Improved battery separator for lithium-ion batteries

Abstract

A non-woven battery separator, a battery including the non-woven battery separator, and a method for manufacturing a non-woven battery separator having improved durability and elasticity for the purpose of better operating characteristics, longer-term durability, and safer battery products, where the non-woven battery separator is coated with an inorganic oxide.

Description

Technical Field

[0001] The present disclosure generally relates to improved nonwoven materials. Specifically, the present disclosure relates to nonwoven battery separators used in lithium ion batteries and methods for manufacturing the battery separators.

Background Art

[0002] Batteries have been used for years as generators in remote locations. By creating an electrical circuit through the controlled movement of an electrolyte (ions) between electrodes (negative and positive), a power source is provided that can be utilized until the electrolyte source is depleted and further power generation is no longer possible. More recently, rechargeable batteries have been created to enable such remote power sources to have a longer lifespan. However, overall, the ability to reuse such batteries has led to greater potential for use in applications such as handheld devices, specifically, for example, mobile phones and laptop computers, and even the potential for automobiles that require electricity to function.

[0003] Such batteries typically include at least five different components. The housing (or container) stores everything in a safe and reliable manner, preventing external leakage and exposure to the internal environment. Inside the housing, there are a negative electrode and a positive electrode effectively separated by a battery separator, as well as an electrolyte (e.g., a low-viscosity liquid) that moves through the battery separator between the negative and positive electrodes. Rechargeable batteries can operate in a variety of areas, from small, portable devices with a large power generation potential that remain effective for long periods between charging episodes, to large types present in automobiles, for example. They include large electrodes that should not contact each other (at least in terms of surface area) and a large amount of electrolyte that requires a membrane to consistently and constantly pass through to complete the necessary circuit, all having a conductive power generation level sufficient to supply enough electricity to operate an automobile engine. And with the further emergence of electric vehicles, the demand for such batteries is expected to grow. Thus, the functions and versatility of future battery separators need to meet certain requirements that are not yet provided within the current industry.

[0004] Battery separators have been used since the emergence of sealed batteries that provide the necessary protection from improper contact between electrodes and enable effective movement of electrolytes within the power generation cell. Usually, such materials have a sufficiently thin film structure that reduces the weight and volume of the battery device while providing the necessary properties mentioned above. Such separators must also exhibit other characteristics to enable the original battery function. These include chemical stability, appropriate porosity for ion species, pore size effective for electrolyte movement, appropriate permeability, effective mechanical strength (both during battery assembly and operation), and the function of maintaining dimensional and functional stability when exposed to high temperatures (and the possibility of shutting down when the temperature rises to an abnormally high level).

[0005] The battery separator material must have sufficient strength and a structure that can withstand various assumptions. First, the separator must not be torn or punctured when the load of battery assembly is applied. In this method, the mechanical strength of the entire separator is extremely important. In particular, high tensile strength materials in both the longitudinal and transverse directions enable the manufacturer to handle such battery separators more easily without requiring strict operating standards, so that the battery separator does not suffer from or lose structural defects during the above procedures. Furthermore, from a chemical perspective, the battery separator needs to withstand the oxidative and reductive environments inside the battery itself, especially when it is fully charged. Any failure during use, specifically in terms of structural integrity, such as allowing an abnormally large amount of electrolyte to pass through or bringing the electrodes into contact, may destroy the power generation capacity and render the battery inefficient as a whole. Thus, even if the above-mentioned ability to withstand weather chemical exposure exists, for the same reasons as above, during storage, manufacturing, or use, the above separator must not lose dimensional stability (i.e., distortion or melting) or mechanical strength.

[0006] At the same time, the battery separator needs to have an appropriate thickness to promote the high energy and power density of the battery itself. Any non-uniform wear in the battery separator can be a weakness in terms of proper electrolyte movement and prevention of electrode contact, so a uniform thickness is also quite important to enable a long-term life cycle. However, the ability to make the above battery separator extremely thin and of uniform dimensions has been shown to be rather difficult, especially since thinning of an already thin structure tends to compromise separator strength.

[0007] Furthermore, with respect to the pore size, the battery separator must exhibit an appropriate porosity and pore size that are compatible with the proper movement of ions through the membrane (and the capacity suitable for retaining a certain amount of liquid electrolyte to facilitate the above-mentioned ion movement during use). The pores themselves need to be small enough to prevent the electrode components from entering and / or passing through the membrane, but it is also necessary to allow the electrolyte ions to pass through at an appropriate rate. Also, since uniform wear of the battery separator enables extending the life cycle, the uniformity of the pore size, as well as the pore size distribution, make the power generation over time more uniform and provide reliable long-term stability throughout the battery. It may be further advantageous to ensure that the pores can close properly to prevent excessive and unwanted ion movement when the pores are exposed to abnormally high temperatures during battery failure (e.g., to prevent fire and other similar hazards). Thus, reducing the pore size uniformly and to a small extent within a thin, highly dense non-woven structure (and thus measuring the appropriate porosity for that purpose) has not yet been fully optimized. The film structure can be manufactured to certain dimensions, but rather than manufacturing or deforming it through additional processing at least after the initial manufacturing, a reduction in porosity is planned for such separators. For example, there remains room to reduce the pore size while maintaining sufficient durability and elasticity against mechanical stress to provide advantageous protection from the perspective of electrode contact.

[0008] Furthermore, the battery separator must not degrade the performance of the electrolyte that completely fills the entire cell during manufacturing, storage, and use. Thus, the battery separator must exhibit appropriate wicking and / or wetting properties during such phases to ensure that the electrolyte can be actually generated properly and ions can pass through the membrane. If the separator is non-conductive in such a situation, the electrolyte will not properly reside on and within the pores of the separator, and the required ion transfer will not occur easily. In other words, generally, the smaller the battery separator, the better. Therefore, it may be highly desirable to provide a strong, thin, and highly dense structure.

[0009] Battery separators made of nanofibers have been supplied to the industry. Such a structure enables the user to adjust the porosity level as desired with an effective isotropic strength level according to the manufacturing process and procedure. The above separator is also effective from the perspective of air resistance and provides a structure highly desired in the market of lithium-ion batteries and other similar batteries. However, there are also drawbacks in that it cannot be highly expected from the perspectives of durability and elasticity.

[0010] One procedure for manufacturing nanofiber-based battery separators was to utilize the meltblow process. In the type of meltblow method, a non-woven web is formed by extruding a molten polymer through a die and then thinning and breaking the filaments obtained with a high-temperature and high-speed gas stream. This process produces very fine short fibers that can be collected on a moving belt that adheres to each other during cooling. The meltblown web can be made to exhibit very good barrier properties and can be used as a battery separator.

[0011] Meltblown fibers are most commonly spun from polypropylene. Other polymers that have been spun as meltblown fibers include polyethylene, polyamide, polyester, and polyurethane. Meltblown fibers have been incorporated into various nonwovens, including, for example, battery separators.

[0012] While existing nonwoven webs formed including meltblown fibers are used as battery separators, there is a desire for a battery separator having improved physical resiliency against wear and puncture of the separator material during battery assembly and operation. Further, the properties of such battery separator webs should be improved to enhance speed and efficiency with the battery separator that infiltrates in the battery electrolyte, which can improve the manufacture of the battery. Additionally, such materials can be improved to speed up the charging cycle, reduce energy consumption, and extend battery life. Ultimately, the physical properties of such nonwovens should be improved to prevent or reduce the formation of dendrites and enhance resiliency against dendrite-induced punctures.

Summary of the Invention

Means for Solving the Problems

[0013] All features of the present disclosure and its preferred embodiments are described in complete detail in connection with the following specific embodiments. The description of the battery separators, battery cells, and methods of manufacturing them of the present invention is not intended to limit their scope in any way.

[0014] It should be noted that the features described in connection with one exemplary embodiment or exemplary aspect can be combined with any other exemplary embodiment or exemplary aspect. Specifically, the features described in any exemplary embodiment of the nonwoven fabric can be combined with any other exemplary embodiment of the nonwoven fabric and / or battery separator, any exemplary embodiment of the manufacturing method of the nonwoven fabric and / or battery separator, any exemplary embodiment of the battery separator, and any exemplary embodiment of the use. And, unless otherwise specifically mentioned, the reverse is also true.

[0015] When an indefinite article or an article is used when referring to the singular form such as "a", "an" or "the", the plural form of the term is also included, and, unless otherwise specifically mentioned, the reverse is also true. However, the word "one (1)" or the number "1" used in this specification usually means "only 1" or "exactly 1".

[0016] The expression "comprising" used in this specification does not only include the meaning of "comprising", "including" or "containing", but may also include "consisting essentially of" and "consisting of".

[0017] Unless otherwise specified, as used herein, the expression "at least a part of" may mean at least 5%, specifically at least 10%, specifically at least 15%, specifically at least 20%, specifically at least 35%, specifically at least 40%, specifically at least 45%, specifically at least 50%, specifically at least 55%, specifically at least 60%, specifically at least 65%, specifically at least 70%, specifically at least 75%, specifically at least 80%, specifically at least 85%, specifically at least 90%, specifically at least 95%, specifically at least 98%, and may also mean 100% thereof.

Mode for Carrying Out the Invention

[0018] In a first aspect, the present disclosure relates to a non-woven material coated on one or both sides with an inorganic oxide and / or infiltrated with an inorganic oxide, such as a battery separator.

[0019] As used herein, the term "non-woven fabric" may specifically mean a web of individual fibers that are at least partially intertwined but not regular like a knitted or woven fabric.

[0020] As described above, the nonwoven fabric can be composed of any polymer (or polymer blend) that is compatible with suitable chemical resistance and heat resistance in combination with the internal battery cell conditions, and the ability to form a suitable fiber structure within the above ranges, and further the surface area of the fiber itself is increased to promote entanglement during nonwoven formation through fibrillation or similar methods. The above fibers can be made from conventionally existing fiber manufacturing methods, such as melt spinning, wet spinning, solution spinning, melt blowing, spunbonding, electrospinning, carding, and other methods. Further, such fibers can be started as bicomponent fibers and their size and / or shape can be reduced or deformed through further processing, such as splittable pie fibers, fibers having a sea-island structure, and other fibers. The above fibers can be cut to a suitable length for further processing, and the length may be less than 1 inch, or less than 1 / 2 inch, or just less than 1 / 4 inch. The above fibers can also be fibrillated into smaller fibers or fibers that advantageously form a wet-laid nonwoven fabric.

[0021] In certain embodiments, the nonwoven fabric may be composed of thermoplastic fibers. Suitable thermoplastic fibers include fibers comprising polypropylene, polyethylene terephthalate, nylon, polycaprolactam, polyphenylene sulfide, polyetherimide, and combinations thereof. The average fiber length of the thermoplastic fibers may be from 0.3 microns to 5 microns, or preferably, from 0.5 microns to 2 microns.

[0022] The nonwoven fabric of the present disclosure may contain nanofibers and can be produced by a plurality of conventional methods for making nanofibers. One example includes a sea-island structure, such as Nano-Front fibers available from Teijin, which are polyethylene terephthalate fibers with a diameter of 700 nm. Hills also manufactures and sells an apparatus that enables nanofibers having a sea-island structure. As another example, there may be electrospinning. Both Dienes and FiberRio sell apparatuses that can be used to provide nanofibers using the electrospinning method. Another example is the electrospinning method implemented by, for example, DuPont, E-Spin Technologies, or apparatuses sold by Elmarco for this purpose. Yet another method for making nanofibers is to fibrillate them from a film or from fibers. Nanofibers fibrillated from a film are disclosed in U.S. Patent No. 6,110,588, U.S. Patent No. 6,432,347, and U.S. Patent No. 6,432,532, and are hereby incorporated by reference in their entirety. Nanofibers fibrillated from other fibers may be so implemented under high shear and abrasion treatment. Nanofibers made from fibrillated cellulose fibers and fibrillated acrylic fibers are sold by Engineered Fiber Technologies under the trade name EFTEC™. Any of the above nanofibers are also further processed through cutting and high shear slurry processing to separate the fibers and enable their wet laid nonwoven processing. Such high shear processing may or may not occur in the presence of the required microfibers.

[0023] Conventional nanofibers produced by fibrillation have a transverse aspect ratio different from the transverse aspect ratio described in detail in U.S. Patent No. 6,110,588. Thus, in one preferred embodiment, the transverse aspect ratio of the nanofibers is >1.5:1, preferably >3.0:1, and more preferably higher than 5.0:1.

[0024] Thus, for the above purposes, acrylic fibers and polyolefin fibers are particularly preferred, and fibrillated acrylic fibers are even more specifically preferred. However, to reiterate, this is presented merely as indicating potentially preferred types of polymers for this purpose and is not intended to limit the scope of possible polymer materials or polymer blends for such purposes.

[0025] One specific embodiment of the combination of microfibers and nanofibers is EFTEC™ A - 010 - 4 fibrillated polyacrylonitrile fibers with high densities of nanofibers as well as microfibers. As an example, these fibers can be used as a base material to which additional microfibers or additional nanofibers can be added as a means of controlling the pore size and other properties of the non - woven fabric.

[0026] The novel and improved non - woven battery separator containing the above - mentioned fibers can be further improved by coating the battery separator with an inorganic oxide and / or infiltrating the inorganic oxide into the battery separator to improve both durability and elasticity during battery manufacture and during the battery life cycle. Suitable inorganic oxides for coating and / or infiltrating the non - woven battery separator may be, for example, aluminum oxide, zinc oxide, silicon oxide, or combinations thereof. By coating the non - woven battery separator with an inorganic oxide and / or infiltrating the inorganic oxide into the non - woven battery separator, the battery separator materials described herein can obtain an exterior coating on the surface and within the porous structure of the substrate / web. The advantages of the above coating include that the coating improves mechanical and thermal elasticity without impairing the high porosity and migration potential of the separator. The above coating, or exterior, can further prevent oxidation and other interactions between the electrolyte and the underlying substrate, enhancing both the electrochemical efficiency and the durability of the battery separator.

[0027] Treating battery separator materials with inorganic oxides, such as ceramics and other coatings, can enhance the modification and operating characteristics of the separator. For example, such treatment can improve the physical elasticity of the battery separator material against wear and puncture during both battery assembly and operation. Further, such treatment can improve the rate and efficiency at which the battery separator infiltrates the battery electrolyte. This improved efficiency contributes to improved efficiency in battery manufacturing. Further, the improved coatings described herein can improve the ion passage rate through the separator during battery charging. Faster charging cycles, reduced energy consumption, and extended battery life are all achievable through the improved coatings. Further, the coatings / enclosures of the present disclosure on non-woven battery separator materials can additionally provide prevention of dendrite formation and enhance elasticity against dendrite-induced puncture. Further, the inventors have also recognized that the coating / enclosure can reduce the thermal shrinkage and thermal runaway vulnerability of the underlying polymer material that makes up the non-woven, which is a known cause of lithium-ion battery failure and a safety concern.

[0028] As will be described in further detail below, a durable film applied to the surface of the battery separator material may serve as an outer coating to coat the surface of the fibers and the interior of the pore structure. As used herein, an outer coating is a coating that thinly coats the inner surfaces of the fibers and pores without closing or significantly narrowing the pores themselves.

[0029] As noted above, the non-woven battery separator may be coated with an inorganic oxide. Generally, the thickness of the battery separator may be on the order of 10 to 30 microns. The thickness of the outer coating described herein may be from a few nanometers to a few microns, for example, from 5 nanometers to 10 microns. Additionally, or alternatively, the outer coating may penetrate into the non-woven porous battery separator. The total amount of the outer coating of the battery separator may also be in the range of 0.1% to 20% relative to the total weight of the battery separator having the outer coating.

[0030] The non-woven nanofiber battery separator may further contain pores having an average pore diameter of 0.2 to 5 microns and / or a porosity of 30% to 60%. As noted above, the outer coating may deposit within the porous structure of the battery separator substrate / web. The outer coating described herein can coat the interior of the pores of the substrate and / or the battery separator without closing or significantly narrowing the pores themselves. Without closing or significantly narrowing the pores themselves means that the average porosity of the web does not change by more than 20% as a result of this coating. Improved durability and elasticity against mechanical damage result in a battery separator having better physical properties even when there is little clogging or small pore diameters.

[0031] As a result of coating the non-woven battery separator with an inorganic oxide, as described herein, the resulting outer-coated battery separator can have a mechanical strength that is at least 5% higher than the same battery separator without the outer coating, as measured by puncture resistance in gf. In some cases, it can be at least 10% higher than the same battery separator without the outer coating. In other embodiments, it may be at least 15% higher, 20% higher, or even at least 25% higher.

[0032] The battery separator coated with the exterior described in this specification may further be included within a battery, for example, within a rechargeable battery. In one embodiment, the battery separator described in this specification may be included within a lithium-ion battery. In another embodiment, the battery separator described in this specification may be included within an automotive battery.

[0033] The battery separator of the present disclosure may have a deposited and / or infiltrated exterior coating applied by several methods. The battery separator of the present disclosure can obtain a deposited and / or infiltrated exterior coating by several methods. As one example, the exterior coating can be applied to the substrate / web of the battery separator, for example, by physical vapor deposition or chemical vapor deposition processes. Based on the desired physical properties of the end use, the exterior coating can be applied to one or both sides of the battery separator substrate / web. Further, as will be described in more detail below, the exterior coating can be applied only to the surface of the nonwoven substrate / web and / or can penetrate into the porous structure of the nonwoven substrate / web.

[0034] When depositing the inorganic oxide described in this specification on the battery separator substrate / web, there are many approaches to achieve the deposition. However, and without wishing to be constrained by any particular mechanism, the goal is to deposit a thin film of elastic material on the outside of the substrate and inside the pore network in such a way that the inorganic oxide adheres strongly. Further, the above deposition should not be such a method that the pores are blocked so that the battery having the treated nonwoven battery separator cannot function.

[0035] Physical vapor deposition processes have the advantages of being relatively easy to use and relatively productive. However, since physical vapor deposition methods operate on a line-of-sight basis, their ability to coat the inner surface of those porous materials is limited. However, these limitations can be overcome through surface activation methods such as plasma etching. Further, the above coating can be applied to both sides of the substrate and can create advantageous performance within the battery separator.

[0036] Generally, physical vapor deposition processes operate under significant vacuum conditions where a coating material, such as the inorganic cladding materials described herein, can sublime from a solid to a vapor phase by heating. The heating may be carried out, for example, in the form of electrical resistance heating, high-frequency ablation through the use of a laser, or any other known heating method for physical vapor deposition processes. The resulting vapor can then be deposited onto the surface of a coated object or substrate, such as a substrate / web and / or a non-woven battery separator. The coated substrate or object may be a static rack, technical foil, film, or membrane of the coated composition and can be applied to a web running in a roll-to-roll configuration. In other methods, the vapor deposition coating can be applied directly onto a stationary substrate or object to be coated. If desired, the wettability and adhesion of the coating material can be optimized by preparing the surface by chemical or physical methods. For example, the surface to be coated can be prepared by chemical pre-coating or etching. Alternatively, or in addition, the surface to be coated can be prepared by physical methods, such as through plasma treatment or corona discharge.

[0037] When using a physical vapor deposition process to manufacture the disclosed battery separator with a cladding, high-purity oxygen of controlled quality is mixed into the metal vapor immediately after it exits the evaporator so that the coating material deposits on the substrate / web and / or battery separator and at the same time reacts to form metal components, such as inorganic oxides, thereby converting metal components, such as inorganic components, into their oxides. The degree of oxidation, and thus the mechanical and electrical properties of the coated substrate, can be adjusted by manipulating the flow rate of oxygen into the metal vapor.

[0038] During a physical vapor deposition process, certain parameters can be adjusted to achieve the desired mechanical and electrical properties of the coated substrate. For example, the level of oxygen used in the preparation of metal oxides for the exterior coating of non-woven materials. Further, the degree of oxidation can regulate the final properties.

[0039] As an example, a thermal evaporation coating of aluminum oxide can be applied to the non-woven substrate surface described herein. Aluminum is vaporized under high vacuum conditions and oxidized in vacuo. The aluminum oxide coating is then deposited on one or both sides of a substrate, such as a battery separator material. In certain embodiments, it is possible to penetrate the porous structure of the battery separator material without completely closing the pores of the non-woven structure of aluminum oxide.

[0040] Alternatively, a chemical vapor deposition method can also be utilized to apply an exterior coating to the battery separator web / substrate. Generally, the chemical vapor deposition process can be very specific and slow to operate. Thus, in certain situations, there may be a risk that the deposition of an inorganic coating cannot be economically carried out through the chemical vapor deposition method. However, as an advantage, the chemical vapor deposition method provides an excellent ability to transport an inorganic coating material inside a pore structure, for example beyond the line of sight, and can achieve excellent products.

[0041] As described herein, the chemical vapor deposition method involves the formation of a gas phase of a chemical precursor. Optionally, the process may include a vacuum for depositing the gas phase on a substrate. Immediately after the deposition step, the chemical precursor reacts with the substrate and, if desired, subsequent precursors are applied to modify the surface and pores. The above reaction can further increase the adhesion of the inorganic material to the surface and pores of the substrate. By controlling the amount and duration of chemical deposition, an exterior coating material of a suitable thickness can be deposited on the substrate.

[0042] Although embodiments have been described, it will be readily understood by those skilled in the art that many variations and adaptations of the compositions, devices, and processes described herein are possible without departing from the spirit and scope of the embodiments of the claims. Accordingly, it should be clearly understood that this specification is provided by way of example only and is not intended to be limiting.

Claims

1. A battery separator comprising a non-woven material containing at least one inorganic oxide.

2. The battery separator according to claim 1, wherein the at least one inorganic oxide is at least partially located on a first outer surface of the non-woven material.

3. The battery separator according to claim 2, wherein the at least one inorganic oxide is at least partially located on a second outer surface of the non-woven material.

4. The battery separator according to claim 1, wherein the at least one inorganic oxide at least partially penetrates into the non-woven material.

5. The battery separator according to claim 1, wherein the at least one inorganic oxide is selected from the group consisting of aluminum oxide, zinc oxide, and combinations thereof.

6. The battery separator according to claim 2, wherein the thickness of the at least one inorganic oxide is from 5 nanometers to 10 microns.

7. The battery separator according to claim 1, wherein the at least one inorganic oxide is contained in an amount of 0.1% to 20% by weight.

8. The battery separator according to claim 1, wherein the non-woven material has an average pore diameter of 0.2 to 5 microns and a porosity of 30% to 60%.

9. The battery separator according to claim 8, wherein the inorganic oxide reduces the porosity of the non-woven material by less than 20%.

10. The battery separator according to claim 1, wherein the non-woven material contains thermoplastic fibers.

11. The battery separator according to claim 10, wherein the thermoplastic fibers have an average fiber length of 0.3 to 5 microns.

12. The battery separator according to claim 10, wherein the thermoplastic fiber is selected from fibers including polypropylene, polyethylene terephthalate, nylon, polycaprolactam, polyphenylene sulfide, polyetherimide, and combinations thereof.

13. The battery separator according to claim 1, wherein the nonwoven material includes fibers selected from the group consisting of meltblown fibers, spunbonded fibers, electrospun fibers, carded fibers, and combinations thereof.

14. A method for manufacturing a battery separator, comprising the step of applying at least one inorganic oxide to at least one outer surface of the nonwoven material The method is characterized by including this.

15. The method according to claim 14, further comprising the step of infiltrating the at least one inorganic oxide into the nonwoven material.

16. The method according to claim 14, wherein the battery separator contains 0.1% to 20% by weight of the at least one inorganic oxide.

17. The method according to claim 14, wherein the at least one inorganic oxide is selected from the group consisting of aluminum oxide, zinc oxide, and combinations thereof.

18. The method according to claim 14, wherein the step of applying the inorganic oxide to the nonwoven material does not reduce the porosity of the nonwoven material by more than 20%.

19. The method according to claim 14, wherein a physical vapor deposition method is used to apply the at least one organic oxide to the nonwoven material.

20. The method according to claim 14, wherein a chemical vapor deposition method is used to apply the at least one organic oxide to the nonwoven material.

21. The method according to claim 14, wherein the nonwoven material includes thermoplastic fibers.

22. The method according to claim 21, wherein the thermoplastic fibers have an average fiber length of 0.3 microns to 5 microns.

23. The method according to claim 21, wherein the thermoplastic fiber is selected from fibers including polypropylene, polyethylene terephthalate, nylon, polycaprolactam, polyphenylene sulfide, polyetherimide, and combinations thereof.

24. The method according to claim 14, wherein the nonwoven material comprises fibers selected from the group consisting of melt blown fibers, spunbonded fibers, electrospun fibers, carded fibers, and combinations thereof.

25. A lithium ion battery and / or an automotive battery, characterized by comprising the battery separator according to claim 1.

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