Improved low electrical resistance microporous battery separator membrane, separator, cell, battery and related methods

Abstract

To provide a microporous separator membrane with extremely low ER, low Gurley number, and low bending degree.SOLUTION: A polyolefin battery separator membrane contains a microporous membrane with an electrical resistance of less than 0.95 ohm cm2, a Gurley number of less than 500 seconds / 100 cc, and a bending degree of less than 1.5. A microporous polyolefin separator membrane has non-circular, trapezoidal pores.SELECTED DRAWING: None

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 170,302, filed June 3, 2015, which is incorporated herein by reference.

[0002] According to at least selected embodiments, the present application provides new or improved microporous battery separator membranes, separators, cells, or methods for manufacturing such membranes or separators. Batteries containing such membranes, separators, cells and / or The present invention is directed to methods, including methods of manufacturing batteries and / or methods of using such membranes, separators, cells and / or batteries. According to at least certain embodiments, the present invention is directed to methods of manufacturing batteries and / or batteries having a resistance of 0.95 ohm-cm. 2 Less than, in some cases, 0.8 ohm-cm 2 The present invention is directed to battery separators for secondary or rechargeable lithium batteries that may have low electrical resistance of less than 1000 kJ / cm. According to at least certain embodiments, the battery separator membranes or separators may provide a means to achieve improved levels of battery performance in rechargeable or secondary lithium batteries based on a potentially synergistic combination of low electrical resistance, low Gurley number, low tortuosity, and / or uniquely shaped pores, in some cases pores that approximate or are trapezoidal in shape. According to at least certain multilayer embodiments (by way of example only, a tri-layer membrane consisting of two polypropylene layers sandwiching a polyethylene layer), the microporous membranes or battery separators described herein may exhibit excellent thermal shutdown initiation and / or thermal shutdown performance rates. [Background technology]

[0003] U.S. Patent Nos. 5,691,077 and 5,952,120, and U.S. Patent Application Publication No. 2007 / 0148538 disclose various methods for producing dry-laid microporous battery separator membranes using uniaxial or machine direction (MD) stretching. When using a uniaxial method of stretching a non-porous semi-crystalline extruded polymer precursor, a dry process (Celgard®) is used. ) method. ) can sometimes produce elongated, slit-like pores. Battery separator membranes made using the dry uniaxial stretching method can sometimes have a higher tensile strength in the machine direction than in the cross direction.

[0004] To increase the transverse tensile strength of various dry porous separator membranes, U.S. Pat. No. 8,795,565 and U.S. Patent Application Publication Nos. 2011 / 0223486, 2014 / 0287322, and 2014 / 0302374 propose various methods involving transverse direction (TD) stretching simultaneously and / or sequentially with machine direction (MD) stretching (or uniaxial stretching).

[0005] U.S. Pat. No. 8,795,565 and U.S. Patent Application Publication Nos. 2014 / 0287322 and 2014 / 0302374 disclose simultaneous controlled machine direction relaxation steps, MD / TD stretch ratios of about 0.5 to about 4.0, and / or stretching rates up to about 1450 kg / cm. 2 of Various transverse stretching methods have been proposed that may include MD tensile strength. The specific stretching process can sometimes change the pore shape from elongated slit-like pores, which can be found in some dry uniaxial stretching processes, to circular pores (or nearly circular pores). Pore size and pore shape can sometimes be important separator membrane performance characteristics, as they can affect the movement of electrolytes and ions between electrodes in lithium-ion rechargeable batteries during charge-discharge cycling. U.S. Patent Application Publication No. 2011 / 0223486 describes, in various embodiments, the creation of porous membranes with balanced MD and TD tensile strength. It has been proposed to adjust the amount of MD and TD stretching so that the MD / TD stretch ratio is approximately equal to 1. And, in various examples, the ER value of known biaxially stretched dry battery separator membranes is 1 ohm cm. 2 It may be larger than that. Summary of the Invention [Problem to be solved by the invention]

[0006] The details of one or more embodiments are set forth in the description below. Other features, objects, and advantages will be apparent from the description and claims.

[0007] The power performance of various lithium batteries, such as secondary lithium-ion batteries or rechargeable lithium-ion batteries, can be limited or affected by the ER, Gurley number, and / or tortuosity of the battery separator used in such batteries. Microporous separator membranes with very low ER, low Gurley number, and low tortuosity are needed to increase the power, improve rate capability, cycle performance, extend cycle life, and / or improve performance after high charge / discharge cycles in lithium-ion rechargeable batteries. In some cases, improved separators with very low ER, low Gurley number, and low tortuosity can result in separators with even lower ionic resistance to electrolyte flow during battery cycling, which can contribute to various improvements in the performance of batteries containing such improved separators. Electric drive vehicles (EDVs) often require batteries with high power performance. One way to achieve higher power performance in lithium-ion batteries for EDV end uses is to use microporous separator membranes with very low ER, low Gurley number, and low tortuosity in lithium-ion rechargeable batteries. [Means for solving the problem]

[0008] According to at least selected embodiments, the present application or invention is directed to improved or novel microporous battery separator membranes for lithium rechargeable batteries, e.g., lithium-ion batteries, and various methods of making such separator membranes. The battery separators described herein have a resistivity of 0.95 ohm-cm in some instances. 2 Less than, in some cases, 0.8 ohm-cm 2 The resulting pores may have low electrical resistivity (ER), low Gurley number, low tortuosity, and characteristic non-circular pores less than 1000 kJ / cm. A method for achieving low ER, low Gurley number, low tortuosity, and non-circular pores (e.g., pores that approximate or are trapezoidal in shape) may be based on novel methods for controlling pore size during the machine direction and / or transverse direction stretching steps.

[0009] According to at least selected embodiments, the present application or invention may address the above-mentioned needs or demands and / or is directed to new or improved separator membranes, separators, batteries including such separators, methods of making such membranes, separators and / or batteries, and / or methods of using such membranes, separators and / or batteries. The present invention relates to new or improved microporous separator membranes for lithium-ion batteries, and methods of making and using the same. Contemplated preferred microporous separator membranes of the present invention are stretched by a novel method that alters the regime of the uniaxial (mechanical) stretching and transverse stretching process steps.

[0010] Additionally, the non-porous precursor membranes are highly crystalline. The highly crystalline non-porous precursor is first stretched in the machine direction, with the amount of MD stretch controlled to produce a "semi-porous intermediate" membrane with high transverse elongation (TD elongation). Initial MD stretching with a highly crystalline non-porous precursor produces a semi-porous intermediate having a TD elongation greater than 600% in some embodiments and / or a pin puncture strength greater than 330 gf in some embodiments, and greater than 350 gf in some embodiments; these properties can be important in achieving the low ER microporous separator membranes of the present invention described in various embodiments herein. Table 1 lists various properties of the semi-porous intermediate membrane. The semi-porous intermediate is not a final product, but rather, in certain embodiments, an intermediate membrane having a target puncture strength and / or a target TD elongation. In various embodiments, the semi-porous intermediate is then stretched in the transverse direction at a preferred temperature and speed, with the TD stretching step being followed by a TD relaxation step, preferably conducted at 120-140°C. Table 4 lists separator properties of the final MD and TD stretched microporous battery separator membranes produced according to various embodiments described herein.

[0011] According to selected embodiments, the microporous separator membrane has a resistance of 0.95 ohm cm 2 Less than, in some cases, 0.8 ohm-cm 2The microporous separator membranes have low Gurley numbers and low tortuosity, along with low electrical resistivity (ER) of less than 1 / 2. Additionally, the microporous separator membranes have unique morphologies, as evidenced by the scanning electron micrographs (SEMs) shown in Figures 9-13. The unique porous structure differs from known dry-drawn uniaxially and biaxially stretched porous separator membranes (such as the membranes whose SEMs are included in Figures 3-8). The porous structure of the membranes described in various embodiments herein may resemble a "knitted-like" structure, in which the layered crystalline domains of the polymer resemble small islands connected by a three-dimensional array of vertically and diagonally elongated fibril structures. Additionally, in some embodiments, the pores may appear to have a four-sided trapezoidal shape, or in some cases, a shape approximating a trapezoidal shape. The unique pore shapes resulting from the porous structure of these membranes appear different from the generally circular pores of certain known biaxially stretched dry microporous battery separator membranes and different from the elongated, slit-like pores of certain known uniaxially stretched dry microporous battery separator membranes. These differences in pore shape are shown in Figure 1 as approximate shapes only. Pore shape can sometimes play a significant role in the ER, Gurley number, tortuosity, and overall porosity of microporous battery separator membranes, as well as their performance, because the pores store electrolyte and also provide tortuous pathways for transporting ions between the anode and cathode through the electrolyte medium during charge-discharge cycling of lithium-ion rechargeable batteries. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 depicts the approximate pore shapes of various microporous separator membranes according to embodiments described herein compared to the approximate pore shapes of microporous separator membranes according to Comparative Examples CE1 and CE3. [Figure 2] FIG. 2 contains plots of electrical resistance (ER) as a function of temperature for various tri-layer microporous battery separator membranes formed as part of Examples 1-4. [Figure 3]FIG. 3 contains a scanning electron micrograph (SEM) image at 20,000x magnification of the surface of a commercially available microporous monolayer polypropylene separator membrane known as Celgard® 2500, which is approximately 25 microns thick. [Figure 4] Figure 4 contains a 5,000x SEM image of the surface of a commercially available Celgard® 2500 separator membrane. [Figure 5] FIG. 5 contains a 20,000x SEM image of a cross section of a commercially available Celgard® 2500 separator membrane. [Figure 6] FIG. 6 includes an SEM image at 20,000x magnification of the surface of a microporous monolayer polypropylene separator membrane produced according to CE1 (Comparative Example 1) herein. [Figure 7] FIG. 7 contains an SEM image at 20,000x magnification of the surface of a microporous tri-layer PP / PE / PP separator membrane prepared according to CE2 (Comparative Example 2) herein. [Figure 8] FIG. 8 contains an SEM image at 20,000x magnification of the surface of a microporous monolayer polypropylene separator membrane produced according to CE5 (Comparative Example 5) herein. [Figure 9] FIG. 9 contains an SEM image at 20,000x magnification of the surface of the microporous PP / PE / PP separator membrane prepared according to Example 2. [Figure 10] FIG. 10 includes an SEM image at 5,000x magnification of the surface of the microporous PP / PE / PP separator membrane prepared according to Example 2. [Figure 11] FIG. 11 contains an SEM image at 4,800x magnification of a cross section of a microporous PP / PE / PP separator membrane prepared according to Example 2. [Figure 12] FIG. 12 contains an SEM image at 20,000x magnification of the surface of the microporous monolayer PP separator membrane produced according to Example 6. [Figure 13] FIG. 13 includes an SEM image at 20,000x magnification of the surface of the microporous monolayer PP separator membrane produced according to Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0013] Before the present membranes, separators, cells, batteries, methods, and / or the like are disclosed and described, it is understood that they are not limited to particular methods, components, specific compositions, or the like. It is also understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0014] As used in this specification and the appended claims, the singular forms "a" and "an" and "the" includes plural referents unless the context clearly dictates otherwise. As used herein, the terms "about" and / or "approximately" refer to one particular value and / or "approximately." or another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value constitutes another embodiment. Further, it will be understood that the endpoints of each of the ranges are significant in relation to the other endpoint, and independently of the other endpoint.

[0015] "Optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes cases where said event or circumstance occurs and cases where it does not occur. Throughout this description and claims, the word "comprise" and variations of this word, such as "comprising" and "comprises," mean "including but not limited to," and may include, for example, other accessories, components, integers, etc. "Exemplary" means "an example of" and is not intended to convey a preferred or ideal embodiment. "Such as" is used for illustrative purposes, not for limitation.

[0016] Disclosed herein are products, shapes, pores, components, materials, layers, or the like that can be used to implement the disclosed properties, performance, methods, and systems. Where these and other components are disclosed herein, and where combinations, subsets, interactions, groups, etc. of these components are disclosed, it is understood that specific reference to each of the various individual and collective combinations, and variations thereof, may not be expressly disclosed, but that all products, methods, and systems are each specifically contemplated and described herein. This applies to all aspects of this application, including, but not limited to, disclosed method steps. Thus, where there are various additional steps that can be implemented, it is understood that each of these additional steps can be implemented with a particular embodiment or combination of embodiments of the disclosed methods.

[0017] According to selected embodiments, the present invention is directed to microporous membranes comprising thermoplastic polymers, which may be characterized as semi-crystalline polymers. Such polymers may include polypropylene (PP), polyethylene (LDPE, LLDPE, HDPE, and UHMWPE), polybutene, polymethylpentene, copolymers thereof, and blends or mixtures thereof. Polyolefins include homopolymers, The polyolefin may be a homopolymer or a blend of polyolefins. The polyolefin may be a copolymer of polyolefins or a blend of copolymers of polyolefins. In one embodiment, the preferred polyolefin may be polypropylene having a melt flow index (mfi) of less than 1.0 g / 10 min. In another embodiment, the preferred polyolefin may be polyethylene having an mfi of less than 0.5 g / 10 min.

[0018] The microporous membranes of the present invention can be single-ply or multi-ply microporous membranes. According to selected embodiments, a method for producing a microporous membrane of the present invention may generally include extruding a nonporous precursor to a blown film through an annular die as a foam, as described in U.S. Pat. No. 5,952,120 and U.S. Patent Application Publication No. 2007 / 0148538, and flattening the tubular bubble membrane to form a "collapsed bubble" nonporous membrane. According to at least selected embodiments, the nonporous precursor may be a collapsed polypropylene (PP) membrane. According to other embodiments, the nonporous precursor is a multilayer precursor membrane, comprising two outer layers of polypropylene (PP) sandwiching a central layer of polyethylene (PE) precursor, forming a stacked precursor membrane in a PP / PE / PP configuration. In some embodiments, such multilayer precursor membranes are formed by stacking PP / PE / PP precursor membranes together. In another embodiment, the non-porous precursor is a multilayer precursor membrane produced by co-extruding polypropylene (PP) / polyethylene (PE) / polypropylene (PP) to form a non-porous tri-layer precursor membrane having a PP / PE / PP configuration, and collapsing the PP / PE / PP tri-layer precursor foam to form a multilayer PP / PE / PP precursor membrane.

[0019] The non-porous single layer or multilayer precursor film can be annealed to increase the amount and size of the layered crystals in the precursor film, thereby increasing the crystallinity of the precursor film.

[0020] In one embodiment of the separator membrane described herein, a nonporous coextruded PP / PE / PP or laminated PP / PE / PP precursor membrane is first stretched in the machine direction (MD). The amount of MD stretching can be selected or optimized to produce a semi-porous intermediate membrane with a high transverse direction (TD) elongation, preferably greater than about 600%. Such a semi-porous intermediate membrane with a high TD elongation can play a role in achieving the desired amount of TD stretching in a subsequent transverse direction stretching process step. Furthermore, the amount of MD stretching performed on the non-porous precursor can be optimized to produce a semi-porous intermediate membrane with a specific porosity, preferably 20-50%, and in some embodiments, about 30-50% porosity. Additionally, the amount of MD stretching performed on the non-porous precursor membrane can be optimized to produce a semi-porous intermediate membrane with a specific porosity, preferably greater than 330 gf. The method can be optimized to produce a semi-porous intermediate membrane with excellent puncture strength.

[0021] Following the MD stretching process step, the semi-porous intermediate membrane can be stretched in the transverse direction, preferably using a stretch ratio of 15 to 400%, in some embodiments 20 to 250%, and more preferably 25 to 100%, where stretch ratio is defined as the difference (final width of membrane - initial width of membrane) divided by the initial width of membrane. TD stretching is preferably carried out at a temperature of 100 to 300°C, and at a line speed of 25 to 250 ft / min, optionally 50 to 200 ft / min, and optionally 50 to 100 ft / min.

[0022] Following the TD stretching step, the microporous tri-layer separator membrane may be relaxed in the transverse direction (TD) preferably by 10-50%, more preferably by 20-40%, at a temperature of preferably 120-140°C.

[0023] Following the TD relaxation step, the microporous tri-layer separator membrane is heated to a temperature of preferably 60°C to The film can be stabilized by heat treatment at a temperature of 100° C., preferably for 8 hours to 2 to 3 days.

[0024] Microporous PP / PE / PP battery separator membranes provide a thermal barrier through the inner PE layer. Thermal barrier is determined by measuring impedance during a linear temperature increase. Thermal barrier is defined as the temperature at which the impedance or electrical resistance (ER) increases by a factor of 1000. A thousand-fold increase in impedance may be required for a battery separator membrane to prevent thermal runaway in a lithium-ion battery. The increase in impedance corresponds to the collapse of the pore structure due to melting of the separator. During thermal barrier, the pores in the inner PE layer of a contemplated preferred separator membrane of the present invention can coalesce and close at temperatures between 130°C and 135°C, resulting in a thousand-fold increase in impedance, as shown in Figure 2.

[0025] Heat rejection can be affected by several separator parameters such as ER, Gurley number, pore size, tortuosity and / or porosity. The balance of these parameters can play an important role in achieving a low onset temperature of heat rejection.

[0026] The excellent onset temperature of thermal insulation of the contemplated preferred microporous membranes of the present invention is achieved in some embodiments by controlling the increase in pore size that occurs during transverse stretching. Transverse stretching of the semi-porous intermediate membrane is performed to achieve a pore size increase of 0.03 to 0.08 μm for the polypropylene layer in the three-layer membrane. In some cases, it can be used to produce pore sizes in the range of 0.04 to 0.06 μm. , which is larger than the typical pore size of the uniaxially dry-stretched polypropylene layer in known multilayer PP / PE / PP microporous membranes. By controlling the pore size reached during the transverse stretching step, a preferred process for the membrane of the present invention is envisaged. 2 Low ER of less than 0.9 ohm cm 2 Less than 0.8 ohm cm 2 Less than 0.7 ohm cm 2 Less than 0.6 ohm cm 2The present invention provides a microporous multi-layer separator membrane having a combination of an ER (e.g., less than 1.2), a low Gurley number (less than 150 sec / 100 cc), and a low tortuosity (less than 1.2).

[0027] In another embodiment for producing a separator membrane according to various embodiments herein, a non-porous monolayer polypropylene precursor membrane is first stretched in the machine direction (MD) to produce a "semi-porous intermediate" membrane. The amount of MD stretching is preferably selected to produce a "semi-porous intermediate" membrane with a high transverse direction (TD) elongation, preferably greater than 600%. Furthermore, the amount of MD stretching is optimized to produce a "semi-porous intermediate" membrane with a specific porosity, preferably 20-50%, and in some cases 30-50%. Additionally, the amount of MD stretching is optimized to produce a "semi-porous intermediate" membrane with sufficient puncture strength of greater than 350 gf. The porous intermediate membrane is optimized to produce a monolayer membrane.

[0028] Following the MD stretching step, the monolayer porous membrane is stretched in the transverse direction preferably using a stretch ratio of 15-400%, optionally 20-250%, and further optionally 25-100%, where stretch ratio is defined as "(final width of membrane - initial width of membrane) divided by initial width of membrane." TD stretching is preferably carried out at a temperature of 100-300°C, preferably at a speed of 25-250 ft / min, optionally 50-200 ft / min, and optionally 50-100 ft / min.

[0029] Following TD stretching, the microporous monolayer separator membrane may be relaxed in the transverse direction (TD), preferably at a TD relaxation of 10-50%, more preferably 20-40%. The TD relaxation temperature is preferably 120-140°C.

[0030] Following TD relaxation, the microporous monolayer separator membrane can be heat treated, preferably at a temperature of 60°C to 100°C, for a period of time preferably from 8 hours to 2-3 days, to stabilize the membrane. .

[0031] Additionally, the monolayer microporous separator membrane of the present invention may, in certain embodiments, have a resistance of 0.95 ohm cm 2 Less than (in some cases, 0.9 ohm cm 2 Less than or equal to 0.85 ohm cm 2 Less than or equal to 0.8 ohm cm 2 ER of less than 250 gf and puncture force of more than 250 gf The microporous monolayer battery separator membrane of the present invention has a combination of low ER, low Gurley number, and low tortuosity, while the pore size is 0.03 to 0.08 μm. In some cases, the thickness is controlled to within a range of 0.04 to 0.06 μm, and in other cases, within a range of 0.050 to 0.060 μm. The porosity of the monolayer separator membrane of the present invention is preferably within a range of 60 to 70% using TD stretching.

[0032] Contemplated preferred multilayer and single-layer microporous battery separator membranes of the present invention have a low tortuosity of less than 1.3. Tortuosity can be described as an indicator of the tortuous path ions take from one surface of the porous membrane, through the pores in the membrane body, to the opposite surface of the membrane. A low tortuosity promotes greater or faster ion and electrolyte migration through the porous battery separator membrane (compared to a high tortuosity) during charge / discharge cycling of a lithium-ion battery. In some cases, a membrane with a low tortuosity can contribute to lithium-ion batteries with higher cycling rates and improved cycle life performance. During the charge cycle of a lithium rechargeable battery, which may have a carbon-based or lithium metal anode, lithium ions are transported from the cathode through the electrolyte medium and the pores in the separator membrane to the battery's anode. The reverse occurs during the discharge cycle, with lithium ions migrating from the anode to the cathode. With continuous charge-discharge cycling, a low tortuosity membrane can potentially increase the rate of cycling, electrode utilization, and electrode cycling, which in some cases can improve the cycle life performance of lithium rechargeable batteries. [Example]

[0033] Example In the following Tables 1-4, separator membrane property data are provided for examples produced using the aforementioned process. Table 1 lists two key properties of the semi-porous tri-layer (PP / PE / PP) intermediate produced after the first MD stretching step, where MD stretching is performed to produce a semi-porous tri-layer (PP / PE / PP) intermediate membrane, with a TD elongation greater than 600% and a puncture strength greater than 330 gf.

[0034] [Table 1]

[0035] [Table 2]

[0036] Table 2 shows examples of the present invention along with Comparative Examples CE 2, CE 3, and CE 4. Separator properties and performance data are listed for Examples 1, 2, 3, and 4 (all four trilayer separator membranes made according to the process described herein). CE 2 is a biaxially MD / TD stretched dry-laminate trilayer microporous membrane. Comparative Example CE 3 is a uniaxially MD stretched dry-laminate trilayer microporous membrane, and Comparative Example CE 4 is a uniaxially MD stretched dry-laminate trilayer microporous membrane. It is a stretch-dry co-extruded three-layer microporous membrane.

[0037] According to selected embodiments shown in these examples, the tri-layer microporous separator membrane of the present invention has a resistance of 0.57 ohm cm 2 It has a very low electrical resistance (ER) of 150 sec / 100cc or less, a low Gurley number of 150 sec / 100cc or less, and a low flexural index of 1.2 or less. is a biaxially stretched, three-layer, microporous membrane with low ER, but has a high Gurley number and very low MD tensile strength, separator properties that can affect battery cycling performance. The separator membrane of the present invention is a porous membrane manufactured without transverse stretching, CE 3 and has significantly improved low ER, low flex and low Gurley numbers over CE 4. The uniqueness of the separator membranes of the present invention is demonstrated by their novel morphology, as evidenced by scanning electron micrograph (SEM) analysis. Figure 9 shows an SEM image of Example 2 of the present invention, which has a unique pore shape different from that of known dry-stretched porous separator membranes (such as the membrane shown in Figure 7). The porous structure of the membranes of the present invention resembles a "woven" structure in which layered crystalline domains of polymer resemble small islands connected vertically and diagonally by a three-dimensional array of elongated fibril structures. The pores of the separator membrane of Example 2, shown in Figures 9 and 10, can be described as having an approximately four-sided geometry, rather than a circular shape, similar to pore shapes that are isosceles rectangles or trapezoidal in appearance. The novel pore shapes can, in certain instances, provide one or more separators with various advantages when compared to other battery separator membranes, such as: 1) other known biaxially stretched dry microporous battery separator membranes, which may have circular or nearly circular pores as shown in FIG. 7, and / or 2) other known uniaxially stretched dry microporous battery separator membranes, such as those shown in FIGS. 3, 4, and 5.

[0038] The superior onset of thermal insulation of the contemplated preferred three-layer microporous membranes of the present invention can be achieved by controlling the increase in pore size that occurs upon transverse stretching. Transverse stretching of the semi-porous intermediate membranes of the present invention results in the incorporation of polyimide into the three-layer membrane with pore sizes of 0.046 to 0.051 μm. Although a propylene layer was produced, this pore size has been shown to be larger than the typical pore size of the various uniaxially oriented polypropylene layers in the multilayer CE 3 and CE 4 microporous membranes. In addition to the small PP pore size, the contemplated preferred microporous separator membranes of the present invention also have a very low ER (in some cases as low as 0.57 ohm cm). 2 They have low flex (in some cases less than 1.2) as well as low Gurley numbers (in some cases less than 150 seconds / 100cc).

[0039] Table 3 lists two properties of the semi-porous monolayer intermediate produced in the first MD stretching step, where MD stretching is performed to produce a semi-porous intermediate membrane, with a TD elongation greater than 600% and a puncture strength greater than 350 gf.

[0040] [Table 3]

[0041] Table 4, along with Comparative Examples CE 1, CE 5, and CE 6, all of which are incorporated herein by reference. The document lists separator properties and performance data for Examples 5, 6, and 7 of the present invention, which are monolayer polypropylene separator membranes made according to the process described in the document. Comparative Example CE 1 is a monolayer biaxially stretched microporous separator membrane, Comparative Example CE 5 is a β-nucleated monolayer biaxially stretched microporous separator membrane, and Comparative Example CE 6 is a monolayer uniaxially stretched microporous separator membrane. MD-stretched microporous separator membrane.

[0042] [Table 4]

[0043] According to selected embodiments, the monolayer microporous separator membrane of the present invention has a dielectric constant of 0.77 ohm cm 2It has a very low electrical resistance (ER) of 1.3 or less, a low Gurley number of 120 seconds / 100cc or less, and a low flexural index of about 1.3 or less.

[0044] Examples 5, 6, and 7 of the present invention have Gurley numbers of 120 seconds / 100cc or less, which is significantly lower than CE El, CE 5, and CE 6. Biaxially stretched CE 5 has a larger pore size and higher tortuosity compared to the membranes of the present invention, but a higher ER. Uniaxially stretched CE 6 has a higher tortuosity and comparable pore size, but a much higher ER. CE 1 has an ER comparable to the membranes of the present invention, but this is due to This comes at the expense of a high Gurley number and a much lower machine direction tensile strength.

[0045] The synergistic combination of low ER, low Gurley number, and low tortuosity in the monolayer separator membranes of the present invention can be attributed to the porous structure of the trilayer membranes of the present invention, which resembles the "woven" structure discussed in various embodiments above, in which the layered crystalline domains of the polymer resemble small islands connected by a three-dimensional array of elongated fibril structures in the vertical and diagonal directions. The monolayer membranes of the present invention also have unique morphologies, as evidenced by scanning electron micrograph (SEM) analysis. SEM images of the surfaces of Example 6 and Example 7 monolayers according to the present invention are shown in Figures 12 and 13, respectively. The pores of the monolayer microporous membranes of the present invention have the same non-circular pore shape as the trilayer microporous membranes of the present invention. The monolayer microporous membranes of the present invention can be prepared by: 1) using Celgard® dry cellulose; 1) has a pore shape that differs from various known dry-laid uniaxially stretched monolayer porous separator membranes (e.g., that shown in FIG. 6 ), which have elongated, slit-like pores typical of dry-laid battery separator membranes, and 2) a prior art dry-laid β-nucleated biaxially stretched porous separator membrane shown in FIG. 8 , which has a vascular-like porous structure with a thick, intertwined layered fibrous structure typical of β-nucleated polypropylene porous membranes.

[0046] The excellent onset of thermal insulation of the monolayer microporous membranes of the present invention is achieved by controlling the increase in pore size that occurs during the transverse stretching process step. By stretching the monolayer film of the present invention in the transverse direction, pore diameters of 0.050 to 0.060 μm are generated. The smaller the pore size, the better the thermal insulation. Upon cutting, the pores close effectively, potentially increasing the rate of heat rejection.

[0047] The battery separator membranes of the present invention can provide a means to achieve improved levels of battery performance in rechargeable or secondary lithium batteries based on a synergistic combination of low electrical resistance, low Gurley number, low tortuosity, and unique non-circular, trapezoidal shaped (less than 90 degree internal angles) pores.

[0048] The present invention may be embodied in other forms without departing from its spirit or essential characteristics, and consequently, reference is made to the appended claims, rather than the foregoing specification, as indicating the scope of the invention. In addition, the invention illustratively disclosed herein may suitably be practiced in the absence of any element not specifically disclosed herein.

[0049] Test Method Thickness Thickness was measured using an Emveco Microgage 210-A precision micrometer according to ASTM D374 test procedure. Thickness values ​​are reported in units of micrometers (μm).

[0050] Gurley number The Gurley number is defined as the Japanese Industrial Standard (JIS Gurley) JIS P8117 and is an air permeability test measured using an OHKEN air permeability tester. The JIS Gurley number is the pressure required to pass 100 cc of air through 1 square inch of film at a constant pressure of 4.8 inches of water. The time (seconds) is

[0051] Puncture strength Test samples are first preconditioned at 73.4°C and 50% relative humidity for a minimum of 20 minutes. Measure the puncture strength of the test samples using an Instron Model 4442. Thirty measurements are taken in the diagonal direction of a 4" x 40" continuous sample specimen and averaged. The needle radius is 0.5 mm. The rate of descent is 25 mm / min. The film is tightly held by a clamping device that utilizes an O-ring to hold the test sample firmly in place. The diameter of this clamping area is 25 mm. The displacement (mm) of the applied film is recorded against the force (gram force) exerted by the tested film. The maximum force is the puncture strength in grams force (gf). This test method produces a plot of load versus displacement.

[0052] Pore ​​diameter Pore ​​size was measured using an Aquapore Porosimeter available from Porous Materials, Inc. (PMI). The pore size is expressed in μm.

[0053] porosity The porosity of the microporous film samples was measured using ASTM method D-2873 and is defined as the percentage of voids in the microporous membrane.

[0054] TD and MD tensile strength Tensile strength in the MD and TD is measured using an Instron Model 4201 according to ASTM D-882 method.

[0055] Electrical Resistivity (ER) (also known as Ionic Resistivity (IR)) The electrical resistance is the resistance (ohm cm) of the separator filled with electrolyte. 2 The unit of electrical resistance is ohm cm. 2The separator resistance is characterized by cutting small pieces of separator from the finished material and then placing these pieces between two blocking electrodes. The separator is then dissolved in 1.0 M EC / EMC solvent in a 3:7 volume ratio. The separator is saturated with a battery electrolyte containing LiPF6 salt. The separator resistance (R) in ohms (Ω) is measured by a four-probe AC ​​impedance method. To reduce measurement errors at the electrode / separator interface, multiple measurements are required by adding more layers. The electrical (ionic) resistance (R) of the separator saturated with electrolyte is then calculated based on the multiple layer measurements. s )(Ω) into the equation R s = p s l / A (where p s is the ionic resistivity of the separator (Ω·cm), and A is the area of ​​the electrode (cm 2 ) and l is the thickness of the separator (cm). s The ratio of / A is the calculated slope of the change in separator resistance (ΔR) with respect to the multilayer (Δδ), where slope = p s / A = ΔR / Δδ.

[0056] High temperature electrical resistance (ER) High temperature electrical resistance is a measure of the resistance of a separator film under 50 pounds of pressure while the temperature is increased linearly at a rate of 60°C / minute. A 3 / 8" diameter piece of separator is saturated with electrolyte and sandwiched between two electrode disks made of Al or Cu. An increase in resistance, measured as impedance, corresponds to the collapse of the pore structure due to melting or "shutdown" of the separator membrane. If the separator membrane maintains a high level of electrical resistance at high temperatures, this indicates that the separator membrane can prevent shorting of the battery electrodes.

[0057] Mixed Penetration The mixture penetration is the force required to create a short circuit through the separator when placed between the cathode and anode materials. This test is used to indicate the tendency of the separator to short circuit during battery assembly. Details of this method are described in U.S. Patent Application Publication No. 2010 / 209758.

[0058] Dielectric breakdown (DB) Dielectric breakdown (DB) is a measure of the electrical insulation of the separator. A voltage is applied to the separator film at a ramp rate of 6,000 V / sec until dielectric breakdown of the sample is observed. A high DB indicates that the separator has sufficient winding yields and a low HiPot failure rate.

[0059] degree of curvature The tortuosity (τ) was calculated using the following formula, where A is the area of ​​the membrane (cm 2 ), R is the membrane resistance in ohm-cm (Ωcm), ε is the porosity, L is the membrane thickness, and ζ is the electrolyte resistance in ohm-cm (Ωcm).

[0060]

number

[0061] According to at least selected embodiments, aspects, or objects, the present application or invention is directed to new or improved microporous battery separator membranes, separators, cells, or batteries including such membranes or separators, and / or methods including methods of making such membranes, separators, cells, and / or batteries, and / or methods of using such membranes, separators, cells, and / or batteries. According to at least certain embodiments, the present invention is directed to a battery separator having a resistance of 0.95 ohm-cm. 2 Less than, in some cases, 0.8 ohm-cm 2 Less than The present invention is directed to battery separators for secondary or rechargeable lithium batteries, which may have electrical resistance. According to at least certain embodiments, the battery separator membranes or separators may provide a means to achieve improved levels of battery performance in rechargeable or secondary lithium batteries based on a potentially synergistic combination of low electrical resistance, low Gurley number, low tortuosity, and / or uniquely shaped pores, in some cases pores that approximate or are trapezoidal. According to at least certain multilayer embodiments (by way of example only, a tri-layer membrane consisting of two polypropylene layers sandwiching a polyethylene layer), the microporous membranes or battery separators described herein may exhibit superior initiation of heat rejection and / or rate of heat rejection.

[0062] According to at least certain embodiments, aspects, or objectives, there are provided new or improved microporous battery separator membranes, separators, cells, or batteries including such membranes, separators, or cells, and / or methods of making such membranes and / or separators, and / or methods of using such membranes and / or separators. According to at least certain embodiments, improved or new battery separators for secondary or rechargeable lithium batteries have a resistance of 0.95 ohm-cm. 2 Less than, in some cases, 0.8 ohm-cm 2 The battery separator membranes of the present invention may have low electrical resistance of less than 1000 kJ / cm. Furthermore, the battery separator membranes of the present invention may provide a means to achieve improved battery performance levels in rechargeable or secondary lithium batteries based on a possible synergistic combination of low electrical resistance, low Gurley number, low tortuosity, and / or unique trapezoidal pores. According to at least certain multilayer embodiments (such as, by way of example only, a tri-layer membrane consisting of two polypropylene layers sandwiching a polyethylene layer), the microporous membranes or battery separators of the present invention may have excellent thermal barrier onset and rate of thermal barrier performance, which can be achieved by using transverse stretching to control the increase in pore size.

[0063] According to at least certain embodiments, aspects, or objectives, the present disclosure or invention may address the aforementioned need, problem, challenge, or demand for more adequate or improved power performance of various lithium batteries, e.g., secondary lithium-ion batteries or rechargeable lithium-ion batteries, which may be affected by the ER, Gurley number, and / or tortuosity of the battery separator used in such batteries. Microporous separator membranes with very low ER, low Gurley number, and low tortuosity are needed to increase the power, improve rate capability, improve cycling performance, extend cycle life, and / or improve performance after high charge / discharge cycling of lithium-ion rechargeable batteries. In some cases, improved separators with very low ER, low Gurley number, and low tortuosity can provide separators with even lower ionic resistance to electrolyte flow during battery cycling, which can contribute to various improvements in the performance of batteries containing such improved separators. Electric drive vehicles (EDVs) often require batteries with high power performance. One way to achieve higher power performance in lithium ion batteries for EDV end uses is to use microporous separator membranes with very low ER, low Gurley number, and low tortuosity in lithium ion rechargeable batteries.

[0064] According to certain embodiments, there is provided a new or improved microporous battery separator membrane, separator, cell, battery, and / or a new, improved, or modified polyolefin battery separator membrane, comprising: The electrical resistance of the microporous separator membrane is 0.95 ohm cm 2 Less than or equal to 0.8 ohm cm 2 is less than The microporous separator membrane has a Gurley number of less than 150 seconds / 100cc; The microporous separator membrane has a tortuosity of less than 1.3; The microporous polyolefin separator membrane has non-circular trapezoidal pores, and / or the improved and modified microporous polyolefin separator membrane is made of polypropylene, The improved and modified microporous polyolefin separator membrane is made of polyethylene, a mixture thereof, or a copolymer thereof, and the improved and modified microporous polyolefin separator membrane can be a single layer membrane, the improved and modified microporous polyolefin separator membrane can be a multilayer membrane with a heat-shielding function, the improved and modified microporous polyolefin separator membrane can be a multilayer membrane consisting of three layers of polypropylene / polyethylene / polyethylene, and the improved and modified microporous polyolefin separator membrane has a thickness of less than 25 μm, and / or The improved and modified microporous polyolefin separator membrane has non-circular, trapezoidal pores, and / or the new, improved or modified polyolefin battery separator membrane has: extruding polypropylene having a melt flow index of less than 1.0 g / 10 min to form a single-layer non-porous precursor membrane; Non-porous polypropylene precursor membranes were stretched in the machine direction to achieve a perforation strength of over 350 gf. and stretching the semi-porous intermediate membrane in the transverse direction using a stretch ratio of 15-400%, preferably 25-100%, to form a microporous separator membrane; and / or formed when the semi-porous intermediate membrane is stretched in the transverse direction at a temperature of 100-130°C, the semi-porous intermediate membrane being stretched in the transverse direction at a temperature of 100-130°C at a speed of 100 feet / minute, preferably 50 feet / minute, and heat relaxing the membrane at 120-140°C; and / or heat treating the membrane at a temperature of 60-100°C, preferably for 8 hours to 2-3 days; and / or the new, improved or modified polyolefin tri-layer battery separator membrane is extruding polyethylene having a melt flow index of less than 1.0 g / 10 min to form a single-layer non-porous polyethylene precursor membrane; extruding polypropylene having a melt flow index of less than 1.0 g / 10 min to form a single-layer non-porous polypropylene precursor membrane; Two layers of polypropylene precursor film were stacked as outer plies sandwiching one inner ply of polyethylene precursor film to form a polypropylene / polyethylene composite. forming a trilayer of a polyethylene / polyethylene non-porous precursor; A non-porous polypropylene / polyethylene / polyethylene precursor film is stretched in the machine direction to produce a semi-porous intermediate film having a puncture strength of greater than 350 gf and a TD elongation of greater than 600%. forming a body membrane; stretching a semi-porous intermediate membrane in the transverse direction using a stretch ratio of 15-400%, preferably 25-100%, to form a microporous tri-layer separator membrane; and / or formed when the semi-porous intermediate membrane is stretched in the transverse direction at a temperature of 100-130°C, the semi-porous intermediate membrane being stretched in the transverse direction at a temperature of 100-130°C at a speed of 100 ft / min, preferably 50 ft / min, and the membrane being heat-relaxed at 120-140°C; and / or formed when the membrane is stretched in the transverse direction at a temperature of 60-100°C. and heat treating the resulting membrane, separator, cell, battery, and / or the novel, improved, or modified polyolefin battery separator membrane, and / or the improved microporous battery separator membrane, separator, cell, or battery comprising such membrane, separator, or cell, and / or the method of making such membrane, separator, cell, and / or battery, and / or the method of using such membrane, separator, cell, and / or battery, 2 Less than, in some cases, 0.8 ohm-cm 2

[0010] Battery separators for secondary or rechargeable lithium batteries are provided that may have low electrical resistance of less than 100 . ... and (iii) a tri-layer membrane consisting of two polypropylene layers sandwiching a polypropylene layer, wherein the microporous membrane or battery separator has excellent thermal barrier initiation and / or thermal barrier performance rate and / or the like as shown or described herein.

[0065] New or improved microporous battery separator membranes, separators, cells, or batteries including such membranes, separators, or cells, and / or methods of making such membranes and / or separators, and / or methods of using such membranes and / or separators are disclosed. According to at least certain embodiments, improved or novel battery separators for secondary or rechargeable lithium batteries have a resistance of 0.95 ohm-cm. 2 Less than, or in some cases 0.8 ohm-cm 2 The microporous membranes or battery separators of the present invention may have low electrical resistances of less than 1000 kJ / cm. Furthermore, the battery separator membranes of the present invention may provide a means to achieve improved battery performance levels in rechargeable or secondary lithium batteries based on a possible synergistic combination of low electrical resistance, low Gurley number, low tortuosity, and / or unique trapezoidal pores. In accordance with at least certain multilayer embodiments (such as, by way of example only, a tri-layer membrane consisting of two polypropylene layers sandwiching a polyethylene layer), the microporous membranes or battery separators of the present invention may exhibit excellent thermal shutdown initiation and / or thermal shutdown performance rates.

[0066] The scope of the present invention is not limited to the above description or examples or the accompanying drawings. Microporous battery separator membranes, separators, cells, or batteries including such membranes, separators, or cells, and / or methods of making such membranes and / or separators, and / or methods of using such membranes and / or separators, and / or compositions and methods of the appended claims are intended to be illustrative of certain aspects of the claims. The scope is not limited by the specific examples, compositions, and methods described herein; functionally equivalent compositions and methods are intended to fall within the scope of the claims. Various modifications of the products, compositions, and methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Furthermore, only certain representative products, compositions, and method steps disclosed herein are specifically described; other combinations of elements, compositions, and method steps are also intended to fall within the scope of the appended claims, even if not specifically recited. Thus, although a combination of steps, elements, components, or constituents may be explicitly or indirectly mentioned herein, other combinations of steps, elements, components, and constituents are included, even if not explicitly mentioned. As used herein, the term "comprising" and variations thereof are used synonymously with the term "including" and variations thereof and are intended to be open, non-limiting, and non-exhaustive. The terms "comprising" and "including" are generic terms used in this specification. As used herein to describe various embodiments, the terms "consisting essentially of" and "consisting of" may be used in place of "comprising" and "including" to describe more specific embodiments of the present invention. Other than as examples, or unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and the like used in the specification and claims are to be understood at least as if they were rounded to the nearest whole number in light of the number of significant digits and ordinary rounding approaches, and are not intended to limit the application of the doctrine of equivalents to the claims. The principles, preferred embodiments, and examples of operation of the present invention have been described in the foregoing specification. However, the invention intended to be protected herein is not to be construed as being limited to the particular forms disclosed, as they are to be considered illustrative and not restrictive. Variations and modifications may occur to those skilled in the art without departing from the spirit of the invention.

Claims

1. 1. A polyolefin battery separator membrane comprising a microporous membrane, The microporous membrane is A small piece was cut from the microporous membrane and placed between two blocking electrodes, followed by immersion in 1.0 M LiPF in EC / EMC solvent at a volume ratio of 3:

7. ６ The battery is saturated with a battery electrolyte containing salt and has an electrical resistance of 0.95 ohm cm as measured by a four-probe AC ​​impedance method. ２ is less than The Gurley number measured using an OHKEN air permeability tester in accordance with Japanese Industrial Standards (JIS Gurley) JIS P8117 is less than 500 seconds / 100 cc; The degree of bending calculated using the following formula is less than 1.5, [Equation 1] In the above formula, A is the area of ​​the microporous membrane (cm ２ ), R is the resistivity of the microporous membrane in ohm-cm (Ωcm), ε is the porosity of the microporous membrane measured using ASTM method D-2873, L is the thickness of the microporous membrane, and ζ is the resistivity of the electrolyte in ohm-cm (Ωcm); A polyolefin battery separator membrane, wherein the microporous membrane has non-circular, trapezoidal shaped pores.

2. 1. A polyolefin battery separator membrane comprising a microporous membrane, The microporous membrane is A small piece was cut from the microporous membrane and placed between two blocking electrodes, followed by immersion in 1.0 M LiPF in EC / EMC solvent at a volume ratio of 3:

7. ６ The battery is saturated with a battery electrolyte containing salt and has an electrical resistance of 0.8 ohm cm as measured by a four-probe AC ​​impedance method. ２ is less than The Gurley number measured using an OHKEN air permeability tester in accordance with Japanese Industrial Standards (JIS Gurley) JIS P8117 is less than 150 seconds / 100 cc; The degree of bending calculated using the following formula is less than 1.3, [Equation 2] In the above formula, A is the area of ​​the microporous membrane (cm ２ ), R is the resistance of the microporous membrane in ohm-cm (Ωcm), ε is the porosity of the microporous membrane measured using ASTM method D-2873, L is the thickness of the microporous membrane, and ζ is the resistance of the electrolyte in ohm-cm (Ωcm).

3. 10. The polyolefin battery separator membrane of claim 1, wherein the microporous membrane can be a single layer membrane or a multi-layer membrane with thermal barrier function.

4. 10. The polyolefin battery separator membrane of claim 1, wherein the microporous membrane is a multi-layer membrane consisting of a polypropylene / polyethylene / polyethylene triple layer.

5. 10. The polyolefin battery separator membrane of claim 1, wherein the microporous membrane has a thickness of less than 25 μm.

6. 10. The polyolefin battery separator membrane of claim 1, wherein the microporous membrane is polypropylene, polyethylene, a mixture thereof, or a copolymer thereof.

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