GB2312003A - Polymeric sheet for electrode separator - Google Patents

Polymeric sheet for electrode separator Download PDF

Info

Publication number
GB2312003A
GB2312003A GB9714925A GB9714925A GB2312003A GB 2312003 A GB2312003 A GB 2312003A GB 9714925 A GB9714925 A GB 9714925A GB 9714925 A GB9714925 A GB 9714925A GB 2312003 A GB2312003 A GB 2312003A
Authority
GB
United Kingdom
Prior art keywords
fabric
hydrophilic
fibres
polymeric sheet
component
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
GB9714925A
Other versions
GB9714925D0 (en
GB2312003B (en
Inventor
Ian Michael Lancaster
Giovanni Gentilcore
Kate Louise Ollerenshaw
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Scimat Ltd
Original Assignee
Scimat Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB969614907A external-priority patent/GB9614907D0/en
Priority claimed from GBGB9616522.0A external-priority patent/GB9616522D0/en
Application filed by Scimat Ltd filed Critical Scimat Ltd
Publication of GB9714925D0 publication Critical patent/GB9714925D0/en
Publication of GB2312003A publication Critical patent/GB2312003A/en
Application granted granted Critical
Publication of GB2312003B publication Critical patent/GB2312003B/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Classifications

    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M14/00—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials
    • D06M14/18—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials using wave energy or particle radiation
    • D06M14/26—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials using wave energy or particle radiation on to materials of synthetic origin
    • D06M14/28—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials using wave energy or particle radiation on to materials of synthetic origin of macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • 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
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M14/00—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials
    • D06M14/18—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials using wave energy or particle radiation
    • D06M14/26—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials using wave energy or particle radiation on to materials of synthetic origin
    • D06M14/30—Graft polymerisation of monomers containing carbon-to-carbon unsaturated bonds on to fibres, threads, yarns, fabrics, or fibrous goods made from such materials using wave energy or particle radiation on to materials of synthetic origin of macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M23/00—Treatment of fibres, threads, yarns, fabrics or fibrous goods made from such materials, characterised by the process
    • D06M23/16—Processes for the non-uniform application of treating agents, e.g. one-sided treatment; Differential treatment
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
    • D21H13/10—Organic non-cellulose fibres
    • D21H13/12—Organic non-cellulose fibres from macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H13/14—Polyalkenes, e.g. polystyrene polyethylene
    • 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
    • H01M50/44—Fibrous material
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M2101/00—Chemical constitution of the fibres, threads, yarns, fabrics or fibrous goods made from such materials, to be treated
    • D06M2101/16—Synthetic fibres, other than mineral fibres
    • D06M2101/18—Synthetic fibres consisting of macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D06M2101/20—Polyalkenes, polymers or copolymers of compounds with alkenyl groups bonded to aromatic groups
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M2101/00—Chemical constitution of the fibres, threads, yarns, fabrics or fibrous goods made from such materials, to be treated
    • D06M2101/16—Synthetic fibres, other than mineral fibres
    • D06M2101/30—Synthetic polymers consisting of macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D06M2101/32—Polyesters
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M2101/00—Chemical constitution of the fibres, threads, yarns, fabrics or fibrous goods made from such materials, to be treated
    • D06M2101/16—Synthetic fibres, other than mineral fibres
    • D06M2101/30—Synthetic polymers consisting of macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • D06M2101/34—Polyamides
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
    • D21H17/20—Macromolecular organic compounds
    • D21H17/33—Synthetic macromolecular compounds
    • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D21H17/37—Polymers of unsaturated acids or derivatives thereof, e.g. polyacrylates
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H25/00—After-treatment of paper not provided for in groups D21H17/00 - D21H23/00
    • D21H25/04—Physical treatment, e.g. heating, irradiating
    • D21H25/06—Physical treatment, e.g. heating, irradiating of impregnated or coated paper
    • 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

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Cell Separators (AREA)
  • Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)

Abstract

A polymeric sheet useful as an electrode separator comprises a fabric formed from fibres which have been treated by a graft-polymerisation reaction with a component which renders the fabric hydrophilic. The grafting conditions are such that the said component grafts preferentially on one surface of the fabric compared with the opposite surface, making that surface more hydrophilic than the opposite surface, and that the hydrophilic character of at least the said opposite surface is substantially homogeneous over that surface.

Description

POLYMERIC SHEET This invention relates to a polymeric sheet, which can be used as an electrode separator in an electrochemical device, to such a device and to a method of making the sheet.
JP-A-57.141862 discloses techniques for rendering a sheet formed from fibres of a hydrophobic polymer hydrophilic by reacting the polymer on the surface of the fibres with a vinylgroup containing monomer such as acrylic acid. This enables the fabric to be wetted by aqueous electrolyte in the device.
Reference is made to initiation of the reaction by ionising radiation such as gamma radiation or an electron beam, or by ultraviolet radiation; the use of gamma radiation is described in the examples. The use of ultraviolet radiation in the formation of such a polymeric sheet is disclosed in WO-A93/01622.
The treatment of a fabric formed from fibres of a hydrophobic material that is discussed in the documents mentioned above is such that the properties of the fabric on its opposite surfaces are identical. It can be advantageous for use in some electrochemical devices for the surface properties of a polymeric sheet separator to differ from one surface to the other, in particular in respect of the wettability of the sheet.
Accordingly, in one aspect, the invention provides a polymeric sheet which comprises a fabric formed from fibres which have been treated by a graft-polymerisation reaction with a component which renders the fabric hydrophilic under such conditions that the said component grafts preferentially on one surface of the fabric compared with the opposite surface, making that surface more hydrophilic than the opposite surface, and that the hydrophilic character of at least the said opposite surface is substantially homogeneous over that surface.
The presence of a surface of a polymeric sheet which is relatively less hydrophobic than another surface has advantages when the sheet is for use as a separator in certain types of electrochemical devices, especially rechargeable batteries such as nickel-hydrogen batteries. The hydrophilic surface is easier wetted by aqueous electrolyte, which can be advantageous in the region of a positive electrode. This can inhibit flow of hydrogen gas from the negative electrode to the positive electrode when the battery is being recharged. The less hydrophilic surface lead to the creation of a three phase boundary at the surface of the negative electrode (between the surface of the electrode, the electrolyte and oxygen gas generated at the electrode), which can help to control the internal pressure in the battery on recharging due to the generation of oxygen.
The homogeneous character of the hydrophilic character of the surfaces has the advantage that it can provide substantially even current density over the surface of an electrode in contact with the sheet when in use as an electrode separator.
This can lead to even discharge of the electrode and therefore efficient utilisation of electrode material. It can minimise the formation of dendrites as can be a problem in certain rechargeable electrochemical cells, for example NiCd cells.
The characteristics of the less hydrophilic surface are substantially homogeneous in that they results from substantially uniform exposure to reaction conditions or materials across the entire surface. Consequently, the surface appears substantially uniform when inspected visually by techniques such as electron microscopy, so that it is not possible to discern differences between regions with different degrees of hydrophilic behaviour.
Preferably, the component which renders the fabric hydrophilic is one which reacts with the material on the surface of the fibres and contains a vinyl monomer capable of reacting with an acid or a base to form a salt. The vinyl monomer which is graft-polymerised with the polypropylene of the fibre surface can be capable of reacting with an acid or a base directly to form a salt, or indirectly to form a salt after appropriate work up, perhaps involving for example hydrolysis or sulphonation. Preferred vinyl monomers include ethylenically unsaturated carboxylic acids and esters thereof such as acrylic acid, methacrylic acid, methyl acrylate, and methylmethacrylate.
Other vinyl monomers which might be used include acrylamide, vinylpyridine, vinylpyrrolidone and styrene-sulphonic acid.
Preferably, the ratio of the amount of the component on the more hydrophilic surface to that on the opposite surface is at least about 1.2, preferably at least about 2.0, more preferably at least about 2.5, especially at least about 3.0, for example at least about 3.5. The amount of the component on the surfaces can be determined by an appropriate microscopic technique. For example, the component can be converted to a salt such as a potassium salt and the amount of potassium on the surface analysed by Energy Dispersive X-ray (EDX) analysis using a scanning electron microscope.
Preferably, the ratio of ion exchange capacity of the sheet measured on the more hydrophilic surface to that measured on the opposite surface is at least about 1.2, preferably at least about 2.0, more preferably at least about 2.5, especially at least about 3.0, for example at least about 3.5. The ratio can be at least about 4.5, preferably at least about 5 or even at least about 6. The ion exchange capacity of the polymeric sheet is measured in meq.g-l according to the test routine referred to below.
Preferably, the ion exchange capacity of the sheet measured on the more hydrophilic surface is at least about 0.1 meq.g1, more preferably at least about 0.5 meq.g-l, for example from about 0.75 to about 1.5 meq.g-l.
Preferably, the ratio of the wettability of the more hydrophilic surface to that of the opposite surface is at least about 1.2, preferably at least about 2.0, more preferably at least about 2.5, especially at least about 3.0, for example at least about 3.5. The wettability of the surface of the sheet is determined by measuring the time taken for a 20 y1 drop of 30% w/w KOH placed on the surface of the sheet to be fully absorbed by the sheet.
Preferably, the absorption time for the droplet of KOH, measured on the more hydrophilic surface of the sheet is not more than about 75 s, more preferably not more than about 50 s, especially not more than about 30 s. Preferably, the difference between the absorption times for the two surfaces is at least about 3 s, more preferably at least about 10 s, especially at least about 15 s, and possibly as much as at least about 20 s or more.
The fibres will comprise a polymeric material such as a polyolefin, polyester, polyamide and so on. Preferably, the material of the fibres comprises a polyolefin. Preferred polyolefins include polyethylene and polypropylene.
Preferably, at least about 40% by weight of the polymeric material of the material of the fibres, preferably at least about 60%, more preferably at least about 80%, is polypropylene.
Preferably, the material of the surface of at least some of the fibres, for example at least about 40% by weight, preferably at least about 60%, more preferably at least about 80%, comprises polypropylene.
Preferably, the material of at least some of the fibres from which the non-woven fabric is formed, for example at least about 40% by weight, preferably at least about 60%, more preferably at least about 80%, is substantially homogeneous throughout the thickness of the fibres. It can be preferred for many applications for the material of substantially all of the fibres to be substantially homogeneous throughout their thickness, so that those fibres are formed only from polypropylene or another suitable material (with appropriate additives where necessary).
The sheet of the invention may be made from non-woven fabric which is made from fibres comprising more than one material, for example more than one polyolefin, or a single polyolefin but having different physical properties in different regions of the fibres. For example, the fabric may be made from at least some fibres formed from two polymers, such as coextruded bicomponent fibres having a polypropylene core and an outer layer of polyethylene, or coextruded fibres with the components positioned side-by-side. Bicomponent fibres can be formed by sintering of particles of a first material onto a core provided by a second material; for example, particles of polyethylene may be sintered onto a core of polypropylene. The fabric might also be made from fibres containing materials having different physical properties as a result of processing or additives.
For example, fibres might be used which contain a polymer which has different molecular weights or different molecular structure (arising for example from differences in tacticity) in different regions of the fibres.
Bicomponent fibres may provide substantially the entire content of the non-woven fabric, or a proportion only, for example less than about 60% by weight, perhaps less than about 40%, for example less than about 30%. A small proportion of bicomponent fibres, for example with a polyethylene outer layer or with a lower molecular weight outer layer, can serve to bind the fibres of the fabric together.
Preferably, the thickness of the fibres from which the nonwoven fabric is formed is not more than about 30 ym, more preferably not more than about 10 Um.
Preferably, the thickness of the sheet, measured using test method DIN 53105 which involves dropping a 2.0 kg weight onto a sample of the sheet of area 2.0 cm2 at a speed of 2.0 mm.s-l, is greater than about 100 ym, more preferably greater than about 150 clam; preferably, the thickness is less than about 600 ym, more preferably less than about 450 Hm.
In another aspect, the invention provides a method of making a polymeric sheet, which comprises: (a) impregnating a non-woven fabric formed from fibres whose surface is provided by a polyolefin with a solution of a component which can render the fabric hydrophilic, and (b) exposing the impregnated fabric to radiation to cause the component and the material of the fibres to co polymerise, under such conditions that the said component grafts preferentially on one surface of the fabric compared with the opposite surface, substantially homogeneously over the surface of the preferentially grafted surface, making that surface more hydrophilic than the opposite surface.
The differences between the surfaces of the fabric can be brought about by differential irradiation of the fabric from one surface to the other so that one surface is irradiated to cause grafting preferentially on that surface compared with the opposite surface. The opposite surface will often not be exposed to radiation, at least directly. However, it could also be irradiated, but generally under such conditions that the extent of the grafting reaction is less (for example by reduced intensity).
Preferably, the reaction between the component and the material of the fibres is initiated by ultraviolet irradiation. It has been found that the use of ultraviolet radiation makes possible selective initiation of the reaction on one surface compared with the opposite surface, so that the resulting product is more hydrophilic on one surface compared with the opposite surface giving rise to advantages in use in certain applications.
The differentiation between the surfaces of the sheet can be obtained by careful selection of the conditions for initiation of the reaction between the material of the fibres and the component to be grafted to the fibres. Relevant process conditions include the nature of the radiation, the power of the radiation source, the distance from the radiation source to the fabric being irradiated, the speed with which the fabric passes the radiation source, the thickness of the fabric, and the transparency of the fabric and the solution containing the component. Preferably, the conditions selected for the ultraviolet radiation include at least one of the following: (a) the power of the lamp providing the radiation is at least about 60 W.cm1, preferably at least about 80 W.cm1; the power is not more than about 250 W.cm1, preferably not more than about 180 W.cm~l.
(b) the distance from the lamp to the sheet is at least about 5 cm, preferably at least about 10 cm; the distance is not more than about 30 cm, preferably not more than about 20 cm.
(c) the speed with which the sheet is passed through the radiation is at least about 1.0 m.min1, preferably at least about 1.2 m.min1; the speed is not more than about 10.0 m.min1, preferably not more than about 7.0 m.min1.
It is an advantage of the method of the invention that it can introduce crosslinks in the polyolefin material of the fabric.
This can enhance the physical properties of the material, such as the tensile strength. Moreover, it has been found that storing the separator in 40% w/w potassium hydroxide at 71 C for 21 days, it has been found that the physical properties change only to an insignificant degree.
In a further aspect, the invention provides an electrochemical device which comprises positive and negative electrodes, a quantity of an electrolyte, and an electrode separator provided by a polymeric sheet of the type discussed above. Preferably, the device is a battery, especially a rechargeable battery.
Preferably, the positive electrode contains a nickel salt such as Ni(OH) Preferably, the negative electrode comprises a hydrogen absorbing alloy. Suitable electrodes include solutions of alkali metal hydroxides such as NaOH, LiON, KOH and mixtures thereof.
EXAMPLES Comnarative example 1 A non-woven meltblown propylene fabric having mean fibre diameter of 3 ym, nominal thickness 200 Zm, and basis weight 46 g.m-2 was selected. A strip of fabric on a roll was impregnated with a solution having the formulation as set out below (percentages by weight) in a nitrogen atmosphere and then passed, while in the nitrogen atmosphere, between 2 pairs of mercury vapour lamps separated by 14 cm and having power of 120 W.cm1 and beam width of 24 cm. The material was washed in deionised water and dried.
Component % w/w Water 69.25 Acrylic acid 30.0 Benzophenone 0.25 Surfactant (Lutensol ON70) 0.5 The material was passed through the lamps at speeds of 1.5, 2,0, and 2.5 m.min-l. This produced material which had ion exchange capacities of 2.8, 2.0, 1.1 meq.g-l respectively.
The time taken for a 20 y1 drop of 30% KOH to be fully absorbed by the material was measured. The mean results for all three materials was 3 seconds.
The amount of material grafted to the surface of the material was determined by Energy Dispersive X-ray analysis using a scanning electron microscope. The material was treated in 1 M KOH for 3 hours at 600C and then washed in water and dried.
The following results were obtained:
Speed (m.min-l) IEC (meq.gl) Atomic K 1.5 2.8 6.04 2.0 2.0 4.35 2.5 1.1 2.82 A calibration curve of atomic W K versus ion exchange capacity is prepared from this data as in Figure 1.
Example 1 A non-woven fabric was treated as described above in comparative example 1 but with the lamps on one side of the fabric turned off. The materials produced had ion exchange capacities of 1.2, 0.5, and 0.15 meq.g1.
A KOH absorption test was performed on the resulting materials and the mean results of a minimum of 7 tests shown below.
KOH (m.min1) KON absorption time (s) Speed (m.min-l) Irradiated side Non-irradiated side 1.5 3 5 2.0 4 14 2.5 15 72 A significant difference can be seen between the properties of the two sides of the material.
The amount of material grafted to the surface of the material was determined by EDX analysis as described above. The following results were obtained:
Speed (m.minl) IEC (meq.gl) Atomic % K 1.5 3.21 0.24 2.0 0.90 0.17 2.5 0.18 0.04 From the calibration curve in Figure 1, the ion exchange capacities of the surfaces were calculated to be as follows:
lEC (meq.g1) Speed (m.minl) Irradiated side Non-irradiated side 1.5 1.46 0.18 2.0 0.40 0.065 2.5 0.065 0.01 Comparative example 2 A non-woven fabric was treated as described above in comparative example 1, but using a non-woven wet laid fabric formed from bicomponent polypropylene/polyethylene fibre material with basis weight 50 g.m-2 and thickness 120 ym. The line speed was 2.3. m.min1 and gave a material with an ion exchange capacity of 0.7 meq.g1.
Example 2 A non-woven fabric was treated as described above in comparative example 2 but with the lamps on one side turned off. The line speed was 2.3 m.min-l and the resulting ion exchange capacity was 0.1 meq.g-l.
The material was treated in 1 M KOH for 3 hours at 600C, and then washed in water and finally dried. EDX analysis was performed using a SEM to analyse the surfaces of the material.
This determined the K* content of each surface which is directly related to the ion exchange capacity of the surface.
At % K KOH absorption (s) Irradiated side 1.26 20 Nonirradiated side 0.38 28 Example 3 A non-woven fabric was treated as described above in example 2 but with a wet laid material with basis weight of 70 g.m2, and thickness 215 ijm. The material was run at 1.7 m.min~l and the resulting ion exchange capacity was 0.2 meq.g-l.
At % K KOH absorption (s) Irradiated side 2.81 76 Nonirradiated side 0.54 97

Claims (8)

  1. CLAIMS: 1. A polymeric sheet which comprises a fabric formed from fibres which have been treated by a graft-polymerisation reaction with a component which renders the fabric hydrophilic under such conditions that the said component grafts preferentially on one surface of the fabric compared with the opposite surface, making that surface more hydrophilic than the opposite surface, and that the hydrophilic character of at least the said opposite surface is substantially homogeneous over that surface.
  2. 2. A polymeric sheet as claimed in claim 1, in which the ratio of the amount of the component on the more hydrophilic surface to that on the opposite surface is at least about 1.2.
  3. 3. A polymeric sheet as claimed in claim 1 or claim 2, in which the ratio of the ion exchange capacity of the sheet measured on the more hydrophilic surface to that measured on the opposite surface is at least about 1.2.
  4. 4. A polymeric sheet as claimed in any one of claims 1 to 3, in which the mean diameter of the fibres of the fabric is not more than about 30 Hm.
  5. 5. A polymeric sheet as claimed in any one of claims 1 to 4, in which the surface of at least some of the fibres of the fabric comprises polypropylene.
  6. 6. An electrochemical device which comprises positive and negative electrodes, a quantity of an electrolyte, and an electrode separator provided by a polymeric sheet as claimed in any one of claims 1 to 5.
  7. 7. A device as claimed in claim 6, in which the more hydrophilic surface of the separator is arranged adjacent to the positive electrode.
  8. 8. A method of making a polymeric sheet, which comprises: (a) impregnating a non-woven fabric formed from fibres whose surface is provided by a polyolefin with a solution of a component which can render the fabric hydrophilic, and (b) exposing the impregnated fabric to radiation to cause the component and the material of the fibres to copolymerise, under such conditions that the said component grafts preferentially on one surface of the fabric compared with the opposite surface, substantially homogeneously over the surface of the preferentially grafted surface, making that surface more hydrophilic than the opposite surface.
GB9714925A 1996-07-16 1997-07-16 Electrochemical device with fabric separator Expired - Lifetime GB2312003B (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB969614907A GB9614907D0 (en) 1996-07-16 1996-07-16 Polymeric sheet
GBGB9616522.0A GB9616522D0 (en) 1996-08-06 1996-08-06 Polymeric sheet

Publications (3)

Publication Number Publication Date
GB9714925D0 GB9714925D0 (en) 1997-09-17
GB2312003A true GB2312003A (en) 1997-10-15
GB2312003B GB2312003B (en) 2000-03-22

Family

ID=26309709

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9714925A Expired - Lifetime GB2312003B (en) 1996-07-16 1997-07-16 Electrochemical device with fabric separator

Country Status (1)

Country Link
GB (1) GB2312003B (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000001468A1 (en) * 1998-07-03 2000-01-13 Scimat Limited A gas filter element
EP1265748A1 (en) * 1999-10-29 2002-12-18 HOLLINGSWORTH & VOSE COMPANY Graft polymerization, separators, and batteries including the separators

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0668390A2 (en) * 1994-02-18 1995-08-23 Kimberly-Clark Corporation Process of enhanced chemical bonding by electron beam radiation
EP0680107A1 (en) * 1994-04-15 1995-11-02 Kabushiki Kaisha Toshiba Nickel-hydrogen secondary battery

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0668390A2 (en) * 1994-02-18 1995-08-23 Kimberly-Clark Corporation Process of enhanced chemical bonding by electron beam radiation
EP0680107A1 (en) * 1994-04-15 1995-11-02 Kabushiki Kaisha Toshiba Nickel-hydrogen secondary battery

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000001468A1 (en) * 1998-07-03 2000-01-13 Scimat Limited A gas filter element
EP1265748A1 (en) * 1999-10-29 2002-12-18 HOLLINGSWORTH & VOSE COMPANY Graft polymerization, separators, and batteries including the separators
EP1265748A4 (en) * 1999-10-29 2003-06-18 Hollingsworth & Vose Co Graft polymerization, separators, and batteries including the separators

Also Published As

Publication number Publication date
GB9714925D0 (en) 1997-09-17
GB2312003B (en) 2000-03-22

Similar Documents

Publication Publication Date Title
EP0593612B1 (en) Polymeric sheet
JP4452738B2 (en) Electrochemical device and method for manufacturing electrode separator for electrochemical device
US5645956A (en) Resilient battery separator
WO1998058111A1 (en) Non-woven fabric laminate
US5589302A (en) Battery separator and battery containing same
US6348286B1 (en) Alkaline battery separator and process for producing the same
GB2312003A (en) Polymeric sheet for electrode separator
EP0989619B1 (en) Alkaline battery separator
US7625955B2 (en) Porous polymeric article
JP3741410B2 (en) Alkaline battery separator and method for producing the same
US20020002904A1 (en) Gas filter element
JP4448255B2 (en) Method for producing separator for alkaline battery
JPH1167183A (en) Separator for alkaline battery
JP2001210298A (en) Separator for alkaline storage battery and its production
JPH10284042A (en) Separator for alkaline battery
JPH1167179A (en) Separator for alkaline battery and manufacture thereof
JP2000164191A (en) Separator for alkaline battery
JPH03291847A (en) Manufacture of separator
JPH1173938A (en) Separator for alkaline battery
JPH09289006A (en) Battery separator

Legal Events

Date Code Title Description
732E Amendments to the register in respect of changes of name or changes affecting rights (sect. 32/1977)
PE20 Patent expired after termination of 20 years

Expiry date: 20170715