Electrolyte wettable meltblown web and structures incorporating same

Abstract

A nonwoven web is disclosed that is well suited for use as a porous separator in an energy storage device. The nonwoven web can be comprised of continuous meltblown filaments. In one aspect, the web can also be densified for reducing the thickness of the web and / or for changing the pore structure of the web.

Description

[0001] ELECTROLYTE WETTABLE MELTBLOWN WEB AND STRUCTURES INCORPORATING SAME

[0002] CROSS-REFERENCE TO RELATED APPLICATION

[0003] The present application is related and has right of priority to U.S. Provisional Patent Application No. 63 / 580,111 filed on September 1, 2023, which is incorporated by reference in its entireties for all purposes.

[0004] BACKGROUND

[0005] Batteries, particularly rechargeable batteries, typically include a cathode spaced from an anode. A porous separator is placed in between the cathode and the anode. An electrolyte, such as a liquid electrolyte, is in contact with the separator and contains ions that may be disassociated from a salt in a polar protic or aprotic solvent. In order to produce an electrical current, ions move from the anode to the cathode while electrons travel through an external circuit. In order to recharge the battery, a reverse process is configured.

[0006] Great efforts are currently underway in order to improve the performance of batteries, particularly batteries designed to power electric vehicles, including cars and trucks. Such batteries can include lithium ion batteries, sodium ion batteries, and the like.

[0007] The separator chosen for a particular battery configuration has a significant impact on the electrical energy potential of the overall system. The separator, for instance, should easily wet with the electrolyte and permit the flow of ions in a manner that produces high power capabilities at both high rates of charge and discharge. The separator should also be able to operate over a relatively wide temperature range. Some separators are also designed to prevent runaway thermal discharge of batteries by blocking the flow of ions once a shutdown temperature is achieved.

[0008] In the past, separators have been formed from porous films. U.S. Patent No. 7,794,511 , U.S. Patent No. 9,455,432, U.S. Patent No. 9,666,847, U.S. Patent No. 10,003,058, U.S. Patent No. 10,559,802, and U.S. Patent Publication No. 2021 / 0143511 , which are all incorporated by reference, disclose various different porous film configurations for use as separators in an energy storage device, such as a battery. These films, however, can include multiple layers and coatings and are formed in a relatively slow process.

[0009] In view of the above, a need currently exists for an improved separator and process for producing a separator for an energy storage device, such as a battery. A need also exists for a separator for an energy storage device that can be produced at high throughput rates with uniform properties. A need also exists for a separator for an energy storage device that can lower cell or battery impedance to increase battery performance characteristics, such as charge rate, discharge rate, cycle life, storage and safety.

[0010] SUMMARY

[0011] In general, the present disclosure is directed to a nonwoven web containing meltblown fibers that is particularly well suited for use as a separator in an electronic device, such as a battery. In one aspect, the nonwoven web is made from continuous meltblown filaments. It was discovered that producing a nonwoven web containing meltblown filaments having a particular size, at a particular density, and within a particular basis weight produces webs having excellent wettability properties when contacted with an electrolyte. In addition, the webs have demonstrated excellent conductive properties which can be demonstrated through impedance spectroscopy tests and through discharge cycling tests. In one aspect, the nonwoven web is compressed, such as through calendering, in order to optimize the thickness and pore structure of the web.

[0012] For example, in one embodiment, the present disclosure is directed to a separator for a battery that is configured to be placed between an anode and a cathode. The battery separator comprises a nonwoven web comprised of continuous meltblown filaments. The continuous meltblown filaments comprise a thermoplastic polymer. For instance, the thermoplastic polymer may comprise a polyolefin polymer, such as a polypropylene polymer or a polyethylene polymer. The nonwoven web is porous for permitting ions to travel therethrough. The meltblown filaments have an average diameter of from about 0.5 m to about 10 pm. The nonwoven web has a thickness of from about 3 pm to about 90 pm. In accordance with the present disclosure, the nonwoven web has a density of greater than about 0.3 g / cm3, such as greater than about 0.35 g / cm3, such as greater than about 0.38 g / cm3, such as greater than about 0.4 g / cm3. The density of the nonwoven web is generally less than about 0.9 g / cm3, such as less than about 0.8 g / cm3, such as less than about 0.7 g / cm3, such as less than about 0.65 g / cm3, such as less than about 0.58 g / cm3.

[0013] In order to achieve a higher density, the nonwoven web can be calendered. In one aspect, the web can be calendered in an amount sufficient to reduce the thickness of the nonwoven web by greater than about 20%, such as greater than about 30%, such as greater than about 40%, such as greater than about 80%.

[0014] The basis weight of the web can vary depending upon the particular application and various factors, including the type of electronic component or battery being constructed. In one aspect, the nonwoven web can have a basis weight of from about 3 gsm to about 60 gsm, including all increments of 1 gsm therebetween. In one aspect, the nonwoven web can be relatively light and have a basis weight of from about 3 gsm to about 15 gsm. Alternatively, higher basis weight webs can be formed that have a basis weight of from about 15 gsm to about 60 gsm, such as from about 15 gsm to about 45 gsm. Similarly, the thickness of the web can vary. For instance, in one application, the thickness can be from about 3 m to about 20 pm. In other applications, however, thicker webs may be preferred having a thickness of from about 20 pm to about 90 pm, such as from about 20 pm to about 55 pm.

[0015] The continuous meltblown filaments generally have a relatively small diameter. In one aspect, at least 90% of the continuous meltblown filaments contained in the nonwoven web have a diameter in a range of from about 0.08 pm to about 25 pm, such as from about 0.08 pm to about 20 pm, such as from about 0.08 pm to about 15 pm. The meltblown filaments in various embodiments can have an average diameter of from about 0.5 pm to about 10 pm, such as from about 0 5 pm to about 8 pm, such as from about 1 pm to about 4 pm.

[0016] In one aspect, the nonwoven web does not include any type of treatment in order to improve the wettability characteristics of the web with respect to an electrolyte solution. The separator can comprise a single fibrous web or can comprise multiple fibrous webs made from multiple nonwoven webs. For instance, in one aspect, the separator comprises a first nonwoven web comprising continuous meltblown filaments made from a polypropylene polymer combined with at least a second nonwoven web comprising continuous meltblown fibers made from a different polymer. The different polymer, for instance, may comprise a polyethylene polymer.

[0017] The nonwoven web can include different fiber layers and / or can be made from a single fiber type or from a mixture of different fiber types. For example, the nonwoven web can comprise monofilament filaments, bicomponent filaments, and mixtures thereof. The filaments can be made of the same polymer or different polymers. For instance, the nonwoven web can contain polyolefin filaments alone or in combination with polyester filaments or can contain a mixture of polypropylene filaments and polyethylene filaments.

[0018] In one aspect, the separator can include at least one coating applied to the nonwoven web. For instance, the at least one coating can comprise a ceramic coating. Alternatively, the at least one coating can comprise an adhesive coating for adhering the nonwoven web to an adjacent surface. The adhesive coating, for instance, can comprise a polyvinylidene fluoride polymer.

[0019] The present disclosure is also directed to a battery comprising a cathode, an anode, and a separator as described above positioned between the anode and the cathode. The battery, for instance, can comprise a lithium ion battery, a sodium ion battery, or the like. The battery can further comprise an electrolyte in contact with the separator that facilitates movement of ions from the anode to the cathode or from the cathode to the anode.

[0020] Other features and aspects of the present disclosure are discussed in greater detail below.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS A full and enabling disclosure of the present disclosure is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:

[0022] Figure 1 illustrates one embodiment of a process for producing continuous meltblown filaments and nonwoven webs made in accordance with the present disclosure;

[0023] Figure 2 is a cross-sectional view of one embodiment of an electronic device, such as a battery, made in accordance with the present disclosure;

[0024] Figure 3 is a graph illustrating some of the results obtained in the example below;

[0025] Figure 4 is a graph showing some of the results obtained in the example below;

[0026] Figure 5 is a graph showing some of the results obtained in the example below;

[0027] Figure 6 is a graph showing some of the results obtained in the example below;

[0028] Figure 7 is a graph showing some of the results obtained in the example below; and

[0029] Figure 8 is a graph showing some of the results obtained in the example below;

[0030] Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

[0031] DEFINITIONS

[0032] As used herein, the fiber diameter of continuous meltblown filaments is determined by obtaining an SEM micrograph of a cross-section of a nonwoven web containing the filaments. Three micrographs are taken at different thicknesses. The different thicknesses are the top one-third of the web, the middle one-third of the web, and the bottom one-third of the web. The diameter of at least 30 filaments is measured in each micrograph.

[0033] In order to prepare the samples, two small strips having dimensions of 1 cm x 2 cm are cut from a sample. Each strip is cooled in liquid nitrogen and then cross-sectioned with a razor blade. Each strip is then mounted vertically so that the cross-section surface can be examined. Each sample can be gold coated to help with charge suppression. An SEM microscope, such as Hitachi brand SU6600 operating at 5 kV accelerating voltage equipped with Quartz PCI Scientific Management System, can be used to capture the micrographs from the cross-section strips and assist in taking measurements.

[0034] As used herein, the term “nonwoven web” refers to a web having a structure of individual fibers that are randomly interlaid, not in an identifiable manner as in a knitted fabric. Nonwoven webs include, for example, meltblown webs, spunbond webs, carded webs, wet-laid webs, airlaid webs, coform webs, hydraulically entangled webs, etc.

[0035] As used herein, the term “meltblown” web or layer generally refers to a nonwoven web that is formed by a process in which a molten thermoplastic material is extruded through a plurality of fine, usually circular, die capillaries as molten fibers into converging high velocity gas (e.g ., air) streams that attenuate the fibers of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Patent No. 3,849,241 to Butin, et al.; U.S. Patent No. 4,307,143 to Meitner, et al.; and U.S. Patent No. 4,707,398 to Wisneski, et al. Meltblown fibers may be substantially continuous or discontinuous, and are generally tacky when deposited onto a collecting surface.

[0036] As used herein, the term “fibers” refer to elongated extrudates formed by passing a polymer through a forming orifice such as a die. Unless noted otherwise, the term “fibers” includes discontinuous fibers having a definite length and substantially continuous filaments. Substantially filaments may, for instance, have a length much greater than their diameter, such as a length to diameter ratio (“aspect ratio”) greater than about 15,000 to 1 , and in some cases, greater than about 50,000 to 1.

[0037] As used herein, the thickness of a nonwoven web can be measured using a Mitutoyo brand digital micrometer, such as Model 293-348-30CAL. While measuring the thickness, a 5 N force is applied to the surface of the web (or a pressure of 0.16 MPa).

[0038] As used herein, basis weight of a nonwoven web can be measured according to ASTM Test D3776-96, option C.

[0039] As used herein, the density of a nonwoven web is calculated from the basis weight and thickness.

[0040] DETAILED DESCRIPTION

[0041] It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only and is not intended as limiting the broader aspects of the present disclosure.

[0042] In general, the present disclosure is directed to the construction of nonwoven webs, particularly meltblown webs, that are well suited for use as separators in electronic devices, such as batteries. The nonwoven webs made according to the present disclosure, for instance, can be placed between an anode and a cathode. The webs are constructed so as to have a controlled porosity that permits ions to travel between the two electrodes. Further, it was unexpectedly discovered that nonwoven webs made according to the present disclosure are easily wettable when contacted with various electrolytes, including electrolytes containing an alkylene carbonate.

[0043] As will be described in greater detail below, in one aspect, the nonwoven web of the present disclosure is formed from continuous filaments. In one embodiment, the nonwoven web formed from the continuous meltblown filaments can also be compressed, such as by being calendered, which can increase the density of the web. Through this process, it is believed that a pore structure is created that not only has optimum porosity, but also creates tortuous pathways particularly well suited for use as a separator in an energy storage device, such as a battery.

[0044] Referring to FIG. 2, for instance, one embodiment of a battery 100 is shown. The battery 100 illustrated in FIG. 2 is merely exemplary and provided for purposes of explanation. It should be understood that any suitable battery arrangement can be used, including spirally wrapped batteries as opposed to the stacked arrangement illustrated.

[0045] As shown in FIG. 2, the battery 100 includes an anode 102 spaced from a cathode 106. The anode 102 serves as a negative electrode, while the cathode is a positive electrode. The cathode 104 can be responsible for releasing and accepting ions during charge and discharge cycles.

[0046] The battery 100 further includes a separator 106 positioned between the anode 102 and the cathode 104. The separator 106 is made according to the present disclosure and can comprise a nonwoven web made from meltblown filaments. The separator 106, as described above, is porous and is provided to prevent short circuits caused by direct contact between the anode 102 and the cathode 104. The separator 106 permits the passage of ions while maintaining a physical barrier.

[0047] The battery 100 can further include current collectors 108 and 110 that are conductive materials for facilitating the flow of electrons between the electrodes and an external circuit. The current collectors can be made of a metal, such as copper on the anode side and aluminum on the cathode side. The battery can further include a cell housing comprised of a cell housing cap 112 that fits together with a cell housing 114. The cell housing encloses the components and provides mechanical support and protection. The cell housing 112 and 114 can be made from a metal or a polymer material. Not shown, the battery 100 can further include positive and negative terminals for a connection to the external circuit.

[0048] As described above, the battery 100 further includes an electrolyte which can be a liquid or paste. The electrolyte facilitates movement of ions between the anode 102 and the cathode 104, which allows the battery 100 to generate and store electrical energy. More particularly, the electrolyte in combination with the separator 106 should allow ions to move freely between the anode 102 and the cathode 104 while preventing direct contact of the electrodes. The movement of ions through the electrolyte creates a flow of electric current between the two electrodes through an external circuit, thus permitting the battery to deliver power. The electrolyte in combination with the separator 106 can also help maintain a balance of charges. For instance, as ions move within the battery, the cathode 104 gains electrons and becomes negatively charged, while the anode 102 loses electrons and becomes positively charged. The ion movement using the electrolyte and the separator 106 helps balance these charges and prevents the buildup of excessive charge. The electrolyte is positioned on opposite surfaces of the separator 106 and in contact with the anode 102 and the cathode 104. In order to permit the flow of ions, the separator 106 should easily wet with the electrolyte and permit conduction to occur over many cycles.

[0049] Electrolytes contained in rechargeable batteries typically are comprised of metal salts dissolved in a solvent or a mixture of solvents. Common solvents used include ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, and the like. In one application, the solvent comprises a mixture of ethylene carbonate and diethyl carbonate.

[0050] The metal salt contained in the one or more solvents depends upon the type of battery being constructed For sodium ion batteries, the metal compound can comprise a sodium compound. For lithium ion batteries, the metal compound can comprise a lithium compound, such as lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethane sulfonate, lithium bis(trifluoromethane sulfonyl)imide, or lithium perchlorate.

[0051] The separator 106 as shown in FIG. 2 can be incorporated into any suitable battery. For instance, the battery can comprise an alkaline battery, such as a nickel cadmium battery, a nickel metal hydride battery, or the like.

[0052] Alternatively, the battery may comprise a lithium ion battery, which is rechargeable. In lithium ion batteries, the cathode may comprise a lithium metal oxide compound, such as lithium cobalt oxide, lithium iron phosphate, or lithium manganese oxide. The anode, on the other hand, may comprise, for instance, graphite.

[0053] In still another embodiment, the battery may comprise a sodium ion battery. In sodium ion batteries, the cathode may comprise sodium ion phosphate, sodium nickel cobalt manganese oxide, or another sodium-containing compound. The anode may comprise graphite, a hard carbon, or graphene.

[0054] As described above, the porous separator of the present disclosure can comprise a nonwoven web containing meltblown filaments. The meltblown filaments, in one aspect, are continuous filaments. One embodiment of a process for forming meltblown webs in accordance with the present disclosure is shown in FIG. 1 In forming the nonwoven web illustrated in FIG. 1 , polymer pellets (not shown) of one or more polymers can be introduced into a pellet hopper 12 of an extruder 14. The one or more polymers may be mixed with other appropriate materials, such as, for example, a tackifier, pigments, antioxidants, stabilizers, waxes, flow promoters, solid solvents, fillers and processing enhancing additives, or the like. The different components can be compounded together and fed to the extruder 14 or can be fed separately.

[0055] As the polymer composition advances through the extruder 14, the composition is progressively heated to a molten state. A die 16 contains orifices at its tip 22. The molten blend emerges from the orifices of the die 16 as molten strands or threads 24, which can form continuous filaments in the resulting nonwoven web. Alternatively, the threads 24 can be formed into fibers having a desired length.

[0056] Generally, to form the filaments, the die 16 can utilize pressurized attenuating gas sources 30 and 32 that converge to form a stream of gas which entrains and attenuates the molten threads 24 into fibers, such as filaments. The filaments 24 are blown by the action of the attenuating gas onto a collecting arrangement illustrated as a foraminous endless belt 52 driven by rollers 54. Other foraminous arrangements such as a rotating drum could also be utilized. One or more vacuum boxes may be located below the surface of the foraminous belt 52 and between the rollers 54 to assist in retention of a matrix of filaments 24 on the belt 52, which is rotating as indicated by the arrow 58. Vacuum boxes can assist in retention of the matrix of filaments on the surface of the belt 52. The thus- collected, entangled filaments 24 are coherent and may be removed from the belt 52 as a self- supporting nonwoven web 56.

[0057] In one aspect, the nonwoven web 56 can be compressed or densified prior to being incorporated into an electronic device, such as a battery. For example, as shown in FIG. 1 , the nonwoven web 56 is fed into a calendering device 64. For instance, a guide roll 62 can direct the nonwoven web 56 from the forming surface 52 into the calendering device 64. The calendering device 64 can include a pair of opposing rollers 66 and 68 that form a nip through which the nonwoven material 56 is fed. Optionally, one or both of the opposing rollers 66 and 68 can be heated. The calendering device 64 calenders and compresses the web for increasing the density of the web. Compressing the web as shown in FIG. 1 not only increases the density but changes the pore structure of the nonwoven material that may provide various advantages and benefits when incorporated into a battery as a separator. In addition, calendering the nonwoven web 56 may improve the handling properties of the web during further processing.

[0058] In addition to changing the porous nature of the nonwoven web, calendering can also reduce the thickness of the nonwoven web. For instance, in one aspect, a nonwoven web made in accordance with the present disclosure can be calendered so as to decrease the thickness of the web by greater than about 20%, such as by greater than about 30%, such as by greater than about 40%, such as by greater than about 50%, such as by greater than about 60%, such as by greater than about 70%, such as by greater than about 80%, such as by greater than about 90%, such as by even greater than about 100%. Calendering can decrease the thickness of the membrane by up to about 300%, such as by up to about 200%, such as by up to about 100%, such as by up to about 80%.

[0059] The nonwoven web 56 made in accordance with the present disclosure can be constructed to have various physical properties. The process of the present disclosure, however, permits significant variation in the characteristics of the nonwoven material and thus allows for the physical properties to be changed based upon a particular application. In general, the nonwoven web 56 can have a basis weight of from about 3 gsm to about 60 gsm, including all increments of 1 gsm therebetween. For instance, the nonwoven web 56 can have a basis weight of greater than about 5 gsm, such as greater than about 10 gsm, such as greater than about 15 gsm, such as greater than about 20 gsm, and less than about 55 gsm, such as less than about 50 gsm, such as less than about 45 gsm, such as less than about 40 gsm, such as less than about 35 gsm. In applications where lightweight materials and / or very thin materials are desired, the nonwoven web can have a basis weight of from about 3 gsm to about 15 gsm. When heavier or thicker materials are desired, the basis weight of the nonwoven web can be from about 15 gsm to about 60 gsm, such as from about 15 gsm to about 45 gsm.

[0060] As described above, the nonwoven web can optionally be compressed or calendered in order to increase the density and change the pore structure of the web. The density of the nonwoven web, for instance, can be greater than about 0.3 g / cm3and less than about 0.9 g / cm3, including all increments of 0.01 g / cm3therebetween. The density of the web, for instance, can be greater than about 0.35 g / cm3, such as greater than about 0.38 g / cm3, such as greater than about 0.4 g / cm3, such as greater than about 0.42 g / cm3, such as greater than about 0.45 g / cm3, such as greater than about 0.47 g / cm3, such as greater than about 0.5 g / cm3. The density of the web is generally less than about 0.8 g / cm3, such as less than about 0.7 g / cm3, such as less than about 0.65 g / cm3, such as less than about 0.58 g / cm3.

[0061] The thickness of the web can depend upon the basis weight and density of the web. The thickness of the web, for instance, can be from about 3 m to about 90 pm, including all increments of 1 pm therebetween. For instance, the web can have a thickness of less than about 80 pm, such as less than about 70 pm, such as less than about 60 pm, such as less than about 50 pm, such as less than about 45 pm, such as less than about 40 pm, such as less than about 35 pm, such as less than about 30 pm, such as less than about 25 pm, such as less than about 20 pm. The thickness of the web is generally greater than about 5 pm, such as greater than about 8 pm, such as greater than about 10 pm, such as greater than about 12 pm, such as greater than about 15 pm, such as greater than about 18 pm. Thinner separators, for instance, can have a thickness of from about 3 pm to about 20 pm. Separators having a higher basis weight, however, may have a thickness of from about 20 pm to about 90 pm, such as from about 20 pm to about 55 pm.

[0062] The porosity of nonwoven webs made in accordance with the present disclosure can generally be from about 20% to about 80%, including all increments of 1% therebetween. The porosity of the nonwoven web, for instance, can be greater than about 23%, such as greater than about 25%, such as greater than about 28%, such as greater than about 30%, such as greater than about 33%, such as greater than about 35%, such as greater than about 38%, such as greater than about 40%. The porosity can be less than about 70%, such as less than about 60%, such as less than about 50%. The porosity of the web can be measured using mercury intrusion porosimetry using ASTM Test D4404.

[0063] The individual filaments contained in the nonwoven web 56 can be relatively fine and have a small diameter. For instance, at least 90% of the filaments contained in the nonwoven web have a diameter of from about 0.08 pirn to about 25 pm, such as from about 0.08 pm to about 20 pm, such as from about 0.08 pm to about 15 pm. The average diameter of the filaments can be from about 0.5 pm to about 10 pm, including all increments of 0.1 pm therebetween. For instance, the filaments can have an average diameter of less than about 8 pm, such as less than about 5 pm, such as less than about 4 pm, such as less than about 3.5 pm. The average diameter of the filaments can be greater than about 0.7 pm, such as greater than about 1 pm, such as greater than about 1 .25 pm, such as greater than about 1 .5 pm, such as greater than about 1 .75 pm, such as greater than about 2 pm, such as greater than about 2.25 pm, such as greater than about 2.5 pm.

[0064] Nonwoven webs made according to the present disclosure can be constructed from various different polymers or blends of polymers. Polymers that can be used to construct the nonwoven webs include polyolefins, polyesters, polyamides, polycarbonates, polyphenylene sulfides, polystyrenes, polyurethanes, polyvinylidene fluorides, or mixtures thereof. Polyesters that can be used to construct the web include polybutylene terephthalate, polyethylene terephthalate, polybutylene naphthalate, or the like.

[0065] In one embodiment, the nonwoven web is made from a polyolefin polymer. The polyolefin polymer, for instance, can comprise a polypropylene homopolymer or copolymer. The polypropylene homopolymer, for instance, can have a density of from about 0.9 g / cm3to about 0.92 g / cm3and can have a melt flow rate of from about 20 g / 10 min to about 2,000 g / 10 min, such as from about 1 ,000 g / 10 min to about 1 ,500 g / 10 min when measured at 230°C and at a load of 2.16 kg. The polypropylene homopolymer can have a melting temperature of less than about 175°C, such as less than about 170°C, such as less than about 165°C, such as less than about 160°C, and greater than about 145°C.

[0066] In an alternative embodiment, the nonwoven web can be made from a polyethylene polymer which can comprise a polyethylene homopolymer or a polyethylene copolymer. In one aspect, the polymer can comprise a copolymer of ethylene and propylene, such as a random copolymer of ethylene and propylene.

[0067] In one embodiment, separators for batteries made in accordance with the present disclosure only contain a single fibrous layer or nonwoven web. In other embodiments, however, the separator can be comprised of multiple webs. For instance, the separator may contain two to four nonwoven webs laminated together that each contain meltblown filaments in accordance with the present disclosure. In one aspect, for instance, a porous nonwoven web comprised of polypropylene continuous meltblown filaments can be laminated with a second nonwoven web also being formed from polypropylene continuous meltblown filaments. Alternatively, the second nonwoven web can be made from a different polymer. For instance, the second nonwoven web may comprise a nonwoven web containing polyethylene continuous meltblown filaments.

[0068] Nonwoven webs made according to the present disclosure can also include various coatings in forming the separator. For instance, in one embodiment, a ceramic coating can be applied to one or both surfaces of the nonwoven web. Ceramic coatings can provide thermal stability and heat resistance to the separator to prevent overheating. Ceramic coatings can also enhance the electrochemical stability of the separator. In addition, ceramic coatings can also improve the mechanical strength of the separator membrane. Overall, ceramic coatings can increase the lifespan of the battery by protecting it from various forms of degradation, such as electro deterioration, electrolyte breakdown, and internal short circuits.

[0069] In one embodiment, the ceramic coating can be comprised of one or more ceramic particles combined with a binder, which can comprise a polymer. The ceramic particles may be inorganic or organic. Examples of ceramic particles include oxides of silicon, aluminum oxide, zirconium, titanium oxides, silicon carbonates, aluminum carbonates, zirconium carbonates, calcium carbonates, zinc carbonates, and mixtures thereof. The ceramic particles can have an average particle size ranging from about 0.05 pm to about 5 pm.

[0070] Binders that can be combined with the ceramic particles include polypropylene, polyethylene, polyesters, polytetrafluoroethylenes, polyvinylidene fluorides, copolymers thereof, and the like. Other binders include polyvinyl alcohol, polyvinyl acetate, polyacrylic acid salts, polyacrylonitrile, polyacrylamides, or blends thereof.

[0071] Any suitable process can be used to apply the ceramic coating to the nonwoven web. Such methods include dip coating, gravure coating, spray coating, electrospun coatings, myer rod dip coatings, slot die or extrusion coatings, sputtering, vapor deposition, and the like. As described above, the ceramic coating can be applied to one side of the nonwoven web or to both sides.

[0072] In an alternative embodiment, a coating can be applied to the nonwoven web that helps adhere the web to an adjacent surface within the battery, such as a cathode or an electrode. An adhesion promoting coating, for instance, can comprise a polymer. Examples of polymers that can be used as the coating can include polyvinylidene fluoride (PVDF); polyurethane, polyethylene oxide (PEO), polypropylene oxide (PPO); polyacrylonitrile (PAN), polyacrylamide, polymethylacrylate, polymethylmethacrylate, polyvinylacetate, polyvinylpyrrolidnone, polytetraethylene glycol diacrylate; copolymers of the foregoing, and combinations thereof.

[0073] The present disclosure may be better understood with reference to the following examples.

[0074] Examples

[0075] Example No. 1

[0076] Two nonwoven webs were made in accordance with the present disclosure and tested for wettability and conductivity. The webs contained continuous meltblown filaments made from a polypropylene homopolymer. The following webs were produced:

[0077] Each of the above nonwoven webs were calendered. For example, Sample No. 1 had an initial thickness of 40 m, while Sample No. 2 had an initial thickness of 90 pm. Both nonwoven webs were untreated meaning that the webs were not treated with any topical solution or contained any additive that promoted wettability. Further, both samples were uncoated.

[0078] Both Sample No. 1 and Sample No. 2 were contacted with a lithium hexafluorophosphate solution that contained ethylene carbonate and diethyl carbonate. It was observed that both of the nonwoven webs were wettable by the electrolyte.

[0079] Sample Nos. 1 and 2 were also subjected to an impedance spectroscopy test. Impedance spectroscopy is a technique used to analyze the electrical properties of materials by measuring their impedance response to an applied AC voltage signal across a range of frequencies. In the context of battery membranes, impedance spectroscopy demonstrates the ability of the material to support ion transport and other electrochemical processes.

[0080] FIG. 3 is a graph illustrating the results of the impedance spectroscopy test. Both Sample Nos. 1 and 2 displayed favorable conductivity characteristics.

[0081] Impedance spectroscopy data correlates with cycling data, particularly discharge cycling. Sample No. 1 was also subjected to a discharge cycle test. The results are illustrated in FIG. 4.

[0082] Discharge cycle testing is used to evaluate the performance and behavior of battery separators. The results in FIG. 4 illustrate that Sample No. 1 performed very well with respect to a charge and discharge cycle.

[0083] Example No. 2 Nonwoven webs were made in accordance with the present disclosure and tested for wettability and conductivity as described in Example No. 1 and compared to a porous polypropylene film.

[0084] Three webs were made and tested. Sample No. 3 contained continuous meltblown filaments

[0085] 5 made from a polypropylene homopolymer. Sample No. 4 contained two layers of continuous meltblown filaments including a polypropylene layer and a polyethylene layer. Sample No. 5 contained three layers of continuous meltblown filaments including a polyethylene layer between two polypropylene layers. Sample No. 6 was the polypropylene film. The following webs were produced with the following properties:

[0086] 10

[0087] The samples were subjected to the discharge cycle test and the results are shown in FIGS. 5 through 8.

[0088] 15 The samples were also heated to 130 F and tested for shrinkage. All the nonwoven samples displayed a shrinkage of 2% or less in the machine direction and the cross machine direction. Film samples displayed a shrinkage of greater than 24%. The samples were also oven tested to 160 C. the nonwoven samples maintained their shape while the film samples curled and shriveled.

[0089] The nonwoven samples made according to the present disclosure displayed excellent thermal 20 stability while also being wettable and having good conductive characteristics.

[0090] These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only and is not intended to limit the invention so further described in such appended claims.

Claims

What Is Claimed:1 . A separator for a battery configured to be placed between an anode and a cathode, the separator comprising: a nonwoven web comprised of continuous meltblown filaments, the continuous meltblown filaments comprising a thermoplastic polymer, the nonwoven web being porous for permitting ions to travel therethrough, the meltblown filaments having an average diameter of from about 0.5 pm to about 10 pm, the nonwoven web having a thickness of from about 3 pm to about 90 pm, the nonwoven web having a density of greater than about 0.3 g / cm3.2 A separator as defined in claim 1 , wherein the nonwoven web has a density of greater than about 0.35 g / cm3, such as greater than about 0.38 g / cm3, such as greater than about 0.4 g / cm3.

3. A separator as defined in any of the preceding claims, wherein the nonwoven web has a density of less than about 0.9 g / cm3, such as less than about 0.7 g / cm3, such as less than about 0.65 g / cm3, such as less than about 0.58 g / cm3.

4. A separator as defined in any of the preceding claims, wherein the nonwoven web has been calendered.

5. A separator as defined in any of the preceding claims, wherein the nonwoven web has been calendered in an amount to reduce the thickness of the nonwoven web by greater than about 20%, such as greater than about 30%, such as greater than about 40%, and less than about 80%.

6. A separator as defined in any of the preceding claims, wherein the nonwoven web has a basis weight of from about 3 gsm to about 60 gsm.

7. A separator as defined in any of the preceding claims, wherein the nonwoven web has a basis weight of from about 3 gsm to about 15 gsm.

8. A separator as defined in any of the preceding claims, wherein the nonwoven web has a basis weight of from about 15 gsm to about 60 gsm, such as from about 15 gsm to about 45 gsm.

9. A separator as defined in any of the preceding claims, wherein the nonwoven web has a thickness of from about 3 pm to about 20 pm.

10. A separator as defined in any of claims 1 through 8, wherein the nonwoven web has a thickness of from about 20 pm to about 90 pm, such as from about 20 pm to about 55 pm.

11. A separator as defined in any of the preceding claims, wherein the meltblown filaments have an average diameter of from about 0.5 pm to about 10 pm, such as from about 0.5 pm to about 8 pm, such as from about 1 pm to about 4 pm.

12. A separator as defined in any of the preceding claims, wherein at least 90% of the continuous meltblown filaments have a diameter in a range of from about 0.08 pm to about 25 pm, such as from about 0.08 pm to about 20 pm, such as from about 0.08 pm to about 15 pm.

13. A separator as defined in any of the preceding claims, wherein the continuous meltblown filaments comprise a polyolefin polymer.

14. A separator as defined in any of the preceding claims, wherein the continuous meltblown filaments comprise a polypropylene polymer.

15. A separator as defined in any of claims 1 through 13, wherein the continuous meltblown filaments comprise a polyethylene polymer.

16. A separator as defined in any of the preceding claims, wherein the nonwoven web does not include a hydrophilic treatment or contain a hydrophilic additive.

17. A separator as defined in any of the preceding claims, wherein the separator comprises a single fibrous web.

18. A separator as defined in any of the preceding claims, wherein the separator comprises multiple fibrous layers.

19. A separator as defined in claim 18, wherein the separator comprises a first nonwoven web comprising continuous meltblown filaments made from a polypropylene polymer and comprises at least a second nonwoven web comprising continuous meltblown filaments made from a different polymer.

20. A separator as defined in claim 19, wherein the different polymer comprises a polyethylene polymer.21 . A separator as defined in any of the preceding claims, wherein the separator includes at least one coating applied to the nonwoven web.

22. A separator as defined in claim 21 , wherein the at least one coating comprises a ceramic coating.

23. A separator as defined in claim 21 , wherein the at least one coating comprises an adhesive coating for adhering the nonwoven web to an adjacent surface.

24. A separator as defined in claim 23, wherein the adhesive coating comprises a polyvinylidene fluoride polymer.

25. A separator as defined in any of the preceding claims, wherein the nonwoven web has a porosity of from about 20% to about 80%, such as from about 25% to about 50%.

26. A battery comprising: a cathode, an anode, and a separator as defined in any of the preceding claims positioned between the anode and the cathode.

27. A battery as defined in claim 26, wherein the battery comprises a lithium ion battery.

28. A battery as defined in claim 26, wherein the battery comprises a sodium ion battery.

29. A battery as defined in any of claims 26 through 28, wherein the battery further comprises an electrolyte in contact with the separator.

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