Bipolar battery

Abstract

To provide a bipolar battery capable of securing the safety against a damage caused due to temperature rise.SOLUTION: In a bipolar battery 10, bipolar electrodes 12 are stacked and sealed in a sealing part 14. In the bipolar electrode 12, a separator with a predetermined shutdown voltage is held between a positive electrode layer and a negative electrode layer. In the sealing part 14, a heterogeneity part 40 is formed at a long side wall 34. The melting point of the heterogeneity part 40 is lower than that of another portion of the sealing part and higher than or equal to the shutdown voltage of the separator. Thus, as the temperature in the sealing part 14 rises to reach the melting point of the heterogeneity part, the heterogeneity part is damaged more easily than the other portion in the bipolar battery 10; therefore, the portion that is likely to be damaged due to the temperature rise becomes clear, making it easy to secure the safety against the damage.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a bipolar battery. [Background technology]

[0002] Patent Document 1 discloses a bipolar battery in which a plurality of bipolar electrodes, each having a positive electrode formed on one side and a negative electrode formed on the other side, are stacked with a separator interposed therebetween to form an electrode stack portion. The bipolar battery also has a seal frame disposed to surround the electrode stack portion, and the seal frame has a plurality of frame-shaped primary seal portions that hold the bipolar electrodes, and a secondary seal portion disposed around the primary seal portions.

[0003] In addition, in bipolar batteries, the internal space between the bipolar electrodes defined by the secondary seal portion is made liquid-tight by the electrolyte, the internal space is sealed by the primary seal portion, and the secondary seal portion surrounds the primary seal portion to further seal the internal space. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-091606 Summary of the Invention [Problem to be solved by the invention]

[0005] In secondary batteries such as bipolar batteries, temperature rises can occur, and gases and other substances can be generated as a result of the temperature rise. In bipolar batteries, if a temperature rise occurs and gas is generated, the generated gas increases the internal pressure, causing changes in the spacing between current collectors or deformation.

[0006] Furthermore, in bipolar batteries, if the internal pressure rises and exceeds the withstand pressure of the frame, the battery will break. The location of this breakage is often influenced by variations in withstand pressure during manufacturing, making it difficult to predict the location of the breakage, and therefore the impact of the breakage.

[0007] An object of the present invention is to provide a bipolar battery that can easily ensure safety in the event that internal pressure increases and damage occurs due to temperature rise. [Means for solving the problem]

[0008] A first aspect of a bipolar battery for achieving the above object includes a bipolar electrode in which a positive electrode layer and a negative electrode layer are disposed between a pair of current collectors, and a separator serving as an electrolyte layer having a predetermined shutdown temperature is disposed between the positive electrode layer and the negative electrode layer; a sealing portion that holds the peripheral edge of each of the pair of current collectors and encloses each of the bipolar electrodes when the bipolar electrodes are stacked and accommodated inside; and a heterogeneous portion that is provided in the sealing portion along the stacking direction of the bipolar electrodes, and has a melting point that is lower than the melting point of other portions of the sealing portion and is equal to or higher than the shutdown temperature of the separator.

[0009] In the bipolar battery of the first aspect, multiple bipolar electrodes are stacked. Each bipolar electrode has a positive electrode layer and a negative electrode layer disposed between a pair of current collectors, and a separator serving as an electrolyte layer with a predetermined shutdown temperature is disposed between the positive electrode layer and the negative electrode layer. When the bipolar electrodes are stacked and housed inside, the sealing portion holds the peripheral portions of each of the pair of current collectors to enclose each bipolar electrode.

[0010] Here, a heterogeneous portion is provided in the sealing portion along the stacking direction of the bipolar battery, and the melting point of the heterogeneous portion is lower than the melting point of other parts of the sealing portion and higher than the shutdown temperature of the separator.

[0011] As a result, the heterogeneous portion functions as a thermally vulnerable portion in the sealing portion, and when the temperature inside the sealing portion rises, the heterogeneous portion begins to melt before other portions of the sealing portion. Therefore, even if the internal pressure inside the sealing portion rises, the pressure can be reduced from the heterogeneous portion, making it possible to appropriately control the location of damage when the internal pressure rises. Furthermore, since it is possible to determine the location where damage will occur when the temperature rises, it becomes easier to ensure safety.

[0012] A bipolar battery of a second aspect is the same as that of the first aspect, except that the sealing portion includes a plurality of frame bodies each containing the bipolar electrode therein, stacked to form a stack of the bipolar electrodes, and a plurality of frame bodies that hold the peripheral portions of each of the pair of current collectors of the bipolar electrodes, and the heterogeneous portion is provided on each of the frame bodies and is arranged in the stacking direction in the sealing portion.

[0013] In the bipolar battery of the second aspect, a plurality of frame bodies are stacked to form a sealing portion. Each frame body houses a bipolar electrode, and the bipolar electrodes are stacked so that the peripheral portions of the pair of current collectors are held and sealed within the frame body.

[0014] Furthermore, each of the frame bodies has a heterogeneous portion, and when the frame bodies are stacked, the heterogeneous portion is formed in the stacking direction in the sealing portion, which makes it possible to easily form the heterogeneous portion corresponding to the bipolar electrode in the sealing portion.

[0015] The bipolar battery of the third aspect is the first or second aspect, wherein the sealing portion is formed in a rectangular shape by a short side wall and a long side wall that is longer than the short side wall when viewed in the stacking direction of the bipolar electrode, and the heterogeneous portion is provided in an intermediate portion of the long side wall along a direction that intersects with the stacking direction.

[0016] In the bipolar battery of the third aspect, a heterogeneous portion is provided on the long side wall, which is longer than the short side wall when viewed in the stacking direction of the bipolar electrodes. Since the long side wall is more susceptible to thermal shrinkage than the short side wall, when the temperature inside the sealing portion rises, damage can be effectively prevented, making it easier to ensure safety.

[0017] A bipolar battery according to a fourth aspect is the bipolar battery according to any one of the first to third aspects, wherein the melting point of the heterogeneous portion is higher than the shutdown temperature of the separator.

[0018] In the bipolar battery of the fourth aspect, the melting point of the heterogeneous portion is set higher than the shutdown temperature of the separator. Therefore, if the separator's shutdown function does not work despite the temperature rise, the sealing portion breaks at the heterogeneous portion. This prevents unnecessary damage to the sealing portion. [Effects of the Invention]

[0019] According to the present invention, even if the temperature inside the sealed portion rises and the internal pressure increases, the sealed portion can be damaged at a predetermined heterogeneous portion, thereby making it easier to ensure safety even if damage occurs. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a cross-sectional side view of a main part showing an outline of a bipolar battery according to an embodiment of the present invention. [Figure 2] FIG. 1 is a plan view showing an outline of a bipolar battery as viewed from above. [Figure 3] (A) is a schematic diagram showing the measurement of the shutdown temperature of the separator, and (B) is a diagram showing the outline of the change in resistance value with temperature. [Figure 4] 1 is a diagram according to a first embodiment. [Figure 5] 10 is a diagram according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, the bipolar battery according to this embodiment will be described in detail with reference to the drawings. Fig. 1 shows a schematic side cross-sectional view of the main parts of a bipolar battery 10 according to this embodiment, and Fig. 2 shows a schematic top plan view of the main parts of the bipolar battery 10. In the drawings, intersecting (orthogonal) directions are indicated by arrows X, Y, and Z, respectively, and in the following description, one side in the width direction, one side in the length direction, and the upper side in the up-down direction of the bipolar battery 10 correspond to arrows X, Y, and Z, respectively. In the following, the up-down direction will also be referred to as the stacking direction.

[0022] The bipolar battery 10 according to this embodiment is a lithium-ion battery that uses a metal oxide containing lithium ions as an electrolyte, and functions as a storage battery (secondary battery). A plurality of bipolar batteries 10 are electrically connected in series (or parallel) to form a power storage device with a predetermined voltage. The bipolar battery 10 is not limited to a lithium-ion battery, and various other batteries, such as nickel-metal hydride secondary batteries, can also be used.

[0023] As shown in Figure 1, the bipolar battery 10 includes a plurality of bipolar electrodes 12 as an electrode assembly, a sealing portion 14, and a laminate portion 16. The bipolar battery 10 is a bipolar (two-pole) battery, and the bipolar battery 10 includes a plurality of bipolar electrodes 12 stacked vertically to form an electrode laminate 18. The electrode laminate 18 is enclosed in the sealing portion 14, and the sealing portion 14 is housed and sealed as a unit in the laminate portion 16.

[0024] The bipolar electrode 12 includes current collectors 20 and 22, a positive electrode layer 24, a negative electrode layer 26, and a separator 28 as an electrolyte layer, which form positive and negative electrodes. The current collectors 20 and 22 are made of conductive metal materials such as Al, SUS, Ni, and Cu. The bipolar electrode 12 has one surface of the current collector 20 coated with a known positive electrode active material to form a positive electrode layer 24 of a required thickness, and one surface of the current collector 22 coated with a known negative electrode active material to form a negative electrode layer 26 of a required thickness.

[0025] In the bipolar electrode 12, a positive electrode layer 24 and a negative electrode layer 26 are opposed to each other, and a separator 28 is disposed between the positive electrode layer 24 and the negative electrode layer 26. In the bipolar electrode 12, the separator 28 is interposed between the positive electrode layer 24 and the negative electrode layer 26. Thus, the bipolar electrode 12 is formed by laminating the current collector 20, the positive electrode layer 24, the separator 28, the negative electrode layer 26, and the current collector 22 in this order.

[0026] When a plurality of bipolar electrodes 12 are stacked in the electrode stack 18, the current collector 20 of one bipolar electrode 12 faces the current collector 22 of the other bipolar electrode 12 between adjacent bipolar electrodes 12. As a result, in the electrode stack 18, the plurality of bipolar electrodes 12 are connected in series.

[0027] In the bipolar battery 10, the current collector 20 on which the final positive electrode layer 24 in the stacking direction is disposed is the final positive electrode 20A, and the current collector 22 on which the final negative electrode layer 26 in the stacking direction is disposed is the final negative electrode 22A (see FIG. 1). In the bipolar battery 10, a positive electrode tab 30A is connected to the final positive electrode 20A, and a negative electrode tab 30B is connected to the final negative electrode 22A, and in the bipolar battery 10, a predetermined voltage is generated between the positive electrode tab 30A and the negative electrode tab 30B.

[0028] The current collectors 20, 22 have a generally rectangular shape in plan view, with the longitudinal direction aligned with the direction of arrow Y and the width direction aligned with the direction of arrow X. In the bipolar electrode 12, a positive electrode layer 24 having a generally rectangular shape in plan view is applied to the center of the current collector 20, and a negative electrode layer 26 having a generally rectangular shape in plan view is applied to the center of the current collector 22. The current collectors 20, 22 each have an uncoated portion outside the positive electrode layer 24 and the negative electrode layer 26, and each current collector 20, 22 has an uncoated portion on its periphery.

[0029] The separator 28 has a substantially rectangular shape similar to that of each of the current collectors 20 and 22, and the longitudinal dimension (longitudinal dimension) and width dimension (width dimension) of the separator 28 are each smaller than those of the current collectors 20 and 22. The longitudinal dimension (longitudinal dimension) and width dimension (width dimension) of the separator 28 are each slightly larger than those of the positive electrode layer 24 and the negative electrode layer 26.

[0030] As a result, in the bipolar electrode 12, the uncoated portions of the current collectors 20, 22 protrude outward from the positive electrode layer 24, the negative electrode layer 26, and the separator 28 along the entire periphery when viewed in the stacking direction.

[0031] A solid electrolyte layer containing a known solid electrolyte is used for the separator 28. The separator 28 forms an electrolyte layer between the positive electrode layer 24 and the negative electrode layer 26 that is electrically insulating, as well as oxidation-resistant and reduction-resistant. This allows the separator 28 to prevent electrical short-circuiting between the positive electrode layer 24 and the negative electrode layer 26 while allowing charge carriers such as lithium ions to pass through (permeate).

[0032] Separator 28 also has a shutdown function that stops its ion permeability when it reaches a preset temperature (shutdown temperature Tsd). As a result, even if unexpected heat generation occurs in bipolar battery 10, charging and discharging is stopped when separator 28 reaches shutdown temperature Tsd, making it possible to suppress temperature rise.

[0033] The sealing portion 14 is formed into a generally box-like shape by stacking a plurality of frame bodies 32, each formed into a rectangular frame. The frame bodies 32 are made of, for example, resin, and include long side walls 34 whose longitudinal direction runs along the direction of arrow Y and short side walls 36 whose longitudinal direction is shorter than the long side walls 34 and runs along the direction of arrow X, with each pair of the long side walls 34 and short side walls 36 being integrated into a rectangular frame shape. The height dimension (dimension in the stacking direction) of the frame bodies 32 is the same as the distance between the lower surface of the current collector 20 and the upper surface of the current collector 22 in the bipolar electrode 12.

[0034] Furthermore, the frame 32 has an inner length dimension (the spacing between the inner surfaces of the short-side walls 36) and a width dimension (the spacing between the inner surfaces of the long-side walls 34) that are smaller than the dimensions of the current collectors 20, 22 along the same directions. Also, the frame 32 has an outer length dimension (the length of the long-side walls 34) and a width dimension (the length of the short-side walls 36) that are larger than the dimensions of the current collectors 20, 24 along the same directions.

[0035] As a result, the bipolar electrode 12 is arranged such that the uncoated portion of the lower peripheral edge of the current collector 20 is positioned on the upper surface of the frame 32, and the uncoated portion of the upper peripheral edge of the current collector 22 is positioned on the lower surface of the frame 32, and the positive electrode layer 24, separator 28, and negative electrode layer 26 are housed within the frame 32.

[0036] In the bipolar battery 10, the bipolar electrodes 12 are stacked by stacking frame bodies 32, each housing a bipolar electrode 12. In the bipolar battery 10, the stacked frame bodies 32 are held in a pressurized and tightly contacted state, so that the bipolar electrodes 12 are housed and sealed within the frame bodies 32, and the electrode stack 18 is sealed and held within the sealing portion 14.

[0037] In the bipolar battery 10, an electrolyte is sealed within the sealing portion 14. The electrolyte is sealed in the internal space between the current collectors 20 and 22 within the frame 32.

[0038] The laminate portion 16 is made of, for example, multiple (for example, two) laminate sheets 16A, and the overlapping portions of the laminate sheets 16A arranged to wrap around the sealing portion 14 are melt-bonded to enclose the sealing portion 14.

[0039] 2, each frame 32 is provided with a heterogeneous portion 40, which is formed with a required length in the longitudinal middle portion of one of the pair of long side walls 34. Therefore, the heterogeneous portion 40 is formed continuously in the vertical direction on the surface of the sealing portion 14 on the side of one of the long side walls 34.

[0040] The heterogeneous portion 40 is a thermally vulnerable portion in the frame body 32, and the heterogeneous portion 40 is made of a material having a melting point (dissolving temperature) Tm lower than the melting point Tms of other portions of the frame body 32 (Tm < Tms). The heterogeneous portion 40 may be made of, for example, the same material as other portions by the frame body 32, or a different material from other portions, but is made of a material having a melting point Tm lower than the melting point Tms of other portions. Also, the melting point Tm of the heterogeneous portion 40 is set to a temperature higher than the shutdown temperature Tsd of the separator 28 (Tsd < Tm < Tms).

[0041] Thereby, in the frame body 32, as the temperature rises, the heterogeneous portion 40 melts earlier than other portions, enabling the inside of the long side wall 34 to be released outward.

[0042] In the bipolar battery 10 configured as described above, each uncoated portion of the current collector 20 coated with the positive electrode layer 24 and the current collector 22 coated with the negative electrode layer 26 is sandwiched between the frame bodies 32 adjacent to each other vertically, and the bipolar electrode 12 is housed in the frame body 32 and held by the sealing portion 14. Thereby, in the bipolar battery 10, the bipolar electrode 12 is housed in the frame body 32 and sealed in the sealing portion 14.

[0043] Also, in the bipolar battery 10, the positive electrode final electrode 20A and the positive electrode tab 30A are connected, and the negative electrode final electrode 22A and the negative electrode tab 30B are connected. Thereby, in the bipolar battery 10, it is charged by the DC power applied between the positive electrode tab 30A and the negative electrode tab 30B, and DC power of a predetermined voltage can be output from between the positive electrode tab 30A and the negative electrode tab 30B.

[0044] By the way, in the bipolar battery 10, the temperature of the bipolar electrode 12 or the like may rise due to various factors such as deterioration due to the usage situation (charge and discharge situation) and deterioration over time. Also, in the bipolar battery 10, gas may be generated as the temperature rises, and in the bipolar battery 10, the internal pressure rises due to the temperature rise and the generation of gas, increasing the possibility that the sealing portion 14 in which the bipolar electrode 12 is enclosed will be damaged.

[0045] Here, each of the frame bodies 32 forming the sealing portion 14 has a heterogeneous portion 40 formed in a predetermined portion with a melting point Tm lower than the melting point Tms of the other portions, and the heterogeneous portion 40 is formed continuously in the vertical direction in the sealing portion 14.

[0046] For this reason, in the frame 32, when the temperature T in the bipolar electrode 12 or the like exceeds the melting point Tm of the heterogeneous portion 40 (T≧Tm), the heterogeneous portion 40 changes from a solid phase to a liquid phase. As a result, in the bipolar battery 10, an increase in temperature T makes the heterogeneous portion 40 more susceptible to breakage in the sealed portion 14 (frame 32), and an increase in internal pressure within the sealed portion 14 causes breakage in the heterogeneous portion 40 that exposes the inside to the outside, reducing the pressure inside the sealed portion 14.

[0047] In this way, in the bipolar battery 10, damage is likely to occur in the heterogeneous portion 40, which is a predetermined portion, as the temperature T inside the sealed portion 14 in which the bipolar electrode 12 is sealed rises. For this reason, in the bipolar battery 10, damage occurs in the heterogeneous portion 40 when the internal pressure inside the sealed portion 14 rises. Thus, in the bipolar battery 10, by providing the heterogeneous portion 40 in the sealed portion 14 (frame 32), the portion of the sealed portion 14 that will break when the temperature T inside the sealed portion 14 rises and the internal pressure rises can be controlled, making it easier to ensure safety when damage occurs to the sealed portion 14.

[0048] In addition, in the bipolar battery 10, a shutdown temperature Tsd is set for the separator 28 of the bipolar electrode 12, and in the bipolar battery 10, the melting point Tm of the heterogeneous portion 40 is set higher than the shutdown temperature Tsd (Tm>Tsd).

[0049] Here, the shutdown temperature Tsd of the separator 28 will be described. FIG. 3(A) shows a schematic diagram of the measurement of the shutdown temperature Tsd, and FIG. 3(B) shows a diagram of the change in resistance value (resistance or impedance) of the separator 28 relative to the change in temperature.

[0050] As shown in FIG. 3(A), for measuring the shutdown temperature Tsd, for example, current collectors (electrodes) 44 each coated with a negative electrode active material to form a negative electrode layer 42 are used, and the negative electrode layer 42 is opposed through the separator 28 to be measured and pressed and adhered at 1 MPa. At this time, the negative electrode layer 42 and the separator 28 are encapsulated in a laminate sheet 46.

[0051] In this state, a voltage of 1 kHz is applied between the pair of current collectors 44, and the resistance value (Ω) between the pair of current collectors 44 is measured while increasing the temperature (for example, increasing from 20°C or 25°C).

[0052] Thereby, as shown in FIG. 3(B), the resistance value between the pair of current collectors 44 initially maintains a high value (for example, a value of about 4 digits), but rapidly decreases when the temperature T becomes high enough. Thereby, for example, the temperature T when the resistance value decreases by two digits or more is set (defined) as the shutdown temperature Tsd of the separator 28 to be measured.

[0053] In the bipolar battery 10, when the temperature T reaches the shutdown temperature Tsd of the separator 28 (T≧Tsd), the ion permeability of the separator 28 stops, and the charge and discharge of the bipolar electrode 12 are stopped. Thereby, the melting point Tm of the heterogeneous part 40 can be set to a temperature (Tsd≦Tm<Tms) that is not lower than the shutdown temperature Tsd of the separator 28 and lower than the melting point Tms of other parts of the frame 32.

[0054] Moreover, it is more preferable that the melting point Tm of the heterogeneous part 40 is set to a temperature higher than the shutdown temperature Tsd of the separator 28 and lower than the melting point Tms of other parts of the frame 32 (Tsd<Tm<Tms). Thereby, in the bipolar battery 10, if the rise in temperature T is suppressed, the heterogeneous part 40 of the sealing part 14 is not damaged, so unnecessary damage to the sealing part 14 can be suppressed.

[0055] Furthermore, in the bipolar battery 10, even if the temperature exceeds the shutdown temperature Tsd, if the temperature rises further, the heterogeneous portion 40 of the sealing portion 14 can be damaged. This allows the bipolar battery 10 to effectively suppress an increase in the temperature T. Furthermore, in the bipolar battery 10, even if damage occurs to the sealing portion 14, the location of the damage can be predicted, making it easy to ensure safety against damage.

[0056] [First Example] Here, a first example of this embodiment will be described. In the first example, an overcharge test was conducted for each of Example A1, Example A2, Comparative Example A1, and Comparative Example A2 to observe changes in the state of the sealed portion (corresponding to sealed portion 14) and the laminated portion (corresponding to laminated portion 16), and the observation results are shown in FIG. 4.

[0057] In the first example, the following configurations were applied to Example A1, Example A2, Comparative Example A1, and Comparative Example A2.

[0058] The bipolar electrode (corresponding to the bipolar electrode 12) uses NCM (nickel-cobalt-manganese lithium oxide) as the positive electrode active material in the positive electrode layer, and uses C (natural graphite) as the negative electrode active material in the negative electrode layer.

[0059] The electrolyte is a solution (solvent) of EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DMC (diethyl carbonate) mixed in a volume ratio of EC:EMC:DMC=1:1:1 to which 1.0M LiPF6 has been added.

[0060] In the sealing portion, PE (polyethylene) is used for the heterogeneous portion (corresponding to the heterogeneous portion 40), and PET (polyethylene terephthalate) is used for the portion other than the heterogeneous portion, so that the melting point Tm of the heterogeneous portion is lower than the melting point Tms of the other portion (Tm <Tms)。

[0061] The separator (corresponding to separator 28) is made of PP (polypropylene), PE, and PP, and has a three-layer structure of PP / PE / PP, with a shutdown temperature Tsd of 130°C.

[0062] The overcharge test was carried out under the conditions that charging was started at 25°C at a C rate of 1C, and charging was continued until the gas generated inside was discharged to the outside (outside the laminated part).

[0063] In addition, the overcharge test was performed three times for each of Example A1, Example A2, Comparative Example A1, and Comparative Example A2, and the gas discharge direction was recorded. If the gas was always discharged in one direction among the four sides of the sealing portion (frame), it was evaluated as "constant," and if the discharge direction was not fixed to one direction, it was evaluated as "undefined."

[0064] The case where a heterogeneous portion was provided in the sealing portion was marked as "present," and the case where a heterogeneous portion was not provided was marked as "absent." Examples A1 and A2 were marked as "present," and Comparative Examples A1 and A2 were marked as "absent."

[0065] In the test, the laminated portion was configured with a "weak portion" that was more vulnerable to internal pressure than other portions. The "weak portion" was formed by placing a sheet tab with an uneven surface that protruded from the inside to the outside at the joint between the two laminated sheets. Example A2 and Comparative Example A2 had a weak portion and were classified as "present," while Example A1 and Comparative Example A1 did not have a "weak portion" and were classified as "absent."

[0066] As shown in Figure 4, Comparative Examples A1 and A2, which do not have a heterogeneous portion, were evaluated as "indeterminate." In particular, Comparative Example A2 was evaluated as "indeterminate" even though a "weak portion" was provided in the laminate portion, making it clear that the "weak portion" in the laminate portion did not contribute to the direction of gas discharge.

[0067] In contrast, Examples A1 and A2, in which a heterogeneous portion was formed in the sealed portion, were evaluated as "constant." It is clear that the heterogeneous portion in the sealed portion is more dominant in the gas discharge direction than the "weak portion" in the laminated portion. Therefore, providing a heterogeneous portion in the sealed portion allows for appropriate control of the gas discharge direction.

[0068] [Second Example] Next, a second embodiment will be described. The basic configuration of Example 2 is the same as Example 1. In Example 2, an overcharge test was conducted on each of Examples B1, B2, B3, B4, and Comparative Example B1 to observe changes in the state of the sealed portion and laminated portion, and the observation results are shown in Figure 5.

[0069] In the second embodiment, in addition to the configuration of the first embodiment, the configuration of the separator, the configuration of the sealing portion, and the configuration and position of the heterogeneous portion in the sealing portion are added to the bipolar electrode.

[0070] The separators were made of PP / PE / PP with melting points of 160°C, 130°C, and 130°C (shutdown temperature Tsd: 130°C), respectively. PET with a melting point of 260°C or PP with a melting point of 160°C was used for the parts excluding the heterogeneous parts of the sealed parts. For the heterogeneous portion, PE with a melting point Tm of 130°C or 135°C, or PP with a melting point of 160°C was used, and the position of the heterogeneous portion was set on the long side wall (corresponding to the long side wall 34) or the short side wall (corresponding to the short side wall 36). Note that Example B1 has the same configuration as Example A1.

[0071] Furthermore, in Example 2, an overcharge test was conducted under the same conditions as in Example 1. The home appliance charging test was conducted three times for each of Example B1, Example B2, Example B3, Example B4, and Comparative Example B1, and the temperature of the discharged gas as well as the direction of gas discharge were measured and recorded.

[0072] 5, Examples B1, B2, and B3 differ in the material of the sealing portion (the portion other than the heterogeneous portion) or the melting point Tm of the heterogeneous portion, but the gas discharge direction is evaluated as being constant, and the temperature of the discharged gas is also similar and lower than that of Example B4 and Comparative Example B1. From this, it can be evaluated that the timing of gas discharge in Examples B1 to B3 is appropriate.

[0073] Furthermore, as shown in Example B3, even if the melting point Tm of the heterogeneous portion is higher than the melting point of the separator (shutdown temperature Tsd), if the difference is small (for example, about 5°C), an evaluation similar to that obtained when the melting point Tm of the heterogeneous portion is the same temperature as the melting point of the separator is obtained.

[0074] Furthermore, in Example B4, the heterogeneous portion is provided on the short side wall, and therefore the temperature of the discharged gas is higher in Example B4 than in Example B3, in which the heterogeneous portion is provided on the long side wall.

[0075] In addition, in comparative example B1, the melting point Tm of the heterogeneous portion is the same as the melting point of the PP of the separator (shutdown temperature Tsd), but because the melting point of the heterogeneous portion is higher, the gas temperature becomes extremely high even though the heterogeneous portion is located on the long side wall.

[0076] Therefore, the heterogeneous portion only needs to have a melting point lower than that of the other portions of the sealing portion and equal to or higher than the shutdown temperature of the separator. Alternatively, the heterogeneous portion may have a melting point lower than that of the other portions of the sealing portion and higher than the shutdown temperature of the separator. Furthermore, the heterogeneous portion may be provided on the short side wall of the sealing portion when viewed in the stacking direction of the bipolar electrodes, but is more preferably provided on the long side wall. [Explanation of symbols]

[0077] 10 Bipolar Battery 12 Bipolar electrodes 14 Sealing part 18 Electrode laminate 20, 22 Current collector 24 Positive electrode layer 26 negative electrode layer 28 Separator 32 Frame 34 Long Side Wall 36 Short Side Wall 40 Heterogeneous Part

Claims

1. a bipolar electrode in which a positive electrode layer and a negative electrode layer are disposed between a pair of current collectors, and a separator serving as an electrolyte layer having a predetermined shutdown temperature is disposed between the positive electrode layer and the negative electrode layer; a sealing portion that holds a peripheral portion of each of the pair of current collectors and seals each of the bipolar electrodes when the bipolar electrodes are stacked and housed therein; a heterogeneous portion provided in the sealing portion along the stacking direction of the bipolar electrodes, the heterogeneous portion having a melting point lower than that of other portions of the sealing portion and equal to or higher than the shutdown temperature of the separator; Bipolar batteries, including:

2. the sealing portion includes a plurality of frame bodies, each of which accommodates the bipolar electrode, stacked to stack the bipolar electrodes, and a plurality of frame bodies that hold peripheral portions of each of the pair of current collectors of the bipolar electrodes; the heterogeneous portion is provided in each of the frames and is arranged in the stacking direction of the sealing portion.

10. The bipolar battery of claim 1, comprising:

3. the sealing portion is formed in a rectangular shape with a short side wall and a long side wall longer than the short side wall when viewed in the stacking direction of the bipolar electrodes, the heterogeneous portion is provided in an intermediate portion of the long side wall along a direction intersecting the stacking direction, 10. The bipolar battery of claim 1.

4. The bipolar battery according to claim 1 , wherein the melting point of the heterogeneous portion is higher than the shutdown temperature of the separator.

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