Secondary battery

Abstract

A secondary battery (10) comprises an electrode body (14) including a positive electrode (11), a negative electrode (12), and a separator (13) disposed between the positive electrode (11) and the negative electrode (12). The negative electrode (12) has a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material. The Young's modulus of the negative electrode (12) is 12 GPa or more, and the thickness of the separator (13) is at least 9 μm but less than 20 μm.

Description

Secondary battery

[0001] The present disclosure relates to a secondary battery, and particularly to the structure of an electrode of the secondary battery.

[0002] Conventionally, as a secondary battery, particularly a non-aqueous electrolyte secondary battery, a cylindrical battery described in Patent Document 1 is known. This cylindrical battery includes an electrode body in which a positive electrode and a negative electrode are wound via a separator, and a bottomed cylindrical outer can that houses the electrode body and has an opening on one side. The positive electrode has a positive electrode mixture layer disposed on a positive electrode current collector, and the negative electrode has a negative electrode mixture layer disposed on a negative electrode current collector.

[0003] This cylindrical battery uses, as a separator, one having a puncture strength greater than 350 g in a puncture test in which a needle with a tip radius of curvature of 0.5 mm is punctured at a puncture speed of 2 mm / s.

[0004] Japanese Patent Application Laid-Open No. 2004-087209

[0005] By ensuring the strength of the separator, the above cylindrical battery prevents breakage of the separator caused by expansion / contraction of the electrode during charge / discharge or an external impact, and suppresses a short circuit between the electrodes caused by breakage of the separator, thereby improving the charge / discharge efficiency of the battery. However, the technique disclosed in Patent Document 1 does not consider the thickness of the separator, and there is still room for improvement in terms of optimizing battery performance such as suppressing the resistance increase rate of the battery.

[0006] The inventor of the present application has found that by imparting rigidity to the negative electrode, deformation of the electrode can be suppressed even if the separator is thin, and has clarified that it is possible to achieve both suppression of short circuit between the electrodes and suppression of the resistance increase rate of the battery.

[0007] The secondary battery according to the present disclosure includes an electrode body including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material, the Young's modulus of the negative electrode is 12 GPa or more, and the thickness of the separator is 9 μm or more and less than 20 μm.

[0008] According to the secondary battery according to the present disclosure, it is resistant to external impact and can also suppress the resistance increase rate of the battery.

[0009] This is an axial cross-sectional view of a secondary battery according to one embodiment of the present disclosure. This is a perspective view of the electrode body. This is a schematic diagram illustrating an example of the structure of the negative electrode mixture layer.

[0010] Hereinafter, embodiments of the secondary battery according to this disclosure will be described in detail with reference to the drawings. The secondary battery of this disclosure may be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. In the following, a cylindrical secondary battery 10 which is a non-aqueous electrolyte secondary battery (lithium-ion battery) using a non-aqueous electrolyte will be given as an example, but the secondary battery of this disclosure is not limited to this.

[0011] It is intended from the outset that new embodiments can be constructed by appropriately combining the characteristic features of the embodiments and modifications described below. In the following embodiments, the same reference numerals are used for the same components in the drawings, and redundant explanations are omitted. In addition, multiple drawings include schematic diagrams, and the dimensional ratios such as length, width, and height of each component do not necessarily match between different drawings. In this specification, the axial (height direction) sealing body 17 side of the cylindrical secondary battery 10 is referred to as "upper," and the bottom 16b side of the axial outer casing 16 is referred to as "lower." Among the components described below, components that are not described in the independent claim indicating the highest-level concept are optional components and are not essential components. Furthermore, this disclosure is not limited to the embodiments and modifications described below, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0012] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to one embodiment of the present disclosure, and Figure 2 is a perspective view of the electrode body 14 of the secondary battery 10. As shown in Figure 1, the secondary battery (hereinafter simply referred to as "battery") 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), a bottomed cylindrical metal casing 16 that houses the electrode body 14 and the non-aqueous electrolyte, and a sealing body 17 that closes the opening of the casing 16. As shown in Figure 2, the electrode body 14 has a wound structure in which a long positive electrode 11 and a long negative electrode 12 are wound around each other via two long separators 13 placed between the positive electrode 11 and the negative electrode 12. In addition to the wound electrode body 14, other forms of electrode bodies may be used, such as a flat electrode body or a stacked electrode body in which multiple positive and negative electrodes are alternately stacked via separators. Examples of the outer casing 16 include cylindrical, square, coin-shaped, button-shaped metal outer cans, and pouch outer casings formed by laminating a resin sheet and a metal sheet.

[0013] The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the longitudinal and widthwise (short-side) directions. The two separators 13 are also formed to be at least slightly larger than the positive electrode 11 and are arranged, for example, to sandwich the positive electrode 11. The negative electrode 12 may constitute the starting end of the winding of the electrode body 14. However, generally, the separator 13 extends beyond the starting end of the winding of the negative electrode 12, and the starting end of the winding of the separator 13 becomes the starting end of the winding of the electrode body 14.

[0014] Non-aqueous electrolytes are ionic conductive (e.g., lithium ion conductive). Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes. Liquid electrolytes (electrolytes) contain a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. Non-aqueous solvents may contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0015] As solid electrolytes, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc., are used. Polymer electrolytes include, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel are used. As polymer materials, for example, fluororesins, acrylic resins, polyether resins, etc., are used. As inorganic solid electrolytes, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0016] The positive electrode 11 comprises a positive electrode current collector and a positive electrode mixture layer disposed on both sides of the positive electrode current collector. The positive electrode current collector can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal disposed on its surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, conductive agent, and binder onto the positive electrode current collector, drying the coating, and then rolling it to adhere the positive electrode mixture layer to both sides of the positive electrode current collector.

[0017] The positive electrode active material is mainly composed of a lithium-containing composite oxide. Examples of metal elements contained in the lithium-containing composite oxide (lithium-containing metal composite oxide) include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. A preferred example of a lithium-containing composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al. The lithium-containing composite oxide may have a spinel structure or an olivine structure. However, it is preferable that the lithium-containing composite oxide has a layered rock salt structure because it makes it easier to produce a positive electrode with a large discharge capacity.

[0018] Examples of conductive agents included in the positive electrode mixture layer include carbon black such as acetylene black and Ketjen black, and carbon materials such as graphite. Examples of binders included in the positive electrode mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These resins may be used in combination with cellulose derivatives such as carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0019] The negative electrode 12 has a negative electrode current collector and a negative electrode mixture layer 52 arranged on both sides of the negative electrode current collector. It is preferable to use a metal foil that is stable within the potential range of the negative electrode 12, such as copper foil or copper alloy foil, or a film with the metal arranged on its surface, for the negative electrode current collector. The negative electrode mixture layer 52 contains a negative electrode active material and a binder. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing the negative electrode active material and binder onto the negative electrode current collector, drying the coating, and then rolling it to adhere the negative electrode mixture layer 52 to both sides of the negative electrode current collector.

[0020] The Young's modulus of the negative electrode 12 is preferably 12 GPa or higher. Young's modulus corresponds to the slope of the straight portion of the stress-strain curve when stress is plotted on the vertical axis and strain on the horizontal axis. A larger Young's modulus means greater rigidity. If the Young's modulus is 12 GPa or higher, the negative electrode 12 is less likely to deform even when subjected to external impact, thus suppressing short circuits between the electrodes.

[0021] The thickness of the negative electrode current collector is not particularly limited, but it is preferably 7.5 μm or more. By making the thickness of the negative electrode current collector 7.5 μm or more, the Young's modulus of the negative electrode 12 can be controlled to be high, and the electrode plates are less likely to deform even when subjected to external impact, so the separator 13 is not damaged and short circuits between the electrodes can be suppressed.

[0022] Generally, carbon materials that reversibly intercept and release lithium ions are used as the negative electrode active material. Preferred carbon materials are graphites such as natural graphite such as flake graphite, lump graphite, and clay graphite, and artificial graphite such as lump graphite and graphitized mesophase carbon microbeads. To improve the rigidity of the negative electrode 12, it is preferable that the negative electrode mixture layer 52 contains a silicon-containing material containing silicon (Si) as the negative electrode active material.

[0023] Figure 3 is a schematic diagram illustrating an example of the structure of the negative electrode mixture layer 52. As shown in Figure 3, it is preferable that the negative electrode mixture layer 52 contains graphite 60 and a silicon-containing material 70. The silicon-containing material 70 includes, for example, an ion-conducting phase 71 and a Si phase 72 dispersed in the ion-conducting phase 71. To improve the rigidity of the negative electrode 12, it is preferable that the Si phase 72 content in the silicon-containing material 70 is 30% by mass or more. Furthermore, it is preferable that the Si phase 72 content in the silicon-containing material 70 is 60% by mass or less, as this reduces the volume change of the negative electrode mixture layer 52 during charging and discharging, thereby suppressing the expansion and contraction of the electrode body 14 during charging and discharging, and making it easier to suppress short circuits between electrodes. The ion-conducting phase 71 may be composed of, for example, an amorphous carbon phase, a lithium silicate phase, a silicon oxide phase, a titanium oxide phase, a zirconium oxide phase, etc. However, in order to suppress volume changes of the negative electrode active material during charging and discharging, it is preferable that the ion-conducting phase 71 contains an amorphous carbon phase.

[0024] From the viewpoint of the mass ratio of silicon element to the negative electrode mixture layer 52, in order to improve the rigidity of the negative electrode 12, it is preferable that the silicon element content in the negative electrode mixture layer 52 be 3% by mass or more, and more preferably 12% by mass or more. Furthermore, since the volume change of the negative electrode mixture layer 52 during charging and discharging can be reduced and the expansion and contraction of the electrode body 14 during charging and discharging can be suppressed, and short circuits between electrodes can be easily suppressed, it is preferable that the silicon element content in the negative electrode mixture layer 52 be 50% by mass or less. When the negative electrode mixture layer 52 contains a silicon-containing material 70, the mass of the silicon element may be about the same as the mass of the Si phase 72. That is, the mass ratio of the Si phase 72 to the negative electrode mixture layer 52 may be 3% by mass or more and 50% by mass or less. The negative electrode active material may be a metal that alloys with lithium other than Si, an alloy containing the metal, a compound containing the metal, etc.

[0025] The binder contained in the negative electrode mixture layer 52 may be fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc., as in the case of the positive electrode 11, but preferably styrene-butadiene rubber (SBR) or a modified version thereof is used. In addition to SBR, the negative electrode mixture layer 52 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, etc.

[0026] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the separator 13 is preferably polyethylene, polyolefin resins such as polypropylene, or cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be placed on the surface of the separator 13.

[0027] The thickness of the separator 13 is preferably 9 μm or more and less than 20 μm. When the negative electrode 12 has a Young's modulus within the above range and the thickness of the separator 13 is within that range, not only is short-circuiting between electrodes suppressed, but the rate of resistance increase of the battery cell can also be suppressed. If the thickness of the separator 13 is less than 9 μm, even if the negative electrode 12 has a Young's modulus within the above range, the separator 13 may break due to external impact, which is undesirable. If the thickness of the separator 13 is 20 μm or more, the capacity of electrodes that can be accommodated per unit volume of the battery is limited, which is undesirable because the rate of resistance increase of the battery cell increases.

[0028] The puncture strength of the separator 13 is preferably 3.0 N or higher. In this case, even if the thickness of the separator 13 is within the above range, it is less likely to break, and short circuits between electrodes can be suppressed. The separator 13 can be made, for example, by extruding a polyolefin resin into a sheet, and then stretching it simultaneously or sequentially in the direction of the machine flow and in a direction perpendicular to the flow direction to make a thin film. By stretching the polyolefin resin, the molecules of the polyolefin resin are oriented and crystallized, which can improve the puncture strength of the separator 13.

[0029] As shown in Figure 1, a positive electrode lead 20 is joined to the positive electrode 11, and a negative electrode lead 21 is joined to the end of the negative electrode 12 on the winding start side in the longitudinal direction. The battery 10 has an insulating plate 18 above the electrode body 14 and an insulating plate 19 below the electrode body 14. The positive electrode lead 20 extends towards the sealing body 17 through a through hole in the insulating plate 18, and the negative electrode lead 21 extends towards the bottom 16b of the outer casing 16 through a through hole in the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the sealing plate 23 of the sealing body 17 by welding or the like. A terminal cap 27 that forms the top plate of the sealing body 17 is electrically connected to the sealing plate 23, and the terminal cap 27 becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom 16b of the metal outer casing 16 by welding or the like, and the outer casing 16 becomes the negative electrode terminal.

[0030] The battery 10 further includes a resin gasket 28 positioned between the outer casing 16 and the sealing body 17. The sealing body 17 is crimped and fixed to the opening of the outer casing 16 via the gasket 28. This seals the internal space of the battery 10. The gasket 28 is sandwiched between the outer casing 16 and the sealing body 17, insulating the sealing body 17 from the outer casing 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer casing 16 and the sealing body 17.

[0031] The outer casing 16 houses the electrode body 14 and the non-aqueous electrolyte. The outer casing 16 has a cylindrical portion 16a and a bottom portion 16b, and the cylindrical portion 16a includes a grooved portion 22 and a shoulder portion. The grooved portion 22 can be formed, for example, by spinning a part of the side surface of the outer casing 16 radially inward to create an annular recess on the radially inward side. The shoulder portion 29 is formed when the sealing body 17 is crimped and fixed to the outer casing 16, by bending the upper end of the outer casing 16 inward toward the peripheral edge 17a of the sealing body 17.

[0032] The sealing body 17 has a structure in which a sealing plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a terminal cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The sealing plate 23 has at least one through hole 23a. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges.

[0033] If the battery 10 overheats and its internal pressure rises, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the terminal cap 27, thus interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is released from the through-hole 27a of the terminal cap 27. This release of gas prevents the battery 10 from rupturing due to an excessive rise in internal pressure, thereby increasing the safety of the battery 10.

[0034] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0035] <Example 1> [Preparation of positive electrode slurry] As the positive electrode active material, the composition formula LiNi ０．９ Co ０．０４ Mn ０．０５ Al ０．０１ O ２ A composite oxide represented by [formula] was used. A positive electrode slurry containing the positive electrode active material, conductive agent, and binder was obtained by adding 100 (mass ratio) of positive electrode active material, 0.80 (mass ratio) of AB as a conductive agent, and 0.82 (mass ratio) of polyvinylidene fluoride (PVdF) as a binder to a liquid component (NMP) and kneading the mixture.

[0036] [Preparation of the positive electrode] The above positive electrode slurry was applied to both sides of a positive electrode current collector made of aluminum foil. After drying and compressing the coating, the positive electrode current collector was cut to a predetermined electrode size to obtain a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode current collector. At this time, a positive electrode current collector exposed portion was provided at the longitudinal center of the positive electrode, with a length of 20 mm (33% of the electrode plate width) in the width direction from one end of the positive electrode current collector. The width (electrode plate width) of the positive electrode current collector (positive electrode) after cutting is 60 mm.

[0037] [Fabrication of the negative electrode] A mixture of graphite and a Si-containing material in a mass ratio of 95:5 was used as the negative electrode active material. The negative electrode active material, styrene-butadiene rubber (SBR) dispersion, and carboxymethylcellulose sodium salt (CMC-Na) were mixed in a solid content mass ratio of 98:1:1, and water was used as the dispersion medium to prepare the negative electrode slurry. Next, the negative electrode slurry was applied to the negative electrode current collector, which was made of copper foil with a thickness of 15 μm, leaving a predetermined exposed portion on both sides of the starting end of the negative electrode. After drying and compressing the coating, the negative electrode current collector was cut to a predetermined electrode size to obtain a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode current collector.

[0038] [Measurement of Young's Modulus of the Negative Electrode] The Young's modulus (E) of the negative electrode is calculated by measuring the amount of strain relative to the compressive stress at room temperature (25°C) in accordance with JIS K7161-1. The relationship is shown below: δ = E・ε (δ: stress, E: Young's modulus, ε: strain)

[0039] [Silicon Element Weight Ratio] The silicon element weight ratio was measured using ICP (Inductively Coupled Plasma: High-Frequency Inductively Coupled Plasma). ICP is one of the methods of emission spectroscopy. When plasma energy is externally applied to an analysis sample, the component elements (atoms) contained therein are excited. In ICP, the emission lines (spectral lines) emitted when the excited atoms return to a lower energy level are measured, and based on the measured emission lines, the content of the component elements (atoms) is measured.

[0040] [Production of Separator] A polyethylene mixture, inorganic fine powder, and a plasticizer were kneaded, formed into a sheet while being heated and melted, and then the inorganic fine powder and the plasticizer were respectively extracted, removed, and dried, and stretched to obtain a 13-μm separator.

[0041] [Measurement of Puncture Strength of Separator] In accordance with JIS Z1707, the test piece was fixed with a jig, and a semicircular needle with a diameter of 1.0 mm and a tip shape radius of 0.5 mm was punctured at a test speed of 50 ± 5 mm / min, and the maximum force until the needle penetrated was measured.

[0042] [Preparation of Non-Aqueous Electrolyte] LiPF was dissolved in a mixed solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 3:7 (25°C) at a concentration of 1.2 mol / L to obtain a non-aqueous electrolyte. ６ to obtain a non-aqueous electrolyte.

[0043] [Production of Battery] The above positive electrode with an aluminum tab welded to the exposed part and an insulating tape attached, and the above negative electrode with a nickel tab welded to the exposed part and an insulating tape attached were wound in a spiral shape through the above separator to produce a wound electrode body. This electrode body was housed in a bottomed cylindrical outer can, the above non-aqueous electrolyte was injected, and then the opening of the outer can was sealed with a sealing body through a gasket to obtain Battery X1.

[0044] [Impact Test] A 9.6-kg weight was dropped from a height of 61 cm onto the central part of a fully charged battery to check for ignition.

[0045] <Example 2> Battery X2 was obtained in the same manner as in Example 1, except that a negative electrode current collector with a thickness of 12 μm was used in the fabrication of the negative electrode, and the thickness of the separator was adjusted to 9 μm in the fabrication of the separator.

[0046] <Example 3> Battery X3 was obtained in the same manner as in Example 1, except that in the preparation of the negative electrode, a mixture of graphite and a Si-containing material in a mass ratio of 70:30 was used as the negative electrode active material, and a negative electrode current collector with a thickness of 10 μm was used.

[0047] <Example 4> In the preparation of the negative electrode, a mixture of graphite and a Si-containing material in a mass ratio of 40:60 was used as the negative electrode active material, and a negative electrode current collector with a thickness of 7.5 μm was used. Except for these differences, a battery X4 was obtained in the same manner as in Example 1.

[0048] <Comparative Example 1> Battery Y1 was obtained in the same manner as in Example 1, except that a negative electrode current collector with a thickness of 7.5 μm was used in the fabrication of the negative electrode, and the thickness of the separator was adjusted to 20 μm in the fabrication of the separator.

[0049] <Comparative Example 2> Battery Y2 was obtained in the same manner as in Example 1, except that a negative electrode current collector with a thickness of 7.5 μm was used in the fabrication of the negative electrode.

[0050] <Comparative Example 3> Battery Y3 was obtained in the same manner as in Example 3, except that the thickness of the separator was adjusted to 8 μm during the preparation of the separator.

[0051] <Comparative Example 4> Battery Y4 was obtained in the same manner as in Example 3, except that the thickness of the separator was adjusted to 20 μm during the preparation of the separator.

[0052] [Evaluation of Battery Resistance] Each of the batteries X1-4 from Examples 1-4 and the batteries Y1-4 from Comparative Examples 1-4 were subjected to a constant voltage charge at 4.2V until the voltage reached 4.2C, then at 4.2V until the current value was 0.02C, followed by a 20-minute pause. After that, a constant current discharge was performed at 0.5C until the battery voltage reached 2.85V, followed by a 20-minute pause. This charge-discharge cycle was repeated 100 times. Then, again at 25°C, the batteries were charged at 4.2V with a constant current of 0.3C until the depth of charge (SOC) reached 50%. After reaching 50% SOC, the batteries were left in an open circuit for 2 hours, and then a constant current discharge was performed at 0.5C for 30 seconds. The Direct Current Resistance (DCR) after 100 cycles, (OCV - CCV) / I30s, was calculated using the open-circuit voltage (OCV), the closed-circuit voltage (CCV) 30 seconds after discharge, and the current value (I30s) 30 seconds after discharge. Before conducting the 100-cycle test, one charge-discharge cycle was performed as described above, and the initial DC resistance (DCR) was measured using the method described above. The DCR increase rate was calculated by dividing the DC resistance after the cycle by the initial DC resistance (DCR). The DCR increase rate for each battery was calculated, with the DCR increase rate of Example 1 set to 100.

[0053]

[0054] As shown in Table 1, none of the example batteries X1 to X4 showed ignition after the impact test, and the rate of resistance increase was also suppressed. In contrast, comparative example batteries Y1 and Y4 showed an increase in resistance because their separator thickness was 20 μm. Furthermore, although the separator thickness of battery Y2 was appropriate, the rigidity of the negative electrode was insufficient because the Young's modulus of the negative electrode was lower than 12 GPa, and therefore ignition was confirmed after the impact test. Battery Y3 also showed ignition after the impact test because its separator thickness was thinner than 9 μm.

[0055] From the above results, it can be seen that when the Young's modulus of the negative electrode is 12 GPa or more and the thickness of the separator is 9 μm or more and less than 20 μm, as in the batteries X1 to X4 of the examples, short circuits between electrodes can be suppressed, and the rate of resistance increase can also be suppressed.

[0056] The above embodiments can be modified as appropriate without impairing the purpose of this disclosure. For example, in the above embodiments, the sealing body 17 was described as having a laminated structure including two rupture plates (lower valve body 24 and upper valve body 26) and a convex terminal cap 27 covering the rupture plates. However, the sealing body may consist only of rupture plates, or it may have a structure in which an internal terminal plate, an insulating plate, and a rupture plate are laminated in order from the electrode body side. Alternatively, the sealing body may not have rupture plates, and the bottom of the outer casing may have a thin, easily breakable portion that breaks when the battery overheats abnormally.

[0057] Furthermore, the secondary battery of this disclosure may have the following configurations: Configuration 1: A secondary battery comprising an electrode body including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, the negative electrode mixture layer contains a negative electrode active material, the Young's modulus of the negative electrode is 12 GPa or more, and the thickness of the separator is 9 μm or more and less than 20 μm. Configuration 2: The secondary battery according to Configuration 1, wherein the negative electrode current collector is copper foil or copper alloy foil, and the thickness of the negative electrode current collector is 7.5 μm or more. Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the negative electrode active material contains a silicon-containing material. Configuration 4: The secondary battery according to Configuration 3, wherein the silicon element content in the negative electrode mixture layer is 3% by mass or more. Configuration 5: The secondary battery according to Configuration 3 or 4, wherein the silicon content in the negative electrode mixture layer is 50% by mass or less. Configuration 6: The secondary battery according to any one of Configurations 3 to 5, wherein the silicon-containing material comprises an ionic conduction phase and a Si phase dispersed in the ionic conduction phase. Configuration 7: The secondary battery according to Configuration 6, wherein the ionic conduction phase comprises an amorphous carbon phase. Configuration 8: The secondary battery according to Configuration 6 or 7, wherein the Si content in the silicon-containing material is 30% by mass or more and 60% by mass or less. Configuration 9: The secondary battery according to any one of Configurations 1 to 8, wherein the puncture strength of the separator is 3.0 N or more.

[0058] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 16a Cylindrical part, 16b Bottom part, 17 Sealing body, 17a Peripheral part, 18,19 Insulating plates, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved part, 23 Sealing plate, 23a Through hole, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Terminal cap, 27a Through hole, 28 Gasket, 52 Negative electrode mixture layer, 60 Graphite, 70 Silicon-containing material, 71 Ion-conducting phase, 72 Si phase

Claims

1. A secondary battery comprising an electrode body including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode has a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, the negative electrode mixture layer contains a negative electrode active material, the Young's modulus of the negative electrode is 12 GPa or more, and the thickness of the separator is 9 μm or more and less than 20 μm.

2. The secondary battery according to claim 1, wherein the negative electrode current collector is a copper foil or a copper alloy foil, and the thickness of the negative electrode current collector is 7.5 μm or more.

3. The secondary battery according to claim 1, wherein the negative electrode active material includes a silicon-containing material.

4. The secondary battery according to claim 3, wherein the silicon element content in the negative electrode mixture layer is 3% by mass or more.

5. The secondary battery according to claim 3, wherein the silicon element content in the negative electrode mixture layer is 50% by mass or less.

6. The secondary battery according to claim 3, wherein the silicon-containing material comprises an ionic conductive phase and a Si phase dispersed in the ionic conductive phase.

7. The secondary battery according to claim 6, wherein the ion conducting phase includes an amorphous carbon phase.

8. The secondary battery according to claim 6, wherein the content of the Si phase in the silicon-containing material is 30% by mass or more and 60% by mass or less.

9. The secondary battery according to claim 1, wherein the puncture strength of the separator is 3.0 N or more.

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