Nonwoven battery separator, batteries including the non-woven battery separator, and processes of manufacture

Abstract

A non-woven battery separator and processes for forming the non-woven battery separator includes a fiber blend including cellulose fibers, microfibrillated fibers, and optionally polyester and / or aramid fibers. Also disclosed are batteries including the non-woven battery separator. During fabrication, the non-woven battery separator can be effectively dried at temperatures between 120°C and 180°C, which results in the fibers absorbing water when in use. Some battery electrolytes such as lithium hexafluorophosphate react with water to form hydrogen fluoride (HF), which can be corrosive and shorten battery lifecycles and affect performance. Absorbing water from the electrolyte increases the battery life cycle by reducing HF generation.

Description

NONWOVEN BATTERY SEPARATOR, BATTERIES INCLUDING THE NON-WOVEN BATTERY SEPARATOR, AND PROCESSES OF MANUFACTURE BACKGROUND

[0001] The present disclosure is generally directed to batteries, battery separators and processes for fabricating the battery separators, and more particularly to, non-woven battery separators formed of a fiber blend that can be dried at relatively high temperatures during fabrication and are configured to provide water adsorption.

[0002] The need for high-quality batteries such as lithium-ion batteries, sodium-ion batteries, lithium primary batteries, and the like is important for commercial usage. Mobile devices, temporary storage for renewable energies or transportation are just a few of the many fields of application where a high capacity, long cycle life and stability against aging is important. Strict quality control along the entire production process is necessary to ensure these properties and in consequence a high-quality product.

[0003] It is well known that moisture can have an impact on quality of the different components used to construct a battery. For example, porous separators are used to separate the anode and cathode in the battery to prevent short circuits as well as permit transport of ions from one electrode to the other. The separators can impact several battery performance parameters, including cycle life, energy and power density, and safety. In lithium-ion batteries, the separators are a key component for lithium-ion transportation, which is generally controlled by pore size, tortuosity and ion conductivity. Small amounts of water are inevitable to occur during the production of the battery, which is especially problematic with batteries employing fluorine-based electrolytes such as, for example, lithium (or sodium) hexafluorophosphate (LiPF6), lithium (or sodium) fluorosulfonyl imide, (LiFSI), combinations thereof, and the like. These electrolytes are moisture sensitive and are reactive towards trace amounts of moisture in the electrolyte solution. The hexafluorophosphate salt is known to undergo hydrolysis, producing hydrofluoric acid (HF), which is a highly toxic and corrosive gas that can damage the inside of the battery. The presence of HF can corrode internal metal components, the battery casing, and seals, whichcan cause the battery to rupture and leak. While fluorosulfonyl imide salt as the electrolyte is expected to be less susceptible to this degradation, such reactions are also expected. Moreover, the presence of water in the battery can generate hydrogen gas, which can be explosive or cause the battery to bulge.

[0004] To overcome the issues related to moisture sensitivity, current battery manufacturing processes utilize dry rooms where the moisture content of the air is meticulously controlled to ensure the safe and high-quality manufacturing of products, particularly as it relates to the manufacture of lithium-ion (Li-ion) batteries. The dew point of these controlled environments is typically maintained at about -40 to -60oC. This controlled environment is crucial in the production of Li-ion batteries to prevent and minimize moisture-related issues that can impact safety, quality, cycle life, and overall manufacturing efficiency.

[0005] However, the use of a controlled environment may not be enough to avoid contamination with water in some cases. For example, battery separators are commonly formed of polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene. These materials cannot be dried or conditioned at temperatures much greater than 120oC due to their inherent degradation at the higher temperatures, which can make it difficult, if not impossible, to completely remove any moisture contained therein during the manufacturing process of the components or during the manufacturing process of the battery. Still further, humidity can alter the chemical and physical properties of the separators (as well as the electrolyte), potentially causing defects in the finished batteries. It is also noted that the electrolytes utilized in these batteries contain trace amounts of water. BRIEF SUMMARY

[0006] The present disclosure is generally directed to battery separators, batteries including the battery separator, processes for using and forming the battery separators, and processes for manufacturing the battery. More particularly, the present disclosure provides a non-woven battery separator configured to prevent formation of hydrofluoric acid (HF) during use by trapping residual water that may be contained within the battery. In one or more aspects, the present disclosure provides non-woven battery separator configured toadsorb water that may be in the electrolyte to prevent formation of HF.

[0007] In one or more embodiments, the battery separator is a non-woven battery separator including regenerated cellulose fibers in an amount from 25 to 95% by weight based on a total weight of the fibers; microfibrillated cellulose fibers in an amount from 5 to 20% by weight based on the total weight of the fibers; and optionally, synthetic fibers having a melting point greater than 200oC. The regenerated cellulose fibers and the microfibrillated cellulose fibers are refined, and the non-woven battery separator is free of a resinous binder or a thermoplastic binder. In one or more aspects, the refined regenerated cellulose fibers comprise lyocell fibers. In other aspects, the regenerated cellulose fibers are fibrillated fibers at a degree of 20 to 70 °SR. The optional synthetic fibers are present in the battery separator in an amount of 5 to 65 wt% based on the total weight of the fibers and can be selected from the group consisting of polyester fibers, and a blend of aramid fibers and polyester fibers. In one or more aspects, the polyester fibers comprise polyethylene terephthalate fibers, and / or the aramid fibers comprise para-aramid fibers. The polyester fibers are present in the non-woven battery separator in an amount of 5 to 40 wt% based on the total weight of the fibers. The aramid fibers are present in the non-woven battery separator in an amount of 20 to 40 wt% based on the total weight of the fibers. The non- woven battery separator in accordance with the disclosure can have a thickness of less than 150 microns, preferably comprised between 10 and 30 microns, or between 80 and 120 microns. The non-woven battery separator has an average pore size between about 0.5 to 4 microns. In one or more aspects, the non-woven battery separator has a porosity between 20 and 65%. In other aspects, the non-woven battery separator according to any one of the preceding claims, wherein it has an air permeability of 200 to 6000 ml / min as measured in accordance with ISO Standard 5636-3.

[0008] In one or more embodiments, a process for manufacturing a non-woven battery separator includes (A) mixing regenerated cellulose fibers with microfibrillated cellulose fibers in a solvent to form a fiber blend suspension, wherein the regenerated cellulose fibers comprise 25 to 95% by weight and the microfibrillated cellulose fibers in an amount from 5 to 20% by weight based on a total weight of the fibers; (B) refining the fiber blend suspension to a freeness of between 50°SR and 85°SR when measured using aSchopper-Reigler (SR) freeness tester, to obtain a slurry of fibers; (C) transferring the slurry of fibers to a headbox of a paper machine; (D) depositing the slurry onto a forming wire or forming fabric of the paper machine; (E) applying a vacuum to the deposited slurry to remove at least a portion of the solvent and form a non-woven fiber substrate; (F) consolidating the non-woven substrate to form a non-woven battery separator; and (G) drying the non-woven battery separator. In one or more aspects, the slurry of fibers further contains synthetic fibers having a melting point greater than 200°C, said synthetic fibers being present in an amount of 5 to 65 wt% by weight based on the total weight of the fibers. In one or more aspects, the synthetic fibers comprise polyester fibers in an amount of 5 to 40 wt% based on the total weight of the fibers, wherein said polyester fibers are introduced in the slurry of fibers after step B. In one or more aspects, the synthetic fibers can include aramid fibers in an amount of 20 to 40 wt% based on the total weight of the fibers, wherein said aramid fibers are introduced in the fiber blend during step A. Consolidating the non- woven substrate to form a non-woven battery separator can include a calendaring step. In the process, the regenerated cellulose fibers can include lyocell fibers.

[0009] In one or more embodiments, a battery includes the non-woven battery separator as described or manufactured according to the above noted process, wherein the non-woven battery separator is intermediate an anode and a cathode; wherein the anode, the cathode and the non-woven battery separator are immersed in an electrolyte solution; and the non-woven battery separator is configured for adsorbing water present in the electrolyte solution. The electrolyte can include a moisture sensitive conductive salt and a solvent, wherein the conductive salt can be reactive with water to produce hydrogen fluoride. In one or more aspects, the non-woven battery separator is conditioned at a temperature between about 120°C and about 180°C prior to assembly. The battery can be a lithium-ion battery, a sodium ion battery or a lithium primary battery. In one or more embodiments, a method of manufacturing a battery includes providing an anode and a cathode; conditioning a battery separator according to any one of claims 1 to 12, wherein the conditioning step is performed at a temperature of between 120°C and 180°C; disposing the battery separator between the anode and the cathode; and introducing an electrolyte solution in the battery. The conditioning step can be performed at a temperature ofbetween 140°C and 160°C.

[0010] Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with advantages and features, refer to the description and to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Example embodiments of the invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout, and wherein:

[0012] FIG.1 schematically illustrates an exemplary battery including the battery separator in accordance with the present disclosure.

[0013] FIG.2 graphically illustrates a bar chart depicting the amounts of residual water detected in an electrolyte used with non-woven battery separators manufactured in accordance with one or more embodiments of the present disclosure and conditioned at 120oC for 16 hours compared to the same electrolyte used with a conditioned non-woven battery separator of the same composition that was not dried, wherein different amounts of water were intentionally added to the electrolyte;

[0014] FIG.3 graphically illustrates a bar chart depicting the amounts of residual water detected in an electrolyte used with non-woven battery separators manufactured in accordance with one or more embodiments of the present disclosure and conditioned at 150oC for 16 hours compared to the same electrolyte used with a conditioned non-woven battery separator of the same composition that was not dried, wherein different amounts of water were intentionally added to the electrolyte;

[0015] FIG.4 graphically illustrates a bar chart depicting the amounts of residualwater detected in an electrolyte used with non-woven battery separators manufactured in accordance with one or more embodiments of the present disclosure and conditioned at 180oC for 16 hours compared to the same electrolyte used with a conditioned non-woven battery separator of the same composition that was not dried, wherein different amounts of water were intentionally added to the electrolyte; and

[0016] FIG.5 graphically illustrates depicting the amounts of residual water detected in an electrolyte used with non-woven battery separators manufactured in accordance with one or more embodiments of the present disclosure and conditioned at 200oC for 16 hours compared to the same electrolyte used with a conditioned non-woven battery separator of the same composition that was not dried, wherein different amounts of water were intentionally added to the electrolyte;. DETAILED DESCRIPTION

[0017] Disclosed herein are non-woven battery separators, batteries including the non-woven battery separator, and processes for fabricating the non-woven battery separators, as well as processes for manufacturing batteries including the non-woven battery separator. The non-woven battery separators are formed of a fiber blend including regenerated cellulose, microfibrillated cellulose, and optionally synthetic fibers having a melting point greater than 200oC including polyester fibers, or a blend of polyester fibers and aramid fibers, wherein the regenerated cellulose fibers and the microfibrillated cellulose fibers are refined, and wherein the non-woven battery separator is free of a resinous binder or a thermoplastic binder. As will be described in greater detail herein, the non-woven battery separators in accordance with the present disclosure overcome many of the problems associated with prior art battery separators as it relates to the presence of residual water remaining after manufacture and during battery assembly. Moreover, compared to the prior art polyolefin battery separators, the non-woven battery separators of the present disclosure can be dried at temperatures as high as about 180oC and the particular regenerated cellulose fibers and microfibrillated cellulose fibers blends have been found to adsorb residual amounts of water when the battery separator may come into contact with the electrolyte during use of said battery separator, e.g., water contained in the electrolyte or the separatoritself, or water entering the battery during its assembly, thereby minimizing and / or preventing the reaction of water with the electrolyte to form hydrogen fluoride (HF) and / or the generation of hydrogen gas during electrolysis, which in turn, increases the operating life cycle and performance of the battery as well as minimizes the occurrence of a potential health hazard in the event of a leakage, or also prevent the risk of explosion of the battery in case of generation of hydrogen gas during electrolysis.

[0018] The non-woven battery separator in accordance with the present disclosure may be used in any number of different types of batteries in the presence of electrolytes that include components that are generally known to react with water and / or may contain some trace amounts of water. Some common types of batteries for which the non-woven battery separator may be used include a lithium-ion battery, a sodium-ion battery, a lithium primary battery, or the like.

[0019] As will be demonstrated in the Examples, the non-woven battery separator in accordance with the present disclosure can be more effectively conditioned at higher temperatures before or after battery assembly than prior art separators to remove water during fabrication of the separator and can absorb residual water that may be present in the electrolyte during use. Moreover, the higher conditioning temperatures afforded by the non- woven battery separator permits the manufacturer to dry the assembled battery in its entirety since prior art separators such as the polyolefin-type were limited to temperatures less than 120oC, thereby providing more effective drying of the assembled battery including the casing and electrodes. By conditioning the assembled battery at these elevated temperatures of up to about 180oC, further decreases in the amount of residual water within the other battery components, e.g., anode, cathode, and the like, can occur compared to the temperature limitations associated with the prior art separators. Moreover, as noted above, once assembled and in use, the battery separator can absorb the trace amounts of water that may be contained in the electrolyte, which advantageously extends operating lifetimes and performance.

[0020] In the present disclosure, conventional techniques related to wet laid manufacturing and calendering processes for forming a non-woven web may or may not bedescribed in detail herein. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein. Various steps in the additive manufacture of three- dimensional articles are well known and so, in the interest of brevity, many conventional steps will only be mentioned briefly herein or will be omitted entirely without providing the well- known process details.

[0021] For the purposes of the description hereinafter, the terms “upper”, “lower”, “top”, “bottom”, “left,” and “right,” and derivatives thereof shall relate to the described structures, as they are oriented in the drawing figures. The same numbers in the various figures can refer to the same structural component or part thereof. Additionally, the articles “a” and “an” preceding an element or component are intended to be nonrestrictive regarding the number of instances (i.e. occurrences) of the element or component. Therefore, “a” or “an” should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular.

[0022] Spatially relative terms, e.g., “beneath,” “below,” “lower,” “above,” “upper,” and the like, can be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures.

[0023] The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

[0024] As used herein, the term “about” modifying the quantity of an ingredient, component, or reactant of the invention employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or solutions. Furthermore, variation can occurfrom inadvertent error in measuring procedures, differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods, and the like.

[0025] It will also be understood that when an element, such as a layer, region, or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present, and the element is in contact with another element.

[0026] As used herein, the term “nonwoven” refers to a manufactured sheet, web, or batt of natural and / or man-made fibers or filaments that are bonded to each other by any of several means that is subsequently used as a battery separator. Manufacturing of nonwoven products is well described in “Nonwoven Textile Fabrics” in Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Ed., Vol.16, July 1984, John Wiley & Sons, p.72˜124 and in “Nonwoven Textiles”, November 1988, Carolina Academic Press. Web bonding methods include mechanical bonding (e.g., needle punching, stitch, and hydro-entanglement), chemical bonding using binder chemicals (e.g., saturation, spraying, screen printing, and foam), and thermal bonding using binder fibers with low-melting points. Two common thermal bonding methods are air heating and calendaring. In the calendaring process, the web is passed and compressed between heated cylinders to produce the non-woven.

[0027] The non-woven battery separator in accordance with the present disclosure is generally formed of a fiber blend including regenerated cellulose fibers in an amount from 25 to 95% by weight based on the total weight of the fibers, microfibrillated cellulose fibers in an amount from 5 to 20% by weight based on the total weight of the fibers, and optionally synthetic fibers having a melting point greater than 200°C. The regenerated cellulose fibers and the microfibrillated cellulose are refined, and preferably refined together. Furthermore, the non-woven battery separator is free of a resinous binder or a thermoplastic binder.

[0028] In the sense of the present specification, a resinous binder is intended to be a binder in a liquid form aimed to crosslink and solidify upon the application of heat thus binding the fibers together to provide the non-woven with some structural integrity.Furthermore, a thermoplastic binder can be in the form of a liquid or fibers having a melting point below 200°C, more particularly thermoplastic binder is intended to mean bi- component fibers or other low melting temperature fibers (below 200°C) aimed at melting during the manufacturing process of the non-woven battery separator and resolidifying in order to provide the non-woven with some structural integrity.

[0029] In the present specification, a microfibrillated cellulose (MFC) fiber is a fiber derived from natural material made up of cellulose fibrils that have been separated from a source such as wood pulp. The MFC fibers have an average width comprised between 10 and 25 µm, an average length comprised between 300 and 600 µm and a content of secondary fibers comprised between 15 and 35%. The MFC fibers have a BET surface area of between 30 m² / g and 150 m² / g.

[0030] The refined cellulose fibers can include regenerated cellulose fibers such as lyocell fibers. As used herein, regenerated cellulose fiber is intended to be interpreted as cellulosic fibers dissolved in a solvent and then wet-spun in order to form new fibers. The regenerated cellulose fibers may have an average length comprised between 522 and 3192 µm and an average width comprised between 10 and 20 µm.

[0031] The MFC fibers function as a binder, providing structural integrity to the non-woven battery separator. Additionally, the MFC fibers also advantageously adsorbs moisture traces possibly contained in the electrolyte or in the other constituents of the battery. The particular MFC fibers are not intended to be limited and can be derived from a variety of sources. By way of example, the MFC fibers can be obtained under the trade name Integrand Strong micro fibrillated cellulosic fibers available from Stora Enso Oyj of Helsinki, Finland. These MFC fibers had an average width of about 15 microns, an average length of 553 microns, and about 30% secondary fine fibers prior to refining. Other MFC fibers available from Suzano, Brazil had an average width of about 20 microns, an average length of 427 microns, and about 23% secondary fine fibers prior to refining. Still further, other suitable MFC fibers were obtained from Borregaard, Norway had an average width of about 17 microns, an average length of 317 microns, and about 17% secondary fine fibers prior to refining.

[0032] The optional synthetic fibers, if present, are present in the battery separator in an amount of 5 to 65 wt% based on the total weight of the fibers forming the non-woven battery separator. These synthetic fibers have a melting point of greater than 200°C and are preferably selected from the group consisting of polyester fibers or a blend of aramid fibers and polyester fibers. These optional synthetic fibers are used in order to improve the mechanical strength of the battery separator. According to some embodiments, these synthetic fibers can be replaced by non-refined cellulosic fibers.

[0033] The synthetic polyester fibers can include, but are not limited to, thermoplastic polyesters, which offers high heat resistance as well as processability, dimensional stability and chemical resistance. Suitable thermoplastic polyesters include, but are not limited to, polycyclohexylene dimethylene terephthalate (PCT), polybutylene terephthalate (PBT), and polyethylene terephthalate (PET). Preferably, the polyester fibers are polyethylene terephthalate fibers and more particularly having a melting point between 210 and 300°C. Preferably, polyester fibers are present in the non-woven battery separator in an amount of 5 to 40 wt% based on the total weight of the fibers in the non-woven battery separator. Preferably, the polyester fibers are present in the non-woven battery separator in an amount of 5 to 30 wt%, more preferably in an amount of 10 to 20 wt%, based on the total weight of fibers in the non-woven battery separator; Preferably, the polyester fibers are not refined. The polyester fibers may have an average linear density of between 0.06 and 1.7 dtex and an average length of between 0.5 and 12 mm.

[0034] According to some embodiments, aramid fibers can be blended with polyester fibers. According to such embodiments, the aramid fibers comprise para-aramid fibers. If present, the aramid fibers are present in the non-woven battery separator in an amount of 20 to 40 wt% based on the total weight of the fibers in the non-woven battery separator. Preferably, the aramid fibers are present in the non-woven battery separator in an amount of 22 to 35 wt% based on the total weight of the fibers in the non-woven battery separator. The aramid fibers have a melting point well above 200°C. Preferably, the aramid fibers have an average length of between 100 and 1500 µm and an average width of between 10 and 200 µm.

[0035] In one or more embodiments, the non-woven battery separator includes a fiber blend of regenerated cellulose fibers such as the lyocell fibers in an amount from about 25% to about 95% by weight, and microfibrillated fibers in an amount from 5 to about 20% by weight based on a total weight of the fibers, the regenerated cellulose fibers and the microfibrillated cellulose fibers being refined, and preferably refined together before the formation of the non-woven battery separator.

[0036] The process for manufacturing the battery separator first includes mixing the regenerated cellulosic fibers with the microfibrillated cellulose fibers in a solvent, such as for example water to form a fiber blend suspension. The fiber blend suspension may comprise 25 to 95 % by weight of regenerated cellulose fibers, based on the total weight of the fibers and 5 to 20 % by weight of microfibrillated cellulose fibers based on the total weight of the fibers. The regenerated cellulosic fibers in this fiber blend suspensions may be fibrillated fibers refined at a degree of between 20 to 70°SR, measured according to NF ISO 5267-1 standard.

[0037] The fiber blend suspension is then refined to a freeness of between 50 and 85°SR when measured using a Schopper-Riegler (SR) freeness tester and using the NF ISO 5267-1 standard, to obtain a slurry of fibers. During this refining step, the fibers are subjected to a surface treatment step to produce fibrils on the surface, which will improve the strength of the fiber web as there will be more entanglement between the fibers. Fiber refinement is a mechanical treatment process applied to the fibers and is often referred to by those skilled in the art as beating. The refining step may include imparting energy (i.e., shear, fibrillation) to the fibers in order to reduce their length and thickness. Upon completion of the refining step, the refined cellulosic fibers will have a refining degree which may be measured using a Schopper-Reigler (SR) freeness tester. The preferred refining degree may be at least 50°SR and less than 85°SR, preferably at least 65°SR and less than 75°SR. The amount of refining may also be measured based on the weight % of secondary fines in the highly refined cellulosic fibers.

[0038] The slurry of fibers, is then transferred to a headbox of a paper machine so as to be deposited onto a forming fabric or forming wire of the paper machine. Oncedeposited to the forming fabric or forming wire, a vacuum may be applied to the deposited slurry to remove at least a portion of the solvent. Removing a portion of the solvent will result in formation of the non-woven substrate.

[0039] The non-woven substrate may then be consolidated, e.g., by a calendaring process, which generally includes passing and compressing the web between cylinders or nips to produce the nonwoven battery separator. By way of example, a consolidation process can include calendering at an elevated temperature and under an applied pressure with the media going through one or more passes between the heated cylinders. By way of example, the thermal consolidation process can include a combination of multiple passes through a nip defined by a rubberized roller and a steel roller at 120oC and a pressure of 100daN. In another example, the thermal consolidation process can include passing the web through two steel rollers at 140oC and a pressure of 400daN, wherein the speed can be varied depending on the desired media properties. The particular consolidation parameters are not intended to be limited and can vary significantly to provide the desired loft and material characteristics. The consolidation of the composite web effects a reduction in the fiber spacing and pore size by increasing density, i.e., by fiber compression and bonding. The density of the web material and the flatness (levelness) of the surface of the web material are substantially enhanced in the consolidation process. Furthermore, the calendering step can also limit the number of pin-holes (considered as defects) in the final non-woven battery separator.

[0040] In one or more embodiments, the consolidation process is configured to provide the battery separator with a thickness of less than about 150 microns (µm) after calendaring. In one or more other embodiments, the thickness after calendaring is less than about 50 µm, and in still one or more other embodiments, the thickness after calendaring is less than about 50 µm. In yet one or more other embodiments, the calendaring process is configured to provide the battery separator with a thickness after calendaring of less than about 30 µm, and in still one or more other embodiments, the calendaring process is configured to provide the battery separator after calendaring with a thickness of less than about 25 µm. In one or more embodiments, the nonwoven battery separator after calendaring in accordance with the present disclosure may have a thickness between about 10 to about 25 microns. According to some embodiments, the nonwoven battery separatorafter calendaring in accordance with the present disclosure may have a thickness between about 80 to about 120 µm. After the consolidating step, the non-woven battery separator is dried and may optionally be wound in a roll.

[0041] The slurry of fibers may further contain synthetic fibers having a melting point greater than 200°C. Such synthetic fibers can be present in an amount of 5 to 65 wt% based on the total weight of the fibers. Such synthetic fibers may comprise polyester fibers in an amount of 5 to 40 wt% based on the total weight of the fibers. If polyester fibers are present in the non-woven battery separator, said fibers are preferably added after the refining step B in order to prevent the removal of surface treatment present on the surface of such polyester fibers. Preferably, these polyester fibers are polyethylene terephthalate fibers. According to other embodiments, the synthetic fibers may comprise aramid fibers in an amount of 20 to 40 wt% based on the total weight of fibers. In case aramid fibers are present in the fiber blend or in the fiber slurry, these fibers can be introduced directly in the fiber blend to be further refined with the regenerated cellulosic fibers and the microfibrillated cellulose fibers.

[0042] By way of example, the separator for lithium primary batteries can be between about 80 and 120 µm whereas for lithium-ion and sodium-ion batteries, the separator can be between 10 and 25 µm, although greater or lesser thicknesses could be used.

[0043] In one or more embodiments, the non-woven battery separator has a porosity between about 20 and 65% and includes an average pore size after calendaring of about 0.5 to 4 microns, preferably comprised between 0.7 and 2 microns, as measured according to ASTM F316- 03 (2011) - Standard Test Methods for Pore Size Characteristics of membrane Filters by Bubbler Point and Mean Flow Pore Test using a Porometer 3G produced by Quantachrome Instruments of Boynton Beach, Florida, U.S.A. Porosity generally relates to the amount of empty space within a given volume of the separator and affects the transport of ions and electrolytes through the separator. The porosity of the non-woven battery separator is calculated following the standard J2983:2019 and using the following formula:[ p y y parator is measured in accordance with the Bendtsen method, which calculates air flow by forcing air through the sheet and measuring the rate of flow, according to ISO Standard 5636-3. In the Bendtsen method, the separator is clamped between a flat glass plate and a circular metal head. The air permeability of the non-woven battery separator after calendaring in accordance with the present disclosure is from about 200 to about 6000 milliliters per minute (ml / min).

[0045] In the machine direction (MD), the nonwoven battery separators can have a dry tensile strength between about 500 to about 2000 Newtons per meter (N / m) and a dry percent elongation of about 1.4 to about 4.0%. In the cross direction (CD), the separators can have a dry tensile strength between about 150 to about 1500 N / m and a dry percent elongation of about 1.5 to about 6.0%. Shrinkage in the MD at 160oC can be less than about -1.50% and in the CD can be less than about -1.00%. If the non-woven battery separator is aimed at being used in a lithium-ion battery or in a sodium-ion battery, it has in MD a dry tensile strength between 500 and 2000 N / m and a dry percent elongation between 1.5% and 4.0%; and in CD a dry tensile strength of between 150 and 550 N / m and a dry percent elongation of between 1.5 and 6.0 %. For lithium primary batteries, the separators have a higher thickness and grammage relative to lithium- and sodium-ion batteries and a dry tensile strength in MD of between1000 and 2000 N / m, a dry percent elongation in MD of between 2.0 and 3.0%, a dry tensile strength in CD of between 1000 and 1500 N / m and a dry percent elongation in CD of between 2.0 and 3.0%.

[0046] The Macmullin number is defined as a ratio of the ionic conductivity of a pure electrolyte (^ electrolyte) to the ionic conductivity of the separator filled with electrolyte (^ separator). In other words, the Macmullin number quantifies the decrease in effective conductivity due to the presence of the separator. Maintaining relatively low resistance in a separator filled with electrolyte is important for battery performance. In one or more embodiments, the Macmullin number for batteries in accordance with the present disclosure is less than about 15.

[0047] The lithium-ion and sodium-ion battery separators have a mass per unit area, expressed in grammage, in a range between about 5 to about 25 grams / square meter (g / m2). For lithium primary batteries, the grammage is between about 40 to100 g / m2.

[0048] A method of manufacturing a battery can include providing an anode and a cathode; conditioning a battery separator, wherein the conditioning step is performed at a temperature of between 120°C and 180°C; disposing the battery separator between the anode and the cathode; and introducing an electrolyte solution in the battery. The battery separator is formed from regenerated cellulose fibers in an amount from 25 to 95% by weight based on a total weight of the fibers; microfibrillated cellulose fibers in an amount from 5 to 20% by weight based on the total weight of the fibers; and optionally, synthetic fibers having a melting point greater than 200oC as previously described. The regenerated cellulose fibers and the microfibrillated cellulose fibers are refined, and the resulting separator is free of a resinous binder or a thermoplastic binder. The conditioning step can be performed at a temperature of between 140°C and 160°C.

[0049] FIG.1 illustrates an exemplary battery 10 including the non-woven battery separator 12, a positive electrode 14 (also known as a cathode), a negative electrode 16 (also known as an anode), and an electrolyte 18. In lithium-ion or lithium primary batteries, the electrolytes 18 can include water sensitive conductive salts, for example, a lithium salt such as lithium hexafluorophosphate, lithium hexafluoroarsenate monohydrate, lithium perchlorate, lithium tetrafluoroborate, lithium triflate, or the like, which are generally provided in an organic solvent such as an ethylene carbonate, a diethyl carbonate, and the like. Likewise, in sodium-ion batteries, the electrolytes 18 can include water sensitive conductive salts such as sodium hexafluorophosphate, sodium hexafluoroarsenate monohydrate, sodium perchlorate, sodium tetrafluoroborate, sodium triflate in similar solvents. The various electrolytes are not intended to be limited.

[0050] The battery may come in many configurations. One such configuration is a cylindrical shape battery in which the battery separator is sandwiched between the positive electrode (cathode) and the negative electrode (anode) and rolled into a single spool. Another configuration is a stacked configuration in which the battery separator issandwiched between a substantially flat sheet positive electrode (cathode) and a substantially flat sheet negative electrode (anode) such as is shown in FIG.1.

[0051] This disclosure is further illustrated by the following examples, which are non-limiting. EXAMPLES

[0052] In this example, water absorption of a non-woven battery separator in accordance with the present disclosure was measured after conditioning at 120oC, 150oC, 180°C and 200°C for a period of 16 hours in an oven. The water absorption of the dried non-woven battery separators was compared to a conditioned non-woven battery separator of the same composition stored in a conditioned room at a temperature of 23oC and 50% humidity for a period of 16 hours. The conditioned non-woven battery separator was not subjected to the drying conditions.

[0053] The non-woven battery separators were immersed in Hydranal™ Coulomat E (“Hydranal”) electrolyte commercially available from Honeywell Corporation / Fluka, which is commonly used as an analyte for coulometric Karl Fisher titration for determining water content in a sample. The electrolyte typically has about 700 parts per million (ppm) of water as received from the manufacturer. In order to estimate the amount of water adsorption, different amounts of water were added to the Hydranal, e.g., 500 ppm, and 1000ppm, and 2000pm, which is in addition to the approximate 700 ppm of water that the electrolyte contains from the manufacturer.

[0054] Water content after immersion of each battery separator in the electrolyte was measured by Karl Fisher Titration. The water content results for the non-woven battery separator dried at 120oC, 150oC, 180°C and 200°C for 16 hours prior to immersion are shown in Table 1 below and the water content of the conditioned battery separator and the dried non-woven battery separators at the four different drying temperatures were compared and are graphically shown in FIGS.2 to 5.

[0055] In FIG.2, the amount of water loading detected in the electrolyte by itself, after immersion of the non-woven battery separator dried at 120oC for 16 hours, and afterimmersion of the conditioned battery separator are shown as a function of the amount of water detected in the electrolyte. As previously mentioned, the Hydranal-Coulomet E had a water content of about 700 ppm as received from the manufacturer. As such, the electrolyte reference value is the sum of the water contained in the electrolyte as received from the manufacturer and the amount intentionally added. For example, the water content of the electrolyte in which 500 ppm was injected was 1184 ppm, which indicates that the electrolyte as received from the manufacturer had a water content of 684 ppm; the water content of the electrolyte in which 1000 ppm was injected was 1659 ppm, which indicates that the electrolyte as received from the manufacturer had a water content of 659 ppm; and the water content of the electrolyte in which 2000 ppm was injected was 2744 ppm, which indicates that the electrolyte as received from the manufacturer had a water content of 744 ppm. It should be apparent that the variability in the amount of water content of the reference electrolyte as received from the manufacturer can be attributed to different lots of the electrolyte from the manufacturer and storage conditions once the electrolyte container was opened.

[0056] The non-woven battery separator dried at 120oC for 16 hours was immersed in this reference electrolyte and exhibited a total water content of 1038 ppm, which is indicative of water absorption in the amount of 146 ppm. However, the conditioned non- woven battery separator that was not subjected to drying at 120oC for 16 hours and immersed in the same reference electrolyte exhibited a release of water in the amount of 839 ppm. Similar behavior of water absorption for the dried non-woven battery separator and water release for the conditioned non-woven battery separator was observed for the reference electrolyte in which 1000 and 2000 ppm of water was added.

[0057] As shown in FIG.3, water absorption of the non-woven battery separator dried at 150oC relative to the conditioned non-woven battery separator is graphically shown for the different amounts of water intentionally added to the reference electrolyte. The amount of water absorption increased as a function of the increased drying temperature. For example, the water content of the electrolyte in which 500 ppm was injected was about 1375 ppm, which indicates that the reference electrolyte as received from the manufacturer was about 875 ppm. The non-woven battery separator dried at 150oC for 16 hours was immersedin this reference electrolyte and exhibited a total water content of 1070 ppm, which is indicative of water absorption in the amount of about 305 ppm. However, the conditioned non-woven battery separator that was not subjected to drying at 150oC and immersed in the same reference electrolyte exhibited a release of water in the amount of 1191 ppm. Again, similar behavior was observed for the reference electrolyte in which 1000 and 2000 ppm of water was added.

[0058] In FIG.4, water absorption of the non-woven battery separator dried at 180oC relative to the conditioned non-woven battery separator is graphically shown for the different amounts of water intentionally added to the reference electrolyte. The amount of water absorption increased as a function of the increased drying temperature. For example, the water content of the electrolyte in which 500 ppm was injected was about 888 ppm, which indicates that the reference electrolyte as received from the manufacturer was about 388 ppm. The non-woven battery separator dried at 180oC for 16 hours was immersed in this reference electrolyte and exhibited a total water content of about 847 ppm, which is indicative of water absorption in the amount of about 41 ppm. However, the conditioned non-woven battery separator that was not subjected to drying at 180oC and immersed in the same reference electrolyte exhibited a release of water in the amount of about 1247 ppm. Again, similar behavior was observed for the reference electrolyte in which 1000 and 2000 ppm of water was added.

[0059] In FIG.5, water absorption of the non-woven battery separator dried at 200oC relative to the conditioned non-woven battery separator is graphically shown for the different amounts of water intentionally added to the reference electrolyte. The amount of water absorption increased as a function of the increased drying temperature. For example, the water content of the electrolyte in which 500 ppm was injected was about 1222 ppm, which indicates that the reference electrolyte as received from the manufacturer had a water content of about 891 ppm. The non-woven battery separator dried at 200oC for 16 hours was immersed in this reference electrolyte and exhibited a total water content of about 1083 ppm, which is indicative of water absorption in the amount of about 139 ppm. However, the conditioned non-woven battery separator that was not subjected to drying at 200oC and immersed in the same reference electrolyte exhibited a release of water in the amount ofabout 913 ppm. Again, similar behavior was observed for the reference electrolyte in which 1000 and 2000 ppm of water was added.

[0060] As shown in Table 1 below, water absorption was observed for the non- woven battery separator dried at 120oC, 150oC, 180oC and 200oC. At the higher drying temperatures of 180oC and 200oC, negative numbers were observed at the higher injected amounts indicating water release but at the lower injected amount of 500 ppm a relatively smaller amount of water was adsorbed. However, it was also observed that if the non- woven battery separator was not dried, the battery separator released significant amounts of water. Accordingly, the non-woven battery separator, when conditioned at temperatures greater than 120oC to less than about of 180oC, can be expected to increase battery lifetimes since it absorbs water produced during the working time of the battery and also can be expected to reduce the emission of HF produced internally. Table 1. Water Adsorption Adsorption Adsorption Adsorption Injected (ppm) (ppm) (ppm) (ppm) (ppm) Drying at Drying at Drying at Drying at 120oC for 150oC for 180oC for 200oC for 16 hours 16 hours 16 hours 16 hours 500 146 305 41 139 1000 218 176 -101 -97 (release) (release) 2000 207 414 -150 0 (release)

[0061] Tables 2-5 show non-woven battery separators aimed at being used in lithium-ion or sodium-ion batteries. These non-woven battery separators were fabricated from various fiber blends and the associated parameters tested. The battery separators shown below were conditioned at a temperature of 23oC, 50% moisture and for a period of 24 hours. The aramid fibers were para-aramid and the polyester fibers were polyethylene terephthalate (PET). In this specific example, Examples 12 and 13 correspond to comparative examples.Table 2.: Compositions of the samples for a use in lithium-ion or sodium-ion batteries Ex. Lyocell MFC Aramid PET 1 87.5 12.5 --- --- 2 87.5 12.5 --- --- 3 50 20 --- 30 4 50 20 --- 30 5 70 10 --- 20 6 70 10 --- 20 7 79 11 --- 10 8 35 10 35 20 9 35 10 35 20 10 35 10 35 20 11 35 10 35 20 12 50 --- 30 20 13 50 --- 30 20 Table 3: Physical properties of the samples: Ex. Grammage Thickness Density Schopper Gurley Bendsten Mean % (g / m2) -100kPa -100kPa (final (s) (mL / min) Pore Size Porosity (µm) (g / m2 / µm) mix) (µm) 1 20 25 0.8 72 26.0 400 1.1 43 2 15 22 0.7 72 34.0 400 1.1 51 3 21 21 1.0 80 50 200 0.7 37 4 15 15 1.0 80 24 400 1.1 40 5 19 24 0.8 78 14.4 800 1.3 43 6 14 18 0.8 78 8.0 1400 1.4 44 7 15 23 0.7 78 16.5 700 1.2 53 8 19 19 1.0 73 5.5 500 1.3 27 9 16 21 0.8 73 3.4 2700 3.8 47 10 16 18 0.9 75 21 600 1.0 35 11 16 16 1.0 64 10.0 1100 1.5 35 12 21 19 1.0 70 4 2200 1.5 24 13 14 19 0.8 66 2 6000 6 48 Table 4.: Mechanical properties of the samples Ex.Dry-MachineDry-Cross Direction Wet-Machine Wet-Cross Direction Direction DirectionTensile Elongation Tensile Elongation Tensile Elongation Tensile Elongation Strength (%) Strength (%) Strength (%) Strength (%) (N / m) (N / m) (N / m) (N / m) 1 1024 2.5 516 2.1 67 3.8 42 5.5 2 629 1.7 298 1.6 95 4.2 56 5.2 3 804 3.7 516 5.5 557 7.5 333 7.0 4 530 2.5 325 4.3 472 6.4 257 7.8 5 854 3.0 500 3.3 82 3.1 54 5.5 6 678 3.3 320 3.0 72 3.3 42 6.4 7 720 2.7 352 3.0 70 4.1 40 6.0 8 803 2.0 210 3.0 157 3.5 55 12.0 9 567 3.0 163 3.0 120 2.7 37 9.5 10 661 1.9 313 3.6 145 4.2 71 6.5 11 492 1.7 349 3.7 435 3.9 304 4.8 12 693 2.0 203 3.0 184 2.6 50 9.3 13 457 2.0 122 3.0 98 4.2 50 9.0 Table 5. Thermal shrinkage of the samples Ex.Thermal Shrinkage (%); (1 hour at 200oC) Machine Direction Cross Direction 1 0.7 0.9 2 0.8 0.6 3 1.1 0.9 4 0.9 0.9 5 0.7 0.8 6 0.7 0.6 7 0.8 0.7 8 0.4 0.4 9 0.5 0.3 10 0.5 0.6 11 0.6 0.3 12 0.8 0.5 13 0.6 0.4

[0062] As shown in Tables 5-7, an exemplary battery separator formulation suitable for use in a lithium primary battery is provided, which is also referred to in the art as a lithium metal battery. Lithium primary batteries refer to non-rechargeable batteries that usemetallic lithium as the anode. Table 5 provides the composition, and Tables 6-7 provides measurement of various properties associated with the battery separator, which advantageously adsorbs the trace amounts of water from the electrolyte when in use, thereby extending operating lifetime and performance. Table 6.: Composition of the sample for a use in a lithium-primary battery Composition (wt%) Lyocell Aramid PET MFC 46 22 20 12 Table 7.: Physical properties of the sample Grammage Thickness Density Schopper Gurley Bendtsen Mean Porosity (g / m2) -100kPa 100kPa (oSR) of (s) (mL / min) Flow (%) (µm) (g / m2 / µm) the final Pore mix Size (µm) 54 98 0.6 73 42.0 300 0.8 61 Table 8.: Mechanical properties of the sample Dry-Machine Dry-Cross Direction Wet-Machine Wet-Cross Direction (MD) (CD) Direction Direction Tensile Elongation Tensile Elongation Tensile Elongation Tensile Elongation Strength (%) Strength (%) Strength (%) Strength (%) (N / m) (N / m) (N / m) (N / m) 1504 2.3 1291 2.2 130 1.8 122 1.5 Table 9: Thermal shrinkage of the sample % Thermal Shrinkage in MD % Thermal Shrinkage in CD(1 hour at 200°C) (1 hour at 200°C) 0.8 0.7

[0063] These and other modifications and variations to the invention may be practiced by those of ordinary skill in the art without departing from the spirit and scope of the 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 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 it is not intended to limit the invention as further described in such appended claims. Therefore, the spirit and scope of the appended claims should not be limited to the exemplary description of the versions contained herein.

Claims

CLAIMS:

1. A non-woven battery separator comprising: regenerated cellulose fibers in an amount from 25 to 95% by weight based on a total weight of the fibers; microfibrillated cellulose fibers in an amount from 5 to 20% by weight based on the total weight of the fibers; and optionally, synthetic fibers having a melting point greater than 200oC, wherein the regenerated cellulose fibers and the microfibrillated cellulose fibers are refined, and wherein the non-woven battery separator is free of a resinous binder or a thermoplastic binder.

2. The non-woven battery separator of claim 1, wherein the refined regenerated cellulose fibers comprise lyocell fibers.

3. The non-woven battery separator according to any one of the preceding claims, wherein the regenerated cellulose fibers are fibrillated fibers at a degree of 20 to 70 °SR.

4. The non-woven battery separator according to any one of the preceding claims, wherein the optional synthetic fibers are present in the battery separator in an amount of 5 to 65 wt% based on the total weight of the fibers.

5. The non-woven battery separator according to any one of the preceding claims, wherein the optional synthetic fibers are selected from the group consisting of polyester fibers, and a blend of aramid fibers and polyester fibers.

6. The non-woven battery separator according to claim 5, wherein the polyester fibers are present in the non-woven battery separator in an amount of 5 to 40 wt% based on the total weight of the fibers.

7. The non-woven battery according to claims 5 and 6, wherein the aramid fibers are present in the non-woven battery separator in an amount of 20 to 40 wt% based on the total weight of the fibers.

8. The non-woven battery separator according to any one of claims 5 to 7, wherein the polyester fibers comprise polyethylene terephthalate fibers, and / or wherein the aramid fibers comprise para-aramid fibers.

9. The non-woven battery separator according to any one of the preceding claims, wherein the non-woven battery separator has a thickness of less than 150 microns, preferably comprised between 10 and 30 microns, or between 80 and 120 microns.

10. The non-woven battery separator according to any one of the preceding claims, wherein the non-woven battery separator has an average pore size between about 0.5 to 4 microns.

11. The non-woven battery separator according to any one of the preceding claims, wherein it has a porosity between 20 and 65%.

12. The non-woven battery separator according to any one of the preceding claims, wherein it has an air permeability of 200 to 6000 ml / min as measured in accordance with ISO Standard 5636-3.

13. A process for manufacturing a non-woven battery separator, the process comprising: (A) mixing regenerated cellulose fibers with microfibrillated cellulose fibers in a solvent to form a fiber blend suspension, wherein the regenerated cellulose fibers comprise 25 to 95% by weight and the microfibrillated cellulose fibers in an amount from 5 to 20% by weight based on a total weight of the fibers; (B) refining the fiber blend suspension to a freeness of between 50°SR and 85°SR when measured using a Schopper-Reigler (SR) freeness tester, to obtain a slurry of fibers; (C) transferring the slurry of fibers to a headbox of a paper machine;(D) depositing the slurry onto a forming wire or forming fabric of the paper machine; (E) applying a vacuum to the deposited slurry to remove at least a portion of the solvent and form a non-woven fiber substrate; (F) consolidating the non-woven substrate to form a non-woven battery separator; and (G) drying the non-woven battery separator.

14. The process of claim 13, wherein the slurry of fibers further contains synthetic fibers having a melting point greater than 200°C, said synthetic fibers being present in an amount of 5 to 65 wt% by weight based on the total weight of the fibers.

15. The process of claim 14, wherein the synthetic fibers comprise polyester fibers in an amount of 5 to 40 wt% based on the total weight of the fibers, wherein said polyester fibers are introduced in the slurry of fibers after step B.

16. The process of claims 14 and 15, wherein the synthetic fibers comprise aramid fibers in an amount of 20 to 40 wt% based on the total weight of the fibers, wherein said aramid fibers are introduced in the fiber blend during step A.

17. The process according to any one of claims 13 to 16, wherein consolidating the non-woven substrate to form a non-woven battery separator comprises a calendaring step.

18. The process of any one of claims 13 to 17, wherein the regenerated cellulose fibers comprise lyocell fibers.

19. A battery comprising a non-woven battery separator according to any one of claims 1 to 12 or manufactured according to the process of claims 13 to 18, wherein the non- woven battery separator is intermediate an anode and a cathode; wherein the anode, the cathode and the non-woven battery separator are immersed in an electrolyte solution; and the non-woven battery separator is configured for adsorbing water present in the electrolyte solution.

20. The battery according to claim 19, wherein the electrolyte comprises a moisture sensitive conductive salt and a solvent, wherein the conductive salt is reactive with water toproduce hydrogen fluoride.

21. The battery separator according to any of claims 19 or 20, wherein the non- woven battery separator is conditioned at a temperature between about 120°C and about 180°C prior to assembly.

22. The battery according to any one of claims 19 to 21, wherein the battery is a lithium-ion battery, a sodium ion battery or a lithium primary battery.

23. A process of manufacturing a battery, said process comprising the steps of: (A) providing an anode and a cathode; (B) conditioning a battery separator according to any one of claims 1 to 12, wherein the conditioning step is performed at a temperature of between 120°C and 180°C; (C) disposing the battery separator between the anode and the cathode; and (D) introducing an electrolyte solution in the battery.

26. The process according to claim 25, wherein the conditioning step is performed at a temperature of between 140°C and 160°C.

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