U.S. patent application number 16/276154 was filed with the patent office on 2019-06-13 for high temperature melt integrity battery separators via spinning.
The applicant listed for this patent is Sabic Global Technologies B.V.. Invention is credited to Qunjian Huang, Roy Martinus Adrianus L 'Abee, Jacob Scott LaBelle, Richard Peters, Wujun Rong, Erich Otto Teutsch, Yanju Wang, Huiqing Wu.
Application Number | 20190181409 16/276154 |
Document ID | / |
Family ID | 49920670 |
Filed Date | 2019-06-13 |
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United States Patent
Application |
20190181409 |
Kind Code |
A1 |
L 'Abee; Roy Martinus Adrianus ;
et al. |
June 13, 2019 |
HIGH TEMPERATURE MELT INTEGRITY BATTERY SEPARATORS VIA SPINNING
Abstract
A method for preparing a high temperature melt integrity
separator, the method comprising spinning a polymer by one or more
of a mechanical spinning process and an electro-spinning process to
produce fine fibers.
Inventors: |
L 'Abee; Roy Martinus Adrianus;
(Veldhoven, NL) ; Peters; Richard; (Hinsdale,
MA) ; Teutsch; Erich Otto; (Richmond, MA) ;
Wu; Huiqing; (Shanghai, CN) ; Wang; Yanju;
(Shanghai, CN) ; Huang; Qunjian; (Shanghai,
CN) ; Rong; Wujun; (Shanghai, CN) ; LaBelle;
Jacob Scott; (Pittsfield, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sabic Global Technologies B.V. |
Bergen op Zoom |
|
NL |
|
|
Family ID: |
49920670 |
Appl. No.: |
16/276154 |
Filed: |
February 14, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15232290 |
Aug 9, 2016 |
10243187 |
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16276154 |
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14132718 |
Dec 18, 2013 |
9577235 |
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15232290 |
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61738810 |
Dec 18, 2012 |
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61808294 |
Apr 4, 2013 |
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61808927 |
Apr 5, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29L 2031/3468 20130101;
D01D 5/18 20130101; D01D 5/003 20130101; H01M 2/162 20130101; B29C
71/00 20130101; D01D 5/0038 20130101; B29K 2995/0058 20130101; B29C
71/02 20130101; B29L 2031/755 20130101; D01D 5/06 20130101; D01F
6/74 20130101; B29C 48/142 20190201; D01D 5/40 20130101; D01D
5/0007 20130101; B29K 2079/085 20130101; H01M 2/145 20130101 |
International
Class: |
H01M 2/14 20060101
H01M002/14; B29C 48/14 20060101 B29C048/14; D01D 5/00 20060101
D01D005/00; D01D 5/06 20060101 D01D005/06; D01D 5/40 20060101
D01D005/40; D01D 5/18 20060101 D01D005/18; D01F 6/74 20060101
D01F006/74; H01M 2/16 20060101 H01M002/16; B29C 71/00 20060101
B29C071/00; B29C 71/02 20060101 B29C071/02 |
Claims
1. A web comprising fine fibers, wherein: the fine fibers have an
individual average diameter of about 10 nm to about 50 .mu.m; and
the web: has a thickness of about 10 .mu.m to about 200 .mu.m; and
has a MacMullin number equal to or lower than 10.
2. The web of claim 1, wherein the web: has a thickness of less
than or equal to 63 .mu.m; has an apparent porosity of greater than
or equal to 67; and has a MacMullin number equal to or lower than
6.
3. The web of claim 2, wherein the web: has a thickness of less
than or equal to 44 .mu.m; and has an apparent porosity of greater
than or equal to 73; and has a MacMullin number equal to or lower
than 4.
4. The web of claim 3, wherein the web has a MacMullin number equal
to or lower than 3.
5. The web of claim 4, wherein the web has an apparent porosity of
greater than or equal to 75.
6. The web of claim 1, wherein the web has an average pore size in
the range of about 0.01 .mu.m to about 20 .mu.m.
7. The web of claim 1, wherein the web has an electrolyte contact
angle of equal to or lower than about 30.degree. in 1:1:1
EC:DMC:EMC and 1 mol/L LiPF.sub.6.
8. The web of claim 1, wherein the fine fibers comprise a
polyetherimide.
9. The web of claim 1, wherein the polyetherimide comprises
structural units based on para-phenylene diamines.
10. The web of claim 1, wherein the fine fibers comprise one or
more of polyetherimide, poly(amic acid), aromatic polyamide,
poly(amide-imide), and polyphenylene oxide.
11. The web of claim 1, wherein the fine fibers comprise a
thermoplastic polymer having a glass transition temperature higher
than about 180.degree. C.
12. The web of claim 1, wherein the fine fibers comprise
poly(4-methylpentene), poly(amide-imide), polyoxymethylene,
polyphthalamide, polysulfone, polyethersulfone, polyphenylsulfone,
polyetherimide, polyketone, polyetherketone, polyetheretherketone,
polyphenylene sulfide, or a copolymer or blend thereof.
13. A method of forming the web of claim 1, the method comprising:
providing a polymer solution comprising a chemical-resistant
polymer in a solvent; spinning the polymer solution into the fine
fibers; and forming the web from the fine fibers.
14. The method of claim 13, wherein spinning the polymer solution
into fine fibers comprises an electro-spinning method.
15. The method of claim 13, wherein spinning the polymer solution
into fine fibers comprises a force-spinning method.
16. The method of claim 13, wherein spinning the polymer solution
into fine fibers comprises a mechanical spinning method.
17. The method of claim 13, wherein spinning the polymer solution
into fine fibers comprises a shear-spinning method.
18. The method of claim 17, wherein the shear-spinning method
comprises injecting the polymer solution into an anti-solvent
medium, and wherein flow rate and viscosity of the anti-solvent
medium are configured to generate shear forces on the injected
polymer solution to form fine fibers.
19. The method of claim 13, wherein spinning the polymer solution
into fine fibers comprises a centrifugal force spinning method.
20. A web comprising fine fibers, wherein: the fine fibers:
comprise a thermoplastic polymer having a glass transition
temperature higher than about 180.degree. C.; and have an
individual average diameter of about 10 nm to about 50 .mu.m; and
the web: has a thickness of less than or equal to 63 .mu.m; has an
apparent porosity of greater than or equal to 67; has a MacMullin
number equal to or lower than 6; and has an average pore size in
the range of about 0.01 .mu.m to about 20 .mu.m.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/232,290, filed Aug. 9, 2016, which is a continuation of U.S.
application Ser. No. 14/132,718, issued as U.S. Pat. No. 9,577,235
on Feb. 21, 2017, which claims priority to U.S. Patent Application
No. 61/738,810, filed Dec. 18, 2012, U.S. Patent Application No.
61/808,924, filed Apr. 5, 2013, and U.S. Patent Application No.
61/808,927, filed Apr. 5, 2013, each of which is hereby
incorporated herein by reference in its entirety.
BACKGROUND
[0002] Battery cells typically consist of a positive and negative
electrode (cathode and anode) and a liquid electrolyte solution,
separated by a thin, porous film known as a separator. A separator
plays a key role in a battery. Its main function is to keep the two
electrodes physically apart from each other in order to prevent an
electrical short circuit. Accordingly, the separator should be
electrically insulating. At the same time, the separator should
allow rapid transport of ionic charge carriers that are needed to
complete the circuit during cell charging and discharging. The
separator should have the capability of conducting ions by either
intrinsic ionic conduction (such as solid electrolytes) or by
soaking the separator with a liquid electrolyte.
[0003] High temperature melt integrity (HTMI) of battery separators
is a key property to ensure the safety of the battery pack.
Specifically, high separator HTMI is important to provide an extra
margin of safety. For example, in case the battery pack is subject
to internal heat build-up from overcharging or internal
short-circuiting, a separator with a high HTMI maintains its
integrity (both shape and mechanical) and as a consequence,
prevents the electrodes from contacting each other at high
temperatures.
[0004] Lithium-ion batteries typically use separators made from
polymers and, more specifically, polyethylene (PE) and
polypropylene (PP), which are produced via melt processing
techniques. These types of separators typically have insufficient
melt integrity at high temperatures and are incompatible, i.e.,
non-wettable, with the electrolyte solutions. Therefore, a need
exists for alternative separators with improved HTMI that can be
produced via a melt or solution process.
[0005] Polyetherimides (for example Saudi Arabia Basic Industries
Corporation's ULTEM branded polyethermide products) are attractive
materials for battery separator applications because they combine
outstanding characteristics, such as good electrolyte wettability,
high solvent resistance, and HTMI typically exceeding 200.degree.
C. Polyphenylene oxides are also particularly suitable for HTMI
battery separators, with HTMI values typically exceeding
200.degree. C. Additionally, polyimides are also suitable to be
used for HTMI separators, which are typically produced by
processing poly(amic acid) into a desired form factor, followed by
a heat treatment to form the polyimide. Alternatively, aromatic
polyamides can be used as HTMI battery separators.
[0006] Conventional PP and PE separators are prepared by either the
"dry process" or the "wet process". Both processes rely on
stretching, crystallization, and annealing of the polymers to
generate the desired pore structure. Since polyetherimides,
polyphenylene oxides, and poly(amic acids) (precursor to
polyimides) are typically amorphous resins, these two conventional
approaches are not suitable to produce polyetherimide,
polyphenylene oxide, or polyimide-based separators. Additionally,
the dry and wet processes lead to relatively low porosities and
high tortuosity, which limits lithium-ion transfer through the
separator, e.g., leading to relatively low power capability battery
cells. Therefore, there exists a need for a membrane preparation
process suitable for amorphous resins like polyetherimides,
polyphenylene oxides, and poly(amic acids), where the process
allows preparing porous structures meeting the requirements of
battery separators.
[0007] In the case of lithium-ion batteries, polymeric separator
films are typically based on PE and/or PP. The porosity is
typically induced by uniaxial stretching of extruded films, which
process is known as the "dry process" and is based on a complex
interplay between extrusion, annealing, and stretching of the film
(see e.g., U.S. Pat. Nos. 3,558,764 and 5,385,777). The "dry
process" typically leads to an open pore structure and a relatively
uniform pore size. However, inherent to the stretching process, the
"dry process" leads to non-spherical pores and to residual stresses
in the material. The latter typically leads to deformation
(shrinkage) of the films over time, especially at elevated
temperatures. Since crystallization/crystallinity is required
during the stretching process in order to develop a porous
structure, the preparation of porous films by the "dry process" is
limited to semi-crystalline polymers only. Although this process
allows for a reasonably high porosity (30-50%), the actual
accessible porosity (as measured e.g., by air permeability) is
often lower, since not all pores are interconnected with each
other.
[0008] Alternatively, porosity can be induced by pre-mixing the
polymer with a low molecular weight extractable, which forms a
specific structure upon cooling from the melt and, after removal of
the low molecular weight species, leaves a porous structure (see
e.g., U.S. Pat. No. 7,618,743, JP1988273651, JP1996064194, and
JP1997259859). This process is known as the "wet process", and
typically uses a polymer/extractable combination that is miscible
during the extrusion process, but phase separates upon cooling.
Removal of the low molecular weight specie can be achieved by
evaporation or extraction. An additional stretching (uniaxial or
biaxial) step is sometimes used to create the desired pore
structure. The "wet process" typically leads to a highly tortuous,
interconnected porous structure. The preparation of porous films by
the "wet process" is limited to polymers with a relatively high
melt strength (e.g., ultra-high molecular weight PE). Also here the
actual accessible porosity (as measured e.g., by air permeability)
is often lower than the total porosity, since not all pores are
interconnected with each other.
[0009] In all cases, high porosity of separator films is beneficial
for the charging and discharging characteristics of batteries,
since the volume resistivity of the cell typically scales inversely
with the accessible separator porosity. Additionally, separator
pore sizes need to be small enough to ensure it functions as an
electrical barrier between the electrode, with pore sizes
preferably smaller than the particle size of the anode and cathode
active material (typically several micrometer). Also, the pore size
distribution is preferably narrow and the pores are preferably
uniformly distributed. Preferably, all pores are in some way
connected from front to backside of the film or, in other words,
the actual accessible porosity equals the total porosity. This
means that all pores are accessible for the electrolyte solution
and contribute to ion transport through the separator. In the case
of lithium-ion batteries, high tortuosity and an interconnected
pore structure is beneficial for long life batteries, since it
suppresses the growth of lithium crystals on the graphite anode
during fast charging or low temperature charging. On the other
hand, an open (low tortuosity) and uniform pore size structure is
beneficial for applications where fast charging and discharging is
required, e.g., for high power density batteries.
[0010] Battery separators with a pore structure that is
significantly more open than that of separators prepared via the
"dry process" and "wet process" can be made via fiber spinning
processes and organizing the spun fibers into woven or non-woven
webs.
[0011] Polymers in the form of fibers are also useful in the
applications of separators (electrolytical capacitors for example)
or for substrates (fuel cell applications for example).
Additionally, webs consisting of fibers, either with a sub-micron
or supra-micron diameter, can be applied as medial implants,
filtration membranes, dialysis membranes, water filtration
membranes, desalination membranes, gas separation membranes,
hospital gowns, electrical insulation paper and personal hygiene
products. Also, webs comprised of polymer fibers can function as a
substrate for further functionalization, e.g., by spinning other
fibers onto the substrate, or by coating with other polymer or
inorganic systems. Additionally, polymer fibers can be useful to
functionalize substrates. An example could be to spin ultra-fine
fibers onto a micro-porous web.
[0012] The conventional fiber fabrication technologies such as melt
spinning, web spinning, dry spinning, or dry jet-wet spinning,
comprise extrusion of a polymer melt or solution through a nozzle
by a mechanical force followed by solidification of the melt or
solution in order to fabricate fibers. These conventional fiber
fabrication technologies typically produce fibers having a diameter
ranging from several micrometers to several scores of micrometers.
Consequently, the woven or nonwoven webs comprising such spun
fibers typically contain pores too large to be applicable for
lithium-ion battery separators, e.g., exceeding 5 .mu.m, as the
fiber diameter scales with the pore size of the web (see G. E.
Simmonds et al., Journal of Engineered Fibers and Fabrics, 2(1),
2007). This large pore size would allow the particles of the anode
and the cathode to migrate towards each other through the large
pores to cause an internal short circuit. Additionally, the large
fiber diameter makes it difficult to achieve thin separators, e.g.,
of 50 .mu.m or less. For example, U.S. Pat. No. 5,202,178 describes
melt spun polyamide with a fineness of 0.5-3.5 denier (fiber
diameter about 8-20 .mu.m), which are applicable as alkaline
battery separators, but not as lithium-ion battery separators.
Various methodologies to produce fine polymer fibers with a
sub-micrometer average diameter have been described, such as in
U.S. Pat. Nos. 4,044,404, 4,639,390, 4,842,505, 4,965,110,
5,522,879, and 6,106,913, where the formation of the fine fibers
out of a polymer melt or a polymer solution typically relies on
applying a pressure or an electro-static force. The latter method,
commonly known as electro-spinning, is by far the most used
technology to prepare fine fibers. Electro-spinning (comprising
electro-blowing, melt-blowing, flash spinning or
air-electro-spinning) is a technology known to be applicable to
polymers of various forms, such as a polymer melt or a polymer
solution, and the technology is able to produce fibers having a
diameter of several nanometers up to thousands of nanometers. Such
a small fiber diameter enables to produce polymer webs having a
high porosity combined with a small pore size and provides new
properties that are impossible to realize via the conventional
fiber spinning technologies. Details around the electro-spinning
method, setup, processing conditions and applications are widely
described in literature, such as for example "Electrospinning
Process and Applications of Electrospun Fibers" by Doshi and
Reneker (J. Electrostatics, 35, 151-160 (1995)), "Electrospinning
of Nanofibers in Textiles" by Haghi (CRC Press, Oct. 31 2011),
"Beaded nanofibers formed during electrospinning" by H. Fong
(Polymer, 40, 4585-4592 (1999)) and U.S. Pat. Nos. 6,616,435,
6,713,011, 7,083,854, and 7,134,857.
[0013] In the process for fabricating a porous polymer web using
electro-spinning, a polymer solution is extruded through fine holes
(e.g., a needle or nozzle) under an electric field to volatilize or
solidify the solvent from the solution, which forms the fibers on
the collector surface located at a predetermined distance. The
polymer web thus obtained is a laminated three-dimensional network
structure of fibers having a diameter of from several nanometers to
several thousands of nanometers and has a large surface area per
unit volume. Accordingly, the polymer web thereby obtained is
typically superior in total porosity and reduced pore size to those
produced by the other, conventional fabrication methods.
[0014] The main advantage of the electro-spinning process is that
it enables to readily control the diameter of fibers in the polymer
web, the total web thickness (i.e., from several micrometers to
several thousands of micrometers) and the size of the pores by
modifying the process conditions. The physical phenomenon that
takes place when applying a high voltage to the liquid drops
hanging on the orifice of e.g., a needle in the electro-spinning
process is called "Taylor cone". Here, a stream is formed to
discharge the liquid drop towards the collector when the force of
charges exceeds the surface tension of a solution to be suspended.
An organic solution having a low molecular weight can be sprayed
into fine liquid drops. However, due to its high viscosity and
rheological characteristics, a polymer solution typically forms a
stream that is split into several sub-streams with densely
accumulated charges as it becomes apart from the Taylor cone to
reduce the diameter. The large surface area of the polymer solution
in the shape of fine streams accelerates solidification of the
polymer solution and volatilization of the solvent, forming a
polymer web with semi-entangled solid fibers on the surface of the
collector.
[0015] Among the various parameters of the electro-spinning process
are the applied voltage, the orifice to collector distance, the
solution delivery rate, the polymer concentration, the viscosity,
the solvent polarity, the surface tension of the solution, the
solvent evaporation rate and the solution dielectric constant. A
great increase in the discharged amount of liquid without adjusting
the applied voltage accordingly will result in liquid drops being
formed, rather than the desired nano-fibers, eventually leading to
a polymer web in which fibers are mixed with liquid drops. A too
high voltage makes the discharged polymer stream unstable and
uncontrollable. A rise of the applied voltage or an increase in the
discharged amount typically increases the diameter of the stream
emitted from the Taylor cone to form a polymer with fibers having a
larger diameter. It can be understood that finding the proper
processing conditions for electro-spinning is, therefore, not
straightforward, as e.g., described by Yao et al. (Yao et al.,
Journal of Membrane Science, 320(1-2), 2008, Pages 259-267).
Additionally, the polymer needs to be well soluble in a solvent,
where the combination of polymer/solvent needs to be suitable for
the electro-spinning process (e.g., in dielectric constant,
evaporation rate, viscosity, etc).
[0016] The electro-spinning process largely depends on the force of
charges, which is a disadvantage in large-scale production over the
conventional fiber fabrication processes, because the discharged
amount from the nozzle is relatively small in production of a
polymer web with fibers having a small diameter compared to the
conventional processes. It is generally stated that the required
time for the polymer solution to move from the orifice or nozzle to
the collector and form solid fibers is significantly shorter than
one second, normally 0.1 to 0.01 second. Assuming a typical
orifice-nozzle distance of 10 cm, the fiber spinning speed is
normally 1 to 10 m/s. Although the fiber spinning speed appears
rather fast at first sight (1-10 m/s), it is important to
understand that a single web of 0.1 m2 with a thickness of 50 .mu.m
and a total porosity of 50% consisting of fibers with a diameter
below 1 .mu.m has a total fiber length exceeding many hundreds of
kilometers. So even at a spinning speed of 10 m/s, the
electro-spinning process to prepare such a 0.1 m2 porous web
typically leads to preparation times of several hours up to several
days, which is not acceptable for large-scale, commercial
nano-fiber web production. Varabhas et al. state that a 0.1 m2
nonwoven mat containing 1 g of 100 nm fibers may take several days
to create from a single jet via an electro-spinning process
(Varabhas et al., Polymer, 49(19), 2008, Pages 4226-4229). Many
other sources state that electro-spinning is a very slow process,
which severely limits its commercial value, for example Wertz et
al., Filtration and Separation, 46(4), 2009, Pages 18-20; Ou et
al., European Polymer Journal, 47(5), 2011, Pages 882-892; WO
Patent Application 2008057426; von Loesecke et al., Filtration and
Separation, 45(7), 2008, Pages 17-19. Additionally, the solvent
handling and recovery in the electro-spinning process is
intrinsically difficult (Ellison et al., Polymer, 48, 2007, Pages
3306-3316).
[0017] As discussed previously, electro-spinning production speeds
cannot simply be improved by increasing the discharge rate out of
the orifice, as this would typically result in the formation of
liquid drops (defects) next to the (nano-)fibers. To increase the
overall production speed of nano-fiber polymer webs, a plurality of
needles, nozzles or orifices for discharging the polymer solution
can be densely arranged, as for example described in Theron et al.,
Polymer, 46, 2005, Pages 2889-2899 or Lukas et al., Journal of
Applied Physics, 103, 2008, 084309. Such a setup enables
simultaneous spinning of multiple fibers, which increases the web
production speed. However, even when 10 to 100 orifices would
electro-spin nano-fibers simultaneously, the preparation of a 0.1
m2 nonwoven mat with a thickness of 50 .mu.m and a total porosity
of 50% consisting of fibers with a diameter below 1 .mu.m will
still take several hours, i.e., the process is still very time
consuming. Additionally, as the orifices are typically densely
arranged in a small space, it is more difficult to volatilize the
solvent of the polymer solution. As a result, there is an increased
possibility to form a polymer web having a film structure rather
than a fiber structure, i.e., more defects will be present. This
problem is a serious obstacle to high-speed or large-scale
production of nano-fiber polymer webs using the electro-spinning
process.
[0018] The application of the electro-spinning method to prepare
nano-fiber webs for battery or capacitor separators has been
explained in literature, e.g., WO Patent Application 2012043718 and
U.S. Pat. Appl. No. 2002/0100725. Additionally, U.S. Pat. Appl. No.
2009/0122466 describes capacitor separators based on polyamide
prepared via an electro-spinning process, where webs made out of
nm-sized fibers were prepared by electro-blowing polyamide and
depositing those directly on a moving collection belt, either in a
single or multiple pass, after which the as-spun nano-web was dried
by transportation through a solvent stripping zone with hot air and
infrared radiation. The nano-webs were also calendared in order to
impart the desired physical properties. U.S. Pat. No. 7,112,389
describes battery separators comprising a porous fine fiber layer
of polyamide or polyvinyl alcohol fibers having a mean diameter of
50 to 3000 nm. The fine fibers are prepared via electro-blowing the
polymer solutions. To improve the strength of the webs, the
polyamide fine fiber web was thermally bonded, while the polyvinyl
alcohol fine fiber web was cross-linked by a chemical procedure.
U.S. Pat. No. 7,170,739 describes the application of such porous
fine fiber layers of polyamide and polyvinyl alcohol for
electrochemical double layer capacitors. U.S. Pat. Appl. No.
2011/0117416 describes that the electrolyte wettability of such
fine fiber web separators can be improved by the introduction of a
surfactant. JP Patent Application 2007211378 describes battery
separators based on poly(4-methyl-1-pentene), where the polymer is
shaped into the geometry of fibers with a diameter of 2 .mu.m or
less. KR Patent Application 2008013208 and 2010072532 and WO Patent
Application 2011055967 describe heat-resistant, fine fibrous
separators for secondary batteries, comprising a fibrous phase
formed by electro-spinning or air-electro-spinning a heat-resistant
polymer material (such as aromatic polyesters, polyimides,
polyphenylene oxide, polyamide) in combination with a fibrous phase
formed by electro-spinning consisting of a polymeric material that
swells in the electrolyte solution (such as polyvinylidene
fluoride, polyvinylchloride, PE oxide, polystyrene, polymethyl
methacrylate). KR Patent Application 2008013209 describes a
heat-resistant separator with a shutdown function for
electrochemical devices used in, e.g., electric automobile,
comprising an fine fibrous layer positioned on a porous substrate,
where the fibrous phase is formed by electro-spinning a
heat-resistant polymer (such as aromatic polyesters, polyimides,
polyphenylene oxide, polyamide) and a polymer material that swells
in the electrolyte solution (such as polyvinylidene fluoride,
polyvinylchloride, PE oxide, polystyrene, polymethyl methacrylate).
JP Patent 04963909 describes the production of fibrous battery
separators based on polyphenylene oxide via an electro-spinning
process, with average fiber diameters of 0.01-10 .mu.m. Polymer
fibers in the form of a woven or nonwoven web can also be used in
laminated structures. JP Patent Application 2011077233 described
the use of polyamide fibers of 10-600 nm in diameter prepared via
an electro-spinning process, where the nano-fibers are spun on a
fibrous support with fiber fineness of 0.01-5 dtex (about 1-25
.mu.m average diameter). As described in U.S. Pat. Appl. No.
2012/0082884, the discussed electro-spinning process can be used to
spin nano-fibers in a continuous fashion onto a substrate.
[0019] Therefore, there exists a need for a fiber preparation
process that allows for the production of fine fibers at a
throughput significantly higher than that of electro-spinning, and
that allows for fiber diameters significantly smaller than those
obtained from traditional melt-spinning techniques.
[0020] An alternative method to electro-spinning does not rely on
an electro-static force to form the fine fibers from a single
orifice, but rather on a centrifugal force. As the centrifugal
force is the driving force for the formation of the fine fibers,
the technology is generally known as force-spinning. U.S. Pat.
Appl. Nos. 2009/0280207, 2009/0232920, 2009/0269429, and
2009/0280325 describe an apparatus that uses a rotating spinneret
comprising an array of capillaries. This spinneret typically
rotates at speeds from 500 to 25000 rpms, thereby creating a
significant centrifugal force responsible for the formation of fine
fibers. By increasing the number of capillaries in a given
spinneret, the volumetric throughput of fiber generation can be
increased to make more fibers in a short period of time. This
technology can be applied to a polymer melt as well as to a polymer
solution and has the advantage of having significantly higher
throughputs as compared to the conventional nano-fiber spinning
technology, such as electro-spinning. WO Patent Application
2012122485 describes the application of the described
force-spinning method to prepare fine fiber of fluoropolymers
having a contact angle greater than 150.degree.. However, this
technique has never been used to produce fibers based on high
temperature materials, such as polyetherimides, polyphenylene
oxides and poly(amic acids), which would be required for e.g., HTMI
battery separators.
[0021] Another alternative to electro-spinning is a process whereby
a polymer solution is injected through one or multiple small
orifices into a non-solvent to the polymer, which, upon mixing of
the solvent and non-solvent, induces precipitation of the polymer
at a solvent/non-solvent composition at which the polymer is no
longer soluble in the solvent/non-solvent mixture. When the
non-solvent is sheared (e.g., flows) upon injection of the polymer
solution, the precipitation of the polymer will occur under shear
conditions, which enables the formation of fibers at very high
throughput. As spinning of the fibers relies on the shear
conditions of the non-solvent in which the polymer solution is
injected, this process is known as shear-spinning. The fiber
diameter is dependent on the process conditions. However, this
technique has never been used to produce fibers based on high
temperature materials, such as polyetherimides, polyphenylene
oxides and poly(amic acids), which would be required for e.g., HTMI
battery separators.
[0022] Therefore, there exists a need for a high throughput fiber
production process based on mechanical spinning, shear spinning
and/or electro-spinning that enables the production of fine fibers
based on high temperature materials.
SUMMARY
[0023] Disclosed are materials that provide solvent resistant
membranes. As an example, membranes can be used in environments
such as battery cells and/or capacitor cells, electrolytical energy
storage devices, a dialysis membrane, a water filtration membrane,
a desalination membrane, a gas separation membrane, and the like.
As a further example, other structures and systems can implement
the disclosed materials.
[0024] Method are disclosed, which do not rely on an electrostatic
force, or a centrifugal force through an orifice. The disclosed
methods can be based on injecting a polymer solution into a flow
stream of an anti-solvent medium, with sufficient pressure to
precipitate the resin in form of fine fibers, for example fibers
having an individual average diameter of about 10 nm to about 50
.mu.m.
[0025] In an aspect, a method can comprise dissolving a polymer in
a solvent to provide a polymer solution, wherein the polymer
comprises one or more of polyetherimide, poly(amic acid), and
polyphenylene oxide and spinning the polymer solution by a
mechanical spinning method into fine fibers.
[0026] In an aspect, a method can comprise dissolving a polymer in
a solvent to provide a polymer solution, wherein the polymer
comprises one or more of polyetherimide, poly(amic acid), aromatic
polyamide, poly(amide-imide) and polyphenylene oxide and spinning
the polymer solution by a mechanical spinning method into fine
fibers.
[0027] In an aspect, a method can comprise dissolving a polymer in
a solvent to provide a polymer solution, wherein the polymer
comprises thermoplastic polymers having a glass transition
temperature higher than about 180.degree. C. and spinning the
polymer solution by a mechanical spinning method into fine
fibers.
[0028] In an aspect, a method can comprise melting a polymer
comprising, poly(4-methylpentene), poly(amide-imide),
polyoxymethylene, polyphthalamide, polysulfone, polyethersulfone,
polyphenylsulfone, polyetherimide, polyketone, polyetherketone,
polyetheretherketone, polyphenylene sulfide, or a copolymer or
blend thereof and spinning the polymer melt by a mechanical
spinning method into fine fibers.
[0029] In an aspect, a method can comprise providing a polymer
solution comprising a chemical-resistant polymer in a solvent and
spinning the polymer solution by an electro-spinning method into
fine fibers.
[0030] Additional advantages will be set forth in part in the
description which follows or may be learned by practice. The
advantages will be realized and attained by means of the elements
and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description
and the following detailed description are exemplary and
explanatory only and are not restrictive, as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate embodiments and
together with the description, serve to explain the principles of
the methods and systems:
[0032] FIG. 1 is a schematic of an exemplary battery cell;
[0033] FIG. 2 is a graph illustrating dissolution temperature of
ULTEM CRS 5001K and CRS 5011K in N-methyl-2-pyrrolidone (NMP) as
function of concentration;
[0034] FIG. 3 is a graph illustrating "steady-state" phase
separation temperature;
[0035] FIG. 4A is a representation of a morphology of PPO 6130
fiber-based structures;
[0036] FIG. 4B is a graph of fiber count to fiber diameter of PPO
6130 fiber-based structures;
[0037] FIG. 5A is a representation of a morphology of PPO 6130
fiber-based structures;
[0038] FIG. 5B is a graph of fiber count to fiber diameter of PPO
6130 fiber-based structures;
[0039] FIG. 6A is a representation of a morphology of ULTEM 1010
fiber-based structures;
[0040] FIG. 6B is a graph of fiber count to fiber diameter of ULTEM
1010 fiber-based structures;
[0041] FIG. 7A is a representation of a morphology of ULTEM 1010
fiber-based structures;
[0042] FIG. 7B is a graph of fiber count to fiber diameter of ULTEM
1010 fiber-based structures;
[0043] FIG. 8A is a representation of a morphology of ULTEM CRS
5001K;
[0044] FIG. 8B is a representation of a morphology of ULTEM CRS
5001K;
[0045] FIG. 8C is a representation of a morphology of ULTEM CRS
5001K;
[0046] FIG. 9A is a representation of a morphology of ULTEM CRS
5001K;
[0047] FIG. 9B is a representation of a morphology of ULTEM CRS
5001K;
[0048] FIG. 9C is a representation of a morphology of ULTEM CRS
5001K;
[0049] FIG. 10A is a representation of a morphology of ULTEM CRS
5001K;
[0050] FIG. 10B is a representation of a morphology of ULTEM CRS
5001K;
[0051] FIG. 10C is a representation of a morphology of ULTEM CRS
5001K;
[0052] FIG. 11A is a representation of a morphology of ULTEM CRS
5001K;
[0053] FIG. 11B is a representation of a morphology of ULTEM CRS
5001K;
[0054] FIG. 11C is a representation of a morphology of ULTEM CRS
5001K;
[0055] FIG. 12A is a representation of a morphology of ULTEM CRS
5001K;
[0056] FIG. 12B is a representation of a morphology of ULTEM CRS
5001K;
[0057] FIG. 12C is a representation of a morphology of ULTEM CRS
5001K;
[0058] FIG. 12D is a representation of a morphology of ULTEM CRS
5001K fiber-based structures;
[0059] FIG. 12E is a graph of fiber count to fiber diameter of
ULTEM CRS 5001K fiber-based structures;
[0060] FIG. 13A is a representation of a morphology of ULTEM 1000
fiber-based structures;
[0061] FIG. 13B is a graph of fiber count to fiber diameter of
ULTEM 1000 fiber-based structures;
[0062] FIG. 14A is a representation of a morphology of ULTEM 1000
fiber-based structures;
[0063] FIG. 14B is a graph of fiber count to fiber diameter of
ULTEM 1000 fiber-based structures;
[0064] FIG. 15A is a representation of a morphology of ULTEM 1010
fiber-based structures;
[0065] FIG. 15B is a graph of fiber count to fiber diameter of
ULTEM 1010 fiber-based structures;
[0066] FIG. 16A is a representation of a morphology of ULTEM 1010
fiber-based structures;
[0067] FIG. 16B is a graph of fiber count to fiber diameter of
ULTEM 1010 fiber-based structures;
[0068] FIG. 17A is a representation of a morphology of PPO 6130
fiber-based structures;
[0069] FIG. 17B is a graph of fiber count to fiber diameter of PPO
6130 fiber-based structures;
[0070] FIG. 18A is a representation of a morphology of PPO 6130
fiber-based structures;
[0071] FIG. 18B is a graph of fiber count to fiber diameter of PPO
6130 fiber-based structures;
[0072] FIG. 19A is a representation of a morphology of PPO 6130
fiber-based structures;
[0073] FIG. 19B is a graph of fiber count to fiber diameter of PPO
6130 fiber-based structures;
[0074] FIG. 20A is a representation of a morphology of PPO 6130
fiber-based structures;
[0075] FIG. 20B is a graph of fiber count to fiber diameter of PPO
6130 fiber-based structures;
[0076] FIG. 21A is a representation of a morphology of PPO 6130
fiber-based structures;
[0077] FIG. 21B is a graph of fiber count to fiber diameter of PPO
6130 fiber-based structures;
[0078] FIG. 22A is a representation of a morphology of poly(amic
acid) fiber-based structures;
[0079] FIG. 22B is a graph of fiber count to fiber diameter of
poly(amic acid) fiber-based structures;
[0080] FIG. 23A is a representation of a morphology of poly(amic
acid) fiber-based structures;
[0081] FIG. 23B is a graph of fiber count to fiber diameter of
poly(amic acid) fiber-based structures;
[0082] FIG. 24A is a representation of a morphology of ULTEM 9011
fiber-based structures;
[0083] FIG. 24B is a graph of fiber count to fiber diameter of
ULTEM 9011 fiber-based structures;
[0084] FIG. 25 illustrates scanning electron microscope (SEM)
micrographs showing typical fiber morphologies of electro-spun
ULTEM CRS 5001K obtained from different solvent systems and
electro-spinning conditions;
[0085] FIG. 26 illustrates SEM micrographs showing typical fiber
morphologies of electro-spun ULTEM CRS 5001K obtained from
different solvents systems and electro-spinning conditions;
[0086] FIG. 27A is an example morphology;
[0087] FIG. 27B is an example morphology;
[0088] FIG. 28 is a graph of pore size distribution of electro-spun
ULTEM CRS 5001K;
[0089] FIG. 29 illustrates images of before (a) and after (b) an
electrolyte droplet was placed onto the electro-spun ULTEM CRS
5001K membrane;
[0090] FIG. 30 illustrates thermal mechanical analysis (TMA) curve
of electro-spun ULTEM CRS 5001K; and
[0091] FIG. 31 illustrates cell cycle performance of an
electro-spun ULTEM CRS 5001K separator.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0092] Before the present methods and systems are disclosed and
described, it is to be understood that the methods and systems are
not limited to specific synthetic methods, specific components, or
to particular compositions. It is also to be understood that the
terminology used herein is for the purpose of describing particular
embodiments only and is not intended to be limiting.
[0093] As used in the specification and the appended claims, the
singular forms "a," "an," and "the" include plural referents unless
the context clearly dictates otherwise. Ranges may be expressed
herein as from "about" one particular value, and/or to "about"
another particular value. When such a range is expressed, another
embodiment includes from the one particular value and/or to the
other particular value. Similarly, when values are expressed as
approximations, by use of the antecedent "about," it will be
understood that the particular value forms another embodiment. It
will be further understood that the endpoints of each of the ranges
are significant both in relation to the other endpoint, and
independently of the other endpoint.
[0094] "Optional" or "optionally" means that the subsequently
described event or circumstance may or may not occur, and that the
description includes instances where said event or circumstance
occurs and instances where it does not.
[0095] Throughout the description and claims of this specification,
the word "comprise" and variations of the word, such as
"comprising" and "comprises," means "including but not limited to,"
and is not intended to exclude, for example, other additives,
components, integers or steps. "Exemplary" means "an example of"
and is not intended to convey an indication of a preferred or ideal
embodiment. "Such as" is not used in a restrictive sense, but for
explanatory purposes.
[0096] Disclosed are components that can be used to perform the
disclosed methods and systems. These and other components are
disclosed herein, and it is understood that when combinations,
subsets, interactions, groups, etc. of these components are
disclosed that while specific reference of each various individual
and collective combinations and permutation of these may not be
explicitly disclosed, each is specifically contemplated and
described herein, for all methods and systems. This applies to all
aspects of this application including, but not limited to, steps in
disclosed methods. Thus, if there are a variety of additional steps
that can be performed it is understood that each of these
additional steps can be performed with any specific embodiment or
combination of embodiments of the disclosed methods.
[0097] The present methods and systems may be understood more
readily by reference to the following detailed description of
preferred embodiments and the Examples included therein and to the
Figures and their previous and following description.
[0098] Efforts have been made to ensure accuracy with respect to
numbers (e.g., amounts, temperature, etc.), but some errors and
deviations should be accounted for. Unless indicated otherwise,
parts are parts by weight, temperature is in .degree. C. or is at
ambient temperature, and pressure is at or near atmospheric.
[0099] FIG. 1 illustrates an exemplary non-aqueous electrolyte
battery. It would be understood by one skilled in the art that an
electrolytic capacitor cell can have a similar configuration as the
battery shown and described in reference with FIG. 1. Other
membranes can be produced using the materials and methods described
herein. The battery cell of FIG. 1 is an example of an environment
for one or more membranes produced using the materials and process
described herein. Other environments can make use if the methods
and materials disclosed herein such as electrolytical energy
storage devices, a dialysis membrane, a water filtration membrane,
a desalination membrane, a gas separation membrane, and the
like.
[0100] In an aspect, the battery comprises a positive electrode 100
(cathode), a negative electrode 102 (anode), and a separator 104
disposed between the positive electrode 100 and the negative
electrode 102. As an example, one or more of the positive electrode
100, the negative electrode 102, and the separator 104 is received
in a battery vessel or casing 106. As a further example, a
non-aqueous electrolyte 108 can be disposed in the casing 106
(e.g., adjacent one or more of the positive electrode 100, the
negative electrode 102, and the separator 104, soaking the
separator 104, immersing the separator 104, and the like).
[0101] In an aspect, the positive electrode 100 can comprise a
positive active material incorporated therein and may further
contain an electrically conductive material such as carbon or a
binder for helping sheet or pelletize the positive active material.
The positive electrode 100 can be used in contact with an
electronically conductive substrate such as metal as a collector.
As an example, the binder can be formed from a
polytetrafluoroethylene (PTFE), a polyvinylidene fluoride (PVdF),
an ethylene-propylene-diene copolymer, a styrene-butadiene rubber
or the like. As another example, the collector can be formed from a
foil, thin sheet, mesh or gauze of metal such as aluminum,
stainless steel and titanium. As a further example, the positive
active material and/or the conductive material may be pelletized or
sheeted with the aforementioned binder by kneading/rolling.
Alternatively, these materials may be dissolved and suspended in a
solvent such as toluene and N-methyl-2-pyrrolidone (NMP) to form
slurry which is then spread over the aforementioned collector and
dried to form a sheet. Other materials and forming processes can be
used.
[0102] In an aspect, the positive electrode 100 can comprise a
lithium composite oxide containing at least one of iron, cobalt,
manganese and nickel incorporated therein as a positive active
material and is capable of insertion/releasing lithium ion. Various
oxides such as chalcogen compound, e.g., lithium-containing iron
composite oxide, lithium-containing cobalt composite oxide,
lithium-containing nickel-cobalt composite oxide,
lithium-containing nickel composite oxide and lithium-manganese
composite oxide may be used as positive active material. Other
materials and forming processes can be used.
[0103] In an aspect, negative electrode 102 can comprise a negative
active material incorporated therein. As an example, the negative
electrode 102 can be formed by pelletizing, tabulating or sheeting
the negative active material with a conductive material, a binder,
etc. In an aspect, the conductive material can be formed from an
electronically conducting material such as carbon and metal. As an
example, the binder can be formed from polytetrafluoroethylene,
polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl
cellulose or the like. As another example, the collector can be
formed from a foil, thin plate, mesh, or gauze of copper, stainless
steel, nickel, or the like. As a further example, the negative
active material and/or the conductive material may be pelletized or
sheeted with the aforementioned binder by kneading/rolling.
Alternatively, these materials may be dissolved and suspended in a
solvent such as water and/or N-methylpyrrolidone to form slurry
which is then spread over the aforementioned collector and dried to
obtain a sheet. Other materials and forming processes can be
used.
[0104] In an aspect, the negative electrode 102 is capable of
containing lithium (or lithium ion) or capable of
occluding/releasing lithium (or lithium ion) similarly to the
aforementioned positive electrode. As an example, the negative
electrode 102 can comprise a negative active material incorporated
therein capable of containing lithium ion or insertion/releasing
lithium ion at a more negative potential than that of the positive
electrode 100 combined with the negative electrode 102. Examples of
negative active materials having such characteristics include:
lithium metal, carbonaceous materials (carbon-based materials) such
as artificial graphite, natural graphite, non-graphitizable carbon,
graphitizable carbon and graphene; lithium titanate; iron sulfide;
cobalt oxide; lithium-aluminum alloy; silicon; and tinoxide. Other
materials and forming processes can be used.
[0105] In an aspect, the separator 104 can be formed from
polyetherimides (e.g., ULTEM 1000 series supplied by SABIC). As an
example, battery separator films (e.g., separator 104) formed from
polyetherimides provide a combination of outstanding performance
characteristics, such as high compatibility with electrolyte and a
high melt integrity temperature exceeding 180.degree. C. In an
aspect, the separator 104 can be formed from polyetherimides based
on para-phenylene diamenes (e.g., ULTEM CRS 5000 series supplied by
SABIC). Polyetherimides based on para-phenylene diamine can fulfill
the critical requirement to be resistant to the battery electrolyte
solution, also at elevated temperatures of 55.degree. C.
Additionally, these materials show an extremely low contact angle
to the electrolyte solution, which favors separator wettability and
electrolyte retention, allowing for a reduced electrolyte filling
time during cell production and improved operating cell
performance. In an aspect, the separators 104 can be formed from
polyphenylene oxides (PPO, also known as polyphenylene ethers,
PPE). As an example, battery separators (e.g., separator 104)
formed from polyphenylene oxides provide an outstanding HTMI
exceeding 180.degree. C. and good electrolyte resistance. In an
aspect, the separators 104 can be formed from polyimides (PI),
e.g., by first preparing a separator based on a poly(amic acid),
followed by a heat treatment (e.g., 325.degree. C. for 2 mins) to
form the polyimide. As an example, battery separators (e.g.,
separator 104) formed from polyimides provide an outstanding HTMI
exceeding 180.degree. C. combined with an excellent electrolyte
wettability and electrolyte resistance. In an aspect, the separator
104 can comprise a fiber-based structure. The fiber-based structure
can be formed from fine fibers spun from one or more polymers.
Various polymers can be formed into fiber-based structure such as
polyetherimide, poly(amic acid), polyphenylene oxide, polymethyl
methacrylate, polystyrene, PE, PP, polytetrafluoroethylene,
polyvinylidene fluoride, polycarbonate, poly(4-methylpentene),
cyclic olefin copolymers, polyamide, aromatic polyamide,
poly(amide-imide), polyoxymethylene, polyphthalamide, polysulfone,
polyethersulfone, polyphenylsulfone, liquid crystalline polymers,
polybutylene terephthalate, PE terephthalate, PE naphthalate,
polymethylpentene, polyketone, polyetherketone,
polyetheretherketone, polyphenylene sulfide, cellulose, cellulose
acetate, cellulose acetate butylate, polyacrylonitrile, or
poly(acrylonitrile-co-methacrylate), or a copolymer or blend
thereof.
[0106] In an aspect, the separator 104 can be prepared by
dissolving solvent-resistant polyetherimides in N-methylpyrrolidone
(N-methyl-2-pyrrolidone) at elevated temperatures (140-202.degree.
C., see FIG. 2) in a closed system (i.e., no direct contact between
the solution and the air atmosphere) or open system, followed by
spinning the solution at reduced temperature (25-140.degree. C.).
As an example, membranes can be prepared using the materials and
processes disclosed herein for environments such as battery cells
and/or capacitor cells, electrolytic energy storage devices, a
dialysis membrane, a water filtration membrane, a desalination
membrane, a gas separation membrane, and the like.
[0107] In an aspect, polyimides can comprise polyetherimides and
polyetherimide copolymers. The polyetherimide can be selected from
(i) polyetherimide homopolymers, e.g., polyetherimides, (ii)
polyetherimide co-polymers, e.g., polyetherimidesulfones, and (iii)
combinations thereof. Polyetherimides are known polymers and are
sold by SABIC under the ULTEM.RTM.*, EXTEM.RTM.*, and Siltem*
brands (Trademark of SABIC Innovative Plastics IP B.V.).
[0108] In an aspect, the polyetherimides can be of formula (1):
##STR00001##
wherein a is more than 1, for example 10 to 1,000 or more, or more
specifically 10 to 500.
[0109] The group V in formula (1) is a tetravalent linker
containing an ether group (a "polyetherimide" as used herein) or a
combination of an ether groups and arylenesulfone groups (a
"polyetherimidesulfone"). Such linkers include but are not limited
to: (a) substituted or unsubstituted, saturated, unsaturated or
aromatic monocyclic and polycyclic groups having 5 to 50 carbon
atoms, optionally substituted with ether groups, arylenesulfone
groups, or a combination of ether groups and arylenesulfone groups;
and (b) substituted or unsubstituted, linear or branched, saturated
or unsaturated alkyl groups having 1 to 30 carbon atoms and
optionally substituted with ether groups or a combination of ether
groups, arylenesulfone groups, and arylenesulfone groups; or
combinations comprising at least one of the foregoing. Suitable
additional substitutions include, but are not limited to, ethers,
amides, esters, and combinations comprising at least one of the
foregoing.
[0110] The R group in formula (1) includes but is not limited to
substituted or unsubstituted divalent organic groups such as: (a)
aromatic hydrocarbon groups having 6 to 20 carbon atoms and
halogenated derivatives thereof; (b) straight or branched chain
alkylene groups having 2 to 20 carbon atoms; (c) cycloalkylene
groups having 3 to 20 carbon atoms, or (d) divalent groups of
formula (2):
##STR00002##
wherein Q1 includes but is not limited to a divalent moiety such as
--O--, --S--, --C(O)--, --SO2-, --SO--, --CyH2y- (y being an
integer from 1 to 5), and halogenated derivatives thereof,
including perfluoroalkylene groups.
[0111] In an embodiment, linkers V include but are not limited to
tetravalent aromatic groups of formula (3):
##STR00003##
wherein W is a divalent moiety including --O--, --SO2-, or a group
of the formula --O--Z--O-- wherein the divalent bonds of the --O--
or the --O--Z--O-- group are in the 3,3', 3,4', 4,3', or the 4,4'
positions, and wherein Z includes, but is not limited, to divalent
groups of formulas (4):
##STR00004##
wherein Q includes, but is not limited to a divalent moiety
including --O--, --S--, --C(O), --SO2-, --SO--, --C.sub.yH.sub.2y--
(y being an integer from 1 to 5), and halogenated derivatives
thereof, including perfluoroalkylene groups.
[0112] In an aspect, the polyetherimide comprise more than 1,
specifically 10 to 1,000, or more specifically, 10 to 500
structural units, of formula (5):
##STR00005##
wherein T is --O-- or a group of the formula --O--Z--O-- wherein
the divalent bonds of the --O-- or the --O--Z--O-- group are in the
3,3', 3,4', 4,3', or the 4,4' positions; Z is a divalent group of
formula (3) as defined above; and R is a divalent group of formula
(2) as defined above.
[0113] In another aspect, the polyetherimidesulfones are
polyetherimides comprising ether groups and sulfone groups wherein
at least 50 mole % of the linkers V and the groups R in formula (1)
comprise a divalent arylenesulfone group. For example, all linkers
V, but no groups R, can contain an arylenesulfone group; or all
groups R but no linkers V can contain an arylenesulfone group; or
an arylenesulfone can be present in some fraction of the linkers V
and R groups, provided that the total mole fraction of V and R
groups containing an aryl sulfone group is greater than or equal to
50 mole %.
[0114] Even more specifically, polyetherimidesulfones can comprise
more than 1, specifically 10 to 1,000, or more specifically, 10 to
500 structural units of formula (6):
##STR00006##
wherein Y is --O--, --SO2-, or a group of the formula --O--Z--O--
wherein the divalent bonds of the --O--, SO2-, or the --O--Z--O--
group are in the 3,3', 3,4', 4,3', or the 4,4' positions, wherein Z
is a divalent group of formula (3) as defined above and R is a
divalent group of formula (2) as defined above, provided that
greater than 50 mole % of the sum of moles Y+moles R in formula (2)
contain --SO2- groups.
[0115] It is to be understood that the polyetherimides and
polyetherimidesulfones can optionally comprise linkers V that do
not contain ether or ether and sulfone groups, for example linkers
of formula (7):
##STR00007##
[0116] Imide units containing such linkers are generally be present
in amounts ranging from 0 to 10 mole % of the total number of
units, specifically 0 to 5 mole %. In one embodiment no additional
linkers V are present in the polyetherimides and
polyetherimidesulfones.
[0117] In another aspect, the polyetherimide comprises 10 to 500
structural units of formula (5) and the polyetherimidesulfone
contains 10 to 500 structural units of formula (6).
[0118] Polyetherimides and polyetherimidesulfones can be prepared
by any suitable process. In one embodiment, polyetherimides and
polyetherimide copolymers include polycondensation polymerization
processes and halo-displacement polymerization processes.
[0119] Polycondensation methods can include a method for the
preparation of polyetherimides having structure (1) is referred to
as the nitro-displacement process (X is nitro in formula (8)). In
one example of the nitro-displacement process, N-methyl phthalimide
is nitrated with 99% nitric acid to yield a mixture of
N-methyl-4-nitrophthalimide (4-NPI) and N-methyl-3-nitrophthalimide
(3-NPI). After purification, the mixture, containing approximately
95 parts of 4-NPI and 5 parts of 3-NPI, is reacted in toluene with
the disodium salt of bisphenol-A (BPA) in the presence of a phase
transfer catalyst. This reaction yields BPA-bisimide and NaNO2 in
what is known as the nitro-displacement step. After purification,
the BPA-bisimide is reacted with phthalic anhydride in an imide
exchange reaction to afford BPA-dianhydride (BPADA), which in turn
is reacted with a diamine such as meta-phenylene diamine (MPD) in
ortho-dichlorobenzene in an imidization-polymerization step to
afford the product polyetherimide.
[0120] Other diamines are also possible. Examples of suitable
diamines include: m-phenylenediamine; p-phenylenediamine;
2,4-diaminotoluene; 2,6-diaminotoluene; m-xylylenediamine;
p-xylylenediamine; benzidine; 3,3'-dimethylbenzidine;
3,3'-dimethoxybenzidine; 1,5-diaminonaphthalene;
bis(4-aminophenyl)methane; bis(4-aminophenyl)propane;
bis(4-aminophenyl)sulfide; bis(4-aminophenyl)sulfone;
bis(4-aminophenyl)ether; 4,4'-diaminodiphenylpropane;
4,4'-diaminodiphenylmethane(4,4'-methylenedianiline);
4,4'-diaminodiphenylsulfide; 4,4'-diaminodiphenylsulfone;
4,4'-diaminodiphenylether(4,4'-oxydianiline);
1,5-diaminonaphthalene; 3,3'dimethylbenzidine;
3-methylheptamethylenediamine; 4,4-dimethylheptamethylenediamine;
2,2',3,3'-tetrahydro-3,3,3',3'-tetramethyl-1,1'-spirobi[1H-indene]-6,6'-d-
iamine;
3,3',4,4'-tetrahydro-4,4,4',4'-tetramethyl-2,2'-spirobi[2H-1-benzo-
-pyran]-7,7'-diamine;
1,1'-bis[1-amino-2-methyl-4-phenyl]cyclohexane, and isomers thereof
as well as mixtures and blends comprising at least one of the
foregoing. In one embodiment, the diaminesare specifically aromatic
diamines, especially m- and p-phenylenediamine and mixtures
comprising at least one of the foregoing.
[0121] Suitable dianhydrides that can be used with the diamines
include and are not limited to
2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenyletherdianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfidedianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)benzophenonedianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenylsulfonedianhydride;
2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenyletherdianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenylsulfidedianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)benzophenonedianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenylsulfonedianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl-2,2-propane
dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyletherdianhydrid-
e;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenylsulfide
dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)benzophenonedianhydride-
; 4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenylsulfone
dianhydride; 1,3-bis(2,3-dicarboxyphenoxy)benzene dianhydride;
1,4-bis(2,3-dicarboxyphenoxy)benzene dianhydride;
1,3-bis(3,4-dicarboxyphenoxy)benzene dianhydride;
1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride;
3,3',4,4'-diphenyl tetracarboxylicdianhydride;
3,3',4,4'-benzophenonetetracarboxylic dianhydride;
naphthalicdianhydrides, such as 2,3,6,7-naphthalic dianhydride,
etc.; 3,3',4,4'-biphenylsulphonictetracarboxylic dianhydride;
3,3',4,4'-biphenylethertetracarboxylic dianhydride;
3,3',4,4'-dimethyldiphenylsilanetetracarboxylic dianhydride;
4,4'-bis (3,4-dicarboxyphenoxy)diphenylsulfidedianhydride; 4,4'-bis
(3,4-dicarboxyphenoxy)diphenylsulphonedianhydride; 4,4'-bis
(3,4-dicarboxyphenoxy)diphenylpropanedianhydride;
3,3',4,4'-biphenyltetracarboxylic dianhydride;
bis(phthalic)phenylsulphineoxidedianhydride;
p-phenylene-bis(triphenylphthalic)dianhydride;
m-phenylene-bis(triphenylphthalic)dianhydride;
bis(triphenylphthalic)-4,4'-diphenylether dianhydride;
bis(triphenylphthalic)-4,4'-diphenylmethane dianhydride;
2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropanedianhydride;
4,4'-oxydiphthalic dianhydride; pyromelliticdianhydride;
3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride;
4',4'-bisphenol A dianhydride; hydroquinone diphthalic dianhydride;
6,6'-bis(3,4-dicarboxyphenoxy)-2,2',3,3'-tetrahydro-3,3,3',3'-tetramethyl-
-1,1'-spirobi[1H-indene]dianhydride;
7,7'-bis(3,4-dicarboxyphenoxy)-3,3',4,4'-tetrahydro-4,4,4',4'-tetramethyl-
-2,2'-spirobi[2H-1-benzopyran]dianhydride;
1,1'-bis[1-(3,4-dicarboxyphenoxy)-2-methyl-4-phenyl]cyclohexane
dianhydride; 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride;
3,3',4,4'-diphenylsulfidetetracarboxylic dianhydride;
3,3',4,4'-diphenylsulfoxidetetracarboxylic dianhydride;
4,4'-oxydiphthalic dianhydride; 3,4'-oxydiphthalic dianhydride;
3,3'-oxydiphthalic dianhydride; 3,3'-benzophenonetetracarboxylic
dianhydride; 4,4'-carbonyldiphthalic dianhydride;
3,3',4,4'-diphenylmethanetetracarboxylic dianhydride;
2,2-bis(4-(3,3-dicarboxyphenyl)propane dianhydride;
2,2-bis(4-(3,3-dicarboxyphenyl)hexafluoropropanedianhydride;
(3,3',4,4'-diphenyl)phenylphosphinetetracarboxylicdianhydride;
(3,3',4,4'-diphenyl)phenylphosphineoxidetetracarboxylicdianhydride;
2,2'-dichloro-3,3',4,4'-biphenyltetracarboxylic dianhydride;
2,2'-dimethyl-3,3',4,4'-biphenyltetracarboxylic dianhydride;
2,2'-dicyano-3,3',4,4'-biphenyltetracarboxylic dianhydride;
2,2'-dibromo-3,3',4,4'-biphenyltetracarboxylic dianhydride;
2,2'-diiodo-3,3',4,4'-biphenyltetracarboxylic dianhydride;
2,2'-ditrifluoromethyl-3,3',4,4'-biphenyltetracarboxylic
dianhydride;
2,2'-bis(1-methyl-4-phenyl)-3,3',4,4'-biphenyltetracarboxylic
dianhydride;
2,2'-bis(1-trifluoromethyl-2-phenyl)-3,3',4,4'-biphenyltetracarboxylic
dianhydride;
2,2'-bis(1-trifluoromethyl-3-phenyl)-3,3',4,4'-biphenyltetracarboxylic
dianhydride;
2,2'-bis(1-trifluoromethyl-4-phenyl)-3,3',4,4'-biphenyltetracarboxylic
dianhydride;
2,2'-bis(1-phenyl-4-phenyl)-3,3',4,4'-biphenyltetracarboxylic
dianhydride; 4,4'-bisphenol A dianhydride; 3,4'-bisphenol A
dianhydride; 3,3'-bisphenol A dianhydride;
3,3',4,4'-diphenylsulfoxidetetracarboxylic dianhydride;
4,4'-carbonyldiphthalic dianhydride;
3,3',4,4'-diphenylmethanetetracarboxylic dianhydride;
2,2'-bis(1,3-trifluoromethyl-4-phenyl)-3,3',4,4'-biphenyltetracarboxylic
dianhydride, and all isomers thereof, as well as combinations of
the foregoing.
[0122] Halo-displacement polymerization methods for making
polyetherimides and polyetherimidesulfones include and are not
limited limited to, the reaction of a bis(phthalimide) for formula
(8):
##STR00008##
wherein R is as described above and X is a nitro group or a
halogen. Bis-phthalimides (8) can be formed, for example, by the
condensation of the corresponding anhydride of formula (9):
##STR00009##
wherein X is a nitro group or halogen, with an organic diamine of
the formula (10):
H.sub.2N--R--NH.sub.2 (10),
wherein R is as described above.
[0123] Illustrative examples of amine compounds of formula (10)
include: ethylenediamine, propylenediamine, trimethylenediamine,
diethylenetriamine, triethylenetetramine, hexamethylenediamine,
heptamethylenediamine, octamethylenediamine, nonamethylenediamine,
decamethylenediamine, 1,12-dodecanediamine, 1,18-octadecanediamine,
3-methylheptamethylenediamine, 4,4-dimethylheptamethylenediamine,
4-methylnonamethylenediamine, 5-methylnonamethylenediamine,
2,5-dimethylhexamethylenediamine,
2,5-dimethylheptamethylenediamine, 2, 2-dimethylpropylenediamine,
N-methyl-bis (3-aminopropyl) amine, 3-methoxyhexamethylenediamine,
1,2-bis(3-aminopropoxy) ethane, bis(3-aminopropyl) sulfide,
1,4-cyclohexanediamine, bis-(4-aminocyclohexyl) methane,
m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene,
2,6-diaminotoluene, m-xylylenediamine, p-xylylenediamine,
2-methyl-4,6-diethyl-1,3-phenylene-diamine,
5-methyl-4,6-diethyl-1,3-phenylene-diamine, benzidine,
3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine,
1,5-diaminonaphthalene, bis(4-aminophenyl) methane,
bis(2-chloro-4-amino-3, 5-diethylphenyl) methane,
bis(4-aminophenyl) propane, 2,4-bis(b-amino-t-butyl) toluene,
bis(p-b-amino-t-butylphenyl) ether, bis(p-b-methyl-o-aminophenyl)
benzene, bis(p-b-methyl-o-aminopentyl) benzene, 1,
3-diamino-4-isopropylbenzene, bis(4-aminophenyl) ether and
1,3-bis(3-aminopropyl) tetramethyldisiloxane. Mixtures of these
amines can be used. Illustrative examples of amine compounds of
formula (10) containing sulfone groups include but are not limited
to, diaminodiphenylsulfone (DDS) and bis(aminophenoxy phenyl)
sulfones (BAPS). Combinations comprising any of the foregoing
amines can be used.
[0124] The polyetherimides can be synthesized by the reaction of
the bis(phthalimide) (8) with an alkali metal salt of a dihydroxy
substituted aromatic hydrocarbon of the formula HO--V--OH wherein V
is as described above, in the presence or absence of phase transfer
catalyst. Suitable phase transfer catalysts are disclosed in U.S.
Pat. No. 5,229,482. Specifically, the dihydroxy substituted
aromatic hydrocarbon a bisphenol such as bisphenol A, or a
combination of an alkali metal salt of a bisphenol and an alkali
metal salt of another dihydroxy substituted aromatic hydrocarbon
can be used.
[0125] In one embodiment, the polyetherimide comprises structural
units of formula (5) wherein each R is independently p-phenylene or
m-phenylene or a mixture comprising at least one of the foregoing;
and T is group of the formula --O--Z--O-- wherein the divalent
bonds of the --O--Z--O-- group are in the 3,3' positions, and Z is
2,2-diphenylenepropane group (a bisphenol A group). Further, the
polyetherimidesulfone comprises structural units of formula (6)
wherein at least 50 mole % of the R groups are of formula (4)
wherein Q is --SO2- and the remaining R groups are independently
p-phenylene or m-phenylene or a combination comprising at least one
of the foregoing; and T is group of the formula --O--Z--O-- wherein
the divalent bonds of the --O--Z--O-- group are in the 3,3'
positions, and Z is a 2,2-diphenylenepropane group.
[0126] The polyetherimide and polyetherimidesulfone can be used
alone or in combination with each other and/or other of the
disclosed polymeric materials in fabricating the polymeric
components of the invention. In one embodiment, only the
polyetherimide is used. In another embodiment, the weight ratio of
polyetherimide:polyetherimidesulfone can be from 99:1 to 50:50.
[0127] The polyetherimides can have a weight average molecular
weight (Mw) of 5,000 to 100,000 grams per mole (g/mole) as measured
by gel permeation chromatography (GPC). In some embodiments the Mw
can be 10,000 to 80,000. The molecular weights as used herein refer
to the absolute weight averaged molecular weight (Mw).
[0128] The polyetherimides can have an intrinsic viscosity greater
than or equal to 0.2 deciliters per gram (dl/g) as measured in
m-cresol at 25.degree. C. Within this range the intrinsic viscosity
can be 0.35 to 1.0 dl/g, as measured in m-cresol at 25.degree.
C.
[0129] The polyetherimides can have a glass transition temperature
of greater than 180.degree. C., specifically of 200.degree. C. to
500.degree. C., as measured using differential scanning calorimetry
(DSC) per ASTM test D3418. In some embodiments, the polyetherimide
and, in particular, a polyetherimide has a glass transition
temperature of 240 to 350.degree. C.
[0130] The polyetherimides can have a melt index of 0.1 to 10 grams
per minute (g/min), as measured by American Society for Testing
Materials (ASTM) DI 238 at 340 to 370.degree. C., using a 6.7
kilogram (kg) weight.
[0131] An alternative halo-displacement polymerization process for
making polyetherimides, e.g., polyetherimides having structure (1)
is a process referred to as the chloro-displacement process (X is
Cl in formula (8)). The chloro-displacement process is illustrated
as follows: 4-chloro phthalic anhydride and meta-phenylene diamine
are reacted in the presence of a catalytic amount of sodium phenyl
phosphinate catalyst to produce the bischlorophthalimide of
meta-phenylene diamine (CAS No. 148935-94-8). The
bischlorophthalimide is then subjected to polymerization by
chloro-displacement reaction with the disodium salt of BPA in the
presence of a catalyst in ortho-dichlorobenzene or anisole solvent.
Alternatively, mixtures of 3-chloro- and 4-chlorophthalic anhydride
may be employed to provide a mixture of isomeric
bischlorophthalimides which may be polymerized by
chloro-displacement with BPA disodium salt as described above.
[0132] Siloxane polyetherimides can include
polysiloxane/polyetherimide block copolymers having a siloxane
content of greater than 0 and less than 40 weight percent (wt %)
based on the total weight of the block copolymer. The block
copolymer comprises a siloxane block of Formula (I):
##STR00010##
wherein R.sup.1-6 are independently at each occurrence selected
from the group consisting of substituted or unsubstituted,
saturated, unsaturated, or aromatic monocyclic groups having 5 to
30 carbon atoms, substituted or unsubstituted, saturated,
unsaturated, or aromatic polycyclic groups having 5 to 30 carbon
atoms, substituted or unsubstituted alkyl groups having 1 to 30
carbon atoms and substituted or unsubstitutedalkenyl groups having
2 to 30 carbon atoms, V is a tetravalent linker selected from the
group consisting of substituted or unsubstituted, saturated,
unsaturated, or aromatic monocyclic and polycyclic groups having 5
to 50 carbon atoms, substituted or unsubstituted alkyl groups
having 1 to 30 carbon atoms, substituted or unsubstitutedalkenyl
groups having 2 to 30 carbon atoms and combinations comprising at
least one of the foregoing linkers, g equals 1 to 30, and d is 2 to
20. Commercially available siloxane polyetherimides can be obtained
from SABIC Innovative Plastics under the brand name SILTEM*
(*Trademark of SABIC Innovative Plastics IP B.V.)
[0133] The polyetherimide resin can have a weight average molecular
weight (Mw) within a range having a lower limit and/or an upper
limit. The range can include or exclude the lower limit and/or the
upper limit. The lower limit and/or upper limit can be selected
from 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000,
14000, 15000, 16000, 17000, 18000, 19000, 20000, 21000, 22000,
23000, 24000, 25000, 26000, 27000, 28000, 29000, 30000, 31000,
32000, 33000, 34000, 35000, 36000, 37000, 38000, 39000, 40000,
41000, 42000, 43000, 44000, 45000, 46000, 47000, 48000, 49000,
50000, 51000, 52000, 53000, 54000, 55000, 56000, 57000, 58000,
59000, 60000, 61000, 62000, 63000, 64000, 65000, 66000, 67000,
68000, 69000, 70000, 71000, 72000, 73000, 74000, 75000, 76000,
77000, 78000, 79000, 80000, 81000, 82000, 83000, 84000, 85000,
86000, 87000, 88000, 89000, 90000, 91000, 92000, 93000, 94000,
95000, 96000, 97000, 98000, 99000, 100000, 101000, 102000, 103000,
104000, 105000, 106000, 107000, 108000, 109000, and 110000 daltons.
For example, the polyetherimide resin can have a weight average
molecular weight (Mw) from 5,000 to 100,000 daltons, from 5,000 to
80,000 daltons, or from 5,000 to 70,000 daltons. The primary alkyl
amine modified polyetherimide will have lower molecular weight and
higher melt flow than the starting, unmodified, polyetherimide.
[0134] The polyetherimide resin can be selected from the group
consisting of a polyetherimide, for example, as described in U.S.
Pat. Nos. 3,875,116, 6,919,422, and 6,355,723; a silicone
polyetherimide, for example, as described in U.S. Pat. Nos.
4,690,997 and 4,808,686; a polyetherimidesulfone resin, as
described in U.S. Pat. No. 7,041,773; or combinations thereof. Each
of these patents are incorporated herein in their entirety.
[0135] The polyetherimide resin can have a glass transition
temperature within a range having a lower limit and/or an upper
limit. The range can include or exclude the lower limit and/or the
upper limit. The lower limit and/or upper limit can be selected
from 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210,
220, 230, 240, 250, 260, 270, 280, 290, 300, 310, and 320 degrees
Celsius. For example, the polyetherimide resin can have a glass
transition temperature (Tg) greater than about 200 degrees Celsius.
The polyetherimide resin can be substantially free (less than 100
ppm) of benzylic protons. The polyetherimide resin can be free of
benzylic protons. The polyetherimide resin can have an amount of
benzylic protons below 100 ppm. In one embodiment, the amount of
benzylic protons ranges from more than 0 to below 100 ppm. In
another embodiment, the amount of benzylic protons is not
detectable.
[0136] The polyetherimide resin can be substantially free (less
than 100 ppm) of halogen atoms. The polyetherimide resin can be
free of halogen atoms. The polyetherimide resin can have an amount
of halogen atoms below 100 ppm. In one embodiment, the amount of
halogen atoms range from more than 0 to below 100 ppm. In another
embodiment, the amount of halogen atoms is not detectable.
[0137] In an aspect, the electrolyte 108 can comprise a molten salt
and/or a lithium salt. As an example, the lithium battery
electrolyte can have a high lithium ionic conductivity and so low
viscosity as to give a high infiltration into the electrode or
separator. In an aspect, the electrolyte 108 can comprise one or
more of lithium tetrafluoroborate (abbreviated as "LiBF4"), lithium
hexafluorophosphate (abbreviated as "LiPF6"), lithium
hexafluoromethanesulfonate, lithium bis(trifluoromethane sulfonyl)
amide (abbreviated as "LiTFSI"), lithium dicyanamide (abbreviated
as "LiDCA"), lithium trifluoromethanesulfonate (abbreviated as
"LiTFS") and lithium bis(pentafluoroethanesulonyl)amide
(abbreviated as "LiBETI"). Other materials and forming processes
can be used.
[0138] The cation contained in the aforementioned molten salt is
not specifically limited but may be one or more selected from the
group consisting of aromatic quaternary ammonium ions such as
1-ethyl-3-methyl imidazolium, 1-methyl-3-propylimidazolium,
1-methyl-3-isopropylimidazolium, 1-butyl-3-methylimidazolium,
1-ethyl-2,3-dimethyl imidazolium, 1-ethyl-3,4-dimethylimidazolium,
N-propylpyridinium, N-butylpyridinium, N-tert-butyl pyridinium and
N-tert-pentylpyridinium, and aliphatic quaternary ammonium ions
such as N-butyl-N,N,N-trimethylammonium,
N-ethyl-N,N-dimethyl-N-propyl ammonium,
N-butyl-N-ethyl-N,N-dimethylammonium,
N-butyl-N,N-dimethyl-N-propylammonium,
N-methyl-N-propylpyrrolidinium, N-butyl-N-methyl pyrrolidinium,
N-methyl-N-pentylpyrrolidinium,
N-propoxyethyl-N-methylpyrrolidinium, N-methyl-N-propyl
piperidinium, N-methyl-N-isopropylpiperidinium,
N-butyl-N-methylpiperidinium, N-isobutyl-N-methyl piperidinium,
N-sec-butyl-N-methyl piperidinium,
N-methoxyethyl-N-methylpiperidinium and
N-ethoxyethyl-N-methylpiperidinium. Among these aliphatic
quaternary ammonium ions, pyrrolidinium ions as nitrogen-containing
5-membered ring or piperidinium ions as nitrogen-containing
6-membered ring are desirable because they have a high reduction
resistance that inhibits side reaction to enhance storage
properties or cycle performances. Other materials and forming
processes can be used.
[0139] The anion contained in the aforementioned molten salt is not
specifically limited but may be one or more selected from the group
consisting of PF6-, (PF3(C2F5)3)-, (PF3(CF3)3)-, BF4-,
(BF2(CF3)2)-, (BF2(C2F5)2)-, (BF3(CF3))-, (BF3(C2F5))-,
(B(COOCOO)2)-(abbreviated as "BOB-"), CF3SO3-(abbreviated as
"Tf-"), C4F9SO3-(abbreviated as "Nf-"), ((CF3SO2)2N)-- (abbreviated
as "TFSI-"), ((C2F5SO2)2N)-- (abbreviated as "BETI-"), ((CF3SO2)
(C4F9SO2)N)--, ((CN)2N)-- (abbreviated as "DCA-") and
((CF3SO2)3C)-- and ((CN)3C)--. Among these there may be desirably
used at least one of PF6-, (PF3(C2F5)3)-, (PF3(CF3)3)-, BF4-,
(BF2(CF3)2)-, (BF2(C2F5)2)-, (BF3(CF3))-, (BF3(C2F5))-, Tf-, Nf-,
TFSI-, BETI- and ((CF3SO2) (C4F9SO2)N), which include F, in view of
excellent cycle performances.
[0140] In use, the positive electrode and the negative electrode
are separated from each other by a separator and are electrically
connected to each other by ion movement through the aforementioned
electrolyte. In order to form a battery including an electrolyte
having the aforementioned constitution, the separator can be formed
from a thermoplastic polymer.
[0141] Suitable polyetherimides that can be used in the disclosed
compositions include, but are not limited to, ULTEM.TM.. ULTEM.TM.
is a polymer from the family of polyetherimides sold by Saudi Basic
Industries Corporation (SABIC). ULTEM.TM. can have elevated thermal
resistance, high strength and stiffness, and broad chemical
resistance. ULTEM.TM. as used herein refers to any or all ULTEM.TM.
polymers included in the family unless otherwise specified. In one
aspect, a polyetherimide can comprise any polycarbonate material or
mixture of materials, for example, as recited in U.S. Pat. Nos.
4,548,997; 4,629,759; 4,816,527; 6,310,145; and 7,230,066, all of
which are hereby incorporated in its entirety for the specific
purpose of disclosing various polyetherimide compositions and
methods. In another aspect, a polyetherimide can comprise any
polyester material or mixture of materials, for example, as recited
in U.S. Pat. Nos. 4,141,927; 6,063,874; 6,150,473; and 6,204,340,
all of which are hereby incorporated in its entirety for the
specific purpose of disclosing various polyetherimide compositions
and methods.
[0142] In certain aspects, the thermoplastic polymer is a
polyetherimide polymer having a structure comprising structural
units represented by an organic radical of formula (I):
##STR00011##
[0143] wherein R in formula (I) includes substituted or
unsubstituted divalent organic radicals such as (a) aromatic
hydrocarbon radicals having about 6 to about 20 carbon atoms and
halogenated derivatives thereof; (b) straight or branched chain
alkylene radicals having about 2 to about 20 carbon atoms; (c)
cycloalkylene radicals having about 3 to about 20 carbon atoms, or
(d) divalent radicals of the general formula (II):
##STR00012##
[0144] wherein Q includes a divalent moiety selected from the group
consisting of a single bond, --O--, --S--, --C(O)--, --SO2-,
--SO--, --CyH2y- (y being an integer from 1 to 5), and halogenated
derivatives thereof, including perfluoroalkylene groups; wherein T
is --O-- or a group of the formula --O--Z--O-- wherein the divalent
bonds of the --O-- or the --O--Z--O-- group are in the 3,3', 3,4',
4,3', or the 4,4' positions, and wherein Z includes, but is not
limited, to divalent radicals of formula (III):
##STR00013##
and wherein the polyetherimides which are included by formula (I)
have a Mw of at least about 40,000.
[0145] In a further aspect, the polyetherimide polymer may be a
copolymer, which, in addition to the etherimide units described
above, further contains polyimide structural units of the formula
(IV):
##STR00014##
wherein R is as previously defined for formula (I) and M includes,
but is not limited to, radicals of formula (V):
##STR00015##
[0146] In a further aspect, the thermoplastic resin is a
polyetherimide polymer having structure represented by a
formula:
##STR00016##
wherein the polyetherimide polymer has a molecular weight of at
least 40,000 Daltons, 50,000 Daltons, 60,000 Daltons, 80,000
Daltons, or 100,000 Daltons.
[0147] The polyetherimide polymer can be prepared by methods known
to one skilled in the art, including the reaction of an aromatic
bis(ether anhydride) of the formula (VI):
##STR00017##
with an organic diamine of the formula (IX):
H2N--R--NH2 (VII),
wherein T and Rare defined as described above in formula (I).
[0148] Illustrative, non-limiting examples of aromatic bis(ether
anhydride)s of formula (VI) include
2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenyl ether dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)benzophenone dianhydride;
4,4'-bis(3,4-dicarboxyphenoxy)diphenyl sulfone dianhydride;
2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl] propane dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenyl ether dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfide dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy) benzophenone dianhydride;
4,4'-bis(2,3-dicarboxyphenoxy)diphenyl sulfone dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl-2,2-propane
dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl ether
dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl sulfide
dianhydride;
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)benzophenone
dianhydride and
4-(2,3-dicarboxyphenoxy)-4'-(3,4-dicarboxyphenoxy)diphenyl sulfone
dianhydride, as well as various mixtures thereof.
[0149] The bis(ether anhydride)s can be prepared by the hydrolysis,
followed by dehydration, of the reaction product of a nitro
substituted phenyl dinitrile with a metal salt of dihydric phenol
compound in the presence of a dipolar, aprotic solvent. A useful
class of aromatic bis(ether anhydride)s included by formula (VI)
above includes, but is not limited to, compounds wherein T is of
the formula (VIII):
##STR00018##
and the ether linkages, for example, are beneficially in the 3,3',
3,4', 4,3', or 4,4' positions, and mixtures thereof, and where Q is
as defined above.
[0150] Any diamino compound may be employed in the preparation of
the polyimides and/or polyetherimides. Illustrative, non-limiting
examples of suitable diamino compounds of formula (VII) include
ethylenediamine, propylenediamine, trimethylenediamine,
diethylenetriamine, triethylenetertramine, hexamethylenediamine,
heptamethylenediamine, octamethylenediamine, nonamethylenediamine,
decamethylenediamine, 1,12-dodecane diamine,
1,18-octadecanediamine, 3-methylheptamethylenediamine,
4,4-dimethylheptamethylenediamine, 4-methylnonamethylenediamine,
5-methylnonamethylene diamine, 2,5-dimethylhexamethylenediamine,
2,5-dimethylheptamethylenediamine, 2, 2-dimethylpropylenediamine,
N-methyl-bis (3-aminopropyl) amine, 3-methoxyhexamethylene diamine,
1,2-bis(3-aminopropoxy) ethane, bis(3-aminopropyl) sulfide,
1,4-cyclohexane diamine, bis-(4-aminocyclohexyl) methane,
m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene,
2,6-diaminotoluene, m-xylylenediamine, p-xylylenediamine,
2-methyl-4,6-diethyl-1,3-phenylene-diamine,
5-methyl-4,6-diethyl-1,3-phenylene-diamine, benzidine,
3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine,
1,5-diaminonaphthalene, bis(4-aminophenyl) methane,
bis(2-chloro-4-amino-3, 5-diethylphenyl) methane,
bis(4-aminophenyl) propane, 2,4-bis(b-amino-t-butyl) toluene,
bis(p-b-amino-t-butylphenyl) ether, bis(p-b-methyl-o-aminophenyl)
benzene, bis(p-b-methyl-o-aminopentyl) benzene, 1,
3-diamino-4-isopropyl benzene, bis(4-aminophenyl) sulfide, bis
(4-aminophenyl) sulfone, bis(4-aminophenyl) ether and
1,3-bis(3-aminopropyl) tetramethyldisiloxane. Mixtures of these
compounds may also be present. Beneficial diamino compounds are
aromatic diamines, especially m- and p-phenylenediamine and
mixtures thereof.
[0151] In a further aspect, the polyetherimide resin includes
structural units according to formula (I) wherein each R is
independently p-phenylene or m-phenylene or a mixture thereof and T
is a divalent radical of the formula (IX):
##STR00019##
[0152] In various aspects, the reactions can be carried out
employing solvents such as o-dichlorobenzene, m-cresol/toluene, or
the like, to effect a reaction between the anhydride of formula
(VI) and the diamine of formula (VII), at temperatures of about
100.degree. C. to about 250.degree. C. Alternatively, the
polyetherimide can be prepared by melt polymerization of aromatic
bis(ether anhydride)s of formula (VI) and diamines of formula (VII)
by heating a mixture of the starting materials to elevated
temperatures with concurrent stirring. Melt polymerizations can
employ temperatures of about 200.degree. C. to about 400.degree. C.
Chain stoppers and branching agents can also be employed in the
reaction. The polyetherimide polymers can optionally be prepared
from reaction of an aromatic bis(ether anhydride) with an organic
diamine in which the diamine is present in the reaction mixture at
no more than about 0.2 molar excess, and beneficially less than
about 0.2 molar excess. Under such conditions the polyetherimide
resin has less than about 15 microequivalents per gram (.mu.eq/g)
acid titratable groups in one embodiment, and less than about 10
.mu.eq/g acid titratable groups in an alternative embodiment, as
shown by titration with chloroform solution with a solution of 33
weight percent (wt %) hydrobromic acid in glacial acetic acid.
Acid-titratable groups are essentially due to amine end-groups in
the polyetherimide resin.
[0153] In a further aspect, the polyetherimide resin has a weight
average molecular weight (Mw) of at least about 24,000 to about
150,000 grams per mole (g/mole), as measured by gel permeation
chromatography, using a polystyrene standard. In a still further
aspect, the thermoplastic resin can have a molecular weight of at
least 20,000 Daltons, 40,000 Daltons, 50,000 Daltons, 60,000
Daltons, 80,000 Daltons, 100,000 Daltons, or 120,000 Daltons. In a
yet further aspect, the thermoplastic resin can have a molecular
weight of at least 40,000 Daltons. In an even further aspect, the
thermoplastic resin can have a molecular weight of at least 45,000
Daltons. In a still further aspect, the thermoplastic resin can
have a molecular weight of at least 50,000 Daltons. In a yet
further aspect, the thermoplastic resin can have a molecular weight
of at least 60,000 Daltons. In an even further aspect, the
thermoplastic resin can have a molecular weight of at least 70,000
Daltons. In a still further aspect, the thermoplastic resin can
have a molecular weight of at least 100,000 Daltons.
[0154] In a further aspect, the thermoplastic resin can comprise a
polyetherimide polymer having a molecular weight of at least 40,000
Daltons, 50,000 Daltons, 60,000 Daltons, 80,000 Daltons, or 100,000
Daltons. In a yet further aspect, polyetherimide polymer has a
molecular weight of at least Daltons, 40,000 Daltons or 50,000
Daltons. In a still further aspect, the polyetherimide polymer has
a molecular weight of at least 40,000 Daltons. In a yet further
aspect, the polyetherimide polymer has a molecular weight of at
least 50,000 Daltons. In an even further aspect, the polyetherimide
polymer has a molecular weight of at least 60,000 Daltons. In a
still further aspect, the polyetherimide polymer has a molecular
weight of at least 70,000 Daltons. In a yet further aspect, the
polyetherimide polymer has a molecular weight of at least 100,000
Daltons.
[0155] Poly(phenylene oxide) (PPO) is also known as poly(phenylene
ether) (PPE) and can comprise homopolymers (e.g., based on
2,6-dimethyl-phenol), copolymers (e.g., based on
2,6-dimethyl-phenol, 2,3,6-trimethylphenol,
2-methyl-6-phenylphenol, 2,4-dimethyl-6-phenylphenol,
eugenol-capped siloxane) or blends with e.g., polystyrene (PS),
high-impact polystyrene (HIPS), styrene block-copolymers (e.g.,
styrene-ethylene-butylene-styrene, SEBS) or PP. Additionally,
stabilizers and/or compatibilizers may be present.
[0156] Poly(amic acid) (PAA) is typically comprised of a
dianhydride (e.g., pyromellitic dianhydride,
4,4',5,5'-sulfonyldiphthalic anhydride, 3,3',4,4'-oxydiphtalic
dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride,
4,4'-diphtalic (hexafluoroisopropylidene) anhydride,
4,4'-biphthalic anhydride, hydroquinone diphthalic anhydride,
4,4'-(4,4'-isopropylidenediphenoxy)bis(phthalic anhydride), or the
like) combined with one or more types of amines, typically
aliphatic or aromatic in nature (see for example Varun Ratta, PhD
Thesis, "Crystallization, Morphology, Thermal Stability and
Adhesive Properties of Novel High Performance Semicrystalline
Polyimides", 1999, Chapter 1). Such poly(amic acid) polymers will
undergo ring close to form polyimide polymers (typically
thermosets), as widely described in literature, e.g., in "Polyamic
Acids and Polyimides: Synthesis, Transformations, and Structure",
M. Bessonov, V. Zubkov, CRC Press, 1993.
EXAMPLES
[0157] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how the compounds, compositions, articles, devices
and/or methods claimed herein are made and evaluated, and are
intended to be purely exemplary and are not intended to limit the
scope of the methods and systems. Efforts have been made to ensure
accuracy with respect to numbers (e.g., amounts, temperature,
etc.), but some errors and deviations should be accounted for.
Unless indicated otherwise, parts are parts by weight, temperature
is in .degree. C. or is at ambient temperature, and pressure is at
or near atmospheric.
Mechanical Spinning
[0158] This disclosure relates to a method for production of fine
fibers from a polymer through a mechanical spinning process such as
solution shear spinning, force spinning, and the like. Force
spinning (comprising centrifugal spinning and rotary jet spinning)
can be a technique where the driving force for the formation of the
fine fibers is a centrifugal force. U.S. Pat. Appl. Nos.
2009/0280207, 2009/0232920, 2009/0269429, and 2009/0280325 describe
an apparatus that uses a rotating spinneret comprising an array of
capillaries. This spinneret typically rotates at speeds from 500 to
25000 rpms, thereby creating a significant centrifugal force
responsible for the formation of fine fibers. By increasing the
number of capillaries in a given spinneret, the volumetric
throughput of fiber generation can be increased to make more fibers
in a short period of time. This technology can typically be applied
to a polymer melt as well as to a polymer solution and has the
advantage of having significantly higher throughputs as compared to
the conventional nano-fiber spinning technologies, such as
electro-spinning. As the polymer is drawn from the orifice by the
rotational (centrifugal) force, the parameters influencing the
final fiber geometry and quality include spinneret angular velocity
and orifice radius, polymer viscoelasticity (which includes
viscosity and relaxation time of the material), surface tension,
evaporation rate (for solvent in solution) and temperature (melting
and solidification) and distance of spinneret orifice to collector.
Shear spinning can be a process whereby a polymer solution is
injected through one or multiple small orifices into a non-solvent
to the polymer, which, upon mixing of the solvent and non-solvent,
induces precipitation of the polymer at a solvent/non-solvent
composition at which the polymer is no longer soluble in the
solvent/non-solvent mixture. When the non-solvent is sheared (e.g.,
flows) upon injection of the polymer solution, the precipitation of
the polymer will occur under shear conditions, which enables the
formation of fibers at very high throughput. As spinning of the
fibers relies on the shear conditions of the non-solvent in which
the polymer solution is injected, this process is known as
shear-spinning. Other spinning and fiber-processing techniques can
be used.
[0159] Certain embodiments of the disclosure are directed to
producing fine fibers having an individual average diameter of
about 10 nm to about 50.mu.m. In an aspect, thermoplastic polymers
having a glass transition temperature higher than 180.degree. C.
can be spun into fine fibers using the systems and methods of the
present disclosure. In another aspect, polymers comprising one or
more of polyetherimide, poly(amic acid), aromatic polyamide,
poly(amide-imide) and polyphenylene oxide can be spun into fine
fibers using the systems and methods of the present disclosure. In
a further aspect, a polymer melt or solution can be spun into fine
fibers using the systems and methods of the present disclosure,
wherein the polymer melt or solution comprises polymethyl
methacrylate, polystyrene, PE, PP, polytetrafluoroethylene,
polyvinylidene fluoride, polycarbonate, poly(4-methylpentene),
cyclic olefin copolymers, polyamide, aromatic polyamide,
poly(amide-imide), poly(amic acid), polyoxymethylene,
polyphthalamide, polysulfone, polyethersulfone, polyphenylsulfone,
liquid crystalline polymers, polyetherimide, polybutylene
terephthalate, PE terephthalate, PE naphthalate, polymethylpentene,
polyketone, polyetherketone, polyetheretherketone, polyphenylene
sulfide, cellulose, cellulose acetate, cellulose acetate butylate,
polyacrylonitrile, or poly(acrylonitrile-co-methacrylate), or a
copolymer or blend thereof. Other materials can be spun using the
systems and methods of the present disclosure.
Materials
[0160] In an aspect, a plurality of high temperature materials can
be used in preparation of fine fibers, to be used as e.g., a HTMI
separator, as described herein and as illustrated below:
TABLE-US-00001 Component CHEMICAL DESCRIPTION SOURCE ULTEM
Polyetherimide based on SABIC 1000 meta-phenylenediamine ULTEM
Polyetherimide based on SABIC 1010 meta-phenylenediamine ULTEM
Polyetherimide based on SABIC 9011 meta-phenylenediamine ULTEM
Polyetherimide based on SABIC CRS 5001K para-phenylenediamine ULTEM
Polyetherimide based on SABIC CRS 5011K para-phenylenediamine PPO
6130 Polyphenyleneoxide SABIC PAA Poly(pyromellitic
dianhydride-co-4,4'- Sigma-Aldrich oxydianiline), amic acid
solution, 11 wt. % +/- 5 wt. % in NMP/aromatic hydrocarbons
(80%/20% solvent ratio) PAA Poly(pyromellitic dianhydride-co-4,4'-
Sigma-Aldrich oxydianiline), amic acid solution, 15 wt. % +/- 5 wt.
% in NMP/aromatic hydrocarbons (80%/20% solvent ratio) PAA
Poly(pyromellitic dianhydride-co-4,4'- Sigma-Aldrich oxydianiline),
amic acid solution, 12.8 wt. % +/- 0.5 wt. % in NMP/aromatic
hydrocarbons (80%/20% solvent ratio) NMP N-methyl pyrrolidone
Spectrochem Pvt Ltd. (HPLC-grade, water content 500 ppm) Mumbai
(India) [e.g., for electrospinning] 2-Cl-phenol 2-Chloro-phenol
Sinopharm Chemical Reagent Co. Ltd HFIP Hexafluoro-isopropanol
Sinopharm Chemical Reagent Co. Ltd DCM Dichloromethane Sinopharm
Chemical Reagent Co. Ltd TFA Trifluoracetic acid Sinopharm Chemical
Reagent Co. Ltd CMP 4-Chloro-2-methyl-phenol Sinopharm Chemical
Reagent Co. Ltd Chloroform Chloroform Sinopharm Chemical Reagent
Co. Ltd TFE 1,1,2,2-Tetrachloroethane Sinopharm Chemical Reagent
Co. Ltd NMP N-methyl pyrrolidone (99%, extra pure) Acros Organics
[e.g., for Solution Forcespinning] Chloroform Chloroform (99+%,
extra pure, Acros Organics stabilized with ethanol) Toluene
Methylbenzene (>99.5%, Certified Fisher Scientific ACS reagent
grade) [e.g., for Solution Forcespinning] Glycerol Glycerol (99.7%)
Brenntag Southwest, Inc. Ethanol Ethanol (Anhydrous ACS/USP
Pharmaco-Aaper grade, 99.5%)
[0161] As shown and described herein, polyetherimides based on
para-phenylene diamines (ULTEM CRS 5000 series from SABIC) can be
used as solvent resistant membranes for lithium-ion battery
applications. The ULTEM CRS 5000 series does not significantly
dissolve (i.e., normalized dry weight of greater than about 90%) in
typical electrolytes (e.g., 1:1:1 EC:DMC:EMC and 1 mol/L LiPF6),
where the normalized dry weight is calculated as the dry weight
after electrolyte soaking divided by the starting weight, and the
dry weight after electrolyte soaking is measured by soaking the
material in the electrolyte for 21 days at about 55.degree. C.,
drying the material in an oven until no further weight reduction is
observed, and recording the dry weight. As an example, fibers and
membranes can be prepared using the materials and processes
disclosed herein for environments such as battery cells and/or
capacitor cells, electrolytic energy storage devices, a dialysis
membrane, a water filtration membrane, a desalination membrane, a
gas separation membrane, and the like.
[0162] In an aspect, chemical resistant, porous membranes can be
prepared by dissolving solvent-resistant polyetherimides in NMP at
elevated temperatures (about 140-202.degree. C., see FIG. 2),
followed by spinning the solution at reduced temperature (about
30-140.degree. C.). The dissolution temperature in FIG. 2 was
determined by visual observation of the polymer dissolving in the
solvent and the complete solution turning transparent. FIG. 3 shows
the phase separation temperature as a function of concentration,
measured by determining the temperature at which the solution shows
a sudden significant increase in viscosity upon slowly cooling down
from about 170.degree. C., which is an indication for gelation
(early stage of phase separation). In an aspect, solutions can be
prepared by boiling the NMP solution for a period of time (e.g.,
3-5 mins). Moisture analysis of NMP using a Karl Fischer titrator
shows that there is a drastic reduction in moisture content, which
is explained by the fact that NMP and water do not form an
azeotrope (reference Raginskaya L. M.:
N-Methyl-2-Pyrrolidon--Wasser. Prom.Sint.Kaucuka (1975) 1-3) and,
therefore, most of the water evaporates from the boiling NMP.
[0163] NMP has a Health Rating of only 2 on the NFPA fire diamond
(according to the Centers for Disease Control and
Prevention--http://www.cdc.gov) and is, therefore, considered to be
much more environmentally friendly as compared to other solvent
systems capable of dissolving ULTEM CRS 5000, such as phenol and
cresol solvent systems as described in U.S. Pat. Appl. Nos.
2007/0056901 and 2007/0060688 and U.S. Pat. No. 7,439,291.
Additionally, as NMP is fully miscible with water, and water is a
poor solvent for polyetherimides, the non-solvent in e.g., the
shear spinning process can be based on water, optionally in
combination with NMP.
[0164] In an aspect, the fibers formed by the processes described
herein can be collected onto a collector substrate to form a
non-woven web. The collector substrate can be a solid or porous
substrate. The collector substrate can be a porous polymer
substrate, such as a micro-porous non-woven web or a polyolefin
porous membrane suitable for lithium ion battery separators.
Additionally, the substrate collector can be an electrode, e.g., a
battery or capacitor electrode. Alternatively, the fibers formed by
the processes as described herein can be further processed to form
the final porous web. Such processes include, but are not limited
to, a drying step, a dispersion step into a solvent, a dry laid
process, a wet laid process, a paper-making process, a dry spraying
method, a wet spraying method, a thermal treatment, a pressure
treatment, or combinations thereof.
Sample Preparation
Shear-Spinning
[0165] In an aspect, shear-spinning method (e.g., as described in
U.S. Pat. Appl. No. 2006/0063882 and U.S. Pat. No. 7,323,540) is a
particularly suitable method to prepare fine or ultra-fine fibers
based on high temperature polymers at high throughputs, which can
be used for e.g., HTMI separators. These porous separators are
particularly useful in electrolytic energy storage devices, such as
lithium-ion, lithium-sulfur and electrolytic double-layer
capacitors.
[0166] Polyphenylene oxide fibers were prepared according to the
following procedure. PPO 6130 (SABIC) was dissolved in chloroform.
The total PPO 6130 concentration was about 8 wt % and the solution
was kept at room temperature. The instrument used to generate the
fibers was a Xanofi Xanoshear.RTM. spinning system. FIG. 4A is a
representation of the morphology of the obtained PPO 6130 fibers
when spun into an anti-solvent made from about 60% Glycerol, about
25% Ethanol and about 15% water by weight. FIG. 4B is a graph of
example fiber count to fiber diameter of the obtained PPO 6130
fibers.
[0167] Distributions of fiber diameters were measured by imaging
the sample using a Phenom Pro Desktop, scanning electron microscope
(SEM). A minimum magnification of 140.times. was used. A minimum of
4 images are retained for fiber diameter analysis. Fiber diameter
analysis software (e.g., Fibermetric software) is used to measure
the sample's images and at least 100 measurements per image, which
are randomly selected by the software, are used in determining the
average fiber diameter and distribution.
[0168] FIG. 5A is a representation of the morphology of the
obtained PPO 6130 fibers when spun into an anti-solvent made from
about 65% Glycerol, about 20% Ethanol and about 15% water. The
instrument used to generate the samples was a Xanofi Xanoshear.RTM.
spinning system. FIG. 5B is a graph of fiber count to fiber
diameter of the obtained PPO 6130 fibers.
[0169] In an aspect, polyetherimide fibers were prepared according
to the following procedure. ULTEM 1010 (SABIC) was dissolved in
chloroform (CHCL3) and the solution was kept at about room
temperature. The instrument used to generate the fibers was a
Xanofi Xanoshear.RTM. spinning system.
[0170] FIG. 6A is a representation of a morphology of ULTEM 1010
fibers made by dissolving ULTEM 1010 in CHCL3 at about 15 wt %,
where the solution was injected into the system at about room
temperature, and the anti-solvent was made from about 60% Glycerol,
about 25% Ethanol and about 15% water. The instrument used to
generate the samples was a Xanofi Xanoshear.RTM. spinning system.
FIG. 6B is a graph of fiber count to fiber diameter of the sample
shown in FIG. 6A.
[0171] FIG. 7A is a representation of a morphology of ULTEM 1010
fibers made by dissolving ULTEM 1010 in CHCL3 at about 25 wt %,
where the solution was injected into the system at room
temperature, and the anti-solvent was made from about 60% Glycerol,
about 25% Ethanol and about 15% water. The instrument used to
generate the samples was a Xanofi Xanoshear.RTM. spinning system.
FIG. 7B is a graph of fiber count to fiber diameter of the sample
shown in FIG. 7A.
[0172] FIGS. 8A, 8B, and 8C are representations of the morphology
of fibers made of a solution comprising ULTEM CRS 5001K in
anti-solvent prepared according to the following procedure. ULTEM
CRS5001K pellets were dissolved in NMP at about 12 wt % and at
about 205.degree. C. The instrument used to generate the samples
was a Xanofi Xanoshear.RTM. spinning system. The solution was
injected into the system at elevated temperature (e.g., prior to
cooling to room temperature), and the anti-solvent was made from
about 30% NMP, 49% Glycerol, about 14% Ethanol and about 7%
Water.
[0173] FIGS. 9A, 9B, and 9C are representations of the morphology
of fibers made of a solution comprising ULTEM CRS 5001K in
anti-solvent prepared according to the following procedure. ULTEM
CRS 5001K pellets were dissolved in NMP at about 12 wt % and at
about 205.degree. C. The instrument used to generate the samples
was a Xanofi Xanoshear.RTM. spinning system. The solution was
injected into the system at elevated temperature, and the
anti-solvent was made from about 50% NMP, 35% Glycerol, about 10%
Ethanol and about 5% Water.
[0174] FIGS. 10A, 10B, and 10C are representations of the
morphology of fibers made of a solution comprising ULTEM CRS 5001K
in anti-solvent prepared according to the following procedure.
ULTEM CRS 5001K pellets were dissolved in NMP at about 12 wt % and
at about 205.degree. C. The instrument used to generate the samples
was a Xanofi Xanoshear.RTM. spinning system. The solution was
injected into the system at elevated temperature, and the
anti-solvent was made from about 70% NMP, 21% Glycerol, about 6%
Ethanol and about 3% Water.
[0175] FIG. 11A is a representation of a morphology of fibers made
of a solution comprising about 12% ULTEM CRS 5001K in anti-solvent
prepared according to the following procedure. ULTEM CRS 5001K
pellets were dissolved in NMP at about 12 wt % and at about
205.degree. C. The instrument used to generate the samples was a
Xanofi Xanoshear.RTM. spinning system. The solution was injected
into the system at elevated temperature, and the anti-solvent was
made from about 70% NMP, 14% Glycerol, about 10% Ethanol and about
6% Water.
[0176] FIGS. 11B and 11C are representations of the morphology of
fibers made of a solution comprising about 12% ULTEM CRS 5001K in
anti-solvent prepared according to the following procedure. ULTEM
CRS 5001K pellets were dissolved in NMP at about 12 wt % and at
about 205.degree. C. The instrument used to generate the samples
was a Xanofi Xanoshear.RTM. spinning system. The solution was
injected into the system at elevated temperature, and the
anti-solvent was made from about 85% NMP, 7% Glycerol, about 5%
Ethanol and about 3% Water.
[0177] FIG. 12A is a representation of a morphology of fibers made
of a solution comprising about 12% ULTEM CRS 5001K in anti-solvent
prepared according to the following procedure. ULTEM CRS 5001K
powder was dissolved in NMP at about 12 wt % and at about
205.degree. C. The instrument used to generate the samples was a
Xanofi Xanoshear.RTM. spinning system. The solution was injected
into the system at elevated temperature, and the anti-solvent was
made from about 80% NMP, 17% Glycerol, about 2% Ethanol and about
1% Water.
[0178] FIG. 12B is a representation of a morphology of fibers made
of a solution comprising about 12% ULTEM CRS 5001K in anti-solvent
prepared according to the following procedure. ULTEM CRS 5001K
powder was dissolved in NMP at about 12 wt % and at about
205.degree. C. The instrument used to generate the samples was a
Xanofi Xanoshear.RTM. spinning system. The solution was injected
into the system at elevated temperature, and the anti-solvent was
made from about 80% NMP, 17% Glycerol, about 1% Ethanol and about
2% Water.
[0179] FIG. 12C is a representation of a morphology of fibers of a
solution comprising about 12% ULTEM CRS 5001K in anti-solvent
prepared according to the following procedure. ULTEM CRS 5001K
powder was dissolved in NMP at about 12 wt % and at about
205.degree. C. The instrument used to generate the samples was a
Xanofi Xanoshear.RTM. spinning system. The solution was injected
into the system at elevated temperature, and the anti-solvent was
made from about 80% NMP, 15% Glycerol, about 3% Ethanol and about
2% Water.
[0180] FIG. 12D is a representation of the morphology of fibers
made of a solution comprising about 12% ULTEM CRS 5001K in
anti-solvent prepared according to the following procedure. ULTEM
CRS 5001K powder was dissolved in NMP at about 12 wt % and at about
205.degree. C. The instrument used to generate the samples was a
Xanofi Xanoshear.RTM. spinning system. The solution was injected
into the system at elevated temperature, and the anti-solvent was
made from about 85% NMP, 7% Glycerol, about 5% Ethanol and about 3%
Water. FIG. 12E is a graph of fiber count to fiber diameter of the
sample shown in FIG. 12D.
Force Spinning
[0181] In an aspect, a force-spinning method (e.g., using the
equipment as described in U.S. Pat. Appl. Nos. 2009/0280207,
2009/0232920, 2009/0269429, and 2009/0280325, i.e., using a
rotating spinneret to spin fine fibers via a centrifugal force) is
a particularly suitable method to prepare fine or ultra-fine fibers
based on high temperature polymers at high throughputs, which can
be used for e.g., HTMI separators. These porous separators are
particularly useful in electrolytical energy storage devices, such
as lithium-ion, lithium-sulfur and electrolytic double-layer
capacitors.
[0182] Table A illustrates exemplary results of fiber spinning a
polymer solution comprising ULTEM 1000 (SABIC) dissolved in NMP.
Table A illustrates spinneret speeds (e.g 12,000 revolutions per
minute (RPM) (12K)) for specific orifice diameters and wt. % of the
polymer (e.g., ULTEM 1000) in the total weight solution. Table A
shows the ranges of spinneret speeds for the different polymer
concentrations and orifice diameters at which fibers were
successfully formed.
TABLE-US-00002 TABLE A ULTEM 1000 (SABIC) dissolved in
N-Methyl-2-pyrrolidone (NMP) Orifice Diameter 25 wt. % 30 wt. % 35
wt. % 14G (1600 .mu.m) 6K-2K 16G (1194 .mu.m) 12K-2K 6K-2K 20G (603
.mu.m) 12K-4K 12K-4K 12K-4K 23G (337 .mu.m) 12K-4K 27G (210 .mu.m)
12K-8K 12K-6K 12K-8K 30G (159 .mu.m) 12K-8K 12K-8K
Example A1
[0183] As an example, a solution comprising of about 35 wt. % ULTEM
1000 dissolved in NMP, with a solution viscosity of about 295,000
centipoise (cP), was spun through an orifice diameter of 1,600
.mu.m (14 G) at a spinneret speed of 2,000 RPM. This example
resulted in fiber diameters between about 1.24 .mu.m and about 35.3
.mu.m, with an average diameter of about 11.4 .mu.m. FIG. 13A
illustrates a representation of the example's fiber morphology.
FIG. 13B illustrates a histogram of the fiber diameter
distribution.
[0184] Solution viscosities were tested using a Brookfield
Engineering viscometer at solution temperatures of about 24.degree.
C.
Example A2
[0185] As a further example, a solution comprising of about 25 wt.
% ULTEM 1000 dissolved in NMP, with a solution viscosity of about
10,000 cP, was spun through an orifice diameter of 159 .mu.m (30 G)
at a spinneret speed of 12,000 RPM. This example resulted in fiber
diameters between about 50.0 nm and about 2.62 .mu.m, with an
average fiber diameter of about 1.02 .mu.m. FIG. 14A illustrates a
representation of the example's fiber morphology. FIG. 14B
illustrates a histogram of the fiber diameter distribution.
[0186] Table B illustrates exemplary results of fiber spinning a
polymer solution comprising ULTEM 1010 (SABIC) dissolved in NMP. In
particular, Table B illustrates spinneret speeds (e.g 12,000
revolutions per minute (RPM) (12K)) for specific orifice diameters
and wt. % of the polymer (e.g., ULTEM 1000) in the total weight
solution. Table B shows the ranges of spinneret speeds for the
different polymer concentrations and orifice diameters at which
fibers were successfully formed.
TABLE-US-00003 TABLE B ULTEM 1010 (SABIC) dissolved in
N-Methyl-2-pyrrolidone (NMP) Orifice Diameter 25 wt. % 30 wt. % 35
wt. % 14G (1600 .mu.m) 4K-2K 16G (1194 .mu.m) 4K-2K 20G (603 .mu.m)
12K-2K 6K-2K 8K-4K 23G (337 .mu.m) 12K-4K 8K-2K 12K-10K 27G (210
.mu.m) 12K-6K 30G (159 .mu.m) 12K-8K 10K-2K
Example B1
[0187] As an example a solution comprised of about 35 wt. % ULTEM
1010 dissolved in NMP, with a solution viscosity of about 190,000
cP, was spun through an orifice diameter of 603 .mu.m (20 G) at a
spinneret speed of 8,000 RPM. This example resulted in fiber
diameters between about 410 nm and about 28.8 .mu.m, with an
average of about 5.35 .mu.m. FIG. 15A illustrates a representation
of the example's fiber morphology. FIG. 15B illustrates a histogram
of the fiber diameter distribution.
Example B2
[0188] As a further example, a solution comprised of about 25 wt. %
ULTEM 1010 dissolved in NMP, with a solution viscosity of about
6,200 cP was spun through an orifice diameter of 159 .mu.m (30 G)
at a spinneret speed of 12,000 RPM. This example resulted in fiber
diameters between about 379 nm and about 4.95 .mu.m, with an
average diameter of about 1.37 .mu.m. FIG. 16A illustrates a
representation of the example's fiber morphology. FIG. 16B
illustrates a histogram of the fiber diameter distribution.
[0189] Table C illustrates exemplary results of fiber spinning a
polymer solution comprising PPO 6130 (Polyphenylene oxide (SABIC))
dissolved in chloroform. In particular, Table C illustrates
spinneret speeds (e.g 4,000 revolutions per minute (RPM) (4K)) for
specific orifice diameters and wt. % of the polymer (e.g., PPO
6130) in the total weight solution. Table C shows the ranges of
spinneret speeds for the different polymer concentrations and
orifice diameters at which fibers were successfully formed.
TABLE-US-00004 TABLE C PPO 6130 (Polyphenylene oxide) dissolved in
chloroform Orifice Diameter 2.5 wt. % 5 wt. % 8 wt. % 10 wt. % 23G
(337 .mu.m) 12K-6K 12K-2K 12K-10K 12K 27G (210 .mu.m) 12K-2K 12K-2K
12K-4K 30G (159 .mu.m) 12K-2K 12K-2K 12K-4K
Example C1
[0190] As an example, a solution comprising about 10 wt. % PPO 6130
dissolved in chloroform, with a solution viscosity of about 2,500
cP was spun through an orifice diameter of 337 .mu.m (23 G) at a
spinneret speed of 12,000 RPM. This example resulted in fiber
diameter between about 267 nm and about 10.3 .mu.m, with an average
diameter of about 2.51 .mu.m. FIG. 17A illustrates a representation
of the example's fiber morphology. FIG. 17B illustrates a histogram
of the fiber diameter distribution.
Example C2
[0191] As a further example, a solution comprising of about 2.5 wt.
% dissolved in chloroform, with a solution viscosity of about 14
cP, was spun through an orifice diameter of 210 .mu.m (27 G) at a
spinneret speed of 12,000 RPM. This example resulted in fiber
diameter between about 63.7 nm and about 2.98 .mu.m, with an
average diameter of about 965 nm. FIG. 18A illustrates a
representation of the example's fiber morphology. FIG. 18B
illustrates a histogram of the fiber diameter distribution.
[0192] Table D illustrates exemplary results of fiber spinning a
polymer solution comprising PPO 6130 (Polyphenylene oxide) was
dissolved in toluene. In particular, Table D illustrates spinneret
speeds (e.g 4,000 revolutions per minute (RPM) (4K)) for specific
orifice diameters and wt. % of the polymer (e.g., PPO 6130) in the
total weight solution.
TABLE-US-00005 TABLE D PPO 6130 (Polyphenylene oxide) dissolved in
toluene Orifice Diameter 5 wt. % 8 wt. % 23G (337 .mu.m) 12K-10K
12K-6K 27G (210 .mu.m) 12K-10K 12K-6K 30G (159 .mu.m) 12K-10K
12K-6K
Example D1
[0193] As an example, a solution comprising about 8 wt. % PPO 6130
dissolved in toluene, with a solution viscosity of about 100 cP was
spun through an orifice diameter of 337 .mu.m (23 G) at spinneret
speed of 6,000 RPM. The example resulted in fiber diameter between
about 50 nm and about 4.62 .mu.m, with an average fiber diameter of
about 871 nm. FIG. 19A illustrates representation of the example's
fiber morphology. FIG. 19B illustrates a histogram of the fiber
diameter distribution.
[0194] Table E illustrates exemplary results of fiber spinning a
polymer solution comprising PPO 6130 (Polyphenylene oxide)
dissolved in solvent system comprising about 50 wt. % toluene and
about 50 wt. % chloroform of the total weight of the solvent
system. In particular, Table E illustrates spinneret speeds (e.g
2,000 revolutions per minute (RPM) (2K)) for specific orifice
diameters and wt. % of the polymer (e.g., PPO 6130) in the total
weight solution. Table E shows the ranges of spinneret speeds for
the different polymer concentrations and orifice diameters at which
fibers were successfully formed.
TABLE-US-00006 TABLE E PPO 6130 (Polyphenylene oxide) dissolved in
50% toluene/50% chloroform solvent system Orifice Diameter 5 wt. %
8 wt. % 10 wt. % 23G (337 .mu.m) 12K-6K 12K-2K 12K-2K 27G (210
.mu.m) 12K-2K 12K-2K 12K-2K 30G (159 .mu.m) 12K-6K 12K-2K
12K-2K
Example E1
[0195] As an example, a solution comprising of about 8 wt % PPO
6130 dissolved in a solvent system comprising of about 50% toluene
and about 50% chloroform of the total weight of the solvent system,
with a solution viscosity of about 380 cP, was spun through an
orifice diameter of 159 .mu.m (30 G) at a spinneret speed of 12,000
RPM. The example resulted in fiber diameter between about 70.6 nm
and about 6.19 .mu.m, with an average fiber diameter of about 1.62
nm. FIG. 20A illustrates representation of the example's fiber
morphology. FIG. 20B illustrates a histogram of the fiber diameter
distribution.
[0196] Table F illustrates exemplary results of fiber spinning a
polymer solution comprising PPO 6130 (Polyphenylene oxide)
dissolved in solvent system comprising about 70 wt % toluene and
about 30 wt % chloroform of the total weight of the solvent system.
In particular, Table F illustrates spinneret speeds (e.g 4,000
revolutions per minute (RPM) (4K)) for specific orifice diameters
and wt. % of the polymer (e.g., PPO 6130) in the total weight
solution. Table F shows the ranges of spinneret speeds for the
different polymer concentrations and orifice diameters at which
fibers were successfully formed.
TABLE-US-00007 TABLE F PPO 6130 (Polyphenylene oxide) dissolved in
70% toluene/30% chloroform solvent system Orifice Diameter 8 wt. %
10 wt. % 12 wt. % 30G (159 .mu.m) 11K-9K 11K-9K 7K
Example F1
[0197] As an example, a solution comprising of about 8 wt. % PPO
6130 dissolved in a solvent system comprising of about 70% toluene
and about 30% chloroform of the total weight of the solvent system,
with a solution viscosity of about 200 cP, was spun through an
orifice diameter of 159 .mu.m (30 G) at a spinneret speed of 11,000
RPM. The example resulted in fiber diameter between about 158 nm
and about 3.51 .mu.m, with an average diameter of about 979 nm.
FIG. 21A illustrates representation of the example's fiber
morphology. FIG. 21B illustrates a histogram of the fiber diameter
distribution.
[0198] Table G illustrates exemplary results of fiber spinning a
polymer solution comprising poly(amic acid) (Sigma-Aldrich)
dissolved in a solvent system comprising about 80 wt % NMP and
about 20 wt % aromatic hydrocarbons of the total weight of the
solvent system. In particular, Table G illustrates spinneret speeds
(e.g., 2,000 revolutions per minute (RPM) (2K)) for specific
orifice diameters and wt. % of the polymer (e.g., poly(amic acid))
in the total weight solution. Table G shows the ranges of spinneret
speeds for the different polymer concentrations and orifice
diameters at which fibers were successfully formed. In an aspect,
poly(amic acid) solutions required elevated temperature inside of
the fiber spinning chamber to produce fibers. Temperatures are
denoted in Table G with spinneret speed. As an example, elevated
temperatures increased solvent evaporation speed.
TABLE-US-00008 TABLE G poly(amic acid) dissolved in solvent system
comprising of about 80 wt. % NMP and about 20 wt. % aromatic
hydrocarbons Orifice Diameter 11 wt. % 15 wt. % 20G (603 .mu.m) 7K
@ 68.degree. C. 23G (337 .mu.m) 27G (210 .mu.m) 12K-6K @ 70.degree.
C. .sup. 30G (159 .mu.m) 12K-6K @ 60-70.degree. C. 2K @ 47.degree.
C.
Example G1
[0199] As an example, a solution comprising about 11 wt. %
poly(amic acid) dissolved in a solvent system comprising about 80
wt. % NMP and about 20 wt. % aromatic hydrocarbons, with a solution
viscosity of about 13,225 cP, was spun through an orifice diameter
of 159 .mu.m (30 G) at spinneret speed of 10,000 RPM. The
environment the spinneret and fiber collection apparatus was
enclosed in during the spinning cycle was heated to an elevated
temperature of 60.degree. C., this elevated temperature aided in
the production of fiber by increasing the rate of solvent
evaporation. The example resulted in fiber diameter between about
89.0 nm and about 4.79 .mu.m, with an average fiber diameter of
about 865 nm. FIG. 22A illustrates representation of the example's
fiber morphology. FIG. 22B illustrates a histogram of the fiber
diameter distribution.
Example G2
[0200] As an example, a solution comprising about 11 wt. %
poly(amic acid) dissolved in a solvent system comprising about 80
wt. % NMP and about 20 wt. % aromatic hydrocarbons, with a solution
viscosity of about 13,225 cP was spun through an orifice diameter
of 159 .mu.m (30 G) at spinneret speed of 6,000 RPM. The
environment the spinneret and fiber collection apparatus was
enclosed in during the spinning cycle was heated to an elevated
temperature of 70.degree. C., this elevated temperature aided in
the production of fiber by increasing the rate of solvent
evaporation. The example resulted in fiber diameter between about
50.7 nm and about 4.34 .mu.m, with an average fiber diameter of
about 1.13 .mu.m. FIG. 23A illustrates representation of the
example's fiber morphology. FIG. 23B illustrates a histogram of the
fiber diameter distribution.
[0201] FIG. 24A is a representation of ULTEM 9011 (SABIC) fibers
generated using a melt process via force spinning in a modified
Fiberio FE type machine. The material was spun at about 450.degree.
C., at a spinneret speed of 3500 rpm through 0.5 mm diameter
orifices. FIG. 24B is a graph of fiber count to fiber diameter of
the sample shown in FIG. 24A.
Electro-Spinning
[0202] This disclosure relates to a method for production of fine
fibers from a solvent-resistant polyetherimide, i.e., a
polyetherimide based on para-phenylene diamine (known as ULTEM CRS
5000 series produced by SABIC), through an electro-spinning process
such as an electro-static, solution-based spinning process.
Electro-spinning (comprising electro-blowing, melt-blowing, flash
spinning or air-electro-spinning) is a technology in which a
polymer solution is extruded through fine holes (e.g., one or more
needles or nozzles) under an electric field to volatilize or
solidify the solvent from the solution, which forms the fibers on
the collector surface located at a predetermined distance. Details
around the electro-spinning method, setup, processing conditions
and applications are widely described in literature, such as for
example "Electrospinning Process and Applications of Electrospun
Fibers" by Doshi and Reneker (J. Electrostatics, 35, 151-160
(1995)), "Electrospinning of Nanofibers in Textiles" by Haghi (CRC
Press, Oct. 31 2011), "Beaded nanofibers formed during
electrospinning" by H. Fong (Polymer, 40, 4585-4592 (1999)) and
U.S. Pat. Nos. 6,616,435, 6,713,011, 7,083,854 and 7,134,857.
Certain embodiments of the disclosure are directed to methods of
making solvent-resistant porous membrane using single solvent or
using two or three solvent combination that can dissolve the
polymer and make it soluble at room temperature. In an aspect,
free-standing, nano-fiber mats of ULTEM series (e.g., ULTEM CRS
5001K) polyetherimides can be produced from such solutions using an
electrostatic spinning process, and certain embodiments of the
disclosure are directed to show that such mats are very suitable to
be applied as separator films in lithium-ion batteries.
Exemplary Testing Procedure
[0203] In an aspect, a polyetherimide (e.g., ULTEM CRS 5001K) was
dissolved in a solvent or a mixture of solvents at a polymer solid
loading ranging from about 5 to about 20 wt %. Solvents used
include 2-chloro-phenol, hexafluorisopropanol (HFIP),
dichloromethane (DCM), trifluoroacetic acid (TFA),
4-chloro-2-methyl-phenol, 1,1,2,2-tetrachloroethane and NMP.
N-cetyltrimethylammonium bromide (CTAB) was used as a salt. All the
obtained solutions are stable at room temperature, with the
exception of solutions based on ULTEM CRS 5000 series in NMP, which
where only stable for a certain amount of time (e.g., several
minutes up to several hours, depending on the polymer/solvent
concentration and preparation method). The solution viscosity
typically varies from 100 to 550 cP depending on the concentration
and solvent type. The solutions were prepared by magnetic-stirring
the ULTEM CRS 5001K resin in the solvent or mixture overnight to
obtain a transparent solution, except for the ULTEM CRS 5001K in
NMP, which was prepared by dissolving the ULTEM CRS 5001K in NMP at
about 205.degree. C., and the solutions were cooled to about
33.degree. C. The solution was loaded into 3-mL syringes (spinneret
ID: 0.45 mm) which were connected to a high voltage system. The
electro-spinning was conducted under high voltages in the range of
10-30 kV. The distance between the spinneret and the collector
ranges from about 10 to about 30 cm. A grounded, conductive
cylinder was used as the collector and the rotation speed varies
from 0-1300 RPM. The experiments were conducted at room temperature
unless specified otherwise and the humidity varies from about 30 to
about 75%. Table H lists the main electro-spinning process
parameters of some of the examples shown below.
[0204] In an aspect, the fiber morphology was characterized by a
FEI Quanta FEG 250 cold field emission scanning electron microscope
(SEM) and Oxford EDS. All images were recorded in the secondary
electron imaging (SEI) mode, at an accelerating voltage of 3-10
kV.
[0205] The fiber diameter was analyzed by Clemex Vision image
analysis software. A thousand fibers were chosen randomly from at
least 5 individual images for statistical analysis of the fiber
diameter and distribution.
Apparent Porosity
[0206] Films were cut to a round slice with 19 mm diameter by a
die; sample thickness is measured by a spiral micrometer (Mitutoyo)
and its weight is measured by an electric balance with .+-.0.05%
variance. The apparent porosity (P) is then calculated by the
following formula:
P ( % ) = ( 1 - M m V m .times. .rho. s ) .times. 100 ,
##EQU00001##
where M.sub.m is the mass of the dry membrane, V.sub.m is the
volume of the dry membrane, and .rho..sub.s is the density of the
solid polymer.
HTMI
[0207] TMA is typically used to characterize the HTMI of separators
according to the NASA/TM--2010-216099 Test Method. Utilizing TMA,
the separator is held under a constant, small load and the degree
of deformation (elongation) is measured as a function of
temperature. At the temperature where the separator loses
mechanical integrity, the elongation increases dramatically.
Typically, the shrinkage onset (temperature at about 2% shrinkage),
the deformation temperature (temperature at about 5% deformation)
and the rupture temperature (the temperature at which the material
breaks) are reported. A TA Instruments Q800 DMA was used with a
film tension setup. Films of about 10 mm long and about 3 mm wide
were tested. The sample is held with a constant 0.02 N load while
the temperature is ramped at about 5.degree. C./min up to failure
of the sample. The experimental parameters are as follows:
a. Test: Temp Ramp/Controlled Force b. Preload Force: 0.02 N c.
Start Temperature: about 30.degree. C. d. Final Temperature: about
300.degree. C. (or rupture of sample) e. Ramp rate: about 5.degree.
C./min
MacMullin Number
[0208] For the separator conductivity test, a 2016 coin cell was
used as the test vehicle. Lithium metal slices (pure lithium metal
(99.9%) from Wisdom Optoelectronic Technology Co., Ltd.) were used
as electrodes. LBC3015B from Shenzhen Capchem Tech was used as the
electrolyte. Electrochemical impedance spectroscopy (EIS, VMP2
MultiPotentiostat from BioLogic Science Instruments) was used to
test the cell resistance. The specific conductivity is calculated
according to Ohmic Law:Separator conductivity=(Film
thickness)/(Separator resistance.times.tested area), wherein film
thickness can be measured by a micrometer; separator resistance can
be read from the EIS Nyquist plot; and a tested area can be
confined by the electrodes (e.g., the diameter is 15.6 mm).
[0209] The MacMullin number, based on the work of MacMullin and
Muccini (R. B. MacMullin and G. A. Muccini, AIChE J., 2, 393,
1956), is defined as NM=C/C0, where C is the conductivity of the
porous media saturated with the electrolyte and C 0 is the bulk
conductivity of the same electrolyte. The obvious advantage of
describing separator conductivities in MacMullin numbers is the
fact that MacMullin numbers are largely independent of the
electrolyte used. The bulk conductivity of the electrolyte (C0) was
8.5.+-.0.5 mS/cm.
Cell Testing
[0210] Battery cycling tests were carried out using 2016 coin cells
on a VMP battery tester at room temperature. Graphite was used as
the anode raw material and was obtained from MTI Co. Lithium Iron
Phosphate (LiFePO.sub.4, purchased from Phostech Lithium Inc.,
Canada) was used as the cathode raw material to test the lifetime
degradation. LBC3015B from Shenzhen Capchem Tech was used as the
electrolyte. Degradation cycles were tested as follows: [0211] a)
Constant current charge at 1.5 mA until the voltage hits 3.8V
[0212] b) Constant voltage charge at 3.8V until the current trip to
0.075 mA [0213] c) Open circuit for 5 minutes [0214] d) Constant
current discharge at -1.5 mA until the voltage hits 2.5V [0215] e)
Open circuit for 5 minutes; repeat the procedure for 100 cycles.
Record the discharged capacity. Its ratio to the discharged
capacity during the formation cycle is recorded as capacity
retention in the unit of percentage.
Electrolyte Wettability
[0216] The electrolyte wettability of the separator samples was
evaluated by contact angle measurements. Contact angle was measured
on Dataphysics OCA according to standard procedure. Each sample was
measured at least five times and images were recorded after
dispensing the droplet onto the surface, where a mathematical
expression was fitted to the shape of the drop and the slope of the
tangent to the drop at the liquid-solid-vapor (LSV) interface line
was calculated. The contact angle was recorded 2-3 seconds after
dispensing the droplet onto the surface, unless stated
otherwise.
Pore Size
[0217] Pore size and pore size distribution were measured by
mercury intrusion porosimetry, using an AutoPore IV 9500
equipment.
Results
TABLE-US-00009 [0218] TABLE H Process parameters for making
electro-spun ULTEM CRS 5001K separators Relative Average fiber
Concentration Feed rate Voltage Temperature Humidity diameter
Example Solvent system (wt %) (uL/min) (kV) (.degree. C.) (%) (nm)
Ex. 1C 2-Cl-phenol/HFIP 8% 2 20 33 41% 343 .+-. 121 25/75 Ex. 2C
2-Cl-phenol/HFIP 10% 2 30 33 40% 661 .+-. 170 25/75 Ex. 3C
2-Cl-phenol/HFIP 10% 2 20 33 56% 416 .+-. 120 25/75 + 1 wt % CTAB
Ex. 4C 2-Cl-phenol/HFIP 10% 2 30 33 50% 1419 .+-. 568 20/80 Ex. 5C
2-Cl-phenol/HFIP 10% 1 30 33 35% 205 .+-. 75 50/50 Ex. 6C
2-Cl-phenol/DCM/HFIP 8% 5 20 33 38% 438 .+-. 106 40/15/45 Ex. 7C
2-Cl-phenol/DCM/HFIP 8% 5 20 23 72% 257 .+-. 52 25/10/65 Ex. 8C
2-Cl-phenol/DCM/HFIP 8% 5 20 23 70% 2042 .+-. 342 25/37.5/37.5 Ex.
9C 2-Cl-phenol/TFA 8% 5 20 23 75% \ 50/50 Ex. 10C Chloroform/HFIP
5% 50 20 23 55% 1176 .+-. 430 90/10 Ex. 11C DCM/HFIP 5% 100 20 23
55% 165 .+-. 94 50/50 Ex. 12C 4-chloro-2-methyl- 10% 1 30 33 35%
197 .+-. 57 phenol/DCM/HFIP 33.3/33.3/33.3 Ex. 13C 1,1,2,2- 7% 2 30
33 40% 107 .+-. 59 tetrachloroethane Ex. 14C NMP 15% 5 30 33 55%
386 .+-. 126 Ex. 15C NMP 10% 2 30 33 55% 186 .+-. 51
Example 1C
[0219] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol) and hexafluoroisopropanol (HFIP) mixture at a solid
loading of about 8 wt %. The ratio of the two solvents was about
25/75 by weight. The electro-spinning conditions: the solution
feeding speed was about 2 uL/min; the distance between the
spinneret and the collector was about 20 cm; the rotation speed of
the collector was about 1300 RPM; the voltage applied was about 20
kV; the experiment was conducted at about 33.degree. C. with a
relative humidity of about 41%.
Example 2C
[0220] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol) and HFIP mixture at a solid loading of about 10 wt %.
The ratio of the two solvents was about 25/75 by weight. The
electro-spinning conditions: the solution feeding speed was about 2
uL/min; the distance between the spinneret and the collector was
about 20 cm; the rotation speed of the collector was about 1300
RPM; the voltage applied was about 30 kV; the experiment was
conducted at about 33.degree. C. with a relative humidity of around
about 40%.
Example 3C
[0221] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol) and HFIP mixture at a solid loading of about 10 wt %.
The ratio of the two solvents was about 25/75 by weight. About 1 wt
% of cetyl trimethylammonium bromide (CTAB) was added to increase
the conductivity of the solution. The electro-spinning conditions:
the solution feeding speed was about 2 uL/min; the distance between
the spinneret and the collector was about 20 cm; the rotation speed
of the collector was about 1300 RPM; the voltage applied was about
20 kV; the experiment was conducted at about 33.degree. C. with a
relative humidity of about 56%.
Example 4C
[0222] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol) and HFIP mixture at a solid loading of about 10 wt %.
The ratio of the two solvents was about 20/80 by weight. The
electro-spinning conditions: the solution feeding speed was 2
uL/min; the distance between the spinneret and the collector was
about 20 cm; the rotation speed of the collector was about 1300
RPM; the voltage applied was about 30 kV; the experiment was
conducted at about 33.degree. C. with a relative humidity of about
50%.
Example 5C
[0223] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol) and HFIP mixture at a solid loading of about 10 wt %.
The ratio of the two solvents was about 50/50 by weight. The
electro-spinning conditions: the solution feeding speed was about 1
uL/min; the distance between the spinneret and the collector was
about 20 cm; the rotation speed of the collector was about 1300
RPM; the voltage applied was about 30 kV; the experiment was
conducted at about 33.degree. C. with a relative humidity of about
35%.
Example 6C
[0224] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol), dichloromethane (DCM) and HFIP mixture at a solid
loading of about 8 wt %. The ratio of the three solvents was about
40/15/45 by weight. The electro-spinning conditions: the solution
feeding speed was about 5 uL/min; the distance between the
spinneret and the collector was about 20 cm; the rotation speed of
the collector was about 1300 RPM; the voltage applied was about 20
kV; the experiment was conducted at about 33.degree. C. with a
relative humidity of about 38%.
Example 7C
[0225] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol), DCM and HFIP mixture at a solid loading of about 8
wt %. The ratio of the three solvents was about 25/10/65 by weight.
The electro-spinning conditions: the solution feeding speed was
about 5 uL/min; the distance between the spinneret and the
collector was about 20 cm; the rotation speed of the collector was
about 1300 RPM; the voltage applied was about 20 kV; the experiment
was conducted at about 23.degree. C. with a relative humidity of
about 72%.
Example 8C
[0226] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol), DCM and HFIP mixture at a solid loading of about 8
wt %. The ratio of the three solvents was about 25/37.5/37.5 by
weight. The electro-spinning conditions: the solution feeding speed
was about 5 uL/min; the distance between the spinneret and the
collector was about 20 cm; the rotation speed of the collector was
about 1300 RPM; the voltage applied was about 20 kV; the experiment
was conducted at about 23.degree. C. with a relative humidity of
about 70%.
Example 9C
[0227] The ULTEM CRS 5001K was dissolved in the 2-chloro-phenol
(2-Cl-phenol) and trifluoroacetic acid (TFA) mixture at a solid
loading of about 8 wt %. The ratio of the two solvents was about
50/50 by weight. The electro-spinning conditions: the solution
feeding speed was about 5 uL/min; the distance between the
spinneret and the collector was about 20 cm; the rotation speed of
the collector was about 1300 RPM; the voltage applied was about 20
kV; the experiment was conducted at about 23.degree. C. with a
relative humidity of about 75%.
Example 10C
[0228] The ULTEM CRS 5001K was dissolved in the chloroform and
hexafluoroisopropanol (HFIP) mixture at a solid loading of about 5
wt %. The ratio of the two solvents was about 90/10 by weight. The
electro-spinning conditions: the solution feeding speed was about
50 uL/min; the distance between the spinneret and the collector was
around about 15 cm; the rotation speed of the collector was about
1300 RPM; the voltage applied was about 20 kV; the experiment was
conducted at about 23.degree. C. with a relative humidity of about
55%.
Example 11C
[0229] The ULTEM CRS 5001K was dissolved in dichloromethane (DCM)
and HFIP mixture at a solid loading of about 5 wt %. The ratio of
the two solvents was about 50/50 by weight. The electro-spinning
conditions: the solution feeding speed was about 100 uL/min; the
distance between the spinneret and the collector was about 15 cm;
the rotation speed of the collector was about 1300 RPM; the voltage
applied was about 20 kV; the experiment was conducted at about
23.degree. C. with a relative humidity of around about 55%.
Example 12C
[0230] The ULTEM CRS 5001K was dissolved in a
4-chloro-2-methyl-phenol, DCM and HFIP mixture at a solid loading
of about 10 wt %. The ratio of the three solvents was about
33/33/33 by weight. The electro-spinning conditions: the solution
feeding speed was about 1 uL/min; the distance between the
spinneret and the collector was about 20 cm; the rotation speed of
the collector was about 1300 RPM; the voltage applied was about 30
kV; the experiment was conducted at about 33.degree. C. with a
relative humidity of about 35%.
Example 13C
[0231] The ULTEM CRS 5001K was dissolved in
1,1,2,2-tetrachloroethane at a solid loading of about 7 wt %. The
electro-spinning conditions: the solution feeding speed was about 2
uL/min; the distance between the spinneret and the collector was
around about 20 cm; the rotation speed of the collector was about
1300 RPM; the voltage applied was about 30 kV; the experiment was
conducted at about 33.degree. C. with a relative humidity of about
40%.
Example 14C
[0232] The ULTEM CRS 5001K was dissolved in boiling NMP
(202.degree. C.) with a solid loading of 15 wt % under nitrogen
atmosphere. The ULTEM CRS 5001K in NMP solution was cooled down to
room temperature and loaded into 3-mL syringes (spinneret ID: 0.45
mm) which was connected to a high voltage system. The
electro-spinning was conducted under high voltage of 30 kV. The
solution feeding speed was 5 uL/min. The distance between the
spinneret and the collector was about 30 cm. A grounded, conductive
cylinder was used as the collector. The experiments were conducted
at about 33.degree. C. at an environmental relative humidity of
about 55%.
Example 15C
[0233] The ULTEM CRS 5001K was dissolved in boiling NMP
(202.degree. C.) with a solid loading of 10 wt % under nitrogen
atmosphere. The ULTEM CRS 5001K in NMP solution was cooled down to
room temperature and loaded into 3-mL syringes (spinneret ID: 0.45
mm) which was connected to a high voltage system. The
electro-spinning was conducted under high voltage of 30 kV. The
solution feeding speed was 2 uL/min. The distance between the
spinneret and the collector was about 20 cm. A grounded, conductive
cylinder was used as the collector. The experiments were conducted
at about 33.degree. C. at an environmental relative humidity of
about 55%.
Morphology
[0234] FIGS. 24-25 illustrate SEM micrographs showing fiber
morphologies of the electro-spun ULTEM CRS 5001K obtained from
different solvent systems and electro-spinning conditions as
presented in Table H (numbers in the figures correlate to the
example numbers in Table H). The magnification is about 10 k and 1
k, respectively.
[0235] The SEM micrographs illustrated in FIGS. 25-26 (with
respectively high (about 10 k) and low (about 1 k) magnifications)
show that the fiber diameter and morphologies heavily depend on the
chosen solvent system and electro-spinning conditions. Although the
ULTEM CRS 5001K can be dissolved in the mixture of 2-Cl-phenol and
HFIP in a wide range of solvent ratio (e.g., about 100/0 to about
10/90 by weight), nano-sized fibers with minimal number of defects
(defined as e.g., beads, droplets and non-uniform fiber
thicknesses) are typically obtained from those solutions with a
2-Cl-phenol content of less than about 40%. At a constant polymer
concentration, the spinability increases with increasing the HFIP
content, i.e., fewer defects are observed. However, a high HFIP
content in the 2-chloro-phenol/HFIP mixture leads to an increase in
the fiber diameter. Compare for example Examples 2C, 4C and 5C,
which show an average fiber diameter of about 205, 661 and 1419 nm
at HFIP contents of about 50, 75 and 80%, respectively. Using the
2-Cl-phenol/HFIP mixture at a 25/75 ratio seems a proper balance,
providing good spinability (i.e., no defects and uniform fibers)
and a small average fiber diameter of 661 nm. Reducing the polymer
concentration to about 8 wt % (Example 1C) also provides good
spinability (i.e., no defects and uniform fibers) and further
reduces the average fiber diameter to 343 nm. Contrary, the webs
spun from a 50/50 2-chloro-phenol/HFIP solution (Example 5C) showed
big liquid-like droplets on the nano-fiber web, although the
average fiber diameter is relatively small (about 205 nm).
[0236] In one aspect, salts soluble in the solution help to improve
the conductivity of the solution and, therefore, help to improve
the spinability (fewer defects) and reduce the average fiber
diameter and its size distribution. Example 3C uses an organic salt
(cetyl trimethylammonium bromide, CTAB) as an example that is
soluble in the HFIP/2-Cl-phenol solvent mixture at room
temperature. Using about 1 wt % of CTAB leads to a significant
reduction in the average fiber diameter from about 661 nm (Example
2C) to about 416 nm (Example 3C).
[0237] Replacing part of the 2-chloro-phenol by DCM (Example 6C)
still provides an ULTEM CRS 5001K solution that is stable at room
temperature. However, the number of defects observed in the
morphologies increases as compared to the 2-chloro-phenol/HFIP
solution (Example 1C). Example 7C shows that increasing the HFIP
content in the 2-chloro-phenol/DCM mixture leads to a reduction in
average fiber diameter, but also to a significant amount of
defects. Further increasing the DCM concentration in the solvent
mixture (Example 8C) leads to much thicker fibers as well as more
defects.
[0238] ULTEM CRS 5001K also forms a room temperature stable
solution in a mixture of 2-chloro-phenol/TFA (Example 9C). Since
TFA is a very polar solvent, it is expected to increase the
conductivity of the solution. Higher conductivity typically helps
the electro-spinability of the solution. However, the SEM results
show that a significant number of defects (beads) are formed. Due
to the high defect rate, no accurate analysis on the average fiber
diameter could be performed.
[0239] ULTEM CRS 5001K can also be dissolved in DCM or Chloroform
mixed with HFIP (Examples 10C and 11C). However, only micro-sized
fibers were obtained from the DCM/HFIP solution, and the
chloroform/HFIP solutions led to significant number of defects
(FIGS. 25-26).
[0240] Example 12C shows that nano-fiber webs can be prepared from
ULTEM CRS 5001K solutions based on 4-chloro-2-methyl-phenol mixed
with DCM and HFIP. The average fiber diameter is only about 197 nm.
A disadvantage of using 4-chloro-2-methyl-phenol is its low
volatility, which leads to defects due to insufficient solvent
evaporation during the electro-spinning process.
[0241] ULTEM CRS 5001K can also be dissolved in
1,1,2,2-tetrachloroethane at about room temperature (Example 13C).
Although nano-fibers with a very small average diameter are
obtained (about 107 nm), they are accompanied by beads.
[0242] The SEM results of Examples 14C and 15C show that
electro-spinning of the ULTEM CRS 5001K in NMP solutions leads to
fibrous webs. This proves that even when the polymer solutions show
only a limited stability at room temperature, these solutions can
still be successfully used to spin ultra-fine fibers are room
temperature. The individual fibers have an average fiber diameter
of 386.+-.126 (Example 14C) and 186.+-.51 (Example 15C), i.e., the
formed fibers are truly nano-fibers. FIG. 27A shows that a real
nano-fibrous web can be formed via the Example 14C. FIG. 27B shows
only a very thin layer of fibers according to Example 15C, i.e., no
real entangled web is formed. However, as is generally known for
the electro-spinning process, the thickness of the nano-fibrous,
porous webs can easily be tuned by the spinning conditions, such as
total spinning time.
[0243] The thicknesses, apparent porosities and MacMullin numbers
of Examples 1C, 2C and 5C are presented in Table I.
TABLE-US-00010 TABLE I Thickness Apparent Example (.mu.m) porosity
(%) MacMullin Example 1C 44 75 3 Example 2C 44 73 4 Example 5C 63
67 6
[0244] The data in Table I shows that the nano-fiber webs of
Examples 1C and 2C have a relatively high apparent porosity (about
75%) and a very low MacMullin number (3 or 4). Example 5C shows a
little lower apparent porosity and higher MacMullin number, which
might be attributed to the presence of defects, leading to a less
open pore structure and, consequently, to a higher MacMullin
number. Note that the nano-fiber, electro-spun ULTEM CRS 5001K
separators have a significant advantage in terms of ionic
conductivity over the commercial polyolefin-based separators, which
typically have a significantly higher MacMullin number, e.g.,
Celgard 2400 and Celgard 2500 have a MacMullin number of 16 and 9,
respectively (K. K. Patel et al., Journal of Power Sources, 122
(2003), 144-152). FIG. 28 shows the pore size distribution of
Example 1C, where the differential cumulative pore volume is
plotted against the pore size diameter. This clearly shows the very
narrow pore size distribution of the electro-spun ULTEM CRS 5001K
separator, with an average pore size of about 4 micron.
Solvent Wettability
[0245] FIG. 29 shows the images of before (a) and after (b) an
electrolyte droplet was placed onto the electro-spun ULTEM CRS
5001K membrane (Example 1C). The electrolyte liquid was absorbed
immediately by the membrane, i.e., within <1 second. The rapid
absorption makes it impossible to perform an actual contact angle
measurement, but it does show that these membranes have an
exceptionally good wettability to the electrolyte. This can
partially be ascribed to the intrinsic compatibility of the ULTEM
CRS 5001K with the electrolyte solution, which shows an electrolyte
contact angle of greater than about 20.degree. after a contact time
of 5 seconds, but the contact angle is further reduced by the very
open porous structure and the small pore size of the e-spun ULTEM
CRS 5001K separator. Note that the nano-fiber, electro-spun ULTEM
CRS 5001K separators have a significant advantage in terms of
electrolyte wettability over the commercial polyolefin-based
separators, which typically have a significantly higher electrolyte
contact angle of greater than about 40.degree..
High Temperature Melt Integrity
[0246] FIG. 30 shows the deformation as a function of temperature
measured by TMA of the electro-spun ULTEM CRS 5001, which was
obtained by electro-spinning ULTEM CRS 5001K form a solvent mixture
consisting of 2-chloro-phenol/HFIP at 25/75 by weight (Example 1C).
The membrane shows about 5% deformation at about 210.degree. C.,
indicating that the membrane has an excellent dimensional stability
at high temperature. Note that the nano-fiber, electro-spun ULTEM
CRS 5001K separators have a significant advantage in terms of high
temperature dimensional stability over the commercial
polyolefin-based separators, which typically have a about 5%
deformation temperature of greater than about 160.degree. C. As
discussed previously, such HTMI performance is key in improving the
safety of lithium ion battery cells.
Battery Cycling Performance
[0247] FIG. 31 shows the cell cycle performance of electro-spun
ULTEM CRS 5001K separator (Example 1C) as compared to a commercial
Celgard 2320 separator (thickness about 20 .mu.m, apparent porosity
about 39%, MacMullin number 11). Example 1C shows a significantly
lower degradation rate (better capacity retention) as compared to
the commercial separator. While the methods and systems have been
described in connection with preferred embodiments and specific
examples, it is not intended that the scope be limited to the
particular embodiments set forth, as the embodiments herein are
intended in all respects to be illustrative rather than
restrictive.
[0248] Unless otherwise expressly stated, it is in no way intended
that any method set forth herein be construed as requiring that its
steps be performed in a specific order. Accordingly, where a method
claim does not actually recite an order to be followed by its steps
or it is not otherwise specifically stated in the claims or
descriptions that the steps are to be limited to a specific order,
it is no way intended that an order be inferred, in any respect.
This holds for any possible non-express basis for interpretation,
including: matters of logic with respect to arrangement of steps or
operational flow; plain meaning derived from grammatical
organization or punctuation; the number or type of embodiments
described in the specification.
[0249] Throughout this application, various publications are
referenced. The disclosures of these publications in their
entireties are hereby incorporated by reference into this
application in order to more fully describe the state of the art to
which the methods and systems pertain.
[0250] It will be apparent to those skilled in the art that various
modifications and variations can be made without departing from the
scope or spirit. Other embodiments will be apparent to those
skilled in the art from consideration of the specification and
practice disclosed herein. It is intended that the specification
and examples be considered as exemplary only, with a true scope and
spirit being indicated by the following claims.
* * * * *
References