JP2020057504A - Secondary battery - Google Patents

Abstract

To provide a secondary battery that can exhibit good heat dissipation while using a separator with a shutdown function.SOLUTION: A secondary battery includes a winding electrode body 10 and an electrolyte. In the winding electrode body 10, a positive electrode 11 and a negative electrode 15 are overlapped with each other via a separator 19 having a shutdown function, and are wound around a shaft core 30. The shaft core 30 of the winding electrode body 10 includes a heat absorbing member 40 and a thermal expansion member 50. The heat absorbing member 40 absorbs the heat generated by the secondary battery. The thermal expansion member expands due to the heat generated by the secondary battery. Even when the separator 19 shuts down and contracts, and the thermal expansion member 50 expands, thereby suppressing the formation of a gap between the electrodes.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a secondary battery provided with a wound electrode body.

  When a rechargeable battery such as a lithium ion rechargeable battery is supplied with a predetermined current or more due to an erroneous operation or the like, the rechargeable battery may exceed the voltage in normal use and may be overcharged. As the overcharge progresses, heat generation of the active material (typically, the positive electrode active material), decomposition of the electrolytic solution, and the like become significant. As a result, the temperature inside the battery may rise excessively, causing a problem in the battery itself. As an example of a safety mechanism for stopping the progress of overcharging, a separator having a so-called shutdown function is known. In such a separator, when the temperature inside the battery rises to the shutdown temperature, the constituent material is softened (melted) or thermally contracted (hereinafter sometimes collectively referred to as “shrinkage”), and the micropores are closed. As a result, the movement of the charge carriers between the positive and negative electrodes is blocked, and the charge / discharge reaction stops.

  Further, the secondary battery described in Patent Literature 1 uses a metal material that causes an endothermic reaction in a temperature range equal to or higher than the shutdown temperature of the separator and lower than the thermal decomposition temperature of the positive electrode, on the axis of the wound electrode body. Prepare. In the secondary battery of Patent Literature 1, the temperature rise after the shutdown of the separator is suppressed by the endothermic reaction of the metal material.

JP-A-2006-152071

  As described above, when the temperature of the separator rises to the shutdown temperature, the constituent material of the separator contracts. The inventor of the present application has found a problem that a gap is generated between the electrodes due to the shutdown and contraction of the separator, the heat radiation path inside the electrode body is reduced, and the heat radiation property of the electrode body is reduced. In order to suppress the malfunction of the secondary battery, it is desirable that the heat radiation property after the shutdown of the separator can be suppressed more appropriately.

  A typical object of the present invention is to provide a secondary battery such as a lithium ion secondary battery that can exhibit good heat dissipation while using a separator having a shutdown function.

  In order to achieve such an object, the secondary battery of one embodiment disclosed herein has an electrode body in which a positive electrode and a negative electrode are stacked and wound around an axis through a separator having a shutdown function, and an electrolyte. Wherein the shaft core includes a heat absorbing member that absorbs heat generated by the secondary battery and a thermal expansion member that expands due to heat generated by the secondary battery.

  In the secondary battery having the configuration described above, the temperature increase of the electrode body is suppressed by the heat absorbing member provided on the shaft core. Furthermore, even when the temperature of the electrode body rises and the separator shuts down and contracts, the expansion of the thermal expansion member provided on the shaft core suppresses generation of a gap between the electrodes. As a result, a decrease in the heat radiation path inside the electrode body is suppressed. Therefore, the heat dissipation of the electrode body is favorably exhibited.

FIG. 2 is a longitudinal sectional view schematically showing an internal configuration of the secondary battery 1 of the embodiment. FIG. 2 is a sectional view taken along line AA in FIG. 1. FIG. 3 is an enlarged cross-sectional view of the wound electrode body 10 shown in FIG. 2 in the vicinity of a central portion O in a thickness direction. 6 is a chart showing DSC measurement results of a member used for the heat absorbing member of the embodiment. It is a graph which shows the result of an overcharge test.

  Hereinafter, one of exemplary embodiments of the present disclosure will be described in detail with reference to the drawings. Matters other than those specifically mentioned in the present specification and necessary for the implementation can be understood as design matters of those skilled in the art based on conventional techniques in the field. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the field. In the following drawings, members / parts having the same function are denoted by the same reference numerals. The dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships.

  The secondary battery 1 illustrated in FIG. 1 is a sealed lithium ion secondary battery including a wound electrode body 10, an electrolyte (here, an electrolyte) 29, and a battery case 20. The battery case 20 accommodates the wound electrode body 10 and the electrolyte solution 29 in a sealed state. The shape of the battery case 20 in the present embodiment is a flat box shape, that is, a rectangular parallelepiped shape (so-called square shape). Specifically, the battery case 20 according to the present embodiment includes a box-shaped main body 22 having an opening at one end, and a plate-shaped lid 24 closing the opening of the main body 22. The battery case 20 (specifically, the lid 24) is provided with a positive terminal 26 and a negative terminal 28 for external connection. As a material of the battery case 20, for example, a lightweight metal material having good heat conductivity such as aluminum is used. However, the configuration of the battery case can be changed. For example, a flexible laminate may be used as the battery case. Further, the shape of the battery case may be a shape other than a square shape (for example, a cylindrical shape).

  The structure of the wound electrode body 10 is such that the positive electrode 11 and the negative electrode 15 (see FIG. 3) are overlapped (laminated) via the separator 19 (see FIG. 3) and wound around the shaft core 30. It is. Typically, a long positive electrode sheet and a long negative electrode sheet are overlapped via a long separator sheet, and are wound around the shaft core 30 in the long direction. As shown in FIGS. 1 and 2, the whole wound electrode body 10 of the present embodiment and the shape of the shaft core 30 are flat. In other words, as shown in FIG. 2, the entire wound electrode body 10 and the shape of the shaft core 30 in a cross section orthogonal to the winding axis are substantially rounded rectangular shapes. The shaft core 30 is located near the center O in the thickness direction (the left-right direction in FIG. 2) of the wound electrode body 10. Details of the shaft core 30 will be described later.

The positive electrode 11 typically includes a long positive electrode current collector 12 and a positive electrode active material layer formed on the surface of the positive electrode current collector 12. As the positive electrode current collector 12, a metal material having good conductivity (for example, aluminum, nickel, titanium, stainless steel, or the like) can be employed. The positive electrode active material layer is typically formed on the surface of the positive electrode current collector 12 with a predetermined width (in a strip shape) along the longitudinal direction. One end in the width direction orthogonal to the longitudinal direction of the positive electrode current collector 12 is a positive electrode active material layer non-formed portion 13 where no positive electrode active material layer is formed. A positive electrode current collector 14 is electrically connected to the portion 13 where the positive electrode active material layer is not formed, and a positive electrode terminal 26 is electrically connected to the positive electrode current collector 14. As the positive electrode active material of the positive electrode active material layer, for example, a lithium composite metal oxide having a layered structure or a spinel structure (eg, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNiO ₂ , LiCoO ₂ , LiFeO ₂ , LiMn ₂ O ₄ , LiNi _0.5 Mn _1.5 O ₄ , LiCrMnO ₄ , LiFePO _{4 and the} like. The positive electrode active material layer is formed by dispersing the positive electrode active material and materials (conductive material, binder, and the like) used as needed in an appropriate solvent (for example, N-methyl-2-pyrrolidone: NMP) and forming a paste (or slurry). ), A suitable amount of the composition is applied to the surface of the positive electrode current collector 12, and the composition is dried.
When the secondary battery disclosed herein is a secondary battery other than a lithium ion secondary battery, a positive electrode active material suitable for each battery is used. For example, in the case of a sodium ion secondary battery, a sodium transition metal composite oxide is used, and in the case of a magnesium secondary battery, a magnesium transition metal composite oxide, sulfide, or the like is used.

  The negative electrode 15 typically includes a long negative electrode current collector 16 and a negative electrode active material layer formed on the surface of the negative electrode current collector 16. As the negative electrode current collector 16, a metal material having good conductivity (for example, copper, nickel, or the like) can be used. The negative electrode active material layer is typically formed on the surface of the negative electrode current collector 16 with a wider width (in a strip shape) than the positive electrode active material layer along the longitudinal direction. Of the both ends in the width direction of the negative electrode current collector 16, the end opposite to the side where the positive electrode active material layer non-formed portion 13 is located is a negative electrode active material layer non-formed portion where no negative electrode active material layer is formed. It is 17. A negative electrode current collector 18 is electrically connected to the negative electrode active material layer non-formed portion 17, and a negative electrode terminal 28 is electrically connected to the negative electrode current collector 18. As the negative electrode active material of the negative electrode active material layer, for example, a particulate (or spherical or flaky) carbon material containing a graphite structure (layer structure) at least in part, a lithium transition metal composite oxide, a lithium transition metal composite nitride Objects and the like. The negative electrode active material layer is prepared by dispersing a negative electrode active material and a material (such as a binder) used as necessary in a suitable solvent (for example, ion-exchanged water) to prepare a paste-like (or slurry-like) composition; The composition can be formed by applying an appropriate amount of the composition to the surface of the negative electrode current collector 16 and drying. When the secondary battery disclosed herein is a secondary battery other than a lithium ion secondary battery, a negative electrode active material suitable for each battery is used.

  The separator 19 has a shutdown function of softening (melting) or heat shrinking (hereinafter sometimes collectively referred to as “shrinking”) at a shutdown temperature to close micropores. For example, a porous resin sheet (a film, a nonwoven fabric, or the like) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, or polyimide can be used. Typically, the melting point of the resin constituting the separator 19 is 100 ° C. or higher, for example, 110 ° C. or higher, or 120 ° C. or higher, and 170 ° C. or lower, for example, 150 ° C. or lower, or 140 ° C. or lower. By shutting down the separator 19 before the internal temperature of the wound electrode body 10 excessively rises, the charge / discharge reaction between the positive and negative electrodes is stopped.

The electrolyte solution 29 typically contains a solvent and a supporting salt. As the solvent, for example, a non-aqueous solvent such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be used. As the supporting salt, various lithium salts can be used, and among them, lithium salts such as LiPF ₆ and LiBF ₄ are preferable. When the secondary battery disclosed herein is a secondary battery other than a lithium ion secondary battery, a solvent and a supporting salt suitable for each battery (for example, a sodium salt and a magnesium secondary battery in the case of a sodium ion secondary battery) In the case of a battery, a magnesium salt or the like is used. In addition, as the electrolyte, in addition to the above-described electrolyte solution (liquid electrolyte), a polymer electrolyte obtained by gelling a predetermined polymer with the electrolyte solution, or a solid electrolyte in which the electrolyte is entirely solid may be used.

  With reference to FIG. 3, the configuration near the center O in the thickness direction of the wound electrode body 10 will be described. As described above, in the wound electrode body 10, the positive electrode 11 and the negative electrode 15 are wound around the shaft core 30 in a state of being stacked with the separator 19 interposed therebetween. In the example illustrated in FIG. 3, after four separators 19 are overlapped and wound at a position adjacent to the shaft core 30, the negative electrode 15, the separator 19, the positive electrode 11, and the separator 19 are sequentially arranged outward from the center. It is laminated and wound. However, the configuration of the separator 19 at a position adjacent to the shaft core 30 can be changed.

  The shaft core 30 includes a heat absorbing member 40 and a thermal expansion member 50. The heat absorbing member 40 absorbs heat generated by the secondary battery 1. Therefore, the temperature rise of the wound electrode body 10 is suppressed. The thermal expansion member 50 expands due to the heat generated by the secondary battery 1. Even when the temperature of the wound electrode body 10 rises and the separator 19 shuts down and contracts, the thermal expansion member 50 expands, so that the space between the electrodes (that is, between the positive electrode 11, the negative electrode 15, and the separator 19). The generation of a gap is suppressed. As a result, a decrease in the heat radiation path inside the wound electrode body 10 is suppressed, and the heat radiation is sufficiently exhibited.

  The entire shaft core 30 including the heat absorbing member 40 and the thermal expansion member 50 or the surface of the shaft core 30 is formed of a member having an electrolytic solution resistance and an insulating property (for example, resin or ceramic). Therefore, the shaft core 30 incorporated in the wound electrode body 10 hardly affects the charge / discharge and the battery life. In the present embodiment, the heat absorbing member 40 and the thermal expansion member 50 themselves have an electrolytic solution resistance and an insulating property. Hereinafter, the heat absorbing member 40 and the thermal expansion member 50 in the present embodiment will be described in detail.

  The heat-absorbing member 40 of the present embodiment includes a plurality of heat-absorbing members having different temperature ranges in which an endothermic reaction occurs. Specifically, the heat absorbing member 40 of the present embodiment includes a first heat absorbing member 42 and a second heat absorbing member 44.

  The temperature range in which the first heat absorbing member 42 generates an endothermic reaction includes the shutdown temperature of the separator 19. Therefore, the timing at which the separator 19 shuts down can be delayed by the first heat absorbing member 42 absorbing heat. More specifically, the peak temperature of heat absorption in the first heat absorbing member 42 is lower than the shutdown temperature of the separator 19. Therefore, the shutdown timing is more efficiently delayed than in the case where the peak temperature of heat absorption in the first heat absorbing member is equal to or higher than the shutdown temperature.

  The temperature range in which the second heat absorbing member 44 generates an endothermic reaction includes a temperature range higher than the temperature range in which the first heat absorbing member 42 generates an endothermic reaction. Specifically, the peak temperature of heat absorption in the second heat absorbing member 44 is equal to or higher than the shutdown temperature of the separator 19. Therefore, the second heat absorbing member 44 absorbs heat, so that the temperature rise of the wound electrode body 10 after the shutdown of the separator 19 is appropriately suppressed.

  As shown in FIG. 3, the second heat absorbing member 44 is provided on the shaft core 30 inside the first heat absorbing member 42. In other words, when a plurality of endothermic members having different endothermic reaction temperature ranges are used, the endothermic member having a higher endothermic reaction temperature range is disposed inside the endothermic member having a lower endothermic reaction temperature range. Is desirable. In this case, heat generated outside the shaft core 30 is conducted to a heat absorbing member having a lower temperature range in which an endothermic reaction occurs, and then to a heat absorbing member having a higher temperature range in which an endothermic reaction occurs. Therefore, the endothermic reaction of the plurality of endothermic members is efficiently exhibited according to the gradually increasing temperature. That is, in the present embodiment, after the shutdown timing is delayed by the first heat absorbing member 42, the temperature rise after the shutdown is efficiently suppressed by the second heat absorbing member 44. However, it is also possible to change the arrangement of a plurality of types of heat absorbing members.

  Various materials can be adopted as the material of the heat absorbing member 40. In the present embodiment, a resin material having resistance to electrolyte, insulation, and appropriate heat absorption is used as the heat absorbing member 40. Specifically, in the present embodiment, high-density polyethylene is used for the first heat absorbing member 42. The second heat absorbing member 44 is made of at least one of polypropylene and cellulose. However, the material of the heat absorbing member 40 is not limited to this. For example, a low melting point metal material such as indium may be used as the heat absorbing member. In this case, as described above, at least a portion of the heat absorbing member located on the surface of the shaft core 30 may be covered with a material having an electrolytic solution resistance and an insulating property.

  The chart shown in FIG. 4 shows the measurement results of the members used for the heat absorbing member 40 (the first heat absorbing member 42 and the second heat absorbing member 44) of the present embodiment by DSC (Differential Scanning Calorimetry). In the chart shown in FIG. 4, the horizontal axis represents temperature, and the vertical axis represents heat quantity. In addition, high-density polyethylene and polypropylene are measured without an electrolyte, and cellulose is measured with an electrolyte.

  As shown in FIG. 4, the temperature range in which the high-density polyethylene causes an endothermic reaction includes the shutdown temperature. Further, the peak temperature of endothermic heat of the high-density polyethylene is lower than the shutdown temperature of the separator 19. Therefore, high-density polyethylene is suitable as the material of the first heat absorbing member 42.

  The temperature range in which the polypropylene generates an endothermic reaction includes a temperature range higher than the temperature range in which the first heat absorbing member 42 (high-density polyethylene in the present embodiment) generates an endothermic reaction. The endothermic peak temperature of the polypropylene is equal to or higher than the shutdown temperature of the separator 19 and equal to or lower than the upper limit temperature of the wound electrode body 10. Therefore, polypropylene is suitable as the material of the second heat absorbing member 44.

  The temperature range in which cellulose causes an endothermic reaction includes a temperature range higher than the temperature range in which first endothermic member 42 (high-density polyethylene in the present embodiment) causes an endothermic reaction. In addition, cellulose does not dissolve and disappear at a high temperature, but remains after being carbonized, and thereafter functions as a heat capacity. Therefore, although the endothermic peak amount of cellulose is smaller than the endothermic peak amount of polypropylene, cellulose is also suitable as the material of the second endothermic member 44.

  The thermal expansion member 50 will be described. In the present embodiment, the thermal expansion member 50 itself has an electrolytic solution resistance and an insulating property. Various members can be adopted as the thermal expansion member 50. The thermal expansion member 50 may expand itself, or may contain an expanding filler or the like. For example, thermal expansion microcapsules containing a liquid or a liquid gas, such as Dyform V (registered trademark), Matsumoto microsphere (registered trademark), Kureha microsphere (registered trademark), and Expancel (registered trademark), are used. It may be used as the expansion member 50.

  As shown in FIG. 3, in this embodiment, the thermal expansion member 50 is provided inside the heat absorbing member 40. Therefore, heat generated outside the shaft core 30 is transmitted to the heat absorbing member 40 and then transmitted from the heat absorbing member 40 to the thermal expansion member 50. In this case, after the timing of shutting down the separator 19 is delayed by the heat absorbing member 40 (particularly, the first heat absorbing member 42), the thermal expansion member 50 provided inside the heat absorbing member 40 expands, and the shutdown causes the gap between the electrodes. A gap is suppressed from being generated. Therefore, the influence of heat generation is more efficiently suppressed. However, it is also possible to change the arrangement of the thermal expansion member 50 and the heat absorbing member 40 in the shaft core 30.

  In addition, the manufacturing method of the wound electrode body 10 can be appropriately selected. As an example, in the present embodiment, the separator 19, the negative electrode 15, and the positive electrode 11 are wound in a state where the separator 19, the negative electrode 15, and the positive electrode 11 are stacked on a surface of a winding shaft around which a member (for example, a resin film or the like) to be the heat absorbing member 40 is wound. You. Next, after the wound shaft is pulled out from the formed wound body, the step of inserting the thermal expansion member 50 into the center and the step of shaping the wound body are performed, so that the wound electrode body 10 is formed. Manufactured. However, the manufacturing method can be changed. For example, the separator 19, the negative electrode 15, and the positive electrode 11 may be wound around a winding shaft formed by the thermal expansion member 50 and the heat absorbing member 40.

<Comparison test>
The results of the overcharge test for confirming the effect of the secondary battery 1 of the above embodiment will be described with reference to FIG. FIG. 5 is a graph showing the results of an overcharge test performed on each of four common secondary batteries in which the configuration of the shaft core in the wound electrode body is different and the other configurations are common. The time and the vertical axis indicate the temperature of the wound electrode body. B1 shows a test result for a conventional secondary battery in which both the heat absorbing member and the thermal expansion member are not included in the shaft core. B2 shows a test result for a secondary battery in which only the high-density polyethylene (the first heat absorbing member 42 in the above embodiment) is included in the shaft core. B3 shows a test result for a secondary battery in which high-density polyethylene and polypropylene (the second heat absorbing member 44 in the above embodiment) are included in the shaft core. The thermal expansion member was not included in the axis of the secondary battery that was tested in B3. B4 shows an evaluation test for the secondary battery 1 of the above embodiment, in which high-density polyethylene, polypropylene, and a thermal expansion member were included in the shaft core. Note that the temperature CS indicates a shutdown temperature of the separator used in each secondary battery. The test conditions other than the configuration of the axis of the wound electrode body are all the same.

  As shown in FIG. 5, in the test of B1, the temperature continued to rise even after the separator was shut down at time T1, and a short circuit occurred. On the other hand, in the test of B2, the shutdown time T2 of the separator was longer than the shutdown time T1 of the test of B1, and no short circuit occurred. This indicates that the first heat absorbing member 42 delays the shutdown timing of the separator.

  Moreover, in the test of B3, the peak temperature C3 after the shutdown of the separator was lower than the peak temperature C2 in the test of B2. Thereby, it turns out that the temperature rise of the wound electrode body after the shutdown of the separator is appropriately suppressed by the second heat absorbing member 44.

  Further, in the test of B4, the peak temperature C4 after the shutdown of the separator was further lower than the peak temperature C3 in the test of B3. Thereby, it turns out that the heat dissipation of a wound electrode body is exhibited more favorably by a thermal expansion member. In the test of B4, the shutdown time T4 of the separator was also longer than the shutdown time T3 of the test of B3. It is considered that this is because the thermal expansion member also functions as a heat absorbing member.

  The technology disclosed in the above embodiment is merely an example. Therefore, the technology exemplified in the above embodiment can be changed. For example, in the above embodiment, two types of heat absorbing members (the first heat absorbing member 42 and the second heat absorbing member 44) are used. However, three or more types of heat absorbing members may be used. Further, only one of the first heat absorbing member 42 and the second heat absorbing member 44 may be used.

DESCRIPTION OF SYMBOLS 1 Secondary battery 10 Wound electrode body 11 Positive electrode 15 Negative electrode 19 Separator 29 Electrolyte 30 Shaft core 40 Heat absorbing member 50 Thermal expansion member

Claims (1)

A secondary battery comprising: an electrode body in which a positive electrode and a negative electrode are stacked via a separator having a shutdown function and wound around an axis, and an electrolyte,
The shaft core is
A heat absorbing member that absorbs heat generated by the secondary battery,
A thermal expansion member that expands due to heat generated by the secondary battery;
A secondary battery, comprising:

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