Patent Publication Number: US-2015086838-A1

Title: Battery separator having improved wettability and methods of use therefor

Description:
BACKGROUND OF THE INVENTION 
     Lead-acid batteries are characterized as being inexpensive and highly reliable. Therefore, they are widely used as an electrical power source for starting motor vehicles or golf carts and other electric vehicles. Lead-acid batteries commonly include a separator that is positioned between the positive and negative electrodes of the battery. The environment with lead-acid batteries is rather harsh. Accordingly, the batteries&#39; components, including the battery separator, must be able to withstand these environments. For example, battery separators are required to fuction in the battery&#39;s electrolyte solution, which commonly includes a relatively high water concentration. As such, conventional binder chemistries are typically hydrophobic. Hydrophobic binders are commonly used to ensure that the binder remains coupled with the fibers instead of dissolving and/or breaking down in the electrolyte&#39;s aqueous solution. Because of an increasing demand for lead-acid batteries, there is a constant need for lead-acid batteries having improved properties or characteristics. 
     BRIEF SUMMARY OF THE INVENTION 
     The embodiments described herein provide lead-acid battery separators that exhibit increased acidophilicity and/or hydrophilicty. Such mats may be especially useful in flooded-type lead acid batteries in which the positive and negative electrodes are immersed in the battery&#39;s electrolyte solution. According to one embodiment, a lead-acid battery is provided. The lead-acid battery includes a positive plate or electrode, a negative plate or electrode, and a separator that is disposed between the positive plate and the negative plate to electrically insulate the positive and negative plates. The separator includes a microporous polymer membrane and at least one nonwoven fiber mat that is positioned adjacent and coupled to a surface of the microporous polymer membrane to reinforce the microporous polymer membrane. The nonwoven fiber mat includes a plurality of glass fibers, an acid resistant binder that couples the plurality of glass fibers together to form the nonwoven fiber mat, and a polymer component that is impregnated within the plurality of glass fibers. The polymer component is capable of interacting with water or an electrolyte of the lead-acid battery to increase the wettability of the nonwoven fiber mat by enabling the polymer coated glass fibers to form a contact angle with a 33 wt. % sulfuric acid solution of 70°, 50°, or less. 
     In some embodiments, the polymer component is a functional group that is coupled with a polymer backbone of the acid resistant binder. The functional group may include a hydroxyl group (OH), a carboxyl group (COOH), a carbonyl group (═O; aldehydes and ketones), an amino group (NH 2 ), a sulfhydryl group (—SH), a phosphate group (—PO 4 ), and the like. These functional groups are said to be hydrophilic because they interact with (or dissolve in) water by forming hydrogen bonds. These functional groups typically are polar or can ionize. In most cases, these functional groups are also acidophilic (to the electrolyte, i.e., ˜30 wt. % sulfuric acid used in lead acid batteries) since the majority of the electrolyte is still water. Due to this hydrophilicity/acidophilicity, the polymer can be wetted by water (or ˜30% wt. % sulfuric acid). Stated differently, hydrophilic, acidophilic, and wettable are considered inter-changeable throughout this application. Similarly, hydrophilicity, acidophilicity, and wettability are inter-changeable. In other embodiments, the polymer component may be a polymer solution or emulsion (e.g., starch solution) that is separate from the acid resistant binder and that is added to the nonwoven fiber mat. In some embodiments, the acid resistant binder and the polymer component may be a blend of a hydrophobic binder and a hydrophilic binder. 
     In some embodiments, the nonwoven fiber mat may be a first nonwoven fiber mat that is positioned adjacent a first side or surface of the microporous polymer membrane and the separator may additionally include a second nonwoven fiber mat that is positioned adjacent a second side or surface of the microporous polymer membrane opposite the first nonwoven fiber mat. The second nonwoven fiber mat may include a plurality of glass fibers and an acid resistant binder that couples the plurality of glass fibers together to form the second nonwoven fiber mat. In some embodiments, the second nonwoven fiber mat also includes a polymer component that is impregnated within the plurality of glass fibers and that increase the wettability of the second nonwoven fiber mat. In such embodiments, the wettability of the first nonwoven fiber mat may be greater than the wettability of the second nonwoven fiber mat. 
     According to another embodiment, a separator for a lead-acid battery is provided. The separator may include a microporous polymer membrane and at least one nonwoven fiber mat that is positioned adjacent the microporous polymer membrane so as to reinforce the microporous polymer membrane. The nonwoven fiber mat may include a plurality of glass fibers and an acid resistant binder that couples the plurality of glass fibers together to form the nonwoven fiber mat. The acid resistant binder may have or include one or more hydrophilic functional groups that are coupled with a backbone of the acid resistant binder. The one or more hydrophilic functional groups may increase the wettability of the nonwoven fiber mat by enhancing the nonwoven fiber mat&#39;s ability to function or interact with water or an electrolyte of a lead-acid battery. In some embodiments, the cured acid resistant binder may form a contact angle with a 33 wt. % sulfuric acid solution of 70° or less. In other embodiments, the cured acid resistant binder may form a contact angle with the 33 wt. % sulfuric acid solution of 50° or less. The acid resistant binder may be applied to the glass and/or polymeric fibers so that upon curing, the acid resistant binder coats the glass and/or polymeric fibers. 
     In some embodiments, the one or more hydrophilic functional groups may include a a hydroxyl group (OH), a carboxyl group (COOH), a carbonyl group (═O; aldehydes and ketones), an amino group (NH 2 ), a sulfhydryl group (—SH), a phosphate group (—PO 4 ), and the like. In some embodiments, the acid resistant binder may include a blend of a hydrophobic binder and a hydrophilic binder. In some embodiments, a second nonwoven fiber mat may be positioned adjacent a second side of the microporous polymer membrane so that the microporous polymer membrane is sandwiched between two nonwoven fiber mats. The second nonwoven fiber mat may include a plurality of glass fibers and an acid resistant binder that couples the plurality of glass fibers together to form the second nonwoven fiber mat. The acid resistant binder of the second nonwoven fiber mat may also include one or more hydrophilic functional groups that increase the wettability of the second nonwoven fiber mat by enhancing the second nonwoven fiber mat&#39;s ability to function or interact with water or an electrolyte of a lead-acid battery. In some embodiments, the wettability of one of the nonwoven fiber mats may be greater than the wettability of the other nonwoven fiber mat. 
     In some embodiments, the acid resistant binder may include at least two different functional groups that are coupled with the backbone of the acid resistant binder. In such embodiments, one of the functional groups may be a hydroxyl group. 
     According to another embodiment, a method of manufacturing a separator for a lead-acid battery is provided. The method may include providing a microporous polymer membrane and providing a plurality of entangled glass fibers. The method may also include applying an acid resistant binder to the plurality of entangled glass fibers to couple the plurality of glass fibers together to form a nonwoven fiber mat. The acid resistant binder may include one or more hydrophilic functional groups that are coupled to a backbone of the acid resistant binder. The one or more hydrophilic functional groups may be functional with water or an electrolyte of a lead-acid battery such that the nonwoven fiber mat exhibits increased wettability. The method may further include coupling the nonwoven fiber mat with the microporous polymer membrane to reinforce the microporous polymer membrane. 
     In some embodiments, the method additionally includes grafting the hydrophilic functional groups onto the backbone of the acid resistant binder. In some embodiments, the method additionally includes neutralizing the one or more hydrophilic functional groups via an acid to increase the hydrophilicity of the acid resistant binder. The one or more hydrophilic functional groups may be neutralized prior to the acid resistant binder being applied to the plurality of entangled fibers, or the one or more hydrophilic functional groups may be neutralized subsequent to formation of the nonwoven fiber mat. 
     In some embodiments, the method may additionally include forming a second nonwoven fiber mat and coupling the second nonwoven fiber mat to the microporous polymer membrane so that the microporous polymer membrane is sandwiched between two nonwoven fiber mats. The second nonwoven fiber mat may include a plurality of entangled fibers and an acid resistant binder that couples the plurality of entangled fibers together to form the second nonwoven fiber mat. The separator may be positioned between electrodes of a lead-acid battery to electrically insulate the electrodes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described in conjunction with the appended figures: 
         FIG. 1  illustrates a battery separator for separating oppositely charged plates or electrodes of a lead-acid battery, according to an embodiment. 
         FIG. 2  illustrates a front exploded view of a lead-acid battery cell, according to an embodiment. 
         FIG. 3  is a method of manufacturing a battery separator for a lead-acid battery, according to an embodiment. 
     
    
    
     In the appended figures, similar components and/or features may have the same numerical reference label. Further, various components of the same type may be distinguished by following the reference label by a letter that distinguishes among the similar components and/or features. If only the first numerical reference label is used in the specification, the description is applicable to any one of the similar components and/or features having the same first numerical reference label irrespective of the letter suffix. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The ensuing description provides exemplary embodiments only, and is not intended to limit the scope, applicability or configuration of the disclosure. Rather, the ensuing description of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing one or more exemplary embodiments. It being understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the invention as set forth in the appended claims. 
     The embodiments described herein provide lead-acid battery separators that exhibit increased acidophilicity and/or hydrophilicty. Such mats may be especially useful in flooded-type lead acid batteries in which the positive and negative electrodes are immersed in the battery&#39;s electrolyte solution. In such environments, the battery separators described herein exhibit increased wettablitiy when compared with conventional battery separators. The increased wettablitiy of the separators described herein facilitate the overall electrochemical reacton within battery cells. For example, the increased wettability may enhance the water/electorlyte availability at the separator/electrode interface and therefore protect the electrodes from exposure to air and/or enhance efficiency of electrochemical reaction, may reduce the internal electrical resistance of the cell, and/or extend the lifteime of the battery. 
     The increased acidophilicity and/or hydrophilicty of the battery separators is achieved by providing a fiber mat having hydrophilic properties. Conventional fiber mats used in battery separators are often made of glass fibers which are typically hydrophilic and/or polymeric fibers (e.g., polyolefin, polyester, etc.), which are inherently hydrophobic. The inherent hydrophobic property of polymeric fibers make the resulting mat relatively hydrophobic, especially if the mat is left untreated. Further, conventional binder chemistries are typically hydrophobic and are commonly used to ensure that the binder remains coupled with the fibers instead of dissolving and/or breaking down in the electrolyte&#39;s aqueous solution. As such, even when hydrophilic glass fibers are used, the resulting mat is typically hydrophobic because the hydrophobic binder covers the glass fibers, which renders the mat hydrophobic. 
     The acidophilicity and/or hydrophilicty of the fiber mats described herein may be increased in several ways. For example, in some embodiments a polymer component or emulsion, such as a starch solution can be added to the fiber mat. In some embodiments, the polymer component or emulsion may be added to the fiber mat separate from an acid resistant binder that is used to couple the glass and/or polymer fibers together. In another embodiment, the polymer component or emulsion may be a hydrophilic functional group of the acid resistant binder so that no additional solutions or materials need be added to the fiber mat. In another embodiment, the binder may include a blend of a hydrophilic binder and a hydrophobic binder. In some embodiments, the polymer component or emulsion can be soluble in water, such as a superabsorbitive polymer. Such components/emulsions may be able to absorb a significant amount of water, for example up to 100 times or more water by weight. In some embodiments, the binder includes less than about 30% by weight of the hydrophilic functional group to prevent the resulting glass mat from swelling due to the absorption of water. In other embodiments, the binder may include more than 30% by weight of the hydrophilic functional group. In such embodiments, the resulting mat may swell due to water absorption. 
     In a specific embodiment, the fiber mat&#39;s binder includes a hydrophilic functional group or groups. The hydrophilic functional groups may be added or grafted onto the binder&#39;s polymer backbone. This is usually achieved during the synthesis of the binder (polymer), i.e., copolymerization. For example, acrylic acid or maleic anhydride monomer can be added into the main monomer (i.e., methyl methacrylate) for the targetted polymer (i.e., polymethyl methacrylate or PMMA) to copolymerize to incorporate carboxyl groups on the polymer backbone. As another example, acrylic acid can be added to ethylene to copolymerize to polymer (ethylene-acrylic acid). By this method, the functional groups are incorporated in the polymer backbone. In addition, different techniques are available to graft desirable functional groups to a polymer and a grafted co-polymer is obtained. By this method, the functional groups are grafted to the polymer backbone but not a part of it. The hydrophilic functional groups may form a hydrogen bond with water so as to allow the resulting fiber mat to be more hydrophilic. Similar to the polymer component/emulsion, the hydrophilic functional groups can be soluble in water and may be able to absorb a significant amount of water (e.g., up to 100 times or more water by weight). In one embodiment, the hydrophilic functional groups include multiple acid groups, which provide the super-absorbtive capabilities. 
     In some embodiments, the hydrophilic functional groups may include a quaternary amine (i.e., N + R 1 R 2 R 3 R 4 , where R 1 , R 2 , R 3 , and R 4  can be hydrogen, alkyl, alkenyl, cycloalkyl or cycloaklkenylene, etc), which allows the binder and fiber mat to be philic to water and sulfuric acid. In some embodiments, the possible counter-ion SO 4   2−  for the quaternary amine may participate in the electrochemical reaction by providing additional SO 4   2−  ions. Such binders and fiber mats may improve the reaction rate of the lead-acid battery thereby providing higher output current and capacity. 
     Having described several embodiments generally, additional aspects and features of the embodiments will be realized in relation to the figures, which are described hereinbelow. For convenience in describing the embodiments, the fibers of the various mats will be generally referred to as glass fibers. It should be realized, however, that other non-glass fibers may be used in the fiber mats in addition to, or in place of, the glass fibers. For example, various polymer fibers (e.g., polyolefin, polyester, and the like) may easily be substitued for, or used in addition to, the glass fibers without significantly affecting the resulting mat. In addition, as used herein, the term hydrophilic/acidophilic binder refers to a binder having a contact angle with 33 wt. % sulfuric acid (water for hydrophilic) medium of less than about 90°, preferably less than 70°, and most preferably less than 50°. In testing the contact angle of a binder, the binder may be spin-coated on a glass slide and then cured before being exposed to the above solution to measure the contact angle. In contrast, acidophobic as used herein refers to a binder having a contact angle with the above sulfuric acid concentration (hydrophobic for water) of greater than 70°, and more commonly greater than 90°. 
     EMBODIMENTS 
     Referring now to  FIG. 1 , illustrated is an embodiment of a battery separator  100  for separating oppositely charged plates or electrodes of a lead-acid battery (hereinafter separator  100 ). Specifically, separator  100  is positionable between a positive electrode and a negative electrode to physically separate the two electrodes while enabling ionic transport and, thus, complete a circuit to allow an electric current to flow between a positive terminal and a negative terminal of the battery. Separator  100  includes a microporous membrane, which is typically a polymeric film having negligible conductance (e.g., polyethylene film). The microporous polymer membrane includes micro-sized voids that allow ionic transport (i.e., transport of ionic charge carriers) across separator  100 . The microporous polymer membrane is typically thin and dimensionally unstable or weak. 
     Positioned adjacent at least one surface of the microporous polymer membrane is a nonwoven fiber mat. The nonwoven fiber mat is typically made of glass fibers, but may be made of other fibers as well, such as various polymer fibers (e.g., polyolefin, polyester, and the like). The nonwoven fiber mat is bonded with the surface of the polymeric film to reinforce the microporous polymer membrane and provide dimensional stability. The reinforcing nonwoven fiber mat allows the separator  100  to be positioned between electrodes of a lead-acid battery while preventing tearing, ripping, or other damage to the microporous polymer membrane. 
     The glass fibers of the nonwoven fiber mat may have a fiber diameter between about 0.1 μm and 30 μm. In one embodiment, the nonwoven fiber mat includes only or mainly larger diameter glass fibers or glass fibers having a fiber diameter between about 10 μm and 20 μm, and more commonly between about 10 μm and 15 μm. In another embodiment, the nonwoven fiber mat includes only or mainly smaller diameter glass fibers or glass fibers having a fiber diameter between about 0.1 μm and 5 μm. In yet another embodiment, the nonwoven fiber mat includes a blend of larger diameter and smaller diameter glass fibers. For example, the blended nonwoven fiber mat may include glass fibers having a fiber diameter between about 0.1 μm and 5 μm and glass fibers having a fiber diameter between about 10 μm and 20 μm. 
     As described briefly above, the glass fibers may be coupled or bonded together via an acid resistant binder to form the nonwoven fiber mat. In some embodiments, the nonwoven fiber mat may also include a polymer component or emulsion that is impregnated within the plurality of glass fibers. The polymer component may interact with water or an electrolyte of the lead-acid battery such that the nonwoven fiber mat exhibits increased wettability. For example, the polymer component/emulsion may increase the wettability of the nonwoven fiber mat by enabling the polymer coated glass fibers to form a contact angle with a 33 wt. % sulfuric acid solution of 70° or less. In some embodiments, the polymer component may enable the polymer coated glass fibers to form a contact angle with the 33 wt. % sulfuric acid solution of 50° or less. The polymer component/emulsion may be added to the nonwoven fiber mat separate from and in addition to the acid resistant binder. More commonly, however, the polymer component/emulsion may be included with the acid resistant binder (e.g., grafted on the polymer backbone) so that only the acid resistant binder needs to be added to the glass fibers to enable the nonwoven fiber mat to exhibit increased wettability. In such embodiments, the cured acid resistant binder—or binder coated glass fibers—may form a contact angle with a 33 wt. % sulfuric acid solution of 70° or less, and in some embodiments, may form a contact angle with the 33 wt. % sulfuric acid solution of 50° or less. 
     As described herein, the acid resistant binder may be applied to a glass or other material slide and cured to form a solid binder surface. The 33 wt. % sulfuric acid solution may then be applied to the solid binder surface to enable measuring of the contact angle between the sulfuric acid solution and the binder. When the acid resistant binder is applied to the glass or polymer fibers of a mat, the binder typically coats the fibers. The binder is then cured so that the fibers include a solid coating of the binder. In such instances, the binder may enable the fibers, which may typically be hydrophobic, to form a contact angle of 70°, 50°, or less with the 33 wt. % sulfuric acid solution. As described herein, hydrophobic binders are commonly used in the formation of fiber mats. As such, the fibers of these conventional fiber mats typically have a hydrophobic binder coating after curing. Therefore, the binders and/or fibers of such conventional mats are unable to form contact angles of 70°, 50°, or less with the 33 wt. % sulfuric acid solution. In other words, the mat is not wettable by the sulfuric acid solution. 
     In some embodiments, the acid resistant binder may include one or more hydrophilic functional groups that interact with water or an electrolyte of the lead-acid battery such that the nonwoven fiber mat exhibits increased wettability. In some embodiments, the one or more hydrophilic functional groups may include: hydroxyl group (OH), a carboxyl group (COOH), a carbonyl group (═O; aldehydes and ketones), an amino group (NH 2 ), a sulfhydryl group (—SH), a phosphate group (—PO 4 ), and the like. In one embodiment, the acid resistant binder may include two or more different functional groups. In a specific embodiment, at least one of the functional groups is a hydroxyl group. The acid resistant binder may include up to about 50 wt. % of the one or more hydrophilic functional groups, although the acid resistant binder more commonly includes 0.01-10% wt. % of the one or more hydrophilic functional groups or 0.1-5% wt. % of the one or more hydrophilic functional groups. 
     The hydrophilic functional group may be added to or otherwise introduced in the polymer backbone of the acid resistant binder, such as by grafting the hydrophilic functional group onto the polymer backbone. In a specific embodiment, the acid resistant binder may be an acrylic copolymer with some self-crosslinking components. The above identified hydrophilic functional groups can be added or grafted onto the polymer backbone of the binder as described herein to make it more hydrophilic. After curing, such polyacrylic acid based binders typically have much lower contact angles in both water and sulfuric acid than conventional binders used for the battery separator mat. For example Table 1 below shows the contact angle of 4 test binders compared with a control binder after exposure to a 33 wt. % sulfuric acid solution. As shown, the 4 test binders exhibited contact angles of less than about 70° or less than about 50°, whereas the control binder exhibited a contact angle of greater than 70°. Incorporation of a —COOH group onto the polymer backbone of the binder may account for the reduction in contact angle of the test binders. 
     
       
         
           
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Binder 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Rhoplex HA-16 from 
                 Test 
                 Test 
                 Test 
                 Test 
               
               
                   
                 Dow Chemical 
                 binder 1 
                 binder 2 
                 binder 3 
                 binder 4 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Contact angle 
                 77.2 +/− 1.0 
                 45.7 +/− 1.5 
                 50.8 +/− 1.4 
                 57.3 +/− 0.3 
                 58.2 +/− 3.5 
               
               
                 (in 33 wt. % 
               
               
                 sulfuric acid) 
               
               
                   
               
            
           
         
       
     
     Table 2 below shows the contact angle of a blended binder and the components of the blended binder after exposure to a 33 wt. % sulfuric acid solution. As shown, the blended binder included a combination of a first binder—i.e., Hycar 26-0688—and a second binder—i.e., Test binder 5. Test binder 5 is based on the chemistry of SMAc-TEA (where SMAc represents Styrene Maleic Anhydride Amic Acid, TEA is triethanolamine). Additional details of the composition of Test binder 5 are provided in U.S. patent application Ser. No. 12/697,968, filed Feb. 1, 2010, entitled “Formaldehyde-Free Protein-Containing Binder Compositions,” the entire disclosure of which is incorporated by reference herein. Test binder 5 is more hydrophilic than Hycar 26-0688 due to its available —COOH functional groups after curing. As shown in Table 2, the blended binder compositions worked synergistically to lower the contact angle to about 77°. 
     
       
         
           
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Avg. Contact 
               
               
                 Binder: 
                 Liquid: 
                 Angle (°): 
               
               
                   
               
             
            
               
                 Hycar 26-0688/Test binder 5 
                 Sulfuric Acid (33 wt. %) 
                 77.7 
               
               
                   
                 Water 
                 66.2 
               
               
                 Hycar 26-0688 
                 Sulfuric Acid (33 wt. %) 
                 84.5 
               
               
                   
                 Water 
                 76.9 
               
               
                 Test binder 5 
                 Sulfuric Acid (33 wt. %) 
                 80.7 
               
               
                   
                 Water 
                 65.7 
               
               
                   
               
            
           
         
       
     
     When an amino group (NH2), or NR 1 R 2  (where R 1  and R 2  can be hydrogen, alkyl, alkenyl, cycloalkyl or cycloaklkenylene, etc), is used as the hydrophilic functional group, its hydrophilicity can be further enhanced through neutralization by an acid, such as sulfuric acid so the polymer binder is cationic. Neutralization by the acid may occur before the binder is used to couple the fiber mat&#39;s glass fibers together, or after the nonwoven fiber mat is formed. Similarly, the inclusion of hydroxyl groups (OH) in addition to one of aforementioned functional groups can significantly enhance the hydrophilicity of the acid resistant binder and, therefore, the resulting nonwoven fiber mat. 
     In another embodiment, the binder used to couple the glass fibers may include a blend of a plurality of components. For example, the binder may include a compatible blend of a hydrophobic binder and a hydrophilic binder. The resulting binder and fiber mat may exhibit some hydrophobic and hydrophilic properties or capabilities. In some embodiments, the binder may include a blend of about 50% of a hydrophobic binder and about 50% of a hydrophilic binder. For example, in a specific embodiment, the binder blend may include Hycar® 26-0688, which is a hydrophobic binder, and a more hydrophilic component, Test binder 5 (or Test binders 1-4), which have carboxylic groups and are compatible with Hycar® 26-0688. In another embodiment, the binder may include a blend of about 1-99% of a hydrophobic binder and about 1-99% of a hydrophilic binder, depending on how much hydrophilicity is needed. 
     In some embodiments, separator  100  may include a second nonwoven fiber mat that is positioned adjacent an opposite surface of the microporous polymer membrane so that the microporous polymer membrane is sandwiched between two nonwoven fiber mats. The second nonwoven fiber mat may also include a plurality of glass fibers and an acid resistant binder that couples the plurality of glass fibers together to form the second nonwoven fiber mat. In some embodiments, the binder of the second nonwoven fiber mat may not include hydrophilic functional groups and/or be impregnated with a polymer component or emulsion. Stated differently, the second nonwoven fiber mat may not have or exhibit increased wettability properties or characteristics like the other nonwoven fiber mat. In such embodiments, the microporous polymer membrane may be sandwiched between one nonwoven fiber mat that exhibits increased wettability and another nonwoven fiber mat that does not exhibit increased wettability. Such a separator  100  may be positioned within a battery cell so that the nonwoven fiber mat exhibiting increased wettability faces the positive electrode. 
     In another embodiment, the acid resistant binder of the second nonwoven fiber mat may also include one or more hydrophilic functional groups, and/or a polymer component or emulsion, that interact with water or an electrolyte of the lead-acid battery such that the second nonwoven fiber mat exhibits increased wettability. In such embodiments, the microporous polymer membrane may be sandwiched between two nonwoven fiber mats that both exhibit increased wettability as compared to conventional mats. In some embodiments, one of the nonwoven fiber mats may be configured to have or exhibit an increased amount of wettability as described herein compared with the other nonwoven fiber mat. The resulting separator  100  may be positioned within a battery cell so that the nonwoven fiber mat exhibiting the most wettability faces the positive electrode. 
     Referring now to  FIG. 2 , illustrated is front exploded view of a lead-acid battery cell  200 . The lead-acid batter cell  200  may represent a cell used in a flooded lead-acid battery. Each cell  200  may provide an electromotive force (emf) of about 2.1 volts and a lead-acid battery may include 3 such cells  200  connected in series to provide an emf of about 6.3 volts or may include 6 such cells  200  connected in series to provide an emf of about 12.6 volts, and the like. Cell  200  includes a positive plate or electrode  204  and a negative plate or electrode  214  separated by battery separator  220 . Positive electrode  204  includes a grid or conductor  206  of lead alloy material. A positive active material (not shown), such as lead dioxide, is typically coated or pasted on grid  206 . Grid  206  is also electrically coupled with a positive terminal  208 . In some embodiments, a reinforcement mat (not shown) may be coupled with grid  206  and the positive active material. The reinforcement mat may provide structural support for the grid  206  and positive active material. 
     Similarly, negative electrode  214  includes a grid or conductor  216  of lead alloy material that is coated or pasted with a negative active material (not shown), such as lead. Grid  216  is electrically coupled with a negative terminal  218 . A reinforcement mat (not shown) may also be coupled with grid  216  and the negative active material. The reinforcement mat may provide structural support for the grid  216  and negative active material. In flooded type lead-acid batteries, positive electrode  204  and negative electrode  214  are immersed in an electrolyte (not shown) that may include a sulfuric acid and water solution. 
     As described herein, separator  220  includes a microporous polymer membrane (e.g., polyethylene porous membrane or film) and a nonwoven fiber mat that is positioned adjacent at least one surface of the microporous polymer membrane. The nonwoven fiber mat reinforces the microporous polymer membrane and/or provides dimensional stability. The nonwoven fiber mat includes a plurality of glass fibers and an acid resistant binder that couples the plurality of glass fibers together to form the nonwoven fiber mat. The nonwoven fiber mat may also include a polymer component that is impregnated within the plurality of glass fibers and that functions or interacts with water or the lead-acid battery&#39;s electrolyte such that the nonwoven fiber mat exhibits increased wettability. As described above, the polymer component/emulsion may increase the wettability of the nonwoven fiber mat by enabling the polymer/binder coated glass fibers to form a contact angle with a 33 wt. % sulfuric acid solution of 70°, 50°, or less. 
     As described above, in some embodiments, the polymer component is a functional group that is coupled with a polymer backbone of the acid resistant binder. The functional group may include hydroxyl group (OH), a carboxyl group (COOH), a carbonyl group (═O; aldehydes and ketones), an amino group (NH 2 ), a sulfhydryl group (—SH), a phosphate group (—PO 4 ), and the like. The acid resistant binder may form a contact angle with a 33 wt. % sulfuric acid solution of 70° or less, and in some embodiments, may form a contact angle with the 33 wt. % sulfuric acid solution of 50° or less. In other embodiments, the polymer component may be a polymer solution or emulsion, such as a starch solution, that is added to the nonwoven fiber mat. The polymer solution or emulsion may be separate from the acid resistant binder. In yet other embodiments, the polymer component may include a blend of a hydrophobic binder and a hydrophilic binder as described above. 
     In some embodiments, separator  220  may also include a second nonwoven fiber mat that is positioned adjacent an opposite surface of the microporous polymer membrane so that the microporous polymer membrane is sandwiched between two nonwoven fiber mats. The second nonwoven fiber mat may include a plurality of glass fibers and an acid resistant binder that couples the plurality of glass fibers together to form the second nonwoven fiber mat. As described above, in some embodiments, the second nonwoven fiber mat may not include a polymer component so that the second nonwoven fiber mat does not exhibit increased wettability when compared with conventional separator fiber mats. In such embodiments, separator  220  includes one surface that exhibits increased wettability and one surface that does not exhibit increased wettability. 
     In other embodiments, the second nonwoven fiber mat may include a polymer component that is impregnated within the plurality of glass fibers and that increases the wettability of the second nonwoven fiber mat. As described herein, the polymer component may include one or more functional groups of the acid resistant binder, may include a solution or emulsion separate from the acid resistant binder, and/or include a blend of hydrophilic and hydrophobic binders. In some embodiments, the wettability of one of the nonwoven fiber mats may be greater than the wettability of the other nonwoven fiber mat. Separator  220  may be positioned within cell  200  so that the surface of separator  220  exhibiting the greatest wettability faces positive electrode  204 . Stated differently, separator  220  may be positioned within cell  200  so that the nonwoven fiber mat exhibiting the greatest wettability is positioned adjacent positive electrode  204 . Positioning the mat exhibiting the greatest wettability adjacent positive electrode  204  may enhance water availability at the PbO2/separator interface, thereby lessening the possibility of the cell drying out. 
     Methods 
     Referring now to  FIG. 3 , illustrated is an embodiment of a method  300  of manufacturing a battery separator that exhibits increased wettability properties or characteristics compared with conventional battery separators. The separators made from method  300  find usefulness in lead-acid battery and especially flooded-type lead-acid batteries. At block  310 , a microporous polymer membrane is provided. At block  320 , a plurality of entangled glass fibers are provided. At block  330 , an acid resistant binder is applied to the plurality of entangled glass fibers to couple the plurality of glass fibers together so as to form a nonwoven fiber mat. As described herein, the acid resistant binder includes one or more hydrophilic functional groups, and/or a polymer component, that function or interact with water or an electrolyte of the lead-acid battery such that the nonwoven fiber mat exhibits increased wettability. In a specific embodiment, hydrophilic functional groups are coupled to a backbone of the acid resistant binder, such as by grafting the hydrophilic functional groups onto the binder&#39;s polymer backbone. At block  340 , the nonwoven fiber mat is coupled with the microporous polymer membrane to reinforce and/or dimensionally stabilize the microporous polymer membrane. 
     In some embodiments, the method may further include neutralizing the one or more hydrophilic functional groups via an acid to increase the hydrophilicity of the acid resistant binder. In such embodiments, the one or more hydrophilic functional groups may be neutralized prior to the acid resistant binder being applied to the plurality of entangled fibers, or the one or more hydrophilic functional groups may be neutralized subsequent to formation of the nonwoven fiber mat. 
     In some embodiments, the method may further include forming a second nonwoven fiber mat and coupling the second nonwoven fiber mat to an opposite side of the microporous polymer membrane so that the microporous polymer membrane is sandwiched between two nonwoven fiber mats. The second nonwoven fiber mat may include a plurality of entangled fibers and an acid resistant binder that couples the plurality of entangled fibers together to form the second nonwoven fiber mat. As described herein, the second nonwoven fiber mat may or may not exhibit increased wettability properties and/or characteristics compared with conventional separator fiber mats. The method may additionally include positioning the separator between electrodes of a lead-acid battery to electrically insulate the electrodes. The separator may be positioned between the electrodes such that a surface exhibiting the greatest wettability is positioned adjacent, or otherwise faces, the positive electrode. 
     Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention. 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included. 
     As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a process” includes a plurality of such processes and reference to “the device” includes reference to one or more devices and equivalents thereof known to those skilled in the art, and so forth. 
     Also, the words “comprise,” “comprising,” “include,” “including,” and “includes” when used in this specification and in the following claims are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, acts, or groups.