Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/06—Lead-acid accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/06—Lead-acid accumulators
  • H01M10/12—Construction or manufacture
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/417—Polyolefins
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/411—Organic material
  • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
  • H01M50/42—Acrylic resins
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
  • H01M50/409—Separators, membranes or diaphragms characterised by the material
  • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the invention relates to separators for lead/sulphuric acid accumulators, hereafter called lead accumulator for short, which have an improved oxidation resistance.
• 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).
• the separators 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.
• 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.
• 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.
• UHMWPE ultra-high molecular-weight polyethylene
• the ultra-high molecular-weight polyethylene (UHMWPE) customarily used to produce separators also generally already has a molecular weight of 5 ⁇ 7 ⁇ 10 6 g/mol and a further increase in the molecular weight would lead to considerable process problems.
• UHMWPE types with a molecular weight of up to approximately 10 ⁇ 10 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.
• 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.
• JP 07130348 A discloses separators which contain mineral oil in combination with a phenolic resin.
• JP 08203493 A discloses the coating of the edges of separators with an insulating resin in order to suppress the oxidative attack.
• 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.
• 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.
• 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.
• 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.
• 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.
• separators containing glass fibres are not very flexible and tend to break when subjected to a mechanical stress.
• 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.
• 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.
• battery separators which contain a compound with the Formula (I) R(OR 1 ) n (COOM x+ 1/x ) m (I) in which
• non-aromatic hydrocarbon radicals 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.
• 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.
• Battery separators are preferred which contain a compound according to Formula (I) in which
• Formula R 2 [(OC 2 H 4 ) p (OC 3 H 6 ) q ]— is to be understood as also including those compounds in which the sequence of the groups in square brackets differs from that shown.
• compounds are suitable in which the radical in brackets is formed by alternating (OC 2 H 4 ) and (OC 3 H 6 ) groups.
• R 2 is a straight-chain or branched alkyl radical with 10 to 20, preferably 14 to 18 carbon atoms
• OC 2 H 4 preferably stands for OCH 2 CH 2
• OC 3 H 6 for OCH(CH 3 )CH 2 and/or OCH 2 CH(CH 3 )
• primary alcohols being particularly preferred
• the fatty alcohol alkoxylates are for example accessible through reaction of the corresponding alcohols with ethylene oxide or propylene oxide.
• battery separators which contain a compound according to Formula (I), in which
• 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.
• poly(meth)acrylic acids which are present entirely in the salt form.
• 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 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).
• 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.
• alkali metal and alkaline-earth metal hydroxides such as potassium hydroxide and in particular sodium hydroxide are particularly suitable.
• Suitable additives according to the invention are known and are commercially available.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the additives used to produce the separators preferably have a high boiling point. Additives with a boiling point of 250° C. or more have proved to be particularly suitable.
• 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.
• 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.
• 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 ⁇ 10 6 and particularly preferably at least 5.0 ⁇ 10 6 g/mol is quite particularly preferred.
• polypropylene, polybutene, polystyrene, ethylene-propylene copolymers, ethylene-hexylene copolymers, ethylene-butene copolymers, propylene-butene copolymers and ethylene-propylene-butene copolymers are also suitable.
• 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.
• a filler preferred according to the invention is SiO 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the accumulators are customary lead/sulphuric acid accumulators with conventional electrodes and sulphuric acid as electrolyte.
• 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.
• 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.
• testpieces from the separator material were treated with a mixture of sulphuric acid and hydrogen peroxide at 80° 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.
• 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 3 , 35 ml sulphuric acid of density 1.84 g/cm 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° 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.
• separator sheets 160 ⁇ 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.
• all weight percentages refer to the weight of the separator after extraction.
• An untreated separator served as comparison (Example 1).
• the weight ratio of filler to polymer was 2.6 in each case.
• Stearyl phthalate is split by the battery acid into phthalic, acid and octadeanol, an additive suitable according to the invention.
• TABLE 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 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.
• UHMWPE polyethylene
• 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.
• Example 27 Analogously to Examples 20 to 26 separators were prepared and tested which contained polyacrylic acid copolymers instead of polyacrylic acid.
• Example 28 the polymer Sokolan CP 10 was used, in Example 28 Sokolan CP 10 S (both Fa. BASF, Ludwigshafen).
• Table 8 the salt form of the polymers produces a good oxidation protection while the acid form is, practically without effect.

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• 2002
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