104269 A1 describes the use of
comparatively low-melting waxes as an admixture to a ceramic
paste.
[0016] WO 2007/028662 A1 describes the addition of polymer
particles having a melting point of above 100.degree. C. to ceramic
fillers in order that the mechanical properties of the separator
may be improved. The materials described are intended for use as a
separator for lithium ion materials. Although these separators do
provide a higher thermal stability than membranes, they have so far
not been a commercial success. This may be due to their relatively
high costs and to the excessive thickness of the material, which is
above 25 .mu.m.
[0017] WO 2000/024075 A1 describes the production of a membrane
which can be used in fuel cells. This membrane consists of glass
fiber materials in which fluorinated hydrocarbon polymers are fixed
by means of a silicate binder.
[0018] Finally, JP 2005268096 A describes a separator for lithium
ion batteries which is produced by melting together thermoplastic
particles in a polyethylene/polypropylene fibrous supporting
material by heating. This separator has a bubble-shaped porous
structure having a pore diameter of 0.1-15 .mu.m.
[0019] The prior art does not show an inexpensive separator which
combines low thickness with high porosity and high thermal
stability and can be safely used, over a wide temperature range, in
batteries having high power and energy density.
SUMMARY OF THE INVENTION
[0020] An aspect of the present invention is to develop and refine
a ply of the type mentioned at the beginning such that it combine
low thickness with high porosity and high thermal stability
following inexpensive fabrication.
[0021] According to that, the ply is characterized in that the
particles in the filled regions form second pores, the average
diameter of the particles being greater than the average pore size
of the majority of the second pores.
[0022] The frequency distribution of the average pore sizes is set
according to the present invention such that more than 50% of the
second pores have average pore sizes which are below the average
diameter of the particles. The inventors recognized that the pore
structure of an inexpensive fibrous nonwoven web fabric can be
modified through suitable arrangement and selection of particles.
Specifically, the porosity of the ply of the present invention was
recognized to be enhanceable compared to polyolefin membranes
without reducing its stability. The arrangement of a multiplicity
of particles whose average diameter is greater than the average
pore size of the majority of the second pores in the filled region
makes it possible to develop a high porosity and hence an enhanced
imbibition of electrolyte by the fibrous nonwoven web fabric. At
the same time, the pore structure created makes it virtually
impossible for harmful metal dendrites to form therein. The present
invention provides an arrangement for the particles which engenders
a pore structure which is not bubblelike but is labyrinthine and
includes elongate pores. In such a pore structure, it is virtually
impossible for dendritic growths to form that extend all the way
from one side of the ply to the other. This is efficacious in
preventing short circuits in batteries or capacitors. The ply of
the present invention is therefore very useful as a separator for
batteries and capacitors having high power and energy density. The
ply of the present invention is safe to use over a wide temperature
range.
[0023] The particles could be spherical. This may advantageously
produce an overwhelmingly closest packing of spheres in the first
pores in the fibrous nonwoven web fabric. The average pore size of
the majority of the second pores is essentially determined by
geometric conditions in the packings of spheres. There are an
infinite number of ways to produce a closest packing of spheres.
Their common feature is that they consist of hexagonal layers of
spheres. The two most important representatives are the hexagonally
closest packing of spheres (layer sequence A, B, A, B, A, B) and
the cubically closest packing of spheres (layer sequence A, B, C,
A, B, C, A). The cubically closest packing of spheres is also known
as the face-centered cubic packing of spheres. Each sphere in a
closest packing of spheres has 12 neighbors, six in its own layer
and three each above and below. They form a cuboctahedron in the
cubic arrangement and an anticuboctahedron in the hexagonal
arrangement. The packing density of a closest packing of spheres is
74%. However, the desire is to produce as high a porosity as
possible. Therefore, not all particles in the first pores of the
fibrous nonwoven web fabric will form a closest packing of spheres.
Rather, there will also be zones where the particles are packed
loosely, which promotes high porosity.
[0024] The particles could form a sheetlike homogeneous
distribution in the foundational structure. This concrete form is a
particularly effective way to prevent short circuits. Metal
dendrites and detritus find it virtually impossible to migrate
through a homogeneously covered sheet. Furthermore, such a sheet
prevents direct contact between electrodes on application of
pressure. It is specifically conceivable against this background
that all the first pores in the fibrous nonwoven web fabric are
homogeneously filled with the particles such that the ply
predominantly exhibits average pore sizes which are smaller than
the average diameters of the particles.
[0025] The foundational structure could have a coating of the
particles. A coating likewise is an advantageous way of effecting
the aforementioned prevention of short circuits. When a ply has a
coating, the foundational structure will inevitably have a boundary
region which is at least partly filled with particles.
[0026] The particles could be united with the fibrous nonwoven web
fabric, or with each other, by a binder. This binder could consist
of organic polymers. The use of a binder consisting of organic
polymers makes it possible to produce a ply having sufficient
mechanical flexibility. Polyvinylpyrrolidone surprisingly shows
excellent binder properties.
[0027] It could be preferable to use thermoplastic and/or
thermosetting binders. Examples which may be mentioned against this
background are polyvinylpyrrolidone, polyacrylic acid,
polyacrylates, polymethacrylic acid, polymethacrylates,
polystyrene, polyvinyl alcohol, polyvinyl acetate, polyacrylamide
and copolymers of the aforementioned, cellulose and its
derivatives, polyethers, phenolic resins, melamine resins,
polyurethanes, nitrile rubber (NBR), styrene-butadiene rubber (SBR)
and also latex.
[0028] The melting point of the binder and/or of the particles
could be below the melting points of the fibers of the fibrous
nonwoven web fabric. By choosing such a binder/particles it is
possible for the ply to realize a shutdown mechanism. In a shutdown
mechanism, the melting particles and/or the binder blind the pores
of the fibrous nonwoven web fabric, so that no dendritic growths
through the pores and hence short circuits can occur.
[0029] It is conceivable against this background to use mixtures of
particles having different melting points. This can be used to
achieve stepwise or stagewise blinding of the pores with increasing
temperature.
[0030] The particles could have an average diameter in the range
from 0.01 to 10 .mu.m. The selection of the average diameter from
this range will be found particularly advantageous to avoid short
circuits through formation of dendritic growths or debris.
[0031] The particles could be fabricated from organic polymers, in
particular from polypropylene, polyvinylpyrrolidone, polyvinylidene
fluoride, polyester, polytetrafluoroethylene,
perfluoroethylene-propylene (FEP), polystyrene, styrene-butadiene
copolymers, polyacrylates or nitrile-butadiene polymers and also
copolymers of the aforementioned polymers. The use of organic
polymers for the particles permits unproblematic melting of the
particles to obtain a shutdown effect. It is further possible to
fabricate a ply which is easy to cut to size without crumbling.
Crumbling of the ply will usually occur when there is a relatively
high proportion of inorganic particles in the ply. It is
conceivable against this background to use mixtures of different
particles or core-shell particles. This can be used to achieve
stepwise or stagewise blinding of the pores with increasing
temperature.
[0032] It is also possible to use inorganic particles or
inorganic-organic hybrid particles. These particles do not melt
below a temperature of 400.degree. C. It is further possible to
choose these particles with basic properties in order that the
proton activity present in batteries may be at least partially
reduced.
[0033] The fibers of the fibrous nonwoven web fabric could be
fabricated from organic polymers, in particular from polybutyl
terephthalate, polyethylene terephthalate, polyacrylonitrile,
polyvinylidene fluoride, polyether ether ketones, polyethylene
naphthalate, polysulfones, polyimide, polyester, polypropylene,
polyoxymethylene, polyamide or polyvinylpyrrolidone. It is also
conceivable to use bicomponent fibers which include the
aforementioned polymers. The use of these organic polymers makes it
possible to produce a ply having only minimal thermal shrinkage.
Furthermore, these materials are substantially electrochemically
stable to the electrolytes and gases used in batteries and
capacitors.
[0034] The average length of the fibers of the fibrous nonwoven web
fabric could exceed their average diameter by at least a factor of
two or more, preferably by a multiple. This concrete development
makes it possible to fabricate a particularly strong fibrous
nonwoven web fabric, since the fibers can become intertwined with
each other.
[0035] At least 90% of the fibers of the fibrous nonwoven web
fabric could have an average diameter of not more than 12 .mu.m.
This concrete development makes it possible to construct a ply
having relatively small pore sizes for the first pores. Still finer
porosity is obtainable when at least 40% of the fibers of the
fibrous nonwoven web fabric have an average diameter of not more
than 8 .mu.m.
[0036] The ply could be characterized by a thickness of not more
than 100 .mu.m. A ply of this thickness can still be rolled up
without problems and permits very safe battery operation. The
thickness could preferably be not more than 60 .mu.m. This
thickness permits improved rollability and yet a safe battery
operation. The thickness could more preferably be not more than 25
.mu.m. Plies having such a thickness can be used to build very
compact batteries and capacitors.
[0037] The ply could have a porosity of at least 25%. A ply of this
porosity is by virtue of its density of material particularly
effective in suppressing the formation of short circuits. The ply
could preferably have a porosity of at least 35%. A ply of this
porosity can be used to produce a battery of high power density.
The ply described herein combines very high porosity with
nonetheless very small second pores, so that no dendritic growths
extending from one side to the other side of the ply can form. It
is conceivable against this background that the second pores form a
labyrinthine microstructure in which no dendritic growths from one
side to the other side of the ply can form.
[0038] The ply could have pore sizes of not more than 3 .mu.m. The
choice of this pore size will be found particularly advantageous in
avoiding short circuits. The pore sizes could more preferably be
not more than 1 .mu.m. Such a ply is particularly advantageous in
avoiding short circuits due to metal dendrite growth, due to debris
from electrode particles and due to direct contact between the
electrodes on pressure application.
[0039] The ply could have an ultimate tensile strength force in the
longitudinal direction of at least 15 newtons/5 cm. A ply of this
strength is particularly easy to roll up on the electrodes of a
battery without rupturing.
[0040] The ply could be mechanically consolidated by calendering.
Calendering is effective in reducing surface roughness. The
particles used at the surface of the fibrous nonwoven web fabric
exhibit flattening after calendering.
[0041] The ply described herein can be used as a separator in
batteries and capacitors in particular, since it is particularly
efficacious in preventing short circuits.
[0042] The ply described herein can also be used as a gas diffusion
layer or membrane in fuel cells, since it exhibits good wetting
properties and can transport liquids.
[0043] There are, then, various ways of advantageously developing
and refining the teaching of the present invention. Reference must
be made, on the one hand, to the subordinate claims and, on the
other, to the following elucidation of a preferred illustrative
embodiment of the present invention with reference to the
drawing.
[0044] The elucidation of the preferred illustrative embodiment of
the present invention with reference to the drawing will also serve
to elucidate generally preferred developments and refinements of
the teaching.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] In the drawing
[0046] FIG. 1 shows a scanning electron micrograph of a ply in
which the particles are present in first pores in a fibrous
nonwoven web fabric and form a porous region filled with
particles,
[0047] FIG. 2 shows a scanning electron micrograph of the particles
of a filled region configured as a coating, and
[0048] FIG. 3 shows a greatly magnified scanning electron
micrograph of the particles of a filled region.
DETAILED DESCRIPTION
[0049] FIG. 1 shows a ply having a foundational structure composed
of a fibrous nonwoven web fabric, the foundational structure
consisting of fibers 1 and having first pores 2 formed by the
fibers 1, the foundational structure being at least partially
filled with particles 3, which particles 3 at least partially fill
the first pores 2 and form regions 4 filled with particles 3.
[0050] FIG. 3 shows a filled region 4 in a magnified view. With
reference to FIG. 3, the particles 3 form second pores 5 in the
filled regions 4, the average diameter of the particles 3 being
greater than the average pore size of the majority of the second
pores 5. The particles 3 are spherical and tend to form a closest
packing of spheres in regions.
[0051] FIG. 2 shows a coating of the particles 3 which has been
applied to the fibrous nonwoven web fabric.
[0052] FIGS. 1 to 3 show scanning electron micrographs of a ply
comprising a fibrous nonwoven web fabric, the fibers 1 of which are
fabricated from polyester. The particles 3 are spherical in
configuration and form in regions agglomerates which fill the first
pores 2 in the fibrous nonwoven web fabric. The fibers 1 have an
average diameter of less than 12 .mu.m. The ply has a thickness of
25 .mu.m. It exhibits a shrinkage in the transverse direction of
less than 1% at a temperature of 170.degree. C.
[0053] The average diameter of the particles 3 is 200 nm The
particles 3 consist of polyvinylidene fluoride and were secured to
the fibers 1 by a polyvinylpyrrolidone binder.
[0054] The average diameter of the particles 3 is determined from
the number of particles 3 in the filled region 4. The particles 3
preferably exhibit a narrow distribution curve; that is, an average
diameter having a low standard deviation. The average pore sizes of
most, viz. the majority, of the second pores 5 is less than 200 nm.
By average pore size of a second pore 5 is meant the diameter of an
imaginative sphere 6 which has the same volume as the pore 5. The
imaginative sphere resides between the particles 3 such that it
touches the surfaces of the neighboring particles 3. Imaginative
spheres 6 which characterize the dimension of the pores are
depicted in FIG. 3 as black-bordered hollow circles.
[0055] A distribution curve where the x-axis indicates the average
pore sizes of the second pores 5 and the y-axis indicates the
number or frequency of the average pore sizes would show that more
than 50% of the second pores 5 have average pore sizes which are
below 200 nm.
[0056] With regard to further advantageous developments and
refinements of the teaching of the present invention reference is
made to the general part of the description and to the accompanying
claims.
[0057] It may finally be emphasized most particularly that the
previously purely arbitrarily selected illustrative embodiment
merely serves to discuss the teaching of the present invention, but
does not limit that teaching to this illustrative embodiment.
* * * * *