U.S. patent application number 10/509723 was filed with the patent office on 2005-05-19 for battery separator with improved oxidation stability.
Invention is credited to Deiters, Jorg, Ihmels, Klaus Heinrich.
Application Number | 20050106468 10/509723 |
Document ID | / |
Family ID | 28685025 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050106468 |
Kind Code |
A1 |
Deiters, Jorg ; et
al. |
May 19, 2005 |
Battery separator with improved oxidation stability
Abstract
The invention relates to a thermoplastic polymer-based battery
separator, which contains a compound of formula R(OR.sup.1).sub.n
(COOM.sup.x+.sub.1/x).sub.m. In said formula, R represents a
non-aromatic hydrocarbon group comprising between 10 and 4,200
carbon atoms, which can be interrupted by oxygen atoms, R.sup.1
represents H, --(CH.sub.2).sub.kCOOM.sup.x+.sub.1/x or
--(CH.sub.2).sub.k--SO.sub.3M.su- p.x+.sub.1/x, whereby k stands
for 1 or 2, M represents an alkali or earth alkaline metal ion,
H.sup.+ or NH.sub.4.sup.+, whereby not all variables of M are
defined simultaneously as H.sup.+, n stands for 0 or 1, m stands
for 0 or a whole number from 10 to 1,400 and x stands for 1 or 2.
The ratio of oxygen atoms to carbon atoms in the compound according
to the aforementioned formula ranges between 1:1.5 and 1:30 and n
and m cannot simultaneously represent zero.
Inventors: |
Deiters, Jorg; (Norderstedt,
DE) ; Ihmels, Klaus Heinrich; (Hamburg, DE) |
Correspondence
Address: |
NIELDS & LEMACK
176 EAST MAIN STREET, SUITE 7
WESTBORO
MA
01581
US
|
Family ID: |
28685025 |
Appl. No.: |
10/509723 |
Filed: |
December 30, 2004 |
PCT Filed: |
April 8, 2003 |
PCT NO: |
PCT/EP03/03639 |
Current U.S.
Class: |
429/254 ;
429/247; 429/249 |
Current CPC
Class: |
Y02E 60/10 20130101;
H01M 50/417 20210101; H01M 50/446 20210101; H01M 10/06 20130101;
H01M 50/411 20210101 |
Class at
Publication: |
429/254 ;
429/247; 429/249 |
International
Class: |
H01M 002/16; H01M
002/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2002 |
DE |
102 16 418.5 |
Claims
1. Battery separator based on thermoplastic, ultra-high
molecular-weight polyolefin with an average molecular weight by
weight of at least 300,000, comprising, relative to the sum of the
weights of filler and polyolefin, 10 to 100 wt.-% polyolefin and 0
to 90 wt.-% filler, and, relative to the weight of the separator, 5
to 35 wt.-% oil and 0.5 to 5.0 wt.-% of a compound according to the
Formula (I)R(OR.sup.1).sub.n(COOM.su- p.X+.sub.1/x).sub.m (I)in
which R is a non-aromatic hydrocarbon radical with 10 to 4200
hydrocarbon atoms, which can be interrupted by oxygen atoms,
R.sup.1 is H, --(CH.sub.2).sub.kCOOM.sup.X+.sub.1/x or
--(CH.sub.2).sub.k--SO.sub.3M.sup.X+.sub.1/x, where k is 1 or 2, M
is an alkali metal or alkaline-earth metal ion, H.sup.+ or
NH.sub.4.sup.+, where not all the M variables simultaneously have
the meaning H.sup.+, n is 0 or 1, m is 0 or an integer from 10 to
1400 and x is 1 or 2, the ratio of oxygen atoms to carbon atoms in
the compound according to Formula (I) lying in the range between
1:1.5 to 1:30 and m and n not being able to simultaneously be
0.
2. Battery separator according to claim 1, wherein R is a
hydrocarbon radical with 10 to 180 carbon atoms, which can be
interrupted by 1 to 60 oxygen atoms, n is 1, m is 0 and x is 1 or
2.
3. Battery separator according to claim 2, wherein R is a
hydrocarbon radical of the formula
R.sup.2--[(OC.sub.2H.sub.4).sub.p (OC.sub.3H.sub.6).sub.q]--, in
which R.sup.2 is an alkyl radical with 10 to 30 carbon atoms, p is
an integer from 0 to 30 and/or q is an integer from 0 to 30.
4. Battery separator according to claim 3, wherein p is an integer
from 0 to 10 and q is an integer from 0 to 10.
5. Battery separator according to claim 3, wherein the sum of p and
q is smaller than or equal to 10.
6. Battery separator according to claim 2, wherein R.sup.1 is
H.
7. Battery separator according to claim 1, wherein R is an alkane
radical with 20 to 4200 carbon atoms, M is an alkali metal or
alkaline-earth metal ion, H.sup.+ or NH.sub.4.sup.+, where not all
the variables M simultaneously have the meaning H.sup.+, n is 0, m
is an integer from 10 to 1400 and x is 1 or 2.
8. Battery separator according to claim 7, wherein R is an alkane
radical with 50 to 750 carbon atoms.
9. Battery separator according to claim 7, wherein the compound
according to Formula (I) is a poly(meth)acrylic acid, whose acid
groups are at least partly neutralized.
10. Battery separator according to claim 9, wherein at least 40% of
the acid groups of the poly(meth)acrylic acid are neutralized.
11. Battery separator according to claim 7, wherein M is Li.sup.+,
Na.sup.+ or K.sup.+.
12. Battery separator according to claim 7, wherein the
poly(meth)acrylic acid has an average molar mass M.sub.w of 1,000
to 100,000 g/mol.
13. Battery separator based on thermoplastic, ultra-high
molecular-weight polyolefin with an average molecular weight by
weight of at least 300,000, comprising a component which, when the
separator is used for the intended purpose, can form a compound of
the Formula (I):R(OR.sup.1).sub.n(COOM.sup.X+.sub.1/x).sub.m (I)in
which R is a non-aromatic hydrocarbon radical with 10 to 4200
hydrocarbon atoms, which can be interrupted by oxygen atoms,
R.sup.1 is H, --(CH.sub.2).sub.kCOOM.- sup.X+.sub.1/x or
--(CH.sub.2).sub.k--SO.sub.3M.sup.X+.sub.1/x, k being 1 or 2, M is
an alkali metal or alkaline-earth metal ion, H.sup.+ or
NH.sub.4.sup.+, where not all the M variables simultaneously have
the meaning H.sup.+, n is 0 or 1, m is 0 or an integer from 10 to
1400 and x is 1 or 2, the ratio of oxygen atoms to carbon atoms in
the compound according to Formula (I) lying in the range between
1:1.5 to 1:30 and m and n not being able to simultaneously be
0.
14. Lead-sulphuric acid accumulator with at least two
oppositely-charged electrode plates, comprising at least one
battery separator according to claim 1.
15. Process for the preparation of a battery separator according to
claim 1, wherein a compound with the Formula (I) or a solution of a
compound with the Formula (I) is applied to a battery separator and
the separator is then optionally dried.
16. Process for the preparation of a battery separator according to
claim 1, wherein a homogenous mixture of ultra-high
molecular-weight thermoplastic polyolefin, at least one compound
with the Formula (I) and optionally filler and further additives
are prepared, formed into a web-shaped material and then one or
more of the further additives are optionally removed.
17. Method for the preparation of battery separators comprising the
addition of a compound with the Formula (I) to a separator.
18. Method for the improvement of the oxidation resistance of
battery separators comprising the addition of a compound with the
Formula (I) to a separator.
19. Battery separator according to claim 4, wherein the sum of p
and q is smaller than or equal to 10.
20. Battery separator according to claim 8, wherein the compound
according to Formula (I) is a poly(meth)acrylic acid, whose acid
groups are at least partly neutralized.
21. Battery separator according to claim 20, wherein at least 40%
of the acid groups of the poly(meth)acrylic acid are neutralized.
Description
[0001] The invention relates to separators for lead/sulphuric acid
accumulators, hereafter called lead accumulator for short, which
have an improved oxidation resistance.
[0002] The separators used today in lead accumulators are mostly
filled, microporous polyolefin separators. These are intended on
the one hand to prevent a direct contact and thus short circuits
between the electrode plates, and on the other hand to make
possible an ionic current flow and offer this the smallest possible
resistance. The composition and production of such separators are
known per se (cf. e.g. DE-PS 1 267 423, DE-PS 1 298 712, DE-AS 1
496 123, DE-OS 35 45 615, DE-PS 35 40 718 and DE-PS 36 17 318).
[0003] According to U.S. Pat. No. 3,351,495, to this end a
homogeneous mixture of polyolefin, filler, plasticizer and
additives is formed and this is formed into a web-shaped layer.
Then the plasticizer and fillers are at least partly removed by
extraction. Polyethylene glycol, glycerin and in particular mineral
oil are used as plasticizer. To prevent an oxidative degradation of
the polyolefin during extrusion the separators can also contain
antioxidants such as 4,4-thio-bis-(6-tert-butyl-m-cresol- ) and
2,6-di-tert-butyl-4-methylphenol.
[0004] When in use the separators must not only resist the
aggressive battery acid but are also exposed, particularly in the
area of the positive plate, to oxidative attacks, for example by
oxidative lead dioxide and the formation of extremely reactive
nascent oxygen and peroxides. In addition to this, lead
accumulators are exposed to ever higher ambient temperatures and
cycle loads, which further intensifies the oxidative attack.
[0005] Although the polyethylene frequently used for the production
of the separators does give the separators, in combination with
small quantities of antioxidant and a larger quantity of oil, a
certain oxidation stability vis--vis the aggressive medium of the
battery, the separator material can still undergo slow oxidative
attack under more difficult conditions of use and finally be
destroyed, which results in a deterioration of the mechanical
stability of the separator and the formation of cracks and holes
and which in the most unfavourable case shortens the battery life
through short circuits.
[0006] Many measures for improving the oxidation stability of
battery separators are known. For example, the oxidative
degradation of the separator can be delayed by increasing the
separator thickness, the molecular weight of the polymer used to
produce the separator or through a significant increase in the
polymer content of the separator.
[0007] However, an increase in the separator thickness leads to
appreciably higher production costs and higher electrical
resistances. The ultra-high molecular-weight polyethylene (UHMWPE)
customarily used to produce separators also generally already has a
molecular weight of 5-7.times.10.sup.6 g/mol and a further increase
in the molecular weight would lead to considerable process
problems. Moreover, although UHMWPE types with a molecular weight
of up to approximately 10.times.10.sup.6 g/mol are commercially
available, the polymer chains of these UHMWPE types are markedly
degraded during extrusion by shearing in the extruder, which again
substantially reduces the molecular weight. An increase in the
polymer content causes the wettability and porosity and thus the
electrical resistance of the separator to deteriorate
significantly.
[0008] It is also known from the state of the art that the process
oils used to produce the battery separators can improve the
oxidation resistance of the separators The maximum oil content of
the separators is restricted however, because the oil also causes
the wettability and porosity of the separator to deteriorate.
[0009] DE 30 04 659 C2 discloses separators which contain oils with
an aromatics content of at least 40%. Because of their composition,
these oils bring about an improvement in the oxidation resistance
of the separators. However, process oils with a high aromatics
content can encourage the formation of dark, often sticky deposits
in the lead accumulator which contaminate the inside and outside of
the accumulator case and can block the valve systems.
[0010] The prevention of such deposits is the subject-matter of DE
39 22 160 A1, which to this end discloses the use of surfactants,
preferably of the amide or amine type.
[0011] JP 02155161 A discloses the use of a combination of paraffin
oil, antioxidant and a peroxide decomposer based on phosphoric acid
to improve the oxidation stability of battery separators at high
temperatures. However this does not provide protection against the
oxidative effect of nascent oxygen or of the lead dioxide of the
positive electrode plate.
[0012] JP 07130348 A discloses separators which contain mineral oil
in combination with a phenolic resin.
[0013] To improve the oxidation stability of pocket separators an
increase in the oil content in the fold edge and along the weld
edge is proposed in U.S. Pat. No. 5,384,211 and JP 10031992 A.
[0014] JP 08203493 A discloses the coating of the edges of
separators with an insulating resin in order to suppress the
oxidative attack.
[0015] JP 2000133239 A describes the coating of the upper part of
the separator, which is in contact with the frame and the electrode
lug of the positive plate, with a hot-melt adhesive.
[0016] The above separators cannot be produced continuously with
today's techniques, and the process is thus time-consuming and
expensive. Moreover only a partial improvement in oxidation
stability is achieved.
[0017] It is customary to provide separators with longitudinal ribs
on at least one side in order to prevent direct contact of the
separator sheet with the positive electrode plate and thus a
premature oxidative destruction.
[0018] JP 04167356 A and JP 2000182593 A disclose separators which
have additional ribs in the area of the weld edges of the
separators in order to prevent in a targeted way the formation of
cracks through oxidation in this area.
[0019] JP 09097601 A discloses separators profiled, in a particular
way which allow the gas which forms on the positive plate to escape
more quickly and are thus, intended to reduce its oxidative effect
on the separator.
[0020] JP 04190554 A describes the addition of glass fibres to the
separator material in order to delay a deterioration of the
mechanical properties of the separator through oxidation. The
introduction of glass fibres into the separator by extrusion is
difficult however, because glass fibres on the one hand are
dispersible only with difficulty in the separator material and on
the other hand break easily during extrusion and block the extruder
screens. Also, separators containing glass fibres are not very
flexible and tend to break when subjected to a mechanical
stress.
[0021] Despite considerable efforts, none of the present methods
for improving the oxidation resistance of battery separators is
completely satisfactory.
[0022] Battery separators are known from U.S. Pat. No. 4,024,323 in
which at least 40% of the ultra-high molecular-weight polyethylene
used for the production of separators are replaced by a copolymer
of an olefin and (meth)acrylic acid or a mixture of a polyolefin of
low molecular weight and a polymer of (meth)acrylic acid. This is
intended to increase the extrusion speed and improve the
incorporation of the filler into the polymer. The replacement of at
least 40% of the ultra-high molecular-weight polyethylene by
low-molecular-weight polymers is disadvantageous, however, because
it leads to a deterioration of the mechanical properties of the
separator.
[0023] The object of the invention is to provide battery separators
with high oxidation stability which are easy and inexpensive to
produce and which are protected over their whole surface against
oxidation.
[0024] According to the invention this object is achieved by
battery separators which contain a compound with the Formula
(I)
R(OR.sup.1).sub.n(COOM.sup.x+.sub.1/x).sub.m (I)
[0025] in which
[0026] R is a non-aromatic hydrocarbon radical with 10 to 4200
carbon atoms, preferably 13 to 4200, which can be interrupted by
oxygen atoms,
[0027] R.sup.1 is H, --(CH.sub.2).sub.kCOOM.sup.x+.sub.1/x or
--(CH.sub.2).sub.k--SO.sub.3M.sup.X+.sub.1/X, preferably H, where k
is 1 or 2,
[0028] M is an alkali metal or alkaline-earth metal ion, H.sup.+ or
NH.sub.4.sup.+, where not all the variables M simultaneously have
the meaning H.sup.+,
[0029] n is 0 or 1,
[0030] m is 0 or an integer from 10 to 1400 and
[0031] x is 1 or 2,
[0032] the ratio of oxygen atoms to carbon atoms in the compound
according to Formula (I) being in the range from 1:1.5 to 1:30 and
m and n not being able to simultaneously be 0. However, preferably
only one of the variables n and m is different from 0.
[0033] By non-aromatic hydrocarbon radicals is meant radicals which
contain no aromatic groups or which themselves represent one. The
hydrocarbon radicals can be interrupted by oxygen atoms, i.e.
contain one or more ether groups.
[0034] R is preferably a straight-chain or branched aliphatic
hydrocarbon radical which can be interrupted by oxygen atoms.
Saturated, uncross-linked hydrocarbon radicals are quite
particularly preferred.
[0035] Surprisingly it was found that through the use of the
compounds of Formula (I) for the production of battery separators,
they can be effectively protected against oxidative
destruction.
[0036] Battery separators are preferred which contain a compound
according to Formula (I) in which
[0037] R is a hydrocarbon radical with 10 to 180, preferably 12 to
75 and quite particularly preferably 14 to 40 carbon atoms, which
can be interrupted by 1 to 60, preferably 1 to 20 and quite
particularly preferably 1 to 8 oxygen atoms, particularly
preferably a hydrocarbon radical of formula
R.sup.2--[(OC.sub.2H.sub.4).sub.p(OC.sub.3H.sub.6).sub- .q]--, in
which
[0038] R.sup.2 is an alkyl radical with 10 to 30 carbon atoms,
preferably 12 to 25, particularly preferably 14 to 20 carbon
atoms,
[0039] p is an integer from 0 to 30, preferably 0 to 10,
particularly preferably 0 to 4 and
[0040] q is an integer from 0 to 30, preferably 0 to 10,
particularly preferably 0 to 4,
[0041] compounds being particularly preferred in which the sum of p
and q is 0 to 10, in particular 0 to 4,
[0042] n is 1 and
[0043] m is 0.
[0044] Formula
R.sup.2--[(OC.sub.2H.sub.4).sub.p(OC.sub.3H.sub.6).sub.q]-- is to
be understood as also including those compounds in which the
sequence of the groups in square brackets differs from that shown.
For example according to the invention compounds are suitable in
which the radical in brackets is formed by alternating
(OC.sub.2H.sub.4) and (OC.sub.3H.sub.6) groups.
[0045] Additives in which R.sup.2 is a straight-chain or branched
alkyl radical with 10 to 20, preferably 14 to 18 carbon atoms have
proved to be particularly advantageous. OC.sub.2H.sub.4 preferably
stands for OCH.sub.2CH.sub.2, OC.sub.3H.sub.6 for
OCH(CH.sub.3)CH.sub.2 and/or OCH.sub.2CH(CH.sub.3)
[0046] As preferred additives there may be mentioned in particular
alcohols (p=q=0; m=0) primary alcohols being particularly
preferred, fatty alcohol ethoxylates (p=1 to 4, q=0), fatty alcohol
propoxylates (p=0; q=1 to 4) and fatty alcohol alkoxylates (p=1 to
2; q=1 to 4) ethoxylates of primary alcohols being preferred. The
fatty alcohol alkoxylates are for example accessible through
reaction of the corresponding alcohols with ethylene oxide or
propylene oxide.
[0047] Additives of the type m=0 which are not, or only
difficultly, soluble in water and sulphuric acid have proved to be
particularly advantageous.
[0048] Also preferred are battery separators which contain a
compound according to Formula (I), in which
[0049] R is an alkane radical with 20 to 4200, preferably 50 to 750
and quite particularly preferably 80 to 225 carbon atoms,
[0050] M is an alkali metal or alkaline-earth metal ion, H.sup.+ or
NH.sub.4.sup.+, in particular an alkali metal ion such as Li.sup.+,
Na.sup.+ and K.sup.+ or H.sup.+, where not all the variables M
simultaneously have the meaning H.sup.+,
[0051] n is 0,
[0052] m is an integer from 10 to 1400 and
[0053] x is 1 or 2.
[0054] As suitable additives there may be mentioned here in
particular polyacrylic acids, polymethacrylic acids and acrylic
acid-methacrylic acid copolymers, whose acid groups are at least
partly, i.e. preferably 40%, particularly preferably 80 %,
neutralized. The percentage refers to the number of acid groups.
Quite particularly preferred are poly(meth)acrylic acids which are
present entirely in the salt form. By poly(meth)acrylic acids are
meant polyacrylic acids, polymethacrylic acids and acrylic
acid-methacrylic acid copolymers. Poly(meth)acrylic acids are
preferred and in particular polyacrylic acids with an average molar
mass M.sub.w of 1,000 to 100,000 g/mol, particularly preferably
1,000 to 15,000 g/mol and quite particularly preferably 1,000 to
4,000 g/mol. The molecular weight of the poly(meth)acrylic acid
polymers and copolymers is ascertained by measuring the viscosity
of a 1% aqueous solution, neutralized with sodium hydroxide
solution, of the polymer (Fikentscher's constant).
[0055] Also suitable are copolymers of (meth)acrylic acid, in
particular copolymers which, besides (meth)acrylic acid contain
ethylene, maleic acid, methyl acrylate, ethyl acrylate, butyl
acrylate and/or ethylhexyl acrylate as comonomer. Copolymers are
preferred which contain at least 40 wt.-%, preferably at least 80
wt.-% (meth)acrylic acid monomer, the percentages being based on
the acid form of the monomers or polymers.
[0056] To neutralize the polyacrylic acid polymers and copolymers,
alkali metal and alkaline-earth metal hydroxides such as potassium
hydroxide and in particular sodium hydroxide are particularly
suitable.
[0057] Suitable additives according to the invention are known and
are commercially available.
[0058] As well as the named additives the separators can
alternatively or additionally contain compounds which can form the
additives according to the invention. Preferred are compounds
which, when the separators are used for the intended purpose
release suitable additives, for example by hydrolysis with the
battery acid. Particularly suitable substances of this type are
esters which form, OH-group-containing compounds of Formula (I).
These include for example phthalic acid esters of the above-named
alcohols.
[0059] The battery separators can be provided in various ways with
the additive or additives. The additives can for example be applied
to the separator when it is finished (i.e. after the extraction) or
added to the mixture, used to produce the separator. According to a
preferred embodiment the additive or a solution of the additive is
applied to the surface of the separator. This variant is suitable
in particular for the application of non-thermostable additives and
additives which are soluble in the solvent used for the subsequent
extractions. Particularly suitable as solvents for the additives
according to the invention are low-molecular-weight alcohols, such
as methanol and ethanol, as well as mixtures of these alcohols with
water. The application can take place on the side facing the
negative electrode, the side facing the positive electrode or on
both sides of the separator. In the case of an application on one
side, an application to the side of the separator facing the
positive electrode plate is preferred.
[0060] The application may also take place by dipping the battery
separator in the additive or a solution of the additive and
subsequently optionally removing the solvent, e.g. by drying. In
this way the application of the additive can be combined for
example, with the extraction often applied during separator
production.
[0061] Another preferred option is to mix the additive or additives
into the mixture of thermoplastic polymer and optionally fillers
and other additives which is used to produce the battery
separators. The additive-containing homogeneous mixture is then
formed into a web-shaped material. Because this usually occurs by
extrusion at high temperature, difficultly volatile and
thermostable additives which are difficultly soluble in the solvent
used for extraction, such as polyacrylic acid polymers and
copolymers or their salts, are particularly suitable for this.
[0062] The additives can be used alone or as a mixture of two or,
more additives. Mixtures of one or more of the additives according
to the invention with surfactants, defoamers and other additives
can also be used.
[0063] The additives used according to the invention are preferably
used in a quantity of 0.5 to 50 wt.-% particularly preferably 1.0
to 5.0 wt.-%, quite particularly preferably 1.5 to 4.0 wt.-% and in
particular 2.0 to 3.5 wt.-% relative to the mass of the separator
after the extraction.
[0064] The additives used to produce the separators preferably have
a high boiling point. Additives with a boiling point of 250.degree.
C. or more have proved to be particularly suitable.
[0065] The additives used according to the invention are suitable
for combining with all separators which are liable to oxidative
attacks, in particular for combining with separators based on
thermoplastics. Separators which, as well as a thermoplastic, also
contain a filler and oil are quite particularly preferred.
[0066] Preferably the additives are combined with separators based
on polyolefins, particularly preferably filler-containing
polyolefins which can be produced by hot-forming such as extrusion
or pressing, and subsequent extraction. The additives are however
also suitable for the protection of separators which contain
polyolefin threads or fibres, e.g. separators in the form of
fleeces.
[0067] Preferred polyolefins are polyethylenes, ultra-high
molecular-weight polyethylene being particularly preferred
according to the invention. Ultra-high molecular-weight polyolefin
with an average molecular weight by weight of at least 300,000,
preferably at least 1.0.times.10.sup.6 and particularly preferably
at least 5.0.times.10.sup.6 g/mol is quite particularly
preferred.
[0068] The molecular weight of the polyethylene is measured by the
Margolies equation: M=5.37.times.10.sup.4[.eta.].sup.1.49; with
.eta.=reduced specific viscosity in dl/g (Josef Berzen, CZ
Chemie-Technik, 3.sup.rd Volume (1974) No. 4, p. 129).
[0069] However polypropylene, polybutene, polystyrene,
ethylene-propylene copolymers, ethylene-hexylene copolymers,
ethylene-butene copolymers, propylene-butene copolymers and
ethylene-propylene-butene copolymers are also suitable.
[0070] The separators according to the invention preferably contain
10 to 100 wt.-%, particularly preferably 15 to 50 wt.-% and quite
particularly preferably 20 to 40 wt.-% polymer, in particular
ultra-high molecular-weight polyethylene, relative to the sum of
the weights of filler and polymer.
[0071] A filler preferred according to the invention is SiO.sub.2,
quite particularly preferred fillers are amorphous precipitation
silicas. Oxides and hydroxides of silicon, aluminium and titanium
as well as mica, talc, silicates and glass beads are also suitable
as fillers. Fillers of this type are disclosed for example in U.S.
Pat. No. 3,351,495 and DE 14 96 123 A.
[0072] The separators according to the invention preferably contain
0 to 90 wt.-%, particularly preferably 50 to 85 wt.-% and quite
particularly preferably 60 to 80 wt.-% filler, relative to the sum
of the weights of filler and polymer, silicas preferably being
exclusively used as filler.
[0073] The weight ratio of filler to polymer is preferably 0 to
9.0, particularly preferably 1.0 to 5.7 and quite particularly
preferably 1.5 to 4.0.
[0074] Extractable oils which tact on the one hand as plasticizers
and on the other hand as pore-formers are in particular used as
further additives. The liquids disclosed in DE 12 67 423 A, such as
for example process oils, are particularly suited. By oils or
process oils are preferably meant mineral oils. The oil content in
the separator is preferably 5 to 35 wt.-%, particularly preferably
8 to 30 wt.-%, and quite particularly preferably 10 to 25 wt.-%
relative to the total mass of the separator after the
extraction.
[0075] Apart from the main constituents named above, the separators
can contain other customary constituents such as carbon black,
antioxidants such as for example alkylidene-bisphenols, lubricants,
other fillers such as for example talc etc., and optionally also
other polymers in more or less secondary quantities. Carbon black
is preferably used in a quantity of at most 5 wt.-%, the other
additives preferably in a quantity of at most 2 wt.-%, relative in
each case to the total mass of the finished separator.
[0076] To produce the separators the named materials are carefully
mixed in the usual way and then formed into a web-shaped material
accompanied by heating. The oil is then extracted from this for
example with an organic solvent such as hexane so that the desired
porosity is obtained. Finally the separator material is cut to size
according to the desired usage form, i.e. preferably cut to the
final width, wound up into rolls approximately 1,000 metres in
length and packed. The surfaces of the separator can be smooth,
ribbed or shaped in any other way. The composition and production
of battery separators is sufficiently known from the
above-mentioned state of the art. In so far as the additives used
according to the invention are soluble in the extraction agent or
are able to be extracted with it, they are applied to the separator
preferably after the extraction step. The additives can however
also be added to the extracting agent and thus be applied to the
separator during the extraction.
[0077] The separators are mostly used in the form of pockets into
which the positive or negative electrode plates are inserted. The
pocketed electrode plates are then joined, to oppositely-charged
non-pocketed electrode plates to form blocks of plates and inserted
into a battery container. After filling with sulphuric acid and
sealing with a battery block cover the lead accumulator is
complete.
[0078] The subject-matter of the invention are also lead-sulphuric
acid accumulators with at least two oppositely-charged electrode
plates which contain at least one, battery separator with one of
the additives according to the invention.
[0079] Apart from the additives used according to the invention the
accumulators are customary lead/sulphuric acid accumulators with
conventional electrodes and sulphuric acid as electrolyte.
Preferably they are starter batteries for motor vehicles. The case
can be made of all the customary materials, e.g. polypropylene,
hard rubber, acrylic glass, polystyrene, glass etc.
[0080] The invention is explained in more detail in the following
with reference to embodiments.
EXAMPLES
Examples 1-7
[0081] Use of 1-Dodecanol as Additive to Prevent Premature
Oxidation of Battery Separators
[0082] Unless stated otherwise battery separators based on
polyethylene (UHMWPE) and precipitation silicic acid, are used in
the examples. The separators are produced on an extruder according
to U.S. Pat. No. 3,351,495 and after extrusion are extracted with
hexane to an oil content in the base sheet of approximately 12
wt.-% The weight ratio of filler to polymer that is used is given
in the respective examples.
[0083] In order to assess the effectiveness of the additives a
standardized oxidation test was used (PEROX 80 Test) which largely
corresponds to the method recommended by the BCI (Battery Council
International) for determining the oxidation stability of battery
separators(TM-3.229: Standard test method to determine resistance
of battery separator to oxidative degradation using hydrogen
peroxide in sulphuric acid as oxidizing medium).
[0084] To this end, testpieces from the separator material were
treated with a mixture of sulphuric acid and hydrogen peroxide at
80.degree. C. for various time periods and the extension of the
material before and after the test was compared. The reduction in
extendability is a measure of the degradation and the
cross-linking, i.e. the oxidative destruction of the polymer.
Separators without additives according to the invention which were
tested under identical conditions served as comparison.
[0085] The testpieces were bone-shaped in accordance with DIN
53455. The oxidation solution was always freshly prepared, and
consisted of 360 ml sulphuric acid of density 1.28 g/cm.sup.3, 35
ml sulphuric acid of density 1.84 g/cm.sup.3 and 105 ml 35%
hydrogen peroxide solution. The components were slowly mixed with
each other accompanied by stirring in the given order and then
heated to 80.degree. C. in a closed glass vessel in a water bath.
Two sample holders each with five testpieces were placed in
solution and left in the solution for the desired test period.
Then, the samples were washed acid free with lukewarm water and the
extension was measured. To this end the testpieces were stretched
to breaking at a test speed of 300 mm/min. The extension in cross
machine direction (CMD) (CMD-expansion) was measured. In each of
the following tables the average of ten measured values is given.
Because the initial extension of the separators can vary for
process reasons, the absolute expansions were normalized to the
initial expansion:
absolute stretching after x h Perox Test in %/absolute stretching
after 0 h Perox Test in %.times.100=relative expansion after x h
Perox Test
[0086] In examples 2 to 7 separator sheets 160.times.300 mm in size
were coated on one side with an ethanol solution of 1-dodecanol so
that after drying there was 0.7 to 7.1 wt.-% 1-dodecanol on the
blade. In the examples, unless stated otherwise, all weight
percentages refer to the weight of the separator after extraction.
An untreated separator served as comparison (Example 1). In
examples 1 to 7 the weight ratio of filler to polymer was 2.6 in
each case.
[0087] The separators coated with the additive were subjected to
the oxidation test described above. After the test had ended the
separators coated with 1-dodecanol showed a considerably higher
residual expansion than the untreated separator (see Table 1). The
results compiled in Table 1 prove that 1-dodecanol, even in extreme
test conditions (80.degree. C., H.sub.2O.sub.2) and in small
concentrations guarantees improved protection of the separator
vis--vis oxidative destruction.
1TABLE 1 Oxidation resistance of separators after treatment with
1-dodecanol (oxidation test) Example 1*) 2 3 4 5 6 7 Quantity of 0
0.7 1.4 2.1 2.8 3.5 7.1 additive [wt.- %] Duration of the oxidation
test Absolute extension [%] 0 h 263 269 282 266 271 267 291 20 h
152 186 234 235 233 252 272 40 h 108 156 204 181 197 249 254 72 h 0
46 82 112 135 234 247 Relative extension [%] 72 h 0 17 29 42 50 88
85 *)Comparison example
Example 8
[0088] Study of Separators with 1-Dodecanol in the Battery Test
[0089] Analogously to Examples 2 to 7 separators were coated with
3.5 wt.-% with 1-dodecanol. The weight ratio of filler to polymer
was 2.2, the oil content 12 wt.-% Untreated separators served as
comparison. The separators were tested in a lead/sulphuric acid
battery. To this end battery cells were assembled from
antimony-containing positive plates and negative lead-calcium
plates (five positive and four negative plates per cell) with a
total capacity of 36 Ah/cell. Three cells were equipped with the
dodecanol-coated separators, the other three cells with the
untreated separators. The battery was subjected to an intensified
stability test at 50.degree. C. according to DIN 43539 Part 2 draft
10/1980. Then the cells were opened and the expansion of the
separators in the pocket area and in the fold edge was
determined.
[0090] The results of the battery test are compiled in Table 2.
These show that, even under conditions reflecting those encountered
in practice, the additive used offers a noticeable improvement in
protection of the separator from oxidative attacks.
2TABLE 2 Oxidation resistance of separators after treatment with
1-dodecanol (battery test) Separator without Separator with 3.5
additive*) wt.- % 1-dodecanol before test after test before test
after test Measuring point Absolute extension [%]**) in the pocket
493 .+-. 42 357 .+-. 46 513 .+-. 39 551 .+-. 49 area in the fold
493 .+-. 42 316 .+-. 24 513 .+-. 39 429 .+-. 33 edge Relative CMD
expansion**) in the pocket 100% 72% 100% 107% area in the fold 100%
64% 100% 84% edge *)Comparison **)measured after 264 test
cycles
Examples 9-11
[0091] Use of Fatty Alcohols as Additives to Prevent Premature
Oxidation of Battery Separators
[0092] Analogously to Examples 1 to 7 separators with alcoholic
solutions of 1-tetradecanol, 1-hexadecanol, and 1-octadecanol were
coated on one side. After drying there was in each case a quantity
of 3.5 wt.-% of the additive on the separator. The separators were
subjected to the oxidation test described in Examples 1 to 7. The
results are compiled in Table 3.
[0093] Separators which are coated with higher-molecular-weight
fatty alcohols also show a clearly improved oxidation stability
compared with the untreated separator (Example 1).
3TABLE 3 Oxidation resistance of separators after treatment with
fatty alcohols (oxidation test) Example 6 9 10 11 Additive 1- 1-
1-hexadecanol 1-octadecanol dodecanol tetradecanol Quantity of 3.5
3.5 3.5 3.5 additive [wt.- %] Duration of the oxidation test
Absolute extension [%] 0 h 267 271 271 268 20 h 252 265 274 265 40
h 249 238 240 238 72 h 234 212 218 201 Relative extension [%] 72 h
88 78 80 75
Examples 12-14
[0094] Comparison of the Antioxidative Effect of Process Oil and
Dodecanol
[0095] It is known from the state of the art that the oxidation
resistance of separators can be improved by increasing the level of
process oil. In a comparative, test the effect of the oil content
on the oxidation stability was compared with the effect of the same
quantity of an additive according to the invention (1-dodecanol).
The results are shown in Table 4. It is to be noted that the
additive according to the invention produces a much more noticeable
improvement in oxidation resistance. The separators were produced
and the test carried out as described in Examples 1 to 7. The
weight ratio of filler to polymer was 2.4. In each case the oil was
extracted to the content given in the Table.
4TABLE 4 Oxidation resistance of separators after treatment with
1-dodecanol and raising of the oil content (oxidation test) Example
12*) 13*) 14 Additive none none 1-dodecanol (3.5 wt.- %) Oil
content 12.4 15.4 11.2 [wt.- %] Duration of oxidation test Absolute
extension [%] 0 h 407 431 419 20 h 313 370 406 40 h 218 346 388 72
h 99 204 326 96 h 0 77 218 Relative extension [%] 96 h 0 18 52
*)Comparison example
Examples 15-18
[0096] Use of Alkoxylated Alcohols as Additives to Prevent
Premature Oxidation of Battery Separators
[0097] Analogously to examples 1 to 7 separators were treated with
alkoxylated alcohols and then subjected to the oxidation test. The
weight ratio of filler to polymer was. 2.6. Compounds of the
general formula R.sup.2--(OC.sub.2H.sub.4).sub.p--OH were studied,
R.sup.2 and p having the meaning given in Table 5. The results
compiled in Table 5 show that the addition products of ethylene
oxide on long-chain alcohols can noticeably improve the oxidation
resistance of battery separators.
5TABLE 5 Oxidation resistance of separators after treatment with
fatty alcohol ethoxylates (oxidation test) Example 1*) 6 15 16 17
18 Additive: R.sup.2--(OC.sub.2H.sub.4).sub.p--OH R.sup.2 C.sub.12
C.sub.12 C.sub.12 C.sub.16/18 C.sub.16/18 C.sub.16/18 P -- -- 2 2 5
11 Quantity of additive 0 3.5 3.5 3.5 3.5 3.5 [wt.- %] Duration of
oxidation test Absolute expansion [%] 0 h 263 267 281 292 279 284
20 h 152 252 246 242 279 257 40 h 108 249 224 260 227 234 72 h 0
234 145 212 159 84 Relative expansion [%] 72 h 0 88 52 73 57 30
*)Comparison example
Example 19
[0098] Use of Phthalic Acid Esters as Additives to Prevent
Premature Oxidation of Battery Separators
[0099] Analogously to Examples 1 to 7 separators were prepared and
their oil content was set at 12 wt.-% by extraction with hexane.
The weight ratio of filler to polymer was 2.2. Differently from
Examples 1 to 7, 1 or 2 wt.-% stearyl phthalate was added to the
hexane bath for the treatment of the separators according to the
invention. The separators were removed from the bath following the
extraction and dried at room temperature after dripping. After
drying the separators contained 1 or 2 wt.-% stearyl phthalate.
According to Table 6 an effective protection of the separator
against premature oxidation is achieved by stearyl phthalate.
Stearyl phthalate is split by the battery acid into phthalic, acid
and octadeanol, an additive suitable according to the
invention.
6TABLE 6 Oxidation resistance of separators after treatment with
stearyl phthalate (oxidation test) Additive none Stearyl phthalate
1 wt.- % 2 wt.- % Duration of oxidation test Absolute extension [%]
0 h 498 498 512 72 h 78 211 251 Relative extension [%] 72 h 16 42
49
Examples 20-26
[0100] Use of Polyacrylates as Additives to Prevent Premature
Oxidation of Battery Separators
[0101] Analogously to Examples 1 to 7 battery separators with a
weight ratio of filler to polymer of 2.2 were prepared based on
polyethylene (UHMWPE) and amorphous silicon dioxide. Differently
from Examples 1 to 7, polyacrylic acid or the sodium salt of
polyacrylic acid were added to the separator material before
extrusion, the quantities of polyacrylic acid present in the
separator after extraction being given in Table 7. The separators
were then subjected to the oxidation test. The results compiled in
Table 7 show that salts of polyacrylic acid give an effective
protection of the separators against premature oxidation possible.
In contrast to this free to polyacrylic acid was practically
without effect. The results also show that polyacrylic acids are
not washed out of the separator during extraction.
7TABLE 7 Oxidation resistance of separators with polyacrylic acid
(oxidation test) Example 20*) 21 22 23 24 25 26*) Additive none
Polyacrylic acid Average molecular -- 1,200 4,000 8,000 15,000
30,000 100,000 weight [g/mol] Form -- salt**) salt**) salt**)
salt**) salt**) acid K-value***) -- 15 25 30 40 50 80 Concentration
-- 2.0 2.0 2.0 2.0 2.0 2.0 [wt.- %] Duration of oxidation test
Absolute extension [%] 0 h 508 522 468 530 499 504 447 20 h 420 446
413 410 456 485 418 40 h 303 427 394 413 450 457 211 72 h 21 333
273 240 244 224 16 Relative extension [%] 72 h 4 64 58 45 49 44 4
*)Comparison example **)The sodium salt of polyacrylic acid was
used (completely neutralized form) ***)Fikentscher's constant,
measured in a 1-% aqueous solution neutralized with sodium
hydroxide solution, parameter for characterization of the degree of
polymerization and the molar mass
Examples 27-28
[0102] Use of Polyacrylic Acid Copolymers as Additives to Prevent
Premature Oxidation of Battery Separators
[0103] Analogously to Examples 20 to 26 separators were prepared
and tested which contained polyacrylic acid copolymers instead of
polyacrylic acid. In Example 27 the polymer Sokolan CP 10 was used,
in Example 28 Sokolan CP 10 S (both Fa. BASF, Ludwigshafen). The
results are shown in Table 8. Here also the salt form of the
polymers produces a good oxidation protection while the acid form
is, practically without effect.
8TABLE 8 Oxidation resistance of separators with polyacrylic acid
copolymers (oxidation test) Example 23*) 27 28 Additive none
Polyacrylic acid copolymer Average molecular -- 4,000 4,000 weight
[g/mol] Form -- salt**) acid Concentration [wt.- %] -- 2.0 2.0
Duration of Absolute oxidation test extension [%] 0 h 508 521 556
20 h 420 465 506 40 h 303 433 375 72 h 21 279 43 Relative extension
[%] 72 h 4 54 8 *)Comparison example **)The sodium salt of
polyacrylic acid was used (completely neutralized form)
* * * * *