Secondary battery with non-aqueous electrolyte

Abstract

Secondary battery with non-aqueous electrolyte, comprising: a flat roll electrode unit (20) in which an elongated positive electrode (50), an elongated negative electrode (60) and an elongated separator (70), which electrically insulates the positive and negative electrodes from each other, are placed one on top of the other and wound together in a longitudinal direction; and a non-aqueous electrolyte; wherein the secondary battery with non-aqueous electrolyte is characterized in that it comprises: a fiber layer (80) which is arranged at least between the separator (70) and the positive electrode (50) or between the separator (70) and the negative electrode (60) and contains fiber made of a synthetic resin, wherein the fiber layer (80) contains at least polyvinylidene fluoride and polytetrafluoroethylene as components of the synthetic resin forming the fiber, Polyvinylidene fluoride and polytetrafluoroethylene both have an average molecular weight greater than or equal to 200,000 and less than or equal to 2,000,000, respectively, and in the components of the fiber-forming synthetic resin, the polyvinylidene fluoride content is greater than the polytetrafluoroethylene content, and the polytetrafluoroethylene content is less than or equal to 45% based on the mass of the components of the synthetic resin.

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The invention relates to a secondary battery with a non-aqueous electrolyte. 2. Description of the related prior art

[0002] Compared to existing batteries, secondary batteries with non-aqueous electrolyte, such as lithium-ion secondary batteries (lithium secondary batteries), are lighter and have a higher energy density. Therefore, secondary batteries with non-aqueous electrolyte have been used in recent years as portable power supplies in personal computers, mobile devices, and the like, or as power supplies for vehicles. Lithium-ion secondary batteries, in particular, which are lightweight and offer high energy density, are preferred as high-output power supplies for vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs).

[0003] A typical non-aqueous secondary battery contains a positive electrode with a positive electrode active material layer, a negative electrode with a negative electrode active material layer, and a non-aqueous electrolyte. It is a battery that is charged and discharged by the movement of charge carriers (such as lithium ions) in the electrolyte between the electrodes. During charging, charge carriers (typically lithium ions) are released (separated) from the positive electrode active material, which forms the positive electrode active material layer, and absorbed (stored) into the negative electrode active material, which forms the negative electrode active material layer.Conversely, during the discharge of a secondary battery with non-aqueous electrolyte, charge carriers (typically lithium ions) are released (separated) from the negative electrode active material and absorbed (stored) into the positive electrode active material. Simultaneously, as the charge carriers (typically lithium ions) are absorbed into and released from the active materials during the charging and discharging of the secondary battery with non-aqueous electrolyte, as described above, the positive and negative electrode active materials (that is, the positive and negative electrode active material layers containing the active materials) expand and contract.

[0004] Typically, such a secondary battery with a non-aqueous electrolyte is created by incorporating an electrode assembly consisting of a positive and a negative electrode laminated together with an intermediate separator, and in some cases, an electrolyte. Known electrode assembly structures include laminate-type electrode assemblies (composed of multiple planar electrode assemblies), coil-type electrode assemblies (obtained by winding a long, web-like electrode assembly into a coil), and similar configurations. If the electrode assembly is designed as described above, the reaction zone between the positive and negative electrodes can be enlarged, thereby improving energy density and output power. In this context, the separator is typically a porous film made of resin.Such a separator serves to electrically isolate the positive electrode from the negative electrode and to retain the non-aqueous electrolyte. Examples of technical documents relating to such a secondary battery with a non-aqueous electrolyte include Japanese patent application publication JP 2008-078008 A and Japanese patent application publication JP 2012-074403 A.

[0005] In the event that the secondary battery designed as above with non-aqueous electrolyte is used in an application involving repeated high-current charging and discharging (for example, in a case where the battery is mounted on a vehicle), the separator may be compressed due to the stretching and contraction of the positive and negative electrode active materials (positive and negative electrode active material layers) associated with charging and discharging, potentially causing pores of the separator to be crushed, and consequently, the non-aqueous electrolyte held in the pores may be forced out of the electrode assembly.As a result, the amount of non-aqueous electrolyte held in the electrode assembly varies, and accordingly, one section of the electrode assembly may hold a large amount of non-aqueous electrolyte, while the other section may, in some cases, hold a small amount (deficiency) of non-aqueous electrolyte. When the electrode assembly is of the coil type, the amount of non-aqueous electrolyte held may vary between the end section and the middle section along the winding axis (that is, in some cases, the amount of non-aqueous electrolyte varies). Within the electrode assembly, the section with a small amount (deficiency) of non-aqueous electrolyte is prone to a so-called fluid deficiency.In the section containing a low amount of non-aqueous electrolyte (typically the section where fluid loss occurs), the amount of non-aqueous electrolyte present is less than necessary, and the overall charging and discharging performance of the battery or accumulator tends to deteriorate. Furthermore, within the electrode assembly, battery reactions occur primarily in the section containing a relatively large amount of non-aqueous electrolyte, thus accelerating the deterioration of such a section. None of the aforementioned phenomena are desirable, as they contribute to performance degradation (increased battery resistance, capacity loss, and the like).In particular, for the secondary battery with non-aqueous electrolyte, which is used in applications where high-current charging and discharging characteristics are required at a high level, it is important to suppress the performance degradation resulting from variations in the amount of non-aqueous electrolyte in the electrode assembly.

[0006] Furthermore, JP 2010-205 719 A, DE 11 2013 000 388 T5, US 2014 / 0 023 908 A1, JP 2013-089 323 A and US 2014 / 0 123 472 A1 disclose secondary batteries from the prior art. SUMMARY OF THE INVENTION

[0007] The invention provides for a secondary battery with a non-aqueous electrolyte that possesses excellent high-current charging and discharging characteristics. Specifically, the invention provides for a secondary battery with a non-aqueous electrolyte that includes an electrode unit which excellently retains a non-aqueous electrolyte.

[0008] A first aspect of the invention relates to a secondary battery with a non-aqueous electrolyte, comprising a flat-roll electrode assembly in which an elongated positive electrode, an elongated negative electrode, and an elongated separator, which electrically separates the positive and negative electrodes from each other, are stacked one on top of the other and wound together longitudinally, as well as a non-aqueous electrolyte. The secondary battery with a non-aqueous electrolyte has a fiber layer containing a fiber made of a synthetic resin at least between the separator and the positive electrode or between the separator and the negative electrode. The fiber layer contains at least polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) as components of the synthetic resin forming the fiber, and the PVDF and the PTFE both have a number-average molecular weight (Mn) of greater than or equal to 200.000 and less than or equal to 2,000,000. In the components of the fiber-forming synthetic resin, the content of PVDF is greater than the content of PTFE, and the content of PTFE is less than or equal to 45% based on the mass of the components of the synthetic resin.

[0009] In this specification, "non-aqueous electrolyte secondary battery" refers to a secondary battery that incorporates a non-aqueous electrolyte (typically a non-aqueous electrolyte containing a carrier salt (carrier electrolyte) in a non-aqueous solvent (organic solvent)). Here, "secondary battery" generally refers to a battery or accumulator that can be repeatedly charged and discharged and is a term that includes a so-called chemical cell, such as a lithium-ion secondary battery, and a physical cell, such as an electrical double-layer capacitor. Furthermore, the "mean molecular weight" of the components of the synthetic resin in this specification means a number-mean molecular weight, and a value that is measured by gel permeation chromatography (GPC), for example, may be chosen.

[0010] As described above, the secondary battery with non-aqueous electrolyte includes the fiber layer between the separator and the positive electrode or between the separator and the negative electrode. Accordingly, crushing of the separator pores can be prevented even if the battery is in an environment where the separator is pressurized. Furthermore, even if the separator is compressed and the non-aqueous electrolyte is forced out, the expelled non-aqueous electrolyte can be retained in the fiber layer adjacent to the separator by positioning the fiber layer between the separator and the positive electrode or between the separator and the negative electrode.Consequently, it is possible to prevent variations (such as fluid loss) in the amount of non-aqueous electrolyte in the electrode assembly. That is, the non-aqueous secondary battery designed as described above can prevent the deterioration in battery performance resulting from variations in the amount of non-aqueous electrolyte in the electrode assembly and can be considered a non-aqueous secondary battery with excellent high-current charging and discharging characteristics. In this case, the fiber layer, due to its PVDF content, possesses excellent non-aqueous electrolyte retention properties (referred to below as "non-aqueous electrolyte retention"). Furthermore, the strength of the fiber forming the layer can be improved by the inclusion of PTFE in the fiber layer.By adjusting the PVDF and PTFE content in the components of the synthetic resin that forms the fiber within the fiber layer to the specified range, both the retention capacity for non-aqueous electrolyte and the strength or strength of the fiber forming the fiber layer can be simultaneously achieved. Furthermore, by using PVDF and PTFE with molecular weights within the specified range, it is possible to create a homogeneous fiber layer in which the fibers forming the layer are exceptionally well interwoven.

[0011] The PVDF content in the components of the fiber-forming synthetic resin can be greater than or equal to 30% and less than or equal to 80% by mass of the synthetic resin components. A fiber layer possessing this characteristic can simultaneously achieve both a high degree of non-aqueous electrolyte retention capacity and a high degree of strength improvement in the fibers forming the layer.

[0012] The average thickness of the fiber layer can be greater than or equal to 0.5 µm and less than or equal to 6 µm. Even with a relatively small average thickness, the fiber layer can exhibit excellent retention capacity for non-aqueous electrolyte. By adjusting the average thickness of the fiber layer to fall within the aforementioned range, the distance between the positive and negative electrodes (electrode spacing) can be reduced. Consequently, the distance traveled by charge carriers in the non-aqueous electrolyte between the two electrodes is shortened (i.e., the movement of charge carriers between the two electrodes becomes more uniform), thus reducing the battery resistance.

[0013] The separator can comprise a resin substrate layer and a heat-resistant layer containing heat-resistant fine particles, which forms on the surface of the substrate layer. The fiber layer can also be formed on the surface of the heat-resistant layer. Forming the fiber layer on the surface of the separator preferably prevents the separator's pores from being crushed. Furthermore, the non-aqueous electrolyte can be retained within the fiber layer even if the separator is compressed and the non-aqueous electrolyte is squeezed out. Typically, minute protrusions and depressions are present on the surface of the heat-resistant layer, and the fiber forming the fiber layer readily engages in these protrusions and depressions. Consequently, the surface of the heat-resistant layer is suitable for the formation of the fiber layer.

[0014] A second aspect of the invention relates to a composite battery in which a plurality of unit cells are electrically interconnected. Each of the unit cells is the secondary battery with a non-aqueous electrolyte of the first aspect. The unit cells can be confined in a state in which a confining pressure of greater than or equal to 0.2 MPa and less than or equal to 10 MPa is applied in a direction orthogonal to a flat surface of the flat-roll electrode assembly contained in each of the unit cells. In the composite battery configured as above, the roller electrode assembly contained in each of the unit cells forming the composite battery is confined under a predetermined confining pressure.When high-current charging and discharging are repeated, the separator in the electrode assembly is therefore slightly compressed, and the non-aqueous electrolyte in the electrode assembly is easily squeezed out of the electrode assembly. Accordingly, by selecting the secondary battery with non-aqueous electrolyte of the first aspect as each of the unit cells used in the composite battery (secondary batteries with non-aqueous electrolyte), it is possible to provide a composite battery that includes unit cells which can exhibit the aforementioned effects of the invention at a high level. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Features, advantages, and the technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which the same symbols denote the same elements. The drawings show: Figs.Figure 1 is a perspective view schematically showing an appearance of a secondary battery with non-aqueous electrolyte according to an embodiment of the invention; Figs. 2 is a longitudinal section view showing a section structure along line II-II in Figs. 1 schematically shows; Figs. Figure 3 is a schematic view showing an embodiment of a roller-type electrode unit according to the embodiment; Figs. 4 is a longitudinal section view showing a section structure along line IV-IV in Figs. 3 schematically shows, and is a partial sectional view which schematically shows, by means of magnification, a section between a positive and a negative electrode of the roller-type electrode unit according to the embodiment; and Figs.Figure 5 is a perspective view schematically showing a composite battery in which a plurality of secondary batteries with non-aqueous electrolyte are combined according to the embodiment of the invention. DETAILED DESCRIPTION OF EXECUTION FORMS

[0016] Embodiments of the invention are described below, possibly with reference to drawings. In the present context, elements not specifically described in the invention but necessary for its implementation can be identified as design considerations, selected from those in the related prior art based on the relevant prior art. The invention is feasible based on the content disclosed in this specification and the general technical knowledge in the relevant prior art. In the following drawings, functionally identical element sections are sometimes described by marking them with the same symbol to avoid or simplify repetitive descriptions.Furthermore, the dimensional ratio (length, width, thickness, or the like) in each drawing does not necessarily reflect the actual dimensional ratio. A lithium-ion secondary battery is merely one example, and the invention also applies to other secondary batteries with non-aqueous electrolyte (for example, magnesium secondary batteries) that contain other charge carriers (for example, magnesium ions).

[0017] An embodiment of the invention is described in detail below, primarily illustrating a case in which the invention applies to a secondary battery with a non-aqueous electrolyte (lithium-ion secondary battery) having a configuration in which a roller-type electrode assembly and an electrolyte are housed in an angled battery casing. However, the invention is not limited to this embodiment. For example, the roller-type electrode assembly is merely one example, and the technical concept of the invention also applies to other shapes (for example, a laminate-type electrode assembly). Furthermore, the shape (appearance or size) of the secondary battery with a non-aqueous electrolyte is not subject to any particular restrictions.

[0018] Apart from having a fiber layer, which will be described later, between a positive electrode and a separator and / or a negative electrode and a separator, the secondary battery with non-aqueous electrolyte of the present embodiment can be designed in the same way as secondary batteries with non-aqueous electrolyte of the related prior art.

[0019] As in Figs. 1 and Figs.Figure 2 shows a lithium-ion secondary battery 100 having a configuration in which an electrode unit (roll-type electrode unit) 20, together with a non-aqueous electrolyte (not shown in the drawing), is housed in a flat, box-shaped battery casing 30. The electrode unit 20 has a shape in which an elongated positive electrode (positive electrode track) 50, an elongated negative electrode (negative electrode track) 60, and an elongated separator (separator track) 70 positioned between these electrodes are wound flat.

[0020] As in Figs. 1 and Figs.As shown in Figure 2, the battery housing 30 is configured with a housing body 32, which has the shape of a box (i.e., the shape of a cuboid with a base) and an opening at one end (which is considered the top section of a battery used in normal conditions), and with a lid unit 34, which seals the opening of the housing body 32. As shown in the drawings, the lid unit 34 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection. The lid unit 34 is also provided with a safety valve 36 for venting gas generated inside the battery housing 30 and an inlet (not shown in the drawings) for injecting a non-aqueous electrolyte into the battery housing.For example, the material of the battery casing 30 would be a metal material (made from an alloy), such as aluminum, an aluminum alloy or stainless steel, and a resin material. <<Elektrodeneinheit 20 vom Rollentyp> >

[0021] As in Figs. 3 and Figs. As shown in Figure 4, the coil-type electrode unit 20 has a fiber layer 80 between the negative electrode 60 and the separator 70. An exemplary embodiment of the invention, a secondary battery with a non-aqueous electrolyte, is described below in which the fiber layer is formed on the surface of the separator, but the invention is not limited to this. The fiber layer 80 can be arranged between the positive electrode 50 and the separator 70, and between the negative electrode 60 and the separator 70. Furthermore, the fiber layer 80 can be arranged only between the positive electrode 50 and the separator 70.

[0022] As in Figs.As shown in Figure 3, the coil-type electrode unit 20 according to the present embodiment has, in the phase before assembly, the structure of a long web (web-like electrode unit). In the coil-type electrode unit 20, the positive electrode (positive electrode web) 50, in which a positive electrode active material layer 54 is formed on one or both surfaces (here, both surfaces) of an elongated positive electrode current collector 52 along a longitudinal direction, and the negative electrode (negative electrode web) 60, in which a negative electrode active material layer 64 is formed on one or both surfaces (here, both surfaces) of an elongated negative electrode current collector 62 along the longitudinal direction, are laid one on top of the other and wound together with the elongated separator (separator web) 70, on which the fiber layer 80 is formed and which is positioned between the electrodes, in the longitudinal direction.The roller-type electrode unit 20 can be flattened by pressing and pushing it further downwards from the transverse direction after winding it up as above.

[0023] As described above, the fiber layer 80 can be arranged between the separator 70 and the negative electrode 60 by placing the separator 70, on which the fiber layer 80 is formed, between the positive electrode 50 (positive electrode active material layer 54) and the negative electrode 60 (negative electrode active material layer 64), and by stacking the electrodes and the separator on top of each other. In the drawings, the positive electrode 50, the negative electrode 60, and the separator 70 are stacked such that the fiber layer 80 formed on one surface of the separator 70 faces the negative electrode active material layer 64. That is, the fiber layer 80 is arranged between the negative electrode 60 (negative electrode active material layer 64) and the separator 70.

[0024] In the present embodiment, the fiber layer 80 is arranged between the separator 70 and the positive electrode 50 and between the separator 70 and the negative electrode 60. As a result, the fiber layer is more effective at retaining the non-aqueous electrolyte squeezed out of the separator. Furthermore, a large quantity of non-aqueous electrolyte can be retained in a section near the negative electrode active material layer 64 and the positive electrode active material layer 54, thus largely preventing a deficiency of non-aqueous electrolyte (typically a lack of fluid) in these layers. Moreover, it is preferable to arrange the fiber layer 80 as described above because this prevents the squeezing of the separator pores.The electrode unit 20 should, for example, be produced by forming the fiber layer 80 on both surfaces of the separator 70 and placing the separator 70, the positive electrode 50 and the negative electrode 60 on top of each other.

[0025] In the present embodiment, one embodiment is described by way of example in which the fiber layer 80 is formed on the surface of the separator 70. However, if the fiber layer 80 is arranged between the separator 70 and the positive electrode 50 and / or between the separator 70 and the negative electrode 60, the invention is not limited to this embodiment. For example, the fiber layer 80 can be formed on the surface (one surface or both surfaces) of the positive electrode 50 (typically the positive electrode active material layer 54) or on the surface (one surface or both surfaces) of the negative electrode 60 (typically the negative electrode active material layer 64).For example, the electrode unit 20, in which the fiber layer 80 is arranged between the separator 70 and the positive electrode 50 and between the separator 70 and the negative electrode 60, can be produced as described above by forming the fiber layer 80 on both surfaces of the positive electrode 50 (typically the positive electrode active material layer 54) and on both surfaces of the negative electrode 60 (typically the negative electrode active material layer 64) and by placing the positive electrode 50, the negative electrode 60 and the separator 70 on top of each other. Alternatively, the long web-like fiber layer 80 can be produced separately, and then the fiber layer 80, the positive electrode 50, the negative electrode 60 and the separator 70 are placed on top of each other such that the fiber layer 80 is arranged between the separator 70 and the positive electrode 50 and / or between the separator 70 and the negative electrode 60.

[0026] As in Figs. 2 and Figs.As shown in Figure 4, a roller core section (i.e., a laminate structure in which the positive electrode active material layer 54 of the positive electrode 50, the negative electrode active material layer 64 of the negative electrode 60, and the separator 70 are laminated together) is formed in the central section of the roller-type electrode unit 20 in the direction of the winding axis. Furthermore, at both ends of the roller-type electrode unit 20, a section of a positive electrode active material layer non-formation section 52a and a section of a negative electrode active material layer non-formation section 62a, respectively, protrude from the roller core section in the direction of the winding axis. A positive electrode current collector plate 42a and a negative electrode current collector plate 44a are attached to the protruding section on the positive electrode side (the positive electrode active material layer non-formation section 52a) and the negative electrode current collector plate 44a, respectively.the protruding section on the negative electrode side (the negative electrode active material layer non-formation section 62a) and electrically connected to the positive electrode connection 42 or the negative electrode connection 44. < <faserschicht>>

[0027] The fiber layer 80 of the present embodiment contains a fiber made of a synthetic resin and has a fiber-containing lattice structure. Typically, the fiber layer 80 has a large number of pores (cavities) (i.e., the fiber layer 80 has a high void content), and thus the non-aqueous electrolyte can be retained in the cavities. That is, the fiber layer 80 has excellent non-aqueous electrolyte retention capacity. Consequently, the amount of non-aqueous electrolyte that can be retained in the electrode assembly 20 with the fiber layer 80 can be increased. Furthermore, since the fiber layer 80 has high porosity and excellent permeability to the non-aqueous electrolyte, it is easily saturated with the non-aqueous electrolyte.Consequently, since such a fiber layer 80 is present in the electrode assembly 20, the electrode assembly 20 can be uniformly impregnated with the non-aqueous electrolyte. In particular, in the coil-type electrode assembly 20, the electrolyte inlet (end of the coil-type electrode assembly 20 in the direction of flow) is slightly constricted relative to the electrode area, and thus the electrode assembly is slightly unevenly impregnated with the non-aqueous electrolyte. Therefore, it is particularly effective if the electrode assembly 20 has the fiber layer 80, so that the electrode assembly 20 is efficiently impregnated with the non-aqueous electrolyte. Typically, the fiber layer 80 is a structure formed by joining fibers three-dimensionally by weaving, knitting, laminating, and the like.

[0028] The fiber layer 80 can be in the form of a woven or nonwoven fabric. For example, the nonwoven-like fiber layer 80 can be in the form of a nonwoven fabric obtained by forming and integrating fibers into a web without weaving. Typically, the nonwoven-like fiber layer 80 is composed of laminated fibers. In the nonwoven-like fiber layer 80, the fibers can, for example, form a web in one piece by being interwoven without being bonded to each other, they can be directly bonded to each other at an intersection point, or they can be bonded to each other at an intersection point by a binder. The woven-like fiber layer 80 can be in the form of a woven fabric, obtained, for example, by weaving fibers into a web (fabric). The fabric structure of the woven-like fiber layer 80 is not subject to any particular restrictions.For example, various structures such as plain weave, twill weave, and satin weave can be selected, and the diameter of the fiber used or the aperture can be arbitrarily adjusted. In the present embodiment, the fabric, woven such that the warp threads describe a sharp curve in the thickness direction (i.e., in the three-dimensionally woven fabric), can reduce air permeability in the plane. In this embodiment, the nonwoven-like fiber layer is described by way of example as fiber layer 80.

[0029] Fiber layer 80 contains at least PVDF and PTFE as components of the synthetic resin that forms the fiber contained within the fiber layer 80. Typically, the fiber can be formulated with a mixture of PVDF and PTFE. PVDF has excellent non-aqueous electrolyte retention properties. Therefore, if the fiber contains PVDF, the electrolyte retention capacity of the fiber layer can be improved. Furthermore, PTFE possesses excellent mechanical strength. Accordingly, the strength (dimensional stability) of the fiber layer can be improved if the fiber contains PTFE. That is to say, fiber layer 80, which contains the fiber formulated with at least PVDF and PTFE as components of the synthetic resin, has excellent non-aqueous electrolyte retention properties and is not easily crushed.Both the PVDF and the PTFE contained in the fiber have a mean molecular weight (number-mean molecular weight: Mn) greater than or equal to 200,000 and less than or equal to 2,000,000. If the mean molecular weight of PVDF and PTFE is too low, this can easily lead to poor fiber interlocking, and thus the formability of the fiber layer 80 can be impaired. Conversely, if the mean molecular weight of PVDF and PTFE is too high, the fibers are easily and excessively interwoven, and consequently, in some cases, it is difficult to form the fiber layer 80 with homogeneous properties (typically mean thickness, pore distribution, and the like).

[0030] The PTFE content in the components of the fiber-forming synthetic resin can be less than or equal to 45% by mass. For example, the PTFE content can be greater than or equal to 10% (typically greater than or equal to 20%) and less than or equal to 45% (typically less than or equal to 30%) by mass. If the PTFE content in the fiber forming the fiber layer 80 is too low, the strength (dimensional stability) of the fiber layer 80 is reduced, and thus the fiber layer 80 is easily crushed. As a result, in some cases it is difficult to retain a sufficient amount of non-aqueous electrolyte in the fiber layer 80. Conversely, if the PTFE content in the fiber is too high, the formability of the fiber layer 80 deteriorates, and accordingly it is difficult to form the fiber layer with homogeneous properties (for example, mean thickness, pore distribution, and the like).In the components of the fiber-forming synthetic resin, the PVDF content is higher than the PTFE content. For example, the PVDF content in the components of the fiber-forming synthetic resin is preferably greater than or equal to 30% (for example, greater than or equal to 50%) and less than or equal to 80% (for example, less than or equal to 70%) based on the mass of the components of the synthetic resin. By adjusting the PVDF content, based on the total mass of the components of the fiber-forming synthetic resin, such that it lies within the aforementioned range, a fiber layer 80 with homogeneous properties (typically average thickness, pore distribution, and the like) can be formed.If the PVDF content in the fiber forming fiber layer 80 is too low, the resulting retention capacity of non-aqueous electrolyte may be insufficient, and thus the electrolyte retention capacity of fiber layer 80 may deteriorate. Conversely, if the PVDF content in the fiber is too high, fiber layer 80 may retain an excess of non-aqueous electrolyte, while the positive electrode 50 (typically the positive electrode active material layer 54) and the negative electrode 60 (typically the negative electrode active material layer 64) will lack the non-aqueous electrolyte.The total content of PVDF and PTFE in the components of the fiber-forming synthetic resin is preferably greater than or equal to 50% (more preferably greater than or equal to 55%, even more preferably greater than or equal to 70%, and still more preferably greater than or equal to 75%) based on the mass of the components of the synthetic resin. The fiber forming the fiber layer 80 can essentially consist only of PVDF and PTFE as the components of the synthetic resin.

[0031] Provided that the effects of the invention are not significantly impaired, the fiber forming the fiber layer 80 may contain, in addition to PVDF and PTFE, one or two or more other types of synthetic resin components. Such synthetic resin components are not subject to any particular restrictions, and examples include a fluoropolymer such as polyvinyl fluoride (PVF) or a perfluoroethylenepropene copolymer (FEP); a polyolefin resin such as polyethylene or polypropylene; a polyester resin such as polyethylene terephthalate; an acrylic resin such as polymethyl methacrylate (PMMA); a polyamide resin such as nylon; a polyimide resin; a vinyl resin such as polyvinyl chloride; a styrene resin such as polystyrene; a carbonate resin such as polycarbonate; and the like.In the case that the fiber layer contains components of the synthetic resin other than PVDF and PTFE as the components of the fiber-forming synthetic resin, the proportion of the components of the synthetic resin other than PVDF and PTFE in the components of the synthetic resin forming the fiber layer is preferably, for example, less than or equal to 45% (more preferably less than or equal to 30%, even more preferably less than or equal to 25%, and even more preferably less than or equal to 10%) based on the mass of the components of the synthetic resin.

[0032] Typically, the fiber forming the fiber layer is preferably a fiber composed solely of the synthetic resin components described above. However, if necessary, the fiber may contain one or more types of material in addition to the synthetic resin components. Examples of such materials include various additives, such as a stabilizer referred to as an oxidation stabilizer, and a modifier referred to as a plasticizer or lubricant. Alternatively, for the purpose of ensuring the strength of the fiber layer, the fiber may also contain glass, ceramics, an inorganic material represented by an inorganic carbon material, a metallic material represented by copper or steel, and the like.In the case that the fiber contains components different from the components of the synthetic resin, the proportion of the components different from the components of the synthetic resin is preferably, for example, greater than or equal to 0.01% (generally greater than or equal to 0.05%) and less than or equal to 1% (generally less than or equal to 0.5%) based on the mass of the fiber. In a preferred aspect, the proportion of the components of the synthetic resin (PVDF, PTFE, and other components of a synthetic resin) contained in the fiber is approximately greater than or equal to 90% (for example, greater than or equal to 95%) based on the mass of the fiber. The fiber forming the fiber layer 80 can be a fiber that is essentially composed only of the components of the synthetic resin described above.

[0033] The diameter of the fiber is not subject to any particular restrictions. However, if a finer fiber is used, the surface area of ​​the fiber can be increased, and therefore the contact area between the fiber forming the fiber layer 80 and the non-aqueous electrolyte can be enlarged. As a result, the leakage of the non-aqueous electrolyte retained in the fiber layer 80 can be suppressed. Furthermore, if a finer fiber is used, the fiber layer 80 can be produced with more pores (i.e., the fiber layer 80 with a large void fraction), and accordingly, the amount of non-aqueous electrolyte that can be retained in the fiber layer 80 can be increased (i.e., the electrolyte retention capacity of the fiber layer 80 can be improved). From the point of view of producing a thinner fiber layer 80, a fiber with a small diameter is preferable.Therefore, the average fiber diameter is preferably, for example, less than or equal to 200 nm (preferably less than or equal to 150 nm). There are no particular restrictions on the lower limit of the fiber diameter. However, if the fiber diameter is too small, the dynamic strength of the fiber layer 80 may be reduced. Furthermore, a fiber with an excessively small diameter is prone to breakage, making the formation of the fiber layer 80 difficult in some cases. Accordingly, the average fiber diameter is preferably, for example, greater than or equal to 50 nm. Generally, the fiber can have a diameter of approximately 100 nm.

[0034] The length of the fiber is not subject to any particular restrictions. However, if long fibers are used, they are exceptionally well interwoven, thus forming the fiber layer 80, which possesses high dynamic strength and is not easily crushed. Therefore, the average fiber length is preferably greater than or equal to 10 mm, more preferably greater than or equal to 100 mm, and even more preferably greater than or equal to 500 mm.

[0035] If necessary, the fiber layer 80 may contain materials other than the fiber made from the aforementioned synthetic resin (that is, the fiber containing at least PTFE and PVDF as components of the synthetic resin). For example, the fiber layer 80 may contain a binder that bonds the fibers together, and the like. Alternatively, the fiber may be used in combination with fibers other than the fiber composed of the components of the synthetic resin, such as fibers made from conductive materials like carbon nanotubes or whiskers, and ceramic fibers made of silicon dioxide, aluminum oxide, or aluminosilicate.In the case that the fiber layer 80 contains materials other than the fiber made from the synthetic resin (i.e., the fiber containing at least PTFE and PVDF as components of the synthetic resin), the proportion of the materials other than the fiber made from the synthetic resin in the entire fiber layer 80 is preferably, for example, greater than or equal to 0.01% (generally greater than or equal to 0.05%) and less than or equal to 1% (generally less than or equal to 0.5%) by mass. In a preferred aspect, the content of the fiber made from the synthetic resin (i.e., the fiber containing at least PTFE and PVDF as components of the synthetic resin) in the fiber layer 80 is approximately greater than or equal to 90% (for example, greater than or equal to 95%) by mass of the entire fiber layer 80.Fiber layer 80 can be a fiber layer that is essentially formed only with fiber containing at least PVDF and PTFE.

[0036] The mean thickness of the fiber layer 80 is not subject to any particular restrictions. However, if the mean thickness of the fiber layer 80 is too large, the energy density of the battery will be reduced. Therefore, it is preferable for the mean thickness of the fiber layer 80 to be small. For example, the mean thickness of the fiber layer 80 can be less than or equal to 6 µm (preferably less than or equal to 3 µm and more preferably less than or equal to 2 µm). Conversely, it is difficult to produce a fiber layer 80 with an extremely small mean thickness, and the thickness, porosity, and the like easily become heterogeneous. Accordingly, the mean thickness of the fiber layer 80 can be, for example, greater than or equal to 0.5 µm. The mean thickness of the fiber layer 80 can be determined, for example, by analyzing a SEM cross-sectional image or the like.

[0037] From the perspective of supplying the non-aqueous electrolyte held in the fiber layer 80 to the positive electrode active material layer 54 and the negative electrode active material layer 64 for use in a battery reaction, it is preferred that the fiber layer 80 be such that it covers at least a section where the positive electrode active material layer 54 and the negative electrode active material layer 64 are opposite each other at the time of electrode assembly. For example, the length of the fiber layer 80 in the lateral direction orthogonal to the longitudinal direction is preferably greater than the length of the positive electrode active material layer 54 in the lateral direction orthogonal to the longitudinal direction (preferably greater than the length of the negative electrode active material layer 64 in a direction orthogonal to the longitudinal direction).In particular, the length of the fiber layer 80 in the width direction is preferably equal to the length of the separator 70 in the width direction orthogonal to the longitudinal direction (preferably, the size of the fiber layer 80 is equal to that of the separator 70). If the fiber layer 80 has a size as described above, the non-aqueous electrolyte squeezed out of the separator 70 can preferably be retained in the fiber layer 80.

[0038] The process for producing the fiber layer 80 is not subject to any particular restrictions, and the fiber layer 80 should be produced by a process known in the related prior art. Preferred examples of the process for producing the nonwoven-like fiber layer 80 include an electrospinning process (also referred to as an electric field spinning process or an electrostatic spinning process). In short, the electrospinning process is a process in which a high voltage is applied to a solution-like spinning material (typically a polymer solution) in a spinneret, and the spinning material charged in the aforementioned manner is ejected from the spinneret to spin a fiber. Nonwoven fabric can be produced by collecting the fiber in a collector (also referred to as a counter electrode or collector electrode substrate).For example, a solution-like composition for forming a fiber layer is prepared by dissolving (melting) the components of the synthetic material contained in the fiber and any materials used as needed in a suitable solvent (for example, NMP or the like), and a fiber is produced (spun) from this composition by the electrospinning process. The resulting fiber is then collected by laminating it in web form onto the surface of the separator 70 (alternatively the positive electrode 50 or the negative electrode 60) mounted on the collector, and in this way the nonwoven-like fiber layer 80 can be formed on the surface of the separator 70 (alternatively the positive electrode 50 or the negative electrode 60).If necessary, the properties (average thickness, void ratio, and base weight) of the fiber layer 80 can be adjusted by performing a rolling treatment (pressing treatment). It is preferred that the fiber layer 80 is formed on the entire surface of the separator 70 (alternatively the positive electrode 50 or the negative electrode 60), that is, on the separator 70 (alternatively the positive electrode 50 or the negative electrode 60) in all longitudinal and transverse directions thereof.

[0039] With the electrospinning process described above, the fiber layer 80 can be formed directly on the surface of the separator 70 (alternatively, the positive electrode 50 or the negative electrode 60). Furthermore, the electrospinning process makes it possible to easily produce fiber (typically nanofiber) with an extremely small diameter of approximately a few nanometers to submicrometers. Accordingly, the electrospinning process is preferable. Moreover, the electrospinning process allows for relatively simple adjustment not only of the fiber diameter, but also of the fiber shape, the mixing ratio between the components of the synthetic resin in the fiber (for example, the mixing ratio between PVDF and PTFE in the components of the synthetic resin forming the fiber), the orientation of the fiber in the fiber layer, and the like.Moreover, the electrospinning process is suitable for producing the fiber layer 80 with a low average thickness or the fiber layer 80 with many pores (with high porosity). < <Positive Elektrode»

[0040] The positive electrode current collector 52, which forms the positive electrode 50, can preferably be a conductive material composed of a metal with excellent conductivity (for example, aluminum, nickel, titanium, stainless steel, or the like). The positive electrode active material layer 54 contains at least one positive electrode active material. For example, the positive electrode active material can preferably be a lithium composite metal oxide with a lamellar structure or a spinel structure (for example, LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0,5 Mn 1,5 O4, LiFePO4, or the like). The positive electrode active material layer 54 can contain a component different from the active material, for example, a conductive material, a binder, or the like. Carbon black, such as acetylene black (AB), or other carbon materials (graphite and the like) can preferably be used as the conductive material. PVDF or the like can be used as the binder. <<Negative Elektrode> >

[0041] The negative electrode current collector 62, which forms the negative electrode 60, can preferably be a conductive material composed of a metal with excellent conductivity (for example, copper, nickel, titanium, stainless steel, or the like). The negative electrode active material layer 64 contains at least one negative electrode active material. For example, a carbon material such as graphite, hard carbon, or soft carbon can be used as the negative electrode active material. The surface of the carbon material (the carbon material that becomes a core) can be coated with an amorphous carbon film. The negative electrode active material layer 64 can contain a component different from the active material, for example, a binder, a thickener, or the like. Styrene-butadiene rubber (SBR) or the like can be used as the binder.For example, carboxymethylcellulose (CMC) or similar substances can be used as the thickening agent. < <separator>>

[0042] The separator 70 can be a separator composed solely of a separator substrate 72 made of a resin. Alternatively, the separator 70 can be a heat-resistant separator obtained by providing a porous heat-resistant layer 74 on one or both surfaces (typically one surface) of the resin-made separator substrate (substrate layer) 72. The heat-resistant layer 74 can be a layer formed over the entire surface of the substrate layer 72, that is, a layer formed on the substrate layer 72 in all its longitudinal and transverse directions.

[0043] Preferred examples of the separator substrate forming substrate layer 72 include a porous resin film made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. Of these, a polyolefin-based porous resin (for example, PE or PP) has a shutdown temperature of 80°C to 140°C (typically 110°C to 140°C and, for example, 120°C to 135°C), which is sufficiently lower than the heat resistance temperature of the battery (typically approximately a temperature greater than or equal to 200°C). Therefore, such a resin can perform the shutdown function at a suitable time.

[0044] The separator substrate (substrate layer) 72 can have a single-layer structure composed of one type of porous resin, or a structure in which two or more porous resin films, composed of different materials or possessing different properties (thickness, void ratio, and the like), are laminated together. For example, separator substrates 72 with a multi-layer structure may preferably be those having a double-layer structure in which PE and PP are laminated together, or a three-layer structure in which a polypropylene (PP) layer is laminated onto both surfaces of a polyethylene (PE) layer (i.e., a three-layer structure consisting of PP / PE / PP).

[0045] For example, even if the internal temperature of the battery is increased due to an internal short circuit or the like (for example, a temperature greater than or equal to 150°C and typically greater than or equal to 200°C), the heat-resistant layer 74 can possess properties such that it is able to retain its shape without softening or melting (slight deformation is acceptable). The heat-resistant layer 74 contains, for example, heat-resistant fine particles and a binder. The heat-resistant fine particles can be an organic filler, an inorganic filler, or the like, used as a filler in the heat-resistant layer 74 of the separator of the secondary battery with non-aqueous electrolyte. Considering heat resistance, durability, dispersibility, stability, and the like, the use of the inorganic filler is preferable.

[0046] Examples of the inorganic filler contained in the heat-resistant layer 74 include metal oxides, metal hydroxides, and the like. For example, aluminum oxide, boehmite, silicon dioxide, titanium dioxide, calcium oxide, magnesium oxide, zirconium dioxide, boron nitride, aluminum nitride, and the like may be used preferentially. These compounds have a high melting point and excellent heat resistance. Furthermore, their Mohs hardness is relatively high, and their resistance (mechanical strength) is also excellent. In addition, raw material costs can be reduced because these compounds are relatively inexpensive. Of the metals, aluminum in particular has a relatively low specific gravity and can therefore reduce the weight of the battery. One type of these inorganic fibers may be used alone, or two or more types may be used in combination.

[0047] The form of the filler is not subject to any particular restrictions and can be, for example, granules, fibers, flakes, or the like. The mean particle size of the filler is not subject to any particular restrictions. However, considering dispersibility or similar factors, it is advisable to adjust the mean particle size of the filler to greater than or equal to 0.01 µm (for example, greater than or equal to 0.05 µm, typically 0.1 µm, and especially 0.2 µm) and less than or equal to 5 µm (for example, less than or equal to 3 µm, typically less than or equal to 2 µm, and especially less than or equal to 1.8 µm).If the particle size of the filler is within the aforementioned range, then the adhesion of the heat-resistant layer 74 to the substrate layer 72, the porosity of the heat-resistant layer 74, and the air permeability of the separator 70 can be adjusted within a preferred range. In this specification, the mean particle size of the filler refers to a particle size (particle size D). 50 , also referred to as a mean diameter), which corresponds to a cumulative 50 vol% of fine particles in the volume-based particle size distribution, measured based on a particle size distribution analysis using a general laser diffraction light scattering method. The particle size of the inorganic filler can be adjusted, for example, by a technique such as pulverizing, sieving, or similar processes.

[0048] The specific surface area of ​​the filler is not subject to any particular restrictions. However, it is preferably approximately greater than or equal to 1 m². 2 / g (for example, greater than or equal to 1.5 m) 2 / g and typically greater than or equal to 2 m 2 / g) and less than or equal to 100 m 2 / g (for example, less than or equal to 50 m) 2 / g and typically less than or equal to 20 m 2 / g). If the specific surface area of ​​the filler lies within the aforementioned range, the porosity of the heat-resistant layer 74 and the air permeability of the separator 70 can be adjusted within a preferred range. In the present case, a general specific BET surface area is chosen as the “specific surface area”.

[0049] The binder contained in the heat-resistant layer 74 may preferably be, for example, an acrylic resin, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), carboxymethylcellulose (CMC), methylcellulose (MC), and the like. One type of these binders may be used alone, or two or more types may be used in combination. In particular, the acrylic resin exhibits strong adhesion (typically initial adhesion and bond strength) and is electrochemically stable. Therefore, the acrylic resin is preferred because it can exhibit a high degree of dimensional stability. If required, the heat-resistant layer 74 may also contain, in addition to the aforementioned filler and binder, one or two or more types of material that can be used as components forming the heat-resistant layer 74 in a general secondary battery.Examples of such materials include various additives, such as a thickening agent, a dispersing agent, and the like.

[0050] Advantageously, the proportion of filler contained in the entire heat-resistant layer 74 should be approximately greater than or equal to 30% by mass. Generally, the proportion of filler can be greater than or equal to 40% (for example, greater than or equal to 50%) and less than or equal to 97% by mass (for example, less than or equal to 90%). The proportion of binder contained in the entire heat-resistant layer 74 can, for example, be approximately greater than or equal to 3% (typically greater than or equal to 10%) and less than or equal to 70% (typically less than or equal to 50%) by mass. If the amount of binder contained in the entire heat-resistant layer 74 is within the above range, the adhesion (typically peel strength) between the substrate layer 72 and the heat-resistant layer 74 can be improved.Consequently, even if the separator substrate (substrate layer 72) is exposed to a high-temperature environment where thermal contraction can occur, the detachment of the heat-resistant layer 74 from the substrate layer 72 can be prevented, and thermal contraction of the separator 70 can also be prevented. That is, the separator 70 with excellent heat resistance can be provided, thus improving the reliability of the battery using the separator 70. For example, a mass ratio (NV-based, i.e., expressed as solids content) between the filler and the binder contained in the heat-resistant layer 74 (filler:binder) can be from 30:70 to 97:3 (for example, 40:60 to 90:10).If the ratio of binder to filler is too low, the anchoring properties of the heat-resistant layer 74 or its strength (dimensional stability) deteriorates, and in some cases, problems such as cracking or peeling occur. If the ratio of binder to filler is too high, the porosity of the heat-resistant layer 74 or the ion permeability of the separator 70 deteriorates in some cases. In a preferred aspect, the total content of the filler and binder is approximately greater than or equal to 90% (for example, greater than or equal to 95%) by mass (expressed as solids content) of the heat-resistant layer 74. The heat-resistant layer 74 can be a heat-resistant layer composed essentially solely of the filler and the binder.

[0051] In general, the mean thickness of the separator substrate (substrate layer) 72 is preferably greater than or equal to 5 µm (typically greater than or equal to 10 µm and, for example, greater than or equal to 17 µm) and less than or equal to 40 µm (typically less than or equal to 30 µm and, for example, less than or equal to 25 µm). If the thickness of the substrate layer 72 is within the aforementioned range, the aforementioned insulating function or electrolyte retention capacity can preferably be present, and the ion permeability can be better maintained. As a result, excellent battery performance can be achieved. The mean thickness of the heat-resistant layer 74 can, for example, be greater than or equal to 1 µm (typically greater than or equal to 3 µm) and less than or equal to 10 µm (typically less than or equal to 5 µm).If the thickness of the heat-resistant layer 74 is within the aforementioned range, the resistance of the separator 70 can be improved, and therefore a high degree of short-circuit prevention can be achieved. The thickness of the substrate 72 and the thickness of the heat-resistant layer 74 can be determined by measurement using a screw gauge or a thickness gauge, or by analysis of a SEM cross-sectional image or the like.

[0052] The porosity (void content) of the separator substrate (substrate layer) 72 is not subject to any particular restrictions. Generally, however, the porosity of the substrate layer 72 is preferably about 20% to 70% by volume, and more preferably, for example, about 30% to 60% by volume. If the porosity of the substrate layer 72 is too high, the mechanical strength becomes insufficient, and thus, in some cases, noticeable thermal contraction occurs. Conversely, if the porosity is too low, the amount of non-aqueous electrolyte that can be retained in the substrate layer 72 is reduced, and thus, in some cases, the charging and discharging characteristics tend to deteriorate. The porosity of the substrate layer 72 can be adjusted, for example, by the type of material that forms the substrate layer 72, its tensile strength, and the like.The porosity (void content) of the heat-resistant layer 74 can be, for example, greater than or equal to 50 vol.% and less than or equal to 70 vol.%. If the porosity of the heat-resistant layer 74 is too high, the mechanical strength may be insufficient in some cases. Conversely, if the porosity is too low, the ion permeability deteriorates, and thus, in some cases, the resistance increases or the input and output characteristics deteriorate. The porosity of the heat-resistant layer 74 can be adjusted, for example, by the shape of the filler (e.g., the average particle size), the binder content, and the like.Therefore, by adjusting the porosity of the substrate layer 72 and the porosity of the heat-resistant layer 74 such that they lie within the aforementioned range, high strength and excellent insulating properties can be achieved, and the battery performance (for example, ion permeability as well as input and output characteristics) can be improved.

[0053] The porosity of the separator substrate (substrate layer) 72 and the porosity of the heat-resistant layer 74 can be determined from a mass W (g), an apparent volume V (cm³). 3 ) and a pure density ρ (g / cm³ 3 ) can be calculated using the equation [1 - (W / ρV)] × 100. The "apparent volume" can be calculated from a product of an area (cm²). 2 ) in plan view and thickness (cm). The "pure density ρ" can be measured using a density measuring device with a general method for the expansion of solid volumes (gas displacement pycnometer method) or the like.

[0054] The air permeability (Gurley number) of separator 70 is preferably, for example, a value greater than 6 seconds (preferably greater than or equal to 10 seconds) and less than or equal to 350 seconds (preferably less than or equal to 240 seconds). Air permeability is a value that simulates the mean pore diameter. If the air permeability is too low, the ion permeability deteriorates, and thus the input and output characteristics may, in some cases, tend to worsen. If the fiber layer 80 is formed on the separator 70, an excess of fiber forming the fiber layer 80 will enter the pores of the separator 70 if the air permeability is too low, and thus the ion permeability or the input and output characteristics may, in some cases, tend to deteriorate.If, on the other hand, the air permeability of the separator 70 is too high, for example, if the fiber layer 80 is formed on the separator 70, then the bond strength between the separator 70 and the fiber layer 80 deteriorates. This is undesirable because separation between the separator 70 and the fiber layer 80 can easily occur. In this context, "air permeability" refers to a degree of air resistance (Gurley second) measured by a Gurley test procedure and is the time (seconds), measured according to a predetermined procedure, that 100 ml of air takes to penetrate the separator. The air permeability can be measured using the procedure specified in JIS P8117 (2009).

[0055] The two paths of the roller-type separators 70 contained in the electrode unit 20 can be separators made of different materials and possessing different properties (i.e., the configurations of the substrate layer 72 and the heat-resistant layer 74). If the heat-resistant layer 74 is formed on both surfaces of the substrate layer 72, the surface of the heat-resistant layer 74 facing the positive electrode 50 and the surface of the other heat-resistant layer 74 facing the negative electrode 60 can have the same properties, while, for example, the type or proportion of the filler contained in the heat-resistant layer 74, the void ratio, the mean thickness, and the like can differ.Furthermore, in the case that the heat-resistant layer 74 is formed only on a surface of the substrate layer 72, the heat-resistant layer 74 can be arranged to be located either opposite the positive electrode 50 (positive electrode active material layer 54) or the negative electrode 60 (negative electrode active material layer 64).

[0056] In the case that the fiber layer 80 is formed on the surface of the separator 70, the fiber layer 80 can be formed either on the surface of the substrate layer 72 or on the surface of the heat-resistant layer 74. The protrusions and depressions on the surface of the heat-resistant layer 74 are larger than those of the substrate layer 72, and thus the fiber forming the fiber layer 80 is easily caught in the heat-resistant layer 74. Therefore, the heat-resistant layer 74 is preferable to the substrate layer 72 for forming the fiber layer 80. <<Nicht-wässriger Elektrolyt> >

[0057] Typically, an electrolyte can be used as the non-aqueous electrolyte obtained by adding a carrier salt to a suitable non-aqueous solvent (typically an organic solvent).

[0058] Various organic solvents commonly used in secondary batteries with non-aqueous electrolytes can be used as the non-aqueous solvent without particular restriction. For example, non-protic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones can be used without particular restriction. Of these, carbonates such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and propylene carbonate (PC) are preferred.

[0059] The carrier salt can preferably be, for example, lithium salts such as LiPF6, LiClO4, LiAsF6, Li(CF3SO2)2N, LiBF4, and LiCF3SO3. One type of carrier salt can be used alone, or two or more types can be used in combination. LiPF6 is particularly preferred. Therefore, the concentration of the carrier salt is preferably, for example, greater than or equal to 0.1 mol / l (for example, greater than or equal to 0.8 mol / l) and less than or equal to 2 mol / l (for example, less than or equal to 1.5 mol / l). The concentration of the carrier salt is preferably 1.1 mol / l.

[0060] Provided the effects of the invention are not significantly impaired, the non-aqueous electrolyte may contain components other than the non-aqueous solvent and the carrier salt. These optional components are used for one or two or more purposes, such as improving the battery's output power, improving its storability (such as preventing capacity degradation during storage), improving cycle characteristics, and improving initial charge and discharge efficiency.Examples of preferred additives include various additives such as a gas-generating agent like biphenyl (BP) or cyclohexylbenzene (CHB); a coating film former such as an oxalate complex compound with a boron and / or phosphorus atom (for example, lithium bis(oxalato)borate (LiBF₂(C₂O₄)), lithium difluorobis(oxalato)phosphate (LiPF₂(C₂O₄)₂ or the like), vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), ethylene sulfite (ES), propane sultone (PS), or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); a dispersant; and a thickener. One type of additive may be used alone, or two or more types may be used in combination as appropriate.

[0061] Next, an example of a composite battery (typically a composite battery in which a plurality of unit cells are connected in series) 200 is described, which includes a plurality of lithium-ion batteries 100 described above, used as cell units. As in Figs. As shown in Figure 5, a plurality of lithium-ion secondary batteries (unit cells) 100 (typically 10 or more lithium-ion secondary batteries 100, preferably about 10 to 30 lithium-ion secondary batteries 100 and, for example, 20 lithium-ion secondary batteries 100) are arranged in a mutually inverse state such that the positive electrode terminal 42 and the negative electrode terminal 44 are arranged alternately, in a direction in which broad surfaces of the battery housing 30 face each other, that is, in a direction in which the flat surfaces of the flat-roll type electrode unit in the battery housing face each other. A cooling plate 110 with a predetermined shape is positioned between the unit cells 100 arranged as above.The cooling plate 110 acts as a radiating element for the efficient dissipation of heat generated inside each of the unit cells 100 at the time of use. It is preferred that the cooling plate 110 has a shape (for example, a shape in which a plurality of parallel grooves, extending vertically from one side of the rectangular cooling plate to the opposite side, are provided on the surface of the cooling plate) that allows a cooling fluid (typically air) to be introduced into a section between the unit cells 100. The cooling plate is preferably made of a metal with excellent thermal conductivity, lightweight rigid polypropylene, or other synthetic resins.

[0062] A pair of end plates (limiting plates) 120 is arranged at both ends of the unit cells 100 and the cooling plates 110 arranged as above. Furthermore, a spacer element 150 or a plurality of spacer elements 150, which function as long devices for adjusting the length and have the form of a track, can be positioned between the cooling plate 110 and the end plate 120. The unit cells 100, the cooling plates 110, and the spacer elements 150 arranged as above are limited by a limiting band 130 for fastening, which is attached to the assembled battery in such a way that it acts as a bridge between the two end plates 120, such that a predetermined limiting pressure is applied in the arrangement direction of the unit cells.This means that the unit cells are confined such that the confining pressure is applied in a direction orthogonal to the flat surface of the flat-roll electrode unit contained within the unit cells. More precisely, the end of the confining band 130 is fastened and fixed to the end plates 120 by screws 155, and in this way the unit cells and the like are confined such that a predetermined confining pressure is applied to their arrangement direction. Furthermore, the positive electrode terminal 42 of one unit cell 100 and the negative electrode terminal 44 of the other unit cell 100 are electrically connected to each other by a connecting element (busbar) 140 between the adjacent unit cells 100. By connecting the respective unit cells 100 in series as described above, the assembled battery 200 with a predetermined voltage is created.

[0063] The limiting pressure that confines the respective unit cells is not subject to any particular restrictions. However, it is preferable that the limiting pressure be set such that a limiting pressure of greater than or equal to 0.2 MPa and less than or equal to 10 MPa is applied in one direction (i.e., the arrangement direction of the unit cells) orthogonally to the flat surface (flat section) of the roller-type electrode unit 20 contained in the unit cells.

[0064] The non-aqueous electrolyte secondary battery according to the present embodiment is a secondary battery in which the occurrence of variations in the amount of non-aqueous electrolyte in the electrode assembly, resulting from repeated high-current charging and discharging, is prevented, even when the battery is used in applications where high-current charging and discharging is repeated. Therefore, the non-aqueous electrolyte secondary battery possesses excellent high-current charging and discharging characteristics. Consequently, by making optimal use of these characteristics, the non-aqueous electrolyte secondary battery of the present embodiment can be used as a power supply for propulsion in vehicles such as plug-in hybrid vehicles (PHVs), hybrid vehicles (HVs), and electric vehicles (EVs).Furthermore, according to the invention, it is possible to provide a vehicle that includes the secondary battery with non-aqueous electrolyte according to the present embodiment as a power supply (typically a composite battery in which a plurality of secondary batteries are electrically connected to each other).

[0065] Examples (experimental examples) relating to the invention are described below, but the invention is not limited to these examples (experimental examples).

[0066] Lithium-ion secondary batteries (non-aqueous electrolyte secondary batteries) were produced using the following materials and methods, according to examples 1 to 64 shown in Tables 1 to 4. <Beispiel 1>

[0067] A separator was manufactured according to the following procedure. First, a substrate film (average thickness: 20 µm, air permeability: 320 sec) with a three-layer structure was produced as a separator substrate (substrate layer). This structure consisted of a porous polypropylene layer on both surfaces of a porous polyethylene layer. Next, a pasty composition was prepared by mixing aluminum oxide as an inorganic filler and an acrylic binder with deionized water, such that the mass ratio between these materials was 97:3. This mixture formed the heat-resistant layer described above.Then, one surface of the separator substrate was completely coated with the composition for forming the heat-resistant layer, and the composition was dried, thus producing a separator with a heat-resistant layer on one surface of the separator substrate. At this point, the mean total thickness of the separator was 25 µm (that is, the mean thickness of the heat-resistant layer was 5 µm).

[0068] The mean particle size (D 50 The specific BET surface area of ​​the inorganic filler used to manufacture the separator was measured using a light scattering particle size analyzer (manufactured by NIKKISO CO., LTD., MICROTRAC HRA) and a specific surface area analyzer manufactured by Shimadzu Corporation, respectively. Furthermore, to prepare the heat-resistant layer composition, the aforementioned materials were mixed and kneaded using an ultrasonic disperser (CLEARMIX, manufactured by M Technique Co., Ltd.) by first dispersing at 15,000 rpm for 5 minutes and then at 20,000 rpm for 15 minutes. Finally, the substrate layer (separator substrate) was uniformly coated with the heat-resistant layer composition using an engraved coating process.

[0069] Subsequently, a fiber layer was formed on the heat-resistant layer of the separator according to the following procedure. PVDF (mean molecular weight: 600,000) and PTFE (mean molecular weight: 600,000) were dissolved in NMP such that the mass ratio between these materials was PVDF:PTFE = 70:30, thus preparing a solution for forming a fiber layer. Using an electrospinning process, the solution was spun to form the fiber layer, and the resulting fiber was deposited onto the heat-resistant layer of the separator, thereby forming a fiber layer. At this point, the mean thickness of the fiber layer was 3.5 µm. The mean molecular weight of the components of the synthetic resin that forms the fiber in the fiber layer represents a number-mean molecular weight (Mn), and the same applies to the following description.Here, the electrospinning process was carried out using an electrospinning apparatus comprising a high-voltage power supply, a solution tank, a syringe pump, and a needle nozzle (spinning nozzle), under the following conditions: a voltage of 10 kV to 15 kV applied to the spinneret (needle nozzle), a distance of 10 cm to 20 cm between the spinneret and the surface for fiber layer formation (here, the surface of the heat-resistant layer of the separator), and a solution feed rate of 0.2 ml / min to 0.3 ml / min. The mean thickness of the fiber layer was determined by analyzing an image acquired using a scanning electron microscope (SEM).

[0070] A positive electrode was fabricated according to the following procedure. LiNi 0,33 Co 0,33 Mn 0,33 O2 (LNCM) as a positive electrode active material powder, AB as a conductive material, and PVDF as a binder were mixed with NMP such that the mass ratio between these materials was LNCM:AB:PVDF = 90:8:2, producing a slurry-like composition for forming a positive electrode active material layer. Both surfaces of an elongated aluminum foil (positive electrode current collector) with a thickness of 15 µm were coated with the composition in a ribbon-like fashion. The composition was then dried and pressed to produce a positive electrode web. The amount of composition used to form the positive electrode active material layer, as well as the pressing conditions, were adjusted such that the mean thickness of the positive electrode was approximately 65 µm (the mean thickness of the positive electrode active material layer on one surface of the foil was approximately 25 µm).

[0071] A negative electrode was manufactured according to the following procedure. First, graphite (C) powder, coated with amorphous carbon, was produced as the negative electrode active material. Then, the graphite (C), styrene-butadiene rubber (SBR), and carbon monoxide (CMC) as a thickening agent were mixed with deionized water in a ratio of C:SBR:CMC = 98:1:1, producing a slurry-like composition for forming a negative electrode active material layer. Both surfaces of an elongated copper foil (negative electrode current collector) with a thickness of 10 µm were coated with the composition in a ribbon-like fashion. The composition was then dried and pressed, producing a negative electrode web.The amount of composition used to form a negative electrode active material layer with which the film was coated, and the pressing conditions were adjusted such that the mean thickness of the negative electrode was approximately 80 µm (the mean thickness of the negative electrode active material layer on a surface of the film was approximately 35 µm).

[0072] By using one positive electrode web and one negative electrode web, manufactured as above, and two separator webs, also manufactured as above, a roll-type electrode assembly was produced. That is, the positive and negative electrodes were laminated to the separators positioned between them, where the fiber layer was formed on the surface of the heat-resistant layer, such that the active material layer non-formation sections of the electrodes were positioned on opposite sides, and the heat-resistant layer of each separator (i.e., the fiber layer on the heat-resistant layer) was oriented in a direction facing the negative electrode (negative electrode active material layer).In the present embodiment, the positive electrode, the negative electrode, and the separators were laminated such that the heat-resistant layer of each separator (i.e., the fiber layer on the heat-resistant layer) was oriented in a direction facing the negative electrode (negative electrode active material layer). However, the heat-resistant layer of each separator (i.e., the fiber layer on the heat-resistant layer) could be oriented opposite the positive electrode (positive electrode active material layer) or opposite both the negative electrode (negative electrode active material layer) and the positive electrode (positive electrode active material layer). The laminated positive electrode, the negative electrode, and the separators were wound 130 times at a winding tension of 1 N / mm². 2 The electrode and separators were rolled lengthwise (that is, the number of times they were rolled was 130). The resulting coiled unit (the positive electrode, the negative electrode, and the separators after winding) was then pressed and compressed downwards in a direction perpendicular to the winding axis, producing a flat coil electrode unit. This coil electrode unit was 130 mm long along the winding axis (longitudinal direction) and 50 mm long in a direction perpendicular to the winding axis (short direction).

[0073] The coil-type electrode assembly of each of the aforementioned examples was then placed in an angled aluminum battery container (angled battery case). A non-aqueous electrolyte was injected through an opening in the battery case, and the opening was then hermetically sealed, thus producing lithium-ion secondary batteries (non-aqueous electrolyte secondary batteries) of the respective examples. The non-aqueous electrolyte used was obtained by dissolving LiPF6 as a carrier salt in a solvent mixture containing EC, EMC, and DMC in a volume ratio of EC:EMC:DMC = 30:40:30 at a concentration of 1.1 mol / L. <Beispiel 2>

[0074] A battery according to Example 2 was manufactured using the same materials and process as in Example 1, except that the mass ratio between PVDF and PTFE in the composition for forming a fiber layer was changed to PVDF:PTFE = 60:40. <Beispiel 3>

[0075] A battery according to Example 3 was manufactured using the same materials and the same process as in Example 1, except that a substrate web (mean thickness: 20 µm, air permeability: 100 sec) of a porous polyethylene (PE) layer was used as the separator substrate and a solution obtained by dissolving PVDF (mean molecular weight: 200,000) in NMP was used as the composition for forming a fiber layer. <Beispiel 4>

[0076] A battery according to Example 4 was manufactured using the same materials and process as in Example 1, except that PVDF with an average molecular weight of 2,000,000 was used as the PVDF forming the fiber layer. <Beispiel 5>

[0077] A battery according to Example 5 was produced using the same materials and the same process as in Example 3, except that a solution obtained by dissolving PVDF (mean molecular weight: 500,000) and PVF (mean molecular weight: 500,000) in a mass ratio of PVDF:PVF = 60:40 in NMP was used as the composition for forming a fiber layer. <Beispiel 6>

[0078] A battery according to Example 6 was produced using the same materials and process as in Example 5, except that the mass ratio of PVDF and PVF in the composition for forming a fiber layer was changed to PVDF:PVF = 70:30. <Beispiel 7>

[0079] A battery according to Example 7 was manufactured using the same materials and process as the battery according to Example 3, except that the fiber layer was not formed. <Beispiel 8>

[0080] A battery according to Example 8 was manufactured using the same materials and process as in Example 1, except that a substrate web (mean thickness: 20 µm, air permeability: 100 sec) of a porous polyethylene (PE) layer was used as the separator substrate; a solution obtained by dissolving PVDF (mean molecular weight: 150,000), PTFE (mean molecular weight: 700,000) and FEP (mean molecular weight: 500,000) in NMP in a mass ratio of PVDF:PTFE:FEP = 56:22:22 was used as the composition for forming a fiber layer; and the mean thickness of the fiber layer was changed to 1 µm. <Beispiele 9 bis 58>

[0081] Secondary batteries with non-aqueous electrolyte according to Examples 9 to 58 were manufactured using the same materials and process as the battery according to Example 8, except that the material and air permeability of the separator substrate, the mean molecular weight of PVDF and PTFE used to form the fiber layer, the content of PVDF and PTFE (that is, the content of PVDF and PTFE in the solution used to form a fiber layer) contained in the fiber layer (fiber), and the mean thickness of the fiber layer were changed from the conditions shown in Tables 2 and 3.In the tables, "PE" indicates a substrate web with a single-layer structure of porous polyethylene (PE); "PE / PP" indicates a substrate web with a double-layer structure in which a porous polypropylene (PP) layer is formed on the surface of a porous polyethylene (PE) layer; and "PP / PE / PP" indicates a substrate web with a three-layer structure in which a porous polypropylene (PP) layer is formed on both surfaces of a porous polyethylene (PE) layer. When the substrate web with a double-layer structure (i.e., PE / PP), in which the PP layer is formed on one surface of the PE layer, was used as a separator substrate, a heat-resistant layer was formed on the surface of the PP layer.Furthermore, unless otherwise specified, in Tables 2 and 3, those batteries where the combined content of PVDF and PTFE does not equal 100% by mass are considered to contain FEP (average molecular weight: 500,000) in addition to PVDF and PTFE as components of the synthetic resin that forms the fiber layer. That is, they are considered batteries where the FEP content (by mass) is 100 - (PVDF content in the table + PTFE content in the table). For example, in the case of the battery according to Example 9, the fiber layer was formed using the composition for forming a fiber layer in which the mass ratio of PVDF, PTFE, and FEP was PVDF:PTFE:FEP = 56:22:22. <Beispiel 59>

[0082] A battery according to Example 59 was manufactured using the same materials and process as in Example 1, except that the fiber layer was formed on both surfaces of the separator (i.e., the surface of the separator substrate and the surface of the heat-resistant layer); a substrate web (mean thickness: 20 µm, air permeability: 100 sec) of a porous polyethylene (PE) layer was used as the separator substrate; a composition prepared by dissolving PVDF (mean molecular weight: 500,000), PTFE (mean molecular weight: 950,000), and FEP (mean molecular weight: 500,000) in NMP in a mass ratio of PVDF:PTFE:FEP = 62:27:11 was used to form a fiber layer; and the mean thickness of the fiber layer was changed to 2.5 µm. <Beispiel 60 bis 62>

[0083] Batteries according to Examples 60 to 62 were manufactured using the same materials and process as in Example 59, except that the fiber layer was formed on the surface of both the positive electrode active layer and the negative electrode active layer, or either on the surface of the positive electrode active layer or on the surface of the negative electrode active layer. The location where the fiber layer is formed is shown in the corresponding column in Table 4. In Table 4, the surface of the positive electrode active layer is described as the "positive electrode," and the surface of the negative electrode active layer is described as the "negative electrode." <Beispiel 63 und 64>

[0084] Batteries according to Examples 63 and 64 were manufactured using the same materials and process as in Example 62, except that the separator substrate used was a substrate sheet (mean thickness: 20 µm, air permeability: 290 sec, with a heat-resistant layer formed on the surface of the PP layer) with a double-layer structure in which a porous polypropylene layer was formed on a surface of a porous polyethylene layer, or a substrate sheet (mean thickness: 20 µm, air permeability: 325 sec) with a three-layer structure in which a porous polypropylene layer was formed on both surfaces of a porous polyethylene layer. [Measurement of initial battery resistance (IV resistance)]

[0085] The initial resistance (IV resistance) of each of the batteries constructed as described above was then measured. First, each battery was charged at a constant current (CC) under a temperature condition of 25°C until the state of charge (SOC) reached 60%, and then charged at a rate of 10C with CC for 10 seconds, during which time a voltage rise (V) was measured. The IV resistance (mΩ) was calculated by dividing the measured voltage rise (V) by the corresponding current value (typically, the IV resistance (mΩ) is calculated from the slope of a first-order approximation of a plotted current (I)-voltage (V) value), and the mean value was used as the initial battery resistance. Unless otherwise stated, "state of charge (SOC)" as used herein refers to a charged state of a battery based on a general voltage range in which the battery is used.For example, “SOC” refers to a charged state based on a nominal capacity measured under a voltage between the terminals (open circuit voltage (OCV)) of 4.1 V (maximum voltage) to 3.0 V (minimum voltage). [Charge and discharge cycle test]

[0086] Then, for each of the battery samples that had undergone initial resistance measurement, a charge and discharge cycle test was performed. In this test, the battery was charged and discharged for 1,000 cycles under a temperature condition of 25°C, and the rate of resistance increase (%) after the cycle test was calculated. Test details are given below. In the charge and discharge cycle test, the battery was charged at a constant current (CC) for 240 seconds at a rate of 2.5C for 240 seconds under a temperature condition of 25°C. It was then discharged for 120 seconds, discharged at a constant current (CC) for 20 seconds at a rate of 30C, and then discharged for another 120 seconds. The aforementioned charge and discharge process was considered one cycle.For each battery that underwent the charge and discharge cycle test, the battery resistance (IV resistance) after the test was measured using the same method as for measuring the initial resistance. The rate of resistance increase (%) was then calculated using the following equation: Rate of resistance increase (%) = (IV resistance after charge and discharge cycle test - initial battery resistance) ÷ initial battery resistance x 100. The results are shown in the corresponding columns in Tables 1 to 4. Table 1 Baseball Substrate separator Faserschicht Widerstandsanstiegsrate (%) Materials Luftdurchlässigkeit (Sec) Average molecular weight (× 10 4 ) Injury (%) MittlereDicke(µm) PVDF PTFE PVF PVDF PTFE PVF 1 PP / PE / PP 320 60 60 - 70 60 0 3,5 35 2 PP / PE / PP 320 60 60 - 60 40 0 3,5 40 3 INSTEAD 100 20 - - 100 0 0 3,5 150 4 INSTEAD 100 200 - - 100 0 0 3,5 100 5 PP / PE / PP 320 50 - 50 60 0 40 3,5 120 6 PP / PE / PP 320 50 - 50 70 0 30 3,5 110 7 INSTEAD 100 - - - 0 0 0 - 250 Table 2 Baseball Substrate separator Faserschicht Widerstandsanstiegsrate (%) Materials Luftdurchlässigkeit (Sec) Average molecular weight (× 10 4 ) Injury (%) MittlereDicke(µm) PVDF PTFE PVDF PTFE 8 INSTEAD 100 15 70 56 22 1 110 9 INSTEAD 100 20 70 56 22 1 20 10 INSTEAD 100 50 70 56 22 1 21 11 INSTEAD 100 100 70 56 22 1 22 12 INSTEAD 100 140 70 56 22 1 25 13 INSTEAD 100 200 70 56 22 1 32 14 PE / PP 280 200 70 56 22 1 40 15 PP / PE / PP 340 200 70 56 22 1 45 16 INSTEAD 100 220 70 56 22 1 170 17 INSTEAD 100 50 15 57 24 1,3 140 18 INSTEAD 100 50 20 57 24 1,3 25 19 INSTEAD 100 50 50 57 24 1,3 31 20 INSTEAD 100 50 100 57 24 1,3 32 21 INSTEAD 100 50 140 57 24 1,3 34 22 INSTEAD 100 50 200 57 24 1,3 36 23 PE / PP 275 50 200 57 24 1,3 44 24 PP / PE / PP 320 50 200 57 24 1,3 49 25 INSTEAD 100 50 220 57 24 1,3 190 26 INSTEAD 100 50 85 80 5 2,2 150 27 INSTEAD 100 50 85 60 10 2,2 14 28 INSTEAD 100 50 85 60 30 2,2 12 29 INSTEAD 100 50 85 50 45 2,2 15 30 PE / PP 277 50 85 50 45 2,2 25 31 PP / PE / PP 345 50 85 50 45 2,2 28 32 INSTEAD 100 50 85 35 55 2,2 210 Table 3 Baseball Substrate separator Faserschicht Widerstandsanstiegsrate (%) Materials Luftdurchlässigkeit (Sec) Average molecular weight (× 10 4 ) Injury (%) MittlereDicke(µm) PVDF PTFE PVDF PTFE 33 INSTEAD 100 50 80 25 20 2 200 34 INSTEAD 100 50 80 30 25 2 24 35 INSTEAD 100 50 80 50 20 2 15 36 INSTEAD 100 50 80 80 10 2 10 37 PE / PP 270 50 80 80 10 2 31 38 PP / PE / PP 330 50 80 80 10 2 34 39 INSTEAD 100 50 80 85 15 2 180 40 INSTEAD 6 50 50 55 20 0,8 120 41 INSTEAD 10 50 50 55 20 0,8 15 42 INSTEAD 30 50 50 55 20 0,8 20 43 INSTEAD 50 50 50 55 20 0,8 23 44 INSTEAD 100 50 50 55 20 0,8 28 45 INSTEAD 180 50 50 55 20 0,8 33 46 INSTEAD 240 50 50 55 20 0,8 40 47 PE / PP 300 50 50 55 20 0,8 45 48 PP / PE / PP 350 50 50 55 20 0,8 48 49 INSTEAD 400 50 50 55 20 0,8 150 50 INSTEAD 100 50 90 60 26 0,2 140 51 INSTEAD 100 50 90 60 26 0,5 9 52 INSTEAD 100 50 90 60 26 1,5 11 53 INSTEAD 100 50 90 60 26 3 12 54 INSTEAD 100 50 90 60 26 4 15 55 INSTEAD 100 50 90 60 26 6 19 56 PE / PP 285 50 90 60 26 6 26 57 PP / PE / PP 310 50 90 60 26 6 28 58 INSTEAD 100 50 90 60 26 7 170 Table 4 Baseball Substrate separator Faserschicht Widerstandsanstiegsrate (%) Materials Luftdurchlässigkeit (Sec) Average molecular weight (×10 4 ) Injury (%) Ort PVDF PTFE PVDF PTFE 59 INSTEAD 100 50 95 62 27 BeideSeparatoroberflächen 5 60 INSTEAD 100 50 95 62 27 Positivewound negative Electrode 7 61 INSTEAD 100 50 95 62 27 PositiveElectrode 12 62 INSTEAD 100 50 95 62 27 NegativeElectrode 10 63 PE / PP 290 50 95 62 27 PositiveElectrode 23 64 PP / PE / PP 325 50 95 62 27 PositiveElectrode 26

[0087] As shown in Table 1, the battery in Example 7, which lacked a fiber layer, exhibited an extremely high resistance rise rate after high-current charging and discharging. This is thought to be due to the expansion and contraction of the active materials in the positive and negative electrodes as the electrodes were charged and discharged, causing the separator pores to be compressed and the non-aqueous electrolyte impregnated with the separator to be expelled, resulting in a variation in the amount of non-aqueous electrolyte held in the electrode assembly. In contrast, the resistance rise rate after repeated high-current charging and discharging was significantly lower (less than or equal to 50%) for the batteries in Example 7, which lacked a fiber layer.This means that if the battery has a fiber layer between the separator and the positive electrode and / or between the separator and the negative electrode, containing fibers that include at least PVDF or PTFE, each with an average molecular weight greater than or equal to 200,000 and less than or equal to 2,000,000, and in which the PVDF content in the components of the synthetic resin forming the fiber is greater than the PTFE content, and the PTFE content is less than or equal to 45% based on the mass of the components of the synthetic resin, then excellent high-current charging and discharging characteristics can be achieved. In other words, according to the invention, it is possible to provide a secondary battery with a non-aqueous electrolyte that possesses excellent high-current charging and discharging characteristics.

[0088] In the batteries of Examples 1 and 2, which used a combination of PVDF and PTFE as the components of the synthetic resin forming the fiber, the rate of resistance increase after repeated high-current charging and discharging was lower than in the batteries of Examples 3 and 4, which used PVDF but no PTFE, and in the batteries of Examples 5 and 6, which used a combination of PVDF and PTFE. These results confirmed that the resistance increase after repeated high-current charging and discharging can be largely suppressed by using at least PVDF and PTFE in combination as the components of the synthetic resin forming the fiber contained in the fiber layer.

[0089] The results of the resistance increase rate after high-current charging and discharging, obtained from the batteries according to Examples 9 to 15, 18 to 24, 27 to 31, 34 to 38, 41 to 48, 51 to 57, and 59 to 64, clearly showed that excellent high-current charging and discharging characteristics can be achieved if the batteries have a fiber layer between the separator and the positive electrode and / or between the separator and the negative electrode, the fiber containing at least PVDF and PTFE, each with an average molecular weight greater than or equal to 200,000 and less than or equal to 2,000,000 than the components of the synthetic resin, and in which the PVDF content in the components of the synthetic resin forming the fiber is greater than the PTFE content, and the PTFE content is less than or equal to 45% by mass of the components of the synthetic resin.

[0090] As can be seen from the results obtained from the batteries according to Examples 8 to 25, which differed from one another with respect to the mean molecular weight of PVDF or PTFE, the resistance increase rate after repeated high-current charging and discharging was lower (the resistance increase rate was less than 50%) in the batteries according to Examples 9 to 15 and 18 to 24, in which PVDF and PTFE both have a mean molecular weight greater than or equal to 200,000 and less than or equal to 2,000,000, than in the batteries according to Examples 8 and 16, in which the mean molecular weight of PVDF or PTFE was less than 200,000, and than in the batteries according to Examples 17 and 25, in which the mean molecular weight of PVDF or PTFE was greater than 2,000,000.This result confirmed that the increase in resistance after repeated high-current charging and discharging can be largely suppressed when PVDF and PTFE both have an average molecular weight greater than or equal to 200,000 and less than or equal to 2,000,000.

[0091] In the batteries of Examples 27 to 31, the rate of resistance increase after repeated high-current charging and discharging was suppressed to a greater extent than in the battery of Example 32. That is, it was confirmed that the resistance increase after repeated high-current charging and discharging can be suppressed to a great extent if the PVDF content in the components of the synthetic resin forming the fiber contained in the fiber layer is greater than the PTFE content, and the PTFE content is less than or equal to 45% by mass of the synthetic resin components. In the battery of Example 26, the resistance after repeated high-current charging and discharging was higher than in the batteries of Examples 27 to 31.It is assumed that this is due to the PTFE content in the fiber forming the fiber layer being too low, causing the fiber layer to be simply crushed and thus preventing the non-aqueous electrolyte from being easily retained within the fiber layer. These results confirmed that the PTFE content in the components of the synthetic resin forming the fiber within the fiber layer is preferably greater than or equal to 10% and less than or equal to 45% by mass of the synthetic resin components.

[0092] In the batteries of Examples 33 and 39, the resistance increase after repeated high-current charging and discharging occurred at a higher rate than in the batteries of Examples 34 to 38. With regard to Example 33, it is assumed that the effect of retaining the non-aqueous electrolyte in the fiber layer was insufficient because the PVDF content in the fiber forming the fiber layer was too low. With regard to the battery of Example 39, it is assumed that the fiber layer retained an excess of non-aqueous electrolyte, while the positive electrode active material layer or the negative electrode active material layer lacked non-aqueous electrolyte because the PVDF content in the fiber forming the fiber layer was too high.These results confirmed that the PVDF content in the components of the synthetic resin forming the fiber contained in the fiber layer is preferably greater than or equal to 30% and less than or equal to 80% based on the mass of the components of the synthetic resin.

[0093] In the batteries according to Examples 40 and 49, the resistance increase after repeated high-current charging and discharging occurred at a higher rate than in the batteries according to Examples 41 to 48. With regard to Example 40, it is assumed that due to the insufficient air permeability of the separator, the fiber forming the fiber layer entered the separator and thus clogged the pores. In contrast, it is assumed that in the battery according to Example 49, the adhesive strength between the fiber layer and the separator deteriorated due to the excessive air permeability of the separator. These results confirmed that the air permeability of the separator is preferably greater than or equal to 10 seconds to less than or equal to 350 seconds.Furthermore, the comparison between the batteries according to Examples 41 to 48 confirmed that the increase in resistance after repeated high-current charging and discharging can be suppressed more the lower the air permeability of the separator.

[0094] In the batteries of Examples 50 and 58, the resistance increased at a higher rate after repeated high-current charging and discharging than in the batteries of Examples 51 to 57. With regard to Example 50, it is assumed that the insufficient thickness of the fiber layer reduced the amount of non-aqueous electrolyte that could be retained within the fiber layer. In contrast, it is assumed that in the battery of Example 58, the thickness of the fiber layer was too great, thus excessively increasing the distance between the positive electrode active material layer and the negative electrode active material layer. These results confirmed that the fiber layer thickness is greater than or equal to 0.5 µm and less than or equal to 6 µm.Furthermore, it was confirmed that the increase in resistance after repeated high-current charging and discharging can be suppressed more the smaller the average thickness of the fiber layer is compared to Examples 51 to 57.

[0095] In light of the results obtained from Examples 59 to 64, the fiber layer in the invention can be formed not only on the surface of the heat-resistant layer of the separator, but also on the surface of the separator substrate, the surface of the positive electrode active material layer (surface of the positive electrode), and the surface of the negative electrode active material layer (surface of the negative electrode). That is, the high-current charging and discharging characteristics can be improved if the battery has the fiber layer between the separator and the positive electrode active material layer and / or between the separator and the negative electrode active material layer.In Example 59, where the fiber layer was formed on both surfaces of the separator, and in Example 60, where the fiber layer was formed on both the surface of the positive electrode active material layer and the surface of the negative electrode active material layer, the resistance increase was particularly well suppressed. These results confirmed that the battery preferentially has the fiber layer between the separator and the positive electrode active material layer and between the separator and the negative electrode active material layer.

[0096] Specific examples of the invention have been described in detail, but the embodiments and examples described above are merely examples.< / separator> < / faserschicht>

Claims

[1] Secondary battery with non-aqueous electrolyte, comprising: a flat roll electrode unit (20) in which an elongated positive electrode (50), an elongated negative electrode (60) and an elongated separator (70), which electrically insulates the positive and negative electrodes from each other, are placed one on top of the other and wound together in a longitudinal direction; and a non-aqueous electrolyte; the secondary battery contains non-aqueous electrolyte characterized by is that it includes: a fiber layer (80) which is arranged at least between the separator (70) and the positive electrode (50) or between the separator (70) and the negative electrode (60) and contains fiber made of a synthetic resin, wherein the fiber layer (80) contains at least polyvinylidene fluoride and polytetrafluoroethylene as components of the synthetic resin forming the fiber, Polyvinylidene fluoride and polytetrafluoroethylene both have an average molecular weight greater than or equal to 200,000 and less than or equal to 2,000,000, respectively, and in the components of the fiber-forming synthetic resin, the polyvinylidene fluoride content is greater than the polytetrafluoroethylene content, and the polytetrafluoroethylene content is less than or equal to 45% based on the mass of the components of the synthetic resin. [2] Secondary battery with non-aqueous electrolyte according to claim 1, wherein the polyvinylidene fluoride content in the components of the fiber-forming synthetic resin is greater than or equal to 30% and less than or equal to 80% based on the mass of the components of the synthetic resin. [3] Secondary battery with non-aqueous electrolyte according to claim 1 or 2, wherein the fiber layer (80) has a mean thickness greater than or equal to 0.5 µm and less than or equal to 6 µm. [4] Secondary battery with non-aqueous electrolyte according to any one of claims 1 to 3, wherein the separator (70) comprises a substrate layer (72) made of a synthetic resin and a heat-resistant layer (74) formed on a surface of the substrate layer and containing heat-resistant fine particles, and the fiber layer (80) is formed on a surface of the heat-resistant layer (74). [5] Compound battery (200) comprising a plurality of unit cells electrically connected to each other, wherein each of the unit cells is the secondary battery (100) with non-aqueous electrolyte according to any one of claims 1 to 4. [6] Compound battery according to claim 5, wherein the unit cells are confined in a state in which a confining pressure of greater than or equal to 0.2 MPa and less than or equal to 10 MPa is applied in a direction orthogonal to a flat surface of the flat roll electrode assembly contained in the unit cells.

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