JP2013157219A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery in which a performance difference between the winding center side and the outside of a wound electrode body is small.SOLUTION: According to the present invention, the nonaqueous electrolyte secondary battery including the wound electrode body formed by winding a positive electrode and a negative electrode is provided. In the nonaqueous electrolyte secondary battery, a heat dissipation material layer is formed in at least one of the positive electrode and the negative electrode so that a temperature difference in a radial direction of the wound electrode body is reduced. The heat dissipation material layer is formed only in a partial range in a winding direction of at least one of the positive electrode and the negative electrode.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, lithium-ion secondary batteries, nickel-metal hydride batteries, and other secondary batteries have become increasingly important as power sources mounted on vehicles using electricity as power sources, or power supplies mounted on personal computers, mobile terminals, and other electrical products. Yes. In particular, lithium ion secondary batteries and other non-aqueous electrolyte secondary batteries that are lightweight and obtain high energy density are expected to be preferably used as high-output power supplies for vehicles. In a typical configuration of such a nonaqueous electrolyte secondary battery, a wound electrode body in which a positive electrode and a negative electrode are wound is used.

  By the way, in the above-mentioned nonaqueous electrolyte secondary battery, when performing the charging process, for example, when the battery to be charged is a defective battery or when the charging device fails and malfunctions, the battery is more than normal. Current may be supplied to cause an overcharge state, which may cause a malfunction. Therefore, in order to prevent such problems, a battery equipped with a mechanism (current interruption mechanism) that detects an overcharge state based on battery temperature, battery internal pressure, etc., and interrupts the current when an overcharge state is detected is adopted. ing. In a battery provided with such a current interruption mechanism, a technique is known in which a gas generating agent such as cyclohexylbenzene (CHB) or biphenyl (BP) having a lower oxidation potential than the nonaqueous solvent of the electrolyte is contained in the electrolyte. ing. The gas generating agent reacts to generate gas before the electrolyte is decomposed when the battery is overcharged. Utilizing this, the amount of increase and the rate of increase of the internal pressure of the battery when the battery is overcharged is increased, and the current interrupting mechanism is operated accurately, thereby improving the safety of the battery. Patent Document 1 is cited as a document related to this type of prior art.

JP 2006-324235 A

  The present invention relates to an improvement in a non-aqueous electrolyte secondary battery using a wound electrode body, and the object thereof is a non-aqueous electrolyte secondary battery having a small performance difference between the winding center side and the outside of the wound electrode body. Is to provide.

  In order to achieve the above object, the present invention provides a nonaqueous electrolyte secondary battery including a wound electrode body in which a positive electrode and a negative electrode are wound. In this nonaqueous electrolyte secondary battery, a heat dissipation material layer is formed on at least one of the positive electrode and the negative electrode so that a temperature difference in the radial direction of the wound electrode body is reduced. It is formed only in a partial range in the winding direction of at least one of the positive electrode and the negative electrode.

  In a non-aqueous electrolyte secondary battery using a wound electrode body, the winding center side is less likely to dissipate heat as the degree of winding of the wound electrode body increases. Is more likely to deteriorate than the outside of the winding. Therefore, the performance differs between the center side and the outside of the wound electrode body while using the battery. Therefore, as described above, by forming a heat dissipation material layer on at least one of the positive and negative electrodes so that the temperature difference in the radial direction of the wound electrode body is reduced, the winding center side and the outer side of the wound electrode body are formed. To reduce the performance difference. Thereby, for example, reaction unevenness between the winding center side and the outside of the wound electrode body is reduced, and the cycle characteristics are improved. Moreover, according to the above-mentioned structure, since the heat radiating material layer is formed only in a partial range of at least one of the positive and negative electrodes, the heat radiating material layer is obtained while obtaining the advantage of the heat radiating material layer. A decrease in battery characteristics (for example, an increase in battery resistance) can be suppressed. Therefore, according to the present invention, a nonaqueous electrolyte secondary battery having excellent output characteristics and durability is provided. Further, such a configuration is advantageous in practical use without increasing the number of parts.

  In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the heat dissipation material layer is within a range defined on the winding center side from the center of the winding thickness in the radial direction of the winding electrode body. Is formed. Thereby, the performance difference between the winding center side and the outside of the wound electrode body can be further reduced. In addition, since the formation of the heat dissipation material layer is limited to the center side of the wound electrode body, the deterioration of the battery characteristics due to the heat dissipation material layer is suitably suppressed.

  In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the heat dissipation material layer is formed to extend in a direction orthogonal to at least one winding direction of the positive electrode and the negative electrode. As a result, the heat accumulated in the central portion of the wound electrode body is external to the wound electrode body from the direction (typically the width direction) orthogonal to the winding direction (typically the longitudinal direction) of the positive electrode or the negative electrode. Easy to be released.

  In a preferred aspect of the nonaqueous electrolyte secondary battery disclosed herein, the heat dissipation material layer includes at least one of the positive electrode and the negative electrode, and a current collector and an active material layer that constitute the positive electrode and the negative electrode, respectively. Is formed between. By comprising in this way, the fall of the battery characteristic resulting from a heat radiating material layer is suppressed.

  In a preferred aspect of the non-aqueous electrolyte secondary battery disclosed herein, the heat dissipation material layer includes crystalline graphite as a main component as a heat dissipation material. By using crystalline graphite as the heat dissipating material, the heat accumulated in the center of the wound electrode body can be suitably released.

  In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous electrolyte is provided with a current interruption mechanism that operates when the internal pressure of the battery case increases, and constitutes the non-aqueous electrolyte secondary battery. Includes a gas generating agent that generates gas prior to decomposition of the nonaqueous solvent contained in the nonaqueous electrolyte when an overcharged state is reached. By applying the heat dissipation material layer to such a configuration, the following specific advantages can be obtained. That is, in a non-aqueous electrolyte secondary battery including a wound electrode body, heat tends to be accumulated on the winding center side of the wound electrode body, and thus various characteristics on the winding center side are more likely to deteriorate than on the outer side of the winding. For this reason, when the battery is overcharged, the amount of gas generated on the winding center side tends to decrease. Therefore, as described above, the heat dissipation material layer is formed on at least one of the positive and negative electrodes so that the temperature difference in the radial direction of the wound electrode body is reduced. As a result, the deterioration of various characteristics on the winding center side is suppressed, and a sufficient amount of gas is generated also on the winding center side, so that the current interrupting mechanism can be accurately operated when an overcharge state occurs.

  Moreover, according to this invention, a vehicle provided with one of the nonaqueous electrolyte secondary batteries disclosed here is provided. Such a nonaqueous electrolyte secondary battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile equipped with an electric motor such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle.

It is a figure which shows typically the structure of the lithium ion secondary battery which concerns on one Embodiment. It is a figure which shows typically the structure of the winding electrode body of FIG. (A) is a top view which shows the positive electrode sheet of FIG. 2 typically, (b) is sectional drawing of the positive electrode sheet of (a). It is a figure which shows typically the cross section orthogonal to the winding axis | shaft of the winding electrode body of FIG. It is a figure which shows the temperature measurement point of the winding electrode body in an overcharge test, Comprising: (a) is the schematic diagram which looked at the winding electrode body from the direction parallel to a winding axis | shaft, (b) is (a). It is a side view of this wound electrode body. 3A and 3B are views corresponding to FIG. 3, in which FIG. 3A is a top view of the positive electrode sheet of Example 9, and FIG. It is a side view which shows typically the vehicle (automobile) provided with the lithium ion secondary battery which concerns on one Embodiment.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship. Further, matters other than matters specifically mentioned in the present specification and matters necessary for the implementation of the present invention (for example, a configuration and a manufacturing method of an electrode body including a positive electrode and a negative electrode, a configuration and a manufacturing method of a separator and an electrolytic solution) The general shape and the like related to the construction of the battery, such as the shape of the battery (case), can be understood as the design items of those skilled in the art based on the prior art in this field.

  As a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, a lithium ion secondary battery will be described as an example. However, the application target of the present invention is not intended to be limited to such a battery. Absent. For example, the present invention can be applied to a non-aqueous electrolyte secondary battery using a metal ion other than lithium ion (for example, sodium ion) as a charge carrier. In the present specification, “secondary battery” generally refers to a battery that can be repeatedly charged and discharged. In addition to a storage battery such as a lithium ion secondary battery (that is, a chemical battery), a capacitor such as an electric double layer capacitor (that is, a physical battery). Battery). Further, in the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of charges accompanying the lithium ions between the positive and negative electrodes.

  As shown in FIG. 1, in a lithium ion secondary battery 100 according to an embodiment, a wound electrode body 80 is housed in a flat rectangular battery case 50 together with a non-aqueous electrolyte (not shown). It has a configuration. The wound electrode body 80 is sealed by closing the opening of the case body 52 with the lid body 54. With this configuration, the lithium ion secondary battery 100 is constructed as a so-called sealed battery having a structure in which the inside of the battery case 50 is sealed.

  The battery case 50 includes a flat box-shaped case main body 52 having an opening on the upper surface, and a lid 54 that closes the opening. A positive electrode terminal 70 and a negative electrode terminal 72 are provided on the upper surface (lid 54) of the battery case 50. The positive electrode terminal 70 is electrically connected to a positive electrode current collector plate 74 attached to an end in the width direction of the positive electrode (positive electrode sheet) 10. The negative electrode terminal 72 is electrically connected to a negative electrode current collector plate 76 attached to the end of the negative electrode (negative electrode sheet) 20 in the width direction.

  Inside the battery case 50, a current interrupting mechanism 30 that operates when the internal pressure of the battery case 50 increases is provided. The current interruption mechanism 30 is provided between the positive electrode terminal 70 fixed to the lid 54 and the wound electrode body 80, and electrically connects a conductive path from the positive electrode terminal 70 to the positive electrode 10 when the internal pressure of the battery case 50 rises. It is constituted so that it may be divided.

  The current interrupt mechanism 30 can include, for example, a first member 32 and a second member 34. When the internal pressure of the battery case 50 increases, at least one of the first member 32 and the second member 34 is deformed and separated from the other, so that the conductive path is electrically separated. In this embodiment, the first member 32 is a deformed metal plate, and the second member 34 is a connection metal plate joined to the deformed metal plate 32. The deformed metal plate (first member) 32 has an arch-shaped curved portion 33 having a central portion curved downward. The peripheral portion of the curved portion 33 is connected to the lower surface of the positive electrode terminal 70 via the current collecting lead terminal 35. Further, a part (tip) of the curved portion 33 of the deformed metal plate 32 is joined to the upper surface of the connection metal plate (second member) 34 at a joint point 36. A positive electrode current collector plate 74 is joined to the lower surface (back surface) of the connection metal plate 34, and the positive electrode current collector plate 74 is connected to the positive electrode 10 of the wound electrode body 80. In this way, a conductive path from the positive electrode terminal 70 to the positive electrode 10 is formed.

  The current interruption mechanism 30 includes an insulating case 38 made of plastic. The material of the insulating case is not limited to plastic, and any material having insulating properties and airtightness may be used. The insulating case 38 is provided so as to surround the deformed metal plate 32, and hermetically seals the upper surface of the deformed metal plate 32. An opening for fitting the curved portion 33 of the deformed metal plate 32 is formed in the insulating case 38, and the curved portion 33 of the deformed metal plate 32 is fitted into the opening to seal the opening. doing. As a result, since the inside of the insulating case 38 is kept in a sealed state, the internal pressure of the battery case 50 does not act on the upper surface side of the sealed curved portion 33. On the other hand, the internal pressure of the battery case 50 acts on the lower surface of the curved portion 33 exposed outside the insulating case 38, that is, inside the battery case 50. In the current interruption mechanism 30 having such a configuration, when the internal pressure of the battery case 50 is increased due to the overcharge current, the internal pressure acts to push up the curved portion 33 curved downward of the deformed metal plate 32. This action (force) increases as the internal pressure of the battery case 50 increases. When the internal pressure of the battery case 50 exceeds the set pressure, the curved portion 33 is turned upside down and deformed so as to bend upward. Due to the deformation of the curved portion 33, the joint point 36 between the deformed metal plate 32 and the connection metal plate 34 is cut. As a result, the conductive path is electrically disconnected and the current is interrupted.

  The current interruption mechanism as described above may be provided not only on the positive electrode terminal side but also on the negative electrode terminal side. In addition, the current interrupt mechanism is a conductive path (for example, a charging path) that conducts between at least one of the positive and negative electrodes and an external terminal (positive terminal or negative terminal) exposed to the outside of the battery case when the internal pressure of the battery case increases. As long as it is configured to be electrically divided, the shape and structure are not limited. Furthermore, the current interruption mechanism is not limited to the one that performs mechanical cutting accompanied by the deformation of the first member described above. For example, it may be a current interruption mechanism provided with an external circuit that detects the internal pressure of the battery case with a sensor and interrupts the charging current when the internal pressure detected by the sensor exceeds a set pressure. Note that there is no need for a current interruption mechanism.

  FIG. 2 is a diagram schematically showing the configuration of the wound electrode body of FIG. 1, and shows a long sheet structure (electrode sheet) in the previous stage of constructing the wound electrode body 80. As shown in FIG. 2, the wound electrode body 80 includes a positive electrode 10 and a negative electrode 20. The positive electrode 10 and the negative electrode 20 have a configuration in which they are wound flatly via separators 40A and 40B. Specifically, the positive electrode 10, the negative electrode 20, and the separators 40A and 40B each have a long sheet shape. The positive electrode (positive electrode sheet) 10 and the negative electrode (negative electrode sheet) 20 are two separators. Overlaid via 40A and 40B. Thereby, a laminated body is formed. In other words, the laminate is laminated in the order of the positive electrode sheet 10, the separator 40B, the negative electrode sheet 20, and the separator 40A. The wound electrode body 80 is formed by winding the laminated body in the longitudinal direction, and further crushing the rolled body from the side surface direction. The shape and configuration of the wound electrode body are not particularly limited, and an appropriate shape and configuration can be appropriately employed depending on the shape and purpose of the battery.

  As shown in FIG. 3, the positive electrode sheet 10 includes a positive electrode current collector 12 and a positive electrode mixture layer 14 formed on at least one surface of the positive electrode current collector 12. The positive electrode mixture layer 14 is provided over the entire length direction (winding direction) of the long positive electrode current collector 12, but is formed at one end in the width direction of the positive electrode current collector 12. Absent. That is, at one end in the width direction of the positive electrode sheet 10, a positive electrode mixture layer non-formed portion 15 in which the positive electrode mixture layer 14 is not formed on any surface is provided. The positive electrode current collector plate 74 is electrically connected to the positive electrode mixture layer non-formed portion 15.

  In the positive electrode sheet 10, a heat dissipation material layer 16 is formed between the positive electrode current collector 12 and the positive electrode mixture layer 14. In other words, the positive electrode sheet 10 includes a positive electrode current collector 12 and a heat dissipation material layer 16 formed on a part of the positive electrode current collector 12, and further, a positive electrode mixture layer 14 formed thereon. With. The heat radiation material layer 16 is formed only in a partial range on the winding center side in the winding direction (longitudinal direction) of the positive electrode sheet 10. Specifically, the heat radiating material layer 16 is formed in a partial range extending outward in the winding direction from the end of the positive electrode sheet 10 on the winding center side in the winding direction. In this embodiment, the heat dissipation material layer 16 is formed within a range defined on the winding center side from the center of the winding thickness in the radial direction of the wound electrode body 80. Further, the heat dissipation material layer 16 is formed over the entire width direction of the positive electrode sheet 10. Therefore, the heat dissipation material layer 16 protrudes from the positive electrode mixture layer 14 and is exposed at the portion 15 where the positive electrode mixture layer is not formed. Thereby, the heat dissipation by the heat radiating material layer 16 is further improved.

  The formation range of the heat dissipation material layer is not limited to the formation range of this embodiment. Moreover, the heat radiating material layer may be formed not on the positive electrode sheet but on the negative electrode sheet, and may be formed on both the positive electrode sheet and the negative electrode sheet. In a lithium ion secondary battery having a current interruption mechanism, the gas generating agent decomposes in the vicinity of the positive electrode when overcharged, so that the heat dissipation material layer is formed on the positive electrode in order to suitably perform such decomposition. Preferably it is. Further, in FIG. 3, the heat dissipation material layer 16 and the positive electrode mixture layer 14 are formed on both surfaces of the positive electrode current collector 12, but the heat dissipation material layer and the positive electrode mixture layer are one of the positive electrode current collectors. It may be formed on the surface (one side).

  The negative electrode sheet 20 includes a long negative electrode current collector 22 and a negative electrode mixture layer 24 formed on at least one surface (typically both surfaces) of the negative electrode current collector 22 along the longitudinal direction. . Moreover, the negative electrode mixture layer non-formation part 25 in which the negative electrode mixture layer 24 is not formed on any surface is provided at one end in the width direction of the negative electrode sheet 20. The negative electrode current collector plate 76 is electrically connected to the negative electrode mixture layer non-formed portion 25.

  Next, each component which comprises the above-mentioned lithium ion secondary battery is demonstrated. As a positive electrode current collector constituting a positive electrode (typically a positive electrode sheet) of a lithium ion secondary battery, a conductive member made of a metal having good conductivity is preferably used. For example, aluminum or an alloy containing aluminum as a main component can be used. The shape of the positive electrode current collector may be a plate shape, a sheet shape, a foil shape, a mesh shape, or the like in consideration of the winding property of the positive electrode. The thickness of the positive electrode current collector is not particularly limited, and can be, for example, 5 μm to 30 μm. In addition to the positive electrode active material, the positive electrode mixture layer can contain additives such as a conductive material and a binder (binder) as necessary.

Examples of the positive electrode active material include a composite oxide containing lithium and at least one transition metal element (preferably at least one of nickel, cobalt, and manganese). Examples of the composite oxide include a so-called binary lithium-containing composite oxide containing one kind of the transition metal element, a so-called binary lithium-containing composite oxide containing two kinds of the transition metal element, nickel as the transition metal element, Examples thereof include ternary lithium-containing composite oxides containing cobalt and manganese as constituent elements, and solid solution lithium-excess transition metal oxides. These can be used alone or in combination of two or more. Examples of the unitary lithium-containing composite oxide include cobalt lithium composite oxide (LiCoO ₂ ), nickel lithium composite oxide (LiNiO ₂ ), and manganese lithium composite oxide (LiMn ₂ O ₄ ). Examples of the binary lithium-containing composite oxide include nickel-cobalt-based LiNi _x Co _1-x O ₂ (0 <x <1) and cobalt-manganese-based LiCo _x Mn _1-x O ₂ (0 < x <1), nickel-manganese-based LiNi _x Mn _1-x O ₂ (0 <x <1) and LiNi _x Mn _2-x O ₄ (0 <x <2) A composite oxide is mentioned. Examples of the ternary lithium-containing composite oxide include a general formula:
_{Li (Li a Mn x Co y} Ni z) O 2
Ternary lithium-containing composite oxides represented by (a, x, y, z in the above formula are real numbers satisfying a + x + y + z = 1). Examples of the solid solution type lithium-excess transition metal oxide include a general formula:
xLi [Li _1/3 Mn _2/3 ] O _2. (1-x) LiMeO ₂
(Wherein, Me is one or more transition metals, and x is 0 <x ≦ 1), a solid solution lithium-excess transition metal oxide. Of these, a ternary lithium-containing composite oxide containing nickel, cobalt and manganese as transition metal elements is preferred.

As the positive electrode active material, the general formula is LiMAO ₄ (where M is at least one metal element selected from the group consisting of Fe, Co, Ni and Mn, and A is P, Si, S and A polyanionic compound represented by the following formula is also preferably used: an element selected from the group consisting of V. In the above general formula, A is P and / or Si (for example, LiFePO ₄ , LiFeSiO ₄ , LiCoPO ₄ , LiCoSiO ₄ , LiFe _0.5 Co _0.5 PO ₄ , LiFe _0.5 Co _0.5 SiO ₄ , _{LiMnPO 4, LiMnSiO 4, LiNiPO 4} , LiNiSiO 4) are suitable examples of the polyanionic compound.

  The positive electrode active material includes aluminum (Al), magnesium (Mg), calcium (Ca), chromium (Cr), vanadium (V), titanium (Ti), copper (Cu), zinc (Zn), gallium (Ga). ), Zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), tin (Sn), lanthanum (La), tungsten (W), and cerium (Ce). Alternatively, two or more metal elements may be further added.

  The proportion of the positive electrode active material in the positive electrode mixture layer is preferably more than about 50% by mass, and preferably about 70% by mass to 95% by mass (for example, 75% by mass to 93% by mass).

  As the conductive material, a conductive powder material such as carbon powder or carbon fiber is preferably used. As the carbon powder, various carbon blacks such as acetylene black, furnace black, ketjen black, and graphite powder are preferable. In addition, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives may be included singly or as a mixture of two or more. it can. Examples of the binder include various polymer materials. For example, when a positive electrode mixture layer is formed using an aqueous composition (a composition using water or a mixed solvent containing water as a main component as a dispersion medium for active material particles), water is used as a binder. A polymer material that dissolves or disperses (water-soluble or water-dispersible) can be preferably employed. Examples of water-soluble or water-dispersible polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC); polyvinyl alcohol (PVA); fluorine resins such as polytetrafluoroethylene (PTFE); vinyl acetate polymers; styrene butadiene rubber Rubbers such as (SBR) and acrylic acid-modified SBR resin (SBR latex); Alternatively, when the positive electrode mixture layer is formed using a solvent-based composition (a composition in which the dispersion medium of active material particles is mainly an organic solvent), polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC) Polymer materials such as vinyl halide resins such as polyethylene oxide, polyalkylene oxide such as polyethylene oxide (PEO), and the like can be used. Such a binder may be used alone or in combination of two or more. In addition, the polymer material illustrated above may be used as a thickener and other additives in the composition for forming a positive electrode mixture layer, in addition to being used as a binder.

  Although the ratio of these additives in the positive electrode mixture layer is not particularly limited, the ratio of the conductive material is about 1 to 20 parts by mass (for example, 2 to 15 parts by mass with respect to 100 parts by mass of the positive electrode active material). Part, typically 3 parts by mass to 12 parts by mass), and the ratio of the binder is about 0.8 parts by mass to 10 parts by mass (eg, 1 part by mass with respect to 100 parts by mass of the positive electrode active material). It is preferable to set it as a mass part-7 mass parts, typically 2 mass parts-5 mass parts.

The basis weight per unit area of the positive electrode mixture layer on the positive electrode current collector (the coating amount in terms of solid content of the composition for forming the positive electrode mixture layer) is not particularly limited, but sufficient conductivity From the viewpoint of securing a path (conductive path), it is 3 mg / cm ² or more (for example, 6 mg / cm ² or more, typically 12 mg / cm ² or more) per side of the positive electrode current collector, and 45 mg / cm ² or less ( For example, it is preferably 28 mg / cm ² or less, typically 18 mg / cm ² or less. Further, the thickness of the positive electrode mixture layer is 30 μm or more (for example, 50 μm or more, typically 70 μm or more) per side of the positive electrode current collector, and is 120 μm or less (for example, 100 μm or less, typically 80 μm or less). It is preferable to do.

  A heat radiating material layer is formed on at least one of the positive electrode and the negative electrode. Here, the heat dissipation material layer formed on the positive electrode will be described. The heat dissipating material layer is formed so as to reduce the temperature difference in the radial direction of the wound electrode body, and only needs to be formed in a partial range in the wound direction, and as long as it is formed, the formation location is not limited. . Moreover, it is preferable that the heat radiating material layer is formed between the positive electrode current collector and the positive electrode mixture layer from the viewpoint of suppressing deterioration of battery characteristics due to the heat radiating material layer. Furthermore, the heat dissipation material layer is preferably formed so as to extend in a direction (width direction) orthogonal to the winding direction (longitudinal direction) of the positive electrode. This makes it easy to release the heat accumulated in the center of the wound electrode body from the width direction to the outside of the wound electrode body. From such a viewpoint, it is more preferable that the heat dissipation material layer is formed over the entire width direction of the positive electrode.

  Moreover, it is preferable that the heat radiating material layer is formed so as to extend outward in the winding direction from the end portion of the positive electrode in the winding direction. The heat radiating material layer is a ratio (A2 / A1) of the range (radial thickness) A2 in which the heat radiating material layer 16 occupies the winding thickness A1 in the radial direction of the wound electrode body 80 schematically shown in FIG. ) Is preferably 5% or more (for example, 10% or more, typically 20% or more). Thereby, the performance difference between the winding center side and the outside of the wound electrode body can be further reduced. Specifically, since the heat at the winding center of the wound electrode body is suitably released, the progress of deterioration on the winding center side is suppressed, and as a result, the winding center side and outer side of the wound electrode body are suppressed. Reaction unevenness is reduced and cycle characteristics are improved. Further, from the viewpoint of suppressing a decrease in battery characteristics (for example, an increase in battery resistance) caused by the heat dissipation material layer, the ratio (A2 / A1) is 70% or less (for example, 60% or less, typically 50% or less). ) Is preferable.

  The heat dissipating material layer includes a heat dissipating material as a main component, and optionally includes additives such as a binder. The heat dissipating material constituting the heat dissipating material layer is a heat dissipating material having a thermal conductivity of 500 W / (m · K) or more (eg 700 W / (m · K) or more, typically 900 W / (m · K) or more). A material is preferred. Although the upper limit of heat conductivity is not specifically limited, For example, 2000 W / (m * K) or less may be sufficient. The thermal conductivity may be the thermal conductivity in at least one direction of the heat dissipation material when the heat dissipation material has a major axis and a minor axis. When the heat dissipation material has a flat plate shape, it is more preferable that the range of the thermal conductivity is applied as a range of the surface direction thermal conductivity. Here, the surface direction thermal conductivity means the thermal conductivity in the surface direction of the flat plate-shaped heat radiation material. By disposing the heat dissipation material having the above-described surface direction thermal conductivity along the surface direction of the heat dissipation material layer (direction perpendicular to the thickness direction), the surface direction thermal conductivity of the heat dissipation material layer is improved, Heat dissipation is improved. The thermal conductivity including the surface direction thermal conductivity can be measured by a conventionally known laser flash method. As a laser flash measuring device, a thermal constant measuring device TC-7000 type manufactured by Vacuum Riko can be used.

  Crystalline graphite is mentioned as a heat radiating material having the above thermal conductivity (typically, the planar thermal conductivity). For example, when copper or aluminum is used as the heat radiating material, the thermal conductivity is as low as about 400 W / (m · K) and 230 W / (m · K) regardless of the surface direction and the thickness direction. Therefore, crystalline graphite having a high thermal conductivity (typically, the surface direction thermal conductivity) can be an excellent heat dissipation material from the viewpoint of heat dissipation at the winding center of the wound electrode body. Of these, crystalline graphite particles having crystal growth in the plane direction are particularly preferable. The average particle diameter of such crystalline graphite particles is 0.5 μm to 20 μm (for example, 1 μm to 15 μm, typically 3 μm to 8 μm) as the major axis (typically the length in the plane direction (diameter)), and the minor axis ( It is preferable that the length (diameter) in the thickness direction is typically 3 nm to 300 nm (for example, 20 nm to 180 nm, typically 40 nm to 100 nm). The average particle diameter is measured by arbitrarily selecting 100 crystalline graphite particles photographed with a scanning electron microscope (SEM), measuring the major axis and the minor axis, and calculating the average value for each. The method can be used. The ratio of the heat radiating material in the heat radiating material layer is preferably more than about 50% by mass and 75% to 99% by mass (for example, 90% to 95% by mass).

  As a binder, as a polymer material dissolved or dispersed in water (water-soluble or water-dispersible), a cellulose polymer such as carboxymethyl cellulose (CMC); polyvinyl alcohol (PVA); polytetrafluoroethylene (PTFE), etc. And fluorinated resins; vinyl acetate copolymers; rubbers such as styrene butadiene rubber (SBR) and acrylic acid-modified SBR resin (SBR latex). When forming a heat dissipation material layer using a solvent-based composition (a composition in which the dispersion medium of active material particles is mainly an organic solvent), halogen such as polyvinylidene fluoride (PVDF) and polyvinylidene chloride (PVDC) Polymer materials such as vinyl fluoride resin; polyalkylene oxide such as polyethylene oxide (PEO); and the like can be used. Such a binder may be used alone or in combination of two or more. When forming a heat-radiating material layer using a solvent, polyvinylidene fluoride (PVDF) is preferable.

  The ratio of these additives (typically binders) in the heat dissipation material layer is not particularly limited, but is approximately 1 part by mass to 30 parts by mass (for example, 2 parts by mass to 20 parts by mass) with respect to 100 parts by mass of the heat dissipation material. It is preferable to set it as a mass part, typically 5-15 mass parts.

  The thickness of the heat dissipation material layer reduces the performance difference between the winding center side and the outer side of the wound electrode body, and suppresses the deterioration of battery characteristics due to the heat dissipation material layer. It is 0.5 μm or more (for example, 0.8 μm or more, typically 1.5 μm or more), and preferably 15 μm or less (for example, 9 μm or less, typically 5 μm or less). In addition, when using a heat dissipation material having a predetermined surface direction thermal conductivity, the thickness of the heat dissipation material layer is set to reflect the surface direction thermal conductivity of the heat dissipation material in the surface direction thermal conductivity of the heat dissipation material layer. It is more preferable to make it smaller than the length in the surface direction.

  The positive electrode as described above can be produced, for example, by the following method. First, a heat radiating material and, if necessary, an additive such as a binder are mixed in an appropriate solvent to prepare a paste or slurry-like heat radiating material layer forming composition. The mixing operation can be performed using, for example, a suitable kneader. As a solvent used for preparing the composition, both an aqueous solvent and a non-aqueous solvent can be used. The aqueous solvent is not particularly limited as long as it is water-based as a whole, and water or a mixed solvent mainly composed of water can be preferably used. Further, preferred examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, toluene and the like. The prepared composition is applied to a predetermined range on the positive electrode current collector, and the solvent is evaporated by drying. The method for applying the composition to the positive electrode current collector is not particularly limited, and conventionally known application means such as a slit coater, a die coater, a gravure coater, and a comma coater can be employed. As a drying method, natural drying, hot air, low-humidity air, vacuum, infrared rays, far-infrared rays, and electron beams can be used alone or in combination. Moreover, you may compress (press) by compression methods, such as a conventionally well-known roll press method and a flat plate press method, as needed. In this way, a heat dissipation material layer is formed on the positive electrode current collector.

  Next, a positive electrode active material, and if necessary, a conductive material, a binder, and the like are mixed with an appropriate solvent to prepare a paste or slurry-like composition for forming a positive electrode mixture layer. The prepared composition is applied to the positive electrode current collector, the solvent is evaporated by drying, and then compressed (pressed). Further, when adjusting the thickness, the thickness may be measured with a film thickness measuring instrument, and the press pressure may be adjusted to perform compression a plurality of times until a desired thickness is obtained. In this way, a positive electrode is obtained in which the positive electrode mixture layer is formed on the positive electrode current collector and the heat dissipation material layer is formed in a predetermined range between the positive electrode current collector and the positive electrode mixture layer. . As the mixing, coating, drying, and compression methods, conventionally known means can be used as appropriate, and for example, the same means as the above-described method for forming the heat dissipation material layer can be adopted.

  As the negative electrode current collector constituting the negative electrode (typically, the negative electrode sheet), a conductive member made of a metal having good conductivity is preferably used as in the conventional lithium ion secondary battery. For example, copper or an alloy containing copper as a main component can be used. The shape of the negative electrode current collector can be a plate shape, a sheet shape, a foil shape, a mesh shape, or the like in consideration of the winding property of the negative electrode. The thickness of the negative electrode current collector is not particularly limited, and can be, for example, 5 μm to 30 μm.

  The negative electrode mixture layer includes a negative electrode active material capable of inserting and extracting lithium ions serving as charge carriers. There is no restriction | limiting in particular in a composition and a shape of a negative electrode active material, The 1 type (s) or 2 or more types of the material conventionally used for a lithium ion secondary battery can be used. Examples of such a negative electrode active material include carbon materials generally used in lithium ion secondary batteries. Typical examples of such a carbon material include graphite carbon (graphite) and amorphous carbon. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least partially is preferably used. Of these, the use of a carbon material mainly composed of natural graphite is preferred. Such natural graphite may be obtained by spheroidizing flaky graphite. Alternatively, a carbonaceous powder having a graphite surface coated with amorphous carbon may be used. In addition, as the negative electrode active material, it is also possible to use oxides such as lithium titanate, simple substances such as silicon materials and tin materials, alloys, compounds, and composite materials using the above materials in combination. The proportion of the negative electrode active material in the negative electrode mixture layer exceeds approximately 50% by mass, and is approximately 90% to 99% by mass (for example, 95% to 99% by mass, typically 97% to 99% by mass). It is preferable that

  In addition to the negative electrode active material, the negative electrode mixture layer needs one or more binders, thickeners, and other additives that can be blended in the negative electrode mixture layer of a general lithium ion secondary battery. Depending on the content. Examples of the binder include various polymer materials. For example, what can be contained in the positive electrode mixture layer can be preferably used for an aqueous composition or a solvent-based composition. In addition to being used as a binder, such a binder may be used as a thickener or other additive in a composition for forming a negative electrode mixture layer. The proportion of these additives in the negative electrode mixture layer is not particularly limited, but is approximately 0.8% by mass to 10% by mass (for example, approximately 1% by mass to 5% by mass, typically 1% by mass to 3% by mass). ) Is preferable.

The basis weight per unit area of the negative electrode composite material layer on the negative electrode current collector (the coating amount in terms of solid content of the negative electrode composite material layer forming composition) is not particularly limited, but sufficient conductivity From the viewpoint of securing a path (conductive path), it is 3 mg / cm ² or more (for example, 6 mg / cm ² or more, typically 10 mg / cm ² or more) per side of the negative electrode current collector, and 40 mg / cm ² or less ( For example, it is preferably 25 mg / cm ² or less, typically 18 mg / cm ² or less. Further, the thickness of the negative electrode mixture layer is 20 μm or more (for example, 40 μm or more, typically 60 μm or more) per side of the negative electrode current collector, and is 100 μm or less (for example, 80 μm or less, typically 70 μm or less). It is preferable to do.

  The method for producing the negative electrode as described above is not particularly limited, and a conventionally known method can be appropriately employed. For example, it can be produced by the following method. First, a negative electrode active material is mixed with a binder or the like in the appropriate solvent (aqueous solvent, organic solvent or a mixed solvent thereof) to prepare a paste or slurry-like composition for forming a negative electrode mixture layer. . The composition prepared in this manner is applied to the negative electrode current collector, the solvent is volatilized by drying, and then compressed (pressed). Thus, a negative electrode provided with a negative electrode mixture layer formed using the above composition on the negative electrode current collector is obtained. In addition, conventionally well-known means can be used for the mixing, application | coating, drying, and compression method similarly to the manufacturing method of the above-mentioned positive electrode.

  Note that a heat dissipation material layer may be formed on the negative electrode. In this case, the formation range of the heat dissipation material layer can be basically the same range as the case where the heat dissipation material layer is formed on the positive electrode. That is, in the description regarding the heat dissipation material layer of the positive electrode, the heat dissipation material layer can be formed on the negative electrode by replacing the positive electrode current collector with the negative electrode current collector and replacing the positive electrode material mixture layer with the negative electrode material mixture layer. . Such a heat dissipation material layer can achieve the same effect as the heat dissipation material layer formed on the positive electrode. Since the constituent components, the ratio, the formation method, and the like of the heat dissipation material layer can be the same as those of the heat dissipation material layer formed on the positive electrode, description thereof will not be repeated here.

  The separator (separator sheet) disposed so as to separate the positive electrode and the negative electrode may be a member that insulates the positive electrode mixture layer and the negative electrode mixture layer and allows the electrolyte to move. Preferable examples of the separator include those made of a porous polyolefin resin. For example, a porous separator sheet made of a synthetic resin having a thickness of about 5 μm to 30 μm (for example, made of polyethylene, polypropylene, or a polyolefin having a structure of two or more layers combining these) can be suitably used. This separator sheet may be provided with a heat-resistant layer. Alternatively, for example, the heat-resistant layer may be composed of a layer of insulating particles formed on the surface of the positive electrode mixture layer or the negative electrode mixture layer. Here, the particles having insulating properties are inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene). Also good. For example, when a solid (gel) electrolyte in which a polymer is added to the above electrolyte is used instead of the liquid electrolyte, the electrolyte itself can function as a separator, so that a separator is not necessary. There can be.

  As the non-aqueous solvent and the supporting salt constituting the non-aqueous electrolyte injected into the lithium ion secondary battery, those conventionally used for lithium ion secondary batteries can be used without particular limitation. Such a non-aqueous electrolyte is typically an electrolytic solution having a composition in which a supporting salt is contained in a suitable non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2- Diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol dimethyl ether, ethylene glycol dimethyl ether, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, γ-butyrolactone These may be used alone or in combination of two or more. Of these, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) is preferable.

Examples of the supporting salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. One or more of lithium compounds (lithium salts) such as LiI can be used. The concentration of the supporting salt is not particularly limited, but is approximately 0.1 mol / L to 5 mol / L (for example, 0.5 mol / L to 3 mol / L, typically 0.8 mol / L to 1.5 mol / L). Concentration.

The non-aqueous electrolyte can also include a gas generant. Here, the gas generating agent is a compound that can be dissolved or dispersed in the non-aqueous electrolyte, and reacts when the battery is overcharged, prior to the decomposition of the non-aqueous solvent contained in the non-aqueous electrolyte. A compound that generates gas. Such a gas generating agent is not oxidized at the operating voltage of the battery, but reacts (oxidizes) prior to oxidative decomposition of the nonaqueous solvent of the nonaqueous electrolyte when the battery is overcharged. Therefore, the oxidation potential (oxidation start potential) of the gas generating agent is higher than the upper limit potential of the positive electrode corresponding to the maximum operating voltage. Moreover, it is lower than the oxidation potential (oxidation start potential) of the nonaqueous solvent of the nonaqueous electrolyte. From the above viewpoint, the oxidation potential (vsLi / Li ⁺ ) of the gas generating agent is 0.1 V or higher (for example, 0.2 V or higher, typically 0.3 V or higher) from the upper limit potential (vsLi / Li ⁺ ) of the positive electrode. High is preferred. Moreover, it is preferable that it is 0.1 V or more (for example, 0.2 V or more, typically 0.3 V or more) lower than the oxidation potential (vsLi / Li ⁺ ) of the nonaqueous solvent. For example, in the case of a secondary battery in which the upper limit potential of the positive electrode is 4.2 V or less (typically 4.0 V to 4.2 V), the preferable range of the oxidation potential of the gas generating agent is 4.3 V or more (for example, 4 0.4V or more, typically 4.5V or more) and 5.0V or less (for example, 4.9V or less, typically 4.8V or less).

  The gas generating agent is preferably a compound having a benzene ring and a tertiary carbon bonded to at least one of carbons constituting the benzene ring. Since such tertiary carbon has high activity, the gas generating agent having the tertiary carbon is likely to react in an overcharged state. The number of tertiary carbons bonded to the carbon constituting the benzene ring is preferably 1 to 3 (eg 1 to 2, typically 1). The group having a tertiary carbon is preferably a phenyl group, a cycloalkyl group having 3 to 6 carbon atoms (carbon atoms), or a branched alkyl group having 3 to 6 carbon atoms. The molecular weight of the gas generating agent is not particularly limited, but is preferably 100 to 400 (for example, 120 to 250, typically 150 to 200) from the viewpoint of solubility (dispersibility) in the nonaqueous electrolyte.

  Preferable examples of the gas generating agent include branched alkylbenzenes, cycloalkylbenzenes, biphenyls, terphenyls, diphenyl ethers, and dibenzofurans. These can be used alone or in combination of two or more. Of these, branched alkylbenzenes, cycloalkylbenzenes, biphenyls, and diphenyl ethers are preferable, and cycloalkylbenzenes and biphenyls are more preferable.

  Examples of the branched alkylbenzenes include branched alkylbenzenes having a branched alkyl group having 3 to 6 carbon atoms, and halides (typically fluorides) of branched alkylbenzenes. Specific examples of branched alkylbenzenes include branched alkylbenzenes such as cumene, diisopropylbenzene, t-butylbenzene, t-dibutylbenzene, t-amylbenzene, and t-diamilbenzene. Examples of the cycloalkylbenzenes include cycloalkylbenzene having a cycloalkyl group having 3 to 6 carbon atoms, and alkyl having at least one hydrogen atom bonded to a carbon atom constituting the cycloalkylbenzene having a linear or branched chain structure. Examples thereof include alkylated cycloalkylbenzene substituted with a group and / or a halogen atom (typically a fluorine atom), and a halide (typically a fluoride) of cycloalkylbenzene. As for carbon number of a linear or branched alkyl group, 1-6 pieces (for example, 3 pieces or 4 pieces) are preferable. Specific examples of the cycloalkylbenzenes include cycloalkylbenzenes such as cyclopentylbenzene and cyclohexylbenzene (CHB), alkylated cycloalkylbenzenes such as t-butylcyclohexylbenzene, and partial fluorides of cycloalkylbenzenes such as cyclohexylfluorobenzene. Biphenyls include biphenyl (BP) and at least one of hydrogen atoms bonded to carbon atoms constituting BP is a linear or branched alkyl group and / or halogen atom (typically a fluorine atom). And alkylbiphenyl substituted with a halide of biphenyl (typically fluoride). Specific examples of biphenyls include BP, alkyl biphenyls such as propyl biphenyl and t-butyl biphenyl, partial phenyls such as 2-fluorobiphenyl, 2,2′-difluorobiphenyl, and 4,4′-difluorobiphenyl. A compound. Terphenyls, diphenyl ethers, dibenzofurans include terphenyl, diphenyl ether, dibenzofuran, and each of which at least one hydrogen atom bonded to the carbon atom constituting them is substituted with a linear or branched alkyl group Alkylates (alkylated terphenyls, alkylated diphenyl ethers, alkylated dibenzofurans) and / or terphenyl, diphenyl ether, dibenzofuran halides (typically fluorides) substituted with halogen atoms (typically fluorine atoms) Is mentioned. Terphenyl may be a partial hydride of terphenyl in which a hydrogen atom is added to a part thereof. These can be used alone or in combination of two or more.

  The amount (addition amount) of the gas generating agent is about 0.01 to 10% by mass (for example, 0.1 to 5% by mass, typically 1 to 3% by mass) in the non-aqueous electrolyte. ) Is preferable.

  The lithium ion secondary battery having the above-described configuration is used as a battery for various applications. Such a lithium ion secondary battery has a small difference in performance between the winding center side and the outside of the wound electrode body, so that reaction unevenness between the winding center side and the outside of the wound electrode body is reduced and cycle characteristics are improved. doing. In addition, in a battery provided with a current interruption mechanism, a sufficient amount of gas is generated even on the winding center side of the winding electrode body, and the current interruption mechanism operates with high accuracy when the battery is overcharged. Such a lithium ion secondary battery can be suitably used as a power source for a motor (electric motor) mounted on a vehicle such as an automobile. Therefore, as schematically shown in FIG. 7, the present invention provides a vehicle 1 (typically an automobile, in particular,) that includes a lithium ion secondary battery 100 (typically, a battery pack formed by connecting a plurality of batteries in series) as a power source. Vehicles equipped with electric motors such as hybrid vehicles, electric vehicles, and fuel cell vehicles).

  Next, some examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on mass unless otherwise specified.

<Example 1>
[Preparation of positive electrode sheet]
As a heat radiating material, graphite particles (crystalline graphite) having crystal growth in the plane direction were prepared. This crystalline graphite has a plane direction thermal conductivity of 1000 W / (m · K), a thickness direction thermal conductivity of 15 W / (m · K), a plane direction length of 5 μm, and a thickness direction The length was 60 nm. The crystalline graphite and polyvinylidene fluoride (PVDF) are mixed with N-methyl-2-pyrrolidone so that the mass ratio of these materials is 100: 10, and a paste-like composition for forming a heat radiation layer is formed. Was prepared.

Lithium nickel manganese cobaltate (Li [Ni _1/3 Mn _1/3 Co _1/3 ] O ₂ ) powder as the positive electrode active material, acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVDF) as the binder ) Was mixed with N-methyl-2-pyrrolidone so that the mass ratio of these materials was 100: 5: 3 to prepare a paste-like composition for forming a positive electrode mixture layer.

  As shown in FIG. 3, the heat dissipation material layer forming composition is wound on both sides of a long sheet-like aluminum foil (positive electrode current collector: thickness 15 μm) in the winding direction of the positive electrode current collector 12. The coating was uniformly applied to a partial range extending outward in the winding direction from the end on the center side so as to cover the entire width of the positive electrode current collector 12. Thereafter, a heat radiating material layer was formed by drying. The heat radiating material layer is a ratio (A2 / A1) of the range (radial thickness) A2 in which the heat radiating material layer 16 occupies the winding thickness A1 in the radial direction of the wound electrode body 80 schematically shown in FIG. ) Was formed in a partial range in the winding direction of the positive electrode sheet so as to be 10%. The thickness of the heat dissipation material layer was 3 μm per side. Subsequently, the said positive electrode compound-material layer formation composition was apply | coated uniformly on both surfaces of the positive electrode electrical power collector in which the heat radiating material layer was formed. The composition was dried, compressed, and cut to prepare a sheet-like positive electrode (positive electrode sheet) having a length of 4500 mm, a width of 94 mm, and a total thickness of 170 μm.

[Preparation of negative electrode sheet]
Natural graphite powder as a negative electrode active material, styrene-butadiene copolymer (SBR) as a binder, carboxymethyl cellulose (CMC: BSH-6 manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a thickener, A paste-like composition for forming a negative electrode mixture layer was prepared by mixing with ion-exchanged water so that the mass ratio of the materials was 100: 1: 1. This composition is uniformly coated on both sides of a long sheet-like copper foil (thickness: 14 μm), dried, and then compressed to form a sheet-like sheet having a length of 4700 mm, a width of 100 mm, and a total thickness of 150 μm. A negative electrode (negative electrode sheet) was produced.

[Construction of lithium ion secondary battery]
The produced positive electrode sheet and negative electrode sheet were wound into an ellipse shape through a separator to produce a wound electrode body. As the separator, a long sheet-like three-layer structure film (thickness: 20 μm) made of polypropylene / polyethylene / polypropylene was used. At this time, to measure the winding center side and outer temperature of the wound electrode body, two places shown in FIG. 5 (the outer end wound in the winding center P _in a wound electrode body of the wound electrode assembly A K-type thermocouple was installed in the part _Pout ). Next, electrode terminals were joined to the ends of the positive and negative electrode current collectors of the wound electrode body, respectively, and accommodated in an aluminum battery case. Thereafter, a non-aqueous electrolyte was injected and sealed to prepare a square lithium ion secondary battery having a rated capacity of 24.0 Ah. In this square lithium ion secondary battery, a current interruption device (CID: Current Interrupt Device) as shown in FIG. 1 is provided between the positive electrode current collector and the positive electrode terminal. The design cutoff pressure of CID was 0.7 MPa. As the non-aqueous electrolyte, a 3: 4: 3 (volume ratio) mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) was used, and about 1 mol / L LiPF ₆ as a supporting salt. Then, an electrolyte solution containing 1% cyclohexylbenzene (CHB) and 1% biphenyl (BP) was used. The amount of non-aqueous electrolyte injected was 125 g.

<Example 2 to Example 5, Example 7>
A positive electrode sheet was produced in the same manner as in Example 1 except that the heat dissipation material layer was formed in the winding direction of the positive electrode sheet so that the ratio (A2 / A1) was in the range shown in Table 1. A square lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode sheet was used.

<Example 6>
A positive electrode sheet was produced in the same manner as in Example 1 except that the heat radiating material layer was not formed. A square lithium ion secondary battery was produced in the same manner as in Example 1 except that this positive electrode sheet was used.

<Example 8>
In forming the heat dissipation material layer, a positive electrode sheet was prepared in the same manner as in Example 4 except that acetylene black was used instead of crystalline graphite as the heat dissipation material, and the positive electrode sheet was used in the same manner as in Example 4. A square lithium ion secondary battery was produced.

<Example 9>
The composition for forming a heat dissipation material layer prepared in Example 1 was wound on both sides of a long sheet-like aluminum foil (positive electrode current collector: thickness 15 μm) as shown in FIG. It was uniformly applied to a partial range in the vicinity of the center in the width direction of the positive electrode current collector 12 so as to cover the entire direction. Otherwise, a positive electrode sheet was produced in the same manner as in Example 4, and a square lithium ion secondary battery was produced in the same manner as in Example 4 except that this positive electrode sheet was used. The formation area of the heat dissipation material layer in this example was the same as the formation area of the heat dissipation material layer in Example 4.

[Number of CID operation during overcharge]
Ten lithium ion secondary batteries of each example were prepared and charged at 24 A (equivalent to 1 C) in an environment at a temperature of 25 ° C., and charged to a charging upper limit voltage of 20 V. After the completion of charging, whether or not the current interrupting mechanism (CID) was activated for each battery was confirmed by measuring the battery voltage. Table 1 shows the number of activated CIDs.

[Temperature difference between winding center side and outside of wound electrode body]
About the lithium ion secondary battery of each example, 24A (equivalent to 1C) was charged in the environment of temperature 25 degreeC, and it charged to the charge upper limit voltage 20V. The temperature at the winding center side and the outside of the wound electrode body in a state of charge of SOC (State of Charge) 160% was measured by a K-type thermocouple installed on the wound electrode body. The difference [Delta] T between the temperature _{T out} of the temperature _{T in} the wound outer end _{P out} of the wound electrode assembly of the winding center _{P in} the measured wound electrode body, wherein: calculated from [Delta] T ₌ T _{in -T out} It was. The results are shown in Table 1.

[Capacity maintenance rate]
In a temperature environment of 25 ° C., 1 C was charged to 4.1 V and rested for 5 minutes, then 1 C was discharged to 3.0 V and rested for 5 minutes. Then, constant current constant voltage (CC-CV) charge (4.1V, 1C, 0.1C cut) and CC-CV discharge (3.0V, 1C, 0.1C cut) were performed. The discharge capacity at this time was measured and used as the initial capacity. After the initial capacity was measured, 2C CC cycle charge / discharge was repeated 1000 cycles in a thermostat at 50 ° C., and the discharge capacity after 1000 cycles was measured. formula:
Capacity retention rate (%) = discharge capacity after 1000 cycles / initial capacity × 100
From this, the capacity retention rate (%) was obtained. The results are shown in Table 1.

[IV resistance]
An IV resistance test was performed on the lithium ion secondary battery of each example. Charging was performed in an environment at a temperature of 25 ° C. to adjust the SOC to 60%. Thereafter, pulse discharge was performed at 25 ° C. with a current of 10 C for 10 seconds, and IV resistance (mΩ) was obtained from the voltage drop amount 10 seconds after the start of discharge. The results are shown in Table 1.

  As shown in Table 1, the lithium ion secondary batteries of Examples 1 to 5 using crystalline graphite as a heat dissipation material and using a positive electrode sheet in which a heat dissipation material layer is formed in a partial range in the winding direction, Example 6 in which the heat dissipation material layer was not formed, Example 8 in which acetylene black was used as the heat dissipation material, the heat dissipation material layer over the entire winding direction of the positive electrode sheet, and in a partial range near the center in the width direction Compared with the formed Example 9, the temperature difference ΔT between the winding center side and the outside of the wound electrode body was small, and the CID operating rate was high. Particularly in Examples 2 to 4, the CID was surely activated when the battery was overcharged. This is because by forming the heat dissipation material layer in a partial range in the winding direction of the positive electrode sheet, the performance difference between the winding center side and the outside of the winding electrode body is reduced, and as a result, the winding electrode body This is probably because a sufficient amount of gas was generated on the winding center side. Further, by forming a heat dissipating material layer, a balance between reducing the temperature difference ΔT between the winding center side and the outside of the wound electrode body and limiting the formation range of the heat dissipating material layer to a predetermined range. The capacity maintenance rate tended to improve. From this result, it was shown that the heat dissipation material layer is effective in terms of improving the cycle characteristics. On the other hand, in Example 7 in which the heat dissipation material layer was formed on the entire surface of the positive electrode current collector (entire range in the winding direction), although the CID worked reliably, the capacity retention rate decreased and the IV resistance also increased. It was seen. Further, in Example 8 using acetylene black as the heat dissipation material, the temperature difference ΔT between the winding center side and the outside of the wound electrode body was larger than Example 6 in which the heat dissipation material layer was not formed. From this result, it can be seen that the heat dissipation material layer of Example 8 was not intended to reduce the temperature difference in the radial direction of the wound electrode body. A similar trend was seen in Example 9.

  From these results, it is possible to reduce the temperature difference in the radial direction of the wound electrode body, and by forming the heat dissipation material layer only in a partial range in the winding direction of the positive electrode, It can be seen that the performance difference between the outer side and the outer side is reduced, and as a result, the cycle characteristics are improved and excellent durability can be realized. In addition, by forming such a heat dissipation material, a sufficient amount of gas is generated at the winding center side of the wound electrode body in the battery provided with the current breaking mechanism, and the current breaking mechanism is activated when the battery is overcharged. It can be seen that it can be operated accurately. In particular, it can be seen that the heat dissipation material layer formed so that the ratio (A2 / A1) is in the range of 20% to 50% can achieve a more excellent effect.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The invention disclosed herein can include various modifications and alterations of the specific examples described above.

1 Automobile (vehicle)
10 Positive electrode sheet (positive electrode)
DESCRIPTION OF SYMBOLS 12 Positive electrode collector 14 Positive electrode compound material layer 15 Positive electrode compound material layer non-formation part 16 Heat radiation material layer 20 Negative electrode sheet (negative electrode)
22 Negative electrode current collector 24 Negative electrode composite material layer 25 Negative electrode composite material layer non-formed part 30 Current interruption mechanism 32 Deformed metal plate (first member)
33 Curved part 34 Connection metal plate (second member)
35 Current collector lead terminal 36 Junction point 38 Insulating case 40A, 40B Separator 50 Battery case 52 Case body 54 Lid 70 Positive electrode terminal 72 Negative electrode terminal 74 Positive electrode current collector plate 76 Negative electrode current collector plate 80 Winding electrode body 100 Lithium ion secondary Battery P _in T _in temperature measurement point P _out T _out temperature measurement point

Claims (7)

A non-aqueous electrolyte secondary battery comprising a wound electrode body formed by winding a positive electrode and a negative electrode,
A heat dissipation material layer is formed on at least one of the positive electrode and the negative electrode so that a temperature difference in the radial direction of the wound electrode body decreases.
The heat dissipation material layer is a non-aqueous electrolyte secondary battery formed only in a partial range of at least one of the positive electrode and the negative electrode in a winding direction.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat dissipation material layer is formed within a range defined on a winding center side from a center of a winding thickness in a radial direction of the wound electrode body.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat dissipation material layer is formed so as to extend in a direction perpendicular to a winding direction of at least one of the positive electrode and the negative electrode.   4. The heat dissipation material layer according to claim 1, wherein at least one of the positive electrode and the negative electrode is formed between a current collector and an active material layer constituting the positive electrode and the negative electrode, respectively. The nonaqueous electrolyte secondary battery as described.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat dissipation material layer includes crystalline graphite as a heat dissipation material as a main component. It has a current interruption mechanism that operates when the internal pressure of the battery case rises,
The nonaqueous electrolyte constituting the nonaqueous electrolyte secondary battery includes a gas generating agent that generates a gas prior to decomposition of the nonaqueous solvent contained in the nonaqueous electrolyte when overcharged. The nonaqueous electrolyte secondary battery according to any one of 1 to 5.   A vehicle comprising the nonaqueous electrolyte secondary battery according to any one of claims 1 to 6.

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