Secondary battery

Abstract

This secondary battery disclosed herein comprises a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode and the negative electrode are wound via the separator, thereby constituting an electrode group that has a plurality of peripheries. The secondary battery further comprises a battery can that houses the electrode group. A heat conduction member is disposed between an inner wall of the battery can and the outermost periphery of the electrode group, and a maximum thermal conductivity σ max of the heat conduction member is 600 W / m・ K or more.

Description

secondary battery

[0001] The present disclosure relates to secondary batteries.

[0002] Non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, have high power output and high energy density, and are therefore used as power sources for small consumer devices, power storage devices, and electric vehicles.

[0003] As demand expands, the demand for higher energy densities of non-aqueous electrolyte secondary batteries is increasing day by day. However, when increasing the energy density of non-aqueous electrolyte secondary batteries, it is also necessary to improve the safety of the batteries in the event of an abnormality.

[0004] Patent Document 1 proposes a nonaqueous electrolyte secondary battery comprising a wound electrode body formed by winding a positive electrode and a negative electrode, wherein a heat dissipation material layer is formed on at least one of the positive electrode and the negative electrode so as to reduce the temperature difference in the radial direction of the wound electrode body, and the heat dissipation material layer is formed only in a partial range in the winding direction of at least one of the positive electrode and the negative electrode. The heat dissipation material layer is formed within a range defined from the center of the winding thickness in the radial direction of the wound electrode body to the winding center side.

[0005] JP 2013-157219 A

[0006] According to Patent Document 1, the heat dissipation agent layer is disposed closer to the center of the secondary battery winding than the center of the winding thickness. However, in the electrode body, the heat dissipation agent layer is subjected to bending stress. Because the radius of curvature is small near the center of the winding, the stress applied to the heat dissipation agent layer is also large, and it is thought that the heat dissipation agent layer may break.

[0007] On the other hand, in non-aqueous electrolyte secondary batteries such as lithium-ion batteries, ensuring fire safety is important, and measures against thermal runaway are also important. In particular, if the battery can is deformed or damaged due to thermal runaway, it may cause serious damage to the user. Therefore, it is important to reduce the maximum temperature during thermal runaway, which has a significant impact on the damage to the battery can.

[0008] One aspect of the present disclosure provides a battery comprising: a positive electrode; a negative electrode facing the positive electrode; a separator disposed between the positive electrode and the negative electrode; and an electrolyte, wherein the positive electrode and the negative electrode are wound with the separator interposed therebetween to form an electrode group having a plurality of turns; the battery further comprises a battery can accommodating the electrode group; a heat conductive member is disposed between an inner wall of the battery can and an outermost periphery of the electrode group; and a maximum thermal conductivity σ ｍａｘ The present invention relates to a secondary battery having a capacitance of 600 W / m·K or more.

[0009] According to the present disclosure, a secondary battery having high safety can be realized by suppressing a temperature rise in the outer can in the event of an abnormality.

[0010] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0011] 1 is a longitudinal sectional view of a secondary battery according to an embodiment of the present disclosure; 2 is a conceptual diagram showing a cross-sectional structure of a secondary battery according to an embodiment of the present disclosure;

[0012] Examples of embodiments according to the present disclosure will be described below. While examples of embodiments according to the present disclosure will be described below, the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and other materials may be applied as long as the effects of the present disclosure are obtained. In this specification, when a "range from numerical value A to numerical value B" is used, the range includes numerical value A and numerical value B, and can be interpreted as "greater than or equal to numerical value A and less than or equal to numerical value B." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. When multiple materials are exemplified, one of the materials may be selected and used alone, or two or more of the materials may be used in combination.

[0013] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0014] (Secondary Battery) The secondary battery according to this embodiment includes a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode and the negative electrode are wound with the separator interposed therebetween to form an electrode group having multiple turns. The electrode group is housed in a battery can.

[0015] A thermally conductive member is disposed between the inner wall of the battery can and the outermost periphery of the electrode group. The thermally conductive member is sheet-shaped and has a maximum thermal conductivity of σ ｍａｘ For example, the thermal conductivity of copper is approximately 400 W / m·K, and the thermal conductivity of the heat conducting member is higher than this.

[0016] By disposing a thermally conductive member with high thermal conductivity between the battery can and the electrode group, heat generated in the electrode group during thermal runaway of the electrode group is diffused via the thermally conductive member before being transferred to the battery can. As a result, the heat is transferred evenly to the battery can, the temperature distribution within the battery can is uniform, and the maximum temperature of the battery can is reduced. Localized concentration of thermal stress on the battery can near the location of an abnormality in the electrode group is suppressed, and deformation and cracking of the battery can are suppressed. This allows for the realization of a highly safe secondary battery.

[0017] In a heat conductive member having isotropic heat conduction characteristics, the heat conductivity of the heat conductive member is 600 W / m K or more, and may be 1100 W / m K or more, or 1950 W / m K or more. A heat conductive member having a high thermal conductivity of 600 W / m K or more reduces the maximum temperature of the battery can caused by heat generation in the electrode group in an abnormal event, suppresses deformation and cracking of the battery can, and realizes a secondary battery with high safety.

[0018] The thermal conduction member may have anisotropy in thermal conductivity. In this case, the thermal conduction member may have different thermal conductivities in a first direction (e.g., a thickness direction) and a second direction perpendicular to the first direction (e.g., a surface direction perpendicular to the thickness direction). When the thermal conduction member has anisotropy in thermal conductivity, the thermal conductivity of the thermal conduction member can be determined by the flash method described below.

[0019] In a sheet-like heat conducting member, a certain point on one main surface of the heat conducting member is irradiated with pulsed light to heat it. The heat from the heating diffuses to the other main surface of the heat conducting member, causing the temperature of the other main surface to rise. The temperature change on the other main surface of the heat conducting member is measured using an infrared sensor or the like. From the obtained temperature rise curve, the thermal diffusivity is calculated, taking into account heat loss to the surroundings and correction for the pulse width. The thermal conductivity is derived from the thermal diffusivity using the following formula: Thermal conductivity (W / m K) = Thermal diffusivity (m ２ / s) x heat capacity (J / kg・K) x density (kg / m ３ )

[0020] When the thermal conductivity is anisotropic, the thermal conductivity obtained by the above method depends not only on the thickness of the thermally conductive member but also on the measurement position of the thermal conductivity in the other principal surface (in other words, the relative position of the measurement position with respect to the position on the other principal surface corresponding to the irradiation position of the pulsed light on one principal surface). Here, the maximum value of the thermal conductivity when the measurement position is changed in the other principal surface is defined as the maximum thermal conductivity σ from one surface to the other surface. ｍａｘ The maximum thermal conductivity σ ｍａｘ depends on the thickness of the heat conducting member. Note that for a heat conducting member with isotropic heat conduction characteristics, the thermal conductivity σ ｍａｘ is equal to the thermal conductivity measured by other methods such as the heat flow meter (HFM) method, regardless of the thickness and the measurement position in the plane.

[0021] Maximum thermal conductivity σ of the heat conducting material ｍａｘ The thermal conductivity of the heat conductive member may be 600 W / m·K or more, 1100 W / m·K or more, or 1950 W / m·K or more. ｍａｘ is the maximum value of thermal conductivity σ, which is significantly higher than that of metal materials such as copper, aluminum, and nickel. ｍａｘIt has a high thermal conductivity of 600 W / m·K or more. ｍａｘ The heat-conducting member having the above structure reduces the maximum temperature of the battery can caused by heat generation in the electrode group in an abnormal event, suppresses deformation and cracking of the battery can, and realizes a secondary battery with high safety.

[0022] The thermally anisotropic thermally conductive member only needs to have a higher thermal conductivity in the plane of the sheet-shaped thermally conductive member than in the thickness direction of the sheet. Heat is uniformly diffused along the thermally conductive member arranged on the side periphery of the electrode group to the side periphery of the battery can. As a result, the maximum temperature of the battery can caused by heat generation in the electrode group during an abnormality can be easily reduced, and deformation and cracking of the battery can can be easily suppressed, making it easy to realize a secondary battery with high safety. Additionally, by reducing the thickness of the thermally conductive member, it is easy to achieve both high capacity and high safety.

[0023] The thickness of the thermally conductive member may be 10 to 80 μm. If the thickness of the thermally conductive member is 10 μm or more, the thermally conductive member is prevented from breaking due to bending stress when a wound electrode group is formed. If the thickness of the thermally conductive member is 80 μm or less, an increase in the volume of the electrode group due to the thermally conductive member is prevented, and the capacity of the secondary battery can be maintained high.

[0024] The thermal conductive member may include a graphite sheet. The graphite sheet has anisotropy in thermal conductivity, with the thermal conductivity in the plane where the six-membered ring structure is formed being greater than the thermal conductivity in the direction perpendicular to the plane. The thinner the thickness of the graphite sheet, the greater the maximum thermal conductivity σ ｍａｘ becomes larger and approaches the in-plane thermal conductivity. Even when the thickness is reduced, the material has sufficient strength against bending stress when a wound electrode group is formed. When the thickness of the thermal conductive member is set to 10 to 80 μm, the thermal conductivity σ of 600 W / m·K or more is ｍａｘ In addition, because the graphite sheet is conductive, it has little effect on battery characteristics such as charge and discharge even when placed between the battery can and the electrode group.

[0025] The graphite sheet can be produced, for example, by heat-treating a sheet-shaped product obtained by impregnating a mesh or nonwoven fabric with polyamic acid to obtain a polyimide sheet by imidizing the polyamic acid, and then firing the polyimide sheet in a non-oxidizing atmosphere.

[0026] The thermally conductive member may be disposed on the negative electrode, positive electrode, or separator, whichever constitutes the outermost periphery of the electrode group, and may be disposed in at least a portion of the region of the member that corresponds to one full turn from the end of the winding to the start of the winding (the outermost periphery). The thermally conductive member may be disposed over one full turn from the end of the winding of the member that constitutes the outermost periphery, or a portion less than one full turn, or may be disposed over a portion exceeding one full turn. The thermally conductive member may also be present inside one full turn from the end of the winding of the member that constitutes the outermost periphery (the outermost periphery). When the thermally conductive member is disposed over a portion exceeding one full turn from the end of the winding of the member that constitutes the outermost periphery, the thermally conductive member is present inside one full turn from the end of the winding of the member that constitutes the outermost periphery (the outermost periphery).

[0027] In order to efficiently dissipate heat generated in the electrode group in the event of an abnormality via the thermally conductive member, it is preferable that the region (outermost periphery) corresponding to one full turn from the end of the winding of the negative electrode or positive electrode to the beginning of the winding has no mixture layer and has an area where the current collector is exposed. The thermally conductive member is in direct contact with the area where the current collector is exposed at the outermost periphery, or is disposed on a separator that is in direct contact with the area where the current collector is exposed at the outermost periphery. In other words, at the outermost periphery of the negative electrode or positive electrode, it is preferable that only the thermally conductive member (apart from the electrolyte) is interposed between the area where the current collector is exposed and the battery can, or that the thermally conductive member and the separator are interposed, and no mixture layer is interposed. The member constituting the outermost periphery of the electrode group may be the negative electrode (negative electrode current collector).

[0028] In order to efficiently dissipate heat generated in the electrode group in the event of an abnormality via the thermally conductive member, it is more preferable that no separator is interposed between the thermally conductive member and the battery can, or that the area of ​​the separator interposed between the thermally conductive member and the battery can is small. The thermally conductive member is preferably in contact with the battery can. Typically, the battery can constitutes the external terminal of one of the positive and negative electrodes. When the thermally conductive member is in contact with the battery can and the outermost periphery of the electrode group is the negative or positive electrode, the battery can can constitute the external terminal of the electrode on which the thermally conductive member is located, out of the positive and negative electrodes.

[0029] By disposing the thermally conductive member at least on the outermost periphery of the negative electrode or positive electrode, the electrode group having the thermally conductive member disposed thereon has the thermally conductive member exposed on its side periphery. The region where the thermally conductive member is exposed may be ⅓ or more of the entire circumference of the side periphery, ½ or more of the entire circumference, ⅔ or more of the entire circumference, or ¾ or more of the entire circumference. The thermally conductive member may be exposed over the entire circumference of the side periphery of the electrode group. The width of the region where the thermally conductive member is exposed may be W / 3 or more, W / 2 or more, 2W / 3 or more, or 3W / 4 or more, where W is the width (height) of the electrode group in the axial direction of the winding. The thermally conductive member may be exposed over the entire width W in the axial direction of the winding of the electrode group. The width W in the axial direction of the winding of the electrode group refers to the axial width of the positive electrode, negative electrode, or separator on which the thermally conductive member is provided.

[0030] The heat conduction members may be arranged symmetrically about the center (position +W / 2) in the axial direction of the electrode group, or may be arranged biased toward one end of the electrode group in the axial direction.

[0031] In preparation for abnormal heat generation in the electrode group, secondary batteries are usually provided with an explosion-proof mechanism to prevent battery components from exploding and scattering due to an excessive increase in internal battery pressure, and an electrode group ejection mechanism. The thermal conductive member may be arranged biased toward the side of the secondary battery where the explosion-proof mechanism or the ejection mechanism is provided, in the axial direction of the electrode group.

[0032] The ratio (coverage) of the area where the heat conduction member is exposed on the side surface to the total area of ​​the side surface of the electrode group may be 70% or more and 100% or less, 80% or more and 100% or less, 90% or more and 100% or less, or even 100%.

[0033] The configuration of the thermally conductive member of this embodiment can be used in any secondary battery configuration to efficiently diffuse heat generated in the electrode group in the event of an abnormality, regardless of the configuration of the positive electrode and negative electrode. The secondary battery may be a non-aqueous electrolyte secondary battery.

[0034] An example of a secondary battery according to this embodiment and examples of its components are described in detail below. Note that known components may be applied to components that are not characteristic of the present disclosure. The secondary battery includes, for example, an exterior body (battery can), and a positive electrode, a negative electrode, an electrolyte, and a separator disposed within the exterior body. The separator is disposed between the positive electrode and the negative electrode.

[0035] The shape of the secondary battery is not limited, and may be cylindrical, rectangular, coin-shaped, button-shaped, etc. The battery can is selected according to the shape of the secondary battery.

[0036] [Negative Electrode] The negative electrode includes a negative electrode active material layer and, if necessary, further includes a negative electrode current collector. The negative electrode active material layer includes a negative electrode active material as an essential component, and may include optional components such as a binder, a conductive material, and a thickener. Known materials can be used as the binder, conductive material, and thickener.

[0037] The negative electrode active material layer can be formed by applying a negative electrode slurry, in which the materials for the negative electrode active material layer are dispersed in a dispersion medium, to the surface of the negative electrode current collector to form a coating film, and then drying the coating film. The dried coating film may be rolled as necessary. Examples of the dispersion medium include water, alcohol, ether, N-methyl-2-pyrrolidone (NMP), and mixed solvents thereof. The ratio of components in the negative electrode active material layer can be adjusted by changing the mixing ratio of the materials for the negative electrode active material. The negative electrode active material layer may be formed on only one surface of the negative electrode current collector, or on both surfaces.

[0038] The negative electrode active material can be at least one selected from materials that electrochemically absorb and release lithium ions, lithium metal, and lithium alloys. Examples of materials that electrochemically absorb and release lithium ions include carbon materials and alloy-based materials. Examples of carbon materials include graphite, easily graphitized carbon (soft carbon), and hardly graphitized carbon (hard carbon). Of these, graphite is preferred because of its excellent charge / discharge stability and low irreversible capacity. Examples of alloy-based materials include those containing at least one metal that can form an alloy with lithium, such as silicon, tin, silicon alloys, tin alloys, and silicon compounds. Silicon oxides and tin oxides formed by bonding these with oxygen may also be used.

[0039] Examples of alloy-based materials containing silicon include a lithium ion conductive phase and a silicon composite material in which silicon particles are dispersed in the lithium ion conductive phase. Examples of lithium ion conductive phases that can be used include a silicon oxide phase, a silicate phase, and / or a carbon phase. The silicon oxide phase may be primarily composed of silicon dioxide (e.g., 95 to 100% by mass). Among these, composite materials composed of a silicate phase and silicon particles dispersed in the silicate phase are preferred because of their high capacity and low irreversible capacity.

[0040] The silicate phase may contain, for example, at least one element selected from the group consisting of Group 1 and Group 2 elements of the long periodic table. Examples of Group 1 elements of the long periodic table and Group 2 elements of the long periodic table include lithium (Li), potassium (K), sodium (Na), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). Other elements may include aluminum (Al), boron (B), lanthanum (La), phosphorus (P), zirconium (Zr), and titanium (Ti). Among these, a silicate phase containing lithium (hereinafter also referred to as a lithium silicate phase) is preferred due to its small irreversible capacity and high initial charge / discharge efficiency.

[0041] The lithium silicate phase may be an oxide phase containing lithium (Li), silicon (Si), and oxygen (O), and may 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. The lithium silicate phase has the formula: Li ２ｚ SiO ２＋ｚ (0<z<2). Preferably, z satisfies the relationship 0<z<1, and more preferably z=1 / 2. Examples of elements other than Li, Si, and O that can be contained in the lithium silicate phase include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and aluminum (Al).

[0042] The carbon phase may be composed of, for example, amorphous carbon with low crystallinity (i.e., amorphous carbon). The amorphous carbon may be, for example, hard carbon, soft carbon, or other.

[0043] The negative electrode current collector may be a non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, or punched sheet). Examples of the material for the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0044] [Positive Electrode] The positive electrode includes a positive electrode active material layer. Typically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer (positive electrode mixture layer) formed on the surface of the positive electrode current collector. The positive electrode active material layer can be formed by applying a positive electrode slurry, in which a positive electrode mixture containing a positive electrode active material is dispersed in a dispersion medium, to the surface of the positive electrode current collector and drying the slurry. The dried coating film may be rolled as necessary. The positive electrode mixture includes a positive electrode active material as an essential component, and may include a binder, a conductive agent, and the like as optional components. Known materials can be used as the binder, conductive material, and thickener. Graphite, such as natural graphite or artificial graphite, or carbon nanotubes may be used as the conductive agent.

[0045] As the positive electrode active material, a lithium composite metal oxide can be used. Examples of the lithium composite metal oxide include Li ａ CoO ２ , Li ａ NiO ２ , Li ａ MnO ２ , Li ａ Co ｂ Ni １－ｂ O ２ , Li ａ Co ｂ M １－ｂ O ｃ , Li ａ Ni １－ｂ M ｂ O ｃ , Li ａ Mn ２ O ４ , Li ａ Mn ２－ｂ M ｂ O ４、 LiGPO ４、 Li ２ GPO ４ Examples of the lithium-ion battery include F. Here, M is at least one selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B. G includes at least a transition element (for example, at least one selected from the group consisting of Mn, Fe, Co, and Ni). Here, 0≦a≦1.2, 0≦b≦0.9, and 2.0≦c≦2.3. The value a, which indicates the molar ratio of lithium, increases or decreases with charge and discharge.

[0046] The shape and thickness of the positive electrode current collector can be selected from the shape and range corresponding to those of the negative electrode current collector. Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.

[0047] [Electrolyte] The electrolyte may be an electrolytic solution containing a solvent and a solute dissolved in the solvent. The solute is an electrolyte salt that ionically dissociates in the electrolytic solution. The solute may include, for example, a lithium salt. Components of the electrolytic solution other than the solvent and the solute are additives. The electrolytic solution may contain various additives.

[0048] A non-aqueous solvent is used as the solvent. Examples of non-aqueous solvents that can be used include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0049] Other examples of the non-aqueous solvent include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.

[0050] Examples of the lithium salt include lithium salts of chlorine-containing acids (LiClO ４ , LiAlCl ４ , LiB １０ Cl １０ etc.), lithium salts of fluorine-containing acids (LiPF ６ , LiPF ２ O ２ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ etc.), lithium salt of fluorine-containing acid imide (LiN(FSO ２ ) ２ , LiN(CF ３ SO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(C ２ F５ SO ２ ) ２ Lithium salts such as lithium halides (LiCl, LiBr, LiI, etc.) can be used. One type of lithium salt can be used alone, or two or more types can be used in combination.

[0051] The concentration of the lithium salt in the electrolyte solution may be 1 mol / L or more and 2 mol / L or less, or 1 mol / L or more and 1.5 mol / L or less. By controlling the lithium salt concentration within the above range, an electrolyte solution having excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.

[0052] The electrolyte may contain other known additives, such as 1,3-propane sultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0053] [Separator] A separator is disposed between the positive electrode and the negative electrode. The separator may be a material having high ion permeability and adequate mechanical strength and insulating properties. The separator may be made of a microporous thin film, a woven fabric, a nonwoven fabric, or the like. Examples of materials for the separator include polyolefins such as polyethylene, polypropylene, and copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyester, and cellulose.

[0054] An example of a secondary battery includes an exterior body, an electrode group housed in the exterior body, and a non-aqueous electrolyte. There are no particular limitations on the structure of the electrode group. One example of an electrode group is formed by winding a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. Another example of an electrode group is formed by stacking a positive electrode, a negative electrode, and a separator so that the separator is disposed between the positive electrode and the negative electrode. There are no limitations on the shape of the secondary battery, and it may be cylindrical, prismatic, coin-shaped, button-shaped, laminate-shaped, or the like.

[0055] There is no particular limitation on the method for manufacturing the secondary battery, and a known manufacturing method may be applied, or a known manufacturing method may be applied with at least a part thereof modified.

[0056] Examples of embodiments according to the present disclosure will be specifically described below with reference to the drawings. The components described above can be applied to the components of the examples described below. Furthermore, the examples described below can be modified based on the above description. Furthermore, the matters described below may be applied to the above embodiments. Furthermore, in the embodiments described below, components that are not essential for the secondary battery according to the present disclosure may be omitted.

[0057] Fig. 1 is a longitudinal cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery 10 (hereinafter also simply referred to as "battery 10") according to a first embodiment of the present disclosure. Fig. 2 is a conceptual diagram showing the cross-sectional structure of battery 10. However, the present disclosure is not limited to the following configuration.

[0058] In FIG. 1 , the battery 10 includes an electrode group 18, a nonaqueous electrolyte (not shown), and a cylindrical battery case (metal can) 22 with a bottom that accommodates these components. A sealing body 11 is crimped to the opening of the battery case 22 via a gasket 21, thereby sealing the interior of the battery 10. The sealing body 11 includes an internal pressure-activated safety valve that cuts off current and, if necessary, ruptures when the battery's internal pressure increases excessively. Specifically, the sealing body includes a valve body 12 having a thin portion, a metal plate 13, and an annular insulating member 14 interposed between the valve body 12 and the metal plate 13. The valve body 12 and the metal plate 13 are electrically connected to each other at their respective centers. A positive electrode lead 15L extending from the positive electrode 15 is connected to the metal plate 13. Thus, the valve body 12 functions as both an external terminal for the positive electrode 15 and a safety valve. When the internal pressure of the battery increases, the connection between the valve body 12 and the metal plate 13 is severed, interrupting the current. Furthermore, when the thin-walled portion breaks, gas is released to the outside, ensuring safety. The negative electrode lead 16L extending from the negative electrode 16 is connected to the inner bottom surface of the battery case 22. An annular groove 22a is formed near the open end of the battery case 22. A first insulating plate 23 is disposed between one end face of the electrode group 18 and the annular groove 22a. A second insulating plate 24 is disposed between the other end face of the electrode group 18 and the bottom of the battery case 22. The electrode group 18 is formed by winding the positive electrode 15 and the negative electrode 16 together with the separator 17 interposed therebetween into a cylindrical shape. The outermost periphery of the electrode group 18 is located at the end of the winding of the negative electrode 16. In other words, in the electrode group 18, the outermost periphery of the negative electrode 16 is disposed outside the outermost periphery of the positive electrode 15.

[0059] 2 is a cross-sectional view of a portion of the electrode group 18 closest to the inner wall of the battery case. A winding end side negative electrode current collector 16b is disposed on the outermost periphery of the electrode group 18. Although not shown, the winding end side of the separator 17 may be further wound around the outer surface of the outermost periphery of the negative electrode 16. Furthermore, the outer surface of the outermost periphery of the negative electrode 16 may be in contact with the inner wall surface of the battery case 22.

[0060] Although the case where the outermost periphery of the electrode group 18 is the negative electrode 16 has been described here, the outermost periphery of the electrode group may also be the positive electrode. In this case, the positive electrode and negative electrode in the description corresponding to FIG. 2 may be interchanged. That is, when the positive electrode and negative electrode are interchanged, the positive electrode current collector at the winding end side is disposed at the outermost periphery of the electrode group 18. Although not shown, the winding end side of the separator 17 is further wrapped around the outer surface of the outermost periphery of the positive electrode, preventing contact between the outer surface of the outermost periphery, which is the positive electrode, and the inner wall surface of the battery case 22 connected to the negative electrode.

[0061] 2, a thermally conductive member 19 is disposed on the outer surface of the negative electrode current collector 16b, which is the outermost periphery of the negative electrode 16. The thermally conductive member has the maximum thermal conductivity σ ｍａｘ The electric current is 600 W / m·K or more, and the outermost negative electrode current collector 16 b is covered by the outermost negative electrode current collector 16 b.

[0062] (Note) The above embodiments disclose the following techniques: (Technology 1) A battery comprising a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are wound with the separator interposed therebetween to form an electrode group having a plurality of turns, and further comprising a battery can containing the electrode group, wherein a heat conductive member is disposed between an inner wall of the battery can and the outermost periphery of the electrode group, and wherein the maximum thermal conductivity σ of the heat conductive member is ｍａｘ The secondary battery according to the first aspect of the present invention is characterized in that the thermal conductivity of the thermal conductive member is 10 to 80 μm.

[0063] The secondary battery according to the present disclosure will be described in further detail with reference to examples.

[0064] Example 1 [Fabrication of Negative Electrode] A mixture of silicon composite material and graphite in a mass ratio of silicon composite material:graphite = 5:95 was used as the negative electrode active material. The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and water were mixed in a predetermined mass ratio to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to the surface of copper foil (negative electrode current collector) to form a coating film. The coating film was dried and then rolled to form a negative electrode active material layer on both sides of the copper foil.

[0065] [Preparation of Positive Electrode] As the positive electrode active material, LiNi ０．８８ Co ０．０９ Al ０．０３ O ２ The positive electrode active material, polyvinylidene fluoride, N-methyl-2-pyrrolidone (NMP), and acetylene black were mixed in a predetermined mass ratio to prepare a positive electrode slurry.

[0066] Next, the positive electrode slurry was applied to the surface of an aluminum foil (positive electrode current collector) to form a coating film, which was dried and then rolled to form a positive electrode mixture layer on both sides of the aluminum foil.

[0067] [Preparation of Electrolyte Solution] LiPF 6 as a lithium salt was added to a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. ６ The electrolyte solution was prepared by adding LiPF in the non-aqueous electrolyte solution. ６ The concentration was 1.3 mol / liter.

[0068] [Preparation of Electrode Assembly] Lead tabs were attached to each electrode. Next, the positive and negative electrodes were spirally wound with a separator made of a porous polyethylene sheet interposed between them so that the leads were positioned at the outermost periphery. In this way, a cylindrical electrode assembly was prepared.

[0069] The positive electrode, negative electrode, and separator were wound so that the negative electrode was positioned at the outermost periphery of the electrode assembly. The negative electrode current collector was exposed on one side of the negative electrode facing outward from the end of the negative electrode winding (i.e., the outermost periphery) without being coated with negative electrode slurry. A thermally conductive member made of a graphite sheet was placed on the exposed portion of the negative electrode current collector so as to completely cover the outermost periphery of the electrode assembly. In other words, the thermally conductive member was exposed over the entire periphery and width of the side periphery of the electrode assembly, and the ratio (coverage rate) of the area exposed on the side periphery of the electrode assembly to the total area of ​​the side periphery of the electrode assembly was 100%.

[0070] The thickness of the graphite sheet was 10 μm. The maximum thermal conductivity σ of the graphite sheet measured by the above-mentioned method was ｍａｘ was 1950 W / m·K.

[0071] The electrode group was vacuum dried at 105°C for 2 hours and then placed in a bottomed cylindrical battery case that also served as a negative electrode terminal. An iron battery case was used. After a nonaqueous electrolyte was poured into the battery case, the opening of the battery case was closed using a metal seal that also served as a positive electrode terminal. A resin gasket was interposed between the seal and the open end of the battery case. The other end of the positive electrode lead was connected to the seal, and the other end of the negative electrode lead was connected to the inner bottom surface of the battery case. In this way, a 2170-type cylindrical secondary battery A1 with a design capacity of 5 Ah was fabricated.

[0072] [Evaluation] The following evaluations were performed on the fabricated secondary batteries. (1) Initial Capacity: The battery was charged at a constant current of 1500 mA in an environment of 25°C until the battery voltage reached 4.2 V, and then continued to be charged at a constant voltage until the current value reached 60 mA. After that, the charged battery was left for 20 minutes and then discharged at a constant current of 3000 mA until the battery voltage reached 2.5 V. The discharge capacity at this time was defined as the initial capacity C ０ It was decided.

[0073] (2) Nail Penetration Test The battery temperature after the nail penetration test was measured for the fabricated secondary batteries using the following procedure. (a) The battery was charged at a constant current of 0.5 C in an environment of 25°C until the battery voltage reached 4.2 V, and then continued to be charged at a constant voltage until the current value reached 0.02 C. (b) In an environment of 25°C, the tip of a round nail (2.7 mm in diameter) was contacted with the center of the battery charged in (a) and penetrated at a speed of 1 mm / sec. Immediately after detecting a drop in battery voltage due to an internal short circuit, the nail penetration was stopped. The surface temperature of the battery was then measured 1 minute after the battery shorted. An infrared camera was used to determine the temperature distribution on the battery case surface, and the highest temperature in the distribution was evaluated as the battery temperature Tx after the nail penetration test.

[0074] The area around the nail insertion position on the battery case was visually observed to check for damage to the circumferential surface of the case. The nail penetration test was performed on ten batteries of the same type (N=10), and the number n of batteries in which damage to the battery case was confirmed was calculated. The probability of battery damage due to the nail penetration test was evaluated as P=n / N.

[0075] Example 2 A graphite sheet having a thickness of 50 μm was used as a heat conducting member. The maximum thermal conductivity σ of the graphite sheet measured by the above-mentioned method was ｍａｘ The electrical conductivity was 1100 W / m·K. Except for this, a secondary battery A2 according to Example 2 was completed in the same manner as in Example 1, and was evaluated in the same manner.

[0076] Example 3: A graphite sheet having a thickness of 80 μm was used as a heat conducting member. The maximum thermal conductivity σ of the graphite sheet measured by the above-mentioned method was ｍａｘ The electrical conductivity was 600 W / m·K. Except for this, a secondary battery A3 according to Example 3 was completed in the same manner as in Example 1, and was evaluated in the same manner.

[0077] Comparative Example 1 A secondary battery B1 according to Comparative Example 1 was completed in the same manner as in Example 1, except that no thermal conductive member was disposed on the exposed portion of the negative electrode current collector, and was evaluated in the same manner.

[0078] Comparative Example 2: A graphite sheet having a thickness of 100 μm was used as the heat conducting member. The maximum thermal conductivity σ of the graphite sheet measured by the above-mentioned method was ｍａｘ The electrical conductivity was 500 W / m·K. Except for this, a secondary battery B2 according to Comparative Example 2 was completed in the same manner as in Example 1, and was evaluated in the same manner.

[0079] In the preparation of an electrode assembly, a thermally conductive member made of a graphite sheet was placed on one side of the negative electrode facing outward from the electrode assembly, in a region located 15 turns from the end of the winding of the negative electrode (corresponding to one turn outside the innermost circumference of the negative electrode). The thickness of the graphite sheet was 10 μm (the same as in Example 1), and the maximum thermal conductivity σ ｍａｘ The electrical conductivity was 1950 W / m·K. Except for this, a secondary battery B3 according to Comparative Example 3 was completed in the same manner as in Example 1, and was evaluated in the same manner.

[0080] In the preparation of the electrode assembly, a thermally conductive member made of a graphite sheet was placed on one side of the negative electrode facing outward from the electrode assembly, in a region that was the ninth turn from the end of winding the negative electrode. The thickness of the graphite sheet was 10 μm (the same as in Example 1), and the maximum thermal conductivity σ ｍａｘ The electrical conductivity was 1950 W / m·K. Except for this, a secondary battery B4 according to Comparative Example 4 was completed in the same manner as in Example 1, and was evaluated in the same manner.

[0081] The evaluation results are shown in Table 1. In Table 1, the battery temperature Tx after the nail penetration test is shown as a relative value (temperature difference from the battery temperature Tx of Battery B1) with the battery temperature Tx of Battery B1 as the reference. Initial capacity C ０ Regarding the initial capacity C of the battery B1, which is expressed by the following formula: ０ The capacity loss rate is expressed as the capacity loss rate from (B1). Capacity loss rate (%) = (1 - C ０ / C ０ (B1) × 100

[0082]

[0083] From Table 1, the thermal conductive member is arranged on the outermost periphery of the electrode group, and the maximum thermal conductivity of the thermal conductive member is σｍａｘ In the batteries A1 to A3, in which the thermal conductivity was set to 600 W / m K or more, the decrease in capacity due to the placement of the thermal conductive member was minimized, while the temperature rise of the exterior body due to heat generation in the event of an abnormality was suppressed, and damage to the exterior body was suppressed.

[0084] The present disclosure can be used in secondary batteries.

[0085] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0086] REFERENCE SIGNS LIST 10 Secondary battery (nonaqueous electrolyte secondary battery) 11 Sealing body 12 Valve body 13 Metal plate 14 Insulating member 15 Positive electrode 15L Positive electrode lead 15a Positive electrode active material layer 15b Positive electrode current collector 16 Negative electrode 16L Negative electrode lead 16a Negative electrode active material layer 16b Negative electrode current collector 17 Separator 18 Electrode group 19 Heat conductive member 21 Gasket 22 Battery case 22a Groove portion

Claims

1. A battery comprising a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode and the negative electrode are wound with the separator interposed therebetween to form an electrode group having a plurality of turns, and further comprising a battery can containing the electrode group, wherein a heat conductive member is disposed between the inner wall of the battery can and the outermost periphery of the electrode group, and wherein the maximum thermal conductivity of the heat conductive member is σ ｍａｘ A secondary battery having a capacitance of 600 W / m·K or more.

2. The secondary battery according to claim 1, wherein the thickness of the heat conducting member is 10 μm to 80 μm.

3. The secondary battery according to claim 1 or 2, wherein the heat conducting member includes a graphite sheet.

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