Nonaqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, the positive electrode includes a positive electrode current collector, a positive electrode active material layer, and a positive electrode tab, the positive electrode current collector includes a first region and a second region, the first region supports the positive electrode active material layer, and the second region does not support the positive electrode active material layer and includes a tab connection portion. The positive electrode tab is connected to the tab connection portion, and in a plan view of the positive electrode, the outer periphery of the positive electrode active material layer has at least one first side adjacent to the second region, a plurality of second sides not adjacent to the second region, and a first corner portion where the first side and the second side intersect, and the positive electrode active material layer is chamfered at the first corner portion.

Description

[0001] Cross-references between related applications

[0002] This disclosure claims the benefit of priority from Japanese Patent Application No. 2023-030106 filed in the Japan Patent Office on February 28, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a nonaqueous electrolyte secondary battery. Background Art

[0004] Patent document 1 proposes "a spiral electrode group for a battery, which is a roughly concentric circle-shaped battery electrode group formed by spirally winding a thin nickel positive electrode and a thin metal hydride negative electrode through a separator, characterized in that the thin nickel positive electrode is formed by continuously winding a plurality of positive electrode plates in sequence, and the thin metal hydride negative electrode is formed by continuously winding one or more negative electrode plates in sequence, (3) in an electrode composed of a plurality of electrode plates, the plurality of electrode plates are combined in a manner such that the total weight of the active material and / or the weight of the quasi-active material of each electrode is maintained at a substantially constant value, the plurality of electrode plates in the electrode composed of the plurality of electrode plates are continuously wound at intervals, and the thickness of the electrode at the start side of the winding is thinner than that of the electrode at the end side of the winding in the plurality of electrode plates in the electrode composed of the plurality of electrode plates." It is an electrode group in which "at least two corners of each of the plurality of electrode plates constituting the positive electrode and the negative electrode are chamfered."

[0005] Prior art literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-134161 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] When repeated charge and discharge cycles occur, the cause of the battery's lifespan is often an internal short circuit. In particular, when current is concentrated locally at the positive electrode, lithium metal deposition is likely to occur, leading to internal short circuits.

[0009] Means for solving problems

[0010] One aspect of the present disclosure relates to a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte. The positive electrode comprises a positive electrode current collector, a positive electrode active material layer, and a positive electrode tab. The positive electrode current collector has a first region and a second region, the first region supports the positive electrode active material layer, the second region does not support the positive electrode active material layer, and has a tab connecting portion, the positive electrode tab is connected to the tab connecting portion. When the positive electrode is viewed from above, the outer periphery of the positive electrode active material layer comprises: at least one first side adjacent to the second region, a plurality of second sides not adjacent to the second region, and a first corner where the first side intersects the second sides, and the positive electrode active material layer is chamfered at the first corner.

[0011] Another aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the positive electrode comprising a positive electrode collector, a positive electrode active material layer, and a positive electrode tab, the positive electrode collector comprising a first region and a second region, the first region carrying the positive electrode active material layer, the second region not carrying the positive electrode active material layer, and comprising a tab connecting portion, the positive electrode tab being connected to the tab connecting portion, and when the positive electrode is viewed from above, the outer periphery of the positive electrode active material layer comprising at least one first side adjacent to the second region and a plurality of second sides not adjacent to the second region, the cross-sectional shape in the thickness direction of an end portion of the positive electrode active material layer corresponding to the first side being chamfered.

[0012] Effects of the Invention

[0013] According to the present disclosure, it is possible to suppress the occurrence of an internal short circuit during the charge and discharge cycle of a non-aqueous electrolyte secondary battery.

[0014] The novel features of the present invention are set forth in the appended claims, but the present invention, both in structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1A This is a plan view conceptually showing the structure of an example of the positive electrode according to the present disclosure.

[0016] Figure 1B This is a longitudinal cross-sectional view conceptually showing a portion of a stacked structure of a positive electrode, a negative electrode, and a separator.

[0017] Figure 1C is a cross-sectional view along the length direction of an example involved in the present disclosure.

[0018] Figure 2AThis is a plan view conceptually showing the structure of another example of the positive electrode according to the present disclosure.

[0019] Figure 2B This is a plan view conceptually showing the structure of another example of the positive electrode according to the present disclosure.

[0020] Figure 3 This is a plan view conceptually showing the structure of another example of the positive electrode according to the present disclosure.

[0021] Figure 4 It is a longitudinal sectional view schematically showing an example of a cylindrical non-aqueous electrolyte secondary battery. DETAILED DESCRIPTION

[0022] Hereinafter, the embodiments of the present disclosure will be described with reference to examples, but the embodiments of the present disclosure are not limited to the examples described below. In the following description, specific numerical values ​​or materials are sometimes exemplified, but other numerical values ​​or other materials may also be applied as long as the invention of the present disclosure can be implemented. In this specification, a description such as "numerical value A to numerical value B" includes numerical value A and numerical value B, which can be replaced by "above numerical value A and below numerical value B". In the following description, when a lower limit and an upper limit are exemplified for a numerical value of a specific physical property or condition, any one of the exemplified lower limits and any one of the exemplified upper limits may be arbitrarily combined as long as the lower limit is not above the upper limit.

[0023] The present disclosure includes combinations of matters described in two or more claims arbitrarily selected from the plurality of claims recited in the appended claims. In other words, matters described in two or more claims arbitrarily selected from the plurality of claims recited in the appended claims may be combined as long as no technical contradiction arises.

[0024] (Non-aqueous electrolyte secondary battery)

[0025] The nonaqueous electrolyte secondary battery disclosed herein comprises a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. The positive electrode, negative electrode, and separator may be in the form of a strip. The strip-shaped positive electrode and negative electrode may be wound with the strip-shaped separator interposed therebetween to form a cylindrical electrode assembly (electrode body). The positive electrode, negative electrode, and separator may also be stacked to form a laminated electrode assembly. In other words, the electrode assembly may be either a wound or laminated type. The nonaqueous electrolyte may have, for example, lithium ion conductivity.

[0026] The positive electrode consists of a positive electrode current collector, a positive electrode active material layer, and a positive electrode tab. The positive electrode tab is the current collecting component that conducts current from the positive electrode to the external terminal. It is typically a conductive strip, bar, or rectangular member (such as metal foil). The positive electrode tab is also called a positive electrode lead.

[0027] The positive electrode current collector has a first region and a second region. The first region carries the positive electrode active material layer. The majority of the positive electrode current collector is the first region. The second region is a region that does not carry the positive electrode active material layer. The second region has an exposed portion of the positive electrode current collector and a tab connection portion. The positive electrode tab is connected to the tab connection portion. Specifically, the tab connection portion is connected to the exposed portion of the positive electrode current collector. The tab connection portion may also be referred to as a positive electrode lead connection portion, etc.

[0028] The tab connection portion is a region connected to a portion of the positive electrode tab and having sides extending from the remaining portion (i.e., the protrusion) of the positive electrode tab. It is typically a rectangular region that at least partially overlaps with the portion of the positive electrode tab other than the protrusion. The entire tab connection portion does not necessarily overlap with the tab. The tab connection portion may constitute the entire second region or at least a portion of the second region. At least a portion of the tab connection portion may be concealed by insulating tape, film, or the like.

[0029] When the positive electrode is viewed from above, the outer periphery (outer shape) of the positive electrode active material layer has at least one first side adjacent to the second region and a plurality of second sides not adjacent to the second region. Furthermore, if the second region includes an area other than the tab connecting portion, the first side is the side adjacent to the tab connecting portion.

[0030] One of the simplest methods is to have a second region consisting of a single rectangular area at one longitudinal end of the positive electrode current collector, with the remainder of the positive electrode current collector serving as the first region. In this case, the entire second region serves as the tab connection portion. Furthermore, the outer periphery of the positive electrode active material layer has one first side and three second sides.

[0031] The positive electrode according to the present disclosure satisfies at least one of the following conditions (A) and (B).

[0032] (A) The outer periphery of the positive electrode active material layer in a plan view of the positive electrode (hereinafter also referred to as “the outer periphery of the positive electrode active material layer”) has a first corner where a first side and a second side intersect. The positive electrode active material layer is chamfered at the first corner.

[0033] (B) In the outer periphery of the positive electrode active material layer, the cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer corresponding to the first side is chamfered.

[0034] By satisfying at least one of conditions (A) and (B), when the charge and discharge cycles are repeated, the probability of the diaphragm being locally compressed due to the expansion of the electrode plates, the distance between the positive and negative electrodes becoming extremely narrow, and the current being concentrated locally on the positive electrode is reduced, and the probability of internal short circuits caused by the precipitation of lithium metal inside and outside the diaphragm is also reduced.

[0035] Condition (A) requires that the corners (first corners) of the positive electrode active material layer near the positive electrode tab be chamfered. If there are multiple first corners, chamfering at least one of them can suppress current concentration and achieve a certain degree of internal short circuit suppression.

[0036] The “cross-sectional shape” in condition (B) refers to the shape of the cross section formed when the region including the first side of the positive electrode active material layer (i.e., the region including the boundary between the first and second regions of the positive electrode current collector) is cut parallel to the thickness direction and perpendicular to the first side.

[0037] The periphery of the positive electrode active material layer may have a second corner where the second sides intersect. In this case, the positive electrode active material layer may be chamfered at the second corner. This further reduces the probability of local current concentration in the positive electrode. In the case of multiple second corners, as long as at least one second corner is chamfered, a certain effect of suppressing current concentration can be achieved.

[0038] The periphery of the positive electrode active material layer may have a third corner where the first sides intersect with each other. For example, in the case where the second region is a rectangular region with a side from which the protrusion of the positive electrode tab protrudes, the remaining three sides of the second region may be the first sides. In this case, the positive electrode active material layer may also be chamfered at the third corner. As a result, the probability of local current concentration in the positive electrode is further reduced. In the case where there are multiple third corners, as long as at least one third corner is chamfered, a certain effect of suppressing current concentration can be achieved.

[0039] Furthermore, the state where the positive electrode active material layer is chamfered may include the state where both the positive electrode active material layer and the positive electrode current collector are chamfered. Thus, the corner (first corner, second corner, or third corner) of the positive electrode active material layer and the positive electrode current collector present on the base thereof may be chamfered together.

[0040] The chamfer shape in conditions (A) and (B) is not particularly limited and may be a C-chamfer or an R-chamfer. In the case of a C-chamfer, the angle relative to the first side is typically 45°, but an angle within the range of 30 to 60° is also possible. An R-chamfer is preferred over a C-chamfer because it easily suppresses current concentration.

[0041] In the case of round chamfering in the condition (A), the curvature radius of the portion with the highest curvature may be, for example, 0.5 mm to 10 mm, or 1 mm to 3 mm.

[0042] In the case of C-chamfering in the condition (A), the length of the slope of the chamfered portion may be, for example, 0.5 mm to 10 mm, or 1 mm to 3 mm.

[0043] In the case of R-chamfering in condition (B), the radius of curvature of the portion with the highest curvature may be equal to or less than the thickness T of the positive electrode active material layer, and may be, for example, 0.01 mm or more, or 0.05 mm or more.

[0044] In the case of C chamfering under condition (B), the angle of inclination of the inclined surface (tapered surface) of the chamfered portion relative to the surface of the positive electrode current collector may be 1° to 80°, or 10° to 45°. Furthermore, the length of the inclined surface (tapered surface) of the chamfered portion may be, for example, 150% to 30,000% or 2,000% to 15,000% of the thickness T of the positive electrode active material layer.

[0045] The nonaqueous electrolyte secondary battery disclosed herein may be a lithium secondary battery (lithium metal secondary battery) in which lithium metal is deposited at the negative electrode during charging and dissolved during discharge. In this case, the negative electrode comprises at least a negative electrode current collector. Lithium metal is deposited on the negative electrode current collector. Because lithium secondary batteries charge and discharge by a mechanism in which lithium metal is deposited between electrodes, the effect of satisfying at least one of conditions (A) and (B) is particularly significant.

[0046] A lithium secondary battery may include a separator disposed between at least one of the positive electrode and the negative electrode and the separator. The separator at least serves to ensure space for lithium metal to precipitate between the electrodes. The positive electrode and negative electrode may be wound with the separator and separator interposed therebetween to form a wound electrode assembly. Alternatively, a stacked electrode assembly may be formed by stacking the positive electrode, negative electrode, separator, and separator.

[0047] In a lithium secondary battery, more than 70% of the rated capacity, for example, is realized by the precipitation and dissolution of lithium metal. The movement of electrons in the negative electrode during charging and discharging is mainly due to the precipitation and dissolution of lithium metal in the negative electrode. Specifically, 70 to 100% (for example, 80 to 100% or 90 to 100%) of the movement of electrons in the negative electrode during charging and discharging (current in other viewpoints) is caused by the precipitation and dissolution of lithium metal. That is, the negative electrode of a lithium secondary battery is different from the negative electrode in which the movement of electrons in the negative electrode during charging and discharging is mainly caused by the absorption and release of lithium ions by the negative electrode active material (graphite, etc.).

[0048] Hereinafter, examples of embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The above-mentioned components can be applied to the components of the non-aqueous electrolyte secondary battery described below. In addition, the components of the non-aqueous electrolyte secondary battery of the example described below can be changed based on the above description. In addition, the matters described below can be applied to the above-mentioned embodiments. Non-essential components of the non-aqueous electrolyte secondary battery of the present disclosure can be omitted.

[0049] Figure 1A 1 is a top view conceptually showing the structure of an example of a positive electrode 15 when viewed from above. Viewing from above means viewing from a direction parallel to the thickness direction of the positive electrode ( Figure 1A Observe the positive electrode 15) in the Z direction. Figure 1A The XY plane is parallel to the surface of the positive electrode current collector.

[0050] The positive electrode current collector 151 is divided into a first region that supports the positive electrode active material layer 152 and a second region that does not support the positive electrode active material layer 152. The second region is the exposed portion of the positive electrode current collector 151 and has a tab connection portion 153 at one end in the longitudinal direction of the positive electrode current collector 151 and small, roughly triangular regions at the two corners of the other end.

[0051] The positive electrode tab 15a is connected to the tab connection portion 153. A portion of the tab connection portion 153, along with a portion of the positive electrode tab 15a, is covered by an insulating tape 19, the outline of which is indicated by a dotted line. The outer periphery of the positive electrode active material layer 152 includes a first side 152x parallel to the Y direction and adjacent to the second region, and three second sides 152y not adjacent to the second region. The positive electrode active material layer 152 is chamfered at a first corner 152a where the first side 152x and the second sides 152y intersect. This satisfies condition (A). The positive electrode active material layer 152 is also chamfered at a second corner 152b where the second sides 152y intersect, but chamfering the second corner 152b is not required.

[0052] Figure 1B This is a longitudinal sectional view conceptually showing a portion of the structure of an example of an electrode group. Figure 1B express Figure 1A The stacked structure of the positive electrode 15, the negative electrode 16 and the separator 17 interposed therebetween is shown. Figure 1A The cross-sectional view of the YZ plane is equivalent to Figure 1A bb line view. Figure 1B ] shows a state where the cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer 152 corresponding to the second side 152y parallel to the X direction is C-chamfered.

[0053] Figure 1C It is along Figure 1AThe cross-sectional view of the positive electrode 15 in the longitudinal direction is shown. Figure 1A The cross-sectional view of the ZX plane is equivalent to Figure 1A The cc line view. Figure 1C , the cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer 152 corresponding to the first side 152 x parallel to the Y direction is shown to be C-chamfered. In this case, the positive electrode 15 also satisfies the condition (B).

[0054] Figure 2A This is a top view conceptually illustrating the structure of another example of a positive electrode 15. The positive electrode current collector 151 includes two first regions that support a positive electrode active material layer 152. An exposed portion of the positive electrode current collector 151 that does not support the positive electrode active material layer 152 is provided between the two first regions, serving as a tab connection portion 153. The second region includes the central tab connection portion 153 and small, roughly triangular regions at the four corners of the positive electrode 15.

[0055] The positive electrode tab 15a is connected to the central tab connection portion 153. The insulating tape covering the tab connection portion 153 is not shown. The outer periphery of each of the two positive electrode active material layers 152 includes a first side 152x parallel to the Y direction, adjacent to the second region, and three second sides 152y not adjacent to the second region. The positive electrode active material layer 152 is chamfered at the four first corners 152a where the first side 152x intersects the second side 152y. This satisfies condition (A). The positive electrode active material layer 152 is also chamfered at the second corners 152b where the second sides 152y intersect.

[0056] Figure 2B This is a plan view conceptually showing the structure of another example of the positive electrode 15 when viewed from above. Figure 2B The positive electrode 15 has the same structure as the positive electrode 15 except that both the positive electrode active material layer 152 and the positive electrode current collector 151 are chamfered in the small approximately triangular regions at the four corners of the two ends. Figure 2A The positive electrode has the same structure.

[0057] Figure 3 FIG. 1 is a top view conceptually showing the structure of another example of the positive electrode 15 when viewed from above. Figure 3 In the positive electrode 15, multiple exposed portions of the positive electrode current collectors 151 are provided as the second region along the edge portion including one end in the short-side direction (Y direction) of the positive electrode. Each of the multiple exposed portions of the positive electrode current collectors 151 constitutes a tab connection portion 153. Specifically, the multiple tab connection portions 153 are intermittently provided along the longitudinal direction (X direction) of the positive electrode. The width of the edge portion (the depth of the tab connection portion 153) extending from one end in the short-side direction of the positive electrode 15 toward the center of the positive electrode 15 is, for example, 8 mm to 12 mm.

[0058] exist Figure 3 In the figure, the outer periphery of the positive electrode active material layer 152 follows the shape of the tab connection portion 153 and includes 2n first corner portions 152a where a first side 152x parallel to the Y direction intersects a second side 152y parallel to the X direction, and 2n third corner portions 152c where a first side 152x parallel to the X direction intersects the first side 152x parallel to the Y direction. Here, n represents the number of tab connection portions 153. At both the first corner portions 152a and the third corner portions 152c, the exposed portions of the positive electrode active material layer 152 or the positive electrode current collector 151 are rounded.

[0059] The non-aqueous electrolyte secondary battery disclosed herein may be a liquid secondary battery containing an electrolyte solution as the electrolyte, or an all-solid secondary battery containing a solid electrolyte as the electrolyte. The structure of a non-aqueous electrolyte secondary battery will be described in detail below, using a lithium-ion secondary battery or a lithium secondary battery as an example.

[0060] Figure 4 1 is a longitudinal cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery as an example of an embodiment of the present disclosure. However, the present disclosure is not limited to the following structure.

[0061] The secondary battery 10 includes an electrode assembly 18, an electrolyte (not shown), and a bottomed cylindrical battery can 22 to house them. A sealing body 11 is riveted to the opening of the battery can 22 via a gasket 21. This seals the interior of the battery. The sealing body 11 includes a valve body 12, a metal plate 13, and an annular insulating member 14 interposed between the valve body 12 and the metal plate 13. The valve body 12 and the metal plate 13 are connected to each other at their respective centers. A positive electrode tab (positive electrode lead) 15a extending from the positive electrode 15 is connected to the metal plate 13. Thus, the valve body 12 functions as an external terminal for the positive electrode. A negative electrode tab (negative electrode lead) 16a extending from the negative electrode 16 is connected to the inner surface of the bottom of the battery can 22. An annular groove 22a is formed near the open end of the battery can 22. A first insulating plate 23 is disposed between one end surface of the electrode assembly 18 and the annular groove 22a. A second insulating plate 24 is disposed between the other end surface of the electrode group 18 and the bottom of the battery can 22. The electrode group 18 is formed by winding the positive electrode 15 and the negative electrode 16 with a separator 17 interposed therebetween. Figure 4 This is a cross-sectional view parallel to the Y direction and passing through the winding axis of the electrode group.

[0062] [positive electrode]

[0063] A positive electrode having the above-mentioned characteristics is used as the positive electrode. The positive electrode comprises a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is composed of a positive electrode mixture. The positive electrode mixture contains the positive electrode active material as an essential component and may also contain optional components. Optional components may include a binder, a conductive additive, a thickener, and the like.

[0064] The positive electrode active material layer is considerably harder than the negative electrode, separator, lithium metal, and the like. The thicker this hard positive electrode active material layer, the more pronounced the effect of satisfying at least one of conditions (A) and (B). The thickness of the positive electrode active material layer can be, for example, 30 μm to 200 μm, 30 μm to 160 μm, 50 μm to 150 μm, or 50 μm to 100 μm.

[0065] The thickness of the positive electrode tab is, for example, not less than 50 μm and not more than 300 μm, and may be 0.5 to 2 times the thickness T of the positive electrode active material layer.

[0066] The average particle size (D50) of the positive electrode active material particles is, for example, 1 μm to 50 μm, or 5 μm to 25 μm. The average particle size (D50) refers to the median diameter at which the cumulative volume in a volume-based particle size distribution reaches 50%.

[0067] The positive electrode active material may contain a lithium-containing transition metal oxide. From the perspective of increasing capacity, the lithium-containing transition metal oxide preferably contains lithium and nickel, and includes a lithium nickel oxide (composite oxide N) having a layered rock salt-type crystal structure. The proportion of the composite oxide N in the positive electrode active material may be, for example, 70% by mass or greater, 90% by mass or greater, or 95% by mass or greater. The proportion of nickel in the metal elements other than lithium contained in the composite oxide N may be 50 atomic % or greater.

[0068] For example, the composite oxide N is represented by the formula (1): Li α Ni x1 M1 x2 M2 (1-x1-x2) O 2+β denoted by . Element M1 is at least one selected from V, Co, and Mn. Element M2 is at least one selected from Mg, Al, Ca, Ti, Cu, Zn, and Nb. Formula (1) satisfies 0.95≤α≤1.05, -0.05≤β≤0.05, 0.5≤x1<1, 0≤x2≤0.5, and 0<1-x1-x2≤0.5. α increases or decreases with charge and discharge.

[0069] The composite oxide N contains Ni and may contain at least one selected from Co, Mn, and Al as the element M1 and the element M2. Co, Mn, and Al contribute to stabilizing the crystal structure of the composite oxide N.

[0070] The composite oxide N can be represented by the formula (2): Li α Ni (1-y1-y2-y3-z) Co y1 Mn y2 Al y3 M z O 2+β . Element M is an element other than Li, Ni, Co, Mn, Al, and oxygen, and may be at least one selected from Ti, Zr, Nb, Mo, W, Fe, Zn, B, Si, Mg, Ca, Sr, Sc, and Y. Formula (2) satisfies 0.95≤α≤1.05, -0.05≤β≤0.05, 0≤y1≤0.1, 0≤y2≤0.1, 0≤y3≤0.1, and 0≤z≤0.10. 1-y1-y2-y3-z (=v), which represents the atomic ratio of Ni, is, for example, 0.8 or greater, 0.85 or greater, 0.90 or greater, or 0.95 or greater. Furthermore, v, which represents the atomic ratio of Ni, may be 0.98 or less, or 0.95 or less.

[0071] As the positive electrode current collector, a sheet of conductive material (metal foil, wire mesh, grid, punched plate, etc.) is used. Metal foil is preferred. Examples of materials for the positive electrode core include stainless steel, aluminum, aluminum alloys, and titanium. The positive electrode current collector may also be a material obtained by applying a metal material to the surface of a resin film using methods such as physical vapor deposition (PVD). The thickness of the positive electrode current collector is not particularly limited, but may be, for example, 1 to 50 μm, or 5 to 30 μm.

[0072] [negative electrode]

[0073] The negative electrode includes at least a negative electrode current collector and may also include a negative electrode active material layer. The negative electrode active material layer may be composed of a negative electrode mixture. The negative electrode mixture contains the negative electrode active material as an essential component and may also contain optional components. As optional components, it may contain a binder, a conductive additive, a thickener, etc. The negative electrode active material layer can be formed by attaching a lithium metal foil or a lithium alloy foil to the surface of the negative electrode current collector. In other words, a base layer containing lithium metal (a layer of lithium metal or lithium alloy (hereinafter also referred to as "lithium base layer")) can be pre-set on the negative electrode current collector. In addition to lithium, the lithium alloy may also contain elements such as aluminum, magnesium, indium, zinc, copper, and silver. By providing a lithium metal base layer, lithium metal is deposited on it during charging, and dendritic precipitation can be more effectively suppressed. The thickness of the lithium metal base layer is not particularly limited and can be, for example, in the range of 5μm to 25μm.

[0074] The negative electrode active material includes materials that electrochemically absorb and release lithium ions, lithium metal, lithium alloys, etc. As materials that electrochemically absorb and release lithium ions, carbon materials, alloy materials, etc. can be used. Examples of carbon materials include graphite, easily graphitized carbon (soft carbon), and non-graphitized carbon (hard carbon). Among them, graphite is preferred because it has excellent charge and discharge stability and a low irreversible capacity. As alloy materials, materials containing at least one metal that can form an alloy with lithium can be mentioned, specifically silicon, tin, silicon alloys, tin alloys, silicon compounds, etc. Silicon oxide, tin oxide, etc. can be used, and other silicon-containing materials can also be used.

[0075] As the negative electrode current collector, a non-porous conductive substrate (metal foil, etc.) or a porous conductive substrate (wire mesh, mesh, punched plate, etc.) is used. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, copper alloys, oxygen-free copper foil, etc. As the negative electrode current collector, a composite current collector comprising a resin film and a transition metal layer laminated with the resin film can also be used. The resin film can contain any one of polyester resin, olefin resin, polyphenylene sulfide resin, acrylic resin, polycarbonate resin, polyetheretherketone resin, polyethersulfone resin, polyamide resin, polyimide resin, nylon resin, polyvinylidene chloride resin, ethylene-vinyl alcohol copolymer, polyvinyl alcohol resin, polystyrene resin, epoxy resin, and polyurethane resin, or can contain two or more of them. The transition metal layer contains at least one of copper, nickel, chromium, titanium, iron, silver, gold, tin, copper alloy, stainless steel, and nickel alloy. The transition metal layer is formed on one or both surfaces of the resin film by a known deposition method, such as vapor deposition, atomic layer deposition (ALD), sputtering, or electroless plating. The composite current collector may further include a surface resin layer between the resin film and the transition metal layer, the surface resin layer comprising a polymer having at least one selected from the group consisting of urethane bonds, urea bonds, melamine bonds, amide bonds, aramid bonds, and imide bonds.

[0076] [Diaphragm]

[0077] The separator has high ion permeability, suitable mechanical strength and insulating properties. Examples of the separator include microporous films, woven fabrics, and nonwoven fabrics.

[0078] The thickness of the separator is, for example, 10 μm, 15 μm or more, 20 μm or more, or 30 μm or more. However, from the perspective of energy density, the separator is preferably thinner than the positive electrode. The thickness of the separator is, for example, preferably less than 80 μm, and more preferably less than 50 μm.

[0079] The separator preferably has a layer with a ratio of tensile strength in the longitudinal direction (MD) to tensile strength in the transverse direction (TD): an MD / TD ratio of 4.5 or greater. In this case, the effect achieved by satisfying at least one of conditions (A) and (B) becomes more pronounced. A high MD / TD ratio improves the separator's ability to follow the expansion and contraction of the electrode assembly, reducing stress buildup between the electrodes and the likelihood of localized current concentration in the positive electrode. The MD / TD ratio can be 5.0 or greater. Furthermore, to ensure sufficient separator flexibility, the MD / TD ratio is preferably 10 or less.

[0080] The separator can be made of a polyolefin, such as polypropylene or polyethylene. When the separator contains polypropylene, the effect achieved by satisfying at least one of conditions (A) and (B) becomes more pronounced. Polyolefins have low polarity and excellent resistance to non-aqueous electrolytes. Polypropylene has higher strength and better compression resistance than polyethylene. Combining a polypropylene separator with excellent compression resistance and chamfered corners or cross-sections of the positive electrode active material layer yields an excellent short-circuit suppression effect.

[0081] The separator may include a substrate layer and a heat-resistant layer laminated on the substrate layer. The substrate layer may be a microporous film, a woven fabric, a non-woven fabric, or the like. The heat-resistant layer may be provided on at least one surface of the substrate layer. The heat-resistant layer is preferably provided at least on the positive electrode side of the separator.

[0082] The heat-resistant layer may contain an inorganic oxide filler as a main component (e.g., 80% by mass or more of the heat-resistant layer), or a heat-resistant resin as a main component (e.g., 40% by mass or more of the heat-resistant layer). The heat-resistant resin may include a polyamide resin such as aromatic polyamide (aramid), a polyimide resin, a polyamide-imide resin, a polyacrylic resin, or a polyvinylidene fluoride resin.

[0083] [Non-aqueous electrolyte]

[0084] Lithium-ion secondary batteries or their non-aqueous electrolytes have lithium-ion conductivity. The non-aqueous electrolyte can be a liquid electrolyte (electrolyte) or a solid electrolyte.

[0085] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, materials known in all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte, for example, contains a lithium salt and a matrix polymer, or contains a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of the polymer material include fluororesins, acrylic resins, and polyether resins.

[0086] The electrolyte solution includes a non-aqueous solvent and an electrolyte salt. In the case of a lithium-ion secondary battery, the electrolyte salt includes at least a lithium salt. The concentration of the lithium salt in the electrolyte solution is, for example, 0.5 mol / L or more and 2 mol / L or less. The non-aqueous electrolyte solution may contain known additives.

[0087] Examples of non-aqueous solvents include cyclic carbonates, chain carbonates, and cyclic carboxylates. Examples of cyclic carbonates include propylene carbonate (PC) and ethylene carbonate (EC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylates include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Non-aqueous solvents may be used alone or in combination of two or more.

[0088] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO4, LiAlCl4, LiB 10 Cl 10 etc.), lithium salts of fluorinated acids (LiPF6, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorinated acid imides (LiN(SO2F)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.), oxalic acid complex salts (lithium bis(oxalatoborate), lithium difluorooxalatoborate (BF2(C2O4) - )、PF4(C2O4) - PF2(C2O4)2 - The lithium salt may be used alone or in combination of two or more.

[0089] (Note)

[0090] Through the above records, the following technical solutions are disclosed.

[0091] (Technical Solution 1)

[0092] A non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0093] The positive electrode comprises a positive electrode current collector, a positive electrode active material layer and a positive electrode tab.

[0094] The positive electrode current collector has a first region and a second region,

[0095] The first region supports the positive electrode active material layer.

[0096] The second region does not support the positive electrode active material layer and has a tab connection portion.

[0097] The positive electrode tab is connected to the tab connection portion,

[0098] When the positive electrode is viewed from above, the periphery of the positive electrode active material layer has: at least one first side adjacent to the second region, a plurality of second sides not adjacent to the second region, and a first corner where the first side intersects the second side.

[0099] The positive electrode active material layer is chamfered at the first corner.

[0100] (Technical Solution 2)

[0101] According to the non-aqueous electrolyte secondary battery of technical solution 1,

[0102] The outer periphery of the positive electrode active material layer further has a second corner portion where the second sides intersect with each other.

[0103] The positive electrode active material layer is chamfered at the second corner.

[0104] (Technical Solution 3)

[0105] The non-aqueous electrolyte secondary battery according to claim 1 or 2,

[0106] The outer periphery of the positive electrode active material layer further has a third corner where the first sides intersect with each other.

[0107] The positive electrode active material layer is chamfered at the third corner.

[0108] (Technical Solution 4)

[0109] A non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

[0110] The positive electrode comprises a positive electrode current collector, a positive electrode active material layer and a positive electrode tab.

[0111] The positive electrode current collector has a first region and a second region,

[0112] The first region supports the positive electrode active material layer.

[0113] The second region does not support the positive electrode active material layer and has a tab connection portion.

[0114] The positive electrode tab is connected to the tab connection portion,

[0115] When the positive electrode is viewed from above, the outer periphery of the positive electrode active material layer has at least one first side adjacent to the second region and a plurality of second sides not adjacent to the second region.

[0116] The cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer corresponding to the first side is chamfered.

[0117] (Technical Solution 5)

[0118] In the non-aqueous electrolyte secondary battery according to any one of technical solutions 1 to 4, lithium metal is deposited on the negative electrode during charge and is dissolved during discharge.

[0119] (Technical Solution 6)

[0120] According to the non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, the chamfered shape is a C-chamfered shape.

[0121] (Technical Solution 7)

[0122] According to the non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, the chamfered shape is an R-chamfered shape.

[0123] (Technical Solution 8)

[0124] According to the nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, the positive electrode and the negative electrode are wound with the separator interposed therebetween to form an electrode group.

[0125] (Technical Solution 9)

[0126] According to any one of claims 1 to 8 of the non-aqueous electrolyte secondary battery, the thickness of the positive electrode active material layer is 30 μm or more and 200 μm or less.

[0127] (Technical Solution 10)

[0128] According to the non-aqueous electrolyte secondary battery according to any one of claims 1 to 9, the thickness of the separator is 30 μm or greater.

[0129] (Technical Solution 11)

[0130] According to the nonaqueous electrolyte secondary battery according to any one of claims 1 to 10, the separator includes a layer having a ratio MD / TD of longitudinal tensile strength to transverse tensile strength of 4.5 or more.

[0131] (Technical Solution 12)

[0132] According to the non-aqueous electrolyte secondary battery according to any one of claims 1 to 11, the material of the separator includes polypropylene.

[0133] [Example]

[0134] The nonaqueous electrolyte secondary battery according to the present disclosure will be described in more detail below based on examples and comparative examples. However, the present disclosure is not limited to the following examples.

[0135] Example 1

[0136] (1) Preparation of positive electrode

[0137] A layered, rock-salt-type lithium-containing transition metal oxide (NCA: positive electrode active material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al being 1.0), acetylene black (AB: conductive material), and polyvinylidene fluoride (PVdF: binder) were mixed at a mass ratio of NCA:AB:PVdF = 95:2.5:2.5. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was then added and stirred to prepare a positive electrode mixture slurry. The resulting positive electrode mixture slurry was applied to both sides of a 15μm-thick strip of Al foil (positive electrode current collector), dried, and rolled using a roller. The resulting stack of positive electrode current collector and positive electrode mixture coating was then cut into the desired electrode size (5×8 cm), yielding a positive electrode with an 80μm-thick positive electrode active material layer on each side of the positive electrode current collector.

[0138] Next, at one end of the positive electrode in the longitudinal direction, the positive electrode active material layer (positive electrode mixture) is peeled off to form Figure 1A The exposed portion of the positive electrode current collector shown serves as the tab connection portion. This divides the positive electrode current collector into a first region carrying the positive electrode active material layer and a second region not carrying the positive electrode active material layer. The periphery of the positive electrode active material layer has one first side adjacent to the second region and three second sides not adjacent to the second region. Next, at the two first corners where the first and second sides intersect, the positive electrode active material layer R is chamfered into an arc shape with a curvature radius of 5 mm, resulting in a positive electrode meeting condition (A). A positive electrode tab (150 μm thick) is then connected to the tab connection portion, and a portion of the tab connection portion and a portion of the positive electrode tab are covered with insulating tape.

[0139] (2) Preparation of negative electrode

[0140] A strip-shaped electrolytic copper foil (thickness 15 μm) was prepared as a negative electrode current collector.

[0141] (3) Diaphragm

[0142] A 20 μm-thick polyethylene microporous film was prepared as a separator having an MD / TD ratio of 1.0.

[0143] (4) Forming a spacer on the main surface of the diaphragm

[0144] 60 parts by volume of insulating particles (median particle size of 3 μm, volume resistivity of 10 14 Ω･cm), 39 parts by volume of a binder resin, 1 part by volume of CMC (sodium salt), and water as a dispersion medium were mixed to prepare a dispersion of the spacer material.

[0145] A dispersion of the spacer material was sprayed onto each surface of a pair of microporous films using a dispenser in a predetermined pattern, and the coating was vacuum-dried to form a spacer.

[0146] (5) Preparation of non-aqueous electrolyte

[0147] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of EC:DMC=30:70, and LiPF6 and LiBF2(C2O4) were dissolved at a concentration of 1 mol / L and 0.1 mol / L in the resulting mixed solvent to prepare a liquid non-aqueous electrolyte.

[0148] (6) Battery assembly

[0149] In an inert gas atmosphere, six positive electrode sheets and seven negative electrode current collectors were stacked with the separator folded 99 times to create a stacked electrode assembly. The separator was positioned so that the separator formed on one side faced the negative electrode. The electrode assembly was housed in a bag-shaped outer casing made of a laminate sheet with an Al layer. After injecting a nonaqueous electrolyte, the outer casing was sealed to complete Battery A1 of Example 1.

[0150] Example 2

[0151] (1) Preparation of positive electrode

[0152] The stack of the positive electrode collector and the positive electrode mixture coating is cut into a specified strip-shaped electrode size. In addition, a positive electrode is produced in the same manner as Example 1, with a positive electrode active material layer having a thickness of 80 μm on both sides of the positive electrode collector, a tab connection portion at one end in the longitudinal direction, and the positive electrode active material layer R chamfered into an arc shape with a curvature radius of 5 mm at the first corner.

[0153] (2) Preparation of negative electrode

[0154] A strip-shaped electrolytic copper foil (thickness 15 μm) was prepared as a negative electrode current collector.

[0155] (3) Diaphragm

[0156] A separator made of a polyethylene microporous film having a thickness of 20 μm and having the same separator as in Example 1 was prepared.

[0157] (4) Preparation of non-aqueous electrolyte

[0158] The same nonaqueous electrolyte as in Example 1 was prepared.

[0159] (5) Battery assembly

[0160] In an inert gas atmosphere, the positive and negative electrode current collectors were spirally wound with the separators mentioned above interposed therebetween to produce a wound electrode assembly. The separators were arranged so that the separators formed on one side of each pair of separators faced the negative electrode. The electrode assembly was housed in a bag-shaped outer casing made of a laminate sheet with an Al layer, and after injecting a nonaqueous electrolyte, the outer casing was sealed to complete Battery A2 of Example 2.

[0161] Example 3

[0162] Battery A3 of Example 3 was completed in the same manner as in Example 1 except that the positive electrode active material layer R was chamfered into an arc shape at the two second corners where the second sides intersected each other.

[0163] Example 4

[0164] Battery A4 of Example 4 was completed in the same manner as in Example 3 except that the thickness of the positive electrode active material layer was changed to 160 μm.

[0165] Example 5

[0166] Battery A5 of Example 5 was completed in the same manner as Example 1 except that the two first corners were not R-chamfered and the cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer corresponding to the first side was C-chamfered (the length of the inclined surface was 10 mm).

[0167] Example 6

[0168] Instead of performing R-chamfering on the two first corners, the cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer corresponding to the first side was C-chamfered (the length of the inclined surface was 10 mm), and the thickness of the positive electrode active material layer was changed to 160 μm. Except for this, the battery A6 of Example 6 was completed in the same manner as Example 2.

[0169] Example 7

[0170] Battery A7 of Example 7 was completed in the same manner as Example 6 except that the cross-section in the thickness direction of the end portion of the positive electrode active material layer corresponding to the second longitudinal side was C-chamfered (the length of the chamfer was 10 mm).

[0171] Example 8

[0172] At the two second corners where the second sides intersect each other, the positive electrode active material layer R is also chamfered into an arc shape, and the cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer corresponding to the first side is C-chamfered (the length of the inclined surface is 10 mm), and then the cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer corresponding to the second side along the length direction is C-chamfered (the length of the inclined surface is 10 mm), and the thickness of the positive electrode active material layer is changed to 160 μm. Except for this, the battery A8 of Example 8 is completed in the same manner as Example 2.

[0173] Example 9

[0174] Battery A9 of Example 9 was completed in the same manner as in Example 8 except that the thickness of the positive electrode active material layer was changed to 80 μm.

[0175] Example 10

[0176] Battery A10 of Example 10 was completed in the same manner as in Example 9 except that the thickness of the separator was changed to 40 μm.

[0177] Example 11

[0178] Battery A11 of Example 11 was completed in the same manner as in Example 10 except that the MD / TD ratio of the separator was changed to 5.5.

[0179] Example 12

[0180] Battery A12 of Example 12 was completed in the same manner as in Example 11 except that the material of the separator was changed to polypropylene.

[0181] Comparative Example 1

[0182] Battery B1 of Comparative Example 1 was completed in the same manner as in Example 1 except that the two first corners were not rounded but the two second corners were rounded.

[0183] Comparative Example 2

[0184] Battery B2 of Comparative Example 2 was completed in the same manner as in Example 2 except that the two first corners were not rounded but the two second corners were rounded.

[0185] Comparative Example 3

[0186] Battery B3 of Comparative Example 3 was completed in the same manner as Comparative Example 2 except that the two second corners were not rounded.

[0187] Comparative Example 4

[0188] Battery B4 of Comparative Example 4 was completed in the same manner as in Comparative Example 3 except that the thickness of the separator was changed to 40 μm, the MD / TD ratio of the separator was changed to 5.5, and the material of the separator was changed to polypropylene.

[0189] [Evaluation 1]

[0190] Each battery was subjected to a charge and discharge test under the following conditions in a thermostatic chamber at 25° C. The rest time between charge and discharge was 20 minutes.

[0191] (Charge)

[0192] The battery was charged at a constant current of 2.15 mA per unit area (cm2) of the electrode until the battery voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V until the current value per unit area of ​​the electrode reached 0.54 mA.

[0193] (Discharge)

[0194] The battery was discharged at a constant current of 2.15 mA per unit area of ​​the electrode until the battery voltage reached 3.75 V.

[0195] The above charge and discharge are considered one cycle, and the cycle is repeated until an increase in apparent charge capacity due to an internal short circuit is observed. The number of cycles at this time is shown in Table 1 along with the battery structure as a relative value when the cycle number of Battery B is set to 100. When an internal short circuit occurs, the capacity is consumed due to the short circuit, so the power supply device requires charging energy exceeding the rated capacity, and the apparent capacity increases. If the relationship between the apparent capacity (A) at the cycle number at which the apparent capacity begins to increase and the maximum apparent capacity (B) during the next 20 cycles satisfies B / A>1.1, a short circuit is determined. The cycle number at which the maximum value (B) is displayed is the cycle number of the short circuit.

[0196] Table 1

[0197]

[0198] Industrial availability

[0199] The non-aqueous electrolyte secondary battery disclosed herein can be used as a main power source for mobile communication devices, portable electronic devices, electric vehicles, and the like.

[0200] The present invention has been described in conjunction with presently preferred embodiments, but this disclosure should not be construed as limiting. Various changes and modifications will become apparent to those skilled in the art upon reading the foregoing disclosure. Therefore, the appended claims should be construed to include all changes and modifications that do not depart from the true spirit and scope of the present invention.

[0201] Description of Reference Numerals

[0202] 10: Secondary batteries

[0203] 11: Sealing body

[0204] 12: Valve body

[0205] 13: Metal Plate

[0206] 14: Insulation parts

[0207] 15: Positive electrode

[0208] 15a: Positive terminal

[0209] 151: Positive electrode collector

[0210] 152: Positive electrode active material layer

[0211] 153: Tab connection

[0212] 152x: Side 1

[0213] 152y: Side 2

[0214] 152a: 1st corner

[0215] 152b: 2nd corner

[0216] 152c: 3rd corner

[0217] 16: Negative electrode

[0218] 16a: Negative terminal

[0219] 17: Diaphragm

[0220] 18: Electrode group

[0221] 19: Insulating tape

[0222] 21: Gasket

[0223] 22: Battery Can

[0224] 22a: Groove

[0225] 23: 1st insulation board

[0226] 24: Second insulation board

Claims

1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, The positive electrode comprises a positive electrode current collector, a positive electrode active material layer and a positive electrode tab. The positive electrode current collector has a first region and a second region, The first region supports the positive electrode active material layer. The second region does not support the positive electrode active material layer and has a tab connection portion. The positive electrode tab is connected to the tab connection portion, When the positive electrode is viewed from above, the periphery of the positive electrode active material layer has: at least one first side adjacent to the second region, a plurality of second sides not adjacent to the second region, and a first corner where the first side intersects the second side. The positive electrode active material layer is chamfered at the first corner.

2. The nonaqueous electrolyte secondary battery according to claim 1, The outer periphery of the positive electrode active material layer further has a second corner portion where the second sides intersect with each other. The positive electrode active material layer is chamfered at the second corner.

3. The nonaqueous electrolyte secondary battery according to claim 1, The outer periphery of the positive electrode active material layer further has a third corner where the first sides intersect with each other. The positive electrode active material layer is chamfered at the third corner.

4. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, The positive electrode comprises a positive electrode current collector, a positive electrode active material layer and a positive electrode tab. The positive electrode current collector has a first region and a second region, The first region supports the positive electrode active material layer. The second region does not support the positive electrode active material layer and has a tab connection portion. The positive electrode tab is connected to the tab connection portion, When the positive electrode is viewed from above, the outer periphery of the positive electrode active material layer has at least one first side adjacent to the second region and a plurality of second sides not adjacent to the second region. The cross-sectional shape in the thickness direction of the end portion of the positive electrode active material layer corresponding to the first side is chamfered.

5. The non-aqueous electrolyte secondary battery according to claim 1 or 4, At the negative electrode, lithium metal is deposited during charging and dissolved during discharging.

6. The nonaqueous electrolyte secondary battery according to claim 1 or 4, The chamfered shape is a C-chamfered shape.

7. The nonaqueous electrolyte secondary battery according to claim 1 or 4, The chamfered shape is an R chamfered shape.

8. The nonaqueous electrolyte secondary battery according to claim 1 or 4, The positive electrode and the negative electrode are wound with the separator interposed therebetween to form an electrode group.

9. The nonaqueous electrolyte secondary battery according to claim 1 or 4, The thickness of the positive electrode active material layer is greater than or equal to 30 μm and less than or equal to 200 μm.

10. The nonaqueous electrolyte secondary battery according to claim 1 or 4, The thickness of the separator is 30 μm or more.

11. The nonaqueous electrolyte secondary battery according to claim 1 or 4, The separator includes a layer having a ratio MD / TD of tensile strength in a longitudinal direction to tensile strength in a transverse direction of 4.5 or more.

12. The nonaqueous electrolyte secondary battery according to claim 1 or 4, The material of the diaphragm includes polypropylene.

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