Classifications

• • 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
  • H01M50/431—Inorganic material
• • 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
  • H01M10/121—Valve regulated lead acid batteries [VRLA]
• • 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
  • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
  • H01M50/494—Tensile strength
• • 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
  • H01M50/431—Inorganic material
  • H01M50/434—Ceramics
  • H01M50/437—Glass
• • 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
• • 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

Definitions

• the present invention relates generally to the field of batteries and, more specifically, to separators containing glass fibers which are positioned between the positive and negative plates of batteries and to a method for producing such separators.
• separators containing glass fibers are well known. Long before glass fiber separators, however, cedar veneers were used as a separator material, and were replaced by microporous, hard rubbery separators and cellulose separators impregnated with resins.
• Valve regulated ("sealed" - “recombinant”) lead acid (VRLA) batteries are known; they usually comprise a plurality of positive and negative plates, as in a prismatic cell, or layers of separator and positive and negative electrodes wound together, as in a "jelly roll” cell.
• the plates are arranged so that they alternate, negative - positive - negative, etc., with separator material and paste separating each plate from adjacent plates.
• the separator which, typically, is a mat of glass fibers, is an inert material; it stores battery acid, applies a force to paste-grid interfaces, and provides low electric resistance.
• Glass fiber separator material typically, is produced commercially on paper making equipment including fourdrinier machines and rotoformers, inclined fourdrinier machines and extended wire rotoformers.
• separator made of glass fibers for VRLA batteries it is preferred that no organic material be added to a furnish from which separator sheets are made; the entanglement of individual fibers serves to maintain the sheet in a cohesive structure, and water glass, which sometimes forms on the fiber surfaces, serves as a binder.
• Organic binders tend to decrease the ability of a separator to wick acid, and to decrease the amount of acid a separator can hold.
• a great deal of work has been directed to modifying the glass fiber furnish from which separators are produced to improve battery performance and/or lower the cost of the separator.
• US Patent No. 4,465,748 discloses glass fiber sheet material for use as a separator in an electrochemical cell, and made from 5 to 35 percent w/w of glass fibers less than 1 ⁇ m in diameter; the patent also discloses a glass fiber sheet for such use wherein there are fibers of a continuous range of fiber diameters and lengths, and most of the fibers are not over 5 mm in length.
• US patent No. 4,216,280 discloses glass fiber sheet material for use as a plate separator in a battery, and made from 50 to 95 percent w/w of glass fibers less than 1 ⁇ m in diameter and 50 to 5 percent w/w of coarser glass fibers.
• the coarser glass fibers the reference says, have a fiber diameter larger than 5 ⁇ m, preferably larger than 10 ⁇ m, and it is advantageous for some of the coarser fibers to have diameters of 10 ⁇ m to 30 ⁇ m.
• US Patent No. 4,205,122 discloses a battery separator of reduced electric resistance comprising a self supporting, non woven mat consisting essentially of a mixture of olefinic resin fibers having a coarseness of from 4 to 13 decigrex and olefinic resin fibers having a coarseness of less than 4 decigrex, the latter fibers being present in an amount of not less than 3 parts by weight per 100 parts by weight of fibers; up to about 600 parts by weight of inert filler materials per 100 parts by of fibers can also be used.
• the battery separator is produced by subjecting a suitable aqueous dispersion to a sheet-forming operation, drying the resulting wet, non-woven mat, and heat treating the dried mat at a temperature ranging from a point 20° lower than the melting point of the aforementioned fibers to a point about 50° higher than the melting point.
• US Patent No. 4,216,281 (O'Rell et al.) discloses a separator material produced from a furnish containing 30 to 70 percent w/w of polyolefin synthetic pulp, 15 to 65 percent w/w of a siliceous filler and 1 to 35 percent w/w of "long" fibers which can be polyester fibers, glass fibers, or a mixture of the two. Cellulose in an amount up to about
• US Patent No. 4,363,856 (Waterhouse) discloses a separator material made from a furnish composed of polyolefin pulp fibers and glass fibers, and names polyester staple fibers, polyolefin staple fibers and cellulose pulp fibers as alternative constituents of the furnish.
• KJ US Patent No. 4,387,144 discloses a battery separator having a low electrical resistance after extended use which is made by thermal consolidation and thermal embossing of a paper web formed from a furnish containing a synthetic pulp the fibrils of which are filled with an inorganic filler, the web incorporating a wetting agent which is preferably an organic sulpho ⁇ atc, and organic succinate. or phenol ethoxylate.
• Sheet separators for use in conventional (not valve regulated) batteries and comprising both glass fibers and organic fibers are disclosed in all of the following US patents: No. 4,529,677 (Bodendorf); No. 4,363,856 (Waterhouse); and No. 4,359,511 (Strzempko).
• US patent No.4,367,271 Hasegawa, discloses storage battery separators composed 25 of acrylic fibrils in an amount of up to about 10 percent w/w, balance glass fibers.
• Japanese patent document 55/146,872 discloses a separator material comprising glass fibers (50-85 percent w/w) and organic fibers (50-15 percent w/w).
• US patent No. 4,245,013, Clegg et al. discloses a separator made by overlaying a first sheet of fibrous material including polyethylene fibers with a second sheet of 30 fibrous material including polyethylene and having a synthetic pulp content higher than the first sheet.
• US Patent No. 4,908,282 discloses a separator comprising a sheet made from first fibers which impart to the sheet an absorbency greater than 90% and second fibers which impart to the sheet an absorbency less than 80% wherein the first and second fibers are present in such proportions that the sheet has an absorbency of from 75 to 95%.
• This patent discloses that fine glass fibers have a high absorbency, that coarse glass fibers have a low absorbency, and that hydrophobic organic fibers have an extremely low absorbency, and that, when this separator is saturated with electrolyte, unfilled voids remain so that gas can transfer from plate to plate for recombination.
• the disclosure of Badger is incorporated herein by reference.
• US Patent No. 5,091,275 discloses a glass fiber separator which expands when exposed to electrolyte.
• the separator comprises glass fibers which are impregnated with an aqueous solution of colloidal silica particles and a sulfate salt.
• the separator is produced by forming a paper making web of glass fibers, impregnating the web with the aqueous mixture of silica and the salt, lightly compressing the impregnated web to remove some of the aqueous solution, partially drying the web, compressing the web to a final thickness and completing the drying of the web.
• the web is preferably compressed to a thickness which is less than the distance between plates in a given cell, so that insertion of an assembled cell stack into a case is facilitated.
• the salt dissolves in the electrolyte and the separator expands to provide good contact between the plates and the separators.
• the silica contributes to the recombination performance of cells incorporating the prc-compressed separator.
• the silica also contributes a great deal of stiffness to the separator, so much so that the separator may be characterized as rigid.
• the patent says thai fibers of cellulose acetate, cellulose nitrate, regenerated cellulose from viscose, "Vinylitc (a synthetic resin made by polymerization of vinyl compounds), Aralac (a fibrous product made from skim milk casein), and spun glass" which range in length from Vt inch to 1 inch and in diameter from 12-80 microns and fibrillae preferably derived from flax, Manila hemp, caroa or hemp can be used to make the paper. At least 90 percent of the fibrillae should be from 0.0015 to 0.0025 inch in length and from 0.0000027 to 0.0000044 inch in width.
• the instant invention is based upon the discovery that comparatively small additions of wood pulp, if beaten or refined to a sufficient degree to produce a highly fibrillated cellulose fiber, to a glass fiber furnish suitable for use in making battery separator material,
• the separator improves the cut through resistance of a separator made from the furnish, (3) and have a unique characteristic in that they hold a greater proportion of acid introduced thereunto when the separator is subsequently compressed.
• the separator is repulpable, in the sense that it can be used as a constituent of a glass fiber which is used to produce "new" separator; furthermore, batteries made from glass fiber separator material which contains comparatively small amounts of wood pulp which has been beaten or refined to a sufficient degree, have remarkably long service lives, as indicated by their performance in cycling tests.
• the pulp slurry should be beaten or refined to a Canadian freeness not greater than about 650 cc, or to an equivalent freeness by other measurement techniques, and a remarkable increase in tensile strength is achieved when the pulp is beaten or refined to a Canadian freeness not greater than about 120 cc, or to an equivalent freeness by other measurement techniques.
• Fig. 1 is a plot of the percent w/w of added cellulose in glass fiber separator material according to the invention vs. the liters per second of air flowing through the separator material under test conditions that are subsequently described herein.
• Fig. 2 is a plot of tensile strength, both machine direction (“Tensile. MD”) and 0 cross direction (“Tensile, CD”), vs. percent w/w of added cellulose in glass fiber battery separator according to the invention.
• Fig. 3 is a plot of percent of initial capacity vs. number of test cycles for a battery according to the invention and for a control battery.
• Figs. 4 through 9 are plots of thickness (the values plotted are 1000 times the 5 thickness of the separator in mm) vs. load and rebound thickness vs. load for five glass fiber separator materials according to the invention and a control, where rebound thickness is 1000 times the thickness of a separator material in mm after that separator has been subjected to a load and the load has been reduced to 0.55 pounds per square inch (3.79 KPa); the data in Figs. 4 through 9 are for dry separator material.
• 0 Figs. 10 through 15 are plots similar to those of Figs. 4 through 9, showing thickness vs. load and rebound thickness vs.
• Figs. 16 and 17 are plots similar to Figs. 4 and 5, differing in that interpolated points are plotted in the former, so that successive points along the X axis represent equal increments of cellulose content, while experimental values are plotted in the latter and, as a consequence, as is subsequently explained herein, successive points along the X axis do not always represent equal increments of cellulose content. 0 DEFINITIONS
• Glass fiber separator hand sheets were produced in a laboratory apparatus by depositing a furnish on a wire or screen, and draining the furnish.
• the apparatus comprised a tank with a screen in the bottom, a drain below the screen, a valve which opened and closed the drain, and a hand paddle which was moved back and forth to simulate the movement of a furnish in commercial papermaking apparatus and establish a "machine direction" parallel to the direction of paddle movement.
• the furnish was produced by charging to the tank acidified water, pH 2.7, and solids composed of 74.5 percent w/w Schuller 206 glass fibers, average fiber diameter 0.76 ⁇ m, 12.8 percent w/w Evanite 610 glass fibers, nominal fiber diameter 2.6 ⁇ m, and 12.8 percent w/w A20-BC- A inch glass fibers, nominal fiber diameter 13 ⁇ m, stirring for about a minute, charging to the tank a kraft pulp slurry which had a Canadian freeness of 57cc and a consistency of 1.235 percent, and stirring for an additional 2 minutes.
• the composition in the mixer after the pulp addition, contained 73 percent w/w Schuller 206 glass fibers, 12.5 percent w/w Evanite 610 glass fibers, 12.5 percent w/w A20-BC-'/2 inch glass fibers and 2 percent w/w pulp fibrils.
• the furnish and the pulp were stirred for about two minutes, after which the valve was opened so that the water drained through the screen while the separator was retained on the screen.
• the furnish contained enough glass fibers to produce a separator having a grammage of 30 g/m 2 at a thickness of 0.15 mm.
• the separator hand sheet was heated in a drying oven to about 150° for 30 minutes.
• Two separator sheets produced as described above were tested and various data, summarized below, were collected (the data are averages of the determinations on the two sheets).
• Frazier permeability in the following data and elsewhere herein, is in L/scc/nr @ 20 mm
• Thickness, mm (under a Ifl load of 10.34 KPa): 0.15
• Frazier Permeability values reported herein were determined using Frazier Permeability tester 91A (TAPPI T2510M-85).
• composition of the Schuller 206 glass fibers used in Example 1 and in subsequent Examples vary slightly from time to time. Mean values, in percent w/w, calculated from data furnished by Schuller for the period when the examples were carried out are given below:
• the glass contains Fe,O-,, TiO 2 , ZrO 2 , Cr 2 O ? , SrO. BaO, MnO, ZnO, Li 2 O, SO 3 and Pb in amounts less than 0.1%.
• the nominal composition of the Evanite 610 glass fibers used in Example 1 and in subsequent Examples varies, in percent w/w, within the following ranges:
• the A20-BC- 1 /2 inch glass fibers used in the procedure described above and in other procedures described herein are commercially available from Schuller under the indicated designation.
• Glass fiber separator sheets according to the invention were produced on a pilot plant paper making machine by depositing a furnish on an advancing wire, through which water from the furnish drained.
• the furnish was produced in a mixer from acidified water. pH 2.7, and solids composed of Schuller 206 glass fibers, Schuller 210X glass fibers, nominal fiber diameter 3.0 ⁇ m and the same composition as the 206 fibers, and A20-BC- Vi inch glass fibers.
• the furnish was stirred in the mixer for about one minute, after which time a kraft pulp slurry which had a Canadian freeness of 57cc and a consistency of 1.235 percent was added to the furnish in the mixer.
• the composition in the mixer after the pulp addition, contained about 7 parts by weight of Schuller 206 glass fibers, about 1 part by weight of each of Schuller 210 glass fibers, A20-BC-y2 inch glass fibers, and about 0.6 part by weight of pulp fibrils.
• the furnish and the pulp were stirred for about two minutes, after which time the pulp-containing furnish was charged to the headbox of the pilot plant machine.
• An addition of 0.6 part by weight of pulp fibrils from red wood pulp that had been beaten to a Canadian freeness less than 100 cc was then made to the material in the headbox, and the furnish which resulted was flowed onto the advancing wire to produce a separator having a grammage of 30 g/m 2 at a thickness of 0.15 mm.
• the separator was ultimately heated in a drying oven to about 150° for 30 minutes.
• the separator had a loss on ignition a little over 12 percent w/w, indicating a total pulp content of about 12 percent w/w.
• the procedure described in this paragraph constitutes the best mode presently contemplated by the inventors with respect to the production of battery separator material according to the invention.
• Glass fiber separator hand sheets were also produced from other furnishes which contained varying amounts of kraft pulp that had been beaten to a consistency of 0.9906 percent and a Canadian freeness of 57cc.
• the furnishes also contained the previously identified Schuller 206, 210X and A20-BC-'/2 inch glass fibers.
• the hand sheets were produced in a laboratory apparatus by depositing a furnish on a wire or screen, and draining the furnish.
• the apparatus comprised a tank with a screen in the bottom, a drain below the screen, a valve which opened and closed the drain, and paddles which were moved back and forth to simulate the movement of a furnish in commercial papermaking apparatus and establish a "machine direction" parallel to the direction of paddle movement.
• the furnish and the pulp were stirred for about two minutes, after which the valve was opened so that the water drained through the screen while the separator was retained on the screen.
• the furnish that was charged contained enough glass fibers to produce a separator having a grammage of 30 g/ ⁇ r at a thickness of 0.15 mm.
• the separator hand sheet was heated in a drying oven to about 150° for 30 minutes.
• compositions, in percent w/w, of representative ones of the furnishes and the properties of the hand sheets that were produced are set forth in Table II, below, where, as in other tables herein, unless otherwise indicated, tensile strength is in pounds per inch of width of the separator (multiply times 0.175 to convert to kilonewtons per meter), elongation is in percent, stiffness is "Gurlcy Stiffness" in mg, pore sizes arc in ⁇ m, electrical resistance is in ohms per square inch of the separator, and loss on ignition is in percent w/w.
• the compositions of the furnishes are given in the following table:
• Control glass fiber separator hand sheets were produced by the same method from a furnish which was composed of 80 percent w/w of Schuller 210X glass fibers, 10 percent w/w of A20-BC- 1 /2 inch glass fibers and 10 percent w/w Schuller 206 glass fibers.
• the average test results for two control sheets are set forth in Table III, below:
• Thickness in mm x 1000 of samples of the hand sheets produced as described in Examples 2 through 6 and of the control sheets was also determined under various loads, both in an as produced condition and after having been wet with 7 times its dry weight of sulfuric acid, specific gravity 1.286. All thicknesses reported herein were determined by the method described in U.S. patent No.5, 336,275. The example numbers are column headings in Table IV, below, and thicknesses (the values reported are measured thicknesses in mm x 1000) when the samples were in the as produced condition, at applied loads in KPa indicated in the left column, are set forth under the identifying headings:
• 4 through 9 are skewed in the sense that, for example, a given distance between the first and second points represents a change from 0.55 psi (3.79 KPa) to 0.88 psi (6.06 KPa), while the same distance between the last two points represents a change from 4.19 psi (28.87 KPa) to 6.19 psi (42.65 KPa).
• Thickness and rebound thickness measurements were also made on the separator materials of Examples 2 through 6 and the controls after the materials had been wet with sulfuric acid having a specific gravity of 1.286.
• the applied loads in KPa are given in the left hand column of Table VII, below, and thicknesses are set forth under the headings which identify the samples; the reported thicknesses are 1000 times the measured thicknesses of the separator in mm:
• Glass fiber separator hand sheets were also produced by the method described in Example 1 from other furnishes which contained varying amounts of kraft pulp that had been beaten to a consistency of 0.9906 percent and a Canadian freeness of 57cc, and were then dipped in a latex, 3 percent w/w solids.
• the final compositions, in percent w/w, of representative ones of the furnishes are set forth in Table IX, below, and the properties of separators produced from the furnishes are set forth in Table X, below, where thickness of the separator material is in mm:
• Example 1 Still other glass fiber separator hand sheets were produced by the method described in Example 1 from substantially the furnish of Examples 7-1 which contained various small amounts of kraft pulp that had been beaten to a consistency of 1.235 percent and a Canadian freeness of 57cc.
• the final compositions, in percent w/w, of representative ones of the furnishes are set forth in Table XI, below, and their properties are set forth in Table XII, below, where thickness is in mm:
• Control glass fiber separator hand sheets were produced by the same method from a furnish which was composed of 80 percent w/w of Schuller 210X glass fibers, 10 percent w/w of A-20-BC Vi inch glass fibers and 10 percent w/w Schuller 206 glass fibers.
• the test results, average of two, are set forth in Table XIII, below, where thickness is in mm:
• Fig. 1 is a computer generated plot of Frazier permeability (called CFM on the drawing) vs. cellulose content. It will be noted that Fig. 1 has points on the X axis for 1.25, 1.5, 1.75. 2.0, 2.25, 2.5 and 2.75 percent pulp. To cause the plot to show these points, for which there was no experimental data, Frazier permeability was calculated 30 for each of these pulp contents by interpolation between the experimental values at 1.0 percent and at 3.0 percent.
• the experimental and calculated data input to generate Fig. 2 are set forth below: Percent w/w cellulose Frazier Permeability
• Fig. 2 is composed of two computer generated plots of tensile strength in pounds per inch (machine direction, in one case, and cross direction in the other) vs. cellulose content. It will be noted that Fig. 2 has points on the X axis for Q 1.25, 1.5, 1.75. 2.0. 2.25, 2.5 and 2.75 percent pulp. To cause the plot to show these ordinate points, for which there was no experimental data, tensile strength in both directions was calculated for each of these pulp contents by interpolation between the experimental values at 1.0 percent and at 3.0 percent.
• the experimental and calculated data input to generate Fig. 2 are set forth below:
• Still other glass fiber separator hand sheets were produced by the method described in Example 1 from furnishes containing 35 parts by weight of 206 glass fibers, 65 parts by weight of 210 glass fibers and about 1-2 parts by weight of kraft pulp that had been beaten to various Canadian freenesses.
• the Canadian freeness of representative ones of the furnishes and various properties of the separators produced therefrom are set forth in Table XIV, below, where thickness is in mm.
• the loss on ignition (“LOI") of the hand sheets is the best indication of the cellulose content of the furnish from which it was produced.
• a hand sheet containing no cellulose can be expected to have a loss on ignition of about l ⁇ %.
• Still other glass fiber separator hand sheets were produced by the method described in Example 1 from furnishes containing 35 parts by weight of 206 glass fibers, 65 parts by weight of 210 glass fibers and 3-5 parts by weight of kraft pulp that had been beaten to various Canadian freenesses.
• the Canadian freeness of representative ones of the furnishes and various properties of the separators produced therefrom are set forth in Table XV, below, where thickness is in mm:
• Still other glass fiber separator hand sheets were produced by the method described in Example 1 from furnishes containing 35 parts by weight of 206 glass fibers, 65 parts by weight of 210 glass fibers and 9 to 11 parts by weight of kraft pulp that had been beaten to various Canadian freeness.
• the Canadian freeness of representative ones of the furnishes and various properties of the separators produced therefrom are set forth in Table XIV, below, where thickness is in mm:
• separator material made from first fibers which impart to the sheet an absorbency greater than 90% and second fibers which impart to the sheet an absorbency less than 80% wherein the first and second fibers arc present in such proportions that the sheet has an absorbency of from 75 to 95%, when saturated with electrolyte, still has unfilled voids so that gas can transfer from plate to plate for recombination.
• Such separator material can be produced according to the instant invention by adding to a slurry containing, in suitable proportions, first fibers which impart to the sheet an absorbency greater than 90% and second fibers which impart to the sheet an absorbency less than 80%, from 0.2 percent w/w to 20 percent w/w of a slurry of cellulose fibrils having a Canadian freeness sufficiently low that a separator material produced from the resulting slurry has a tensile strength greater than an otherwise identical separator where glass fibers having an average diameter greater than 1 ⁇ m replace the cellulose fibrils.
• the fibers which impart to the sheet an absorbency less than 80% include both relatively coarse glass fibers and hvdrophobic organic fibers.
• Polyethylene, polypropylene, acrylic and polyester fibers are examples of preferred hydrophobic organic fibers.
• a preferred separator according to the invention having an absorbency (as defined in the above identified Badger patent, of from 75 to 95% which, when saturated with electrolyte, still has unfilled voids so that gas can transfer from plate to plate for recombination contains 33.6 parts by weight Schuller 206 glass fibers or an equivalent, 50.4 parts by weight Schuller 210X fibers or an equivalent, 11 parts by weight Schuller A20-BC V ⁇ inch glass fibers or equivalent, and 5 parts by weight of polyethylene fibers, and, in addition, from 0.2 percent w/w to 20 percent w/w of cellulose fibrils from a slurry having a Canadian freeness sufficiently low that the separator material has a tensile strength greater than an otherwise identical separator where glass fibers having an average diameter greater than 1 ⁇ m replace the cellulose fibrils.
• an absorbency as defined in the above identified Badger patent, of from 75 to 95% which, when saturated with electrolyte, still has unfilled voids so that gas can transfer from plate to plate for

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• 1997
  • 1997-06-30 EP EP97931533A patent/EP0913006A4/en not_active Withdrawn
  • 1997-06-30 JP JP10504455A patent/JP2000513865A/ja not_active Ceased
  • 1997-06-30 BR BR9710134A patent/BR9710134A/pt not_active Application Discontinuation
  • 1997-06-30 CA CA002260005A patent/CA2260005C/en not_active Expired - Fee Related
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  • 1997-06-30 WO PCT/US1997/011579 patent/WO1998000875A1/en active IP Right Grant
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