Oxidation-resistant laminated separator

Abstract

Solves the problem of acid stratification and / or separator oxidation caused by contaminants. [Solution] A separator includes a microporous membrane and a diffusive mat attached thereto, the diffusive mat having a wick stress of at least about 2.5 cm in a "3-hour wick test." The diffusive mat may be made of synthetic fibers, glass fibers, natural fibers, or combinations thereof. The diffusive mat may include silicon dioxide. The separator may include rubber.

Description

[Technical field]

[0001] (Related Applications) This application claims the benefit of co-pending U.S. Provisional Application No. 61 / 774,144, filed March 7, 2013, which is incorporated herein by reference.

[0002] The present invention relates to a lead / acid battery separator having a diffusion mat applied to a microporous membrane. [Background technology]

[0003] In harsh thermal environment applications (e.g., congested areas with high traffic density, tropical or desert regions, applications other than power storage, etc.), batteries (e.g., lead acid batteries, particularly flooded lead acid (FLA) batteries) are prone to electrolyte loss. The electrolyte may be a mixture of water and acid (e.g., sulfuric acid). Loss of electrolyte exposes the electrodes to the gaseous environment contained within the cell head space, and the heat ultimately leads to dry-out of the electrode plates, which in turn accelerates corrosion of the electrodes leading to premature battery failure.

[0004] Also, during charging of a battery (e.g., a lead-acid battery), the acid in the electrolyte may stratify. Acid stratification adversely affects the performance and life of the battery. Traditional solutions to the problem of acid stratification in batteries (e.g., lead-acid batteries) include the use of "glass mats" that are applied to the separator. However, these glass mats significantly increase the cost of the separator, have large pores, and in some cases do not lend themselves to high speed manufacturing methods (e.g., forming "pockets" and applying them to the separator).

[0005] In some parts of the world (e.g. Asia), lead / acid batteries are sold as "dry charged" batteries. These dry charged batteries are purchased without water / acid. Dry charged batteries have a longer shelf life. However, users may not be careful to fill the battery with clean water / acid. Contaminated water / acid can result in oxidation of the separator and ultimately battery failure. The water / acid contaminants can be sourced from the water / acid container, e.g. a steel drum.

[0006] Also, oxidation of the separator, e.g., for lead / acid batteries, can reduce the cycle life of the battery, and thus the useful life of the battery. This oxidation is due to water or acid contaminants that are added to "dry charged" batteries. Oxidation causes embrittlement of the separator (e.g., as measured by loss of % elongation) that can lead to partial or complete failure of the battery.

[0007] Contaminants typically come from water and / or sulfuric acid added to the battery, as well as from impurities in the alloys and active materials contained in the electrode plates, and such contaminants can cause oxidation. For example, such contaminants typically include transition metals from the periodic table, such as chromium (Cr), manganese (Mn), titanium (Ti), and copper (Cu). Contaminant concentrations (Cr, Mn, and / or Ti) greater than about 2.0 ppm (2.0 mg / L) are not recommended. Cu contaminant concentrations greater than 26 ppm (26 mg / L) are not recommended.

[0008] US Patent No. 5,221,587 discloses the use of latex in separators to prevent antimony (Sb) poisoning in lead / acid batteries. Antimony is supplied by the lead plates (electrodes) of the battery. Antimony is used as an alloying element for lead to improve the manufacture of the plates and the cycle life of the battery. , would not consider the teachings of US Pat. No. 5,221,587 in arriving at a solution to the aforementioned separator oxidation problem.

[0009] US Pat. No. 6,242,127 discloses the use of a cured, porous rubber in a conventional polyolefin separator to improve the electrochemical properties (antimony inhibition) of the separator. There is a need for new separators (eg, for lead / acid batteries) that solve the aforementioned acid stratification and oxidation problems. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent No. 5,221,587 [Patent Document 2] US Patent No. 6,242,127 Summary of the Invention [Problem to be solved by the invention]

[0011] There is a need for battery separators for lead acid batteries that address the problem of acid stratification and / or oxidation of the separator due to contaminants. [Means for solving the problem]

[0012] The separator of the present disclosure includes a microporous membrane and a diffusive mat attached thereto. The diffusive mat has a wick stress of at least about 2.5 cm in the "3-hour wick test." The diffusive mat may be made of synthetic fibers, glass fibers, natural fibers, and combinations thereof. The diffusive mat may include silicon dioxide. The separator may include rubber. [Brief description of the drawings]

[0013] For the purpose of illustrating the invention, there is shown in the drawings a form which is preferred, however, the invention is not limited to the precise arrangements and instrumentalities shown. [Figure 1] FIG. 1 is a graph comparing the separator of the invention (diffusive mat) with a separator having a conventional glass mat. [Diagram 2] FIG. 2 is a graph comparing the separator of the invention (diffusive mat) with a separator having a conventional glass mat. [Diagram 3] FIG. 3 is a graph comparing the separator of the invention (diffusive mat) with a separator having a conventional glass mat. [Figure 4] FIG. 4 is a graph comparing the separator of the invention (diffusive mat) with a separator having a conventional glass mat. [Diagram 5] FIG. 5 is a graph comparing the separator of the invention (diffusive mat) with a separator having a conventional glass mat. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Lead / acid batteries are well known, for example, Linden's Battery Handbook, McGraw-Hill, New York NY (1995) and / or Besenhard's Battery Materials Handbook, Wiley, VCH Verlag, Weinheim, Germany (1999), both of which are incorporated herein by reference. The separator can be used in any lead / acid battery. In one embodiment, the lead / acid battery is a liquid lead / acid battery (FLA), such as those used in inverter batteries, enhanced liquid batteries (EFB), ISS batteries, stationary batteries, golf cart batteries, and the like.

[0015] In a first embodiment of the invention, a diffusive mat (DM) is included with a microporous membrane, e.g. For example, they enhance cell performance by providing superior diffusion properties that retard acid stratification, reduce antimony toxicity, increase oxidation resistance, and improve micro-short protection (due to dendrite growth). The DM laminate and microporous membrane also protect against water loss by preventing the electrodes from drying out due to electrolyte wicking (capillary action), thus resolving the dry-out phenomenon and protecting against acid stratification through improved diffusion properties.

[0016] Diffusive mats (DM) are not conventional glass mats. Conventional glass mats are passive and have no diffusivity or wicking ability. DMs have a wicking ability 25x or greater than conventional wet or dry glass mats. Wick rate is inversely proportional to acid stratification. Conventional glass mats have a wicking ability of 0.6cm or less in the "3 hour wick test." Meanwhile, DMs have a wicking ability of at least about 2.5cm in the "3 hour wick test." Alternatively, DMs can have a wicking ability of at least about 2.5cm in the "3 hour wick test," or at least about 3.0cm, or at least about 4.0cm, or in the range of about 2.5 to about 10.0cm, or in the range of about 4.0 to about 10.0cm, or combinations thereof.

[0017] The "3-Hour Wick Test" is performed by immersing a standard size coupon of the material in a liquid (sulfuric acid with a specific gravity of 1.280), waiting for three hours, and measuring the height of the liquid's movement up the material by capillary action. "Standard size coupon" means the same width and length so that a meaningful comparison can be made, although the thickness may vary depending on the natural thickness of the material being tested. For the "3-Hour Wick Test", the specimen has a width of 1 inch and a length of at least 40 cm. The specimen is marked every centimeter on the vertical axis of the specimen. The specimen is held in a clamp above the liquid and immersed in the liquid to a depth of 2 cm. Measurements on the specimen at 1, 5, 10 and 15 minutes are performed. scale Also, the wick height is measured for the maximum wick height on the sample after 3 hours.

[0018] The DM may be laminated onto the microporous membrane in any manner. The DM may be affixed to the microporous membrane by fusion or adhesive. The DM may be formed into a pocket, sleeve, leaf of an "S" wrap. The DM may be a nonwoven or woven or knitted fabric of fibers. The DM may be made of glass fiber, synthetic fiber, natural fiber, or a combination thereof. In one embodiment, the DM may be made of glass fiber and synthetic fiber. The DM has sufficient physical integrity to function as a positive electrode active material (PAM) retention mat and prevent the PAM from falling off. The DM protects the separator from strong oxidizing agents (e.g., Cr, Mn, Ti). Some examples of suitable DMs (INV) along with a comparison to a conventional glass mat (prior art) are listed in Table 1 below.

[0019] During use of the battery, a separator is placed in the battery against the DM or in contact with the battery's positive electrode (or plate). In one embodiment, the separator may encase the negative and / or positive plates. In another embodiment, the separator may encase the negative plate.

[0020] [Table 1]

[0021] The microporous membrane can be made of the following: a polyolefin sheet (e.g., polyethylene, polypropylene, ultra-high molecular weight polyethylene (UHMWPE) and combinations thereof), polyvinyl chloride (PVC), phenol-formaldehyde resin (e.g., including cellulose derivatives and / or synthetic fibers impregnated with phenol-formaldehyde resin), crosslinked rubber, or nonwoven fabric (e.g., non-combustible fibers including cellulose fibers or glass fibers). In one embodiment, the microporous membrane can be made of polyethylene, UHWMPE, or a combination of both, and can include particulate fillers, as is well known. The microporous membrane can have a ribbed profile. The ribs can be conventional, passing in the machine direction (MD) on the positive electrode side (e.g., to separate the separator from the anode in other components, or to form gas channels to facilitate gas escape and mixing during charging), but the ribs can also extend in the cross machine direction (CMD) on the negative electrode side (to retard acid stratification).

[0022] In another aspect of the invention, rubber can be added to the separator to solve oxidation problems caused by contaminants. Rubber as used herein means rubber latex, tire crumb, and combinations thereof. In one embodiment, the rubber can be uncrosslinked or uncured rubber. In another embodiment, the rubber latex can be natural or synthetic rubber latex. In another embodiment, the rubber can be natural rubber latex. In yet another embodiment, the rubber can be tire crumb. Natural rubber can be, for example, any grade (e.g., latex grade), including, for example, ribbed smoked sheet, white and light colored crepe, pure all-inclusive crepe or re-mill, dark brown crepe or amber, and plain bark crepe. Natural rubber can include Hevea rubber. Synthetic rubber can include, for example, methyl rubber, polybutadiene, chloropene rubber, and copolymer rubber. Copolymer rubbers include, for example, styrene / butadiene rubber, acrylonitrile / butadiene rubber, ethylene / propylene rubber (ELM and PERM), and ethylene / vinyl acetate rubber. Other rubbers include, for example, butyl rubber, bromobutyl rubber, polyurethane rubber, epichlorohydrin rubber, polysulfide rubber, chlorosulfonyl polyethylene, polynorborene rubber, acrylate rubber, fluorinated rubber, isoprene rubber, and silicone rubber. These rubbers can be used alone or in various combinations.

[0023] In one embodiment, the rubber can be filled into the microporous membrane. Filled, as used herein, means that the rubber is incorporated into the body of the separator and is not a layer formed onto the separator. Thus, the rubber is mixed or compounded into one or more materials used to form the separator. The rubber, e.g., latex, is chemically active (i.e., uncured and / or uncrosslinked) even after extrusion. Thus, the rubber is a component that is incorporated or dispersed or mixed uniformly throughout or into the separator material.

[0024] The rubber can be present in any proportion in the microporous membrane, as described above. In one embodiment, the rubber can be present in an amount of about 12% by weight or less, based on the weight of the microporous membrane when added to the compound (i.e., by weight of the raw materials prior to extrusion). In another embodiment, the rubber can be present in an amount of about 1-12% by weight of the microporous membrane. In another embodiment, the rubber can be present in an amount of about 1.2-6% by weight of the microporous membrane. In yet another embodiment, the rubber can be present in an amount of about 2-4% by weight of the microporous membrane. In yet another embodiment, the rubber can be present in an amount of about 2.5-3.5% by weight of the microporous membrane. In another embodiment, the rubber can be present in an amount of about 3% by weight of the microporous membrane. The microporous membrane can be manufactured by any conventional method, for example, a PE microporous membrane can be made by mixing the rubber with the processing oil, or by mixing the PE during extrusion.

[0025] (Example) Figures (graphs) 1-5 compare a separator with a conventional glass mat and a separator of the present invention with a diffusive mat (DM). The separators are the same, but one separator has a DM and the other has a conventional glass mat. The information shown in these graphs was generated using a 12V 150Ah battery (≈100% depth of discharge, DoD) with an enclosed positive plate (Figures 1-2) or an enclosed negative plate (Figures 3-5), discharged at 10.50V, 43A for 1 hour 54 minutes, followed by a recharge at 13.80V, 15A for 10 hours 6 minutes, using a conventional inverter battery simulation. The present invention may be embodied in other forms than those described in the specification without departing from the spirit and essential attributes of the present invention, as set forth within the scope of the present invention.

Claims

1. A separator for a lead-acid battery comprising a microporous membrane and a diffusion mat attached to the microporous membrane, The microporous membrane contains one or more selected from a polyolefin resin, a polyvinyl chloride resin, and a phenol-formaldehyde resin; The microporous membrane is impregnated with an uncrosslinked rubber, the diffusing mat has an electrolytic wicking capacity as defined by a wicking height of 2.5 cm to 10.0 cm when immersed in sulfuric acid having a specific gravity of 1.280 for 3 hours; The diffusion mat faces or contacts the anode or anode plate, the diffusing mat is made of synthetic fibers, glass fibers, or a combination thereof, and contains granular silica; The diffusion mat improves lead acid battery performance by preventing dryout of battery electrodes due to the electrolyte wicking ability and by preventing acid stratification due to the improved diffusion properties resulting from the electrolyte wicking ability, as compared to lead acid batteries having a glass mat.

2. The diffusion mat is 35 g / m ２ 10. The separator of claim 1 having a basis weight of greater than 100 gsm.

3. 2. The separator according to claim 1, wherein the uncrosslinked rubber is contained in the separator in an amount of 12% by weight or less.

4. 2. The separator according to claim 1, wherein the uncrosslinked rubber is contained in the separator in an amount of 2.5 to 3.5% by weight.

5. 2. The separator according to claim 1, wherein the uncrosslinked rubber is natural latex.

6. The separator according to claim 1 , wherein the uncrosslinked rubber is a synthetic latex.

7. The separator according to claim 1 , wherein the uncrosslinked rubber is a natural rubber.

8. 2. The separator of claim 1, wherein the microporous membrane is made from a microporous sheet of polyolefin.

9. The separator of claim 1 , wherein the diffusion mat comprises fiberglass.

10. The separator of claim 1 , wherein the diffusion mat comprises natural fibers.

11. The separator according to claim 1, wherein the diffusion mat has a thickness of 0.2 to 0.5 mm.

12. A lead-acid battery comprising the separator of claim 1.

13. 13. The lead acid battery of claim 12, wherein the lead acid battery is an inverter battery, an enhanced flooded battery (EFB), an ISS battery, a stationary battery, or a golf cart battery.

14. The separator of claim 1 , wherein the diffusion mat has a thickness greater than 0.2 mm.

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