Paper containing aerogel powder and aramid polymer fibrils

Abstract

To provide paper suitable for use in a battery or a battery pack as a flame barrier or a thermal insulator.SOLUTION: There is provided paper suitable for use in a battery or a battery pack as a flame barrier or a thermal insulator, the paper including 60 to 95 wt.% of aerogel powder and 5 to 40 wt.% of aramid polymer fibrils and having a thickness of 50 to 4000 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] Technical field. The present invention relates to paper suitable for use in battery cells, battery modules, or battery packs as a flame shield or thermal insulator; and to battery cells, battery modules, or battery packs containing paper. [Background technology]

[0002] Description of the prior art. The growing use of lithium-ion batteries and other batteries in electric vehicles has been accompanied by a significant increase in battery failures, including overheating and ignition. Flame shields and flame-retardant insulators are needed for applications such as separating battery cells to help prevent overheating points and hot spots within a single cell from causing thermal runaway conditions that could lead to fire or explosion in the entire battery pack.

[0003] Furthermore, some of the materials proposed for such insulators have properties undesirable to battery manufacturers. Some insulating materials have a high tendency to shed particles during either manufacturing or use, which is undesirable in that it causes dust and other problems in methods such as those requiring the application of high-speed automatic adhesive tape on the surface of the insulating material. Also, particle detachment affects the bond between the insulating material surface and the adhesive tape, causing movement and / or misalignment of the insulating material due to vibrations that most electric vehicles experience during normal operation (such as road vibrations). Moreover, material loss during manufacturing is undesirable as it reduces yield.

[0004] What is needed is a flame shield structure that can provide improved thermal insulation and have acceptable detachment performance both during manufacturing and use, and can be used in applications requiring flame shields or thermal insulation, such as in various locations of battery cells, battery modules, or battery packs. [Overview of the project] [Means for solving the problem]

[0005] The present invention relates to a paper suitable for use in batteries or battery packs as a flame shield or thermal insulator, comprising 60 to 95 weight percent of aerogel powder and 5 to 40 weights of aramid polymer fibrils, and having a thickness of 50 to 4000 micrometers. [Brief explanation of the drawing]

[0006] [Figure 1] These are SEM images at 500x and 1000x magnification, respectively, of the surface of paper manufactured from a combination of aerogel powder and aramid polymer fibrils. [Figure 2] These are SEM images at 500x and 1000x magnification, respectively, of the surface of paper manufactured from a combination of aerogel powder and aramid polymer fibrils. [Figure 3] These are cross-sectional views at 500x and 1000x magnification, respectively, of calendered or compressed paper produced from a combination of aerogel powder and aramid polymer fibrils. [Figure 4] These are cross-sectional views at 500x and 1000x magnification, respectively, of calendered or compressed paper produced from a combination of aerogel powder and aramid polymer fibrils. [Figure 5] These are SEM images at 500x and 1000x magnification, respectively, of the surface of paper manufactured from a combination of aerogel powder, aramid polymer fibrils, and mica. [Figure 6] These are SEM images at 500x and 1000x magnification, respectively, of the surface of paper manufactured from a combination of aerogel powder, aramid polymer fibrils, and mica. [Figure 7] This plot shows the thermal conductivity of several papers manufactured from combinations of aerogel powder and aramid polymer fibrils, illustrating the effect of different amounts of total aerogel powder and aramid polymer fibrils on the thermal conductivity of the paper. [Figure 8] This is a digital photograph taken at 1000x magnification of an aramid polymer fibril. [Figure 9] This is a digital photograph taken at 500x magnification of commercially available aramid pulp. [Figure 10] This graph compares the pore distribution in PPD-T / PVP filaments versus PPD-T filaments. [Modes for carrying out the invention]

[0007] The present invention relates to paper suitable for use in battery cells, battery modules, or battery packs as a flame shield or thermal insulator, and to battery cells, battery modules, or battery packs containing this paper. The paper comprises 60 to 95 weight percent aerogel powder and 5 to 40 weight percent aramid polymer fibrils, and the paper has a thickness of 50 to 4000 micrometers. This high percentage of aerogel powder in the sheet is made possible by the use of aramid polymer fibrils, which are thought to capture or confine particles either by entanglement or by forming a mesh structure that prevents the aerogel powder from flowing out of the structure during papermaking.

[0008] The paper contains 60 to 95 weight percent of aerogel powder and 5 to 40 weight percent of aramid polymer fibrils, based on the total weight of aerogel powder and aramid polymer fibrils in the paper. In some embodiments, the paper contains 65 to 95 weight percent of aerogel powder and 5 to 35 weight percent of aramid polymer fibrils, based on the total weight of aerogel powder and aramid polymer fibrils in the paper. In some preferred embodiments, the paper contains 75 to 95 weight percent of aerogel powder and 5 to 25 weight percent of aramid polymer fibrils, based on the total weight of aerogel powder and aramid polymer fibrils in the paper, and in some most preferred embodiments, the paper contains 80 to 95 weight percent of aerogel powder and 5 to 20 weight percent of aramid polymer fibrils, based on the total weight of aerogel powder and aramid polymer fibrils in the paper.

[0009] Figures 1 and 2 are SEM images at 500x and 1000x magnification, respectively, of the surface of paper manufactured from a combination of aerogel powder and aramid polymer fibrils. Figures 3 and 4 are cross-sectional images at 500x and 1000x magnification, respectively, of calendered or compressed paper manufactured from a combination of aerogel powder and aramid polymer fibrils.

[0010] The paper has a thickness of 100 to 4000 micrometers (0.1 to 4 millimeters). The minimum gap between cells (either pouch or prismatic cells) is approximately 0.1 mm, which allows for current battery design standards and enables battery cell and module designers to miniaturize battery pack designs as much as possible for the limited space in electric vehicles. Therefore, gaps of more than 4 mm between two cells are generally undesirable. In some embodiments, the paper has a thickness of 300 to 3000 micrometers (0.3 to 3 millimeters). In some embodiments, the paper can have a basic weight of 50 to 500 grams / square meter. In some embodiments, the paper has a basic weight of 100 to 300 grams / square meter.

[0011] Aerogels are porous, ultralight synthetic materials derived from gels, where the liquid component of the gel is replaced by a gas. The result is a solid with extremely low density and low thermal conductivity. Aerogels can be produced from various compounds, but silica aerogels are the preferred and most common type.

[0012] As used herein, the terms “aerogel,” “aerogel powder,” and “aerogel particles” are all used interchangeably and refer to preferred aerogels which are highly porous, hydrophobic, high-surface-area, preferably amorphous silica particles or granules having a particle size range of 10 nanometers to 50 micrometers (0.00001 to 0.05 millimeters), preferably 0.05 to 20 micrometers. Generally, they are chemically similar to common fumed silica products but with higher porosity (>95%) and lower density (0.03 to 0.1 g / cm³). 3), small average pore diameter (20 nm), lower thermal conductivity (0.017~0.022 W / mK), higher surface area (600~800 m²) 2 Aerogels, such as those described in ( / g), have larger aggregate sizes, higher surface area, and larger pore volume, and are generally manufactured using sol-gel manufacturing processes. Pioneering patents describing aerogels include U.S. Patents Nos. 2,093,454, 2,188,007, and 2,249,767 to Kistler, and more recent disclosures such as U.S. Patents Nos. 8,518,335 and 8,961,919 to Joung et al. are available.

[0013] As used herein, the term “aramid polymer fibril” refers to a fibrous material having a diameter of 10 to 2000 nanometers, preferably 10 to 1200 nanometers, produced from an aramid polymer or a polymer blend containing at least two polymers, the majority (more than 50 weight percent) being an aramid polymer. Figure 8 is a representative digital photograph of an aramid polymer fibril. The aramid polymer fibril further has a preferred length of 0.2 to 3 millimeters. The “length” of fibrous materials referred to herein, such as aramid polymer fibril and pulp, means the length of the measured “length-weighted average.” In some preferred embodiments, the aramid polymer fibril is a purified aramid polymer fibril produced from flocs by subjecting the flocs to a purification process that shears the flocs into smaller aramid polymer fibrils. In some preferred embodiments, the aramid polymer fibril has a length of 0.4 to 3 millimeters (mm), preferably 0.8 to 3 mm.

[0014] The diameter of the aramid polymer fibril affects the distribution and size of pores in the paper structure when it is formed, and specifically, it is considered to provide a structure designed to capture or confine the aerogel powder. Aramid polymer fibrils having a diameter greater than 2000 nanometers result in undesirably high pore diameters in the paper, which ultimately leads to large pores in the paper when formed, and can easily allow nano-sized and micro-sized aerogel powders to flow out during the papermaking process. Also, aramid polymer fibrils having a diameter less than 10 nanometers or a length less than about 0.2 millimeters are considered not to contribute to the mechanical strength of the paper because the entanglement of the aramid polymer fibrils is lower, and thus it is desirable that most of the aramid polymer fibrils have a length of 0.2 millimeters or more.

[0015] Furthermore, the aramid polymer fibril can have an aspect ratio that can range from about 150 to 300,000. Also, the aspect ratio is known as the length divided by the diameter, and the terms "aspect ratio", "average length-to-diameter ratio", and "length-to-diameter" are used interchangeably herein. In some embodiments, the average length-to-diameter ratio of the aramid polymer fibril is about 1000 or more. In some embodiments, the aramid polymer fibril has an average length-to-diameter ratio of about 3000 or less. In some preferred embodiments, the average length-to-diameter ratio ranges from about 1000 to 3000. When the average length-to-diameter ratio of the aramid polymer fibril is higher, it is considered to contribute to better mechanical reinforcement of the paper.

[0016] Qualitative measurement of a specific fiber material such as an aramid polymer fibril can sometimes be difficult, so such fiber materials can be compared by measuring the "drainage degree" of the fiber material. The most common techniques for measuring the drainage degree are to measure either the Canadian Standard Freeness (CSF) or the Schopper-Riegler Freeness (SRF).

[0017] The inventor is considering the Canadian Standard Freeness (CSF) as a preferred technique for characterizing the aramid polymer fibrils used in this specification. The aramid polymer fibrils are preferably produced by purifying aramid polymer fibers or flocks to produce fibrils. Such fibrils preferably have a CSF of 0 to 50 milliliters, and in some embodiments, a CSF of 0 to 20 milliliters. The CSF is one indicator of the fineness of the aramid polymer fibrils or the degree of fibrillation during purification, and very fine aramid polymer fibrils have a very low CSF. Also, materials with a wide size distribution generally have high CSF values, so low CSF values indicate fibrils of uniform size.

[0018] The aramid polymer fibrils defined herein are fibrous materials and are quite different from prior art aramid polymer pulps. Such aramid polymer pulps are preferably produced by purifying flocks or can be produced directly from the components taught in U.S. Patent Nos. 5,202,184, 5,523,034, and 5,532,034. However, such methods are difficult to control and thus not only provide fibrous materials with a wider range of fiber sizes and lengths, but also provide both "stalks" and fibrils extending from the stalks, where the stalks are the substantially columnar remnants of the original aramid polymer flocks and have a diameter of about 10 to 50 microns. Further, in the case of aramid polymer pulps, the length measurements are understood to be the characteristic lengths of the pulp stalks, also called "pulp stalks".

[0019] Furthermore, the average length-to-diameter ratio of aramid polymer fibrils is much larger than that of conventional aramid polymer pulps, such as those produced by the processes described in U.S. Patent Applications No. 5,084,136, No. 5,171,402, and No. 8,211,272, which are generally considered to have an average length-to-diameter ratio of less than 150, or the average length-to-diameter ratio of highly refined pulps, such as those disclosed in U.S. Patent Application Publication No. 2016 / 0362525 and No. 2017 / 0204258, is generally considered to be smaller than that of conventional pulps (e.g., generally less than 100).

[0020] Furthermore, when used in paper, aramid polymer fibrils are aramid polymer fibrils that are essentially stalk-free or stalk-free. As used herein, the term “stalk-free aramid polymer fibrils” means that at least 95% by weight of the fiber material is aramid polymer fibrils having a desired diameter of 10 to 2000 nanometers as determined by optical measurement of fibril samples using a magnification of 500x or 1000x. In some embodiments, it means that at least 98% by weight of the fiber material is aramid polymer fibrils having a desired diameter of 10 to 2000 nanometers as determined by optical measurement of fibril samples using a magnification of 500x or 1000x. In some embodiments, it means that 100% by weight of the fiber material is aramid polymer fibrils having a desired diameter of 10 to 2000 nanometers as determined by optical measurement of fibril samples using a magnification of 500x or 1000x.

[0021] One preferred method for producing stalk-free aramid polymer fibrils is to purify fibers or flocs produced from a polymer blend containing at least two polymers in which the majority (more than 50 weight percent) of the aramid polymer is present. One preferred polymer blend is a blend of 80–96 weight percent poly(p-phenylene terephthalamide) (PPD-T) and 4–20 weight percent polyvinylpyrrolidone (PVP). When aramid fibers or aramid flocs produced from this PPD-T / PVP polymer blend are purified, the resulting fibrous material is essentially all fibrils, and as shown in the digital photograph in Figure 8, there are essentially no larger stalks in the material. It is considered that at least 4 weights of PVP must be present in the fibers or flocs for the original fibers or flocs to be purified to fibrils without essentially leaving any stalks. This is compared to conventional purified aramid pulp produced from poly(p-phenylene terephthalamide) homopolymer, shown in Figure 9, which has visible stalks.

[0022] The porosity and crystallinity of filaments made from a blend of 80–96 weight percent PPD-T and 4–20 weight percent PVP have been found to be dramatically different from those of filaments made solely from PPD-T. In this specification, the terms “fiber” and “filament” are used interchangeably. Fibers spun directly from a polymer solution onto a bobbin without cutting are generally called continuous fibers or continuous filaments, while multifilament yarns contain multiple continuous filaments.

[0023] Figure 10 illustrates the difference in X-ray scattering between two types of filaments. Curve 20 represents a filament made from a PPD-T / PVP blend, and curve 30 represents a filament made from PPD-T alone. Curve 30 illustrates that the PPD-T filament has a significant peak centered at approximately 2 angstroms (and a much smaller peak centered at 4 angstroms), which indicates very small pores in the fiber. Curve 20 illustrates that the pore size distribution of the PPD-T / PVP blend is much broader, with a peak centered at approximately 3 angstroms and a very broad sloped peak centered at approximately 250 angstroms, but extending into the region of approximately 70–600 angstroms. This suggests that the filament made from the PPD-T / PVP blend has a much larger number of pores than the PPD-T filament.

[0024] Furthermore, as illustrated in Figure 8, this difference in fiber crystallinity and pore structure is thought to result in a much finer and more uniform distribution of fibrils when the filaments are mechanically purified. In other words, the very high crystallinity and low porosity of PPD-T fibers mean that when mechanically purified, the purification shear action mainly polishes the surface of the filaments, producing a typical fibrilized stalk structure (shown in Figure 9), whereas the low crystallinity and high porosity of the filaments of the PPD-T / PVP blend are thought to allow for easy separation into individual purified fibrils under the same shear action, resulting in a large number of smaller, relatively more uniform diameter fibrils, and, more importantly, the absence of any stalks whatsoever (i.e., no stalks). The aramid polymer fibrils are thought to have a relatively uniform diameter with a total diameter size range of approximately 300 nanometers, as can be visually measured from SEM micrographs.

[0025] Aramid polymer fibrils are preferably produced from aramid flocs having PPD-T and at least one other polymer material component as the majority by weight of the polymer material component. These components are preferably immiscible with respect to each other so that at least two polymer materials are well mixed but exist as separate solid phases in the floc. When such aramid flocs are purified, they produce aramid polymer fibrils having domains of two different polymer materials, one phase being a continuous or primary polymer phase or PPD-T polymer, and the other phase being a discontinuous or secondary polymer phase, which is preferably a PVP polymer.

[0026] The discontinuous or secondary polymer phases are thought to exist as small nanometer-sized crystalline domains of material that pass through the flocs and act as breaking points in the floc structure during the purification process, facilitating the rapid and more complete purification of the flocs and the formation of fibrils. After purification, portions of the discontinuous or secondary polymer from each breaking point are present on or on the surface of each fibril resulting from the purification process.

[0027] Furthermore, aramid polymer fibrils have a high surface area. The terms "surface area," "specific surface area," and "BET surface area" are used interchangeably in this specification. Aramid polymer fibrils have a surface area of ​​approximately 3-40 m 2 It has a specific surface area of ​​ / g. In some embodiments, the specific surface area is 6m 2 It is 1 / g or more, and in some embodiments, the specific surface area is 8m 2 It is 1 / g or more. One particularly preferred range for specific surface area is 6-20 m². 2 It is / g.

[0028] In comparison, conventional pulp refined from flocs made from a single polymer material or from miscible blends of polymer materials without discontinuous secondary polymer domains would not possess such high surface area. Furthermore, if this floc is refined sufficiently to have such a measured high surface area, the resulting pulp particles will have such a low aspect ratio (resulting from a very low average length) that they will not provide sufficient paper reinforcement.

[0029] Preferred aramid fibrils contain 80–96 weight percent poly(paraphenylene terephthalamide) (also known and used herein as polyparaphenylene terephthalamide or PPD-T). PPD-T refers to homopolymers obtained from molar-to-molar polymerization of p-phenylenediamine and terephthaloyl chloride, as well as copolymers obtained from the incorporation of small amounts of other diamines with p-phenylenediamine and small amounts of other dioxides with terephthaloyl chloride. Typically, other diamines and dioxides can be used in amounts of up to about 10 mole percent of p-phenylenediamine or terephthaloyl chloride, or perhaps slightly higher, provided that the other diamines and dioxides do not have reactive groups that interfere with the polymerization reaction. Furthermore, PPD-T refers to copolymers obtained from the incorporation of other aromatic diamines and other aromatic dioxides, such as 2,6-naphthaloyl chloride or chloro- or dichloro-terephthaloyl chloride, provided that the other aromatic diamines and aromatic dioxides are present in amounts that enable the preparation of anisotropic spinning dopes. The preparation of PPD-T is described in U.S. Patents No. 3,869,429, No. 4,308,374, and No. 4,698,414.

[0030] Furthermore, preferred aramid fibrils contain 4 to 20 weight percent poly(vinylpyrrolidone) (also known and used herein as polyvinylpyrrolidone or PVP). PVP refers to a polymer resulting from the linear polymerization of monomer units of N-vinyl-2-pyrrolidone and containing small amounts of comonomers that may be present at concentrations lower than those that do not interfere with the interaction of PVP with PPD-T. PVPs with molecular weights ranging from a minimum of about 5,000 to a maximum of about 1,000,000 can be used. Very high molecular weight PVPs produce high-viscosity spinning dopes. PVPs with molecular weights of about 10,000 to about 360,000 are preferred.

[0031] Aramid polymer fibrils are preferably produced by solution spinning a continuous filament yarn from a dope containing an aramid polymer, cutting the continuous filament yarn into flocs, and then mechanically purifying the flocs into fibrils using one or more purifiers. In the preferred method, the dope is a solution containing a combination of PPD-T polymer and PVP polymer in sulfuric acid. Examples of typical processes for producing continuous filament yarns are found in U.S. Patent Nos. 5,073,440 and 5,094,913 and U.S. Patent Application Publication No. 2006 / 0113700. Next, the aramid flocs are cut from the continuous filament yarn. Before purification, the aramid flocs generally have a length of about 2 mm to about 25.4 mm, and optionally 2 to 10 mm or even 3 to 10 mm.

[0032] Aramid polymer fibrils are preferably produced from flocs by purifying or fibrillating preferred PPD-T / PVP flocs using techniques such as cutting, kneading into pulp, or polishing, using mechanical methods that are easy to use with paper, for example, dry and wet disc or cone purification, hydra pulping and beating. Preferably, purification is performed on a dispersion of flocs in water, and preferably the dispersion is purified by passing through the purifier multiple times. That is, the purified dispersion that leaves the purifier is recycled through the same or a second purifier for a second pass through the purifier. The starting dispersion generally has a solid content of about 1 to 4 weight percent of the flocs in water.

[0033] If the floc is a PPD-T / PVP floc, the floc can be completely fibrillated into stalk-free aramid polymer fibrils after just three passes through the purifier, in which case it is suitable for papermaking. Stalk-free aramid polymer fibrils have a very low Canadian standard filtration efficiency (CSF) compared to pulp produced from fibers that tend to fibrillate and form a mixture containing large-character stalks combined with the fibrils. A suitable fibril can be obtained by three passes through the purifier, but it can pass through the purifier further, and it is thought that more than 20 passes can help to further disperse and homogenize the fibrils, as long as it does not adversely affect the final strength of the paper. Preferably, the fibrils are produced by recirculating the dispersion through the purifier for 3 to 20 passes, and in some embodiments, 3 to 10 passes through the purifier are used.

[0034] When separating or recovering fibrils from stalks using subsequent processes after the purification step, stalk-free aramid polymer fibrils can be obtained from conventional PPD-T, acrylic, or cellulose pulp, provided that sufficient care is taken. If such fibrils meet the definition of "stalk-free" as described herein, they are considered suitable for use in paper.

[0035] If necessary, the paper may further contain 10% by weight or more of mica based on the total weight of the aerogel powder, aramid polymer fibrils, and mica in the paper. Adding mica to the paper structure is thought to further enhance the flame barrier and dimensional stability of the paper. The planar or flake shape of the mica provides anisotropic flame barrier (in the z-direction perpendicular to the plane of the flake), and the thermal conductivity in the z-direction is 1 / 100th of the thermal conductivity in the x and y directions. Planar mica is advantageous because it aligns with and within the planar structure of the paper; therefore, the z-direction properties of the mica provide improved thermal insulation across the plane of the paper. In some cases, at least 20% by weight of mica in the paper is desirable to provide excellent dimensional stability and flame barrier.

[0036] Figures 5 and 6 are SEM images at 500x and 1000x magnification, respectively, of the surface of paper manufactured from a combination of aerogel powder, aramid polymer fibrils, and mica.

[0037] Mica includes muscovite or phlogopite mica, or blends thereof, and may be calcined or uncalcined mica. As used herein, “calcined mica” means mica obtained by heating natural mica to high temperatures (usually above 800°C, and sometimes above 950°C). This process removes water and impurities and improves the temperature resistance of the mica. Calcined mica is usually used in the form of flake particles, with muscovite-type mica being preferred. As used herein, “uncalcined mica” means mica in its naturally occurring, essentially high-purity form, preferably homogenized and purified to remove defects and impurities. Uncalcined mica can form a highly porous mica layer due to the larger size of natural mica flakes. The preferred mica is calcined mica due to its improved dielectric properties and corona resistance, which surpasses that of uncalcined mica.

[0038] As used herein, the term aramid means an aromatic polyamide in which at least 85% of the amide (-CONH-) bonds are directly bonded to two aromatic rings. Additives may be used with aramid and may be dispersed throughout the polymer structure. It has been found that up to about 10 weight percent of other supporting materials can be blended with aramid. It has also been found that copolymers can be used having about 10 percent of other diamines substituting the diamine of aramid, or about 10 percent of other dioxides substituting the dioxide of aramid. Aramid may preferably be para-aramid or aramid copolymer. An aramid polymer is considered para-aramid when two rings or radicals are oriented para-relative to each other along the molecular chain. Methods for producing para-aramid fibers are generally disclosed, for example, in U.S. Patent Nos. 3,869,430, 3,869,429, and 3,767,756. One preferred para-aramid is poly(paraphenylene terephthalamide), and one preferred para-aramid copolymer is copoli(p-phenylene / 3,4'-diphenyl ester terephthalamide). U.S. Patents Nos. 3,063,966, 3,227,793, 3,287,324, 3,414,645, and 5,667,743 describe other methods for producing aramid fibers.

[0039] Specifically, a preferred and commercially viable process for producing the paper of the present invention involves placing an aqueous dispersion containing aerogel powder and aramid polymer fibrils and any optional material in desired amounts and ratios into the headbox of a papermaking machine, and then uniformly wet-laid and dispersed these solids as a web on papermaking wires, removing most of the liquid water, thereby utilizing the papermaking machine. The wet web can then be dried on a dryer drum to form paper. In some embodiments, it is preferable to further calender or pressurize the paper under pressure and heat in the nip of a hot roll calender or by other means to solidify and densify the paper into a layer of desired thickness and properties. If necessary, two or more lighter base weight or thinner wet webs of the same composition can be separately produced and then calendered together to solidify into a single layer.

[0040] Typical apparatus and machinery that may be used to produce paper include, but are not limited to, continuous processing equipment such as wire screens or inclined wire machines, or batch processing equipment such as equipment for manually producing paper in hand-sheet molds including shaping screens. In general processes for forming aramid materials into paper, refer to Gross's U.S. Patent No. 3,756,908 and Hesler et al.'s U.S. Patent No. 5,026,456.

[0041] In some embodiments, the paper has a tensile strength of 0.5 to 100 megapascals (MPa). In some applications, it is desirable for the paper to have a tensile strength of at least 15 megapascals. For example, the paper is thought to require this level of tensile strength to withstand some battery manufacturing processes, which may include the automatic insertion of flame shields and insulation between cells. The tensile strength also contributes to flame shielding during use. While a tensile strength of paper exceeding 100 megapascals does not have adverse effects, the parameter reaches a point where its value decreases. Therefore, in some preferred embodiments, the paper has a tensile strength of 15 to 50 megapascals. In some embodiments, the paper has a tensile strength of 15 to 100 megapascals.

[0042] In some embodiments, the paper has a thermal conductivity of 0.015 to 0.05 watts / meter Kelvin (W / mK). To effectively prevent heat transfer, paper with a lower thermal conductivity that is stable over a wide range of operating temperatures, such as battery operating temperatures (-40°C to 80°C), and up to the hot spot temperature (800°C to 1,000°C) is preferred. In some embodiments, the paper has a thermal conductivity of 0.015 to 0.04 W / mK.

[0043] In some embodiments, a 1 mm (+ / -30%) thick paper containing aerogel powder and aramid polymer fibrils exhibits TPP flame performance equivalent to a second-degree burn for at least 10 seconds as measured by the Thermal Protection Performance (TPP) test, and in some embodiments, the paper exhibits TPP flame performance equivalent to a second-degree burn for at least 12 seconds.

[0044] A synergistic effect is believed to exist on the thermal and mechanical properties of paper obtained from a combination of aerogel powder and aramid polymer fibrils. The paper of the present invention shows a definite increase in dielectric strength with increasing mica content, but also a definite decrease in mechanical strength and toughness (tensile strength and elongation). However, increasing the amount of aerogel powder improves thermal insulation (reduced thermal conductivity) and provides better flame protection (TPP). In some cases, the paper of the present invention containing a combination of aerogel powder and aramid polymer fibrils has approximately 75% greater thermal protection (TPP) while having approximately 1 / 3 the thermal conductivity (i.e., greater insulation properties) compared to paper produced by simply mixing mica, aerogel, and fibrils together and papermaking. These remarkable properties and significant improvements in the degranulation problem indicate that these papers are suitable for use as battery thermal insulators and flame shields (between cells, between cells and modules, inside modules and packs, etc.).

[0045] Multi-cell battery structures have battery cells arranged in either parallel or series and are commonly known as battery blocks and battery packs. In these multi-cell battery structures, thermal energy from an abnormal thermal event, such as a defect or failure in one cell, can propagate to adjacent cells. If the thermal event is severe enough, it can propagate from cell to cell, causing a runaway thermal condition that can cascade to all cells in the battery block or pack. This can result in ignition or, worse, a fire.

[0046] To protect adjacent battery cells from an overheated cell, better flame shields and flame-retardant insulators have lower thermal conductivity at higher temperatures and higher dimensional stability. When a thermal event occurs, the temperature of an overheated cell can rise to 800°C or higher. However, it is preferable that adjacent cells be kept below 200°C. Therefore, the thermal insulation between adjacent cells is preferably sufficiently thermally stable up to at least 800°C.

[0047] The paper-containing batteries described herein can be manufactured by using paper as an insulator between cells. "Insulator between cells" is intended to include materials inserted between individual battery cells in a multi-cell battery structure that provide thermal insulation. That is, they attempt to thermally isolate each battery cell and slow down the transfer of thermal energy in the event that a battery cell has an abnormal thermal problem such as thermal runaway, which could cause a thermal "hot spot" or explosion.

[0048] In one application, paper is inserted between individual battery cells in a multi-cell battery structure to provide flame shielding and thermal insulation between the individual battery cells. Typical battery types include, but are not limited to, multi-cell battery structures having battery cells arranged in either parallel or series, commonly known as battery blocks and battery packs. However, other batteries incorporating this paper are possible, as the described paper is intended to thermally isolate each battery cell and slow the transfer of thermal energy and / or flame from one cell to another or to the structure.

[0049] Test method In the embodiments provided below, the following test methods were used.

[0050] Thickness 5 N / cm 2 The weight was used to measure according to TAPPI411 and recorded in millimeters.

[0051] Basis weight was measured according to ASTM D 645 and ASTM D 645-M-96, in g / m². 2 It was recorded there.

[0052] Tensile strength was measured according to ASTM D 828-93 using a 2.54 cm wide specimen and an 18 cm gauge length, and recorded in N / cm or MPa units.

[0053] The dielectric strength was measured according to ASTM D149-97A and recorded in kV / cm.

[0054] The thermal conductivity was measured according to ASTM E1530 and recorded in W / mK.

[0055] The Thermal Performance Protection Test (TPP) is a measure of the flammability performance of fabric and sheet materials, providing realistic conditions exposed to a combination of radiant and convective heat. Samples are exposed to a constant heat flux of 84 kW / m 2 (2 cal / cm 2 / s), a constant combination of 50% radiant heat and 50% convective heat. Then, in this test, when the material is worn, the elapsed time until the temperature and energy transmitted to the back side of the fabric reach a level equivalent to a second-degree burn, and the amount of thermal energy per unit surface area (TPP value) are measured. The TPP test method used is the test method adopted by ISO as the standard (ISO17492) for test methods involving a heat flux exposure of 80 kW / m 2 However, in the US NFPA 1971 standard, the ISO17492 test is required to be changed to a heat flux exposure of 84 kW / m 2 and increased for implementation, and this higher heat flux is used in this specification.

Examples

[0056] Example 1 Four different papers called 1-1 to 1-4 were produced from aramid polymer fibrils and aerogel powder. The aramid polymer fibrils had a Canadian standard filter fineness of 0 ml and a length of 13.8 m 2The dry specific surface area was 0.18 / g. The aramid polymer fibrils consisted of 87 wt percent PPD-T and 13 wt percent PVP, and had an average length-to-diameter ratio of approximately 2000. The aerogel powder was type IC3100 Enova® aerogel obtained from Cabot Corp. of Boston, MA. Four well-mixed aqueous dispersions were prepared, each having a different amount of aramid polymer fibrils and aerogel powder but all having approximately the same solids content of 0.18%, and having the compositions shown in Table 1.

[0057] Next, each of the four aqueous dispersions was poured into a 21 × 21 cm hand sheet mold along with approximately 8 liters of water to create a finished paper stock with a total solid content of approximately 0.05%, forming wet-laid hand sheets. Then, each hand sheet was removed, placed between two sheets of blotting paper, and couched by hand using a cotton swab. The sheets were then dried in a hand sheet dryer at 150°C for 10 minutes. The paper was then dried, and the dried paper exhibited a smooth, non-shedding surface. As shown in Figure 1, the aerogel powder particles were trapped within a network structure of nanofibrils around the particles. The structural properties of the obtained paper are described in Table 1.

[0058] Comparative example A Comparative paper A was prepared by first forming an aqueous dispersion of 8 grams of aerogel powder and 2 grams of MPD-I fibrid in water. The fibrid contained no aerogel polymer whatsoever. The MPD-I fibrid was manufactured by the method generally described in U.S. Patent No. 3,756,908.

[0059] As used herein, the term fibride refers to very small non-granular, fibrous, or film-like particles in which at least one of their three dimensions is smaller in scale than the largest dimension. These particles are prepared by precipitating a solution of a supporting material with a non-solvent under high shear. Aramid fibrides are non-granular film-like particles of aromatic polyamides having a melting or decomposition point above 320°C. Preferred aramid fibrides are meta-aramid fibrides, and particularly preferred are fibrides produced from meta-aramid poly(meta-phenylene isophthalamide) (MPD-I).

[0060] Fibrids generally have a maximum dimensional length in the range of approximately 0.1 mm to 1 mm, with a length-to-width aspect ratio of approximately 5:1 to 10:1. The thickness dimension is on the order of a fraction of a micron, e.g., approximately 0.1 microns to 1.0 micron. Undried fibrids were used in the dispersion.

[0061] Next, a hand sheet was formed using an aqueous dispersion as in Example 1. The dried paper exhibited a rough, granular surface. The physical and thermal properties are shown in Tables 1 and 2.

[0062] Thermogravimetric analysis (TGA) of the dried paper showed that approximately 5.15 grams of aerogel particles remained, meaning that nearly 51.2% of the original aerogel powder was lost during the papermaking process. The data in Table 2 show the synergistic effect on the thermal and mechanical properties of the paper obtained from the combination of mica and aerogel-containing fibrils. This paper shows a definite increase in dielectric strength with increasing mica content, but also a definite decrease in mechanical strength and toughness (tensile strength and elongation). However, increasing the amount of aerogel powder in the paper resulted in improved thermal insulation (reduced thermal conductivity) and better flame protection (TPP). Both the paper of Comparative Example A and Example 2-3 were manufactured using 20 weight percent aerogel powder. However, the paper of Example 2-3 has nearly half the thermal conductivity (i.e., twice the insulation properties) and twice the thermal protection (TPP) of the paper of Comparative Example A. These remarkable properties, along with significant improvements in the granulation problem, indicate that these papers are suitable for use as battery thermal insulators and flame shields (between cells, between cells and modules, inside modules and packs, etc.).

[0063] Comparative example B Comparative paper B was prepared from an aqueous dispersion containing only fibrites. However, these fibrites were modified fibrites produced from a polymer dispersion containing aerogel powder. In other words, the actual fibrites contained a blend of polymer and aerogel powder.

[0064] Specifically, a polymer dispersion was prepared by compounding 65 parts by weight of the solvent dimethylacetamide, 15 parts by weight of poly(methaphenylene isophthalamide) (MPD-I) polymer, 5 parts by weight of calcium chloride (as a solubility enhancer), and 15 parts by weight of aerogel powder (Type IC 3100 Enova® aerogel obtained from Cabot Corp. of Boston, MA) in a kettle, stirring until a homogeneous mixture was obtained. The mixture was then slowly poured into a vigorously stirring Waring blender, which simultaneously solidified the polymer from the solvent into a film-like fibrilate, where the MPD-I polymer and aerogel powder were present in a 1:4 ratio. The resulting modified fibrilate was collected on a Buchner funnel as wet-laid paper and thoroughly washed with deionized water. Using the procedure of Example 1, aqueous dispersions and hand sheets were prepared using these modified fibrilates. The compositions and test results are shown in Tables 1 and 2.

[0065] To analyze the different amounts of silicate, and therefore the amount of aerogel fixed in all samples, TGA thermogravimetric analysis (TGA) was performed on all of the paper samples 1-1 to 1-4 and comparative A and B using a high-resolution TA analyzer Q500TGA (40-700C) in air. The results are shown in Tables 1 and 2. As expected, the paper samples prepared simply by mixing the fibrid and aerogel powder together showed the highest reduction in aerogel in the final structure, retaining just 64% of the added aerogel powder. Paper samples prepared by encapsulating the aerogel within the fibrid performed better, retaining 71% of the aerogel powder. Surprisingly, however, the paper samples prepared by mixing aramid polymer fibrils with aerogel powder increased the retention of aerogel powder to over 90%, ranging from 92-95% for the four paper samples. This adequately explains how the aerogel powder particles are trapped within the network structure of the aramid polymer fibrils.

[0066] Next, the thermal conductivity of these paper samples was measured by a thin-film method using a transient planar heat source (TPS1500) with a pressure of 2.45 kg on a 2-inch diameter laminated sample. The practical effect of retained aerogel particles on the thermal conductivity of the paper samples is shown graphically in Figure 7. Paper samples prepared by mixing aramid polymer fibrils and aerogel powder samples had the lowest thermal conductivity, and when the thermal conductivity of all samples prepared at an 80 wt percent aerogel addition level was compared, Examples 1-3 were found to have thermal conductivity 29% and 22% lower than Comparative Examples A and B, respectively.

[0067] [Table 1]

[0068] [Table 2]

[0069] Example 2 The paper was manufactured from aerogel powder, aramid polymer fibrils, and mica. Compared to paper without mica or an equal amount of aerogel powder, the paper exhibited lower thermal conductivity and higher flame resistance.

[0070] Two separate aqueous dispersions were prepared using the procedure of Example 1. However, a considerable amount of calcined mica flakes was added to both dispersions, replacing 10% and 20% by weight of the aerogel powder in each dispersion, as shown in Table 3. The mica was of the muscovite type, available from Electrical Samica Flake Co., Rutland, Vermont. Hand sheets were then prepared using the procedure of Example 1 and tested for burn resistance. All dried papers showed a smooth, non-shedding surface. The composition and test results are shown in Table 3.

[0071] [Table 3] This disclosure includes the following embodiments. (Embodiment 1) Paper suitable for use in batteries or battery packs as a flame shield or thermal insulator, 60-95% by weight of aerogel powder, It contains 5 to 40 weights of aramid polymer fibrils; Paper with a thickness of 50 to 4000 micrometers. (Embodiment 2) The paper according to Embodiment 1, further comprising 10% by weight or more of mica based on the total weight of the aerogel powder, aramid polymer fibrils, and mica in the paper. (Embodiment 3) The paper according to Embodiment 1 or 2, wherein the aramid polymer fibrils contain poly(paraphenylene terephthalamide). (Embodiment 4) The paper according to Embodiment 3, wherein the aramid polymer fibrils comprise a blend of polymers, the blend of polymers comprising 80 to 96 weight percent poly(paraphenylene terephthalamide) and 4 to 20 weight percent poly(vinylpyrrolidone). (Embodiment 5) A paper according to any one of Embodiments 1 to 4, having a thickness of 500 to 3000 micrometers. (Embodiment 6) A paper according to any one of Embodiments 1 to 5, having a tensile strength of 0.5 to 100 MPa. (Embodiment 7) A paper according to any one of Embodiments 1 to 6, having a thermal conductivity of 0.015 to 0.05 W / mK. (Embodiment 8) A battery cell, battery module, or battery pack containing paper as described in any one of Embodiments 1 to 7.

Claims

1. Paper suitable for use in batteries or battery packs as a flame shield or thermal insulator, 60-95% by weight of aerogel powder, It comprises 5 to 40 weights of aramid polymer fibrils; The aramid polymer fibril comprises poly(paraphenylene terephthalamide), Paper with a thickness of 50 to 4000 micrometers.

2. The paper according to claim 1, further comprising 10% by weight or more of mica based on the total weight of the aerogel powder, aramid polymer fibrils, and mica in the paper.

3. The paper according to claim 1 or 2, wherein the aramid polymer fibrils comprise a blend of polymers, the blend of polymers comprising 80 to 96 weight percent poly(paraphenylene terephthalamide) and 4 to 20 weight percent poly(vinylpyrrolidone).

4. A paper according to any one of claims 1 to 3, having a thickness of 500 to 3000 micrometers.

5. A paper according to any one of claims 1 to 4, having a tensile strength of 0.5 to 100 MPa.

6. A paper according to any one of claims 1 to 5, having a thermal conductivity of 0.015 to 0.05 W / mK.

7. A battery cell, battery module, or battery pack containing paper as described in any one of claims 1 to 6.

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