ENHANCED LEAD-ACID BATTERY USING

POLYACRYLONITRILE FIBERS IN ACTIVE MATERIAL

RELATED APPLICATIONS

[0001] This application claims priority to United States Provisional Application No. 62/782,483, filed under 35 U.S.C. § 111(b) on December 20, 2019. The entire disclosure of the aforementioned application is incorporated by reference herein for all purposes.

BACKGROUND

[0002] The lead-acid battery is recognized for its advantages, such as low cost and high recycle rate. However, it also has its shortcomings, such as low energy density, low cycle-service life, and poor charge acceptance.

[0003] It is known to make use of polymeric material in a lead-acid battery for the purpose of enhancing electrical performance and cycle life, and also to prevent shedding of the active material and to reduce the antimony poisoning effect.

[0004] U.S. Patent No. 10,044,043 claims to improve capacity and cycle life and reduce shedding. The preferred embodiment disclosed involves large PET fibers (10-25 pm, point-bonded, density 0.5 oz./yd ² , and 4.3 mil thick). PET is a polymer that is melt-spun. The problem in actual use with this is that PET only reduces material shedding. PET staple fiber is commonly used as a binder in paste mixes. Its only benefit is to reduce shedding, and it has no influence on electrical properties.

[0005] U.S. Patent No. 6,509,118 discloses coating glass fiber surfaces with various polymers, including polyacrylonitriles and amphiphilic nitrogen-containing polymers. These patents claim to improve electrical performance and cycle life and to enhance the efficiency of the closed oxygen recombination cycle. However, the disclosed application is reserved to valve -regulated batteries.

[0006] U.S. Patent Application Publication No. 2018/0269451 discloses coating or impregnating a polymeric fiber with various materials. It also discloses enhancement of capacity, cycle life,“metalloid” poisoning, reduction in acid stratification, and reduction in material shedding on all forms of lead acid batteries. The material disclosed consists of fibers such as glass, synthetic, ceramic, or a combination thereof. Synthetic material is an overly broad category as synthetic material, such as nylon, easily degrades in the sulfuric acid concentrations found in lead-acid batteries. Fiber dimensions are also not identified. [0007] There is a need in the art for new and improved lead-acid batteries, and methods for making the same.

SUMMARY

[0008] The present disclosure provides for the incorporation of polymeric nanofibers such as polyacrylonitrile (PAN) fibers as an additive in the active material (positive, negative, or both), or as a woven or nonwoven mat used to cover the surface of the pasted electrode (positive, negative, or both) as a pasting paper or laminated onto or placed adjacent to a porous battery separator layer separating positive and negative electrodes, in a lead-acid battery. The polymeric nanofibers can enhance capacity, cycle life, and charge acceptance. The polymeric nanofibers can also reduce water loss and shedding of the active material. The polymeric nanofibers may generally have an average size of less than 1 micron, but may include a distribution of fiber sizes depending on the application.

[0009] The use of PAN fibers as an additive or woven or nonwoven mat solves the typical low electrical performance of a lead-acid battery by enhancing discharge capacity, cycle life, and charge acceptance. A PAN nonwoven mat can also reduce material shedding, both during handling in assembly and during battery use.

[0010] Provided herein is a lead-acid battery comprising an active material and an acid electrolyte, wherein the active material comprises polymeric nanofibers and a lead alloy, lead oxide, or a combination thereof. In certain embodiments, the polymeric nanofibers comprise PAN nanofibers.

[0011] Also provided herein is a method of making a lead-acid battery, the method comprising combining lead, lead oxide, water, acid, and a polymeric nanofiber to produce a paste mix; pasting the paste mix onto grids to produce coated grids; curing the coated grids to cure the paste mix on the coated grids; and adding an acid electrolyte to contact the coated grids to make a lead-acid battery.

[0012] Various aspects of the present disclosure will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1: Sectional view of a non-limiting example battery plate for a lead-acid battery.

[0014] FIG. 2: Sectional view of a non-limiting example battery architecture for a lead-acid battery.

[0015] FIG. 3: Graph showing that a lead-acid battery incorporating PAN pasting paper generates a higher discharge capacity than a standard lead-acid battery without PAN pasting paper. [0016] FIG. 4: Graph showing that a lead-acid battery incorporating PAN pasting paper has higher end-of-charge voltage than a lead-acid battery without PAN pasting paper. Higher end-of-charge voltage indicates better suppression of antimony poisoning with PAN pasting paper.

[0017] FIG. 5: Graph showing a 12V lead-acid battery operating at 50 cycles and 25A discharging at 100% depth of discharge. The lead-acid battery with PAN fiber in the active material had a higher end of charge voltage and charge efficiency than a lead-acid battery without PAN fiber.

[0018] FIG. 6: Graph showing a lead-acid battery with PAN fiber in the active material has a higher discharge and longer cycle life than a lead-acid battery without PAN fiber.

DETAILED DESCRIPTION

[0019] The present disclosure relates to lead-acid batteries that use polymeric nanofibers in the active material. The polymeric nanofibers may include, for example, polyacrylonitrile (PAN) fibers.

[0020] In general, a lead-acid battery is a rechargeable battery formed from a positive plate separated from a negative plate by an acid electrolyte. Lead acid batteries are a well-known source of energy. The conventional lead-acid battery consists of a plurality of positive plates and a plurality of negative plates separated by porous separators in an acid electrolyte. The electrolyte is generally a solution of sulfuric acid. The negative electrode of a fully charged lead-acid battery includes lead (Pb), and the positive electrode of a fully charged lead-acid battery includes lead dioxide (Pb0 ₂ ). In the discharged state, both the positive and negative plates become lead(II) sulfate (PbS04), and the electrolyte loses much of its dissolved sulfuric acid to become primarily water. The discharge process is driven by hydrated protons of the acid reacting with O ² ions of Pb0 ₂ to form strong O-H bonds in H2O.

[0021] At the negative battery plate, the following reaction occurs:

Pb (s) A HSO-4- (aq) PbS0 (s) ÷ H ^÷ (a ) + 2e - [0022] The release of two conducting electrons gives the lead electrode a net negative charge. As electrons accumulate, they create an electric field which attracts hydrogen ions and repels sulfate ions, leading to a double-layer near the surface. The hydrogen ions screen the charged electrode from the solution which limits further reactions unless charge is allowed to flow out of the electrode.

[0023] At the positive battery plate, the following reaction occurs:

PbQ ₂ (s) A HS0 <aq} + 3H*(aq) + 2e - PbS0 ₄ (s) A 2¾0(I)

[0024] Thus, the total reaction is as follows:

Pb(s) % PbOiCs) + 2H SC ₄ -(a ) 2PbS0 ₄ (s) + 2H ₂ G(1)

[0025] Certain aspects of lead-acid batteries are described in, for example, U.S. Patent No.

10,403,901, which is incorporated herein by reference for all purposes. In a non-limiting example, the plates of a lead-acid battery are generally made by pasting a leady oxide material over a lead wire grid, though other materials are possible and encompassed within the scope of the present disclosure. Separate positive and negative plates are pasted and cured, with each of the plates having a lug disposed on the top portion of the plate. Lead-acid batteries can include one or more battery separators that divide, or “separate”, the positive electrode from the negative electrode within a lead-acid battery cell. The separators are electrically insulating and keep the positive electrode physically apart from the negative electrode in order to prevent any electronic current passing between the two electrodes but allow ionic current between the electrodes with the least possible resistance. Prior to the plates being placed in the battery container, a separator is placed between each plate and the negative and positive plate lugs are joined by two separate plate straps, one for the positive plate lugs and one for the negative plate lugs.

[0026] Once the separators are placed into the container, the intercell connections may be made and the battery container and cover can be sealed together. The positive and negative posts may be welded in the cover, the acid is added, and the battery is formed electrochemically. As is well known, the chemical reaction between the battery plates and the acid produces an electric charge which can be used, for example, to start an automobile. The chemical reaction is reversible so that a generator in an automobile, for example, can recharge the battery. The electrochemical reactions occur at the interfaces between the active material and the acid electrolyte.

[0027] Referring now to FIGS. 1-2, an embodiment of an example lead-acid battery in accordance with the present disclosure is depicted. FIG. 1 depicts an example battery plate arrangement, and FIG. 2 depicts a corresponding example battery architecture. A grid 104 can provide the substrate for the battery plate 120A assembly, such as to provide the current collector (i.e., a substrate on which electrochemical active materials are pasted). Such a current collector can include a substrate having apertures (hence the term“grid”), such as can provide mechanical and structural support for the active material pastes and electrical conduction channels for current flow to and from the active materials. A corrosion layer that can develop at a surface of a generally available lead alloy grid 104 can maintain adhesion and electrical contact to the pasted active material. Accordingly, such grids 104 are generally specified to include good mechanical strength and hardness, low electrical resistivity, good corrosion resistance (e.g., with respect to a sulfuric acid electrolyte), a selective electrochemical activity window towards side reactions, recycle- ability, and economical manufacturability in high volumes.

[0028] Referring still to FIGS. 1-2, the grid 104 can include lead or a lead alloy. Lead alloys may include one or more of calcium, silver, tin, silicon, antimony, or carbon, and may optionally include one or more impurity species (e.g., dopants or other species) so as to enhance conduction. In alternative embodiments, the grid 104 may include, or may be formed entirely from, silicon. The grid 104 can include an ohmic contact layer 106A, such as a metal silicide, to enhance conduction between an active material 112A and the grid 104. Such a silicide can include a metal species such as nickel, cobalt, titanium, tantalum, tungsten, molybdenum, or combinations thereof. In an example, a corrosion layer 108 A can be included, such as to promote adhesion or to provide compatibility with an electrolyte in the electrolyte region 116A, or to strengthen contact between the active material 112A and the grid 104.

Other configurations can be used, such as including multiple film layers to provide one or more of the ohmic contact layer 106 A or adhesion layer 108 A.

[0029] The active material 112A can be provided in paste form, such as cured during fabrication. In accordance with the present disclosure, the active material 112A may include polymeric nanofibers, and may further include a lead alloy, lead oxide, or a combination thereof. Suitable lead alloys may include one or more of calcium, silver, tin, silicon, antimony, or carbon. The polymeric nanofibers may include, but are not limited to, PAN nanofibers. In some embodiments, the polymeric nanofibers have a size of less than 1 micron, as discussed in more detail below.

[0030] Referring still to FIGS. 1-2, one or more separators such as separator 114A can be used to create a cavity or preserve a region 116A for electrolyte. In an example, the electrolyte can be a liquid or gel, or can be included such as impregnating another material, to provide a combination of electrolyte and separator. In the example of FIGS. 1-2, a housing 122 can be provided, and can (but need not) fluidically isolate the electrolyte region 116A from other electrolyte regions between other plates.

[0031] Battery plates 120A can optionally include a tab 126 that extends from the battery plate 120A. Tab 126 can be made from any suitable conductive material, such as copper, aluminum, lead, lead alloy, silicon, or a combination thereof. Tab 126 can be formed integrally with the battery plates 120A at the time of the formation of the battery plate 120A. For example, both the tab 126 and the battery plate 120 A may be integrally formed as a one-piece construction from silicon by one or more methods such as casting, laser cutting, masked wet etching, molding, or silicon ingot casting. The tab 126 may, in some cases, be coated with a corrosion resistance layer including lead or a lead alloy.

[0032] The second surface of the battery plate 120A may include a second ohmic contact layer 106B, a second adhesion layer 108B, and a second active material 112B, such as generally including the same material as the layers on the first surface of the grid 104 described above. For example, the second active material 112B may include the same active material and polarity as the first active material 112A. Thus, the second active material 112B may include polymeric nanofibers, such as, but not limited to,

PAN nanofibers.

[0033] A positive -negative pair can be formed such as including the first plate 120A having a first polarity active material and a second plate 120B having an opposite second polarity active material, to form an electrochemical cell in the electrolyte 114, such as shown in FIG. 2. Such a single cell voltage can be around 2.1V, as one non-limiting example. A number of plates 120 of the same polarity can be arranged electrically in a parallel configuration to form a stack. Two stacks of opposite polarity can be arranged as a cell 132A. Individual cells 132A through 132N can be connected in series to assemble a battery pack 102 such that the voltage can be represented as N _s *V _ceii , where N _s represents the number of cells and V _ceii represents the cell voltage. In FIG. 2, a first terminal 130A can provide a first polarity, and a second terminal 130B can provide an opposite second polarity. The first and second terminals 130A, 130B can be coupled to the first cell 132A and the last cell 132N, respectively, and the cells can be coupled together serially using a first bus 123A through an“Nth” bus 124N. The battery plates 120A, 120B of the cells 132A through 132N can be connected by buses 124A through 124N connected with the optional tabs 126 that extend from the battery plates 120A, 120B. In an example, buses 124A through 124N for connecting battery plates 120A, 120B of the cells 132A through 132N together can be formed by coupling together the tabs 126 of each battery plate 120A of each cell 132A through 132N, respectively, and coupling together the tabs 126 of each battery plate 120B of each cell 132A through 132N, respectively, and coupling the coupled tabs 126 of battery plates 120A of each battery cell to the coupled tabs 126 of battery plates 120B of each adjoining battery cell serially, so the positive polarity battery plates and negative polarity battery plates of adjacent cells are linked, by using any suitable method, such as a cast-on strap (COS) lead casting process, by use of a torch and a comb shaped alignment, arc welding, or any other suitable welding method.

[0034] As noted above, the active material 112A, 112B may include polymeric nanofibers such as PAN nanofibers. In particular, the grids 104 may be pasted with a paste mix incorporating polymeric nanofibers such as PAN nanofibers. Polymeric nanofibers such as PAN nanofibers in the form of a slurry suspension may be added to the paste mix that forms the active material 112A, 112B. In other embodiments, polymeric nanofibers may be present in a pasting paper that covers the grids 104.

However, other polymeric nanofibers are possible and encompassed within the scope of the present disclosure. PAN is a polymer that may include at least 85% acrylonitrile monomer (having the basic monomer formula of -CH2CH(CN)-), typically about 89-90% acrylonitrile monomer, but may also include 4-10% non-ionic co-monomer (for example, vinyl acetate), and around 1% ionic co-monomer containing a sulfo (SO3H) or sulfonate (OSO3H) group. PAN nanofibers can also be substituted or combined with other polymers produced by wet-spinning processes, such as aramids (Kevlar, Nomex, Technora, Heracron, etc.), acrylics, and modacrylics (Nytril, Lastrile, etc.).

[0035] In some embodiments, the PAN nanofibers have a weight-average molecular weight of about 55,500 Da. PAN nanofibers may have a softening point in the range of from 190 °C to 240 °C, with no obvious melting point, and a decomposition temperature of about 327 °C. PAN may have a dielectric constant (i.e., a ratio of the permittivity of the material to the permittivity of free space) of 6.5, and a specific resistance of 2 x 10 ⁴ W-cm. [0036] PAN nanofibers may be produced from a variety of methods, including wet spinning, dry spinning, melt spinning, and electrospinning. Wet spinning is based on precipitation, where a polymer is drawn through a spinneret into a non-solvent. The prepared spinning dope is extruded into the non solvent and precipitation or coagulation occurs, producing fibers. Dry spinning is used to form polymeric fibers from solution. In dry spinning, the polymer is dissolved in a volatile solvent and the solution is pumped through a spinneret (die) with numerous holes (one to thousands).

[0037] PAN nanofibers may also be produced by melt spinning. In contrast to polymers such as PET, PAN will generally decompose if processed by melting. PAN degrades before reaching its melting point of 320 °C. However, water has a plasticizing effect on acrylic polymers and blocks the polar interactions between nitrile groups, causing a lowering of the melting point (to about 180 °C at 33% by weight water) and thus making melt spinning of PAN possible. Furthermore, adding a comonomer to PAN can also effectively reduce its melting point to make melt spinning of PAN possible.

[0038] PAN nanofibers may also be produced by electrospinning, in which a continuous strand of a PAN liquid (i.e., solution or melt) is ejected through a nozzle by a high electrostatic force onto a grounded collector as a non-woven fiber mat. Electrospinning can produce ultrafine nanofibers from commercially available PAN microfibers.

[0039] The polymeric nanofibers may be present in the active material in an amount ranging from about 1% by weight to about 3% by weight. In some embodiments, the active material includes PAN nanofibers in an amount of between 1-3% w/w ratio of PAN to oxide.

[0040] The incorporation of PAN as a fiber additive or as a woven or nonwoven covering can be done without any significant changes to current lead-acid battery manufacturing processes. For example, a PAN nonwoven mat can be wet laid without necessity for point bonding. In addition to improving electrical performance and life, its use as a nonwoven pasting paper can eliminate the need for a flash drying oven and reduce the generation of lead dust during handling and assembly of lead-acid battery cells. Thus, the cost to manufacture and capital expense of expanding environmental controls is reduced.

[0041] The preferred size of polymeric nanofibers is 100 nanometers to 5 pm, with a higher distribution of nanometer fibers. In some embodiments, the fiber diameter is less than 10 pm, with a preferred diameter in the range of 100-500 nm. In some embodiments, the polymeric nanofibers have an average size of less than 1 micron. The polymeric nanofibers may have an aspect ratio (i.e., ratio of length:width) of at least about 5:1. In some embodiments, the polymeric nanofibers have an aspect ratio of at least about 10:1. The polymeric nanofibers can be added directly in the paste mixing process for either positive or negative active material. The polymeric nanofiber content in the paste mix may range from 0.25% - 12% w/w ratio of polymeric nanofiber to oxide. [0042] The polymeric nanofiber can be added to the positive or negative paste mix as an additive, or it can be used to produce a woven or nonwoven mat useable as a pasting paper that covers the surface of the positive or negative pasted plate, or laminated onto a porous separator. A nonwoven mat may be preferable over a woven mat, but a woven mat is nonetheless possible and encompassed within the scope of the present disclosure. The pasting paper thickness can range from about 2 mils (0.002") to about 15 mils (0.015"), with preferred embodiment of about 4 mils (0.004"). Either form enhances the discharge capacity, cycle -life, and charge acceptance of the lead-acid battery.

[0043] As seen in the examples herein, the use of PAN in fiber or nonwoven mat form suppresses the antimony poisoning effect in lead-acid batteries. The use of PAN nanofibers can be a less expensive alternative to rubber or hybrid rubber-PE separators or modified PE separators to suppress the antimony poisoning effect. The PAN nanofibers can be used in flooded, gel, or valve -regulated lead-acid batteries.

[0044] The PAN fiber can also be combined with other polymeric or glass fibers in the pasting paper form for the purpose of improving its adherence to the active material surface. The PAN fiber can also be combined with carbon fiber in a pasting paper to further enhance battery electrical performance. The w/w content of the PAN fiber in a pasting paper can range from about 10% to about 100%, with a preferred embodiment of about 90-95% w/w content of PAN fiber. The PAN can be substituted or combined with other polymers produced by dry or wet-spinning such as Kevlar, Nomex, acrylics, or modacrylics.

[0045] Important to understanding the benefits of polymeric nanofibers in the active material of lead- acid batteries is the knowledge that there are many different pathways by which a lead-acid battery can fail or lose power or lifespan. As one example, if the active material is flaked or otherwise sheds from the positive electrode and comes into contact with the negative electrode, battery performance is reduced. Such a process is known as positive active material (PAM) shedding. As another example, as noted above, grids of positive electrodes in certain lead-acid batteries are made of lead antimony alloys to enable deep cycling performance. However, during deep cycling, antimony from the grid alloy dissolves into the electrolyte and reaches the negative electrode and deposits on it, dropping overvoltage for hydrogen evolution resulting in enhanced water hydrolysis, water loss, and poisoning of the negative electrode. This is known as antimony poisoning. Due to this phenomenon, such deep cycle batteries typically require maintenance through the periodic addition of water to make up for loss of water. As another example, a barrier of lead sulfate, which is not conductive, may form on the surface of the active material.

[0046] In accordance with the present disclosure, a lead-acid battery having polymeric nanofibers in the active material alleviates or eliminates the above issues, and provides for an improved battery in various ways. The polymeric nanofibers may be incorporated into the active material in any suitable way. The polymeric nanofiber may be coated onto the active material, or may be impregnated into the active material.

[0047] A paste mix with fibers may be created by combining lead oxide, lead, water, acid, and polymeric nanofibers. The lead oxide and lead may be in the form of a commercially available mix such as a litharge mix. The paste mix can then be pasted onto grids and cured to form the plates of active material. The polymeric nanofibers may be in a suspension, such as, for example, a 2% by weight suspension. The total amount of the polymeric nanofibers in the paste mix may be from about 0.33% w/w to about 1 % w/w. However, other amounts are possible and encompassed within the scope of the present disclosure.

[0048] As noted above, the grid may be a lead alloy grid. The lead alloy may include a metal such as antimony, calcium, or silver. This active material is generally very porous, having a typical pore size of a few microns. The active material may be, for instance, about 45% porous. The pores become sulfated as the battery is discharged. Advantageously, the polymeric nanofibers are small enough in size that they are able to penetrate the pores of the active material, which tend to be a few microns in size.

[0049] As noted above, in another embodiment, the polymeric nanofibers may be made into a pasting paper. Pasting paper is conventionally a microfiber product used to support wet lead paste in the manufacturing process. As an example, the polymeric nanofibers may be present in a slurry in water. A screen may be laid in the slurry, and water may be pulled out to create a pasting paper that can be pasted onto the grids. The polymeric nanofibers bind metal ions on the surface of the negative plate. Antimony goes into solution as the positive plate oxidizes. By having pasting paper on both plates, the release of antimony from the positive plate is slowed down.

[0050] PAN is particularly advantageous as the polymeric nanofiber. PAN enhances battery performance regardless of whether the material is coated or impregnated into the active material. The functional groups on PAN, namely, the carboxyl, hydrazine, or imidazoline groups, have a chelating effect on the antimony, lead, and other metals in the lead alloy. Furthermore, PAN is hydrophilic.

Because of this, PAN is very wettable and improves diffusion of the electrolyte into the pores of the grid. Moreover, as mentioned above, because the PAN fibers include nanosized fibers, they fit into the pores of the active material. The size of the polymeric nanofibers matters. The pores on the active material are generally 1 micron or less in size. Thus, a 10-micron fiber will not effectively penetrate the pores.

Accordingly, the polymeric nanofibers are nano-sized fibers. To produce suitable nano-sized PAN fibers, PAN fibers can be exposed to a high shear mixing process to create nanofibers. Whereas many other types of fibers are not splittable in this manner, PAN nanofibers are splittable under shear to create a size of nanofibers desirable for use in lead-acid batteries. [0051] It is somewhat surprising that improved lead-acid battery performance results from the inclusion of PAN nanofibers in the active material because the metal chelating effect of PAN is known to be pH-dependent, and acid conditions are not favorable for this chelation due to a competitive adsorption between the H ⁺ ions and the metal ions. In fact, a low pH has been used specifically for desorption of metals from PAN. For instance, at a pH below 2.3, PAN nanofibers adsorbs almost no lead ions. At a higher pH, more amine groups are available to capture the metal ions via the interaction of the metal ions with the lone pair of electrons on the nitrogen. The maximum adsorption of metal ions by PAN has previously been observed in a pH range of 6.0-7.5. Thus, in the acid environment of a lead-acid battery, one would expect that PAN nanofibers would not chelate metal ions effectively. However, despite this, as the results in the examples herein show, the incorporation of PAN nanofibers into the active material of a lead-acid battery results in improved battery performance.

[0052] There may also be strong electrostatic repulsive force to the positively-charged metal ions created from the inclusion of PAN that may result in weak adsorption between metal ions, such as antimony ions, and the negative active material. The strong electrical repulsions may prevent metal ions from contacting the surface of the PAN nanofibers. As the pH increases, this electrostatic hindrance is reduced. Thus, PAN may chelate metal ions but may also repulse metal ions, such as antimony ions, and in this manner, PAN is especially advantageous as the polymeric nanofibers in the active material of a lead-acid battery.

[0053] The PAN nanofibers may also help with dynamic charge acceptance by helping the acid diffuse better, as evidenced by the improvement in charge efficiency in the antimony-containing battery. This prevents having to overcharge the battery.

[0054] PAN nanofibers may also alleviate the issue of a lead sulfate barrier by helping to transport the electrolyte deeper into the active material. The PAN nanofibers help with diffusion of the acid electrolyte into the active material. PAN nanofibers also retain the active material on the plates, preventing shedding from the positive plate.

[0055] For all the above reasons, PAN nanofibers are especially advantageous as the polymeric nanofibers. As shown in the examples herein, having PAN nanofibers in the active material of a lead-acid battery results in a higher discharge capacity than a standard lead-acid battery, a higher end-of-charge voltage than a standard lead-acid battery, which indicates better suppression of antimony poisoning, a higher end of charge voltage and charge efficiency than a standard lead-acid battery, and a higher discharge and longer cycle life than a standard lead-acid battery.

[0056] Furthermore, in some embodiments, the PAN nanofibers may be modified in various ways, or with various functional groups, for instance to enhance the chelating ability of the PAN fibers in an acid environment. As one non-limiting example, the PAN fibers may be surface modified with diethylenetriamine (DETA). To modify PAN with DETA, aminated PAN nanofibers can be prepared through electrospinning and then placed in a solution of DETA and AICT· 6H ₂ O. However, other methods are possible and entirely encompassed within the scope of the present disclosure.

[0057] As another non-limiting example, the PAN nanofibers may be treated with a sodium hydroxide ethanolic/aqueous solution at an elevated temperature (for example, 75 °C for 20 minutes) to improve the ability to chelate metal ions by converting some of the nitrile functional groups on the surface of the PAN nanofibers into imine conjugated groups (-C=N-).

[0058] As another non-limiting example, the PAN nanofibers may be modified to introduce additional chelating groups such as amine groups, carboxyl groups, imine groups, metal oxides, amidoxime, imidazole, carboxyl or phosphoryl derivatives, or pendant amine groups. Such modified PAN nanofibers may have advantageous characteristics such as large surface area, chemical resistance, thermal stability, low flammability, and good mechanical properties. Such modifications may be achieved through chemical reactions such as amination, amidoximation, or hydrolysis. For example, amination may involve the grafting of amine -containing ligands onto the surfaces of PAN nanofibers (e.g., onto the carbons of the nitrile groups). Amidoximation may involve introducing amine and oxime groups to the surface of the PAN nanofibers through reaction between the nitrile groups of PAN and hydroxylamine.

[0059] PAN has nitrile groups attached in the polymeric chain that can be hydrolyzed to strong chelating carboxylate and amine groups during treatment with sodium hydroxide. Hydrolysis may involve hydrolyzing PAN with NaOH/KOH. Alternatively, PAN may be enzymatically hydrolyzed using a nitrilase that catalyzes the hydrolysis of a nitrile directly to the corresponding acid, or a nitrile hydratase / amidase enzyme system that catalyzes the hydrolysis in two steps (first obtaining an amide and then the corresponding acid). Ultimately, hydrolysis of PAN may result in nitrile groups being rearranged to carboxyl and amine groups, which attract heavy metals electrostatically.

[0060] Without wishing to be bound by theory, it is believed that the presence of nitrogen- containing groups, such as amino, hydrazine, thioamide, and imidazoline, on the surface of PAN aid in chelation.

[0061] Furthermore, PAN may be modified in a variety of ways without regard for its chelating abilities. For example, the PAN nanofibers may be sulfurized through a dehydrogenation, cyclization, and sulfurization process to produce sulfurized PAN (SPAN). As another example, nanotubes such as multiwalled carbon nanotubes (MWCNTs) may be incorporated into PAN or SPAN to improve the structural stability and electronic conductivity of the material. Any modified PAN may be used to produce PAN nanofibers useable in a lead-acid battery as described herein. [0062] EXAMPLES

[0063] A lead-acid battery was made with PAN pasting paper, and compared to an otherwise identical lead-acid battery without the PAN pasting paper. A 2% w/w PAN fiber suspension was combined with litharge, which was 25% by weight free Pb with the remainder being PbO, and sulfuric acid to prepare a paste mix. The paste mix was pasted onto a Pb ahoy grid containing antimony and subsequently cured to form the active material. FIG. 3 shows that the battery incorporating PAN pasting paper generates a higher discharge capacity than the standard battery. FIG. 4 shows that the battery incorporating PAN pasting paper has a higher end-of-charge voltage than the standard battery, which indicates better suppression of antimony poisoning.

[0064] A lead-acid battery was made with PAN fibers in the active material, and compared to an otherwise identical lead-acid battery without PAN fibers in the active material. FIG. 5 shows that the battery with PAN fibers in the active material had a higher end of charge voltage and charge efficiency than the standard battery. FIG. 6 shows the battery with the PAN fibers in the active material had a higher discharge and longer cycle life than the standard battery.

[0065] The porosity of cured and formed pasted plates, without polymeric nanofibers present, was evaluated using a micromeritics instrument. Table 1 below shows the results.

[0066] Table 1 - Porosity of formed and cured pasted plates

[0067] As seen from the results in Table 1, the active materials are highly porous.

[0068] Certain embodiments of the lead-acid batteries and methods disclosed herein are defined in the above examples. It should be understood that these examples, while indicating particular embodiments of the invention, are given by way of illustration only. From the above discussion and these examples, one skilled in the art can ascertain the essential characteristics of this disclosure, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt the lead-acid batteries and methods described herein to various usages and conditions. Various changes may be made and equivalents may be substituted for elements thereof without departing from the essential scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof.