Secondary battery

Abstract

This secondary battery has a positive electrode (11), a negative electrode (12), and a separator (13) provided between the positive electrode (11) and the negative electrode (12), the positive electrode (11) having a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector, the negative electrode (12) having a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and the separator (13) being provided between the positive electrode (11) and the negative electrode (12). The negative electrode mixture layer has a negative electrode active material containing a Si-containing material, and the 1% extension strength CM (MPa) of the positive electrode current collector and / or the negative electrode current collector and the average thickness CT ([mu] m) of the current collector satisfy the relationship CM * CT < = 1700. At least one of the first separator surface (13a) and the second separator surface (13b) of the separator (13) has a ten-point average roughness (Rz) of 2.7 [mu] m or more.

Description

Technical Field

[0001] The present disclosure relates to secondary batteries. Background Art

[0002] In recent years, as secondary batteries with high power and high energy density, secondary batteries such as lithium-ion secondary batteries having an electrode body in which a positive electrode and a negative electrode are disposed opposite to each other with a separator therebetween have been widely used.

[0003] Lithium-ion secondary batteries and other secondary batteries are used as power sources for a wide range of devices typified by electric vehicles, and further high-capacity is required. For example, in Patent Document 1, in the face of high-capacity of secondary batteries, a solution of using a Si-containing material as a negative electrode active material is disclosed.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: WO 2016 / 035290 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] However, the volume change (expansion / contraction) during charge and discharge of the Si-containing material is large, so that the electrode body may be buckled during charge and discharge. Further, there may be cases where the current collectors used in the positive electrode and the negative electrode are damaged, etc., and the battery resistance increases.

[0009] Therefore, an object of the present disclosure is to suppress the occurrence of buckling of the electrode body and to suppress an increase in battery resistance in a secondary battery using a Si-containing material as a negative electrode active material.

[0010] The secondary battery of the present disclosure includes: an electrode body having a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the positive electrode having: a positive electrode current collector, and a positive electrode composite material layer disposed on the positive electrode current collector, the negative electrode having: a negative electrode current collector, and a negative electrode composite material layer disposed on the negative electrode current collector, the negative electrode composite material layer having a negative electrode active material containing a Si-containing material, the 1% extension strength CM (MPa) of the current collector of at least any one of the positive electrode current collector and the negative electrode current collector, and the average thickness CT (μm) of the current collector satisfy the relationship of CM×CT≤1700, the separator having: a first separator surface facing the positive electrode, and a second separator surface facing the negative electrode, and at least any one of the first separator surface and the second separator surface has a ten-point average roughness (Rz) of 2.7 μm or more.

[0011] According to the present disclosure, in a secondary battery using a Si-containing material as a negative electrode active material, the occurrence of buckling of the electrode body can be suppressed, and an increase in battery resistance can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a cross-sectional view of a secondary battery as an example of an embodiment.

[0013] Figure 2 It is a schematic view showing a state in which a separator is disposed between a positive electrode and a negative electrode.

[0014] Figure 3 It is a schematic cross-sectional view showing an example of the separator of the present embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] A secondary battery as one aspect of the present disclosure includes: an electrode body having a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, the positive electrode having: a positive electrode current collector, and a positive electrode composite material layer disposed on the positive electrode current collector, the negative electrode having: a negative electrode current collector, and a negative electrode composite material layer disposed on the negative electrode current collector, the negative electrode composite material layer having a negative electrode active material containing a Si-containing material, the 1% elongation strength CM (MPa) of the current collector of at least any one of the positive electrode current collector and the negative electrode current collector, and the average thickness CT (μm) of the current collector satisfy the relationship of CM×CT≤1700, the separator having: a first separator surface facing the positive electrode, and a second separator surface facing the negative electrode, and at least any one of the first separator surface and the second separator surface has a ten-point average roughness (Rz) of 2.7 μm or more.

[0016] The inventors of the present invention conducted in-depth research and found that by using a current collector that satisfies the relationship of CM×CT≤1700, buckling of the electrode body during charge and discharge of the battery can be suppressed. It is also known that by using a separator having a ten-point average roughness (Rz) of 2.7 μm or more on the surface of the separator, breakage of the current collector can be suppressed, and thus an increase in battery resistance can be suppressed. The mechanism is not yet clear, but it is considered that a current collector that satisfies the relationship of CM×CT≤1700 has appropriate flexibility, and the current collector follows the volume change of the Si-containing material during charge and discharge, so buckling of the electrode body can be suppressed. If stress caused by the volume change of the Si-containing material is applied to the current collector that satisfies the relationship of CM×CT≤1700 for a long time, the current collector may be damaged. However, it is considered that by using a separator having a ten-point average roughness (Rz) of 2.7 μm or more on the surface of the separator, an appropriate space is formed in the electrode body, so the stress applied to the current collector due to the volume change of the Si-containing material during charge and discharge is alleviated. Therefore, it is considered that by suppressing breakage of the current collector and the like, an increase in battery resistance can be suppressed.

[0017] Hereinafter, an example of an embodiment of the secondary battery of the present disclosure will be described in detail.

[0018] Figure 1 It is a cross-sectional view of a secondary battery as an example of an embodiment. Figure 1 The secondary battery 10 shown includes: a wound electrode body 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, a non-aqueous electrolyte, insulating plates 18 and 19 respectively disposed above and below the electrode body 14, and a battery case 15 for housing the above components. The battery case 15 is composed of a bottomed cylindrical case body 16 and a sealing body 17 that closes the opening of the case body 16. It should be noted that other forms of electrode bodies such as a stacked electrode body in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween can also be applied instead of the wound electrode body 14. In addition, as the battery case 15, a metal case such as a cylindrical shape, a square shape, a coin shape, a button shape, or a resin case (so-called laminated type) formed by laminating resin sheets can be exemplified.

[0019] The non-aqueous electrolyte has, for example, ion conductivity (for example, lithium ion conductivity). The non-aqueous electrolyte can be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0020] The liquid electrolyte (electrolyte solution) contains, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, esters, ethers, nitriles, amides, and a mixed solvent of two or more of them are used, for example. As an example of the non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and a mixed solvent thereof can be cited. The non-aqueous solvent may also contain a halogen-substituted body (for example, fluoroethylene carbonate, etc.) in which at least a part of the hydrogen in these solvents is substituted with a halogen atom such as fluorine. As the electrolyte salt, a lithium salt such as LiPF6 is used, for example.

[0021] In addition, as the solid electrolyte, for example, a solid or gel polymer electrolyte, an inorganic solid electrolyte, etc. can be used. The polymer electrolyte contains, for example, a lithium salt and a matrix polymer, or contains a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, a polymer material that gels by absorbing a non-aqueous solvent is used, for example. As the polymer material, fluororesin, acrylic resin, polyether resin, etc. can be cited, for example. As the inorganic solid electrolyte, a material known in a full solid-state lithium ion secondary battery or the like (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used, for example. It should be noted that the non-aqueous electrolyte is an example, and as long as it can be applied, it can also be an aqueous electrolyte.

[0022] The outer shell main body 16 is, for example, a metal container having a bottomed cylindrical shape. A gasket 28 is provided between the outer shell main body 16 and the sealing body 17 to ensure the airtightness inside the battery. The outer shell main body 16 has, for example, a protruding portion 22 that protrudes inwardly from a part of the side surface and supports the sealing body 17. The protruding portion 22 is preferably formed in a ring shape along the circumferential direction of the outer shell main body 16, and the sealing body 17 is supported by its upper surface.

[0023] The sealing body 17 has a structure in which a partially opened metal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a lid 27 are laminated in sequence from the side of the electrode body 14. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and the members other than the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their central portions, and the insulating member 25 is interposed between their peripheral portions. When the internal pressure of the secondary battery 10 rises due to heat generation caused by internal short circuit or the like, for example, the lower valve body 24 deforms and breaks in such a way as to push the upper valve body 26 toward the lid 27 side, and the current path between the lower valve body 24 and the upper valve body 26 is blocked. When the internal pressure further rises, the upper valve body 26 breaks, and gas is discharged from the opening portion of the lid 27.

[0024] Figure 1 In the secondary battery 10 shown, the positive electrode lead 20 attached to the positive electrode 11 extends toward the sealing body 17 through the through hole of the insulating plate 18, and the negative electrode lead 21 attached to the negative electrode 12 extends toward the bottom side of the outer shell main body 16 through the outside of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the bottom plate of the sealing body 17, that is, the partially opened metal plate 23, by welding or the like, and the lid 27, which is the top plate of the sealing body 17 and is electrically connected to the partially opened metal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the outer shell main body 16 by welding or the like, and the outer shell main body 16 becomes the negative electrode terminal.

[0025] Hereinafter, the positive electrode 11, the negative electrode 12, and the separator 13 will be described in detail.

[0026] [Positive Electrode]

[0027] The positive electrode 11 has a positive electrode current collector and a positive electrode composite material layer disposed on the positive electrode current collector. The positive electrode composite material layer may be disposed on one side of the positive electrode current collector or on both sides. As the positive electrode current collector, a foil of a metal such as aluminum that is stable within the potential range of the positive electrode 11, a thin film having the metal disposed on the surface layer, or the like can be used. The 1% elongation strength and the average thickness of the positive electrode current collector will be described later.

[0028] The positive electrode composite material layer contains, for example, a positive electrode active material, a binder material, a conductive material, etc. The positive electrode 11 can be produced, for example, by coating a positive electrode composite material slurry containing a positive electrode active material, a binder material, a conductive material, etc. on a positive electrode current collector, drying the coating film, and then calendering.

[0029] As the positive electrode active material, lithium transition metal oxides containing transition metal elements such as Co, Mn, Ni, etc. can be exemplified. The lithium transition metal oxide is, for example, Li x CoO2, Li x NiO2, Li x MnO2, Li x Co y Ni 1-y O2, Li x Co y M 1-y O z , Li x Ni 1- y M y O z , Li x Mn2O4, Li x Mn 2-y M y O4, LiMPO4, Li2MPO4F (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). They can be used alone or in combination of two or more. In terms of achieving high capacity of the secondary battery, the positive electrode active material preferably contains Li x NiO2, Li x Co y Ni 1-y O2, Li x Ni 1-y M y O z (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3) and other lithium nickel composite oxides.

[0030] Examples of the conductive material include carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphite, etc. They can be used alone or in combination of two or more.

[0031] Examples of the binder material include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, polyolefin-based resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (such as PAA-Na and PAA-K, and partially neutralized salts are also possible), polyvinyl alcohol (PVA), etc. They can be used alone or in combination of two or more.

[0032] [Negative electrode]

[0033] The negative electrode 12 has a negative electrode current collector and a negative electrode composite material layer disposed on the negative electrode current collector. The negative electrode composite material layer can be disposed on one side of the negative electrode current collector or on both sides. As the negative electrode current collector, foils of metals such as copper and copper alloys that are stable within the potential range of the negative electrode, thin films having such metals disposed on the surface layer, etc. can be used. The 1% elongation strength and average thickness of the negative electrode current collector will be described later.

[0034] The negative electrode composite material layer contains, for example, a negative electrode active material, a binder material, a conductive material, etc. The negative electrode 12 can be produced, for example, by coating a negative electrode composite material slurry containing a negative electrode active material, a binder material, etc. on the negative electrode current collector and calendering after drying the coating film.

[0035] As the negative electrode active material, a Si-containing material is included. Examples of the Si-containing material include Si, Si alloys, Si compounds, etc. In addition, the Si-containing material can be, for example, composite particles containing an ion conduction phase and a silicon phase (in one view, silicon particles) dispersed in the ion conduction phase. The ion conduction phase is a phase that conducts ions, and examples thereof include a silicate phase, a carbon phase, a silicon oxide phase, etc. The Si-containing material preferably contains, for example, at least any one of: a first composite particle having a carbon phase and a silicon phase dispersed in the carbon phase, a second composite particle having a silicate phase and a silicon phase dispersed in the silicate phase, and a third composite particle having a silicon oxide phase and a silicon phase dispersed in the silicon oxide phase.

[0036] The carbon phase can be composed of amorphous carbon, for example. Examples of the amorphous carbon constituting the carbon layer include hard carbon, soft carbon, and other amorphous carbon. Amorphous carbon is a carbon material with an average plane spacing d of the (002) plane measured by X-ray diffraction 002 exceeding 0.34 nm.

[0037] The main component (for example, 95 mass% or more and 100 mass% or less) of the silicon oxide phase can be disilicon oxide. The composition of the composite particles containing a silicon oxide phase and a silicon phase dispersed therein can be represented as a whole by SiO x for example. SiO xA structure in which silicon-containing fine particles are dispersed in amorphous SiO2. The oxygen content ratio x relative to silicon is, for example, preferably 0.5 ≤ x < 2.0, more preferably 0.8 ≤ x ≤ 1.5.

[0038] The silicate phase may satisfy the following conditions (1) and / or (2).

[0039] (1) The silicate phase contains at least one selected from the group consisting of alkali metal elements and Group 2 elements (Group 2 elements in the long-period type periodic table).

[0040] (2) The silicate phase contains element L. The element L is at least one selected from the group consisting of B, Al, Zr, Nb, Ta, V, lanthanide elements, Y, Ti, P, Bi, Zn, Sn, Pb, Sb, Co, Er, F, and W. It should be noted that the lanthanide elements are a general term for 15 elements from lanthanum (La) with an atomic number of 57 to lutetium (Lu) with an atomic number of 71.

[0041] Regarding the above condition (1), examples of the alkali metal element include lithium (Li), potassium (K), and sodium (Na). Examples of the Group 2 element include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). By containing an alkali metal element and / or a Group 2 element, the irreversible capacity of the silicate phase may sometimes be reduced. The silicate phase containing lithium (hereinafter, sometimes referred to as "lithium silicate phase") is, for example, preferable in terms of having a small irreversible capacity and a high initial charge-discharge efficiency.

[0042] The lithium silicate phase may be an oxide phase containing Li, Si, and O, and may also contain other elements. The atomic ratio of O to Si in the lithium silicate phase: O / Si is, for example, greater than 2 and less than 4. Preferably, O / Si is greater than 2 and less than 3. The atomic ratio of Li to Si in the lithium silicate phase: Li / Si is, for example, greater than 0 and less than 4.

[0043] The lithium silicate phase may contain a lithium silicate phase represented by the formula: Li 2z SiO (2+z) (0 < z < 2), and may also be composed of this lithium silicate phase. z preferably satisfies the relationship of 0 < z < 1, more preferably z = 1 / 2 (i.e., Li2Si2O5).

[0044] In addition, the Si-containing material may contain: composite particles including an ion conduction phase and a silicon phase dispersed in the ion conduction phase, and a coating layer covering at least a part of the surface of the composite particles.

[0045] The coating layer present on the surface of the composite particles, for example, includes a conductive layer. By forming a conductive layer on the surface of the composite particles, the conductivity of the Si-containing material can sometimes be improved. As the conductive material constituting the conductive layer, a conductive material containing carbon is preferred. Examples of the conductive material containing carbon include conductive carbon materials. Examples of the conductive carbon material include carbon black, graphite, and amorphous carbon with low crystallinity (non-crystalline carbon). Amorphous carbon is preferred in terms of having a large buffering effect on the silicon phase that undergoes volume change during charge and discharge. The amorphous carbon can be easily graphitizable carbon (soft carbon) or hardly graphitizable carbon (hard carbon). Examples of carbon black include acetylene black and Ketjen black. The thickness of the conductive layer can be in the range of 1 to 200 nm, for example. The thickness of the conductive layer can be measured by cross-sectional observation of the Si-containing material using SEM or TEM (transmission electron microscope).

[0046] For example, in terms of increasing the capacity of the battery, etc., the content of the Si-containing material is preferably 3% by mass or more relative to the total mass of the negative electrode active material. The upper limit of the content of the Si-containing material is preferably 20% by mass or less, for example.

[0047] In addition to the Si-containing material, the negative electrode active material can, for example, also contain known materials that can reversibly store and release lithium ions. For example, in terms of further suppressing the deterioration of the charge-discharge cycle characteristics of the battery, the negative electrode active material preferably contains a carbon material. Examples of the carbon material include graphite materials such as natural graphite and artificial graphite. The content of the carbon material is preferably 80% by mass or more relative to the total mass of the negative electrode active material, for example. In addition, as known materials that can reversibly store and release lithium ions, the negative electrode active material can also contain Sn-containing materials, Ti-containing materials, etc.

[0048] As the binder material, for example, fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide-based resins, acrylic resins, polyolefin-based resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., and can also be partially neutralized salts), polyvinyl alcohol (PVA), etc. can be cited. They can be used alone or in combination of two or more.

[0049] As the conductive material, for example, carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), and graphite can be cited. They can be used alone or in combination of two or more.

[0050] [1% elongation strength CM (MPa) of the current collector × average thickness CT (μm) of the current collector]

[0051] For example, in terms of suppressing the occurrence of buckling of the electrode body 14, the 1% extension strength CM (MPa) of the current collector of at least one of the positive current collector and the negative current collector, and the average thickness CT (μm) of the current collector satisfy CM × CT ≤ 1700, preferably satisfy 500 ≤ CM × CT ≤ 1700, and more preferably satisfy 870 ≤ CM × CT ≤ 1560. The 1% extension strength CM of the current collector is the strength (1%) measured by the tensile test method for metallic materials of JIS Z2241. The 1% extension strength CM of the current collector can be adjusted, for example, by the thickness of the current collector and the crystal grain size of the material of the current collector. The average thickness CT of the current collector is a value obtained by cutting along a plane perpendicular to the plane direction of the current collector, measuring the thickness at 10 or more points in its cross-section, and averaging them.

[0052] For example, in terms of suppressing the occurrence of buckling of the electrode body 14, the average thickness CT of the current collector of at least one of the positive current collector and the negative current collector is preferably 5.0 μm or more and 25.0 μm or less, and more preferably 7.8 μm or more and 15.0 μm or less. In addition, for example, in terms of suppressing the occurrence of buckling of the electrode body 14, the 1% extension strength CM of the current collector of at least one of the positive current collector and the negative current collector is preferably 50 MPa or more and 300 MPa or less, and more preferably 58 MPa or more and 200 MPa or less.

[0053] [Separator]

[0054] Figure 2 It is a schematic diagram showing a state where a separator is disposed between the positive electrode and the negative electrode. Figure 2 The shown positive electrode 11, negative electrode 12, and separator 13 are in a state before winding. And by winding the positive electrode 11 and the negative electrode 12 with the separator 13 interposed therebetween, an electrode body 14 is formed. It should be noted that Figure 2 The gaps between the positive electrode 11 and the separator 13, and between the negative electrode 12 and the separator 13 are exaggeratedly shown.

[0055] The separator 13 has a first separator surface 13a facing the positive electrode 11 and a second separator surface 13b facing the negative electrode 12. And at least one of the first separator surface 13a and the second separator surface 13b has a ten-point average roughness (Rz) of 2.7 μm or more. The ten-point average roughness (Rz) means that only the sampling length is selected in the direction of the average line from the roughness curve, and the absolute value average of the elevation (Yp) between the highest peak and the fifth peak and the absolute value average of the elevation (Yv) between the lowest valley and the fifth valley measured in the longitudinal magnification direction from the average line of the selected part are obtained, and this value is expressed in micrometers (μm). The larger the value of the ten-point average roughness (Rz), the rougher the overall separator surface, and the smaller the value of the ten-point average roughness (Rz), the smoother the overall separator surface. For example, the separator surface can be observed with a laser microscope (OLYMPUS CORPORATION OLS4100), and the ten-point average roughness (Rz) can be measured by the method according to JIS B0601:2001.

[0056] In the present embodiment, both the first separator surface 13a and the second separator surface 13b may have a ten-point average roughness (Rz) of 2.7 μm or more. However, for example, considering process ease, etc., it is preferable that only one of the first separator surface 13a or the second separator surface 13b has a ten-point average roughness (Rz) of 2.7 μm or more, and it is more preferable that only the first separator surface 13a has a ten-point average roughness (Rz) of 2.7 μm or more.

[0057] In terms of suppressing the increase in battery resistance, the ten-point average roughness (Rz) of at least one of the first separator surface 13a and the second separator surface 13b is 2.7 μm or more, preferably 3.0 or more and 10 or less, and more preferably 3.5 or more and 8 or less.

[0058] Hereinafter, an example of the configuration of a separator having a separator surface with a ten-point average roughness of 2.7 μm or more will be described in detail.

[0059] Figure 3 is a schematic cross-sectional view showing an example of the separator of the present embodiment. As Figure 3 shown, the separator 13 includes: a base material 30 having a first surface 30a and a second surface 30b; and a functional layer 32 disposed on the first surface 30a of the base material 30. It should be noted that the functional layer 32 may also be disposed on the first surface 30a and the second surface 30b.

[0060] The base material 30 is, for example, a porous sheet having ion permeability and insulation properties. Specifically, microporous films, woven fabrics, non-woven fabrics, etc. can be cited. The material of the base material 30 is not particularly limited, and examples thereof include polyolefins such as polyethylene, polypropylene, and copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyester, cellulose, polyimide, polyphenylene sulfide, polyether ether ketone, fluororesins, etc.

[0061] The functional layer 32 contains a heat-resistant layer 34 containing inorganic particles and resin particles 36 dispersed in the heat-resistant layer 34. A part of the resin particles 36 forms a convex portion 36a protruding from the surface of the heat-resistant layer 34. The outer surface of the functional layer 32, that is, the surface on the opposite side to the base material 30, is formed by the surface of the heat-resistant layer 34 and the convex portion 36a protruding from the surface of the heat-resistant layer 34. Moreover, the outer surface of the functional layer 32 has a ten-point average roughness (Rz) of 2.7 μm or more. For example, by increasing the average particle diameter (D50) of the resin particles 36 or increasing the amount of the resin particles 36 dispersed in the heat-resistant layer 34, the outer surface of the functional layer 32 is roughened to increase the ten-point average roughness (Rz).

[0062] The outer surface of the functional layer 32 is the first separator surface 13a facing the positive electrode 11 or the second separator surface 13b facing the negative electrode 12, and preferably the first separator surface 13a facing the positive electrode 11.

[0063] In terms of facilitating the roughening of the outer surface of the functional layer 32, the average particle diameter (D50) of the resin particles 36 is preferably larger than the average thickness of the heat-resistant layer 34, and the difference between the average particle diameter (D50) of the resin particles 36 and the average thickness of the heat-resistant layer 34 is, for example, preferably 0.5 μm or more, more preferably 1.0 μm or more. The upper limit of the difference between the average particle diameter (D50) of the resin particles 36 and the thickness of the heat-resistant layer 34 is not particularly limited, but for example, in terms of reducing the ion conductivity of the separator, etc., it is preferably 10 μm or less, more preferably 5 μm or less. The average particle diameter (D50) of the resin particles 36 also depends on the thickness of the heat-resistant layer 34, but for example, it is preferably in the range of 1.0 μm or more and 8.0 μm or less. In this specification, D50 refers to the particle diameter at which the cumulative frequency in the volume-based particle size distribution becomes 50% starting from the smaller particle diameter, and is also called the median particle diameter. The particle size distribution of the resin particles 36 can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by Microtrac·BEL Co., Ltd.) with water as the dispersion medium. The average thickness of the heat-resistant layer 34 refers to the value obtained by cutting along a plane perpendicular to the plane direction of the separator 13, measuring the thickness of the heat-resistant layer 34 at 10 or more points in this cross-section, and averaging them.

[0064] The content of the resin particles 36 is preferably in the range of 4:96 to 20:80, for example, based on the mass ratio of the resin particles 36 to the heat-resistant layer 34 (resin particles: heat-resistant layer).

[0065] In terms of roughening the outer surface of the functional layer 32, the area occupancy rate of the resin particles 36 when looking down at the surface of the functional layer 32 is preferably 2% or more and 30% or less, more preferably 10% or more and 25% or less. The area occupancy rate of the resin particles 36 can be calculated by observing the surface of the functional layer 32 using a scanning electron microscope and measuring the total area of the convex portions 36a present in the range of 100 μm × 100 μm.

[0066] As the resin particles 36, for example, known polymers used as binder materials when forming the functional layer 32 can be used. Examples of monomer units constituting the resin particles 36 (polymers) include aromatic vinyl monomer units, (meth)acrylate monomer units, fluorine-containing monomer units, etc. It should be noted that in the present disclosure, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid. It should be noted that the resin particles 36 (polymers) "contain monomer units" means that the polymer obtained using the monomer contains repeating units derived from the monomer.

[0067] Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units are not particularly limited. For example, styrene, α-methylstyrene, styrenesulfonic acid, butoxystyrene, vinylnaphthalene, etc. can be cited. Examples of (meth)acrylate monomers that can form (meth)acrylate monomer units include: acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, etc., amyl acrylate, hexyl acrylate, heptyl acrylate, 2-ethylhexyl acrylate, etc., octyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, etc.; and methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, etc., amyl methacrylate, hexyl methacrylate, heptyl methacrylate, 2-ethylhexyl methacrylate, etc., octyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, etc.

[0068] In addition, examples of fluorine-containing monomers that can form fluorine-containing monomer units are not particularly limited. For example, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluoroethylene, perfluoroalkyl vinyl ether, etc. can be cited.

[0069] In addition to the above monomer units, the resin particles 36 may further contain crosslinkable monomer units. Here, the crosslinkable monomer unit refers to a monomer that can form a crosslinked structure during or after polymerization by heating or irradiation with energy rays. As monomers that can form crosslinkable monomer units, for example, polyfunctional monomers having two or more polymerizable reactive groups in the monomer can be cited. As such polyfunctional monomers, for example, divinyl compounds such as allyl methacrylate and divinylbenzene; di(meth)acrylate compounds such as diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and 1,3-butanediol diacrylate; tri(meth)acrylate compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; and ethylenically unsaturated monomers containing an epoxy group such as allyl glycidyl ether and glycidyl methacrylate can be cited.

[0070] The resin particles 36 can be prepared by polymerizing a monomer composition containing the above monomers in an aqueous solvent such as water, for example. And the polymerization method is not particularly limited. For example, it can be a suspension polymerization method, an emulsion polymerization coagulation method, a pulverization method, etc. In addition, as the polymerization reaction, any reaction such as radical polymerization or living radical polymerization can be used.

[0071] In the monomer composition used for preparing the resin particles 36, other compounding materials such as a chain transfer agent, a polymerization regulator, a polymerization reaction retarder, a reactive fluidizing agent, a filler, a flame retardant, an antioxidant, and a coloring agent can be compounded in any compounding amount.

[0072] As the inorganic particles contained in the heat-resistant layer 34, for example, metal oxide particles, metal nitride particles, metal fluoride particles, metal carbide particles, etc. can be cited.

[0073] As the metal oxide particles, for example, alumina, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, manganese oxide, etc. can be cited. As the metal nitride particles, for example, titanium nitride, boron nitride, aluminum nitride, magnesium nitride, silicon nitride, etc. can be cited. As the metal fluoride particles, for example, aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, etc. can be cited. As the metal carbide particles, for example, silicon carbide, boron carbide, titanium carbide, tungsten carbide, etc. can be cited.

[0074] The inorganic particles can be zeolite (M 2 / n O·Al2O3·xSiO2·yH2O, M is a metal element, n is the valence of M, x≥2, y≥0), etc., porous aluminosilicates, talc (Mg3Si4O 10 (OH)2), etc., layered silicates, minerals such as barium titanate (BaTiO3) and strontium titanate (SrTiO3), etc. It should be noted that they can be used alone or in combination of two or more.

[0075] The heat-resistant layer 34 preferably further contains a binder material. The binder material has, for example, a function of bonding the inorganic particles to each other and of bonding the inorganic particles to the substrate 30. As an example of the binder material, fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide-based resins, acrylic resins, polyolefin-based resins, styrene-butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC) or its salts, polyvinyl alcohol (PVA), etc. may be mentioned. They may be used alone by 1 type, or 2 or more types may be used in combination. The content of the inorganic particles contained in the heat-resistant layer 34 is, for example, preferably 400% by mass or more and 9900% by mass or less with respect to the mass of the binder. In addition, the content of the binder material contained in the heat-resistant layer 34 is, for example, preferably 3% by mass or more and 30% by mass or less with respect to the total mass of the heat-resistant layer 34.

[0076] The heat-resistant layer 34 preferably contains a binder material and a polymer having an aromatic amide bond. The polymer having an aromatic amide bond has, for example, a function of improving the heat resistance of the heat-resistant layer 34. As the polymer having an aromatic amide bond, for example, aromatic polyamides such as meta-oriented aromatic polyamide and para-oriented aromatic polyamide may be mentioned. The content of the inorganic particles contained in the heat-resistant layer 34 is, for example, preferably 25% by mass or more and 900% by mass or less with respect to the total mass of the binder material and the polymer having an aromatic amide bond. The content of the binder material contained in the heat-resistant layer 34 is, for example, preferably 3% by mass or more and 30% by mass or less with respect to the total mass of the heat-resistant layer 34. The content of the heat-resistant polymer contained in the heat-resistant layer 34 is, for example, preferably 10% by mass or more and 80% by mass or less with respect to the total mass of the heat-resistant layer 34.

[0077] An example of the manufacturing method of the separator 13 of the present embodiment will be described. For example, inorganic particles, resin particles 36, water as a dispersion medium, and other components (such as a binder material, a polymer having an aromatic amide bond, etc.) used as needed are mixed to prepare a slurry composition for a functional layer. Then, the separator 13 of the present embodiment can be manufactured by coating the slurry for the functional layer on the substrate and then drying it.

[0078] As another example of the separator 13 of the present embodiment, there may be mentioned: a base material 30 having a first surface 30a and a second surface 30b, and a functional layer 32 disposed on the first surface 30a of the base material 30, wherein the second surface 30b of the base material 30 has a ten-point average roughness (Rz) of 2.7 μm or more, or the outer surface of the functional layer 32 and the second surface 30b of the base material 30 have a ten-point average roughness (Rz) of 2.7 μm or more. The second surface 30b of the base material 30 may be the first separator surface 13a facing the positive electrode 11, or the second separator surface 13b facing the negative electrode 12. However, when only the second surface 30b of the base material 30 among the outer surface of the functional layer 32 and the second surface 30b of the base material 30 has a ten-point average roughness (Rz) of 2.7 μm or more, it is preferable that the second surface 30b of the base material 30 is the first separator surface 13a facing the positive electrode 11.

[0079] In addition, the separator 13 of the present embodiment is not limited to the separator having the base material 30 and the functional layer 32 disposed on the base material 30, and may be, for example, a separator composed only of the base material 30. In addition, the functional layer 32 does not necessarily include the heat-resistant layer 34 containing inorganic particles as a constituent. The functional layer 32 is, for example, a layer containing known additives, and in addition to the heat-resistant layer, examples thereof may include an antistatic layer, an adhesive layer, a sliding layer, a leveling layer, a flame-retardant layer, a layer having good compatibility with the electrolyte, an antioxidant layer, a lubricating and softening layer, and the like.

[0080] When the separator 13 is composed only of the base material 30, at least one of the first surface 30a and the second surface 30b of the base material 30 has a ten-point average roughness (Rz) of 2.7 μm or more. As a method of roughening the surface of the base material 30 to adjust the ten-point average roughness (Rz) to 2.7 μm or more, for example, there may be mentioned: a method of mixing the resin particles 36 into the raw material of the base material 30 to form the base material 30, or a method of embedding the resin particles 36 into the formed base material 30. In this case, it is desirable that the average particle diameter (D50) of the resin particles 36 is larger than the thickness of the base material 30.

[0081] As a method of adjusting the ten-point average roughness (Rz) of the separator surface to 2.7 μm or more, in addition to using the resin particles 36, for example, there may be mentioned a method of calendering through a calender roll having irregularities. For example, after forming a layer such as the heat-resistant layer 34 on the base material 30, the surface of the layer is calendered through a calender roll having irregularities, thereby adjusting the ten-point average roughness (Rz) of the separator surface to 2.7 μm or more.

[0082] Examples

[0083] Hereinafter, the present disclosure will be further described based on examples, but the present disclosure is not limited to the following examples.

[0084] <Comparative Example 1>

[0085] [Fabrication of the positive electrode]

[0086] Mix 100 parts by mass of LiNi 0.88 Co 0.09 Al 0.03 O2 with 1 part by mass of acetylene black (AB) and 0.9 part by mass of polyvinylidene fluoride (PVDF), and add an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composite material slurry. Then, coat the positive electrode composite material slurry on both sides of an aluminum foil (positive electrode current collector) with a thickness of 15.0 μm and a 1% elongation strength of 190 MPa, and dry the coating film. Then, after rolling the coating film with a roller, cut it into a specified electrode size to fabricate a positive electrode having a positive electrode composite material layer formed on both sides of the positive electrode current collector. An exposed portion where the positive electrode current collector is exposed without forming a positive electrode composite material layer is provided at the central portion in the length direction of the positive electrode, and an aluminum positive electrode lead is welded to this exposed portion.

[0087] [Fabrication of the negative electrode]

[0088] Mix 95 parts by mass of graphite powder with 5 parts by mass of Si oxide, 1 part by mass of carboxymethyl cellulose, and a dispersion of 1 part by mass of styrene-butadiene rubber (SBR), and add an appropriate amount of water to prepare a negative electrode composite material slurry. Then, coat the negative electrode composite material slurry on both sides of a copper foil (negative electrode current collector) with a thickness of 7.8 μm and a 1% elongation strength of 550 MPa, and dry the coating film. Then, after rolling the coating film with a roller, cut it into a specified electrode size to fabricate a negative electrode having a negative electrode composite material layer formed on both sides of the negative electrode current collector. An exposed portion where the negative electrode current collector is exposed without forming a negative electrode composite material layer is provided at one end portion in the length direction of the negative electrode (the end portion located on the inner side of the rolled electrode body), and a nickel negative electrode lead is welded to this exposed portion.

[0089] [Fabrication of the separator]

[0090] Prepare a porous polyethylene substrate with a thickness of 12 μm. Mix α-Al2O3 powder (inorganic particles) and a binder at a solid component mass ratio of 75:25, and then add an appropriate amount of water to prepare a slurry for the functional layer. Coat this slurry for the functional layer over the entire surface of one side of the substrate using a gravure coater, and heat and dry the coating film in an oven at 50 °C for 4 hours to obtain a separator having a functional layer with a heat-resistant layer having an average thickness of 3.0 μm formed on one side of the substrate.

[0091] The result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 2.2 μm.

[0092] [Fabrication of the electrode body]

[0093] The positive electrode and the negative electrode are wound into a vortex shape with a separator in between to produce a wound electrode body. At this time, the separator is arranged such that the functional layer of the separator faces the positive electrode.

[0094] [Preparation of non-aqueous electrolyte]

[0095] A non-aqueous electrolyte is prepared by adding 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 3:7, and dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1.5 mol / L.

[0096] [Fabrication of secondary battery]

[0097] Insulating plates are respectively arranged above and below the above electrode body, and the electrode body is housed in an outer can. The negative electrode lead is welded to the bottom of the bottomed cylindrical outer can, and the positive electrode lead is welded to the sealing body. After injecting the non-aqueous electrolyte into the outer can, the opening of the outer can is sealed through the sealing body with a gasket in between, and then left standing in a constant temperature bath at 60 °C for 15 hours to fabricate a secondary battery.

[0098] <Comparative Example 2>

[0099] A secondary battery is fabricated in the same manner as in Comparative Example 1, except that a copper foil with a thickness of 7.8 μm and a 1% elongation strength of 300 MPa is used for the negative electrode current collector.

[0100] <Comparative Example 3>

[0101] A secondary battery is fabricated in the same manner as in Comparative Example 1, except that a copper foil with a thickness of 7.8 μm and a 1% elongation strength of 200 MPa is used for the negative electrode current collector.

[0102] <Comparative Example 4>

[0103] A secondary battery is fabricated in the same manner as in Comparative Example 1, except that an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 120 MPa is used for the positive electrode current collector.

[0104] <Comparative Example 5>

[0105] A secondary battery is fabricated in the same manner as in Comparative Example 1, except that an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used for the positive electrode current collector.

[0106] <Comparative Example 6>

[0107] In the positive current collector, an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used, and in the negative current collector, a copper foil with a thickness of 7.8 μm and a 1% elongation strength of 200 MPa is used. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1.

[0108] <Comparative Example 7>

[0109] In the preparation of the functional layer slurry, α-Al2O3 powder, a binder material, and acrylic resin particles with an average particle diameter (D50) of 3.5 μm are mixed at a solid component mass ratio of 70.6:23.5:5.9. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1.

[0110] The surface of the functional layer of the separator obtained in Comparative Example 7 was observed by a scanning electron microscope, and as a result, a plurality of protrusions where a part of the acrylic resin particles protruded from the heat-resistant layer were confirmed. The same plurality of protrusions were also confirmed in other comparative examples and examples containing acrylic resin particles described below.

[0111] The difference between the average particle diameter (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer is 0.5 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 2.7 μm.

[0112] <Comparative Example 8>

[0113] In the positive current collector, an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 120 MPa is used, and in the negative current collector, a copper foil with a thickness of 7.8 μm and a 1% elongation strength of 300 MPa is used. In the preparation of the functional layer slurry, α-Al2O3 powder, a binder material, and acrylic resin particles with an average particle diameter (D50) of 5.0 μm are mixed at a solid component mass ratio of 68.9:22.9:8.2. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1.

[0114] The difference between the average particle diameter (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer is 2 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 2.7 μm.

[0115] <Battery Evaluation>

[0116] At an ambient temperature of 25 °C, for the secondary batteries of each comparative example, after charging at a constant current of 0.2It until the voltage reaches 4.2 V, charging is continued at 4.2 V until the current value becomes 0.02It. Then, discharging is performed at a constant current of 0.2It until the voltage reaches 3.0 V. This charge and discharge is regarded as one cycle, and 300 cycles are performed.

[0117] The secondary battery after 300 cycles was charged to 3.7 V and the voltage was maintained at 3.7 V for 1 hour. The battery resistance after 300 cycles was calculated based on the voltage drop after 5 seconds when discharging at 4.8 mA.

[0118] In addition, an X-ray image of the secondary battery after 300 cycles was taken. When bending was confirmed at the positive electrode and negative electrode of the electrode body, it was evaluated that buckling occurred. When bending was not confirmed at the positive electrode and negative electrode of the electrode body, it was evaluated that buckling did not occur. The number of tests was set to 20.

[0119] Table 1 summarizes the evaluation of the occurrence of buckling of the electrode bodies and the results of the battery resistance in Comparative Examples 1 to 6. Among them, the value of the battery resistance is based on the result of Comparative Example 1 (100), and Comparative Examples 2 to 6 are represented by relative values.

[0120] [Table 1]

[0121]

[0122] From the results in Table 1, it can be seen that buckling of the electrode body occurred in Comparative Examples 1 to 2, 4, 7 to 8 where both the positive current collector and the negative current collector did not satisfy the relationship of CM×CT≤1700. In addition, in Comparative Examples 3, 5 to 6 where the positive current collector or the negative current collector satisfied the relationship of CM×CT≤1700, but the ten-point average roughness (Rz) of the separator surface (outer surface of the functional layer) was less than 2.7 μm, buckling of the electrode body did not occur, but the battery resistance increased compared to Comparative Example 1.

[0123] <Comparative Example 9>

[0124] A copper foil with a thickness of 7.8 μm and a 1% yield strength of 200 MPa was used for the negative current collector. In the preparation of the slurry for the functional layer, α-Al2O3 powder, a binder, and acrylic resin particles with an average particle diameter (D50) of 3.1 μm were mixed at a solid component mass ratio of 71.0:23.7:5.3. Except for this, a secondary battery was fabricated in the same manner as in Comparative Example 1 and the same tests were conducted.

[0125] The difference between the average particle diameter (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer was 0.1 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer was 2.3 μm.

[0126] <Comparative Example 10>

[0127] A copper foil with a thickness of 7.8 μm and a 1% elongation strength of 200 MPa is used in the negative electrode current collector. In the preparation of the slurry for the functional layer, α-Al2O3 powder, a binder, and acrylic resin particles with an average particle size (D50) of 3.3 μm are mixed at a solid component mass ratio of 71.0:23.6:5.4. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0128] The difference between the average particle size (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer is 0.3 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 2.4 μm.

[0129] <Example 1>

[0130] A copper foil with a thickness of 7.8 μm and a 1% elongation strength of 200 MPa is used in the negative electrode current collector. In the preparation of the slurry for the functional layer, it is mixed under the same conditions as in Comparative Example 7. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0131] The difference between the average particle size (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer is 0.5 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 2.7 μm.

[0132] <Example 2>

[0133] A copper foil with a thickness of 7.8 μm and a 1% elongation strength of 200 MPa is used in the negative electrode current collector. In the preparation of the slurry for the functional layer, α-Al2O3 powder, a binder, and acrylic resin particles with an average particle size (D50) of 4.0 μm are mixed at a solid component mass ratio of 70.0:23.3:6.7. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0134] The difference between the average particle size (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer is 1 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 3.4 μm.

[0135] <Example 3>

[0136] A copper foil with a thickness of 7.8 μm and a 1% elongation strength of 200 MPa is used in the negative electrode current collector. In the preparation of the slurry for the functional layer, it is mixed under the same conditions as in Comparative Example 8. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0137] The difference between the average particle diameter (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer is 2 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 4.7 μm.

[0138] <Example 4>

[0139] In the negative electrode current collector, a copper foil with a thickness of 7.8 μm and a 1% elongation strength of 200 MPa is used. In the preparation of the slurry for the functional layer, α-Al2O3 powder, a binder, and acrylic resin particles with an average particle diameter (D50) of 8.0 μm are mixed at a solid component mass ratio of 65.6:21.8:12.6. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0140] The difference between the average particle diameter (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer is 5 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 7.8 μm.

[0141] Table 2 summarizes the evaluation of buckling occurrence and the results of battery resistance for the electrode bodies of Comparative Examples 9 and 10 and Examples 1 to 4. Among them, the battery resistance values are represented as relative values for Comparative Examples 9 and 10 and Examples 1 to 4 with the result of Comparative Example 1 as the reference (100).

[0142] [Table 2]

[0143]

[0144] From the results in Table 2, it can be seen that in Comparative Examples 9 and 10 where the negative electrode current collector satisfies the relationship CM×CT≤1700 but the ten-point average roughness (Rz) of the separator surface (outer surface of the functional layer) is less than 0.7 μm, buckling of the electrode body did not occur, but the battery resistance increased compared to Comparative Example 1. On the other hand, in Examples 1 to 4 where the negative electrode current collector satisfies the relationship CM×CT≤1700 and the ten-point average roughness (Rz) of the separator surface (outer surface of the functional layer) is 2.7 μm or more, buckling of the electrode body did not occur, and in addition, the battery resistance was equivalent to that of Comparative Example 1. That is, it can be said that Examples 1 to 4 suppressed the increase in battery resistance.

[0145] <Comparative Example 11>

[0146] In the positive electrode current collector, a copper foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used. The same slurry for the functional layer as that used in Comparative Example 9 is used. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0147] <Comparative Example 12>

[0148] In the positive current collector, an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used. The same functional layer paste as in Comparative Example 10 is used. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0149] <Example 5>

[0150] In the positive current collector, an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used. The same functional layer paste as in Example 1 is used. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0151] <Example 6>

[0152] In the positive current collector, an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used. The same functional layer paste as in Example 2 is used. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0153] <Example 7>

[0154] In the positive current collector, an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used. The same functional layer paste as in Example 3 is used. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0155] <Example 8>

[0156] In the positive current collector, an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used. The same functional layer paste as in Example 4 is used. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0157] <Example 9>

[0158] In the positive current collector, an aluminum foil with a thickness of 15.0 μm and a 1% elongation strength of 58 MPa is used. In the negative current collector, a copper foil with a thickness of 7.8 μm and a 1% elongation strength of 200 MPa is used. The same functional layer paste as in Example 4 is used. Except for this, a secondary battery is fabricated in the same manner as in Comparative Example 1, and the same tests are conducted.

[0159] Table 3 summarizes the evaluation of buckling occurrence and the results of battery resistance for the electrode bodies of Comparative Examples 11 and 12 and Examples 5 to 9. Among them, the battery resistance values are based on the results of Comparative Example 1 (100), and the relative values are used to represent Comparative Examples 11 and 12 and Examples 5 to 9.

[0160] [Table 3]

[0161]

[0162] As can be seen from the results in Table 3, in Comparative Examples 11 and 12 where the positive current collector satisfies the relationship CM×CT≤1700, but the ten-point average roughness (Rz) of the separator surface (the outer surface of the functional layer) is less than 2.7 μm, buckling of the electrode body did not occur, but the battery resistance increased compared to Comparative Example 1. On the other hand, in Examples 5 to 8 where the positive current collector satisfies the relationship CM×CT≤1700 and the ten-point average roughness (Rz) of the separator surface (the outer surface of the functional layer) is 2.7 μm or more, buckling of the electrode body did not occur. In addition, the battery resistance was equivalent to that of Comparative Example 1. That is, it can be said that Examples 5 to 8 suppressed the increase in battery resistance. In addition, in Example 9 where both the positive current collector and the negative current collector satisfy the relationship CM×CT≤1700 and the ten-point average roughness (Rz) of the separator surface (the outer surface of the functional layer) is 2.7 μm or more, buckling of the electrode body did not occur, and the increase in battery resistance was also suppressed.

[0163] [Supplementary Note] (1)

[0165] A secondary battery, comprising: an electrode body having a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode,

[0166] The positive electrode has: a positive current collector, and a positive composite material layer disposed on the positive current collector,

[0167] The negative electrode has: a negative current collector, and a negative composite material layer disposed on the negative current collector,

[0168] The negative composite material layer contains a negative electrode active material containing a Si material,

[0169] The 1% elongation strength CM (MPa) of at least one of the positive current collector and the negative current collector and the average thickness CT (μm) of the current collector satisfy the relationship CM×CT≤1700,

[0170] The separator has: a first separator surface facing the positive electrode, and a second separator surface facing the negative electrode, and at least one of the first separator surface and the second separator surface has a ten-point average roughness (Rz) of 2.7 μm or more. (2)

[0172] For the secondary battery according to (1) above, the first separator surface facing the positive electrode has a ten-point average roughness (Rz) of 2.7 μm or more. (3)

[0174] The secondary battery according to (1) or (2) above, wherein the average thickness CT of the current collector is in the range of 5.0 μm or more and 25.0 μm or less. (4)

[0176] The secondary battery according to any one of (1) to (3) above, wherein the separator includes: a base material having a first surface and a second surface opposite to the first surface; and a functional layer disposed on at least the first surface of the base material between the first surface and the second surface.

[0177] The outer surface of the functional layer is the first separator surface facing the positive electrode or the second separator surface facing the negative electrode, and has a ten-point average roughness (Rz) of 0.7 μm or more. (5)

[0179] The secondary battery according to (4) above, wherein the outer surface of the functional layer is the first separator surface facing the positive electrode. (6)

[0181] The secondary battery according to (4) or (5) above, wherein the functional layer contains: a heat-resistant layer containing inorganic particles, and resin particles dispersed in the heat-resistant layer.

[0182] A part of the resin particles forms convex portions protruding from the surface of the heat-resistant layer. (7)

[0184] The secondary battery according to (6) above, wherein the difference between the average particle diameter (D50) of the resin particles and the average thickness of the heat-resistant layer is 0.5 μm or more. (8)

[0186] The secondary battery according to (6) or (7) above, wherein the area occupancy rate of the resin particles when looking down at the surface of the functional layer is 2% or more and 30% or less. (9)

[0188] The secondary battery according to any one of (6) to (8) above, wherein the heat-resistant layer contains a binder material, and the content of the inorganic particles is 400% by mass or more and 9900% by mass or less relative to the mass of the binder material. (10)

[0190] The secondary battery according to any one of (6) to (8) above, wherein the heat-resistant layer contains a binder material and a polymer having an aromatic amide bond, and the content of the inorganic particles is 25% by mass or more and 900% by mass or less relative to the total mass of the binder material and the polymer having an aromatic amide bond. (11)

[0192] The secondary battery according to any one of (1) to (10) above, wherein the content of the Si-containing material is 3% by mass or more based on the total mass of the negative electrode active material. (12)

[0194] The secondary battery according to any one of (1) to (11) above, wherein the separator includes: a base material having a first surface and a second surface opposite to the first surface; and a functional layer disposed on the first surface of the base material.

[0195] The second surface of the base material is the first separator surface opposite to the positive electrode or the second separator surface opposite to the negative electrode, and has a ten-point average roughness (Rz) of 2.7 μm or more.

[0196] Description of Reference Numerals

[0197] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 13a First separator surface, 13b Second separator surface, 14 Electrode body, 15 Battery case, 16 Case main body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protrusion, 23 Locally opened metal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cover, 28 Gasket, 30 Base material, 30a First surface, 30b Second surface, 32 Functional layer, 34 Heat-resistant layer, 36 Resin particle, 36a Convex portion.

Claims

1. A secondary battery, comprising: an electrode body having a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, The positive electrode has: a positive electrode current collector, and a positive electrode composite material layer disposed on the positive electrode current collector, The negative electrode has: a negative electrode current collector, and a negative electrode composite material layer disposed on the negative electrode current collector, The negative electrode composite material layer has a negative electrode active material containing a Si-containing material, The 1% elongation strength CM (MPa) of the current collector of at least one of the positive electrode current collector and the negative electrode current collector and the average thickness CT (μm) of the current collector satisfy the relationship of CM×CT≤1700, The separator has: a first separator surface facing the positive electrode, and a second separator surface facing the negative electrode, and at least one of the first separator surface and the second separator surface has a ten-point average roughness (Rz) of 2.7 μm or more.

2. The secondary battery according to claim 1, wherein, The surface of the first separator opposite to the positive electrode has a ten-point average roughness (Rz) of 2.7 μm or more.

3. The secondary battery according to claim 1 or 2, wherein, The average thickness CT of the current collector is in the range of 5.0 μm or more and 25.0 μm or less.

4. The secondary battery according to claim 1 or 2, wherein, The separator includes: a substrate having a first surface and a second surface opposite to the first surface; and a functional layer disposed on at least the first surface of the substrate among the first surface and the second surface. The outer surface of the functional layer is the surface of the first separator opposite to the positive electrode or the surface of the second separator opposite to the negative electrode, and has a ten-point average roughness (Rz) of 2.7 μm or more.

5. The secondary battery according to claim 4, wherein, The outer surface of the functional layer is the surface of the first separator opposite to the positive electrode.

6. The secondary battery according to claim 4, wherein, The functional layer contains: a heat-resistant layer containing inorganic particles, and resin particles dispersed in the heat-resistant layer. A part of the resin particles forms protrusions protruding from the surface of the heat-resistant layer.

7. The secondary battery according to claim 6, wherein, The difference between the average particle diameter (D50) of the resin particles and the average thickness of the heat-resistant layer is 0.5 μm or more.

8. The secondary battery according to claim 6, wherein, The area occupancy rate of the resin particles when looking down on the surface of the functional layer is 2% or more and 30% or less.

9. The secondary battery according to claim 6, wherein, The heat-resistant layer contains a binder material, and the content of the inorganic particles is 400% by mass or more and 9900% by mass or less relative to the mass of the binder material.

10. The secondary battery according to claim 6, wherein, The heat-resistant layer contains a binder material and a polymer having an aromatic amide bond, and the content of the inorganic particles is 25% by mass or more and 900% by mass or less relative to the total mass of the binder material and the polymer having an aromatic amide bond.

11. The secondary battery according to claim 1 or 2, wherein, The content of the Si-containing material is 3% by mass or more relative to the total mass of the negative electrode active material.

12. The secondary battery according to claim 1 or 2, wherein, The separator includes: a substrate having a first surface and a second surface opposite to the first surface; and a functional layer disposed on the first surface of the substrate. The second surface of the substrate is the surface of the first separator opposite to the positive electrode or the surface of the second separator opposite to the negative electrode, and has a ten-point average roughness (Rz) of 2.7 μm or more.

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