Siloxane dispersion cross-linked separator

Abstract

To provide a separator for a nonaqueous secondary battery that can achieve both safety and a long life for the nonaqueous secondary battery, and a method for manufacturing the same, or a nonaqueous secondary battery including the same.SOLUTION: A separator for a nonaqueous secondary battery includes a polyethylene microporous membrane, and has an air permeability change ratio (air permeability Sh after compression / air permeability Sj before compression) of 1.1 to 7.0 times when compressed by 30% of its thickness.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a separator for a non-aqueous secondary battery, a method for producing the same, or a non-aqueous secondary battery including the same. [Background technology]

[0002] Microporous membranes are widely used as separation or permselective separation membranes for various substances, separators, etc., and examples of their applications include microfiltration membranes, separators for fuel cells and capacitors, base materials for functional membranes in which functional materials are filled into the pores to exhibit new functions, battery separators, etc. In particular, polyolefin microporous membranes are preferably used as separators for lithium-ion batteries, which are widely used in electric vehicles, notebook personal computers, mobile phones, digital cameras, etc.

[0003] To ensure battery safety, battery separators are required to have both a shutdown function and an improved membrane rupture temperature.

[0004] Furthermore, to ensure the safety and cycle characteristics of batteries, battery separators are required to have improved mechanical strength, shutdown function, and membrane rupture temperature. From the perspective of imparting functionality to battery separators, the inclusion of modified polyolefins in microporous membranes, the crystalline structure of the resin that constitutes the microporous membrane, and coating the microporous membrane with a resin- or inorganic-containing slurry are being considered.

[0005] For example, it has been proposed to incorporate inorganic particles and a polyolefin resin into a microporous polyolefin film that can be used as a separator for lithium ion batteries (Patent Document 1).

[0006] Furthermore, from the viewpoint of improving safety by introducing a higher-order structure such as a silane crosslinked structure into a polyolefin microporous membrane, a battery separator in which a silane crosslinking reaction is initiated within the battery (Patent Document 2) and a polyolefin microporous membrane having a sea-island structure obtained by blending a silane-modified polyethylene with a medium-molecular-weight polyethylene (Patent Document 3) have been proposed.

[0007] Patent Document 2 also describes incorporating a silane-modified polyolefin or the like into a polyolefin microporous membrane, and disposing an inorganic porous layer containing inorganic particles and a resin binder on at least one side of the polyolefin microporous membrane.

[0008] For example, in the manufacturing process of a silane-crosslinkable polyolefin separator described in Patent Document 4, the carbon numbers of the repeating units derived from ethylene, the repeating units derived from olefins other than ethylene, and the branched chains of the repeating units derived from olefins other than ethylene in the silane-modified polyolefin are investigated.

[0009] For example, a polyolefin microporous membrane containing a silane-modified polyolefin or the like has been investigated for its polyethylene crystallinity, polyethylene crystallite size, and cross-sectional crystal orientation measured by X-ray diffraction (XRD) (Patent Document 5). Furthermore, the crystal long period measured by small-angle X-ray scattering (SAXS) has also been investigated for a polyolefin microporous membrane (Patent Document 6) and an oriented polypropylene film (Patent Document 7).

[0010] Patent Document 8 examines the thickness of a stretched polyethylene film and the area ratio R=I(110) / (I(110)+I(200)), which is the area I(110) of the diffraction peak of the (110) plane when irradiated with X-rays in the film thickness direction and the area I(200) of the diffraction peak of the (200) plane, and describes coating the stretched polyethylene film with an aramid resin or the like.

[0011] Non-Patent Document 1, for example, discusses a synthetic scheme for converting a tetracoordinate allylsilane into a pentacoordinate allylsilicate. Non-Patent Document 1 describes that a low-molecular-weight organic Si compound forms a high-coordinate complex in the presence of an alkali metal fluoride, and not only does Si exhibit Lewis acid properties, but also, due to its high affinity for oxygen, it can adopt a structure in which the lone electron pair of the oxygen compound is coordinated, thereby accelerating the electron addition reaction from the β-position of the high-coordinate complex due to thermodynamic stabilization caused by the influence of stereoregularity.

[0012] Non-Patent Document 2 describes that in a battery using a Si-containing negative electrode active material, as lithium ions are charged and discharged to and from the Si-containing particles, the Si-containing negative electrode active material undergoes a large volume expansion or contraction. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] International Publication No. 2008 / 035674 [Patent Document 2] International Publication No. 2020 / 075866 [Patent Document 3] International Publication No. 2020 / 040389 [Patent Document 4] Korean Patent Publication No. 10-2020-0078407 [Patent Document 5] International Publication No. 2020 / 067161 [Patent Document 6] International Publication No. 2014 / 175252 [Patent Document 7] International Publication No. 2015 / 012324 [Patent Document 8] Patent No. 6012839 [Non-patent literature]

[0014] [Non-Patent Document 1] "Special Feature: Silicone Polymers, Organosilicon Chemistry," Journal of the Society of Rubber Science and Technology, Japan, Vol. 62, No. 12 (1989) [Non-patent document 2] "Volume Expansion during Lithiation of Amorphous Silicon Thin Film Electrodes Studied by In-Operando Neutron Reflectometry" J.Phys.Chem. C2014,118,9395-9399 [Non-patent document 3] "Near-Shore Aggregation Mechanism of Electrolyte Decomposition Products to Explain Solid Electrolyte Interphase Formation" J. Electrochem. Soc.C2015, 162, 2670-2678 [Non-patent document 4] "Coupled LiPF6 Decomposition and Carbonate Dehydrogenation Enhanced by Highly Covalent Metal Oxides in High-Energy Li-Ion Batteries" J. Phys. Chem. C2018, 122, 48, 27368-27382 Summary of the Invention [Problem to be solved by the invention]

[0015] In recent years, while lithium-ion secondary batteries for mobile devices or automobiles have been increasing in output and energy density, there is also a demand for smaller battery cells and improved productivity and stable cycle performance during long-term use. Furthermore, the required battery safety standards are becoming stricter than those of conventional products. Therefore, the battery separators described in Patent Documents 1 to 4 have room for improvement in terms of achieving a longer battery life while ensuring battery safety. The battery separators described in Patent Documents 2 and 5 to 8 have room for improvement in terms of ensuring productivity, improving battery safety, extending battery life, and / or achieving a balance between these.

[0016] It is generally known that SFC (SEI film components) generated on the surface of the positive electrode material aggregate and accumulate on the surface of the negative electrode material, forming a solid electrolyte interface (SEI) layer that covers the surface of the negative electrode material (Non-Patent Document 3). The SEI layer prevents the decomposition of the electrolyte on the electrode surface, suppressing battery degradation, while also allowing lithium ions (Li + ) and increase internal resistance. Furthermore, SFC formation is temperature-dependent; the higher the temperature, the thicker the SEI layer formed. For example, when batteries are enlarged to improve the energy density or power output of batteries, the difference in heat dissipation capacity between the center and the outside of the battery tends to result in a higher temperature at the center compared to the outside, resulting in more pronounced SFC formation near the center of the battery. Insufficient SFC dispersion leads to the formation of a non-uniform SEI layer, which in turn results in the binding of Li ions in the SEI layer, resulting in a decrease in cycle test capacity retention. One way to enlarge batteries is to increase the diameter and length of the battery. Consider using a 4680-type cylindrical battery instead of the 18650-type cylindrical battery currently in widespread use. In addition, in batteries using cathode materials containing nickel oxide, increasing the nickel (Ni) content can improve energy density. However, as described in Non-Patent Document 4, the oxidation potential decreases, promoting SFC formation. Therefore, insufficient SFC diffusion tends to result in the formation of a non-uniform SEI layer.

[0017] Furthermore, during charging and discharging, lithium-ion secondary batteries experience volumetric changes in the electrodes and internal temperature increases. This volumetric change in the electrodes creates a non-uniform stress distribution within the battery. When the temperature inside the battery rises under this non-uniform stress distribution, the separator deforms non-uniformly due to thermal creep, a phenomenon in which resins subjected to stress at high temperatures gradually deform. This causes the separator's microporous structure to collapse non-uniformly. This partially impedes the flow of lithium ions during charging and discharging, resulting in reduced cycle performance. Furthermore, non-uniform movement of lithium ions into and out of the negative electrode leads to the growth of lithium dendrites, ultimately deteriorating cycle performance and crush test pass rates. Cylindrical and prismatic batteries in particular are prone to internal stress distribution due to winding tension during the winding process and over time, which can easily lead to poor cycle performance and crush test pass rates.

[0018] As mentioned above, the SEI layer suppresses electrolyte decomposition and battery degradation. However, excessive formation of the SEI layer increases the battery's internal resistance and accumulates Li ions in the electrolyte, deteriorating cycle performance. Therefore, it is preferable to uniformly form an SEI layer of appropriate thickness. Nonuniform deformation of the separator and uneven collapse of the separator's microporous structure partially obstruct the flow of electrolyte decomposition products. This results in an uneven formation of the SEI layer and reduced cycle performance. In particular, increasing the battery size increases power output and energy density, but also increases stress differences within the battery, making it more likely for the separator to deform unevenly. Furthermore, the larger the battery, the greater the temperature difference between the center and outer edges of the battery due to differences in heat dissipation capacity. This increases the likelihood of thermal deformation of the electrodes, thermal shrinkage of the separator, thermal creep, and other problems, thereby increasing stress differences within the battery. Ultimately, the above mechanisms lead to deterioration of cycle performance and reduced safety in crush tests. Examples of large-scale batteries include 4680-type cylindrical batteries and large prismatic batteries.

[0019] Furthermore, although batteries using silicon-containing negative electrode materials can improve energy density, the negative electrode material has a large expansion rate during charging and discharging, which tends to cause non-uniform deformation of the separator and uneven crushing of the separator's microporous structure. Ultimately, the above mechanism leads to deterioration of cycle characteristics and reduced safety in crush tests. Furthermore, batteries using positive electrode materials containing nickel oxide can improve energy density, but the electrolyte tends to decompose on the electrode surface, leading to non-uniform generation of SFC. If the SFC reaches the negative electrode surface without being sufficiently diffused, a non-uniform SEI layer is likely to form, which can lead to deterioration of cycle characteristics. Examples of positive electrode materials containing nickel oxide include NMC111, NMC611, and NMC811.

[0020] In view of the above problems, an object of the present invention is to provide a separator for a nonaqueous secondary battery that can achieve both safety and a long life of the nonaqueous secondary battery, a method for producing the same, or a nonaqueous secondary battery including the same. [Means for solving the problem]

[0021] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that the above-mentioned problems can be solved by using a separator for a nonaqueous secondary battery having the following configuration, a method for producing the same, or a nonaqueous secondary battery including the same, and have thus completed the present invention. One example of an aspect of the present invention is as follows. (1) A non-aqueous secondary battery separator containing silicon (Si)-containing molecules, The Voronoi area (mu) of the maximum frequency among the Voronoi polygons obtained by Voronoi division of the Si-containing image detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement of the nonaqueous secondary battery separator is 1.0 μm 2 ~17.5μm 2 and The spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by the TOF-SIMS measurement is 0.5 μm 2 ~8.5μm 2 A non-aqueous secondary battery separator within the range of (2) The separator for a nonaqueous secondary battery according to item 1, wherein the ratio (σ / mu) of the spread (σ) of the Voronoi area frequency distribution to the Voronoi area (mu) of the maximum frequency is 0.06 to 0.70. (3) A non-aqueous secondary battery separator containing silicon (Si)-containing molecules, The Voronoi area (mu) of the maximum frequency among the Voronoi polygons obtained by Voronoi division of the Si-containing image detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement of the nonaqueous secondary battery separator is 6.0 μm 2 ~12.0μm 2 A non-aqueous secondary battery separator within the range of (4) The spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by the TOF-SIMS measurement is 2.0 μm 2 ~4.0μm 2 4. The separator for a non-aqueous secondary battery according to item 3, wherein the non-aqueous secondary battery separator has a molecular weight of 1000 or more and a molecular weight of 1000 or more. (5) The separator for a nonaqueous secondary battery according to item 3 or 4, wherein the ratio (σ / mu) of the spread (σ) of the Voronoi area frequency distribution to the Voronoi area of ​​maximum frequency (mu) is 0.20 to 0.40. (6) The nonaqueous secondary battery separator according to any one of items 1 to 5, wherein the Si-containing molecules are dispersed in a state other than a sea-island structure. (7) The nonaqueous secondary battery separator is a polyethylene microporous membrane, and 7. The separator for a nonaqueous secondary battery according to any one of items 1 to 6, wherein the air permeability change ratio (air permeability Sh after compression / air permeability Sj before compression) when compressed by 30% of the thickness is 1.1 to 7.0 times. (8) A separator for a non-aqueous secondary battery including a polyethylene microporous membrane, A separator for a non-aqueous secondary battery, in which the air permeability change ratio (air permeability Sh after compression / air permeability Sj before compression) when compressed by 30% of its thickness is 1.1 to 7.0 times. (9) The separator for a non-aqueous secondary battery according to item 8, comprising a silane-modified polyethylene and a polyolefin other than the silane-modified polyethylene. (10) A separator for a non-aqueous secondary battery containing a silane-modified polyolefin, wherein the polyethylene has a crystal long period of 20 to 50 nm as measured by small-angle X-ray scattering, a crystallinity of 60% to 80% as measured by wide-angle X-ray scattering, and a crystallite size (110) of the polyethylene as measured by wide-angle X-ray scattering is 10 to 50 nm. (11) The crystal long period of polyethylene detected by the small-angle X-ray scattering measurement and the crystallinity detected by the wide-angle X-ray scattering measurement are calculated by the following formula: Formula: Amorphous thickness [nm] = (crystalline long period [nm]) × (1 - crystallinity [%] / 100) Item 11. The separator for a nonaqueous secondary battery according to item 10, wherein the amorphous portion has a thickness calculated by the above formula of 3 to 23 nm. (12) The separator for a nonaqueous secondary battery according to item 10 or 11, wherein the cross-sectional crystal orientation degree of the polyethylene measured in the MD direction by wide-angle X-ray scattering measurement is 0.70 to 0.99, and the cross-sectional crystal orientation degree of the polyethylene measured in the TD direction is 0.70 to 0.99. (13) The separator for a nonaqueous secondary battery according to any one of items 10 to 12, wherein the ratio MD / TD of the cross-sectional crystalline orientation of the polyethylene measured in the MD direction to the cross-sectional crystalline orientation of the polyethylene measured in the TD direction is 0.5 to 1.2. (14) The separator for a nonaqueous secondary battery according to any one of items 10 to 13, wherein the ratio (110) / (200) of the crystallite size of the polyethylene (110) to the crystallite size of the polyethylene (200) as measured by wide-angle X-ray scattering is 0.9 to 2.0. (15) The separator for a non-aqueous secondary battery according to any one of items 10 to 14, wherein the silane-modified polyolefin is a silane-modified polyethylene. (16) The separator for a nonaqueous secondary battery according to any one of items 10 to 15, wherein the number of methylene (CH2) groups constituting the linking portion of the organic moiety to the main chain in the silicon (Si)-containing functional group of the silane-modified polyolefin is 2 to 10. (17) The separator for a nonaqueous secondary battery according to any one of items 10 to 16, comprising: a polyolefin microporous membrane as a substrate; and an inorganic porous layer containing inorganic particles and a resin binder, laminated on at least one surface of the polyolefin microporous membrane. (18) The separator for a nonaqueous secondary battery according to item 17, wherein the content of the inorganic particles contained in the inorganic porous layer is 5% by mass to 99% by mass based on the total mass of the inorganic porous layer. (19) The nonaqueous secondary battery separator according to item 17 or 18, wherein the inorganic particles are at least one selected from the group consisting of alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum oxide hydroxide, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, diatomaceous earth, silica sand, and glass fiber. (20) The separator for a nonaqueous secondary battery according to any one of items 10 to 16, comprising a polyolefin microporous membrane as a substrate and a thermoplastic polymer-containing layer formed on at least one surface of the polyolefin microporous membrane, wherein the thermoplastic polymer contained in the thermoplastic polymer-containing layer contains at least one of a polymerized unit of a (meth)acrylic acid ester and / or a (meth)acrylic acid, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE). (21) The separator for a nonaqueous secondary battery according to any one of Items 10 to 16, comprising: a polyolefin microporous membrane as a substrate; and an active layer disposed on at least one surface of the polyolefin microporous membrane, wherein the active layer contains at least one fluorine atom-containing polyvinyl compound selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE), and inorganic particles. (22) The separator for a nonaqueous secondary battery according to any one of items 10 to 16, comprising: a polyolefin microporous membrane as a substrate; and a heat-resistant resin layer containing a heat-resistant resin laminated on at least one surface of the polyolefin microporous membrane, wherein the heat-resistant resin contains at least one selected from the group consisting of wholly aromatic polyamide, polyimide, polyamideimide, polysulfone, polyketone, polyether, polyetherketone, polyetherimide, and cellulose. (23) The separator for a nonaqueous secondary battery according to item 22, wherein the heat-resistant resin layer contains 30% by mass to 90% by mass of an inorganic filler having an average particle size of 0.2 μm to 0.9 μm. (24) The separator for a non-aqueous secondary battery according to any one of items 10 to 23, further comprising a polyolefin other than the silane-modified polyolefin. (25) For the Si-containing image detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement of the nonaqueous secondary battery separator, the Voronoi area (mu) of the Voronoi polygons with the highest frequency obtained by Voronoi division is 6.00 μm 2 ~12.00μm 2 25. The separator for a non-aqueous secondary battery according to any one of items 10 to 24, wherein the range is: (26) The spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by the TOF-SIMS measurement is 2.00 μm 2 ~4.00μm 2 Item 26. The separator for a non-aqueous secondary battery according to Item 25, wherein the non-aqueous secondary battery separator has a molecular weight of 1000 or more and a molecular weight of 1000 or more. (27) The separator for a nonaqueous secondary battery according to item 25 or 26, wherein the ratio (σ / mu) of the spread (σ) of the Voronoi area frequency distribution to the Voronoi area of ​​the maximum frequency (mu) is 0.20 to 0.40. (28) A non-aqueous secondary battery comprising a positive electrode, a negative electrode, the separator for a non-aqueous secondary battery according to any one of items 1 to 27, and a non-aqueous electrolyte solution. (29) The positive electrode has the formula: Li-Ni x -Mn y -Co z 29. The nonaqueous secondary battery according to item 28, comprising a lithium (Li)-nickel (Ni)-manganese (Mn)-cobalt (Co) composite oxide represented by the formula: {wherein x represents the Ni proportion, y represents the Mn proportion, z represents the Co proportion, and x+y+z=1}, wherein the Ni proportion x in the formula is 5 to 9. (30) The nonaqueous secondary battery according to item 28 or 29, wherein the negative electrode contains a negative electrode active material, and the proportion of Si in the negative electrode active material is 5% by weight to 90% by weight. (31) The nonaqueous secondary battery according to any one of items 28 to 30, wherein the nonaqueous electrolyte solution contains a lithium salt at a concentration in the range of 1.2 mol / L to 10 mol / L. (32) The nonaqueous secondary battery according to any one of items 28 to 31, wherein the nonaqueous electrolyte solution contains ethyl methyl carbonate (EMC) and / or acetonitrile (AcN), and the total content of EMC and AcN in the nonaqueous electrolyte solution is within a range of 50% by mass to 90% by mass. (33) The following steps: (1) a sheet-forming step of extruding the silane-modified polyolefin, polyethylene, and plasticizer into a sheet using an extruder, cooling and solidifying the extruded material, and processing the extruded material into a sheet-shaped product; (2) a stretching step of biaxially stretching the sheet-like molded body at an areal magnification of 20 times or more and 250 times or less to form a stretched body; (3) a porous body forming step of extracting the plasticizer from the stretched material to form a porous body; (4) a heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing in the width direction to obtain a heat-treated porous body; (5A) a coating step of applying a coating liquid containing the inorganic particles, the resin binder, and a surfactant and having a pH of 6.7 or less or 7.5 or more to at least one surface of the heat-treated porous body, thereby forming the inorganic porous layer on at least one surface of the heat-treated porous body; (6) a drying step of drying and removing the solvent in the inorganic porous layer; and (7) an assembly step of housing a laminate or a wound body of the electrodes and the non-aqueous secondary battery separator, and a non-aqueous electrolyte solution in an outer casing; and wherein the silane-modified polyolefin forms a crosslinked structure in at least one of steps (5A), (6), and (7). (34) The following steps: (1) a sheet-forming step of extruding the silane-modified polyolefin, polyethylene, and plasticizer into a sheet using an extruder, cooling and solidifying the extruded material, and processing the extruded material into a sheet-shaped product; (2) a stretching step of biaxially stretching the sheet-like molded body at an areal magnification of 20 times or more and 250 times or less to form a stretched body; (3) a porous body forming step of extracting the plasticizer from the stretched material to form a porous body; (4) a heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing in the width direction to obtain a heat-treated porous body; (5B) a coating step of applying a coating liquid containing the thermoplastic polymer and a surfactant and having a pH of 6.7 or less or 7.5 or more to at least one surface of the heat-treated porous body to form the thermoplastic polymer-containing layer on at least one surface of the heat-treated porous body; (6) a drying step of drying and removing the solvent in the thermoplastic polymer-containing layer; and (7) an assembly step of housing a laminate or a wound body of the electrodes and the non-aqueous secondary battery separator, and a non-aqueous electrolyte solution in an outer casing; and wherein the silane-modified polyolefin forms a crosslinked structure in at least one of steps (5B), (6), and (7). (35) The following steps: (1) a sheet-forming step of extruding the silane-modified polyolefin, polyethylene, and plasticizer into a sheet using an extruder, cooling and solidifying the extruded material, and processing the extruded material into a sheet-shaped product; (2) a stretching step of biaxially stretching the sheet-like molded body at an areal magnification of 20 times or more and 250 times or less to form a stretched body; (3) a porous body forming step of extracting the plasticizer from the stretched material to form a porous body; (4) a heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing in the width direction to obtain a heat-treated porous body; (5C) a coating step of applying a coating liquid containing the fluorine atom-containing polyvinyl compound, the inorganic particles, and an organic solvent to at least one surface of the heat-treated porous body, thereby forming the active layer on at least one surface of the heat-treated porous body; (6) a drying step of drying and removing the solvent in the active layer; and (7) an assembly step of housing a laminate or a wound body of the electrodes and the non-aqueous secondary battery separator, and a non-aqueous electrolyte solution in an outer casing; and wherein the silane-modified polyolefin forms a crosslinked structure in at least one of steps (5C), (6), and (7). (36) Between the coating step (5C) and the drying step (6), the following steps are carried out: (5.5C) a water washing step of replacing the organic solvent in the active layer with an aqueous solvent; and wherein the silane-modified polyolefin forms a crosslinked structure in the step (5.5C). (37) The following steps: (1) a sheet-forming step of extruding the silane-modified polyolefin, polyethylene, and plasticizer into a sheet using an extruder, cooling and solidifying the extruded material, and processing the extruded material into a sheet-shaped product; (2) a stretching step of biaxially stretching the sheet-like molded body at an areal magnification of 20 times or more and 250 times or less to form a stretched body; (3) a porous body forming step of extracting the plasticizer from the stretched material to form a porous body; (4) a heat treatment step of subjecting the porous body to heat treatment, stretching and relaxing in the width direction to obtain a heat-treated porous body; (5D) a coating step of applying a coating liquid containing the heat-resistant resin and an organic solvent to at least one surface of the heat-treated porous body to form the heat-resistant resin layer on at least one surface of the heat-treated porous body; (6) a drying step of drying and removing the solvent in the heat-resistant resin layer; and (7) an assembly step of housing a laminate or a wound body of the electrodes and the non-aqueous secondary battery separator, and a non-aqueous electrolyte solution in an outer casing; and wherein the silane-modified polyolefin forms a crosslinked structure in at least one of steps (5D), (6), and (7). (38) Between the coating step (5D) and the drying step (6), the following steps are carried out: (5.5D) a water-washing step of replacing the organic solvent in the heat-resistant resin layer with an aqueous solvent; Item 38. The method for producing a separator for a non-aqueous secondary battery according to Item 37, wherein the silane-modified polyolefin forms a crosslinked structure in the step (5.5D). [Effects of the Invention]

[0022] According to the present invention, it is possible to achieve both safety and a long life for a nonaqueous secondary battery including a separator for a nonaqueous secondary battery. More specifically, it is possible to improve, for example, safety in a nail penetration test and a hotbox test, cycle characteristics including low-temperature cycle characteristics and high-temperature cycle characteristics, and productivity. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is an image showing the results of TOF-SIMS analysis of the separator according to Example 1. [Figure 2] 1 is an example of a filtered three-dimensional image in image processing of a TOF-SIMS spectrum in Example 1. [Figure 3]1 is an example of a filtered two-dimensional image in image processing of a TOF-SIMS spectrum in Example 1. [Figure 4] 1 shows an example of a state in which image processing (1) and (2) are performed on the TOF-SIMS spectrum of Example 1. [Figure 5] 1 shows an example of a state in which image processing (1) to (6) have been performed on the TOF-SIMS spectrum of Example 1. [Figure 6] 1 illustrates an example of a Voronoi region obtained by Voronoi division of a TOF-SIMS spectrum in Example 1. [Figure 7] An example of a Voronoi area determined to be effective from the results of Example 1 is shown in the figure. [Figure 8] 10 is a histogram of Voronoi areas in Example 1. [Figure 9] 10 is a histogram after the Voronoi area in Example 1 is converted into an actual area. [Figure 10] 10 is an example illustrating a fitting result of the Voronoi area in the first embodiment. [Figure 11] 1 is an image showing the results of TOF-SIMS analysis of the separator according to Comparative Example 1. [Figure 12] 1 is an example of a state in which image processing (1) and (2) are performed on the TOF-SIMS spectrum of Comparative Example 1. [Figure 13] 1 shows an example of a state in which image processing (1) to (6) have been performed on the TOF-SIMS spectrum of Comparative Example 1. [Figure 14] 10 illustrates an example of a Voronoi region obtained by Voronoi division of the TOF-SIMS spectrum of Comparative Example 1. [Figure 15] An example of a Voronoi area determined to be effective from the results of Comparative Example 1 is shown in the figure. [Figure 16] 10 is a histogram of Voronoi areas in Comparative Example 1. [Figure 17] 10 is a histogram after the Voronoi area of ​​Comparative Example 1 is converted into an actual area. [Figure 18] 10 is an example illustrating a fitting result of the Voronoi area in Comparative Example 1. [Figure 19] 1A and 1B are schematic diagrams illustrating the repeating periodic structure of crystalline portions and amorphous portions in a separator made of a crystalline resin such as polyethylene, and a partially enlarged view thereof. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, modes for carrying out the present invention (hereinafter simply referred to as "embodiments") will be described in detail. The present invention is not limited to the following embodiments, and various modifications are possible without departing from the gist thereof. In this specification, a numerical range described using "to" includes the numerical values ​​described before and after it. The abbreviation "MD" refers to the machine direction when continuously forming a separator and the longitudinal direction of a battery wound body. The abbreviation "TD" refers to the direction crossing the MD at an angle of 90° (hereinafter also referred to as the width direction) and is an abbreviation for transverse direction. The various measurement methods and evaluation methods described below are performed according to the methods described in the examples, unless otherwise specified.

[0025] <Separator for non-aqueous secondary batteries> Separators for nonaqueous secondary batteries (hereinafter simply referred to as "separators") are required to have insulating properties and ion permeability, and are therefore generally formed from insulating materials with a porous structure, such as paper, polyolefin nonwoven fabric, or resin microporous membrane. In particular, polyolefin microporous membranes, which are oxidation-reduction resistant and capable of forming a dense, uniform porous structure, are excellent separator substrates for use in nonaqueous secondary batteries comprising positive and negative electrodes capable of absorbing and releasing lithium and a nonaqueous electrolyte solution prepared by dissolving an electrolyte in a nonaqueous solvent. Therefore, separators for nonaqueous secondary batteries can include a polyolefin microporous membrane. If desired, the separator for nonaqueous secondary batteries may include, in addition to the polyolefin microporous membrane, layers formed on one or both sides thereof, such as a thermoplastic polymer-containing layer, an active layer, an inorganic porous layer, or a heat-resistant resin layer.

[0026] <Embodiment 1: Silicon-containing structure of separator and Voronoi tessellation (1)> The separator according to the first embodiment contains silicon (Si)-containing molecules, and the maximum frequency Voronoi area (mu) of the Voronoi polygons obtained by Voronoi division of an Si-containing image detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement of the separator is 1.0 μm 2 ~17.5μm 2 and the spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by TOF-SIMS measurement is within 0.5 μm 2 ~8.5μm 2 is within the range.

[0027] When the separator according to embodiment 1 is subjected to TOF-SIMS measurement in a 100 μm square area, at least one silicon-containing structure is detected, and preferably, the Si-containing molecules are detected to be dispersed in the separator in a state other than a sea-island structure. Note that a sea-island structure is a structure in which a solid substance is broadly composed of two types of material, and one type (likely islands) is discontinuously present in one that appears relatively continuous (likely a sea).

[0028] In embodiment 1, the various values ​​obtained by Voronoi tessellation are measured when the separator is a polyolefin microporous membrane and can serve as indicators of the level of variation in Si-containing molecules on the separator surface. TOF-SIMS measurement of the separator can be performed as described in the Examples with reference to Figures 1 to 6 and 11 to 14, and Voronoi tessellation of TOF-SIMS images can be performed with reference to Figures 7 to 10 and 15 to 18.

[0029] The Voronoi area (mu) of the Voronoi polygons obtained by the above Voronoi division is 1.0 μm 2 ~17.5μm 2Within this range, the Si-containing molecules tend to be dispersed in the separator without forming a sea-island structure. For example, when the nonaqueous secondary battery is a lithium-ion secondary battery, if a separator in which Si elements are uniformly dispersed coexists with a lithium (Li) complex solvated with an electrolyte solution having an unshared electron pair such as an oxygen atom, the following phenomena (A) and (B) may be considered to extend the product life in a battery cycle characteristic test: (a) Li complexes exhibit high affinity with Si atoms, and therefore are likely to exist around dispersed Si atoms. The key to this phenomenon is the reaction in which non-donor electron pairs in the molecular structure of the electrolyte are coordinated to Si atoms. As described in Non-Patent Document 1, Si atoms have a large atomic radius, allowing for four or more coordinations, and have the unique property of allowing for the existence of structures using four-electron, three-center bonds and d-orbitals. In other words, a path that allows Li ions to flow easily and uniformly is formed across the entire separator surface. Therefore, when a secondary battery containing a positive electrode, such as an NMC positive electrode containing a lithium (Li)-nickel (Ni)-manganese (Mn)-cobalt (Co) composite oxide, is uniformly charged and discharged, crystal destruction tends to be suppressed; and (i) Furthermore, for example, when the negative electrode is a Si-containing negative electrode, the Si element in the negative electrode can be uniformly charged and discharged, and the uniform expansion and convergence of the Si-containing negative electrode can suppress deformation inside the secondary battery.

[0030] Although not wishing to be bound by theory, the above phenomena (a) and (b) are thought to occur in a non-aqueous secondary battery according to the following scheme 1: [ka] In the formula, Sol represents a non-aqueous solvent in the electrolyte, and X -represents a counter anion of a lithium salt as an electrolyte, an example of a non-aqueous solvent includes ethylene carbonate (EC), an example of a constituent resin of the separator according to embodiment 1 includes silane-modified polyethylene, and R represents, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc., or a siloxane bond crosslinked with a nearby silanol group. As shown in Fig. 1, a complex is uniformly formed on the separator, and the Li + It is thought that this is also caused by the flow of ions becoming uniform.

[0031] Furthermore, in non-aqueous secondary battery systems containing lithium hexafluorophosphate (LiPF6) as an electrolyte, due to the Jahn-Teller effect of phosphorus atoms, a certain concentration of dissociated F anions or lithium fluoride (LiF) exists in the system. Therefore, when LiF is added to Si, it exhibits a stronger Lewis acid effect than before addition. This makes the above phenomena (A) and (B) more pronounced, and ultimately leads to good low-temperature cycle characteristics. This was discovered by the present inventors and is shown in Scheme 2 below: [ka] In the formula, Sol represents a non-aqueous solvent in the electrolytic solution, an example of a non-aqueous solvent is ethylene carbonate (EC), an example of an electrolyte is LiPF, an example of a constituent resin of the separator according to embodiment 1 is silane-modified polyethylene, and R represents, for example, H, Me, Et, Bu, or the like, or a siloxane bond crosslinked with a nearby silanol. As shown in Fig. 1, physically solvated Li +This is thought to be because there is a high probability that coordination complexes are formed when the Si atoms of the Si-containing molecules in the separator's polymer are stably coordinated to the Si atoms of the Si-containing molecules in the separator's polymer. This concept is specific to the amorphous structure obtained by forming a film from a polymer composition using Resin A, Resin B, or Resin C, which will be described later, and is a different approach from the Lewis acid properties of Si in coordination complexes of low-molecular-weight allylsilane compounds as described in Non-Patent Document 1.

[0032] Furthermore, Si-containing molecules often possess crosslinking properties. For example, if they possess silane crosslinking properties, the silane crosslinking properties of the dispersed Si-containing molecules can be ensured even in nonaqueous secondary batteries, further ensuring the stability of siloxane bonds and preserving the crosslinked structure of the separator over a long period of time. This contributes to ensuring safety in safety tests such as nail penetration tests. During charging and discharging of lithium-ion batteries, if the flow of lithium ions is uneven and moves at a rate slower than the intercalation reaction into the electrodes, the lithium ions can accumulate in electrical stagnation areas and form dendrites. In particular, during low-temperature operation of the battery, the increased viscosity of the electrolyte makes it difficult for ions to move within the system, leading to the tendency for dendrite formation. This raises concerns about a significant decrease in battery safety after low-temperature cycling. This phenomenon poses a major challenge when used in seasons and regions with extreme temperature differences, such as for mobile device power sources and battery-powered automobile batteries. In the first embodiment, the problem was solved by designing a separator in which Si-containing atoms are dispersed not in a sea-island structure (not in a matrix structure), thereby improving the uniformity of the lithium ion flow.

[0033] From the viewpoint of further improving the safety of the separator and the nonaqueous secondary battery including the separator, it is preferable that the separator includes, for example, silane-modified polyethylene as the Si-containing molecule, and it is more preferable that a silane crosslinking reaction of the silane-modified polyethylene proceeds when the separator comes into contact with the electrolyte solution.

[0034] From the viewpoint of achieving both long life and safety in the cycle characteristics of the non-aqueous secondary battery and / or achieving a balance between them, the Voronoi area (mu) of the Voronoi polygons obtained by the Voronoi division is set to 1.5 μm 2 ~17.0μm 2 Preferably, the thickness is in the range of 4.0 μm 2 ~16.0μm 2 More preferably, the thickness is in the range of 6.0 μm. 2 ~13.0μm 2 From the same viewpoint, it is more preferable that the spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by the above TOF-SIMS measurement is within the range of 0.5 μm 2 ~8.5μm 2 It is within the range of 1.7 to 6.3, and preferably within the range of 1.8 μm 2 ~4.2μm 2 It is more preferable that the temperature is in the range of

[0035] Voronoi tessellation is the process of dividing a number of points (kernel points) placed at any position in a metric space into regions based on which of the kernel points other points in the same space are closest to. A diagram containing the regions obtained in this way is called a Voronoi diagram. Generally, in a Voronoi diagram, the boundaries of the multiple regions become part of the bisectors of each of the kernel points, and each region forms a polygon (Voronoi polygon).

[0036] Note that when Voronoi division is performed on the observation field of view, any unclosed region is excluded from the Voronoi division. An example of an unclosed region is a region obtained by performing Voronoi division on an object that exists on the boundary of the observation field of view and is not entirely observed. Therefore, in an image obtained by photographing at least a partial region of the separator surface, it is preferable to check whether the entire object, for an object located at the edge of the image, is observed.

[0037] For a Si-containing image detected by TOF-SIMS measurement, it is preferable that the ratio (σ / mu) of the spread (σ) of the Voronoi area frequency distribution to the Voronoi area (mu) of maximum frequency satisfies the following relationship: 0.06≦σ / mu≦0.70 In the first embodiment, the ratio (σ / mu) in the Voronoi tessellation can be regarded as an index indicating whether the Si-containing molecules are uniformly dispersed on the separator surface. When the ratio (σ / mu) is within the range of 0.06 to 0.70, the Si-containing molecules are uniformly dispersed on the separator surface, and in nonaqueous secondary batteries, this sufficiently contributes to the coexistence of the Li complex derived from the electrolyte and the separator, the silane crosslinking reaction of the separator, and the like, thereby extending the cycle life of the battery. While not wishing to be bound by theory, the concentration of the intermediate in which the Li complex is coordinated within the separator surface, or the equilibrium life of the intermediate, are important. In the first embodiment, it was experimentally discovered that a limited ratio (σ / mu) in the Voronoi tessellation can uniformly contribute to the intercalation reaction into the electrode. From the viewpoint of further extending the cycle life of the battery, the ratio (σ / mu) is preferably within the range of 0.07 to 0.57, and more preferably within the range of 0.19 to 0.38.

[0038] The numerical values ​​obtained by Voronoi tessellation of the separator according to embodiment 1 can be adjusted to fall within the ranges described above by controlling, for example, the structure of the Si-containing molecule, the molecular weight or molecular weight distribution of the separator constituent raw materials, the blending range of the separator constituent raw materials, etc.

[0039] <Embodiment 2: Silicon-containing structure of separator and Voronoi tessellation (2)> The separator according to the second embodiment contains silicon (Si)-containing molecules, and the Voronoi area (mu) of the most frequent Voronoi polygons obtained by Voronoi division of an Si-containing image detected by TOF-SIMS measurement of the separator is 6.0 μm 2 ~12.0μm 2 is within the range.

[0040] When the separator according to the second embodiment is subjected to TOF-SIMS measurement in a 100 mm square area, at least one silicon-containing structure is detected, and preferably, Si-containing molecules are detected to be dispersed in the separator in a state other than a sea-island structure.

[0041] In the second embodiment, the various numerical values ​​obtained by Voronoi tessellation are measured when the separator is a microporous polyolefin membrane, and can serve as indicators of the level of variation in Si-containing molecules on the separator surface.

[0042] The Voronoi area (mu) of the most frequent Voronoi polygon is 6.0 μm 2 ~12.0μm 2 When the ratio is within this range, as in the first embodiment, the Si-containing molecules tend to be dispersed in the separator in a state other than a sea-island structure, and the safety of the non-aqueous secondary battery including the separator is ensured while the cycle characteristics are extended. + The uniformity of ion flow, the Lewis acid effect, and the cross-linking properties of Si-containing molecules ensure low-temperature cycle characteristics and safety in nail penetration tests. In addition, in embodiment 2, when a separator in which Si elements are uniformly dispersed coexists with oligomers (SFC: SEI film components) generated by a chemical reaction of the electrolyte on the surface of the positive electrode material, the lone electron pair of oxygen in the molecular structure of SFC can coordinate to the Si atom, as shown in Scheme 3 below, and SFC exhibits affinity for the Si atom, improving the diffusibility of SFC. [ka] In the formula, Sol represents a non-aqueous solvent in the electrolyte, and X -represents the counter anion of the lithium salt used as the electrolyte. As an example, the right side shows a case in which the non-aqueous solvent is ethylene carbonate (EC), SFC is an oligomer formed by the reduction polymerization of EC2 molecules, and the separator resin contains silane-modified polyethylene. R represents, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc., or a siloxane bond crosslinked with a nearby silanol.

[0043] In the second embodiment, the Voronoi area (mu) of the separator is 6.0 μm 2 ~12.0μm 2 When the Voronoi area of ​​the separator is within this range, the Si-containing molecules are finely and uniformly dispersed in the separator, and as shown in Scheme 3, the SFC is uniformly dispersed throughout the separator. This allows a uniform SEI layer with a thickness sufficient to suppress electrolyte decomposition to be formed on the negative electrode, which is believed to improve the cycle test capacity retention. If the Voronoi area of ​​the separator is too large (i.e., the distance between Si-containing molecules is too large), the SFC diffusion is insufficient, leading to the formation of a non-uniform SEI layer and ultimately to a deterioration in the cycle test capacity retention. On the other hand, if the Voronoi area is too small (i.e., the distance between Si atoms is too small), the SFC coordinated to the Si atoms is concentrated in a narrow area, which inhibits the movement of the SFC due to steric hindrance, resulting in insufficient SFC diffusion and ultimately a deterioration in the cycle test capacity retention.

[0044] From the viewpoint of further improving the safety of the separator and the nonaqueous secondary battery including the separator, the separator according to the second embodiment preferably includes, for example, silane-modified polyethylene as the Si-containing molecule, and more preferably, a silane crosslinking reaction of the silane-modified polyethylene proceeds when the separator comes into contact with the electrolyte solution.

[0045] From the viewpoint of uniformly dispersing the SFC throughout the separator and simultaneously achieving both cycle characteristics and safety of the non-aqueous secondary battery and / or achieving a balance between them, the separator according to embodiment 2 is designed so that the Voronoi area (mu) of the Voronoi polygons with the highest frequency obtained by performing the Voronoi tessellation is 6.5 μm 2 ~11.5μm 2 Preferably, the thickness is in the range of 7.0 μm 2 ~11.0μm 2 More preferably, it is in the range of 7.5 μm 2 ~10.5μm 2 From the same viewpoint, it is more preferable that the spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by the above TOF-SIMS measurement is within the range of 2.0 μm 2 ~4.0μm 2 Preferably, the thickness is in the range of 2.2 μm 2 ~3.8μm 2 More preferably, it is in the range of 2.5 μm 2 ~3.5μm 2 It is more preferable that the temperature is in the range of

[0046] For a Si-containing image detected by TOF-SIMS measurement, it is preferable that the ratio (σ / mu) of the spread (σ) of the Voronoi area frequency distribution to the Voronoi area (mu) of maximum frequency satisfies the following relationship: 0.20≦σ / mu≦0.40 In the second embodiment, the ratio (σ / mu) in the Voronoi tessellation can be regarded as an index indicating whether the Si-containing molecules are uniformly dispersed on the separator surface. When the ratio (σ / mu) in the second embodiment is within the range of 0.20 to 0.40, the Si-containing molecules are uniformly dispersed on the separator surface, as in the first embodiment. In a nonaqueous secondary battery, this sufficiently contributes to the coexistence of the Li complex derived from the electrolyte with the separator and the silane crosslinking reaction of the separator, thereby extending the cycle characteristics of the battery. Additionally, in the second embodiment, the dispersibility of the SFC is improved, promoting the uniform formation of the SEI layer, thereby improving the cycle characteristics of the battery. From the viewpoint of further extending the cycle life of the battery, the ratio (σ / mu) in the second embodiment is more preferably within the range of 0.22 to 0.38, and even more preferably within the range of 0.25 to 0.35.

[0047] The numerical values ​​obtained by Voronoi tessellation of the separator according to embodiment 2 can be adjusted within the ranges described above by controlling, for example, the structure of the Si-containing molecule, the molecular weight or molecular weight distribution of the separator constituent raw materials, the blending range of the separator constituent raw materials, etc.

[0048] <Embodiment 3: Change in air permeability before and after separator compression> The separator according to embodiment 3 includes a polyethylene microporous membrane, and the air permeability change ratio (air permeability Sh after compression / air permeability Sj before compression) when compressed by 30% of its thickness is in the range of 1.1 to 7.0 times.

[0049] In the third embodiment, when the air permeability change ratio (air permeability Sh / air permeability Sj) is within the range of 1.1 to 7.0, even if a nonaqueous secondary battery including the separator is compressed in the thickness direction of the separator, ion permeability can be maintained, and safety in a nail penetration test and low-temperature cycle characteristics of the battery tend to be ensured. This tendency is remarkable when the negative electrode of the battery is an easily expandable negative electrode such as a Si-containing negative electrode. From this viewpoint, the air permeability change ratio (air permeability Sh / air permeability Sj) is preferably 1.3 to 6.9.

[0050] The air permeability change ratio (air permeability Sh / air permeability Sj) is measured when the separator is a polyolefin microporous membrane, and can be measured by the method described in the examples.

[0051] <Embodiment 4: Silane-modified polyolefin content and crystalline structure> The separator according to embodiment 4 contains a silane-modified polyolefin, and has a polyethylene crystal long period of 20 to 50 nm as measured by small-angle X-ray scattering (SAXS), a crystallinity of 60% to 80% as measured by wide-angle X-ray scattering (WAXS), and a polyethylene crystallite size (110) of 10 to 50 nm as measured by wide-angle X-ray scattering (WAXS).

[0052] Generally, separators made of crystalline resins such as polyethylene have a repeating periodic structure of crystalline and amorphous parts (Fig. 19). c ) means the average length of one period of the repeating period of the crystalline and amorphous parts, and the crystalline part thickness (t c ) means the average thickness of the crystalline part in the repeating period of the crystalline part and the amorphous part, and the amorphous part thickness (t a ) refers to the average thickness of the amorphous part in the repeating cycle of the crystalline part and the amorphous part, crystallite size refers to the average size of each crystallite, crystallinity refers to the proportion of the crystalline part in the whole, and the degree of crystal orientation (a c) refers to the degree of orientation of the crystalline portion in a certain direction. For example, crystallite size (110) refers to the average size of individual polyethylene crystallites in the (110) direction, and crystallite size (200) refers to the average size of individual polyethylene crystallites in the (200) direction. MD cross-section crystal orientation refers to the degree to which the (110) plane of the polyethylene crystal is aligned parallel to the MD-TD plane in a cross-section of the separator cut along a plane perpendicular to the MD (MD cross-section). TD cross-section crystal orientation refers to the degree to which the (110) plane of the polyethylene crystal is aligned parallel to the MD-TD plane in a cross-section of the separator cut along a plane perpendicular to the TD (TD cross-section). The crystalline structure of the separator can be measured using an X-ray structure evaluation device.

[0053] In Embodiment 4, SAXS and WAXS measurements are performed on the separator as a substrate. Therefore, when the separator is in the form of a multilayer film or a laminate film, the SAXS and WAXS measurements are performed after removing layers other than the polyolefin microporous film.

[0054] In the fourth embodiment, when the crystal long period is in the range of 20 nm to 50 nm, the crystallinity is in the range of 60% to 80%, and the crystallite size (110) of the polyethylene is in the range of 10 to 50 nm in a combination of specific X-ray structural analyses, namely, SAXS and WAXS, the distance between the silane-modified units is optimized while improving the heat creep resistance of the separator, and the crosslinking reaction is promoted when the separator comes into contact with the coating liquid in the coating process. As a result, the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the battery can be improved without adding a process for crosslinking.

[0055] After the separator is coated, the battery goes through assembly, finishing (charging / discharging, degassing), and inspection processes, and the non-aqueous secondary battery is manufactured in as little as 1 to 5 days after coating. From the perspective of ensuring that the crosslinking reaction has progressed sufficiently by that time, the ease with which the crosslinking proceeds (the speed of the reaction) is important.

[0056] The crosslinking reaction rate is known to depend on environmental factors such as the solvent's liquidity and temperature. However, the effects of structural factors such as the distance between functional groups and steric hindrance have not been fully studied. The inventors have identified conditions that favor the crosslinking reaction in separators by combining specific X-ray structural analyses (SAXS and WAXS) with, optionally, specific functional group dispersion analysis (TOF-SIMS). They have also identified optimal conditions for separators for nonaqueous secondary batteries, taking into account thermal creep resistance. While not wishing to be bound by theory, the present invention believes that by designing a specific crystalline structure, the number of tie molecules in the amorphous layer increases, improving thermal creep resistance. This in turn suppresses nonuniform deformation of the separator even when nonuniform stress occurs within the battery. This suppresses partial obstruction of the flow of Li ions and electrolyte decomposition products, thereby improving high-temperature cycle life.

[0057] In addition, in the present invention, by designing to determine the numerical values ​​related to the crystal structure and the dispersion state of the silicon (Si)-containing functional groups, the diffusivity of the Li-ion complex is improved through interaction with the Si element in the silicon (Si)-containing functional groups, which is believed to suppress the local growth of Li dendrites and thereby improve cycle performance. Furthermore, by designing to determine the numerical values ​​related to the crystal structure and the dispersion state of the silicon (Si)-containing functional groups, the silicon (Si)-containing functional groups are brought closer together, facilitating the crosslinking reaction, which is believed to facilitate the crosslinking reaction during the coating process in the separator manufacturing process. Furthermore, by designing to determine the numerical values ​​related to the crystal structure and the dispersion state of the silicon (Si)-containing functional groups, the number of crosslinks increases, reducing the fluidity of the resin at high temperatures and improving safety in crush tests. In the coating process, by using a coating solution with high polyolefin impregnation, the solvent that penetrates between the polyolefin molecular chains promotes thermal vibration of the silicon (Si)-containing functional groups, further accelerating the cross-linking reaction. By using a coating solution containing polar molecules, the polar molecules and / or hydrogen ions and / or hydroxide ions in the coating solution act as catalysts, further accelerating the cross-linking reaction between the silicon (Si)-containing functional groups. These factors reduce the fluidity of the separator at high temperatures, thereby improving the high-temperature cycle life and crush safety of non-aqueous secondary batteries.

[0058] From the viewpoints of improving the ease of crosslinking in the separator, the crush test pass rate of the battery, the cycle test capacity retention rate, and the high-temperature cycle life, and / or achieving a balance among these, SAXS and WAXS measurements of the separator preferably analyze the crystalline structure of the polyolefin, and more preferably analyze the crystalline structure of polyethylene. The silane-modified polyolefin according to embodiment 4 may be contained at any position in the separator. For example, in the case of a single-layer separator consisting of only a polyolefin microporous membrane, it may be present in the microporous membrane or on the surface of the microporous membrane. In the case of a multilayer separator including layers formed on one or both sides of the microporous membrane, it may be present in the microporous membrane or on the surface of the microporous membrane, or in or on the surface of the formed layer. From the same viewpoints as above, it is preferable that the silane-modified polyolefin be present in or on the surface of the polyolefin microporous membrane used as the substrate. WAXS measurements may be performed by transmission or reflection (XRD). From the viewpoint of analyzing not only the separator surface but also the internal crystalline structure, WAXS measurements of the separator are preferably performed by transmission.

[0059] From the same viewpoint, the crystal long period detected by SAXS is preferably more than 20 nm and not more than 49 nm, and more preferably 22 nm to 47 nm. From the same viewpoint, the crystallinity detected by WAXS is preferably more than 60% and less than 80%, and more preferably 62% to 78%. From the viewpoint of improving the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the battery, and / or achieving a balance among them, the crystallite size (110 plane) of the polyethylene detected by WAXS measurement of the separator containing the silane-modified polyolefin is preferably in the range of 10 nm to 50 nm, and more preferably in the range of 12 nm to 47 nm.

[0060] If the crystal long period is too large, the Gibbs-Thomson effect will raise the crystal's melting temperature, increasing the shutdown temperature. Also, if the crystal long period is too large, the number of tie molecules will decrease, resulting in reduced thermal creep resistance. This will ultimately lead to a lower crush test pass rate and a shorter high-temperature cycle life. Increasing the crystal long period also requires a larger deformation amount during the stretching process, which worsens the separator's thermal shrinkage.

[0061] On the other hand, if the crystal long period is too small, the distance between silane-modified units in the amorphous portion becomes too small, reducing solvent impregnation and / or crosslinking due to steric hindrance between the silane-modified groups, resulting in a decrease in viscoelasticity during melting and a decrease in meltdown temperature. This, in turn, leads to a decrease in the crush test pass rate and high-temperature cycle life. Furthermore, to reduce the crystal long period, it is necessary to reduce the stretching amount in the stretching process, which reduces the separator's pore size and number of pores, resulting in poor permeability. This, in turn, leads to a decrease in the crush test pass rate, a decrease in cycle test capacity retention rate, and a decrease in high-temperature cycle life.

[0062] Similarly, if the crystallinity is too high, the Gibbs-Thomson effect increases the melting temperature of the crystals, raising the separator's shutdown temperature. The number of tie molecules decreases, reducing the distance between silane-modified units on opposing crystal faces, reducing solvent impregnation and crosslinking due to steric interference of branched chains, lowering viscoelasticity during melting and the meltdown temperature. This ultimately leads to a decrease in the crush test pass rate and a decrease in high-temperature cycle life.

[0063] On the other hand, if the crystallinity is too low, the separator film formation is limited, resulting in poor heat shrinkage and a reduced number of tie molecules, which reduces heat creep resistance. Furthermore, the distance between silane-modified units between opposing crystal faces increases, reducing crosslinking, lowering viscoelasticity during melting, and lowering the meltdown temperature. This ultimately leads to a lower crush test pass rate and a shorter high-temperature cycle life.

[0064] If the crystallite size is too large, the Gibbs-Thomson effect will increase the melting temperature of the crystals, and the shutdown temperature will also increase. Furthermore, the number of tie molecules will decrease, which will reduce the thermal creep resistance. This will ultimately result in a decrease in the crush test pass rate and a decrease in the high-temperature cycle life.

[0065] On the other hand, reducing the crystallite size requires stretching and heat treatment at low temperature and high tensile force after sheet formation, which tends to leave residual stress in the separator, leading to deterioration of the separator's heat shrinkability, and ultimately to a decrease in the crush test pass rate and a decrease in the high-temperature cycle life.

[0066] From the viewpoint of improving the ease of crosslinking in the separator, the crush test pass rate of the battery, the cycle test capacity retention rate, and the high-temperature cycle life, and / or achieving a balance among them, the crystallite size (110) of the polyethylene in the separator as measured by XRD is preferably 14.2 to 40.0 nm, and / or the crystallinity as measured by XRD is preferably 80 to 99%.

[0067] The ratio (110) / (200), which is the ratio of the crystallite size perpendicular to the (110) plane to the crystallite size perpendicular to the (200) plane, detected in WAXS measurement of a separator containing silane-modified polyolefin, is preferably 0.9 to 2.0, more preferably 1.0 to 1.7, from the viewpoint of improving the crush test pass rate of the battery, the cycle test capacity retention rate, the high-temperature cycle life, etc., and / or achieving a balance among them.

[0068] From the same viewpoint as above, the amorphous thickness (amorphous length) of a separator containing silane-modified polyolefin is calculated from the following formula using the crystal long period of polyethylene detected by small-angle X-ray scattering measurement and the crystallinity detected by wide-angle X-ray scattering measurement: Formula: Amorphous thickness [nm] = (crystalline long period [nm]) × (1 - crystallinity [%] / 100) The thickness is calculated as follows: and is preferably in the range of 3 nm to 23 nm, more preferably in the range of 5 nm to 15 nm, and even more preferably in the range of 8 nm to 13 nm. If the amorphous portion thickness (amorphous length) is too large, the entanglement of molecular chains in the amorphous portion increases, strengthening intercrystalline constraint and raising the shutdown temperature. Furthermore, the distance between silane-modified units between opposing crystal faces increases, reducing crosslinkability and lowering the viscoelasticity and meltdown temperature during melting. This ultimately leads to a decrease in the crush test pass rate and a decrease in high-temperature cycle life. On the other hand, if the amorphous length is too small, the entanglement of molecular chains decreases and the heat creep resistance decreases. Furthermore, the distance between silane-modified units between opposing crystal faces decreases, reducing solvent impregnation and steric hindrance of the branched chains, reducing crosslinkability and lowering the viscoelasticity and meltdown temperature during melting. This ultimately leads to a decrease in the crush test pass rate and a decrease in high-temperature cycle life.

[0069] From the same viewpoints as above, the crystalline thickness of a separator containing silane-modified polyolefin is preferably in the range of 15 nm to 36 nm, and more preferably in the range of 17 nm to 34 nm. If the crystalline thickness (crystal length) is too large, the Gibbs-Thomson effect increases the melting temperature of the crystal, and the shutdown temperature also increases. Furthermore, the number of tie molecules decreases, resulting in a decrease in thermal creep resistance. This ultimately leads to a decrease in the crush test pass rate and a decrease in high-temperature cycle life. On the other hand, attempts to reduce the crystal length require stretching and heat treatment at low temperature and high tensile force after sheet formation, which tends to leave residual stress in the separator and ultimately leads to a deterioration in heat shrinkability. This ultimately leads to a decrease in the crush test pass rate and a decrease in high-temperature cycle life.

[0070] From the same viewpoint as above, in WAXS measurement of a separator containing a silane-modified polyolefin, it is preferable that the cross-sectional crystalline orientation of the polyethylene measured in the MD direction of the separator is in the range of 0.70 to 0.99, and the cross-sectional crystalline orientation of the polyethylene measured in the TD direction is in the range of 0.70 to 0.99. A cross-sectional crystalline orientation of 0.70 or more measured in the MD and TD directions makes it easier to ensure separator strength, while a cross-sectional crystalline orientation of 0.99 or less makes it easier to form a separator into a film. From the viewpoint of separator strength and film formability, it is more preferable that the cross-sectional crystalline orientation of the polyethylene measured in the MD direction of the separator is in the range of 0.76 to 0.98, and / or the cross-sectional crystalline orientation of the polyethylene measured in the TD direction of the separator is in the range of 0.74 to 0.93.

[0071] If the cross-sectional crystal orientation is too high, the amount of deformation in the orientation direction during melting will increase, resulting in poor thermal shrinkage. This will ultimately result in a lower crush test pass rate and a lower high-temperature cycle life. On the other hand, if the cross-sectional crystal orientation is too low, the crush test pass rate and high-temperature cycle life will also decrease. It is generally known that when stress is applied to a resin material, the fewer tie molecules oriented in the stress direction, the lower the thermal creep resistance. If the cross-sectional crystal orientation is too low, the separator will deform unevenly when uneven stress occurs within the battery, causing uneven flow of SFC and the formation of an uneven SEI layer, ultimately resulting in a lower crush test pass rate and a lower high-temperature cycle life.

[0072] From the viewpoint of improving the mechanical strength of the separator, the crush test pass rate of the battery, the cycle test capacity retention rate, and the high-temperature cycle life, and / or achieving a balance among them, the cross-sectional crystal orientation degree of the polyethylene in the MD direction of the separator measured by XRD is preferably 0.85 to 0.99, and / or the cross-sectional crystal orientation degree of the polyethylene in the TD direction is preferably 0.85 to 0.99.

[0073] From the same viewpoints as above, the ratio (MD / TD) of the cross-sectional crystalline orientation of the polyethylene measured in the MD direction of the separator to the cross-sectional crystalline orientation of the polyethylene measured in the TD direction is preferably in the range of 0.45 to 1.35 or 0.5 to 1.2, more preferably in the range of 0.50 to 1.20 or 0.60 to 1.25, and even more preferably in the range of 0.80 to 1.15. When the ratio (MD / TD) of the cross-sectional crystalline orientation of the polyethylene measured in the MD direction of the separator to the cross-sectional crystalline orientation of the polyethylene measured in the TD direction is within the above range, the mechanical strength of the separator is increased and creep deformation is less likely to occur due to complex stresses that occur non-uniformly within the battery, which in turn improves the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the battery.

[0074] The values ​​detected by SAXS and / or WAXS measurements of the separator can be adjusted to fall within the ranges described above, for example, by quantifying or selecting the Si modification rate, C3 / C4 molecular structure, number average molecular weight (Mn), weight average molecular weight (Mw), dispersity (Mn / Mw) of the silane-modified polyolefin to achieve a uniform arrangement of Si-containing molecular structures in the separator manufacturing process, and / or by quantifying or selecting the polyolefin resin other than the silane-modified polyolefin based on Mn, Mw, Mn / Mw, etc., and / or by quantifying the blending ratio of the silane-modified polyolefin and the polyolefin resin other than the silane-modified polyolefin.

[0075] For the Si-containing image detected by TOF-SIMS measurement of a separator containing silane-modified polyolefin, the Voronoi area (mu) of the most frequent Voronoi polygon obtained by Voronoi division was 6.00 m 2 ~12.00μm 2 It is preferable that the Voronoi area (mu) of the maximum frequency is within the range of 6.00 μm 2 ~12.00μm 2This tends to improve the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the battery, and / or makes it easier to balance these. More specifically, when the Voronoi area (mu) of the Voronoi polygon with the highest frequency obtained by the Voronoi division is 6.00 μm 2 ~12.00μm 2 Within this range, the Si-containing molecules tend to be dispersed in the separator without forming a sea-island structure. For example, when the nonaqueous secondary battery is a lithium ion secondary battery, if a separator in which Si elements are uniformly dispersed coexists with a lithium (Li) complex solvated with an electrolyte solution having an unshared electron pair such as an oxygen atom, the phenomena of items (A) and (B) described in the first embodiment may extend the product life in a cycle characteristic test of the battery.

[0076] Furthermore, Si-containing molecules often have crosslinking properties. For example, when the Si-containing molecules have silane crosslinking properties, the silane crosslinking properties of the dispersed Si-containing molecules can be ensured even in a nonaqueous secondary battery, and the stability of the siloxane bonds can be ensured, which is thought to enable the crosslinked structure of the separator to be maintained over a long period of time. As a result, safety can be ensured in safety tests such as crushing tests.

[0077] When the separator according to the fourth embodiment is subjected to TOF-SIMS measurement in a 100 μm square area, at least one silicon-containing structure is detected, and preferably, Si-containing molecules are detected to be dispersed in the separator in a state other than a sea-island structure.

[0078] From the viewpoint of further improving the safety of the separator and the nonaqueous secondary battery including the separator, the separator according to embodiment 4 preferably includes, for example, silane-modified polyethylene as the Si-containing molecule, and more preferably, a silane crosslinking reaction of the silane-modified polyethylene proceeds when the separator comes into contact with the coating solution or the electrolyte solution.

[0079] From the viewpoint of improving the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the battery, and / or achieving a balance among them, the Voronoi area (mu) of the Voronoi polygons obtained by the Voronoi division described above is set to 6.20 μm 2 ~11.80μm 2 It is more preferable that the temperature is in the range of

[0080] The spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by the above TOF-SIMS measurement was 2.00 μm 2 ~4.00μm 2 It is preferable that the σ of the separator is in the range of 2.00 μm. 2 If it is more than 4.00 μm, it is easy to form a separator film. 2 If the σ of the separator is less than 2.30 μm, the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the battery can be improved. 2 ~3.60μm 2 It is more preferable that the temperature is in the range of

[0081] For a Si-containing image detected by TOF-SIMS measurement, it is preferable that the ratio (σ / mu) of the spread (σ) of the Voronoi area frequency distribution to the Voronoi area (mu) of maximum frequency satisfies the following relationship: 0.20≦σ / mu≦0.40 The ratio (σ / mu) in Voronoi tessellation can be regarded as an index indicating whether Si-containing molecules are uniformly dispersed on the separator surface. When the ratio (σ / mu) is within the range of 0.20 to 0.40, the Si-containing molecules are uniformly dispersed on the separator surface, which contributes sufficiently to the coexistence of the electrolyte-derived Li complex with the separator and the silane crosslinking reaction of the separator in nonaqueous secondary batteries, thereby achieving both the film-forming properties of the separator containing the silane-modified polyolefin and the cycle characteristics of the nonaqueous secondary battery. While not wishing to be bound by theory, the concentration of the intermediate in which the Li complex is coordinated in the separator surface and the equilibrium life of the intermediate are important. In the fourth embodiment, it was experimentally discovered that a ratio (σ / mu) within the above numerical range contributes uniformly to the intercalation reaction into the electrode. From the viewpoint of further extending the cycle life of the battery while maintaining the separator's film-forming properties, the ratio (σ / mu) is more preferably 0.22 or more and 0.38 or less.

[0082] The numerical values ​​obtained by Voronoi tessellation of the separator according to embodiment 4 can be adjusted within the ranges described above by controlling, for example, the structure of the Si-containing molecule, the molecular weight or molecular weight distribution of the separator constituent raw materials, the blending range of the separator constituent raw materials, etc.

[0083] If desired, the separator according to embodiment 4 may have a multi-layer structure, and can be provided as a non-aqueous secondary battery comprising the separator.

[0084] <Embodiment 5: Silane-modified polyolefin-containing structure of separator, Voronoi tessellation, change in air permeability before and after compression, and crystal structure> In the fifth embodiment, a separator for a non-aqueous secondary battery is provided that combines the configurations according to the first to fourth embodiments.

[0085] The separator for a non-aqueous secondary battery according to embodiment 5 is a polyolefin microporous film containing a silane-modified polyolefin, and the maximum frequency Voronoi area (mu) of Voronoi polygons obtained by Voronoi division of an Si-containing image detected by TOF-SIMS measurement of the separator is 1.0 μm 2 ~17.5μm 2 or 6.0 μm 2 ~12.0μm 2 The spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by TOF-SIMS measurement is within the range of 0.5 μm 2 ~8.5μm 2 the air permeability change ratio (air permeability Sh after compression / air permeability Sj before compression) when compressed by 30% of the separator thickness is in the range of 1.1 to 7.0 times, the crystalline long period of the polyethylene as detected by SAXS measurement is 20 to 50 nm, the crystallinity as detected by WAXS measurement is 60% to 80%, and / or the crystallite size (110) of the polyethylene as detected by WAXS measurement is 10 to 50 nm.

[0086] The components of the separators according to the first to fifth embodiments will be described below.

[0087] <Polyolefin> The polyolefin is not particularly limited, but examples include homopolymers of ethylene or propylene, and copolymers formed from at least two monomers selected from the group consisting of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, norbornene, and modified polyolefins. Among these, high-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene (UHMWPE), and modified polyolefins are preferred, with high-density polyethylene, UHMWPE, and modified polyolefins being more preferred, from the viewpoint of being able to perform heat setting (sometimes abbreviated as "HS") at higher temperatures without pore clogging. It is generally known that UHMWPE has a weight-average molecular weight of 1,000,000 or more. The polyolefins may be used alone or in combination of two or more.

[0088] From the viewpoint of imparting to the separator the properties obtained by Voronoi tessellation described above, the properties obtained by SAXS and / or WAXS, etc., it is preferable to use a modified polyolefin as the polyolefin, and it is more preferable to use a silane-modified polyethylene (hereinafter referred to as resin A).

[0089] From the viewpoints of achieving both long life and safety in the cycle characteristics of nonaqueous secondary batteries and striking a balance between them, as well as optimizing the various values ​​explained above for the uniform arrangement of Si-containing molecular structures, SAXS and / or WAXS measurement, and Voronoi tessellation, and improving the ease of crosslinking in the separator, as well as the battery's crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life, and / or striking a balance between them, it is preferable to use at least one polyolefin other than silane-modified polyethylene in addition to resin A, and it is more preferable to use UHMWPE having a viscosity average molecular weight (Mv) of 1,800,000 or more (hereinafter referred to as resin B) as the polyolefin other than silane-modified polyethylene, and it is even more preferable to use polyethylene having an Mv of less than 1,800,000 (hereinafter referred to as resin C) in addition to resin B.

[0090] (Silicon-containing structure of separator and Voronoi tessellation) In the silicon (Si)-containing functional group of the silane-modified polyolefin in the separator, the number of methylenes (CH2) constituting the linkages to the main chain is preferably 2 to 10. The number of methylenes (CH2) constituting the linkages to the main chain refers to the number of (CH2) linking the main chain of the silane-modified polyolefin to the Si atom, and is, for example, the value of n in the following formula (I): [ka] In the formula, R includes methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, etc., and n is the number of methylene (CH) that constitutes the linkage to the main chain described above. For example, with regard to the Si-containing functional group of the silane-modified polyolefin, when the number of CH2 constituting the linking portion is within the range of 2 to 10 relative to the polyolefin main chain containing polyethylene or the like as the main component, it becomes easier to construct a higher-order structure that readily undergoes a silane crosslinking reaction. From the viewpoints of ensuring the ease of crosslinking of the separator, improving the crush test pass rate of the battery, the cycle test capacity retention rate, and the high-temperature cycle life, and / or achieving a balance among them, it is more preferable that the number of CH2 is within the range of 2 to 6.

[0091] <Resin A: Silane-modified polyethylene> A separator containing silane-modified polyethylene (resin A) is preferred because a silane crosslinking reaction of the silane-modified polyethylene proceeds when the separator comes into contact with a coating solution or an electrolyte. Examples of silane-modified polyethylene include silane-graft-modified polyethylene. It is believed that the functional groups contained in the polyolefin constituting the separator are not incorporated into the crystalline portion of the polyolefin but are crosslinked in the amorphous portion. Therefore, when the separator according to embodiments 1 to 5 comes into contact with an electrolyte, it forms a crosslinked structure using chemicals in the electrolyte, thereby suppressing an increase in internal stress or deformation of the fabricated battery and improving safety in tests such as nail penetration tests.

[0092] In addition, the separators according to the first to fifth embodiments are formed by the H + The crosslinking reaction can proceed by reacting with ions or -OH groups, thereby suppressing an increase in internal stress or deformation of the manufactured battery, thereby improving safety in crush tests and the like. Without wishing to be bound by theory, it is thought that when the aqueous coating liquid is acidic, the activation energy of the reaction system decreases, making it easier for the crosslinking reaction of the separator to proceed. When the aqueous coating liquid is basic, the OH - In the case of a non-aqueous coating solution, the organic solvent in the coating solution penetrates into the amorphous polyethylene part of the separator, promoting molecular motion and thereby accelerating the silane crosslinking reaction.

[0093] By creating a silane-crosslinked structure (gelled structure) in the separator using silane-modified polyethylene, high-temperature membrane rupture resistance can be achieved, improving safety in crush tests and other tests. This is thought to be due to the fact that the polyethylenes dispersed in the mixed resin, and / or the polyethylene and polyolefins other than polyethylene, are favorably linked by the silane-crosslinked structure. In other words, the change in the morphology of the entire separator, including the polyolefin microporous membrane, also improves tensile elongation, which is expected to reduce the possibility of the separator rupturing when the battery is deformed by external force.

[0094] Silane-modified polyolefins have a polyolefin main chain and are constructed with alkoxysilyl groups grafted onto the main chain. Silane-modified polyolefins can be obtained, for example, by grafting alkoxysilyl groups onto the main chain of a polyolefin. Examples of silane-unmodified polyolefins include polyethylene, polypropylene, and copolymers of ethylene and propylene. Examples of silane-modified polyethylenes include graft copolymers obtained by grafting unsaturated silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyltriacetoxysilane onto polyethylene such as high-density polyethylene, low-density polyethylene, and linear low-density polyethylene, or ethylene-ethylenically unsaturated silane compound copolymers.

[0095] It is believed that the alkoxysilyl groups of silane-modified polyethylene are converted to silanol groups via a hydrolysis reaction with water, which then undergoes a crosslinking reaction to form siloxane bonds (see the hydrolysis reaction, condensation reaction, and dehydration condensation reaction shown in the following formulas; the rate at which the TO structure changes to the T1 structure, T2 structure, or T3 structure is arbitrary, and the following formula describes the case where the number n of methylenes (CH2) constituting the linkage to the main chain described in formula (I) above is 2, but n may be 3 to 10). The alkoxide substituted on the alkoxysilyl group is not particularly limited, and examples thereof include methoxide, ethoxide, and butoxide. For example, in the following formula, R may be methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, or tert-butyl. [ka]

[0096] In silane-modified polyethylene, the main chain and the grafts are connected by a covalent bond. The structure forming such a covalent bond is not particularly limited, but examples thereof include alkyl, ether, glycol, and ester.

[0097] From the viewpoints of not only the uniform arrangement of Si-containing molecular structures and the lifespan of the equilibrium state intermediate the Li complex coordination, but also the optimization of the various values ​​explained above for SAXS and / or WAXS measurement and Voronoi tessellation, the ease of proceeding of separator crosslinking, and improving the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the battery, and / or achieving a balance among them, prior to the crosslinking reaction of Resin A, Resin A preferably contains 0.03 to 1.0 mol % of silanol units (i.e., a silanol unit modification rate of 0.03 to 1.0 mol %), and this silanol unit modification rate is more preferably 0.05 to 0.35 mol %, even more preferably 0.07 to 0.32 mol %, particularly preferably 0.08 to 0.30 mol %, and most preferably 0.12 to 0.28 mol %. In embodiments 1 to 5, the silane-modified units are present only in the amorphous portion of the separator, and a molecular structure that facilitates the construction of a crosslinking reaction was designed by focusing on the distance between the silane-modified units and the thermal vibration motion at -10°C to 80°C. In the above formula, the TO, T1, T2, and T3 structures can all construct coordination intermediates with the Li complex. However, since the Li complex is thought to undergo coordination, decoordination, and recoordination between Si atoms in the amorphous portion randomly, the effect was maximized by adjusting the amount of silanol unit modification in resin A.

[0098] From the same viewpoint as above, it is preferable that resin A is modified with 0.01 to 2.0 mol % of propylene-modified (C3) units, 0.01 to 2.0 mol % of butene (C4) units, or a total of 0.01 to 2.0 mol % of C3 units and C4 units.

[0099] From the same viewpoint as above, the C3 unit modification rate of Resin A is more preferably 0.01 to 1.2 mol%, further preferably 0.01 to 0.75 mol%, particularly preferably 0.02 to 0.60 mol%, and most preferably 0.05 to 0.30 mol%.

[0100] From the viewpoint of the FUSE function of the separator as well as the cycle characteristics and safety of the nonaqueous secondary battery, the C4 unit modification rate of Resin A is more preferably 0.01 to 1.0 mol%, further preferably 0.30 to 0.70 mol%, and particularly preferably 0.48 to 0.65 mol% before the crosslinking reaction of Resin A. On the other hand, in the heat setting (HS) step during separator formation, the C4 unit modification rate of Resin A is preferably 0.43 mol% or less, more preferably 0.40 mol% or less, and even more preferably 0.1 mol% or less.

[0101] From the viewpoints of not only the cycle characteristics and safety of the nonaqueous secondary battery but also of optimizing the various values ​​described above for the SAXS and / or WAXS measurement and Voronoi tessellation of the separator, thereby improving the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the nonaqueous secondary battery, and / or achieving a balance therebetween, the total modification rate of the C3 units and C4 units of Resin A is more preferably 1.5 mol% or less, even more preferably 1.0 mol% or less, particularly preferably 0.6 mol% or less, and most preferably 0.3 mol% or less.

[0102] From the viewpoint of cycle characteristics and safety of the non-aqueous secondary battery, the number average molecular weight (Mn) of the resin A is preferably 10,000 to 20,000, more preferably 16,000 or less, and even more preferably 15,000 or less.

[0103] From the same viewpoint as above, the weight average molecular weight (Mw) of Resin A is preferably 45,000 to 200,000, more preferably 140,000 or less, even more preferably 129,000 or less, particularly preferably 100,000 or less, and most preferably 72,000 or less.

[0104] From the same viewpoint as above, the Mw / Mn of Resin A is preferably 3.0 to 12, more preferably 4.0 to 9.0, and even more preferably 4.1 to 8.0.

[0105] From the same viewpoint as above, the crystallinity of Resin A is preferably 40 to 70%, more preferably 50 to 68%, and even more preferably 60 to 65%.

[0106] From the same viewpoint as above, the crystallite size (110) of resin A is preferably 15 to 30 nm, more preferably 17 to 28 nm, and even more preferably 20 to 25 nm.

[0107] From the same viewpoint as above, the crystalline long period of resin A is preferably 15 to 30 nm, more preferably 17 to 27 nm, and even more preferably 20 to 25 nm.

[0108] Resin A is not limited, but its viscosity average molecular weight (Mv) may be, for example, 20,000 to 150,000, and its density may be, for example, 0.90 to 0.97 g / cm 3 The melt mass flow rate (MFR) at 190°C may be, for example, 0.1 to 15 g / min.

[0109] The polyethylene constituting the silane-modified polyethylene may be composed of a single type of ethylene or may be composed of two or more types of ethylene. Two or more types of silane-modified polyethylene composed of different ethylenes may be used in combination.

[0110] <Resin B: UHMWPE with Mv of 1,800,000 or more> Resin B is UHMWPE having an Mv of 1,800,000 or more, and is preferably used in combination with Resin A, and can also be used in combination with Resin C if desired.

[0111] The Mn of Resin B is preferably 200,000 to 1,400,000, more preferably 210,000 to 1,200,000, and even more preferably 250,000 to 1,000,000, not only from the viewpoint of the cycle characteristics and safety of the nonaqueous secondary battery, but also from the viewpoint of optimizing the various values ​​described above for the SAXS and / or WAXS measurement and Voronoi tessellation of the separator, and improving the crush test pass rate, cycle test capacity retention rate, high-temperature cycle life, etc. of the nonaqueous secondary battery, and / or achieving a balance therebetween.

[0112] From the same viewpoint as above, the Mw of Resin B is preferably 1,500,000 to 8,800,000, more preferably 1,600,000 to 7,100,000, and even more preferably 1,700,000 to 6,200,000.

[0113] From the same viewpoint as above, the ratio of Mw to Mn (Mw / Mn) of Resin B is preferably 3.0 to 12, more preferably 4.0 to 9.0, and even more preferably 6.0 to 8.8.

[0114] From the same viewpoint as above, the Mv of Resin B is preferably more than 1,800,000 and not more than 10,000,000, more preferably from 1,850,000 to 8,500,000, even more preferably from 1,950,000 to 7,800,000, and particularly preferably from 2,000,000 to 6,500,000.

[0115] <Resin C: Polyethylene with Mv less than 1,800,000> Resin C is a polyethylene having an Mv of less than 1,800,000, and is preferably used in combination with Resin A, and can also be used in combination with Resin B if desired.

[0116] The Mn of Resin C is preferably 20,000 to 250,000, more preferably 30,000 to 200,000, even more preferably 32,000 to 150,000, and particularly preferably 40,000 to 110,000, not only from the viewpoint of the cycle characteristics and safety of the nonaqueous secondary battery but also from the viewpoint of optimizing the various values ​​described above for the SAXS and / or WAXS measurement and Voronoi tessellation of the separator, thereby improving the crush test pass rate, cycle test capacity retention rate, high-temperature cycle life, etc. of the nonaqueous secondary battery, and / or achieving a balance therebetween.

[0117] From the same viewpoint as above, the Mw of Resin C is preferably 230,000 to 1,500,000, more preferably 280,000 to 1,300,000, still more preferably 320,000 to 1,200,000, and particularly preferably 400,000 to 1,000,000.

[0118] From the same viewpoint as above, the ratio of Mw to Mn (Mw / Mn) of Resin C is preferably 3.0 to 12, more preferably 4.0 to 9.0, and even more preferably 6.0 to 8.8.

[0119] From the same viewpoint as above, the Mv of resin C is preferably 250,000 or more and less than 1,800,000, more preferably 300,000 or more and 1,600,000 or less, even more preferably 320,000 or more and 1,100,000 or less, and particularly preferably 450,000 to 800,000.

[0120] <Optional ingredients> Optional components that can be contained in the separator include components different from any of Resins A to C, such as at least one of a polymer different from any of Resins A to C or an additive described below. The optional component is not limited to a single type. The separator may contain multiple types of polymers different from any of Resins A to C, or multiple types of additives, or the separator may contain both the polymer and the additive. Examples of optional polymer components include polypropylene (PP), polystyrene (PS), polyacrylate, polymethacrylate, polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polyester, polycarbonate (PC), polysulfone (PSU), polyethersulfone (PES), polyphenylene oxide (PPO), polyarylene ether polymers, polyphenylene sulfide (PPS), polyphenylene sulfide sulfone, polyparaphenylene (PPP), polyarylene polymers, polyarylene ketone, polyether ketone (PEK), poly Examples of the separator include homopolymers and copolymers containing at least one of arylene phosphine oxide, polyether phosphine oxide, polybenzoxazole (PBO), polybenzthiazole (PBT), polybenzimidazole (PBI), polyamide (PA), polyimide (PI), polyetherimide (PEI), and polyimide sulfone (PIS). Examples of additives include antioxidants such as phenolic compounds, phosphorus compounds, and sulfur compounds; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. When the separator contains multiple optional components, the total content of the multiple optional components may be 20% by mass or less.

[0121] The separator may contain not only the additives exemplified above but also known additives such as plasticizers, but preferably does not contain an organometallic catalyst (dehydration condensation catalyst).

[0122] (Dehydration condensation catalyst) The alkoxysilyl group undergoes a hydrolysis reaction with water to form a siloxane bond. However, because the reaction rate is slow, an organometallic catalyst can often be used to promote the condensation reaction. The metal of the organometallic catalyst can be, for example, at least one selected from the group consisting of scandium, vanadium, copper, zinc, zirconium, palladium, gallium, tin, titanium, iron, nickel, and lead. Organometallic catalysts, particularly di-butyltin dilaurate, di-butyltin diacetate, di-butyltin dioctoate, and the like, are known to be able to dramatically accelerate the reaction rate through the reaction mechanism proposed by Wei et al. (FW van. de R. Wei, Macromol. Chem., 181, 2541, 1980). However, in recent years, in order to avoid the environmental and human health hazards posed by organotins, it has become known that the Lewis function of copper or titanium chelate complexes can be utilized in combination with an organic base to accelerate the reaction of forming siloxane bonds between alkoxysilyl groups, similar to organotin complexes.

[0123] It is known that organometallic catalysts (dehydration condensation catalysts) also function as catalysts for the siloxane bond-forming reaction of alkoxysilyl group-containing resins. In this specification, a resin containing silane-modified polyethylene to which an organometallic catalyst (or dehydration condensation catalyst) has been added beforehand, prior to the sheet forming process (for example, in the stage of a kneading process that is performed as needed), is referred to as a masterbatch resin.

[0124] The separator preferably does not contain an organometallic catalyst (dehydration condensation catalyst) or a masterbatch resin containing the same.

[0125] <Separator characteristics> The following separator properties are for a polyolefin microporous flat membrane or monolayer membrane. If the microporous membrane is in the form of a laminate membrane, the following properties can be measured after removing layers other than the polyolefin microporous membrane from the laminate membrane.

[0126] The porosity of the separator is preferably 20% or more, more preferably 30% or more, and even more preferably 32% or more or 35% or more. A porosity of 20% or more tends to further improve the separator's puncture strength and its ability to follow the rapid movement of lithium ions. On the other hand, the porosity of the separator is preferably 90% or less, more preferably 80% or less, and even more preferably 50% or less. A porosity of 90% or less tends to further improve membrane strength, further suppress self-discharge, and / or optimize air permeability. The porosity of the separator can be measured by the method described in the Examples.

[0127] The air permeability of the separator, before or without being subjected to a compression test, is preferably 1 second or more, more preferably 30 seconds or more, even more preferably 50 seconds or more, even more preferably 55 seconds or more, particularly preferably 70 seconds or more, and most preferably 75 seconds or more. An air permeability of 1 second or more tends to improve the balance between membrane thickness, porosity, and pore size, or tends to improve pin puncture strength. Furthermore, the air permeability of the separator is preferably 400 seconds or less, more preferably 300 seconds or less, and even more preferably 270 seconds or less. An air permeability of 400 seconds or less tends to further improve ion permeability. The air permeability of the separator can be measured by the method described in the Examples.

[0128] The tensile strength of the separator is preferably 1000 kgf / cm in both the MD and TD directions. 2 More preferably, it is 1050 kgf / cm 2 More preferably, it is 1100 kgf / cm 2 Tensile strength is 1000kgf / cm or more. 2 By satisfying the above conditions, breakage during lamination or winding with slits or electrodes is more likely to be suppressed, and short circuits due to foreign matter in the battery are more likely to be suppressed. On the other hand, the tensile strength of the separator is preferably 5000 kgf / cm 2 More preferably, it is 4500 kgf / cm or less. 2More preferably, it is 4000 kgf / cm or less. 2 Tensile strength is 5000kgf / cm or less. 2 By satisfying the condition below, the separator will relax early during the heat test, weakening the contraction force, and as a result, safety tends to be improved.

[0129] The tensile modulus of the separator is preferably 120 N / cm or less, more preferably 100 N / cm or less, and even more preferably 90 N / cm or less, in both the MD and TD directions. A tensile modulus of 120 N / cm or less indicates that the separator is not highly oriented for a nonaqueous secondary battery. During a heating test, for example, when a blocking agent such as polyethylene melts and shrinks, the polyethylene undergoes early stress relaxation, which tends to suppress separator shrinkage within the battery and facilitate prevention of short-circuiting between electrodes (i.e., improve the safety of the separator during heating). A separator with such a low tensile modulus can be easily achieved by including polyethylene with a weight-average molecular weight of 500,000 or less in the polyolefin forming the polyolefin microporous membrane as the separator substrate. While there is no particular restriction on the lower limit of the separator's tensile modulus, it is preferably 10 N / cm or more, more preferably 30 N / cm or more, and even more preferably 50 N / cm or more. The tensile modulus can be appropriately adjusted by adjusting the degree of stretching, or by relaxing the film after stretching as necessary.

[0130] The separator membrane thickness is preferably 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more, or 4.0 μm or more. A membrane thickness of 1.0 μm or more tends to further improve membrane strength. Furthermore, the separator membrane thickness is preferably 24 μm or less, more preferably 22 μm or less, and even more preferably 20 μm or less, or 18 μm or less. A membrane thickness of 24 μm or less tends to further improve ion permeability. The separator membrane thickness can be measured by the method described in the Examples.

[0131] In the polyethylene crystalline structure of the separator, the polyethylene crystallinity measured by X-ray diffraction (XRD) is preferably 60 to 99%, the polyethylene (110) crystallite size is preferably 14.2 to 50.0 nm, the cross-sectional orientation is preferably 0.65 to 0.99, the lamellar thickness is preferably 15 to 40 nm, and the crystalline long period is preferably 25 to 55 nm. The separator has an excellent crystalline structure determined by such X-ray structural analysis due to its mechanical properties such as high compressive elastic recovery and resistance to creep deformation due to external forces.

[0132] From the viewpoints of ensuring ease of handling, safety in the Hot Box test, and stabilizing the thermal shrinkage rate, the puncture strength of the separator is preferably in the range of 200 gf to 600 gf, and more preferably in the range of 210 gf to 390 gf. From the same viewpoint, the puncture strength converted into the basis weight of the separator (puncture strength of separator (gf) / basis weight of separator (g / m 2 )) is 50gf m 2 / g~100gf m 2 / g, and preferably in the range of 60 gf m 2 / g~90gf·m 2 More preferably, it is in the range of / g.

[0133] <Layer configuration> The separator may have either a single-layer structure or a multilayer structure, and preferably includes at least one polyolefin microporous membrane from the viewpoint of redox resistance and a dense, uniform porous structure. The polyolefin microporous membrane may be a single-layer membrane consisting of a single polyolefin-containing microporous layer, a multilayer membrane consisting of multiple polyolefin-containing microporous layers, or a multilayer membrane consisting of a polyolefin resin layer and a layer containing another resin as a main component, such as a thermoplastic polymer-containing layer, an active layer, a heat-resistant resin layer, or an inorganic porous layer.

[0134] In the case of a bilayer membrane formed from two polyolefin-containing microporous layers, the polyolefin compositions of the two layers can be different, and in the case of a multilayer membrane formed from three or more polyolefin-containing microporous layers, the polyolefin compositions of the outermost and innermost layers can be different, for example, a three-layer membrane.

[0135] (Preferred multilayer structure 1) A separator having a preferred multilayer structure 1 preferably comprises a polyolefin microporous membrane as a substrate and an inorganic porous layer containing inorganic particles and a resin binder laminated on at least one side of the polyolefin microporous membrane. From the viewpoints of suppressing thermal shrinkage and improving the crushing test pass rate, cycle test capacity retention rate, and high-temperature cycle life of a nonaqueous secondary battery, and / or achieving a balance among these, the content of inorganic particles in the inorganic porous layer is preferably 5% by mass to 99% by mass, and more preferably 10% by mass or more and less than 99% by mass, based on the total mass of the inorganic porous layer.

[0136] (Other preferred multilayer structures 2 to 4) Separators having the following multilayer structures 2 to 4 are also preferred. Any combination of the multilayer structures 1 to 4 is also preferred.

[0137] The separator having the multilayer structure 2 comprises a polyolefin microporous membrane as a substrate and a thermoplastic polymer-containing layer formed on at least one side of the polyolefin microporous membrane. The thermoplastic polymer contained in the thermoplastic polymer-containing layer preferably contains polymerized units of a (meth)acrylic acid ester and / or (meth)acrylic acid, or at least one fluorine-containing polyvinyl compound selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE). The inclusion of the thermoplastic polymer-containing layer improves the adhesive strength between the electrodes and the separator, thereby improving handling during battery production.

[0138] The separator having a multilayer structure (3) comprises a polyolefin microporous membrane as a substrate and an active layer disposed on at least one side of the polyolefin microporous membrane. The active layer is preferably at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE), PVDF homopolymer, a mixture of PVDF and tetrafluoroethylene-ethylene copolymer (ETFE), or vinylidene fluoride-tetrafluoroethylene-ethylene terpolymer, and more preferably at least one selected from the group consisting of PVDF-HFP and PVDF-CTFE. Copolymerizing HFP or CTFE with vinylidene fluoride allows the crystallinity of the fluororesin to be controlled within an appropriate range, thereby suppressing the flow of the active layer during adhesion to electrodes. Furthermore, improved adhesion during adhesion to electrodes reduces interfacial slippage when used as a separator for secondary batteries, resulting in an improved crush test pass rate.

[0139] Specific examples of PVDF include the Kynar Flex (registered trademark) series from Arkema, e.g. LBG, LBG8200, etc.; Solef (registered trademark) series from SOLVAY, for example , grade 1015, 6020 etc.

[0140] Specific examples of polymeric PVDF-HFP include the Solef (registered trademark) series from SOLVAY, For example, grades 21216 and 21510 (both of which are soluble in acetone). Specific examples of molecular PVDF-CTFE include the Solef (registered trademark) series from SOLVAY, e.g. For example, grade 31508 (dissolves in acetone).

[0141] The separator having a multilayer structure 4 includes a polyolefin microporous membrane as a substrate and a heat-resistant resin layer containing a heat-resistant resin laminated on at least one side of the polyolefin microporous membrane. The heat-resistant resin preferably contains at least one selected from the group consisting of wholly aromatic polyamides (also called aramids), polyimides, polyamideimides, polysulfones, polyketones, polyethers, polyetherketones, polyetherimides, and cellulose. Among these, wholly aromatic polyamides are preferred from the viewpoint of durability, with para-aromatic polyamides and / or meta-aromatic polyamides being more preferred. Furthermore, meta-aromatic polyamides are preferred from the viewpoints of porous layer formability and oxidation-reduction resistance. Examples of meta-polyamides include polymetaphenylene isophthalamide. Examples of para-polyamides include copolyparaphenylene-3,4'-oxydiphenylene terephthalamide and polyparaphenylene terephthalamide. The heat-resistant resin layer preferably contains 30% to 90% by mass of inorganic material having an average particle size of 0.2 μm to 0.9 μm. The heat-resistant resin layer suppresses thermal deformation of the separator even when a local short circuit occurs inside the battery, improving the crush test pass rate.

[0142] The inorganic particles for multilayer structure 1 and / or 3 and the inorganic filler for multilayer structure 4 may be inorganic materials described later in the manufacturing method for a separator for a nonaqueous secondary battery, and among them, it is preferable that the inorganic material be at least one selected from the group consisting of alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum oxide hydroxide, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, diatomaceous earth, silica sand, and glass fiber.

[0143] <Method for manufacturing a separator for a non-aqueous secondary battery> (Method for producing a polyolefin microporous membrane) The method for producing a separator for a non-aqueous secondary battery will be described below for the case where the polyolefin microporous membrane is a single-layer membrane (flat membrane), but is not intended to exclude forms other than flat membranes. The method for producing a microporous membrane according to embodiments 1 to 5 includes the following steps: (1) Sheet forming process; (2) Stretching process; (3) porous body forming step; and (4) Heat treatment process; The method for producing a microporous membrane according to embodiments 1 to 5 may optionally include a resin modification step or kneading step before the sheet-forming step (1) and / or a winding and slitting step after the heat-treatment step (3), but preferably does not include a crosslinked structure formation step or a contact step with a crosslinking-accelerating catalyst, from the viewpoint of maintaining the crosslinkability of the microporous membrane until it is installed in a battery.

[0144] The crosslinked structure formation process includes (1) a secondary process of condensing multiple functional groups contained in the microporous membrane, (2) a secondary process of reacting the functional groups contained in the microporous membrane with chemicals inside the battery, or (3) a secondary process of reacting the functional groups contained in the microporous membrane with other functional groups. The crosslinking-promoting catalyst is any catalyst capable of promoting a crosslinking reaction, such as (I) a condensation reaction of multiple identical functional groups, (II) a reaction between multiple different functional groups, (III) a chain condensation reaction between a functional group and an electrolyte, or (IV) a chain condensation reaction between a functional group and an additive. The crosslinking-promoting catalyst may be, for example, an organometallic catalyst.

[0145] (Method of manufacturing multilayer film) Next, a method for producing a separator for a non-aqueous secondary battery will be described below, taking the case of a multilayer film as an example. The method for producing a multilayer film includes the following steps: (1) Sheet forming process; (2) Stretching process; (3) Porous body formation process; (4) Heat treatment process; (5) Coating process; (6) a drying step; and (7) Assembly process and a water washing step (5.5) may be included between step (5) and step (6).

[0146] The multilayer film manufacturing method includes steps (1) to (4) performed in the same manner as in the monolayer film manufacturing method to form a polyolefin microporous film. The method then includes a coating step (5) in which a coating liquid is applied to at least one surface of the resulting polyolefin microporous film or the heat-treated porous body obtained by the heat-treatment step (4), a drying step (6) in which the coating liquid is dried and removed, and an assembly step (7) in which the electrode and separator laminate or its wound body, and a nonaqueous electrolyte are housed in an outer package. A water-washing step (5.5) in which the solvent component in the coating liquid is replaced with another solvent component may be included between steps (5) and (6). The multilayer film manufacturing method is also characterized by forming a crosslinked structure of the silane-modified polyolefin contained in the multilayer film in at least one of the coating step (5), the water-washing step (5.5), the drying step (6), and the assembly step (7). Preferably, the crosslinked structure of the silane-modified polyolefin is formed in the coating step (5) and the assembly step (7).

[0147] Each step involved in the manufacturing method of the single layer film and the multilayer film will be described below.

[0148] In the kneading step, for example, a polyolefin, and optionally other resins, and a plasticizer or inorganic material can be kneaded using a kneader. From the viewpoints of suppressing the generation of resin aggregates in the production process and maintaining the crosslinkability of the microporous membrane until it is installed in a battery, it is preferable not to add a masterbatch resin containing a crosslinking-accelerating catalyst to the kneaded mixture.

[0149] The polyolefin used in the kneading step or the sheet-forming step (1) is not limited to an olefin homopolymer, but may be a polyolefin copolymerized with a monomer having a functional group, or a functional-group-modified polyolefin. The functional group is a functional group capable of participating in the formation of a crosslinked structure, such as the alkoxysilyl group described above. By preparing silane-modified polyethylene (resin A) as a raw material, the resin modification step can be omitted.

[0150] On the other hand, if the polyolefin raw material does not have functional groups capable of participating in the formation of crosslinked structures or the mole fraction of such functional groups is less than a predetermined ratio, the polyolefin raw material can be subjected to a resin modification process to incorporate functional groups into the resin skeleton or increase the mole fraction of functional groups to obtain a functionally modified polyolefin. The resin modification process can be carried out by known methods. For example, the polyolefin raw material can be contacted with a reaction reagent by liquid spraying, gas spraying, dry mixing, immersion, coating, etc., so that crosslinkable functional groups can be introduced into the polyolefin skeleton.

[0151] It is preferable to prepare silane-modified polyethylene (resin A) as the polyolefin raw material, and it is more preferable to prepare not only resin A but also resin B and / or resin C described above, not only from the viewpoint of imparting to the separator the properties obtained by the Voronoi tessellation or the rate of change in air permeability before and after compression described above, but also from the viewpoint of optimizing the crystal structure of the Si-containing molecules and the various values ​​described above for the SAXS and / or WAXS measurements and Voronoi tessellation.

[0152] The molecular design or blending of resin A and resins B and C can be performed from the perspectives of uniform Si-containing molecular structure arrangement and the equilibrium lifetime of the coordination intermediate of the Li complex; uniform extrusion and kneading; and optimizing the crystalline structure of the Si-containing molecules, as well as the various values ​​described above for SAXS and / or WAXS measurements and Voronoi tessellation. As described above, Si-containing molecules exist only in the amorphous portion of the polyolefin resin. By incorporating the siloxane units and C3 and C4 units of resin A into the overall design, the equilibrium lifetime of the coordination intermediate of the Li complex can be controlled. On the other hand, blending resin A with resins B and C can construct an appropriate amorphous entanglement structure, and by developing reaction selectivity through molecular orbital angle design as described in Non-Patent Document 1, the equilibrium lifetime of the coordination intermediate of the Li complex can be controlled from the perspective of controlling molecular thermal vibration, i.e., from a thermodynamic perspective.

[0153] The content of resin A in the polyolefin raw material subjected to the sheet forming step (1) is preferably 3 to 70 mass%, more preferably 5 to 60 mass%, and even more preferably 10 to 50 mass%, based on the total mass of the solid content of the polyolefin raw material, not only from the viewpoint of imparting to the separator the properties obtained by Voronoi tessellation described above, but also from the viewpoint of optimizing the crystal structure of the Si-containing molecule and the various values ​​described above for SAXS and / or WAXS measurement and Voronoi tessellation.

[0154] From the same viewpoint as above, the content of resin B in the polyolefin raw material is preferably 3 to 70 mass %, more preferably 5 to 60 mass %, and even more preferably 5 to 40 mass %, based on the total mass of the solid content of the polyolefin raw material.

[0155] From the same viewpoint as above, the content of resin C in the polyolefin raw material is preferably 1 to 90 mass %, more preferably 5 to 60 mass %, and even more preferably 5 to 50 mass %, based on the total mass of the solid content of the polyolefin raw material.

[0156] From the same viewpoint as above, the mass ratio (A / B) of resin A to resin B used in the sheet molding step (1) is preferably 0.07 to 12.00, more preferably 0.10 to 11.00, and even more preferably 0.50 to 10.00.

[0157] From the same viewpoint as above, the mass ratio (A / C) of resin A to resin C used in the sheet molding step (1) is preferably 0.07 to 12.00, more preferably 0.10 to 11.00, and even more preferably 0.20 to 10.00.

[0158] From the same viewpoint as above, the mass ratio (B / C) of resin B to resin C used in the sheet molding step (1) is preferably 0.06 to 7.00, more preferably 0.10 to 7.00, and even more preferably 0.12 to 6.90.

[0159] From the same viewpoint as above, it is preferable that the molecular weights Mn, Mw, Mv, or Mw / Mn of the resins A to C subjected to the sheet forming step (1) are the same as those explained above for the separator components.

[0160] By appropriately controlling the molecular weight, molecular weight distribution, compounding ratio, etc. of the raw materials used in the sheet forming step (1) as described above, the characteristics related to Voronoi tessellation of the separators according to the first to fifth embodiments can be easily achieved.

[0161] From the viewpoint of improving safety by suppressing thermal runaway upon battery breakdown while maintaining low-temperature cycle properties and resistance to membrane rupture at high temperatures, it is preferable that in the sheet molding step, Resin A is not a masterbatch resin that contains, before the sheet molding step, a catalyst that promotes the crosslinking reaction of alkoxysilyl groups.

[0162] The plasticizer used in the sheet forming step (1) is not particularly limited, but examples thereof include organic compounds that can form a homogeneous solution with polyolefin at temperatures below its boiling point. More specific examples include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, and paraffin oil. Among these, paraffin oil and dioctyl phthalate are preferred. One plasticizer may be used alone, or two or more may be used in combination. The proportion of the plasticizer is not particularly limited, but from the viewpoint of the porosity of the resulting microporous film, the proportion of polyolefin and silane-modified polyolefin is preferably 20% by mass or more of the total mass, as needed, and from the viewpoint of viscosity during melt-kneading, preferably 90% by mass or less.

[0163] The sheet-forming step (1) is a step in which the obtained kneaded product or a mixture of polyolefin and plasticizer is extruded using an extruder, cooled and solidified, and molded into a sheet to obtain a sheet. The sheet-forming method is not particularly limited, but examples include a method in which the melt-kneaded and extruded molten product is solidified by compression cooling or deformation cooling. Cooling methods include a method in which the molten product is directly contacted with a cooling medium such as cold air or cooling water, and a method in which the molten product is contacted with a roll or press cooled with a refrigerant. The method in which the molten product is contacted with a roll or press cooled with a refrigerant is preferred because of its excellent film thickness controllability.

[0164] The stretching step (2) involves extracting plasticizers or inorganic materials from the resulting sheet, if necessary, and then stretching the sheet in at least one direction. Examples of sheet stretching methods include MD uniaxial stretching using a roll stretching machine, TD uniaxial stretching using a tenter, sequential biaxial stretching using a combination of a roll stretching machine and a tenter or a tenter and a tenter, and simultaneous biaxial stretching using a simultaneous biaxial tenter or inflation molding. Simultaneous biaxial stretching is preferred from the viewpoint of obtaining a more uniform membrane. The total areal stretching ratio is preferably 8 times or more, more preferably 15 times or more, and even more preferably 20 times or more or 30 times or more, from the viewpoints of uniformity of membrane thickness and the balance between tensile elongation, porosity, and average pore size. A total areal stretching ratio of 8 times or more tends to facilitate the production of a film with high strength and good thickness distribution. Furthermore, from the viewpoint of preventing breakage, this areal stretching ratio may be 250 times or less.

[0165] The porous body forming step (3) is a step of extracting the plasticizer from the stretched product after the stretching step to make the stretched product porous. The method for extracting the plasticizer is not particularly limited, but examples include immersing the stretched product in an extraction solvent and showering the stretched product with the extraction solvent. The extraction solvent is not particularly limited, but for example, it is preferable that it is a poor solvent for polyolefins and a good solvent for plasticizers or inorganic materials, and has a boiling point lower than the melting point of polyolefins. Examples of such extraction solvents include, but are not limited to, hydrocarbons such as n-hexane or cyclohexane; halogenated hydrocarbons such as methylene chloride, 1,1,1-trichloroethane, and fluorocarbons; alcohols such as ethanol or isopropanol; ketones such as acetone or 2-butanone; and alkaline water. The extraction solvents may be used alone or in combination.

[0166] The heat treatment step (4) is a step in which, after the stretching step, plasticizer is extracted from the sheet as needed, followed by further heat treatment to obtain a microporous membrane. The heat treatment method is not particularly limited, but examples include heat setting methods in which stretching and relaxation are performed using a tenter or roll stretching machine. The relaxation operation refers to a reduction operation performed in the machine direction (MD) and / or transverse direction (TD) of the membrane at a predetermined temperature and relaxation rate. The relaxation rate is the value obtained by dividing the MD dimension of the membrane after the relaxation operation by the MD dimension of the membrane before the operation, or the value obtained by dividing the TD dimension of the membrane after the relaxation operation by the TD dimension of the membrane before the operation, or, when relaxation is performed in both MD and TD, the value obtained by multiplying the MD relaxation rate by the TD relaxation rate. The stretching and relaxation operation in the heat treatment step (4) is preferably performed at least in TD.

[0167] In the coating step (5), a coating liquid is applied to at least one surface of the polyolefin microporous membrane obtained as described above, or to at least one surface of the heat-treated porous body obtained in the heat-treatment step (4). A known coating method can be used in the coating step (5), and examples include a method in which the coating liquid is applied to the substrate, microporous membrane, or heat-treated porous body, a method in which the raw material for the microporous membrane and the raw material for the other layer are laminated and extruded by coextrusion, and a method in which both layers are produced separately and then bonded together.

[0168] More specifically, the coating step (5) may be any one or any combination of the following steps (5A) to (5D): (5A) a coating step of applying a coating liquid containing inorganic particles, a resin binder, and a surfactant and having a pH of 6.7 or less or 7.5 or more to at least one surface of the polyolefin microporous monolayer membrane or the heat-treated porous body to form an inorganic porous layer on at least one surface of the polyolefin microporous monolayer membrane or the heat-treated porous body; (5B) a coating step of applying a coating liquid containing a thermoplastic polymer and a surfactant and having a pH of 6.7 or less or 7.5 or more to at least one surface of the polyolefin microporous monolayer membrane or the heat-treated porous body to form a thermoplastic polymer-containing layer on at least one surface of the polyolefin microporous monolayer membrane or the heat-treated porous body; (5C) a coating step of applying a coating liquid containing a fluorine atom-containing polyvinyl compound, inorganic particles, and an organic solvent to at least one surface of a polyolefin microporous monolayer film or a heat-treated porous body to form an active layer on at least one surface of the polyolefin microporous monolayer film or the heat-treated porous body; and (5D) A coating step of applying a coating liquid containing a heat-resistant resin and an organic solvent to at least one surface of a polyolefin microporous monolayer film or a heat-treated porous body to form a heat-resistant resin layer on at least one surface of the polyolefin microporous monolayer film or the heat-treated porous body.

[0169] By the coating step (5A), a multilayer film comprising a microporous polyolefin film and an inorganic porous layer according to the preferred multilayer structure 1 described above can be formed.

[0170] By the coating step (5B), a multilayer film comprising a microporous polyolefin film and a thermoplastic polymer-containing layer according to the preferred multilayer structure 2 described above can be formed.

[0171] By the coating step (5C), a multilayer film can be formed that includes a microporous polyolefin film and an active layer according to the preferred multilayer structure 3 described above.

[0172] By the coating step (5D), a multilayer film comprising a microporous polyolefin film and a heat-resistant resin layer according to the preferred multilayer structure 4 described above can be formed.

[0173] In the coating steps (5A) and (5B), if the pH of the aqueous or non-aqueous coating solution is 6.7 or less, the activation energy of the reaction system of the silane-modified polyolefin in contact with the coating solution decreases, making the silane crosslinking reaction more likely to occur. On the other hand, if the pH of the aqueous or non-aqueous coating solution is 7.5 or more, the OH - The presence of the silane crosslinking reaction of the silane-modified polyolefin can be accelerated.

[0174] In the coating steps (5C) and (5D), the organic solvent contained in the non-aqueous coating liquid penetrates into the amorphous portion of the polyolefin microporous monolayer film or the heat-treated porous body, thereby promoting the silane crosslinking reaction of the silane-modified polyolefin.

[0175] The coating liquid for forming the thermoplastic polymer-containing layer contains a thermoplastic polymer, and the thermoplastic polymer preferably contains at least one selected from the group consisting of polymerized units of (meth)acrylic acid ester and / or (meth)acrylic acid, polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE).

[0176] The coating liquid for forming the active layer contains a fluorine atom-containing polyvinyl compound, and the fluorine atom-containing polyvinyl compound is preferably at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE).

[0177] The coating liquid may contain, as desired, a resin binder, inorganic particles or inorganic filler, a dispersant, a surfactant, a solvent, etc. The coating liquid for forming the inorganic porous layer contains inorganic particles and a resin binder.

[0178] Examples of the resin binder include the following: Polyolefin resins such as polyethylene, polypropylene, and α-polyolefin; Fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene, or copolymers containing these; Diene-based polymers containing conjugated dienes such as butadiene and isoprene as monomer units, copolymers containing these, or hydrogenated products thereof; an acrylic polymer containing a (meth)acrylate, (meth)acrylic acid, or the like as a monomer unit and having no polyalkylene glycol unit, an acrylic polymer containing a (meth)acrylate, (meth)acrylic acid, or the like as a monomer unit and having one or two polyalkylene glycol units, or a copolymer containing these, or a hydrogenated product thereof; Rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; Polyalkylene glycols having no polymerizable functional groups, such as polyethylene glycol and polypropylene glycol; Resins such as polyphenylene ether, polyphenylene sulfide, and polyester; A copolymer having, as a copolymerization unit, an ethylenically unsaturated monomer having a repeating number of alkylene glycol units of 3 or more; and combinations of these; or the thermoplastic polymers mentioned above can be used. Among these, from the viewpoint of improving safety in a puncture test of a battery including the separator, it is preferable that the resin binder contains polymerized units of a (meth)acrylic acid ester and / or (meth)acrylic acid.

[0179] The resin binder described above can be produced by a known polymerization method using the corresponding monomer or comonomer, such as solution polymerization, emulsion polymerization, or bulk polymerization.

[0180] For the resin binder, it is preferred to form a particulate binder polymer by emulsion polymerization, and use the resulting polymer emulsion as the water-based latex.

[0181] The coating liquid for forming the inorganic porous layer, active layer, or heat-resistant resin layer contains inorganic particles or inorganic fillers. The inorganic particles or inorganic fillers are not particularly limited, but include, for example, oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum oxide hydroxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. These may be used alone or in combination.

[0182] Among these, from the viewpoint of improving the electrochemical stability and heat resistance of the separator, at least one selected from the group consisting of alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, silicon nitride, titanium nitride, boron nitride, silicon carbide, aluminum oxide hydroxide, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, diatomaceous earth, silica sand, and glass fiber is preferred, and aluminum oxide compounds such as alumina and aluminum oxide hydroxide; and aluminum silicate compounds having no ion exchange capacity such as kaolinite, dickite, nacrite, halloysite, and pyrophyllite are more preferred.

[0183] Alumina exists in many crystalline forms, such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of these can be suitably used. Among these, α-alumina is preferred because it is thermally and chemically stable.

[0184] As the aluminum oxide compound, aluminum oxide hydroxide (AlO(OH)) is particularly preferred. As the aluminum oxide hydroxide, boehmite is more preferred from the viewpoint of preventing internal short circuits caused by the generation of lithium dendrites. For example, by using particles containing boehmite as the inorganic filler constituting the heat-resistant resin layer, a very lightweight porous layer can be realized while maintaining high permeability. In addition, even in a thinner porous layer, thermal shrinkage of the microporous film at high temperatures is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite, which can reduce ionic impurities that adversely affect the characteristics of electrochemical devices, is even more preferred.

[0185] The content of inorganic particles contained in the coating liquid for forming the inorganic porous layer is preferably 5% by mass to 99% by mass, and more preferably 10% by mass or more but less than 99% by mass, based on the mass of the total solid content of the coating liquid.

[0186] The inorganic filler contained in the coating liquid for forming the heat-resistant resin layer preferably has an average particle size of 0.2 μm to 0.9 μm, and / or the content of the inorganic filler in the coating liquid is preferably 30% by mass to 90% by mass based on the mass of the total solid content of the coating liquid.

[0187] Examples of dispersants contained in the coating liquid include aqueous solutions of ammonium polycarboxylate, etc. Examples of surfactants contained in the coating liquid include emulsifiers and soaps.

[0188] Examples of the solvent contained in the coating liquid include water (e.g., ion-exchanged water, pure water, etc.), aqueous solvents (e.g., a mixture of water and alcohol, etc.), organic solvents, etc. Examples of the organic solvent that can be used include alcohol, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), ethanol, toluene, hot xylene, methylene chloride, and hexane.

[0189] Examples of methods for preparing a coating liquid containing inorganic particles or an inorganic filler include mechanical stirring methods using a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and a stirring blade.

[0190] Examples of methods for applying a coating liquid containing inorganic particles or an inorganic filler include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, and spray coating method.

[0191] The coating step (5D) may include a step of placing the coated film in an atmosphere with a humidity of 50% or more after the formation of the coated film, or a step of blowing steam onto the coated surface. By providing humidity to the coated surface, precipitation of the aramid resin can be promoted.

[0192] In the drying step (6), the solvent is removed from the coating film formed in the coating step (5). Methods for removing the solvent include drying at a temperature below the melting point of the material constituting the microporous membrane, drying under reduced pressure at a low temperature, and substituting the solvent contained in the coating liquid with another solvent followed by drying. Furthermore, some of the solvent may remain as long as it does not significantly affect the characteristics of the nonaqueous secondary battery. Methods for substituting the solvent contained in the coating liquid with another solvent include immersing the film in the other solvent described above and spraying the other solvent described above onto the film.

[0193] In the water washing step (5.5), the solvent in the coating film formed in the coating step (5) may be replaced with another solvent. Examples of the solvent before replacement include DMF, DMA, NMP, DMSO, etc., and examples of the solvent after replacement include water, alcohol, etc.

[0194] The method for producing a separator may optionally include a winding / slitting step, in which the obtained microporous membrane is slit as necessary and wound around a predetermined core.

[0195] In the assembly step (7), the laminate of electrodes and separators or a wound body thereof, and the nonaqueous electrolyte are housed in an outer casing. Step (7) can be performed in the same manner as in the manufacture of a nonaqueous secondary battery described below, and the electrodes, nonaqueous electrolyte, and outer casing used in step (7) may be those described for a nonaqueous secondary battery.

[0196] In the coating step (5) and / or the water-washing step (5.5) and / or the drying step (6) and / or the assembling step (7), preferably in the coating step (5), the water-washing step (5.5), the drying step (6) and the assembling step (7), the silane-modified polyolefin contained in the separator forms a crosslinked structure.

[0197] The separator obtained by the method including the various steps described above can be used in a non-aqueous secondary battery including a positive electrode and a negative electrode capable of absorbing and desorbing lithium and a non-aqueous electrolyte solution obtained by dissolving an electrolyte in a non-aqueous solvent, and preferably can be used in a lithium secondary battery or a lithium ion secondary battery.

[0198] <Non-aqueous secondary battery> A non-aqueous secondary battery is constructed by housing a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution in any battery exterior.

[0199] The positive electrode is connected to a positive electrode lead body within the non-aqueous secondary battery, and the negative electrode is connected to a negative electrode lead body within the non-aqueous secondary battery. One end of each of the positive electrode lead body and the negative electrode lead body is drawn out to the outside of the battery exterior body so that they can be connected to external devices, etc., and their ionomer portions are heat-sealed to one side of the battery exterior body.

[0200] The positive electrode is composed of a positive electrode current collector and a positive electrode active material layer. The negative electrode is composed of a negative electrode current collector and a negative electrode active material layer. The positive electrode active material layer contains a positive electrode active material, and the negative electrode active material layer contains a negative electrode active material. The positive electrode and negative electrode are arranged with the positive electrode active material layer and the negative electrode active material layer facing each other via a separator.

[0201] As the positive electrode, known battery positive electrodes can be used, and from the viewpoint of the effects of the present invention, positive electrodes that easily decompose or release O2 can also be used. Also, composite positive electrode active materials of lithium and other metals can be used, and composite positive electrodes of lithium and at least one metal selected from the group consisting of nickel, manganese, and cobalt, such as LNO positive electrodes, NCA positive electrodes, LCO positive electrodes, and positive electrodes containing lithium (Li)-nickel (Ni)-manganese (Mn)-cobalt (Co) composite oxide as the positive electrode active material (NMC positive electrodes), can also be used.

[0202] Among these, from the viewpoint of the effects of the present invention, an NMC positive electrode is preferred, and among NMC positive electrodes, one having a relatively high nickel content is more preferably used, and the molar ratio of the amount of nickel (Ni) to the total amount of nickel, manganese, and cobalt in the positive electrode is more preferably 3 to 9, 5 to 9, 6 to 9, 5 to 8, or 6 to 8, and particularly preferably 5 to 9. Specifically, the formula: Li-Ni x -Mn y -Co z For a positive electrode containing a lithium (Li)-nickel (Ni)-manganese (Mn)-cobalt (Co) composite oxide represented by the formula {wherein x represents the Ni proportion, y represents the Mn proportion, z represents the Co proportion, and x+y+z=1}, the Ni proportion x in the formula is preferably 5 to 9.

[0203] The positive electrode current collector can be made of a metal foil such as aluminum foil, nickel foil, or stainless steel foil.

[0204] Examples of the negative electrode active material constituting the negative electrode include carbon materials such as hard carbon, graphite, pyrolytic carbon, coke, glassy carbon, baked bodies of organic polymer compounds, microbeads, carbon fiber, activated carbon, carbon colloid, and carbon black, as well as metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon (Si)-containing materials, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, organic polymer compounds, etc. The negative electrode active material may be used alone or in combination of two or more.

[0205] Among these, from the viewpoint of the effects of the present invention, Si-containing materials are preferred as the negative electrode active material, such as silicon, Si alloys, Si oxides, etc. From the same viewpoint, the Si content in the negative electrode active material is preferably 5 to 90 mol %.

[0206] It is known that Si-containing negative electrode active materials have significantly improved lithium ion storage capacity compared to carbonaceous negative electrodes. At the same time, as lithium ions are charged and discharged to and from the Si-containing particles, the Si-containing negative electrode active material undergoes significant volume expansion and contraction, as shown in Non-Patent Document 2. During this process, the battery internal volume remains constant, and the separator is significantly compressed or deformed in the thickness direction by the Si-containing negative electrode active material. According to the present invention, by adjusting the type and composition of the resin raw materials, optimizing the various values ​​described above for SAXS and / or WAXS measurements of the separator and Voronoi tessellation, it has been discovered that, even when the separator is compressed or deformed in the thickness direction in a non-aqueous secondary battery, permeability can be maintained, a good balance between strength and ion diffusivity can be achieved, and the crush test pass rate, cycle test capacity retention rate, and high-temperature cycle life of the non-aqueous secondary battery can be improved, and / or a balance thereof can be achieved.

[0207] Furthermore, the separator discovered by the present invention, which has a structure in which Si atoms are dispersed in a state other than a sea-island structure, allows the intercalation reaction of the Si-containing negative electrode active material to proceed uniformly, as described above, leading to uniform expansion and contraction of the Si-containing negative electrode active material inside the battery, and suppressing misalignment of the wound structure inside the battery, thereby achieving improvements in battery cycle performance and battery safety.

[0208] The negative electrode current collector can be made of a metal foil such as copper foil, nickel foil, or stainless steel foil.

[0209] <Non-aqueous electrolyte> In this specification, a non-aqueous electrolyte solution refers to an electrolyte solution containing an electrolyte in a non-aqueous solvent, with the amount of water being 1% by mass or less based on the total mass. The non-aqueous electrolyte solution preferably contains as little water as possible, but may contain a very small amount of water. The water content is preferably 300 ppm by mass or less, more preferably 200 ppm by mass or less, based on the total amount of the non-aqueous electrolyte solution.

[0210] The electrolyte in the battery may contain water, and the water contained in the system after the battery is fabricated may be water contained in the electrolyte or water carried over from components such as electrodes or separators. The electrolyte may contain a non-aqueous solvent. Examples of solvents contained in the non-aqueous solvent include alcohols such as methanol and ethanol; aprotic solvents, etc. Among these, aprotic solvents are preferred as the non-aqueous solvent.

[0211] Examples of aprotic solvents include cyclic carbonates, fluoroethylene carbonates, lactones, organic compounds having sulfur atoms, chain fluorinated carbonates, cyclic ethers, mononitriles, alkoxy group-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, chain ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the above aprotic solvents have been substituted with halogen atoms.

[0212] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, cis-2,3-pentylene carbonate, vinylene carbonate, 4,5-dimethylvinylene carbonate, and vinylethylene carbonate.

[0213] Examples of fluoroethylene carbonate include 4-fluoro-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one, cis-4,5-difluoro-1,3-dioxolan-2-one, trans-4,5-difluoro-1,3-dioxolan-2-one, 4,4,5-trifluoro-1,3-dioxolan-2-one, 4,4,5,5-tetrafluoro-1,3-dioxolan-2-one, and 4,4,5-trifluoro-5-methyl-1,3-dioxolan-2-one.

[0214] Examples of lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone.

[0215] Examples of organic compounds having a sulfur atom include ethylene sulfite, propylene sulfite, butylene sulfite, pentene sulfite, sulfolane, 3-sulfolene, 3-methyl sulfolane, 1,3-propane sultone, 1,4-butane sultone, 1-propene 1,3-sultone, dimethyl sulfoxide, tetramethylene sulfoxide, and ethylene glycol sulfite.

[0216] Examples of the chain carbonate include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, and ethyl propyl carbonate.

[0217] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane.

[0218] Examples of mononitriles include acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile.

[0219] Examples of alkoxy-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile.

[0220] Examples of dinitriles include malononitrile, succinonitrile, methylsuccinonitrile, glutaronitrile, 2-methylglutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, 2,4-dimethylglutaronitrile, and ethylene glycol bis(propionitrile) ether.

[0221] Examples of cyclic nitriles include benzonitrile.

[0222] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, and isopropyl pivalate. , isopropyl hydroangelate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyl isobutyrate, isobutyl butyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelate, and tert-butyl caproate.

[0223] Examples of chain ethers include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme. Examples of fluorinated ethers include those represented by the general formula Rf aa -OR bb (In the formula, Rf aa is an alkyl group containing a fluorine atom, and R bb is an organic group which may contain a fluorine atom). Examples of ketones include acetone, methyl ethyl ketone, and methyl isobutyl ketone.

[0224] Examples of the compounds in which some or all of the H atoms of the above aprotic solvents have been substituted with halogen atoms include compounds in which the halogen atoms are fluorine atoms.

[0225] Examples of fluorinated chain carbonates include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethylmethyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The fluorinated chain carbonates are represented by the following general formula: R cc -OC(O)OR dd {where, R cc and R dd is CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and the formula CH2Rf ee (In the formula, Rf ee is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom), and R cc and / or R dd contains at least one fluorine atom. It can be expressed as:

[0226] In addition, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters are represented by the following general formula: R ff -C(O)OR gg {where, R ff is CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2H, CF2Rf hh , CFHRf hh, and CH2Rf ii and R is at least one selected from the group consisting of gg are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf ii and Rf hh is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom may be substituted with at least one fluorine atom, and Rf ii is an alkyl group having 1 to 3 carbon atoms in which a hydrogen atom is substituted with at least one fluorine atom, and R ff and / or R gg contains at least one fluorine atom, and R ff If is CF2H, R gg can be expressed as {is not CH3}.

[0227] From the viewpoint of the effects of the present invention, the non-aqueous electrolyte preferably contains ethyl methyl carbonate (EMC) and / or acetonitrile (AcN) as a non-aqueous solvent, and / or the total content of EMC and AcN in the non-aqueous electrolyte preferably falls within the range of 50% by mass to 90% by mass.

[0228] The electrolyte is preferably a lithium salt, and from the viewpoint of promoting the silane crosslinking reaction, a fluorine-containing lithium salt that generates hydrogen fluoride (HF) is more preferable. Examples of fluorine-containing lithium salts include lithium hexafluorophosphate (LiPF), lithium fluorosulfonate (LiFSO), lithium bis(trifluoromethanesulfonyl)imide (LiN(SOCF), lithium bis(fluorosulfonyl)imide (LiN(SOF), lithium fluoroborate (LiBF), and lithium bis(oxalatoborate) (LiBCO). Without being bound by theory, for example, when the electrolyte contains LiPF, LiPF reacts with small amounts of water contained in the power storage device (e.g., water contained in components such as electrodes, separators, and electrolyte) to produce HF or a fluorine-containing organic substance derived from HF. It is believed that these HFs or fluorine-containing organic substances derived from HF dissolve in the electrolyte solution, swell, and diffuse into the amorphous portion of the polyolefin having crosslinkable silane groups, thereby catalyzing the silane crosslinking reaction.

[0229] From the viewpoint of the effects of the present invention, the nonaqueous electrolyte preferably contains a relatively high concentration of lithium salt. It is more preferable to contain the lithium salt at a concentration in the range of 1.2 mol / L to 10 mol / L, more preferably at a concentration of 1.5 mol / L or higher, and particularly preferably at a concentration of 3.0 mol / L or higher. In particular, in nonaqueous secondary battery systems containing lithium hexafluorophosphate (LiPF6) as the electrolyte, the phosphorus atom exists as a certain concentration of dissociated F anions or lithium fluoride (LiF) in the system due to the Jahn-Teller effect. While dissociated F anions are generally known to reduce battery life, such as electrode corrosion, LiF exhibits a stronger Lewis acid effect when attached to Si than before, thereby making the above-mentioned phenomena (a) and (b) more pronounced and ultimately resulting in good low-temperature cycle characteristics. It is preferable to select a combination of electrolyte and electrolyte so that the lithium salt concentration does not exceed its saturated solubility concentration.

[0230] In addition to the above, the non-aqueous electrolyte may contain, as a catalyst for the silane crosslinking reaction, a substance (acid source) such as an inorganic acid or organic acid that reacts with the non-aqueous electrolyte and / or trace amounts of water contained therein to generate hydrogen ions, or a substance (alkali source) that reacts with the non-aqueous electrolyte and / or trace amounts of water contained therein to generate hydroxide ions. Examples of alkali sources include alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkali metal phosphates, ammonia, and amine compounds. Among these, from the viewpoints of safety and silane crosslinking ability of the power storage device, alkali metal hydroxides or alkaline earth metal hydroxides are preferred, alkali metal hydroxides are more preferred, and sodium hydroxide is even more preferred.

[0231] The battery exterior of the non-aqueous secondary battery may have a known structure, for example, a battery can or a laminate film exterior.

[0232] The shape of the non-aqueous secondary battery may be, for example, a square type, a rectangular cylinder type, a cylindrical type, an elliptical type, a button type, a coin type, a flat type, a laminate type, or the like.

[0233] The nonaqueous secondary battery can be produced in the same manner as known production methods, except that the above-described nonaqueous electrolyte solution, positive electrode, negative electrode, separator, and battery outer casing are used. [Example]

[0234] The present invention will be described in more detail below with reference to examples, but is not limited to these examples. The physical properties in the examples were measured by the following methods. For the substrate basis weight, substrate film thickness, substrate porosity, substrate air permeability, substrate pin puncture strength, SAXS, WAXS, NMR, and TOF-SIMS, measurements were taken after scraping off a coating layer from the substrate if present. For the crush test pass rate, cycle test capacity retention rate, and cycle life test, measurements were taken without scraping off the coating layer even if present on the substrate. Battery evaluation tests (crush test, cycle capacity retention rate, and high-temperature cycle life) were all performed 4 days after the coating liquid was applied to the separator.

[0235] <Method for detecting silane-modified polyolefin contained in separator> When the silane-modified polyolefin contained in the separator is crosslinked, it is insoluble or has insufficient solubility in organic solvents, making it difficult to measure the content of the silane-modified polyolefin directly from the separator. In such cases, sample pretreatment can be performed using methyl orthoformate, which does not cause side reactions, to decompose the siloxane bonds into methoxysilanols, followed by solution NMR measurement to detect the silane-modified polyolefin contained in the separator or GPC measurement. Pretreatment experiments can be performed with reference to Japanese Patent Publication Nos. 3529854 and 3529858. After the depolymerization reaction, thermal analysis such as TMA and DMA is also possible.

[0236] Specifically, the silane-modified polyolefin used as a raw material for separator production 1 H or 13 The NMR identification of C can be used to detect silane-modified polyolefins contained in separators. 1 H and 13 An example of a C NMR measurement technique is described below.

[0237] ( 1 H NMR measurement) The sample was dissolved in o-dichlorobenzene-d4 at 140°C, and the proton resonance frequency was 600 MHz.1 Obtain a H-NMR spectrum. 1 The H-NMR measurement conditions are as follows: Equipment: Bruker AVANCE NEO 600 Sample tube diameter: 5mmφ Solvent: o-dichlorobenzene-d4 Measurement temperature: 130℃ Pulse angle: 30° Pulse waiting time: 1 sec Accumulation count: 1000 times or more Sample concentration: 1 wt / vol%

[0238] ( 13 C NMR measurement) The sample was dissolved in o-dichlorobenzene-d4 at 140°C. 13 Obtain a C-NMR spectrum. 13 The measurement conditions for C-NMR are as follows: Equipment: Bruker AVANCE NEO 600 Sample tube diameter: 5mmφ Solvent: o-dichlorobenzene-d4 Measurement temperature: 130℃ Pulse angle: 30° Pulse waiting time: 5 seconds Accumulation count: 10,000 times or more Sample concentration: 10 wt / vol%

[0239] 1 H and / or 13 C NMR measurement can be used to confirm the amount of silane unit modification in the silane-modified polyolefin, the amount of alkyl group modification in the polyolefin, the C4 unit modification rate (mol%), and the number of methylene (CH2) groups in the silane graft linkages in the polyolefin raw material, and can also be used to identify the presence of silane-modified polyolefin in the separator. The degree of modification of the silanol unit in resin A was quantified by the NMR chemical shift and integral value of the methylene next to the Si atom (-CH2-Si: 1 H, 0.69 ppm, t; 13C, 6.11 ppm, s) can be determined. Propylene-modified (C3) can be quantified by the NMR chemical shift and integral value of the terminal methyl group (-CH3: 13 C, 19.42 ppm, s) can be determined. Butene modification (C4) can be quantified by the NMR chemical shift and integral value of the terminal methyl group (-CH3: 13 C, 10.63 ppm, s) is possible.

[0240] <Weight average molecular weight and number average molecular weight> A calibration curve was created by measuring standard polystyrene under the following conditions using a Waters ALC / GPC 150C (trademark). Chromatograms of the following polymers were also measured under the same conditions, and the weight-average molecular weight of each polymer was calculated based on the calibration curve using the following method. Column: Tosoh GMH6-HT (trademark) x 2 + GMH6-HTL (trademark) x 2 Mobile phase: o-dichlorobenzene Detector: Differential refractometer Flow rate: 1.0ml / min Column temperature: 140℃ Sample concentration: 0.1 wt%

[0241] (Weight-average molecular weight and number-average molecular weight of polyethylene, polypropylene, and silane-modified polyolefin) Each molecular weight component in the calibration curve was multiplied by 0.43 (polyethylene Q factor / polystyrene Q factor = 17.7 / 41.3) or 0.64 (polypropylene Q factor / polystyrene Q factor = 26.4 / 41.3) to obtain a polyethylene-equivalent or polypropylene-equivalent molecular weight distribution curve, from which the weight-average molecular weight and number-average molecular weight were calculated. Note that the same Q factor as polyethylene was used for silane-modified polyethylene, and the same Q factor as polypropylene was used for silane-modified polypropylene. (Weight average molecular weight of resin composition) The weight average molecular weight was calculated using the Q factor value of the polyolefin with the largest mass fraction, in the same manner as for polyethylene.

[0242] <Viscosity average molecular weight (Mv)> The intrinsic viscosity [η] in decalin solvent at 135°C was determined according to ASTM-D4020. The Mv of polyethylene and silane-modified polyethylene was calculated using the following formula: [η]=6.77×10 -4 Mv 0.67 The Mv of polypropylene was calculated using the following formula. [η]=1.10×10 -4 Mv 0.80

[0243] <Melt mass-flow rate (MFR) (g / 10 min)> Using a Toyo Seiki melt mass flow rate measuring instrument (Melt Indexer F-F01), polyethylene and silane-modified polyethylene were extruded for 10 minutes at 190°C under a load of 2.16 kg, and the weight of the resin was determined as the MFR value. Polypropylene and silane-modified polypropylene were measured at 230°C.

[0244] <Film thickness (μm)> The thickness of the microporous membrane was measured using a micro thickness gauge, KBM (trademark), manufactured by Toyo Seiki Seisaku-sho, at room temperature of 23±2°C and a relative humidity of 60%. Specifically, the thickness was measured at five points at approximately equal intervals across the entire width in the TD direction, and the average value was obtained. The coating thickness is calculated by observing the cross section or side surface at any magnification using an SEM.

[0245] <Porosity (%) and substrate porosity (%)> A 10cm x 10cm square sample was cut from the microporous membrane and its volume (cm 3 ) and mass (g), and then calculate the density (g / cm 3 ) and the porosity was calculated using the following formula: The density of the mixed composition was determined by calculation from the density of each of the raw materials used and the mixing ratio. Porosity (%) = (volume - mass / density of mixed composition) / volume × 100

[0246] <Air permeability (sec / 100cm 3 ) and base material air permeability (sec / 100cm 3 )> In accordance with JIS P-8117 (2009), the air permeability of the sample was measured using the Oken air permeability and smoothness tester, EGO1-55-1MR (trademark), manufactured by Asahi Seiko Co., Ltd.

[0247] <Puncture strength (gf) and base material puncture strength (gf)> Using a handy deformation tester "KES-G5" (manufactured by Kato Tech Co., Ltd., trademark), the puncture strength of the microporous membrane was determined by conducting a puncture test under the conditions of a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / sec.

[0248] <SAXS (transmission method) measurement and crystal long period (nm)> Small-angle X-ray scattering (SAXS) by the transmission method of the microporous membrane made of polyolefin as the separator base material was measured under the following conditions. (Measurement) Using a Nano-Viewer manufactured by Rigaku Corporation, small-angle X-ray scattering (SAXS) measurement by the transmission method was performed. CuKα rays were irradiated onto the separator base material as the sample (however, the X-ray incident direction was parallel to the film thickness direction of the sample), and scattering was detected by PILATUS 100K manufactured by DECTRIS. The measurement was carried out under the conditions of a distance of 841.5 mm between the sample and the detector, an output of 60 kV, and 45 mA. The optical system adopted a point focus, and the slit diameters were 1st slit: ψ = 0.4 mm, 2nd slit: ψ = 0.2 mm, and guard slit: = 0.8 mm. As a pretreatment for the measurement, in order to reduce scattering due to particle size, a slurry was prepared by mixing the sample and propylene glycol at a weight ratio of 1:1 and measured.

[0249] (Analysis: Crystal long period (nm)) Regarding the obtained peaks, the analysis of the crystal long period was carried out by the following method. For the X-ray scattering pattern obtained from the imaging plate, air cell scattering correction was performed, and a one-dimensional SAXS profile I(q) was obtained by circular averaging. Here, q is the absolute value of the scattering vector. To calculate the crystal long period d, the square of the absolute value of the scattering vector was multiplied by the SAXS profile to emphasize the scattering derived from the crystal long period. Subsequently, the square of the absolute value of the scattering vector multiplied by the SAXS profile and the absolute value of the scattering vector were each logarithmically plotted with base 10 as the vertical and horizontal axes. The horizontal axis is log 10 q, and the vertical axis is log 10 (I(q)×q2). For the plotted data, a tangent line was drawn that touches one point each on the small-angle side and the wide-angle side from the peak position derived from the lamella, and an operation of subtracting the tangent line from the data was performed. Subsequently, the horizontal axis position Xm at which the maximum value is taken between the two contact points was determined. Finally, the crystal long period d was determined by the following formula. qm = 10 Xm d = 2π / qm

[0250] <WAXS (reflection method) and MD, TD cross-section crystal orientation degree (%)> Wide-angle X-ray scattering (WAXS) by the reflection method of the polyolefin microporous membrane as the separator substrate was measured under the following conditions. (Measurement) Using the X-ray structure evaluation apparatus NANO-Viewer manufactured by Rigaku Corporation, wide-angle X-ray scattering measurement by the reflection method was performed. The sample was irradiated with CuKα rays, and the scattering was detected by an imaging plate. Wide-angle X-ray scattering measurement was performed under the conditions of a sample-detector distance of 95.2 mm, an output of 60 kV, and 45 mA. A point focus was adopted for the optical system, and the measurement was performed under the conditions of a 1st slit: φ = 0.4 mm and a 2nd slit: φ = 0.2 mm for the slit diameter. The sample was set so that the sample cross-section and the X-ray incident direction formed an angle of 10.5°. Since the measurement accuracy cannot be obtained when the thickness of the microporous membrane is thin, the measurement is performed after stacking to a film thickness that can obtain sufficient intensity as needed.

[0251] (Analysis: MD, TD cross-section crystal orientation degree (%)) Among the directions of the sample surface normal, the direction facing the upstream side is projected onto the detector surface, and the direction is defined as the azimuth angle φ = 0°. On the detector surface, it is defined clockwise from φ = -180° to φ = 180°. Subsequently, background correction of the detector and air cell scattering correction were performed on the X-ray scattering pattern obtained from the imaging plate. Then, the integrated intensity I(φ) in the range of 19.5° < 2θ < 21.3° where the (110) plane diffraction peak of polyethylene exists at each azimuth angle φ is plotted against the azimuth angle φ in the range of azimuth angle -45° < φ < 45°. I(φ) becomes a single peak centered at φ = 0° when the molecular chains are oriented parallel to the film surface in the cross-section. This curve was fitted with the sum of a constant and a Gaussian function as shown in Equation 2, and the cross-sectional orientation degree f’ was calculated according to Equation 3 from the full width at half maximum of the Gaussian function in the fitting result. I(φ)=A + B×exp(-((φ - φ0) / w)2) Equation 2 Explanation of symbols in Equation I(φ): Integrated intensity in the range of 19.5° < 2θ < 21.3° at a certain azimuth angle φ after background correction and air cell scattering correction φ: Azimuth angle (rad) f’ = 1 - FWHM / 180 Equation 3 Explanation of symbols in Equation f: Cross-sectional orientation degree FWHM: Full width at half maximum of the Gaussian function obtained from the fitting result (°)

[0252] <WAXS (transmission method) measurement, crystallinity (%), crystallite size (110) (nm), crystallite size (200) (nm), and crystal orientation degree in the film thickness direction (%)> Wide-angle X-ray scattering (WAXS) by the transmission method of the polyolefin microporous membrane as a separator substrate was measured under the following conditions. (Measurement) Wide-angle X-ray scattering measurements were performed using the transmission method with a Rigaku NANO-Viewer X-ray structure evaluation system. The sample was irradiated with CuKα radiation, and scattering was detected using an imaging plate. Wide-angle X-ray scattering measurements were performed under conditions of a sample-to-detector distance of 95.2 mm, output of 60 kV, and 45 mA. A point focus was used for the optical system, and measurements were performed under conditions of slit diameters of 1st slit: φ = 0.4 mm and 2nd slit: φ = 0.2 mm. The sample was set so that the angle between the sample surface and the X-ray incidence direction was 10.5°. Since precision is poor when the microporous membrane is thin, measurements are performed after stacking the membrane as necessary to achieve a thickness that provides sufficient strength.

[0253] (Analysis: Crystallite size (110) (nm) and Crystallite size (200) (nm) and Crystallinity %) The X-ray scattering pattern obtained from the imaging plate was separated into three peaks: the orthorhombic (110) diffraction peak, the orthorhombic (200) diffraction peak, and the amorphous peak, from the full width at half maximum of the (110) diffraction peak using the Scherrer equation (Equation 1). The (110) and (200) diffraction peaks were approximated with a Voigt function, and the amorphous peak was approximated with a Gaussian function. The position of the amorphous peak was fixed at 2θ = 19.6° and the full width at half maximum was 6.3°, while the position and full width at half maximum of the crystalline peak were not fixed. The crystallite size was calculated from the full width at half maximum of the (110) diffraction peak calculated by peak separation using the Scherrer equation (Equation 1). D(110 or 200) = Kλ / (βcosθ) Equation 1 Explanation of symbols in formula 1 D (110 or 200): Crystallite size (nm) K: 0.9 (constant) λ: X-ray wavelength (nm) β:(β1 2 -β2 2 )0.5 β1: Full width at half maximum (rad) of the (hkl) peak calculated as a result of peak separation β2: Full width at half maximum of the incident beam divergence (rad) θ: Bragg angle

[0254] The crystallinity (X) was calculated using the following formula. Crystallinity X={I(110)+I(200)} / {I(110)+I(200)+Iamr}×100 Iamr: Area of ​​amorphous peak

[0255] The crystallite size ratio (110) / (200) is calculated by the following formula using the crystallite size calculated by formula 1. Crystallite size ratio (110) / (200) = (crystallite size (110) [nm]) / (crystallite size (200) [nm])

[0256] <Amorphous thickness (nm) and crystalline thickness (nm)> Using the SAXS crystal long period and WAXS crystallinity measured by the above methods, the amorphous thickness (nm) and crystalline thickness (nm) were calculated according to the following formula. Amorphous thickness [nm] = (crystalline long period [nm]) × (1 - crystallinity [%] / 100)

[0257] <Substrate separator TOF-SIMS analysis and image processing> (I) TOF-SIMS analysis of separator The separators obtained in the examples and comparative examples were subjected to TOF-SIMS analysis. A nano-TOF manufactured by ULVAC-PHI, Inc. was used as the TOF-SIMS mass spectrometer. The analysis conditions were as follows: (Image measurement conditions) Primary ion: Bismuth (Bi) Accelerating voltage: 30 kV Ion current: Approx. 0.5nA (DC) Analysis area: 100μm x 100μm Analysis time: 90 minutes Detected ion: positive ion (m / z=28) Neutralization: Electron gun + Ar monomer ion Vacuum degree: approx. 5.0×10 -5 Pa (oxygen is introduced to increase the detection intensity of Si) (Measurement conditions in the depth direction) 《Analysis conditions》 Primary ion: Bismuth (Bi) Accelerating voltage: 30 kV Ion current: Approx. 1.2nA (DC) Analysis area: 100μm x 100μm Analysis time: 5 frames / cycle Detected ion: positive ion (m / z=28) Neutralization: Electron gun + Ar monomer ion Vacuum degree: approx. 5.0×10 -5 Pa (oxygen is introduced to increase the detection intensity of Si) <Sputtering conditions> Sputter ion: GCIB (Ar 2500 + ) Accelerating voltage: 20 kV Ion current: approx. 5nA Sputtering area: 400 μm x 400 μm Sputtering time: 30 seconds / cycle Neutralization: Electron gun + Ar monomer ion

[0258] Under the above conditions, spectral detection of Si ions (corresponding to positive ions with m / z=28) was performed. As an example, the TOF-SIMS analysis results of the separator of Example 1 are shown in FIG. 1, and the TOF-SIMS analysis results of the separator of Comparative Example 1 are shown in FIG. 11. The units of the vertical and horizontal axes in FIG. 1 and FIG. 11 are also in pixels.

[0259] (II) Image Processing The TOF-SIMS spectrum image data obtained as described above was subjected to image processing according to the following procedure. (1) Create a filter that matches the beam shape (diameter 2 μm, pixel resolution 0.39 μm). A 3D image of the filter is shown in Figure 2, and a 2D image is shown in Figure 3. The filter value h1 is shown in Table 1 below. Note that the units of the vertical and horizontal axes in Figure 2 are pixels, and the units of each axis in Figure 3 are pixels.

[0260] [Table 1]

[0261] (How filter values ​​are calculated) The calculation was performed using the function fspecial in the Image Processing Toolbox of the numerical calculation software MATLAB (registered trademark) manufactured by Mathworks. fspecia(``gaussian'',

[1313] ,1.69865)

[0262] (2) Apply the created filter to the two-dimensional data. (3) Calculate the mean and standard deviation of the two-dimensional data after applying the filter. (4) Binarize using the mean value + standard deviation x 3 as the threshold value. (However, in the case of a normal distribution, 99.74% of the values ​​fall within the range of the mean value + 3 times the standard deviation, so the intention was to extract numerically anomalous parts.)

[0263] (5) Dilation and contraction of 7 pixels are performed to connect adjacent extracted regions. (6) Remove small areas (less than 50 pixels). (7) Calculate the parameters for each remaining region. Extraction area (pixels), simple center of gravity position (x0, y0) Maximum value in the region, average value in the region, weighted center of gravity position (xm, ym)

[0264] (8) Calculate the distance between each weighted center of gravity position The calculation was performed using the WeightedCentroid option of the regionprops function in the Image Processing Toolbox of the numerical calculation software MATLAB manufactured by Mathworks. regionprops(cc,I,'WeightedCentroid') Here, cc is a variable indicating the extracted region, and I is a variable storing the two-dimensional data after the filter is applied.

[0265] As an example, the TOF-SIMS analysis results of the separator after image processing in the above steps (1) and (2) are shown in Fig. 4 (Example 1) and Fig. 12 (Comparative Example 1), and the results after image processing in the above steps (1) to (6) are shown in Fig. 5 (Example 1) and Fig. 13 (Comparative Example 1). The units of the vertical and horizontal axes in Fig. 4 are pixels, the units of the vertical and horizontal axes in Fig. 12 are pixels, the units of the vertical and horizontal axes in Fig. 5 are pixels, and the units of the vertical and horizontal axes in Fig. 13 are pixels.

[0266] (III) Voronoi tessellation Voronoi division was performed based on the weighted center of gravity position (xm, ym) calculated earlier to obtain the Voronoi region, and its area was calculated. The calculation was performed using the numerical calculation software MATLAB from Mathworks.

[0267] The Voronoi region diagram shown in Fig. 6 (Example 1) or Fig. 14 (Comparative Example 1) can be obtained by the following calculation procedure. Note that the units of the vertical and horizontal axes in Fig. 6 are pixels, and the units of the vertical and horizontal axes in Fig. 14 are pixels. VXB and VYB are temporary variables used in the calculation. [VXB,VYB]=voronoi(xm,ym); plot(VXB,VYB,'-b',xm,ym,'.r'); The calculation of the region and its area by Voronoi division was carried out according to the following procedure. First, the following calculation procedure is carried out. DTB=delaunayTriangulation([xm,ym]); [VB,rB]=voronoiDaigram(DTB); DTB is a temporary variable used during the calculation, and delaunayTriangulation(xm,ym) is a function that creates the Delaunay triangulation, which is an element of that temporary variable. VB is a matrix variable that stores a list of positions indicating the positions of the endpoints of the triangles that make up the Voronoi tessellation, and rB is a list of columns that indicate which endpoints in VB each Voronoi tessellated region uses. Next, the following calculation is performed on each Voronoi region indicated by each column of rB in the order of the columns. The calculation is performed on the columns of the list indicated in rB in order from 1 to the end. The calculation for the kth column of the list is performed as follows:

[0268] (1) If the endpoints of VB indicated by the kth list rB{k} of rB include points that correspond to the outside of the image area, that area is excluded from the calculation as an unclosed area. This is because areas that contact the edge of the image include a boundary called the edge of the image, which is not a Voronoi tessellation that indicates an island structure, and therefore this area is considered to not have an area that shows the characteristics of the original island structure. Here, the list indicated by k that does not have any points to be excluded is determined to represent a valid Voronoi area.

[0269] (2) For the Voronoi region k that was determined to be valid by the previous determination, its area A is calculated as follows: rBK=rB{k}; XPB=VB(rBK,1); YPB=VB(rBK,2); A(i)=polyarea(XPB,YPB); i is a number assigned sequentially to areas that are determined to be valid, starting from 1 and incrementing by 1 each time a substitution is made in the above calculation. rBK, XPB, and YPB are temporary variables used in the calculation.

[0270] For these calculations (1) and (2), k is increased sequentially from 1, and when the calculation is completed until the end of the list of rB, only the area of ​​the area that is determined to be valid as a Voronoi region is assigned to A.

[0271] As a result of this calculation, the Voronoi areas that are determined to be valid and have their areas calculated are shown in, for example, Fig. 7 (Example 1) and Fig. 15 (Comparative Example 1). Note that the units of the vertical and horizontal axes in Fig. 7 are pixels, and the units of the vertical and horizontal axes in Fig. 15 are pixels.

[0272] As an example of the calculation results of the area, histograms of the separator are shown in FIG. 8 (Example 1) and FIG. 16 (Comparative Example 1).

[0273] The Voronoi area is calculated based on the image, so it is expressed in pixels, but it can be converted to the actual area based on the imaging conditions when this image was obtained. If the length of one side of the pixel obtained from the conditions set during imaging is lp (μm), the area corresponding to one pixel is lp 2 (μm 2 ) The actual area can be obtained by multiplying the area of ​​the Voronoi region expressed in pixels by the area of ​​one pixel. For example, if a 100 μm square area is imaged using 256 × 256 pixels, the length of one side of the pixel is 0.39 μm, and the area of ​​one pixel is 0.153 μm. 2 For example, the area of ​​a Voronoi region calculated to be 100 pixels is actually 153 μm 2 In this way, the area obtained from the image in pixel units can be easily converted into an actual area. Examples of histograms after conversion are shown in Figure 9 (Example 1) and Figure 17 (Comparative Example 1). Also, if the length of one side of a pixel is lp (μm), the area corresponding to one pixel is lp 2 (μm 2 ) in the same manner as above, except that the actual area of ​​the Voronoi region is converted to obtain the converted histogram.

[0274] Next, we will show how to calculate the parameters that represent the characteristics of the area distribution of Voronoi regions from this histogram. This calculation was performed by fitting the area distribution to the following probability distribution function.

number

[0275] Here, x is the input data. There are three fitting parameters: a shape parameter k, a position parameter μ indicating the maximum value, and a scale parameter σ indicating the dispersion. The calculation was performed using the GeneralizedExtremeValueDistribution option of the fitdist function in the Statistics and Machine Learning Toolbox of the numerical calculation software MATLAB manufactured by Mathworks, Inc. The calculation is performed as follows, using the area A calculated previously as x. pd=fitdist(A,'GeneralizedExtremeValueDistribution'); The output pd is a structure containing the fitting results, and holds the aforementioned values ​​of k, μ, and σ, and the individual data can be accessed as pd.k, pd.mu, and pd.sigma, respectively. Examples of the fitting results are shown in Figure 10 (Example 1) and Figure 18 (Comparative Example 1). Of the distribution parameters obtained by this fitting, the peak position and σ, which indicates the dispersion, were used in this example. σ / mu can also be calculated using the obtained mu and σ.

[0276] <Compression resistance test> Two separators were cut into 10 cm x 10 cm pieces, stacked, and their air permeability (Sj) was measured. Furthermore, the thickness was measured at nine random points within an 8 cm x 8 cm area, based on the intersection of the diagonal lines from the top view, and the average value was calculated. The laminate was then covered from above with two 10 cm x 10 cm PET films. The laminate was then sandwiched between two 5 mm thick rubber sheets (10 cm x 10 cm) from above and below, and pressure was applied while heating using a TOYOSEIKI mini test press (product number: MP-WCH). The PET film and rubber sheets were used to apply pressure uniformly across the entire surface, and the uniformity was confirmed with a pressure sensor. The upper and lower heater temperatures of the press were set to 90°C, and the 10 cm x 10 cm sample was held for 3 minutes to apply a uniform pressure of 8 MPa. After the heating and compression operation, the air permeability (Sh) of the two stacked separators was measured. Furthermore, the thickness of two stacked separators was measured at nine arbitrary points within an 8 cm × 8 cm area, based on the intersection of the diagonal lines, when viewed from above, and the average value was calculated. According to the following formula, the change in thickness before and after compression was quantified as the thickness reduction rate (%), and the change in air permeability after compression compared to before compression was quantified as the air permeability change ratio. Thickness reduction rate (%) = ((thickness after compression (μm) - thickness before compression (μm)) / thickness before compression (μm)) × 100 Air permeability change ratio (%) = ((Air permeability after compression Sh (sec) - Air permeability before compression Sj (sec)) / Air permeability before compression Sj (sec)) × 100

[0277] <Contact angle of coating liquid (°)> Using a contact angle meter (CA-V) manufactured by Kyowa Interface Science Co., Ltd., 2 μl of each coating solution was dropped onto a clean separator substrate surface, and the contact angle was measured 40 seconds later. The contact angle was measured three times in both the MD and TD directions, and the average value was used. This measurement method was also performed on both the front and back surfaces of the microporous membrane used as the separator substrate, and the larger value from either side was used.

[0278] <Checking the progress of the crosslinking reaction during the coating process> The TMA rupture temperature was measured before and after applying the coating solution to a polyolefin microporous membrane used as a separator substrate, and the progress of the crosslinking reaction during the coating process was confirmed by comparing the two temperatures. The progress of the crosslinking reaction was evaluated based on the TMA rupture temperature according to the following criteria. (Coating of inorganic porous layer or thermoplastic polymer-containing layer) 〇(Good): 190℃ or higher △(Acceptable): 170℃~190℃ × (defective): 170℃ or less (Coating of active layer or heat-resistant resin layer) 〇(Good): 200℃ or more △(Acceptable): 180℃~200℃ × (defective): 180℃ or less

[0279] <Battery Evaluation I: Cycle Test, Hot Box Test, and Nail Penetration Test> Laminated cells or 4680-type cylindrical batteries were fabricated according to the following procedure. Cycle test (1), hot box test, and nail penetration test were conducted using the laminated cells, and cycle test (2) was conducted using the 4680-type cylindrical batteries. (Preparation of batteries for use in safety tests) a. Preparation of the positive electrode LiNi as the positive electrode active material 0.8 Mn 0.1 Co 0.1 O2, carbon black as a conductive additive, and polyvinylidene fluoride solution as a binder were mixed in a solids mass ratio of 91:5:4, and N-methyl-2-pyrrolidone was added as a dispersion solvent to a solids content of 68 mass%. The mixture was further mixed to prepare a slurry solution. This slurry solution was applied to both sides of a 15 μm thick aluminum foil so that a portion of the aluminum foil was exposed, and the solvent was then dried and removed. Furthermore, the density of the positive electrode mixture portion was 2.8 g / cm. 3 The aluminum foil was then cut to include the exposed portion of the aluminum foil, to obtain a positive electrode.

[0280] b. Preparation of negative electrode Artificial graphite as the negative electrode active material, styrene butadiene rubber as the binder, and a carboxymethyl cellulose aqueous solution were mixed in a solid content mass ratio of 96.4:1.9:1.7, and water was added as a dispersion solvent to a solid content of 50 mass%. The mixture was further mixed to prepare a slurry solution. This slurry solution was applied to a 10 μm-thick copper foil so that a portion of the foil was exposed, and the solvent was then dried and removed. Furthermore, the density of the negative electrode mixture portion was 1.45 g / cm. 3 The laminate was then rolled using a roll press so that the thickness of the laminate was 1 / 4 of the thickness of the copper foil.

[0281] c. Preparation of non-aqueous electrolyte As shown in Tables 18 and 19, the electrolytic solution and electrolyte were mixed to prepare non-aqueous electrolytic solutions.

[0282] d-1. Battery assembly of laminated cells A 55 mm-wide long separator was folded zigzag to form a stack consisting of 15 double-sided negative electrodes and 14 double-sided positive electrodes, with the active material surfaces of the positive and negative electrodes facing each other and interposed between the positive and negative electrodes. The heat-resistant B layer of Sample 1 was placed facing the positive electrode. Aluminum lead pieces with sealant were welded to the exposed portions of 14 aluminum foil positive electrodes, and nickel lead pieces with sealant were welded to the exposed portions of 15 copper foil negative electrodes. The stack was then inserted into an aluminum laminate exterior, and three sides (the exposed sides of the positive and negative electrode lead pieces and the other two sides) were laminated and sealed. The nonaqueous electrolyte solution was then poured into the exterior, and the opening was sealed to form a 28-sided laminate battery. The resulting battery was left at room temperature for one day, and then charged at a constant current of 330 mA (0.3 C) in an atmosphere of 25°C up to a battery voltage of 4.2 V, and then charged at a constant voltage to maintain 4.2 V. This method was used for the first charge after battery fabrication for a total of 8 hours. The battery was then discharged at a current of 330 mA (0.3 C) down to a battery voltage of 3.0 V.

[0283] d-2. Cylindrical battery assembly Using the above positive and negative electrodes and electrolyte, a cylindrical (4680-type) lithium secondary battery (battery dimensions: diameter 46 mm, height 80 mm) was fabricated with the active material surfaces of the positive and negative electrodes facing each other and a long separator interposed between the positive and negative electrodes. When fabricating the battery, the positive and negative electrodes were sealed with the maximum length that could be accommodated inside the battery container. The separator coating layer was positioned facing the positive electrode. After leaving the battery at room temperature for one day, it was charged at a constant current of 5 A (0.3 C) in a 25°C atmosphere to a battery voltage of 4.2 V, and then continuously charged at a constant voltage to maintain 4.2 V. This method was used for the first charge after fabrication, for a total of 8 hours. The battery was then discharged at a current of 5 A (0.3 C) to a battery voltage of 3.0 V.

[0284] (Cycle test (1): at 5°C and 50°C) The battery obtained in "d-1. Battery Assembly of Laminated Cell" above was charged and discharged 1000 times in atmospheres at 5°C and 50°C. The battery was charged at a constant current of 1 A (1.0 C) up to a battery voltage of 4.2 V, and then charged at a constant voltage to maintain 4.2 V for a total of 3 hours. The battery was discharged at a current of 1 A (1.0 C) down to a battery voltage of 3.0 V. The capacity retention rate was calculated from the discharge capacity at the 1000th cycle and the discharge capacity at the first cycle. A high capacity retention rate was evaluated as having good cycle characteristics.

[0285] (Hot Box Test) The battery obtained by the above "d-1. Battery assembly of laminated cell" was subjected to 300 charge / discharge cycles at 5°C, and then stored for 1 hour in a hot box set at a high temperature of 136°C, and the state of the battery was observed during and after storage.

[0286] When the microporous membrane contained in the battery as a separator undergoes thermal shrinkage during high-temperature storage, an internal short circuit may occur between the positive and negative electrodes of the battery, resulting in fire or explosion. Batteries in which fire or explosion was observed were evaluated as unacceptable. Batteries in which fire or explosion was not observed were evaluated as acceptable.

[0287] This hot box test was carried out on 100 batteries using the same separator, and the pass rate (%) was calculated.

[0288] (nail penetration test) A test was conducted to induce an internal short circuit in a battery obtained by the above "d-1. Battery Assembly of Laminated Cells" after charging to 4.2 V. A 3mm diameter iron nail was driven at a speed of 20mm / sec, penetrating the battery. This test can clarify the phenomenon of an internal short circuit by measuring the time-dependent behavior of the battery's voltage drop and the behavior of the battery surface temperature rise due to an internal short circuit. In addition, insufficient shutdown function of the separator or rupture at low temperatures during an internal short circuit can cause the battery to suddenly heat up, which can lead to the electrolyte ignition, smoke emission, and / or explosion of the battery.

[0289] The nail penetration test was carried out as described above and the pass / fail status of the batteries was judged. This nail penetration test was carried out on 100 batteries using the same separator, and the number of batteries X that did not catch fire, emit smoke, or explode was calculated as the pass rate (X / 100), which is shown in Tables 2 to 17.

[0290] (Cycle test (2)) The battery obtained in "d-2. Cylindrical Battery Assembly" above was charged and discharged 500 times in a 40°C atmosphere. The battery was charged at a constant current of 17.5 A (1.0 C) up to a battery voltage of 4.2 V, and then charged at a constant voltage to maintain 4.2 V for a total of 3 hours. The battery was discharged at a current of 17.5 A (1.0 C) down to a battery voltage of 3.0 V. The capacity retention rate was calculated from the discharge capacity at the 1000th cycle and the discharge capacity at the 1st cycle. A high capacity retention rate was evaluated as having good cycle characteristics.

[0291] <Battery Evaluation II> (battery manufacturing) The battery evaluation was performed by fabricating a non-aqueous secondary battery containing the sample piece using the following procedure: Crush test and cycle test Capacity retention rate and cycle life test were performed by fabricating a 4680-type cylindrical battery and measuring the results four days after coating the separator.

[0292] a. Preparation of the positive electrode LiNi as the positive electrode active material 0.6 Mn 0.2 Co 0.2 O2, carbon black as a conductive additive, and polyvinylidene fluoride solution as a binder were mixed in a solids mass ratio of 91:5:4, and N-methyl-2-pyrrolidone was added as a dispersion solvent to a solids content of 68 mass%. The mixture was further mixed to prepare a slurry solution. This slurry solution was applied to both sides of a 15 μm thick aluminum foil so that a portion of the aluminum foil was exposed, and the solvent was then dried and removed. Furthermore, the density of the positive electrode mixture portion was 2.8 g / cm. 3 The aluminum foil was then cut to include the exposed portion of the aluminum foil, to obtain a positive electrode.

[0293] b. Preparation of negative electrode Carbon-coated silicon powder, lithium-doped carbon-coated silicon oxide powder, and graphite powder were mixed as negative electrode active materials in a solids mass ratio of 3:27:66.4:1.9:1.7 with styrene butadiene rubber and carboxymethyl cellulose aqueous solution as binders. Water was added as a dispersion solvent to a solids content of 50% by mass, and further mixed to prepare a slurry solution. This slurry solution was applied to both sides of a 10 μm-thick copper foil so that a portion of the copper foil was exposed, and the solvent was then dried and removed. Furthermore, the density of the negative electrode mixture portion was 1.45 g / cm. 3 The laminate was then rolled using a roll press so that the thickness of the laminate was 1 / 4 of the thickness of the copper foil.

[0294] c: Preparation of electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0295] d. Battery assembly Using the above positive and negative electrodes and electrolyte, a cylindrical (4680-type) lithium secondary battery (battery dimensions: diameter 46 mm, height 80 mm) was fabricated with the active material surfaces of the positive and negative electrodes facing each other and a long separator interposed between the positive and negative electrodes. When fabricating the battery, the positive and negative electrodes were sealed with the maximum length that could be accommodated inside the battery container. The separator coating layer was positioned facing the positive electrode. After leaving the battery at room temperature for one day, it was charged at a constant current of 1 A (0.06 C) in a 25°C atmosphere to a battery voltage of 4.2 V, and then continuously charged at a constant voltage to maintain 4.2 V. This method was used for the first charge after fabrication, for a total of 8 hours. The battery was then discharged at a current of 1 A (0.06 C) to a battery voltage of 3.0 V.

[0296] (Bar impact test (crushing test)) Using the batteries obtained in "d. Battery Assembly" of Battery Evaluation II above, a 15.8mm diameter SUS rod was placed perpendicular to the length of the battery, and then a 9.1kg weight was dropped from a height of 61cm, causing it to collide with the battery. The temperature rise and ignition status of the battery were checked on a specified number of cells. After the collision, cells that generated heat of 80°C or more were evaluated as failing the test, and the pass rate (%) based on the total number of cells was calculated.

[0297] (Cycle test capacity retention rate (%)) The battery obtained in "d. Battery Assembly" of Battery Evaluation II above was charged and discharged 500 times in an atmosphere at 55°C. The battery was charged at a constant current of 8.7 A (0.5 C) up to a battery voltage of 4.2 V, and then charged at a constant voltage to maintain 4.2 V for a total of 3 hours. The battery was discharged at a current of 8.7 A (0.5 C) down to a battery voltage of 3.0 V. The capacity retention rate was calculated from the discharge capacity at the 1000th cycle and the discharge capacity at the 1st cycle. A high capacity retention rate was evaluated as having good cycle characteristics.

[0298] (Cycle life test) The battery obtained in "d. Battery Assembly" of Battery Evaluation II above was repeatedly charged and discharged in an atmosphere of 65°C until the capacity retention rate reached 50% or less. The battery was charged at a constant current of 8.7 A (0.5 C) up to a battery voltage of 4.2 V, and then charged at a constant voltage to maintain 4.2 V. This method was used for a total of 3 hours. The battery was discharged at a current of 8.7 A (0.5 C) down to a battery voltage of 3.0 V. The number of cycles at which the capacity retention rate reached 50% or less was recorded as the cycle life. A long cycle life was evaluated as having good cycle characteristics.

[0299] [Manufacturing method for silane-modified polyolefin] The raw polyolefin used for silane-modified polyolefin may have a viscosity-average molecular weight (Mv) of 10,000 to 1,000,000, a weight-average molecular weight (Mw) of 30,000 to 920,000, and a number-average molecular weight of 10,000 to 150,000. It may also be a propylene or butene copolymerized α-olefin. While melt-kneading the raw polyethylene in an extruder, an organic peroxide (di-t-butyl peroxide) is added to generate radicals within the α-olefin polymer chain. Then, trimethoxyalkoxide-substituted vinylsilane is added to introduce alkoxysilyl groups into the α-olefin polymer through an addition reaction, forming a silane-grafted structure. At the same time, an appropriate amount of antioxidant (pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]) is added to adjust the radical concentration in the system and suppress chain reaction (gelation) within the α-olefin. The resulting silane-grafted polyolefin molten resin was cooled in water and pelletized, followed by heating and drying at 80°C for two days to remove moisture and unreacted trimethoxyalkoxide-substituted vinylsilane. The residual concentration of unreacted trimethoxyalkoxide-substituted vinylsilane in the pellets was 3000 ppm or less. By using octenyltrialkoxysilane instead of trimethoxyalkoxide-substituted vinylsilane, a silane-modified polyolefin having 8 methylene (CH2) groups constituting the linkage to the main chain can be produced. By using dodecyltrialkoxysilane instead of trimethoxyalkoxide-substituted vinylsilane, a silane-modified polyolefin having 12 methylene (CH2) groups constituting the linkage to the main chain can be produced.

[0300] [Manufacturing methods for polyolefins other than silane-modified polyolefins] Polyolefins used in the production of polyolefins other than silane-modified polyolefins are not limited, but can be produced by the following method. Hexane, ethylene, α-olefins such as 1-pentene or 1-butene, hydrogen, catalyst components such as Ziegler-Natta catalysts or metallocene catalysts, cocatalyst components such as triisobutylaluminum and diisobutylaluminum hydride, and an antistatic agent are continuously fed into a vessel-type polymerization reactor equipped with a stirrer to produce a polyethylene polymerization slurry. The polymerization temperature is maintained constant by jacket cooling, and the polymerization slurry is continuously discharged into a flash drum at a constant temperature so that the reactor level remains constant, and unreacted ethylene and hydrogen are separated. The solvent is then separated using a centrifuge, and the mixture is dried with nitrogen to obtain polyethylene powder. To the resulting polyethylene powder, an aliphatic saturated alcohol such as methanol and calcium stearate are added, and the mixture is homogenized in a Henschel mixer. The remaining material is then removed using a sieve with appropriate mesh size to obtain polyolefins other than silane-modified polyolefins.

[0301] [Preparation of resin raw materials] (Preparation of resin raw material A1) 100 parts by mass of polyolefin having a viscosity average molecular weight of 150,000 was compounded with 1.4 parts by mass of vinyltrimethoxysilane, 0.025 parts by mass of di-t-butyl peroxide as an organic peroxide, and 0.15 parts by mass of calcium stearate, and the mixture was mixed in a Henschel mixer. The mixture was then melt-kneaded at 220°C using a twin-screw extruder, TEX-44 (screw diameter 44 mm, L / D=35), manufactured by The Japan Steel Works, Ltd., to granulate resin raw material A1.

[0302] (Preparation of resin raw material B1) Hexane 55L / h, Mg6(C4H9) as catalyst component 12A 300-L vessel-type polymerization reactor was maintained at 53°C by jacket cooling. 0.5 g / h of Ziegler-Natta catalyst containing Al(C2H5)3 and titanium tetrachloride, along with 9 mmol / h of a 9:1 mixture of triisobutylaluminum and diisobutylaluminum hydride as cocatalysts, were fed into the reactor at a rate of 0.5 g / h. Ethylene was continuously added to maintain a polymerization pressure of 0.3 MPa, yielding a polyethylene polymerization slurry. STATSAFE 3000 was added as an antistatic agent to a concentration of 15 ppm relative to the polyethylene powder. 1-Butene was also added continuously as an α-olefin to a concentration of 6.9 mol% relative to the gas-phase ethylene concentration. The polyethylene polymerization slurry was continuously discharged into a flash drum at a pressure of 0.05 MPa to maintain a constant reactor level, and unreacted ethylene was separated. The solvent was then separated by centrifugation, and the mixture was dried under a nitrogen stream using a drum dryer with the jacket adjusted to 80°C and an oxygen concentration of 80 ppm, yielding polyethylene powder. Methanol was added to the obtained polyethylene powder to a concentration of 150 ppb, and calcium stearate (wet process) was added to a concentration of 1,000 ppm. The mixture was then sieved using a 425 μm mesh sieve to remove any material that did not pass through the sieve, yielding a resin raw material B1.

[0303] (Preparation of resin raw material C2) 40L / h of hexane prepared at 3℃, Mg6(C4H9) as catalyst component 12A 300-L vessel-type polymerization reactor was maintained at 80°C with jacket cooling, and 0.2 g / h of Ziegler-Natta catalyst containing Al(C2H5)3 and titanium tetrachloride, and 10 mmol / h of a 9:1 mixture of triisobutylaluminum and diisobutylaluminum hydride as cocatalysts, were fed into the reactor. Ethylene was continuously added at a polymerization pressure of 0.5 MPa to produce a polyethylene polymerization slurry. STATSAFE 3000 was added as an antistatic agent to a concentration of 15 ppm relative to the polyethylene powder. 1-Butene was continuously added as an α-olefin to a concentration of 5 mol% relative to the gas-phase ethylene. Hydrogen was also added to a concentration of 5.5 mol% relative to the gas-phase ethylene. The polyethylene polymerization slurry was continuously discharged into a flash drum at a pressure of 0.05 MPa to maintain a constant reactor level, and unreacted ethylene was separated. The solvent was then separated by centrifugation, and the mixture was dried under a nitrogen stream using a drum dryer with the jacket adjusted to 80°C and an oxygen concentration of 80 ppm to obtain polyethylene powder. Methanol was added to the obtained polyethylene powder at 150 ppb and calcium stearate (wet process) at a concentration of 1,000 ppm, and the mixture was passed through a sieve with 425 μm openings to remove any material that did not pass through the sieve, yielding resin raw material C2.

[0304] (Production of other resin raw materials) Resin materials A2 to A12 and D1 to D14 shown in Tables 20 to 25 were prepared in the same manner as resin material A1, except for the molecular weight and copolymer concentration of the raw material polyolefin, the amount of trimethoxyalkoxide-substituted vinylsilane added, and the kneading conditions. However, when preparing resin material D13, octenyloctenyltrialkoxysilane was used instead of trimethoxyalkoxide-substituted vinylsilane, and when preparing resin material D14, dodecyltrialkoxysilane was used instead of trimethoxyalkoxide-substituted vinylsilane. Resin materials B2 to B6 and E1 to E5 shown in Tables 20 to 25 were prepared in the same manner as resin material B1, except for the amount of raw material added, polymerization reactor temperature, and polymerization pressure. Resin materials C1, C3 to C5, and F1 to F4 shown in Tables 20 to 25 were prepared in the same manner as resin material C2, except for the amount of raw material added, polymerization reactor temperature, and polymerization pressure.

[0305] [Example 1] Preparation and evaluation of separator (Preparation of microporous polyolefin membranes as separators) To a mixed resin composition consisting of 30% by mass of Resin A1, 30% by mass of Resin B1, and 40% by mass of Resin C2, 1000 ppm by mass of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant, and the mixture was dry-blended using a tumbler blender to obtain a mixture. The resulting mixture was fed into a twin-screw extruder using a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump.

[0306] The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the liquid paraffin content in the extruded polyolefin composition was 75% by mass (i.e., the polymer concentration was 25% by mass). The melt-kneading conditions were a set temperature of 230°C, a screw rotation speed of 100 rpm, and a discharge rate of 80 kg / h. Subsequently, the melt-kneaded product was extruded through a T-die onto a cooling roll whose surface temperature was controlled to 25°C, thereby obtaining a gel sheet (molded sheet) having a thickness of 1250 µm.

[0307] The sheet-like molded product was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were an MD magnification of 7.0x, a TD magnification of 6.4x (i.e., 7x6.4x), and a biaxial stretching temperature of 125°C. The stretched gel sheet was then introduced into a dichloromethane bath and thoroughly immersed in dichloromethane to extract and remove the liquid paraffin. The dichloromethane was then dried and removed to obtain a porous body. The porous body was then introduced into a TD tenter for heat setting (HS), where it was subjected to HS at a heat setting temperature of 133°C and a stretching ratio of 1.8x based on the sheet width at the TD tenter entrance. The stretched porous body was then relaxed to a TD stretching ratio of 1.6x based on the sheet width at the TD tenter entrance to obtain a microporous membrane. The resulting microporous membrane was then trimmed and wound into a mother roll with a width of 1,100 mm and a length of 5,000 m.

[0308] <Coating of inorganic coating layer> (Acrylic latex manufacturing method) The acrylic latex used as the resin binder was produced as follows. 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of emulsifiers "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and 0.5 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer. The temperature inside the reaction vessel was then raised to 80°C. While maintaining the temperature at 80°C, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. The addition of the ammonium persulfate aqueous solution was then completed. Five minutes later, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes. The above emulsion was prepared by mixing a mixture of: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water using a homomixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water was added to obtain an acrylic latex with a solids content of 40%. The resulting acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -23°C.

[0309] (Formation of inorganic porous layer) A dispersion was prepared by uniformly dispersing 95 parts by weight of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles and 0.4 parts by weight (solids equivalent) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco, 40% solids concentration) as an ionic dispersant in 100 parts by weight of water. The resulting dispersion was milled using a bead mill (cell volume 200 cc, zirconia beads 0.1 mm diameter, 80% loading) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm. To the adjusted dispersion, 4.6 parts by weight (solids equivalent) of acrylic latex (40% solids concentration, average particle size 145 nm, glass transition temperature -23°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) was added as a resin binder to prepare an inorganic particle-containing slurry. Next, a microporous membrane was continuously unwound from the microporous membrane mother roll, and one side of the microporous membrane was coated with the inorganic particle-containing slurry using a gravure reverse coater. The microporous membrane was then dried in a dryer at 60°C to remove water, and taken up to obtain a separator mother roll. At the time of evaluation, the separator unwound from the mother roll was slit as necessary and used as the separator for evaluation.

[0310] The thickness, air permeability, porosity, puncture strength, and air permeability change ratio before and after a compression test in which the resulting polyolefin microporous membrane was compressed by 30% of its thickness were measured, and the results are shown in Table 2. The separator for evaluation and the battery containing the separator were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are shown in Table 2.

[0311] [Examples 2 to 33, Comparative Examples 4 and 7] Preparation and evaluation of separators The separators shown in Tables 2 to 8 were obtained by the same procedures as in Example 1, except that the molecular weight mixture composition, production conditions, composite formation conditions, etc. of the polyolefin microporous membrane were changed as shown in Tables 2 to 8. The obtained separators and batteries containing them were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are also shown in Tables 2 to 8.

[0312] The silane-modified PP described in Examples 28 and 30 was produced using polypropylene (E-100GV) manufactured by Prime Polymer Co., Ltd. in the same manner as described in the above section "Production method of silane-modified polyolefin." The PP used was polypropylene (E-100GV) manufactured by Prime Polymer Co., Ltd. The PP-PE used in Example 28 was a block polymer (DYNARON 6201B) of olefin crystals, ethylene butylene, and olefin crystals manufactured by JSR Corporation.

[0313] [Comparative Example 1] Preparation and evaluation of separator The separators shown in Table 7 were obtained by the same procedure as in Example 1, except that Resin B1 and Resin C2 were used in a mass ratio of 50:50, and the conditions for producing the polyolefin microporous membrane and the conditions for composite construction were changed as shown in Table 7. The obtained separators and batteries containing them were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 7.

[0314] [Comparative Example 2] Preparation and evaluation of separator In the extruder, 24 kg / h of silane-unmodified polyethylene (VH035 manufactured by Daehan Yuhka Industrial Co., Ltd.) with a weight-average molecular weight of 350,000 and a melting point of 136.2°C, 24 kg / h of resin raw material A1, and 24 kg / h of liquid paraffin (kinematic viscosity at 37.78°C of 7.59 × 10 -5 m 2The mixture was mixed at a flow rate of 112 kg / h (1 / s). The weight ratio of silane-unmodified polyethylene:silane-modified polyethylene:liquid paraffin was 15:15:70. Furthermore, based on 100 parts by mass of the total of silane-unmodified polyethylene, silane-modified polyethylene, and liquid paraffin, 0.5 parts by mass of vinyltriethoxysilane as a carbon-carbon double bond group-containing alkoxysilane compound, based on 100 parts by mass of the carbon-carbon double bond group-containing alkoxysilane compound, 2 parts by mass of dibutyltin dilaurate as a crosslinking catalyst based on 100 parts by mass of the carbon-carbon double bond group-containing alkoxysilane compound, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP) as an initiator based on 100 parts by mass of the carbon-carbon double bond group-containing alkoxysilane compound were introduced into the extruder and mixed. The mixture was then extruded at a temperature of 200°C to obtain a silane-modified polyethylene composition. The obtained silane-modified polyethylene composition was molded into a sheet using a T-die and a cooled casting roll, and then biaxially stretched in the MD and then the TD using a tenter-type sequential stretching machine. The MD stretch ratio was 5.5 times and the TD stretch ratio was 5.0 times. The stretching temperatures were 105°C in MD and 125°C in TD. Liquid paraffin was extracted from the stretched sheet using methylene chloride, and the sheet was heat-set at 126°C with a stretch ratio of 1.3 to 1.1 times to produce a porous membrane. This porous membrane was subjected to aqueous crosslinking for 48 hours under conditions of 85°C and 85% relative humidity to obtain the separators shown in Table 7. The obtained separators and batteries containing them were evaluated according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 7.

[0315] [Comparative Example 3] Preparation and evaluation of separator Modified polyolefin H3-1 (VH035H manufactured by Daehan Yuhka Industrial Co., Ltd.) containing an average of 7.7 alkylene groups with 3 carbon atoms as short chain branches (SCB) based on a carbon number of 1,000 was prepared. This modified polyolefin had a weight-average molecular weight of 380,000 and a melting point of 129.1°C. The modified polyolefin contained repeating units derived from ethylene and repeating units derived from an α-olefin, and the repeating units derived from the α-olefin were derived from 1-pentene. The modified polyolefin H3-1 prepared above was fed at 7.5 kg / h, along with 7.5 kg / h of silane-unmodified polyethylene (VH035 manufactured by Daehan Yuhka Industrial Co., Ltd.) with a weight-average molecular weight of 300,000 and a melting point of 135°C, and liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) as a plasticizer. -5 m 2The extruder was operated at a flow rate of 35 kg / h (1 / s), and the initiator, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP), a crosslinker, and a carbon-carbon double bond group-containing alkoxysilane such as vinyltrimethoxysilane (VTMS), and the catalyst, dibutyltin dilaurate (DBTDL), were fed and mixed. The weight ratio of modified polyolefin H3-1 to unmodified polyolefin was 50:50. The alkyl group of the repeating unit derived from the α-olefin had 3 carbon atoms, and the main polyolefin chain of the polyolefin fed had 1,000 carbon atoms. The weight ratio of polyolefin to plasticizer fed was 30:70. The content of the carbon-carbon double bond-containing alkoxyvinylsilane was 0.3 parts by weight based on 100 parts by weight of the total content of the polyolefin and plasticizer added. The content of the initiator was 1.7 parts by weight based on 100 parts by weight of the carbon-carbon double bond-containing alkoxysilane. The content of the crosslinking catalyst was 6.7 parts by weight based on 100 parts by weight of the carbon-carbon double bond-containing alkoxysilane. The components were then mixed in an extruder, and the resulting mixture was extruded at a temperature of 190°C to obtain silane-modified polyolefin composition H3-2. The resulting silane-modified polyolefin composition H3-2 was formed into a sheet using a T-die and a cooled casting roll, and then biaxially stretched using a tenter-type sequential stretching machine, which performed MD stretching followed by TD stretching. The MD stretch ratio and TD stretch ratio were both 7.0 times. The stretching temperatures were 103°C in MD and 118°C in TD. Considering the melting temperature of the modified polyolefin, the sheet was stretched at a temperature lower than that used for compositions containing general polyolefins alone. Liquid paraffin was extracted from the stretched sheet using methylene chloride, and the sheet was heat-set at 124°C to produce a porous membrane. This porous membrane was subjected to aqueous crosslinking at 85°C and 85% relative humidity for 24 hours to obtain the separators shown in Table 7. The resulting separators and batteries containing them were evaluated according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 7.

[0316] [Comparative Example 5] Preparation and evaluation of separator 18 parts by weight of high-density polyethylene "SH800" (trademark, manufactured by Asahi Kasei Chemicals Corp.) with a viscosity-average molecular weight (Mv) of 270,000, 12 parts by weight of ultra-high molecular weight polyethylene "UH850" (trademark, manufactured by Asahi Kasei Chemicals Corp.) with a Mv of 2 million, 20 parts by weight of silica "DM10C" (trademark, manufactured by Tokuyama Corp., hydrophobized with dimethyldichlorosilane) with an average primary particle size of 15 nm, 30 parts by weight of liquid paraffin "Sumoil P-350P" (trademark, manufactured by Matsumura Oil Research Institute Co., Ltd.) as a plasticizer, and 0.3 parts by weight of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] as an antioxidant were premixed in a supermixer. The resulting mixture was fed to the feed port of a twin-screw co-rotating screw extruder via a feeder. Liquid paraffin was side-fed into the twin-screw extruder cylinder so that the liquid paraffin content was 50 parts by mass relative to the total mixture (100 parts by mass) melt-kneaded and extruded. The melt-kneading conditions in the extruder were a set temperature of 200°C, a screw rotation speed of 180 rpm, and a discharge rate of 12 kg / h. The melt-kneaded mixture was then extruded through a gear pump, a conduit, and a T-die, each set at 220°C, between cooling rolls whose surface temperature was controlled at 25°C, to obtain a sheet-like polyolefin composition. The sheet-like polyolefin composition was then continuously introduced into a simultaneous biaxial tenter and simultaneously biaxially stretched 7 times in the longitudinal direction and 7 times in the transverse direction. The set temperature of the simultaneous biaxial tenter was 123°C. The sheet-like polyolefin composition was then introduced into a methylene chloride tank and thoroughly immersed in methylene chloride to extract and remove the liquid paraffin. The methylene chloride was then dried. The sheet-like polyolefin composition was then introduced into a transverse tenter and stretched to 1.4 times its original length in the transverse direction, and then relaxed to 1.2 times its original length at the final outlet and wound up to obtain the separators shown in Table 7. The set temperature in the transverse stretching section was 132°C, and the set temperature in the relaxation section was 137°C. The obtained separators and batteries containing them were subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 8.

[0317] [Comparative Example 6] Preparation and evaluation of separator 25 parts by weight of high-density polyethylene (HDPE) with a weight-average molecular weight (Mw) of 380,000 and a molecular weight distribution (Mw / Mn) of 5, 0.5 parts by weight of resin raw material A1 with a kinematic viscosity at 40°C, and 70 parts by weight of paraffin oil were mixed and introduced into a twin-screw extruder (inner diameter 58 mm, L / D = 56, twin-screw extruder). This mixture was extruded from the twin-screw extruder at 200°C and a screw rotation speed of 40 rpm into a 300 mm wide T-die. The extruded material was then passed through a casting roll at 40°C to produce an 800 μm thick base sheet. This base sheet was stretched six times in the longitudinal direction using a roll stretcher at 110°C, and then seven times in the transverse direction using a tenter stretcher at 125°C to produce a stretched film. This stretched film was then immersed in a dichloromethane leaching bath at 25°C for 1 minute to extract and remove the paraffin oil, producing a porous membrane. This porous membrane was dried at 50°C, then heated to 125°C in a tenter-type stretching machine and heat-set at 1.25 times the stretching magnification in the transverse direction (TD) compared to before stretching. This porous membrane was crosslinked for 72 hours in a thermo-hygrostat at 85°C and 85% humidity to obtain the separators shown in Table 8. The obtained separators and batteries containing them were evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 8.

[0318] [Comparative Example 8] Preparation and evaluation of separator In the extruder, silane-unmodified polyethylene with a weight-average molecular weight of 900,000 and a melting point of 135°C was fed at 22.4 kg / h, resin raw material A1 was fed at 22.4 kg / h, and liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10 -5 m 2The mixture was mixed at a flow rate of 115.2 kg / h (flow rate: 1 / s). The weight ratio of silane-unmodified polyethylene:silane-modified polyethylene:liquid paraffin was 14:14:72. Furthermore, based on 100 parts by mass of the total of silane-unmodified polyethylene, silane-modified polyethylene, and liquid paraffin, 0.5 parts by mass of vinyltriethoxysilane as a carbon-carbon double bond group-containing alkoxysilane compound, based on 100 parts by mass of the carbon-carbon double bond group-containing alkoxysilane compound, 2 parts by mass of dibutyltin dilaurate as a crosslinking catalyst based on 100 parts by mass of the carbon-carbon double bond group-containing alkoxysilane compound, and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DHBP) as an initiator based on 100 parts by mass of the carbon-carbon double bond group-containing alkoxysilane compound were introduced into the extruder and mixed. The mixture was then extruded at a temperature of 200°C to obtain a silane-modified polyethylene composition. The obtained silane-modified polyethylene composition was molded into a sheet using a T-die and a cooled casting roll, and then biaxially stretched in the MD and then the TD using a tenter-type sequential stretching machine. The MD stretch ratio was 5.5 times and the TD stretch ratio was 5.0 times. The stretching temperatures were 105°C in MD and 125°C in TD. Liquid paraffin was extracted from the stretched sheet using methylene chloride, and the sheet was heat-set at 126°C with a stretch ratio of 1.3 to 1.1 times to produce a porous membrane. This porous membrane was subjected to aqueous crosslinking for 48 hours under conditions of 85°C and 85% relative humidity to obtain the separators shown in Table 8. The obtained separators and batteries containing them were evaluated according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 8.

[0319] [Examples 1, 34 to 39, Comparative Examples 1, 4, 7, 9, and 10] As shown in Tables 2, 7, and 9 to 14, the separators obtained in Examples 1, 34 to 39 and Comparative Examples 1, 4, 7, 9, and 10 were arranged in order of the air permeability change ratio when compressed by 30% in the thickness direction, and the effects on the first battery configuration (Tables 9 and 10), the second battery configuration (Tables 11 and 12), and the third battery configuration (Tables 13 and 14) were tested, respectively.

[0320] [Relationship between the separator of Example 1 and various battery configurations: Examples 1A to 1Q] The separator obtained in Example 1 was used to evaluate batteries fabricated by changing the battery configuration as shown in Tables 15 to 17. The battery evaluation results are also shown in Tables 15 to 17, with sub-numbers of Examples 1A to 1Q assigned according to the battery configuration.

[0321] [Electrolyte blending conditions, electrolyte blending conditions, resin raw material composition] Table 18 shows the electrolyte blending conditions used in the production of batteries and separators and various evaluations, Table 19 shows the electrolyte blending conditions, and Tables 20 to 22 show the resin raw material compositions, respectively.

[0322] [Table 2]

[0323] [Table 3]

[0324] [Table 4]

[0325] [Table 5]

[0326] [Table 6]

[0327] [Table 7]

[0328] [Table 8]

[0329] [Table 9]

[0330] Table 10

[0331] Table 11

[0332] Table 12

[0333] Table 13

[0334] Table 14

[0335] Table 15

[0336] Table 16

[0337] Table 17

[0338] Table 18

[0339] Table 19

[0340] [Table 20]

[0341] [Table 21]

[0342] [Table 22]

[0343] <Evaluation of a separator having a multilayer structure and a battery including the same>

[0344] [Table 23-1]

[0345] [Table 23-2]

[0346] [Table 24]

[0347] [Table 25]

[0348] (Acrylic latex manufacturing method) Acrylic latex used as a thermoplastic polymer or resin binder was produced by the following method. 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of emulsifiers "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and 0.5 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer. The temperature inside the reaction vessel was then raised to 80°C. While maintaining the temperature at 80°C, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. The addition of the ammonium persulfate aqueous solution was then completed. Five minutes later, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes. The above emulsion was prepared by mixing a mixture of: 70 parts by mass of butyl acrylate; 29 parts by mass of methyl methacrylate; 1 part by mass of methacrylic acid; 3 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 3 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) as emulsifiers; 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate; and 52 parts by mass of ion-exchanged water using a homomixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature. The resulting emulsion was adjusted to pH 8.0 with a 25% aqueous ammonium hydroxide solution, and a small amount of water was added to obtain an acrylic latex with a solids content of 40%. The resulting acrylic latex had a number average particle size of 145 nm and a glass transition temperature of -23°C.

[0349] (Other resins) Commercially available PVDF latex and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) were prepared. The acrylic latex and PVDF latex were used to prepare aqueous mixtures of PVDF and acrylic (the mixing ratios are shown in the table below). Furthermore, acrylic resin was formed by core-shell polymerization to prepare PVDF / acrylic (core-shell polymerization) mixtures.

[0350] <Confirmation of crosslinking by coating an inorganic porous layer on a separator substrate> [Example 40-1: Preparation and evaluation of separator and confirmation of crosslinking during coating process] (Preparation of polyolefin microporous membrane as separator substrate) To a mixed resin composition consisting of 30.0 mass% of Resin D2 (number of silane graft linkages CH2: 2), 30.0 mass% of Resin E3, and 40.0 mass% of Resin F3, 1000 mass ppm of pentaerythrityl tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] was added as an antioxidant, and the mixture was dry-blended using a tumbler blender to obtain a mixture. The resulting mixture was fed into a twin-screw extruder using a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was added. -5 m 2 / s) was injected into the extruder cylinder by a plunger pump.

[0351] The mixture and liquid paraffin were melt-kneaded in the extruder, and the feeder and pump were adjusted so that the liquid paraffin content in the extruded polyolefin composition was 75% by mass (i.e., the polymer concentration was 25% by mass). The melt-kneading conditions were a set temperature of 230°C, a screw rotation speed of 100 rpm, and a discharge rate of 80 kg / h. The melt-kneaded product was then extruded through a T-die and cast onto a cooling roll whose surface temperature was controlled at 25°C, yielding a gel sheet (sheet-shaped molded product) with a film thickness of 1250 μm.

[0352] The sheet-like molded product was then introduced into a simultaneous biaxial tenter stretching machine and biaxially stretched to obtain a stretched product. The stretching conditions were an MD magnification of 7.0x, a TD magnification of 6.4x (i.e., 7x6.4x), and a biaxial stretching temperature of 125°C. The stretched gel sheet was then introduced into a dichloromethane bath and thoroughly immersed in dichloromethane to extract and remove the liquid paraffin. The dichloromethane was then dried and removed to obtain a porous body. The porous body was then introduced into a TD tenter for heat setting (HS), where it was subjected to HS at a heat setting temperature of 133°C and a stretching ratio of 1.8x. The sheet width at the TD tenter entrance was then relaxed to 1.6x TD to obtain a microporous membrane. The resulting microporous membrane was then trimmed and wound into a mother roll with a width of 1,100 mm and a length of 5,000 m.

[0353] The obtained polyolefin microporous membrane was used as a separator substrate, and measurements and evaluations were carried out according to the above-mentioned methods. The evaluation results are shown in Table 26.

[0354] (Coating of inorganic porous layer and cross-linking confirmation) Next, boehmite was selected as the inorganic particles as shown in Table 26. Furthermore, inorganic particles and an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco, 40% solids concentration) as an ionic dispersant were uniformly dispersed in 100 parts by weight of water at a predetermined ratio to prepare a dispersion. The resulting dispersion was crushed using a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling weight 80%) to adjust the particle size distribution of the inorganic particles to D50 = 1.0 μm. To the dispersion with the adjusted particle size distribution, the above-mentioned acrylic latex (40% solids concentration, average particle size 145 nm, glass transition temperature -23°C, constituent monomers: butyl acrylate, methyl methacrylate, methacrylic acid) was added as a resin binder to obtain the inorganic particle weight ratio shown in Table 26 to prepare an inorganic particle-containing slurry. According to the above-mentioned methods, the pH of the inorganic particle-containing slurry and the contact angle of the coating liquid with respect to the clean separator substrate surface were also measured. A microporous membrane was continuously unwound from the microporous membrane mother roll, and one side of the microporous membrane was coated with an inorganic particle-containing slurry using a gravure reverse coater, followed by drying in a dryer at 60°C to remove water and winding up to obtain a mother roll for a multilayer separator having a coating thickness shown in Table 26. The progress of the crosslinking reaction in the coating process was confirmed by comparing the TMA rupture temperatures before and after coating. During evaluation, the multilayer separator unwound from the mother roll was slit as needed and used as an evaluation separator. The obtained separator for evaluation was subjected to various evaluations according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 26.

[0355] (Testing of a battery containing a multilayer separator coated with an inorganic porous layer) In Example 40-1, a separator substrate made of a polyolefin microporous membrane and a multilayer separator coated with an inorganic porous layer were obtained. Furthermore, a nonaqueous secondary battery was fabricated using the multilayer separator according to the battery fabrication method described above, and the battery evaluation results are also shown in Table 26.

[0356] [Examples 40-2 to 40-53, Comparative Examples 11-1 to 11-7] As shown in Table 26, the resin composition and molecular weight mixture composition of the polyolefin microporous membrane, the preparation conditions, the substrate characteristics, the type and ratio of inorganic particles, and the composition and physical properties of the coating solution were changed. Separator substrates made of polyolefin microporous membranes and multilayer separators coated with inorganic porous layers were obtained by the same procedures as in Example 40-1. The obtained separator substrates and multilayer separators were evaluated according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 26. Furthermore, nonaqueous secondary batteries were obtained using the multilayer separators coated with inorganic porous layers. The obtained batteries were evaluated according to the above-mentioned evaluation methods, and the evaluation results are also shown in Table 26.

[0357] [Table 26-1]

[0358] [Table 26-2]

[0359] [Table 26-3]

[0360] [Table 26-4]

[0361] [Table 26-5]

[0362] [Table 26-6]

[0363] [Table 26-7]

[0364] <Confirmation of crosslinking by coating a thermoplastic polymer-containing layer on a separator substrate> [Example 41-1] As shown in Table 27, separator substrates made of polyolefin microporous membranes were obtained by the same procedures as in Example 40-1, except that the preparation conditions for the polyolefin microporous membranes were changed. Next, as shown in Table 27, the type of resin and the concentration of the organic solvent were adjusted to obtain a thermoplastic polymer-containing coating solution, and the pH of the coating solution and the contact angle of the coating solution with the clean separator substrate surface were also measured according to the method described above. Furthermore, the coating liquid was applied to the separator substrate using a gravure reverse coater in the same manner as in Example 40-1, to obtain a multilayer separator with a coating thickness as shown in Table 27. Furthermore, the progress of the crosslinking reaction during the coating process was confirmed by comparing the TMA rupture temperature before and after coating. The obtained multilayer separator was subjected to various evaluations according to the evaluation methods described above, and the evaluation results are also shown in Table 27. Furthermore, a non-aqueous secondary battery was fabricated using the multilayer separator according to the battery fabrication method described above, and the battery was evaluated. The results of the battery evaluation are also shown in Table 27.

[0365] [Examples 41-2 to 41-49, Comparative Examples 12-1 to 12-7] Separator substrates made of polyolefin microporous membranes and multilayer separators coated with a thermoplastic polymer-containing layer were obtained by the same procedures as in Example 41-1, except that the resin composition and molecular weight mixture composition of the polyolefin microporous membrane, production conditions, substrate characteristics, type of thermoplastic resin, and composition and physical properties of the coating liquid were changed as shown in Table 27. The obtained separator substrates and multilayer separators were evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 27. Furthermore, a non-aqueous secondary battery was obtained using a multilayer separator coated with a thermoplastic polymer-containing layer. The obtained battery was evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 27.

[0366] [Table 27-1]

[0367] [Table 27-2]

[0368] [Table 27-3]

[0369] [Table 27-4]

[0370] [Table 27-5]

[0371] [Table 27-6]

[0372] <Confirmation of crosslinking by coating the active layer on the separator substrate> [Example 42-1] As shown in Table 28, separator substrates made of polyolefin microporous membranes were obtained by the same procedures as in Example 40-1, except that the preparation conditions for the polyolefin microporous membranes were changed. Next, commercially available PVDF-HFP was prepared as a fluororesin, as shown in Table 28. Furthermore, a coating liquid was prepared containing 95 parts by weight of aluminum hydroxide oxide (average particle size 1.4 μm) as inorganic particles, PVDF-HFP, and N-methyl-2-pyrrolidone (NMP) as an organic solvent, with the organic solvent concentration shown in Table 28. Furthermore, the coating liquid was applied to the separator substrate using a gravure reverse coater in the same manner as in Example 40-1, followed by washing with water and drying to obtain a multilayer separator with a coating thickness as shown in Table 28. The progress of the crosslinking reaction during the coating process was confirmed by comparing the TMA rupture temperature before and after coating. The obtained multilayer separator was evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 28. Furthermore, a non-aqueous secondary battery was fabricated using the multilayer separator according to the battery fabrication method described above, and the battery was evaluated. The results of the battery evaluation are also shown in Table 28.

[0373] [Examples 42-2 to 42-43, Comparative Examples 13-1 to 13-7] Separator substrates made of polyolefin microporous membranes and multilayer separators coated with active layers were obtained by the same procedures as in Example 42-1, except that the resin composition and molecular weight mixture composition of the polyolefin microporous membrane, production conditions, substrate characteristics, type of fluororesin, and composition and physical properties of the coating liquid were changed as shown in Table 28. The obtained separator substrates and multilayer separators were evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 28. Furthermore, a non-aqueous secondary battery was obtained using a multilayer separator coated with an active layer. The obtained battery was evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 28.

[0374] [Table 28-1]

[0375] [Table 28-2]

[0376] [Table 28-3]

[0377] [Table 28-4]

[0378] [Table 28-5]

[0379] [Table 28-6]

[0380] <Confirmation of crosslinking by coating a heat-resistant resin layer on a separator substrate> [Example 43-1] As shown in Table 29, separator substrates made of polyolefin microporous membranes were obtained by the same procedures as in Example 40-1, except that the preparation conditions for the polyolefin microporous membranes were changed. Next, as shown in Table 29, an inorganic filler having a predetermined inorganic particle size was prepared and blended into a coating solution containing para-aromatic aramid or meta-aromatic aramid so as to achieve a predetermined inorganic particle weight ratio and organic solvent concentration.

[0381] (In the case of para-aromatic aramid) 150 parts by mass of paraphenylenediamine was added to 5,000 parts by mass of N-methyl-2-pyrrolidone (NMP) / calcium chloride solution (calcium chloride concentration = 7.1% by mass), and the mixture was dissolved and stirred under a N2 atmosphere. 273.94 parts by mass of terephthalic acid dichloride was then added, stirred, and reacted for 1 hour to obtain a polyparaphenylene terephthalamide polymerization solution. 1,000 parts by mass of the polymerization solution, 3,000 parts by mass of NMP, and a predetermined amount of alumina (Al2O3) particles (having the particle size shown in Table 29) were mixed and stirred, and dispersed with a homogenizer to obtain a coating solution. The coating solution was applied to one side of a polyolefin microporous membrane using a drum-mounted bar coater with a clearance of 20 to 30 μm and a coating thickness shown in Table 29, and then dried at approximately 70°C to obtain a multilayer separator.

[0382] (In the case of meta-aromatic aramid) A coating solution was prepared by mixing 100 parts by mass of meta-aromatic polyamide with a predetermined amount of boehmite (having the particle size shown in Table 29) and then mixing this with a mixed solvent of dimethylacetamide (DMAc) and tripropylene glycol (TPG) (mass ratio = 1:1) so that the meta-aromatic polyamide concentration was 3 mass%. The coating solution was applied to one side of a polyolefin microporous membrane using a Mayer bar coater with a clearance of 20 μm to 30 μm and a coating thickness shown in Table 29 to obtain a coated separator. The coated separator was immersed in a coagulation solution with a mass ratio of water:DMAc:TPG = 2:1:1 at 35°C, followed by water washing and drying to obtain a multilayer separator.

[0383] For multilayer separators coated with a heat-resistant resin layer containing para- or meta-aromatic aramid and an inorganic filler, the progress of the crosslinking reaction during the coating process was confirmed by comparing the TMA rupture temperature before and after coating. The obtained multilayer separators were evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 29.

[0384] (Testing of batteries containing multi-layer separators coated with heat-resistant resin layers) In Example 43-1, a non-aqueous secondary battery was fabricated using the multilayer separator according to the battery fabrication method described above, and the battery evaluation results are also shown in Table 29.

[0385] [Examples 43-2 to 43-50, Comparative Examples 14-1 to 14-7] Separator substrates made of polyolefin microporous membranes and multilayer separators coated with heat-resistant resin layers were obtained by the same procedures as in Example 43-1, except that the resin composition and molecular weight mixture composition of the polyolefin microporous membrane, production conditions, substrate characteristics, type, particle size and ratio of the inorganic filler, type of aramid resin, composition and physical properties of the coating liquid, etc. were changed as shown in Table 29. The obtained separator substrates and multilayer separators were evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 29. Furthermore, a non-aqueous secondary battery was obtained using a multilayer separator coated with a heat-resistant resin layer. The obtained battery was evaluated in various ways according to the evaluation methods described above, and the evaluation results are also shown in Table 29.

[0386] [Table 29-1]

[0387] [Table 29-2]

[0388] [Table 29-3]

[0389] [Table 29-4]

[0390] [Table 29-5]

[0391] [Table 29-6] [Explanation of symbols]

[0392] t c Crystal thickness t a Amorphous part thickness f c crystal long period a c crystal orientation degree

Claims

1. A separator for a non-aqueous secondary battery comprising a polyolefin microporous membrane, A silane-modified polyethylene and a polyethylene other than the silane-modified polyethylene, a Voronoi area (mu) of the maximum frequency among Voronoi polygons obtained by Voronoi division of a Si-containing image detected by time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurement of the nonaqueous secondary battery separator is within a range of 1.0 μm 2 to 17.5 μm 2 ; the spread (σ) of the Voronoi area frequency distribution of the Si-containing image detected by the TOF-SIMS measurement is within a range of 0.5 μm 2 to 8.5 μm 2 ; a ratio (σ / mu) of the spread (σ) of the Voronoi area frequency distribution to the Voronoi area of ​​maximum frequency (mu) is 0.06 to 0.70; and A separator for a non-aqueous secondary battery, in which the rate of change in air permeability (air permeability Sh after compression / air permeability Sj before compression) when compressed by 30% of its thickness is 1.1 to 7.0 times.

2. A non-aqueous secondary battery comprising: a positive electrode; a negative electrode; the separator for a non-aqueous secondary battery according to claim 1; and a non-aqueous electrolyte solution.

3. The positive electrode has the formula: Li—Ni ｘ -Mn ｙ -Co ｚ 3. The nonaqueous secondary battery according to claim 2, comprising a lithium (Li)-nickel (Ni)-manganese (Mn)-cobalt (Co) composite oxide represented by the formula: {wherein x represents the Ni proportion, y represents the Mn proportion, z represents the Co proportion, and x + y + z = 1}, wherein the Ni proportion x in the formula is 5 to 9.

4. 4. The nonaqueous secondary battery according to claim 2, wherein the negative electrode contains a negative electrode active material, and the proportion of Si in the negative electrode active material is 5% by weight to 90% by weight.

5. 5. The nonaqueous secondary battery according to claim 2, wherein the nonaqueous electrolyte solution contains a lithium salt at a concentration in the range of 1.2 mol / L to 10 mol / L.

6. The non-aqueous electrolyte solution contains ethyl methyl carbonate (EMC) and / or acetonitrile (AcN), and the total content of EMC and AcN in the non-aqueous electrolyte solution is in the range of 50% by mass to 90% by mass. The non-aqueous secondary battery according to any one of claims 2 to 5.

Images