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, the 1% extension strength of the positive electrode current collector and / or the negative electrode current collector is 190 MPa or more, and the first separator surface (13a) and / or 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: International Publication No. 2016 / 035290 Summary of the Invention

[0007] However, the volume change (expansion / contraction) during charge and discharge of the Si-containing material is large. Therefore, the current collectors used in the positive electrode and the negative electrode will elongate, and in order to ensure reliability, the width of the electrode has to be cut, resulting in a sometimes reduced capacity. Therefore, by increasing the strength of the current collector of either or both of the positive electrode and the negative electrode, elongation of the current collector can be suppressed. However, on the other hand, there is a problem that the electrode body including the positive electrode and the negative electrode becomes less likely to change in volume (for example, less likely to elongate in the vertical direction, horizontal direction, or radial direction), the liquid flow of the electrolyte into the electrode body deteriorates, and the charge-discharge cycle characteristics are reduced.

[0008] Therefore, an object of the present disclosure is to suppress elongation of the current collector and suppress reduction of the charge-discharge cycle characteristics in a secondary battery using a Si-containing material as a negative electrode active material.

[0009] 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% elongation strength of at least either one of the positive electrode current collector and the negative electrode current collector being 190 MPa or more, the separator having: a first separator surface opposite to the positive electrode and a second separator surface opposite to the negative electrode, and at least either one of the first separator surface and the second separator surface having a ten-point average roughness (Rz) of 2.7 μm or more.

[0010] According to the present disclosure, in a secondary battery using a Si-containing material as a negative electrode active material, elongation of a current collector can be suppressed, and deterioration of charge-discharge cycle characteristics can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a cross-sectional view of a secondary battery as an example of an embodiment.

[0012] Figure 2 is a schematic view showing a state in which a separator is disposed between a positive electrode and a negative electrode.

[0013] Figure 3 is a schematic cross-sectional view showing an example of the separator of the present embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] A secondary battery according to 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 of at least any one of the positive electrode current collector and the negative electrode current collector being 190 MPa or more, the separator having: a first separator surface facing the positive electrode, and a second separator surface facing the negative electrode, at least any one of the first separator surface and the second separator surface having a ten-point average roughness (Rz) of 2.7 μm or more. Further, according to the secondary battery according to one aspect of the present disclosure, elongation of the current collector can be suppressed, and deterioration of charge-discharge cycle characteristics can be suppressed. The mechanism for achieving the above effects is not clear, but the following is considered.

[0015] During charge and discharge of the battery, even if the Si-containing material expands / contracts, elongation of the current collector on the positive electrode side, the negative electrode side, or both can be suppressed by making the 1% elongation strength of at least any one of the positive electrode current collector and the negative electrode current collector 190 MPa or more. In addition, by making the surface of the separator disposed between the positive electrode and the negative electrode have a ten-point average roughness (Rz) of 2.7 μm or more, an appropriate gap is formed between the positive electrode and the separator, between the negative electrode and the separator, or both. Therefore, when using a current collector with a high 1% elongation strength, even if the volume change of the electrode body during charge and discharge of the battery becomes small (for example, it is not easily elongated in the vertical direction, horizontal direction, or radial direction), deterioration of liquid flow of the electrolyte into the electrode body is suppressed, and deterioration of charge-discharge cycle characteristics is suppressed.

[0016] Hereinafter, an example of an embodiment of the secondary battery of the present disclosure will be described in detail.

[0017] 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, examples include metal cases such as cylindrical, square, coin-shaped, and button-shaped cases, and resin cases (so-called laminated types) formed by laminating resin sheets.

[0018] The non-aqueous electrolyte has, for example, ion conductivity (such as lithium ion conductivity). The non-aqueous electrolyte can be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0019] 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 mixed solvents 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 their mixed solvents can be cited. The non-aqueous solvent may also contain a halogen-substituted body (such as fluoroethylene carbonate) 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.

[0020] 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, fluororesins, acrylic resins, polyether resins, etc. can be cited, for example. As the inorganic solid electrolyte, materials known in all-solid-state lithium ion secondary batteries and the like (such as oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, 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.

[0021] 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 is used to support 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.

[0022] 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 is deformed and broken 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 is broken, and gas is discharged from the opening portion of the lid 27.

[0023] 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.

[0024] Hereinafter, the positive electrode 11, the negative electrode 12, and the separator 13 will be described in detail.

[0025] [Positive Electrode]

[0026] 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 can 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, etc. can be used. The 1% elongation strength of the positive electrode current collector will be described later.

[0027] 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 the positive electrode current collector and calendering the coating film after drying.

[0028] 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.

[0029] Examples of the conductive material include carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), and graphite. They can be used alone or in combination of two or more.

[0030] Examples of the binder material include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (such as PAA-Na, PAA-K, etc., and partial neutralized salts are also possible), polyvinyl alcohol (PVA), etc. They can be used alone or in combination of two or more.

[0031] [Negative electrode]

[0032] 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, a foil of a metal such as copper or a copper alloy that is stable within the potential range of the negative electrode, or a thin film having such a metal disposed on the surface layer, etc. can be used. The 1% elongation strength of the negative electrode current collector will be described later.

[0033] 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 drying the coating film and then calendering it.

[0034] 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, a composite particle 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.

[0035] The carbon phase can be composed of amorphous carbon (non-crystalline carbon), for example. Examples of the amorphous carbon constituting the carbon layer include hard carbon, soft carbon, and other amorphous carbon, etc. Amorphous carbon is a carbon material in which the average plane spacing d of the (002) plane measured by X-ray diffraction method 002 exceeds 0.34 nm.

[0036] The main component (for example, 95% by mass or more and 100% by mass or less) of the silicon oxide phase can be silicon dioxide. The composition of the composite particle containing the silicon oxide phase and the silicon phase dispersed therein as a whole can be represented by SiO x SiO xA structure in which silicon-containing fine particles are dispersed in amorphous SiO2. The oxygen content ratio x relative to silicon is preferably, for example, 0.5 ≤ x < 2.0, more preferably 0.8 ≤ x ≤ 1.5.

[0037] The silicate phase can satisfy the following conditions (1) and / or (2).

[0038] (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).

[0039] (2) The silicate phase contains element L. This 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 the general term for 15 elements from lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71.

[0040] Regarding the above condition (1), examples of the alkali metal elements can include lithium (Li), potassium (K), and sodium (Na). Examples of the Group 2 elements can include magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). By containing alkali metal elements and / or Group 2 elements, 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.

[0041] 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.

[0042] 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 0 < z < 1, more preferably z = 1 / 2 (i.e., Li2Si2O5).

[0043] 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.

[0044] The coating layer present on the surface of the composite particles contains, for example, 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, for example, 1 to 200 nm. 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).

[0045] 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.

[0046] In addition to the Si-containing material, the negative electrode active material can, for example, also contain a known material that can reversibly store and release lithium ions. For example, in terms of further suppressing the degradation 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. In addition, as a known material that can reversibly store and release lithium ions, the negative electrode active material can also contain an Sn-containing material, a Ti-containing material, etc.

[0047] 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 also can be a partially neutralized salt), polyvinyl alcohol (PVA), etc. can be cited. They can be used alone or in combination of two or more.

[0048] 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.

[0049] [1% elongation strength]

[0050] In terms of suppressing the elongation of the current collector, the 1% elongation strength of at least one of the positive electrode current collector and the negative electrode current collector is 190 MPa or more. In addition, the upper limit of the above 1% elongation strength is preferably 700 MPa or less, more preferably 550 MPa or less. The 1% elongation strength is the strength (1%) measured by the tensile test method for metallic materials of JIS Z 2241. The 1% elongation strength 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. In the present embodiment, the 1% elongation strength of the positive electrode current collector and the 1% elongation strength of the negative electrode current collector can both be 190 MPa or more. However, for example, if considering aspects such as the cost of the battery, it is preferable that only the 1% elongation strength of the positive electrode current collector or the 1% elongation strength of the negative electrode current collector is 190 MPa or more. From the viewpoint of suppressing the expansion and contraction of the negative electrode active material, the 1% elongation strength of the negative electrode current collector is preferably 190 MPa or more. The thickness of the positive electrode current collector is, for example, in the range of 1 μm to 50 μm. The same applies to the thickness of the negative electrode current collector.

[0051] [Separator]

[0052] Figure 2 It is a schematic diagram showing a state in which a separator is disposed between the positive electrode and the negative electrode. Figure 2 The positive electrode 11, the negative electrode 12, and the separator 13 shown 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.

[0053] 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, from the roughness curve, only the sampling length is selected in the direction of its average line, 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, by observing the separator surface with a laser microscope (OLYMPUS OLS4100 Co., Ltd.), the ten-point average roughness (Rz) can be measured according to the method of JIS B0601:2001.

[0054] In the present embodiment, the ten-point average roughness (Rz) of both the first separator surface 13a and the second separator surface 13b may be 2.7 μm or more. However, for example, when considering aspects such as the cost of the battery, it is preferable that only 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. Further considering process ease and the like, it is more preferable that only the first separator surface 13a has a ten-point average roughness (Rz) of 2.7 μm or more.

[0055] In terms of suppressing the deterioration of the liquid flow of the electrolytic solution to the electrode body and suppressing the reduction of the charge-discharge cycle characteristics, 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 or more and 10 or less, and more preferably 3.5 or more and 8 or less.

[0056] 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.

[0057] Figure 3 FIG. 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.

[0058] 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.

[0059] 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 protrusions 36a protruding from the surface of the heat-resistant layer 34. The outer surface of the functional layer 32, that is, the surface opposite to the base material 30, is formed by the surface of the heat-resistant layer 34 and the protrusions 36a protruding from the surface of the heat-resistant layer 34. And 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).

[0060] The outer surface of the functional layer 32 is the aforementioned first separator surface 13a facing the positive electrode 11 or the second separator surface 13b facing the negative electrode 12, preferably the first separator surface 13a facing the positive electrode 11.

[0061] In terms of easily roughening 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 in terms of, for example, reducing the ion conductivity of the separator, it is preferably 10 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 is, for example, preferably in the range of 1.0 μm or more and 8.0 μm or less. In the present 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 referred to as 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.

[0062] The content of the resin particles 36 is, for example, in the range of 4:96 to 20:80 in terms of the mass ratio of the resin particles 36 to the heat-resistant layer 34 (resin particles: heat-resistant layer), more preferably.

[0063] 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, preferably 5% or more and 20% 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.

[0064] As the resin particles 36, for example, known polymers used as binder materials when forming the functional layer 32 can be used. As the monomer units constituting the resin particles 36 (polymers), for example, aromatic vinyl monomer units, (meth)acrylate monomer units, fluorine-containing monomer units, etc. can be cited. 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.

[0065] Examples of the aromatic vinyl monomer that can form an aromatic vinyl monomer unit are not particularly limited, and examples thereof include styrene, α-methylstyrene, styrenesulfonic acid, butoxystyrene, vinylnaphthalene, and the like. Examples of the (meth)acrylate monomer that can form a (meth)acrylate monomer unit include: acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, butyl acrylate such as n-butyl acrylate, tert-butyl acrylate, amyl acrylate, hexyl acrylate, heptyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; and methacrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, butyl methacrylate such as n-butyl methacrylate, tert-butyl methacrylate, amyl methacrylate, hexyl methacrylate, heptyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and the like.

[0066] In addition, examples of the fluorine-containing monomer that can form a fluorine-containing monomer unit are not particularly limited, and examples thereof include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene, fluoroethylene, perfluoroalkyl vinyl ether, and the like.

[0067] In addition to the above monomer units, the resin particles 36 may further contain a crosslinkable monomer unit. 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. Examples of the monomer that can form a crosslinkable monomer unit include polyfunctional monomers having two or more polymerizable reactive groups in the monomer. Examples of such polyfunctional monomers include divinyl compounds such as allyl methacrylate and divinylbenzene; di(meth)acrylate compounds such as diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, 1,3-butanediol diacrylate; tri(meth)acrylate compounds such as trimethylolpropane trimethacrylate, trimethylolpropane triacrylate; and ethylenically unsaturated monomers containing an epoxy group such as allyl glycidyl ether and glycidyl methacrylate.

[0068] The resin particles 36 can be prepared by polymerizing a monomer composition containing the above monomers in an aqueous solvent such as water. The polymerization method is not particularly limited, and examples thereof include suspension polymerization, emulsion polymerization coagulation method, pulverization method, and the like. In addition, as the polymerization reaction, any reaction such as radical polymerization or living radical polymerization can be used.

[0069] 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, a coloring agent, etc. can be compounded in any compounding amount.

[0070] 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.

[0071] 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.

[0072] 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), strontium titanate (SrTiO3), etc. It should be noted that they can be used alone or in combination of two or more.

[0073] The heat-resistant layer 34 preferably further contains a binder material. The binder material, for example, has 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), 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. can be cited. They can be used alone or in combination of two or more. 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 relative 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 relative to the total mass of the heat-resistant layer 34.

[0074] 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, for example, has 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 can be cited. 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 relative 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 relative 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 relative to the total mass of the heat-resistant layer 34.

[0075] An example of the method for manufacturing 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 a substrate and then drying it.

[0076] As another example of the separator 13 of the present embodiment, there can be cited: a substrate 30 having a first surface 30a and a second surface 30b, and a functional layer 32 disposed on the first surface 30a of the substrate 30, where the second surface 30b of the substrate 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 substrate 30 have a ten-point average roughness (Rz) of 2.7 μm or more. The second surface 30b of the substrate 30 can 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 substrate 30 has a ten-point average roughness (Rz) of 2.7 μm or more among the outer surface of the functional layer 32 and the second surface 30b of the substrate 30, it is preferable that the second surface 30b of the substrate 30 is the first separator surface 13a facing the positive electrode 11.

[0077] In addition, as the separator 13 of the present embodiment, it is not limited to the separator having the substrate 30 and the functional layer 32 disposed on the substrate 30. For example, it can be composed only of the substrate 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 having a known additive. In addition to the heat-resistant layer, for example, an antistatic layer, an adhesive layer, a sliding layer, a leveling layer, a flame-retardant layer, a layer that is compatible with the electrolyte, an antioxidant layer, a lubricating and softening layer, etc. can be cited.

[0078] In the case where 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, the following methods can be cited: mixing the aforementioned resin particles 36 into the raw material of the base material 30 to form the base material 30, or embedding the aforementioned resin particles 36 into the formed base material 30. In this case, it is preferable that the average particle diameter (D50) of the resin particles 36 is larger than the thickness of the base material.

[0079] 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 aforementioned resin particles 36, for example, a method of calendering with a calender roll having irregularities can be cited. For example, after forming a layer such as a heat-resistant layer 34 on the base material 30, the surface of the layer is calendered with a calender roll having irregularities, thereby adjusting the ten-point average roughness (Rz) of the separator surface to 2.7 μm or more.

[0080] Examples

[0081] Hereinafter, the present disclosure will be further described based on examples, but the present disclosure is not limited to the following examples.

[0082] <Comparative Example 1>

[0083] [Fabrication of positive electrode]

[0084] 100 parts by mass of LiNi 0.88 Co 0.09 Al 0.03 O2, 1 part by mass of acetylene black (AB), and 0.9 part by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode composite material slurry. Then, the positive electrode composite material slurry was coated on both sides of an aluminum foil (positive electrode current collector) having a 1% elongation strength of 53 MPa, and the coating film was dried. Then, after calendering the coating film with a roll, it was cut 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 was exposed without forming a positive electrode composite material layer was provided at the central portion in the length direction of the positive electrode, and an aluminum positive electrode lead was welded to the exposed portion.

[0085] [Fabrication of negative electrode]

[0086] Mix 95 parts by mass of graphite powder with 5 parts by mass of Si oxide, 1 part by mass of carboxymethyl cellulose, and 1 part by mass of a dispersion of styrene-butadiene rubber (SBR), and add an appropriate amount of water to prepare a negative electrode composite material slurry. Next, coat both sides of a copper foil (negative electrode current collector) with an elongation strength of 85 MPa at 1% with the negative electrode composite material slurry, 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 in the length direction of the negative electrode (the end portion located on the inner side of the winding of the electrode body), and a negative electrode lead made of nickel is welded to this exposed portion.

[0087] [Fabrication of separator]

[0088] Prepare a porous polyethylene substrate with a thickness of 12 μm. Mix α-Al2O3 powder (inorganic particles) and a binder in 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 the entire surface of one side of the substrate with this slurry for the functional layer using a microgravure 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.

[0089] The result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer is 2.2 μm.

[0090] [Fabrication of electrode body]

[0091] Wind the positive electrode and the negative electrode in a spiral shape with the separator in between to fabricate a wound-type electrode body. At this time, arrange the separator such that the functional layer of the separator faces the positive electrode.

[0092] [Preparation of non-aqueous electrolyte]

[0093] Prepare a non-aqueous electrolyte by adding 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a volume ratio of 3:7, and dissolving lithium hexafluorophosphate (LiPF6) at a concentration of 1.5 mol / L.

[0094] [Fabrication of secondary battery]

[0095] Arrange insulating plates above and below the above-mentioned electrode body, and accommodate the electrode body in an outer can. Weld the negative electrode lead to the bottom of the bottomed cylindrical outer can respectively, and weld the positive electrode lead to the sealing body. After injecting the non-aqueous electrolyte into the outer can, seal the opening of the outer can through the sealing body with a gasket in between, and then leave it standing in a constant temperature bath at 60 °C for 15 hours to fabricate a secondary battery.

[0096] <Comparative Example 2>

[0097] In the preparation of the slurry for the functional layer, except that α-Al2O3 powder, the binder, and acrylic resin particles with an average particle size (D50) of 3.5 μm were mixed at a solid component mass ratio of 70.6:23.5:5.9, a secondary battery was fabricated in the same manner as in Comparative Example 1.

[0098] The surface of the functional layer of the separator obtained in Comparative Example 2 was observed by a scanning electron microscope, and as a result, a plurality of protrusions were confirmed where a part of the acrylic resin particles protruded from the heat-resistant layer. The same plurality of protrusions were also confirmed in other comparative examples and examples containing acrylic resin particles described below.

[0099] The difference between the average particle size (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer was 0.5 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer was 2.7 μm.

[0100] <Comparative Example 3>

[0101] In the preparation of the slurry for the functional layer, except that α-Al2O3 powder, the binder, and acrylic resin particles with an average particle size (D50) of 4.0 μm were mixed at a solid component mass ratio of 70.0:23.3:6.7, a secondary battery was fabricated in the same manner as in Comparative Example 1.

[0102] The difference between the average particle size (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer was 1 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer was 3.4 μm.

[0103] <Comparative Example 4>

[0104] In the preparation of the slurry for the functional layer, except that α-Al2O3 powder, the binder, and acrylic resin particles with an average particle size (D50) of 5.0 μm were mixed at a solid component mass ratio of 68.9:22.9:8.2, a secondary battery was fabricated in the same manner as in Comparative Example 1.

[0105] The difference between the average particle size (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer was 2 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer was 4.7 μm.

[0106] <Charge and Discharge Cycle Test>

[0107] At an ambient temperature of 25 °C, for the secondary batteries of each comparative example, charging was carried out at a constant current of 0.2It until the voltage reached 4.2V, and then charging was carried out at 4.2V until the current value became 0.02It. Thereafter, discharging was carried out at a constant current of 0.2It until the voltage reached 3.0V. This charge-discharge cycle was regarded as one cycle, and 300 cycles were performed. According to the following formula, the capacity retention rate during the charge-discharge cycle of the secondary battery was calculated.

[0108] Capacity retention rate = (discharge capacity of the 300th cycle / discharge capacity of the 1st cycle) × 100

[0109] The secondary battery after the above charge cycle test was disassembled to take out the negative electrode and the positive electrode, and the lengths in the width direction of the negative electrode and the positive electrode after the test were measured. The elongation amount (AEE) of the negative electrode was calculated from the length in the width direction of the negative electrode before the test and the length in the width direction of the negative electrode after the test. In addition, the elongation amount (CEE) of the positive electrode was calculated from the length in the width direction of the positive electrode before the test and the length in the width direction of the positive electrode after the test. The smaller the sum of them (AEE + CEE), the more the elongation of the current collector is suppressed.

[0110] Table 1 summarizes the capacity retention rates and the values of AEE + CEE for Comparative Examples 1 to 4. Among them, the results of the capacity retention rate and AEE + CEE take the result of Comparative Example 1 as the reference (100), and the values of Comparative Examples 2 to 4 are expressed as relative values.

[0111] [Table 1]

[0112]

[0113] From the results in Table 1, it can be seen that when using a positive current collector and a negative current collector with a 1% yield strength lower than 190 MPa, whether using a separator with a ten-point average roughness (Rz) less than 2.7 μm on the surface of the separator (outer surface of the functional layer) or using a separator with a ten-point average roughness (Rz) of 2.7 μm or more on the surface of the separator (outer surface of the functional layer), the results of the capacity retention rate did not change.

[0114] <Comparative Example 5>

[0115] Except for using an aluminum foil (positive current collector) with a 1% yield strength of 190 MPa, a secondary battery was fabricated in the same manner as Comparative Example 1, and the same test was conducted.

[0116] <Example 1>

[0117] Except for using an aluminum foil (positive current collector) with a 1% yield strength of 190 MPa, a secondary battery was fabricated in the same manner as Comparative Example 2, and the same test was conducted.

[0118] <Example 2>

[0119] A secondary battery was fabricated in the same manner as in Comparative Example 3, except that an aluminum foil (positive current collector) with a 1% elongation strength of 190 MPa was used, and the same tests were conducted.

[0120] <Example 3>

[0121] A secondary battery was fabricated in the same manner as in Comparative Example 4, except that an aluminum foil (positive current collector) with a 1% elongation strength of 190 MPa was used, and the same tests were conducted.

[0122] <Example 4>

[0123] An aluminum foil (positive current collector) with a 1% elongation strength of 190 MPa was used. 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 8.0 μm were mixed at a solid component mass ratio of 65.6:21.8:12.6. Except for this, a secondary battery was fabricated in the same manner as in Comparative Example 1, and the same tests were conducted.

[0124] The difference between the average particle size (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer was 5 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer was 7.8 μm.

[0125] <Example 5>

[0126] An aluminum foil (positive current collector) with a 1% elongation strength of 190 MPa was used. 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 13.0 μm were mixed at a solid component mass ratio of 60.8:20.3:18.9. Except for this, a secondary battery was fabricated in the same manner as in Comparative Example 1, and the same tests were conducted.

[0127] The difference between the average particle size (D50) of the acrylic resin particles and the average thickness (Db) of the heat-resistant layer was 10 μm. In addition, the result of measuring the ten-point average roughness (Rz) of the outer surface of the functional layer was 13.9 μm.

[0128] Table 2 summarizes the capacity retention rates and the values of AEE + CEE for Comparative Example 5 and Examples 1 to 5. Among them, the results of Comparative Example 1 were used as the reference (100) for the capacity retention rate and AEE + CEE values, and the values of Comparative Example 5 and Examples 1 to 5 were expressed as relative values.

[0129] [Table 2]

[0130]

[0131] In Comparative Example 5 and Examples 1 to 5 that used a positive current collector with a 1% elongation strength of 190 MPa or more, the elongation of the current collector was suppressed compared to Comparative Example 1. Although there is a concern that the charge-discharge cycle characteristics may deteriorate when using a current collector with a high 1% elongation strength, in Examples 1 to 5 that used a separator with a ten-point average roughness (Rz) of 2.7 μm or more on the surface of the separator (outer surface of the functional layer), the average capacity retention rate was high and the deterioration of the charge-discharge cycle characteristics was suppressed compared to Comparative Example 5 that used a separator with a ten-point average roughness (Rz) of less than 2.7 μm on the surface of the separator (outer surface of the functional layer).

[0132] <Comparative Example 6>

[0133] A secondary battery was fabricated in the same manner as in Comparative Example 1, except that a copper foil (negative current collector) with a 1% elongation strength of 200 MPa was used, and the same tests were conducted.

[0134] <Example 6>

[0135] A secondary battery was fabricated in the same manner as in Comparative Example 2, except that a copper foil (negative current collector) with a 1% elongation strength of 200 MPa was used, and the same tests were conducted.

[0136] <Example 7>

[0137] A secondary battery was fabricated in the same manner as in Comparative Example 3, except that a copper foil (negative current collector) with a 1% elongation strength of 200 MPa was used, and the same tests were conducted.

[0138] <Example 8>

[0139] A secondary battery was fabricated in the same manner as in Comparative Example 4, except that a copper foil (negative current collector) with a 1% elongation strength of 200 MPa was used, and the same tests were conducted.

[0140] <Example 9>

[0141] A copper foil (negative current collector) with a 1% elongation strength of 200 MPa was used, and mixing was carried out under the same conditions as in Example 4 during the preparation of the functional layer slurry. Otherwise, a secondary battery was fabricated in the same manner as in Comparative Example 1, and the same tests were conducted.

[0142] <Example 10>

[0143] A copper foil (negative current collector) with a 1% elongation strength of 200 MPa was used, and mixing was carried out under the same conditions as in Example 5 during the preparation of the functional layer slurry. Otherwise, a secondary battery was fabricated in the same manner as in Comparative Example 1, and the same tests were conducted.

[0144] Table 3 summarizes the capacity retention rates and the values of AEE + CEE for Comparative Example 6 and Examples 6 to 10. Among them, the results of Comparative Example 1 are used as the reference (100) for the capacity retention rate and the value of AEE + CEE, and Comparative Example 6 and Examples 6 to 10 are represented by relative values.

[0145] [Table 3]

[0146]

[0147] In Comparative Example 6 and Examples 6 to 10 using a negative electrode current collector with a 1% elongation strength of 190 MPa or more, the elongation of the current collector was suppressed compared to Comparative Example 1. As described above, when using a current collector with a high 1% elongation strength, there is a concern about a decrease in charge-discharge cycle characteristics. However, in Examples 6 to 10 using a separator having a ten-point average roughness (Rz) of 2.7 μm or more on the surface of the separator (outer surface of the functional layer), compared to Comparative Example 6 using a separator having a ten-point average roughness (Rz) of less than 2.7 μm on the surface of the separator (outer surface of the functional layer), the average capacity retention rate was high and the decrease in charge-discharge cycle characteristics was suppressed.

[0148] <Comparative Example 7>

[0149] A secondary battery was fabricated in the same manner as in Comparative Example 1, except that an aluminum foil (positive electrode current collector) with a 1% elongation strength of 190 MPa and a copper foil (negative electrode current collector) with a 1% elongation strength of 200 MPa were used, and the same tests were conducted.

[0150] <Example 11>

[0151] A secondary battery was fabricated in the same manner as in Comparative Example 2, except that an aluminum foil (positive electrode current collector) with a 1% elongation strength of 190 MPa and a copper foil (negative electrode current collector) with a 1% elongation strength of 200 MPa were used, and the same tests were conducted.

[0152] <Example 12>

[0153] A secondary battery was fabricated in the same manner as in Comparative Example 3, except that an aluminum foil (positive electrode current collector) with a 1% elongation strength of 190 MPa and a copper foil (negative electrode current collector) with a 1% elongation strength of 200 MPa were used, and the same tests were conducted.

[0154] <Example 13>

[0155] A secondary battery was fabricated in the same manner as in Comparative Example 4, except that an aluminum foil (positive electrode current collector) with a 1% elongation strength of 190 MPa and a copper foil (negative electrode current collector) with a 1% elongation strength of 200 MPa were used, and the same tests were conducted.

[0156] <Example 14>

[0157] An aluminum foil (positive current collector) with a 1% elongation strength of 190 MPa and a copper foil (negative current collector) with a 1% elongation strength of 200 MPa were used. In the preparation of the slurry for the functional layer, mixing was carried out under the same conditions as in Example 4. Except for this, a secondary battery was fabricated in the same manner as in Comparative Example 1, and the same tests were conducted.

[0158] <Example 15>

[0159] An aluminum foil (positive current collector) with a 1% elongation strength of 190 MPa and a copper foil (negative current collector) with a 1% elongation strength of 200 MPa were used. In the preparation of the slurry for the functional layer, mixing was carried out under the same conditions as in Example 5. Except for this, a secondary battery was fabricated in the same manner as in Comparative Example 1, and the same tests were conducted.

[0160] Table 4 summarizes the capacity retention rates and the values of AEE + CEE for Comparative Example 7 and Examples 11 to 15. Among them, for the capacity retention rate and the value of AEE + CEE, the results of Comparative Example 1 were used as the reference (100), and Comparative Example 7 and Examples 11 to 15 were represented by relative values.

[0161] [Table 4]

[0162]

[0163] In Comparative Example 7 and Examples 11 to 15 where a positive current collector and a negative current collector with a 1% elongation strength of 190 MPa were used, the elongation of the current collector was suppressed compared to Comparative Example 1. In addition, as described above, there is a concern that the charge-discharge cycle characteristics may deteriorate when using a current collector with a high 1% elongation strength. However, in Examples 11 to 15 where a separator having a ten-point average roughness (Rz) of 2.7 μm or more on the surface of the separator (outer surface of the functional layer) was used, compared to Comparative Example 7 where a separator having a ten-point average roughness (Rz) of less than 2.7 μm on the surface of the separator (outer surface of the functional layer) was used, the average capacity retention rate was high and the deterioration of the charge-discharge cycle characteristics was suppressed.

[0164] [Supplementary Note] (1)

[0166] A secondary battery, comprising: an electrode body having a positive electrode, a negative electrode, and a separator disposed between the aforementioned positive electrode and the aforementioned negative electrode,

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

[0168] The aforementioned negative electrode has: a negative current collector, and a negative composite material layer disposed on the aforementioned negative current collector,

[0169] The aforementioned negative electrode composite material layer has: a negative electrode active material containing a Si-containing material,

[0170] The 1% elongation strength of at least any one of the aforementioned positive electrode current collector and the aforementioned negative electrode current collector is 190 MPa or more.

[0171] The aforementioned separator has: a first separator surface facing the aforementioned positive electrode, and a second separator surface facing the aforementioned negative electrode. 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. (2)

[0173] The secondary battery according to (1) above, wherein the 1% elongation strength of the aforementioned negative electrode current collector is 190 MPa or more. (3)

[0175] The secondary battery according to (1) or (2) above, wherein the first separator surface facing the aforementioned positive electrode has a ten-point average roughness (Rz) of 2.7 μm or more. (4)

[0177] The secondary battery according to any one of (1) to (3) above, wherein the aforementioned 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 aforementioned base material among the first surface and the second surface of the aforementioned base material.

[0178] The outer surface of the aforementioned functional layer is the first separator surface facing the aforementioned positive electrode or the second separator surface facing the aforementioned negative electrode, and has a ten-point average roughness (Rz) of 2.7 μm or more. (5)

[0180] The secondary battery according to (4) above, wherein the outer surface of the aforementioned functional layer is the first separator surface facing the aforementioned positive electrode. (6)

[0182] The secondary battery according to (4) or (5) above, wherein the aforementioned functional layer contains: a heat-resistant layer containing inorganic particles, and resin particles dispersed in the aforementioned heat-resistant layer.

[0183] A part of the aforementioned resin particles forms convex portions protruding from the surface of the aforementioned heat-resistant layer. (7)

[0185] The secondary battery according to (6) above, wherein the difference between the average particle diameter (D50) of the aforementioned resin particles and the average thickness of the aforementioned heat-resistant layer is 0.5 μm or more. (8)

[0187] The secondary battery according to (6) or (7) above, wherein the area occupancy of the resin particles when looking down on the surface of the functional layer is 2% or more and 30% or less. (9)

[0189] 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)

[0191] 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)

[0193] 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 relative to the total mass of the negative electrode active material. (12)

[0195] 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.

[0196] 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.

[0197] Description of Reference Numerals

[0198] 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 open 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 particles, 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, wherein 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 of at least any one of the positive electrode current collector and the negative electrode current collector is 190 MPa or more, the separator has: 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.

2. The secondary battery according to claim 1, wherein, The 1% elongation strength of the negative electrode current collector is 190 MPa or more.

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

4. The secondary battery according to claim 1 or 2, 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, 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 2.7 μm or more.

5. The secondary battery according to claim 4, wherein, The outer surface of the functional layer is the first separator surface facing 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 a convex portion 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 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, the second surface of the base material 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 2.7 μm or more.

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