Battery pack

Abstract

The present invention prevents thermal runaway of one battery cell from inducing thermal runaway of another battery cell, thereby preventing the battery cells from catching fire and securing excellent safety.　A battery pack according to the present invention is provided with: a battery assembly wherein a plurality of battery cells (1), each having a discharge valve in an end face, are arranged parallel to each other so that end face electrodes (1a, 1b) at end portions are positioned on a same plane, and a welding surface (3B) of a lead plate (3) is connected to the end face electrodes (1a, 1b) positioned on the same plane; and an outer case (4) in which the battery assembly is contained. This battery pack is provided with a reverse flow limiting layer (5) within the outer case (4), said reverse flow limiting layer (5) being arranged on a non-welding surface (3A) of the lead plate (3); the lead plate (3) has a gas permeation gap (33) which enables the passing of a discharge gas discharged through the discharge valve from the battery cell (1) side to the discharge direction of the reverse flow limiting layer (5); and the reverse flow limiting layer (5) has a resistive part (7) which has the discharge gas passing through the gas permeation gap (33) pass therethrough to the discharge direction, thereby suppressing or preventing reverse flow of the discharge gas in a direction opposite to the discharge direction.

Description

[Technical field]

[0001] The present invention relates to a battery pack that prevents thermal runaway in any battery cell from inducing thermal runaway in other battery cells. [Background technology]

[0002] Rechargeable battery cells can go into thermal runaway due to various reasons, such as an internal short circuit or overcharging. For example, when a lithium-ion battery goes into thermal runaway, the exhaust valve opens and forcefully ejects exhaust gases for several seconds. The exhaust gases are extremely hot, exceeding 700°C, and are ejected into the exterior case, inducing thermal runaway in other battery cells; in other words, the battery cell that has gone into thermal runaway will spread fire to other battery cells, significantly increasing the thermal energy and causing the spread of thermal damage. Battery packs of various structures have been developed with the aim of preventing the induction of thermal runaway. (See Patent Document 1)

[0003] 9, in a battery pack with this structure, a cylinder 102 into which cylindrical batteries 101 are inserted is connected to a thermally conductive plate 103, and the thermal energy of the cylindrical batteries 101 that have become hot due to thermal runaway is conducted to and absorbed by the thermally conductive plate 103. The thermally conductive plates 103 are arranged separately in a two-layer structure, and the cylinders 102 into which adjacent cylindrical batteries 101 are inserted are connected to separate thermally conductive plates 103, resulting in a structure in which the thermal energy of the adjacent cylindrical batteries 101 is absorbed by the separate thermally conductive plates 103.

[0004] A battery pack with this structure can prevent thermal runaway from being induced in adjacent battery cells, but cannot prevent thermal runaway from occurring in battery cells located far from the battery cell that has gone into thermal runaway. This is because, although it can prevent the thermal energy of the battery cell that has gone into thermal runaway from being thermally transferred to the adjacent battery cells, it cannot prevent the induction of thermal runaway caused by exhaust gas emitted from the thermally expanded battery cell. When a battery cell goes into thermal runaway, the exhaust valve opens and extremely high-temperature exhaust gas is instantly ejected with great force. This high-temperature exhaust gas flows inside along the inner surface of the exterior case, and may overheat a battery cell located far from the battery cell and cause it to go into thermal runaway. Thermal runaway is induced in a battery cell located far from the battery cell when the exhaust gas melts the insulating material that insulates the end electrodes of the battery cell. One end electrode of the battery cell is insulated and fixed to the battery case, and the end electrode is insulated from the battery case, which is the other electrode. Therefore, when the insulating material melts, the end electrode that is insulated from the battery case is short-circuited to the battery case, causing an excessive short-circuit current to flow. An excessive short circuit current can cause the battery cells to heat up due to Joule heat, resulting in thermal runaway. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-045919 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention was developed with the further objective of eliminating the above-mentioned drawbacks, and one object of the present invention is to provide a battery pack which ensures excellent safety by preventing thermal runaway of a battery cell from inducing damage to other battery cells housed in the outer case, thereby preventing the spread of fire among the battery cells. [Means for solving the problem]

[0007] A battery pack according to one aspect of the present invention comprises a battery assembly comprising a plurality of battery cells each having a vent valve on its end surface, oriented in parallel with end electrodes at the ends arranged on the same plane, and a lead plate welded surfaces connected to the end electrodes arranged on the same plane, and an exterior case housing the battery assembly. The battery pack comprises a backflow limiting layer arranged on the inside of the exterior case and on the non-welded surfaces of the lead plates, the lead plates having gas permeable gaps that allow exhaust gas discharged from the vent valves to pass from the battery cell side in the discharge direction towards the backflow limiting layer, and the backflow limiting layer has a resistance portion that allows exhaust gas passing through the gas permeable gaps to pass in the discharge direction and suppresses or prevents exhaust gas passing in the opposite direction to the discharge direction. Effect of the Invention

[0008] The battery pack of the present invention can prevent thermal runaway of a battery cell from inducing damage to other battery cells housed in the exterior case, thereby preventing the spread of fire among the battery cells and ensuring excellent safety. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic vertical cross-sectional view of a battery pack according to an embodiment of the present invention; [Diagram 2] 2 is a horizontal cross-sectional view of the battery pack shown in FIG. 1. [Diagram 3] FIG. 2 is a perspective view of a battery assembly of the battery pack shown in FIG. [Figure 4] FIG. 4 is a side view of the battery assembly shown in FIG. [Diagram 5] FIG. 4 is an exploded perspective view of the battery assembly shown in FIG. [Figure 6] 4 is an exploded perspective view showing the positional relationship between the battery holder and the lead plates of the battery assembly shown in FIG. 3. [Figure 7] 3 is an enlarged cross-sectional view of the battery pack shown in FIG. 2. [Figure 8] 4 is an enlarged cross-sectional view showing a state in which exhaust gas passes through the backflow limiting layer in a direction opposite to the exhaust direction. FIG. [Figure 9] FIG. 1 is a schematic cross-sectional view of a conventional battery pack. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The embodiment of the present invention may be specified by the following configurations. A battery pack according to a first embodiment of the present invention comprises a battery assembly in which a plurality of battery cells, each having a vent valve on its end face, are arranged in parallel with end electrodes at the ends on the same plane, and the welded surfaces of lead plates are connected to the end electrodes arranged on the same plane, and an exterior case housing the battery assembly. The battery pack comprises a backflow limiting layer arranged on the inside of the exterior case and on the non-welded surfaces of the lead plates, and the lead plates have gas permeation gaps that allow exhaust gas discharged from the vent valves to pass from the battery cell side in the discharge direction of the backflow limiting layer, and the backflow limiting layer has resistance sections that allow the exhaust gas that passes through the gas permeation gaps to pass in the discharge direction and suppress or block exhaust gas passing in the direction opposite to the discharge direction.

[0011] The above battery pack has the feature of being able to ensure excellent safety by preventing the spread of fire of other battery cells housed in the exterior case due to a thermally runaway battery cell. In particular, the above battery pack has a backflow limiting layer disposed on the surface of the lead plate with gas permeable gaps. This backflow limiting layer allows the high-temperature, high-pressure exhaust gas emitted from the thermally runaway battery cell to pass through the gas permeable gaps in the lead plate in the discharge direction and be discharged to the inside of the exterior case, where it is diffused on the inner surface of the exterior case to attenuate its energy. Furthermore, the exhaust gas that has diffused on the inner surface of the exterior case and has attenuated its energy is prevented by a resistance section from flowing in the reverse direction toward other battery cells, thereby further attenuating its energy. This makes it possible to prevent other battery cells from being overheated to high temperatures by the high-temperature, high-pressure exhaust gas emitted from the thermally runaway battery cell. This prevents the high-temperature, high-pressure exhaust gas from melting the insulating material that insulates the positive and negative electrode terminals and causing a short circuit, effectively preventing the harmful effect of the battery cell itself being short-circuited, causing an excessive short-circuit current to flow and causing thermal runaway. Therefore, the above battery pack has the advantage that even if a specific battery cell experiences thermal runaway, it can prevent the thermal runaway from inducing the same in other battery cells, thereby ensuring a high level of safety.

[0012] A battery pack according to a second embodiment of the present invention has a battery assembly comprising a battery holder in which multiple battery cells are arranged in fixed positions, the battery holder comprising a surface plate for arranging lead plates in fixed positions, the surface plate having electrode windows that expose the end electrodes of the battery cells arranged in fixed positions, and the lead plates are connected to the end electrodes of the battery cells in the electrode windows.

[0013] In the above battery pack, the lead plate is positioned in a fixed position on the surface plate of the battery holder and a backflow limiting layer can be laminated to the lead plate. This prevents exhaust gas ejected from a thermally runaway battery cell from passing between the lead plate and the battery cell and flowing toward adjacent battery cells, thereby preventing the spread of fire to adjacent battery cells.

[0014] In a battery pack according to a third embodiment of the present invention, the lead plates arranged at fixed positions on the surface plate have a plurality of gas permeable gaps.

[0015] The above battery packs have multiple gas permeation gaps in the lead plates, so exhaust gas that passes through a specific gas permeation gap due to thermal runaway can be dispersed among multiple gas permeation gaps. This has the advantage of more effectively attenuating the energy of high-temperature, high-pressure exhaust gas and more reliably preventing the spread of fire to other battery cells.

[0016] In a battery pack according to a fourth embodiment of the present invention, the backflow limiting layer forms a through hole that allows exhaust gas to pass through, and has a resistance portion that blocks a position facing the gas permeation gap around the through hole.

[0017] The battery pack described above has a through hole formed in the backflow limiting layer and a resistance portion provided around the through hole to block the position facing the gas permeation gap, thereby preventing exhaust gas flowing in the reverse direction from passing directly through the gas permeation gap. Exhaust gas flowing in the reverse direction through the through hole does not flow directly into the gas permeation gap, but passes through the gas permeation gap with its energy attenuated by colliding with the surface of the lead plate, which has the advantage of effectively preventing the spread of ignition of the battery cells. In addition, exhaust gas discharged from a battery cell that has gone into thermal runaway can be passed through the through hole in the backflow limiting layer and smoothly flow between the backflow limiting layer and the exterior case, which prevents the exhaust gas pressure from increasing on the inner surface of the backflow limiting layer and leaking through the gap toward the adjacent battery cell, thereby effectively suppressing the spread of ignition of the adjacent battery cell.

[0018] In a battery pack according to a fifth embodiment of the present invention, the gas permeable gap in the lead plate is an annular slit opening, and the through hole in the backflow limiting layer is opened facing the inside of the annular slit opening, thereby forming a resistance portion.

[0019] The above-described battery pack has the advantage that exhaust gas that passes through the through hole in the opposite direction is dispersed and flows into the annular slit opening, preventing the exhaust gas from flowing directly into the inner surface of the lead plate and inducing thermal runaway in the battery cells.

[0020] In a battery pack according to a sixth embodiment of the present invention, the backflow limiting layer has cuts extending radially from the through hole.

[0021] The above battery pack has the advantage that it allows high-temperature, high-pressure exhaust gas caused by thermal runaway to pass more smoothly in the exhaust direction and flow smoothly into the inside of the exterior case. This prevents the exhaust gas from leaking through gaps toward adjacent battery cells due to the high pressure of the exhaust gas on the inner surface of the backflow limiting layer, and effectively suppresses the spread of combustion of adjacent battery cells. The exhaust gas flows smoothly into the inner surface of the exterior case because the cuts enlarge the through holes in the backflow limiting layer, allowing the exhaust gas to pass through smoothly.

[0022] In a battery pack according to a seventh embodiment of the present invention, the reverse flow limiting layer is a radially extending cutout that allows exhaust gas to pass through. the law of nature The cut has a resistance portion that closes a position facing the gas permeation gap.

[0023] The above battery packs have a cut-off in which the backflow limiting layer extends radially. the law of nature The slits have a groove that deforms due to the high-temperature exhaust gas ejected from the battery cell, allowing the exhaust gas to be exhausted. Furthermore, the slits can prevent exhaust gas flowing in the reverse direction from passing through.

[0024] In a battery pack according to an eighth embodiment of the present invention, the backflow limiting layer is made of a rubber material.

[0025] In the above battery packs, the backflow limiting layer is made of rubber, so that the exhaust gas ejected from exhaust gas that has gone into thermal runaway burns off part of the backflow limiting layer, allowing high-temperature, high-pressure exhaust gas to flow more smoothly into the inside of the exterior case.

[0026] In a battery pack according to a ninth embodiment of the present invention, the backflow limiting layer is made of foam.

[0027] The battery packs described above have a foam backflow limiting layer, which allows the exhaust gas ejected from thermal runaway exhaust gas to quickly burn off part of the backflow limiting layer, allowing high-temperature, high-pressure exhaust gas to flow more smoothly into the exterior case. The foam backflow limiting layer is able to quickly burn off the area where the exhaust gas is ejected because it has a small heat capacity relative to its volume and can be burned off with little thermal energy.

[0028] In a battery pack according to a tenth embodiment of the present invention, a battery cell has a protruding electrode on an end face, and an exhaust port of a discharge valve is opened on the outer periphery of the protruding electrode.

[0029] A battery pack according to an eleventh embodiment of the present invention has cylindrical battery cells.

[0030] In a battery pack according to a twelfth embodiment of the present invention, the lead plate has a flat plate-like portion that forms the non-welded surface, and an electrode connection piece that forms the welded surface that is connected to the end face electrode of the battery cell, and a slit opening that forms a gas permeable gap is provided along the outer periphery of the electrode connection piece.

[0031] In a battery pack according to a thirteenth embodiment of the present invention, a backflow limiting layer is bonded to the surface of a lead plate.

[0032] The present invention will be described in detail below with reference to the drawings. In the following description, terms indicating specific directions or positions (e.g., "upper", "lower", and other terms including these terms) are used as necessary, but the use of these terms is for the purpose of facilitating understanding of the invention with reference to the drawings, and the meanings of these terms do not limit the technical scope of the present invention. In addition, parts with the same reference numerals appearing in multiple drawings indicate the same or equivalent parts or members.

[0033] Furthermore, the embodiments shown below are specific examples of the technical ideas of the present invention, and do not limit the present invention to the following. Furthermore, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described below are intended to be illustrative and not to limit the scope of the present invention. Furthermore, the contents described in one embodiment or example can be applied to other embodiments or examples. Furthermore, the sizes and positional relationships of the components shown in the drawings may be exaggerated to clarify the explanation.

[0034] The battery pack of the present invention is suitable for mounting on an electric device, mainly an electric vehicle, and for supplying power to a driving motor. The battery pack of the present invention is used, for example, as a power source for an electric-assisted bicycle, an electric motorcycle, an electric wheelchair, an electric tricycle, an electric cart, etc. However, the present invention does not specify the use of the battery pack, and it can also be used as a power source for various other electric devices, such as a cleaner, an electric tool, etc. (Embodiment 1)

[0035] The battery pack 100 shown in Figs. 1 and 2 has a battery assembly 10, which is made up of multiple battery cells 1 housed in a battery holder 2, housed in an exterior case 4. In the battery assembly 10, multiple battery cells 1, each having a discharge valve on its end face, are arranged in a parallel posture with end electrodes 1a, 1b at the ends arranged on the same plane. The welded surface 3B of a lead plate 3 is connected to the end electrodes 1a, 1b arranged on the same plane. Furthermore, the battery pack 100 has a backflow limiting layer 5 arranged on the inside of the exterior case 4, on the non-welded surface 3A of the lead plate 3. The backflow limiting layer 5 controls the flow of high-temperature, high-pressure exhaust gas ejected by a battery cell 1 that has experienced thermal runaway, thereby preventing thermal runaway from being induced in other battery cells 1. (Battery Assembly 10)

[0036] The battery assembly 10 shown in Figures 3 to 6 comprises multiple battery cells 1 with different positive and negative end electrodes 1a, 1b at both ends, a battery holder 2 in which the battery cells 1 are oriented parallel to one another and arranged in multiple rows and columns with the end electrodes 1a, 1b of the battery cells 1 arranged on the same plane, and lead plates 3 connected to the end electrodes 1a, 1b of the battery cells 1 housed in the battery holder 2 and connecting adjacent battery cells 1 in series and parallel. (Battery cell 1)

[0037] The battery cell 1 has positive and negative electrodes at both ends, with one end electrode 1a being a convex electrode and the other end electrode 1b being a flat electrode. The battery cell 1 shown in the figure is a cylindrical battery. Although not shown, a cylindrical battery has an electrode body housed in a cylindrical outer can, which is filled with an electrolyte and the opening of the outer can is sealed with a sealing plate via an insulating material such as a gasket. The cylindrical battery has a convex electrode provided on a sealing plate insulated by an insulating material to serve as one end electrode 1a, and the bottom surface of the outer can to serve as the other end electrode 1b, providing positive and negative electrodes. Furthermore, the battery cell 1 is provided with a discharge valve (not shown) on the inside of the convex electrode that opens when the internal pressure exceeds a set pressure, and an exhaust port for the discharge valve is provided on the outer periphery of the convex electrode.

[0038] The battery cell 1 is a rechargeable lithium-ion secondary battery. However, the battery cell 1 is not limited to a lithium-ion battery, and may be a rechargeable battery such as a nickel-metal hydride battery or a nickel-cadmium battery. Furthermore, although a cylindrical battery is used in the battery pack 100 of this embodiment, the present invention is not limited to this, and a square battery or a flat battery may also be used. The battery assembly 10 has a plurality of battery cells 1 arranged in multiple rows and columns in a parallel posture and stored in a battery holder 2. The number of battery cells 1 in the battery assembly 10 is determined to be an optimal number taking into consideration the use of the battery pack 100, the charge / discharge capacity, the maximum load current, the capacity of each battery cell 1, and the like, and may be, for example, 10 to 100. The battery assembly 10 can increase the maximum current supplied to the load by increasing the number of battery cells 1 connected in parallel, and can increase the overall charge / discharge capacity by increasing the total number of battery cells. In the battery pack 100 shown in Figures 1 and 2, the battery cells 1 are arranged in a parallel position as shown in Figure 5, but two or more cells may be connected in a vertical row and multiple battery cells in this state may be arranged in a parallel position. (Battery holder 2)

[0039] The battery holder 2 is made of thermoplastic resin such as plastic, which is an insulating material. As shown in FIG. 2, the battery holder 2 has surface plates 21 integrally molded and connected to both ends of a holding section 22 through which the battery cell 1 is inserted and held. The battery holder 2 has a battery storage section 23 formed by providing the holding section 22 on the inner side of the pair of surface plates 21 that face each other. The holding section 22 shown in FIG. 1 and FIG. 5 is tubular and conforms to the outer circumferential surface of the cylindrical battery cell 1, or is tubular with partial openings. The pair of surface plates 21 are located at both ends of the holding section 22 and are arranged in parallel to each other. The surface plates 21 are molded into a plate shape that is perpendicular to the holding section 22. The surface plates 21 are shaped to conform to the inner shape of the exterior case 4.

[0040] 2 and 5, the holding section 22 is divided into two at the axial center, and the ends of the divided holding section 22 are molded integrally with the surface plate 21 to form a pair of holder units 2A, 2B. This battery holder 2 forms a battery storage section 23 that holds the battery cell 1 in a fixed position by connecting the pair of holder units 2A, 2B with a battery cell 1 stored in the holding section 22 of each of the holder units 2A, 2B. The pair of holder units 2A, 2B are connected by a locking structure. However, the divided holder units can also be connected by screwing a set screw into a boss or by adhesive bonding.

[0041] 1 and 5, the battery holder 2 arranges multiple battery cells 1 inserted into each holding section 22 in multiple rows and columns and holds them in fixed positions. Furthermore, the battery holder 2 has lead plates 3 arranged on surface plates 21 located on both sides, and the multiple battery cells 1 held in fixed positions in the battery holder 2 are connected by the lead plates 3. On the outside of the holding sections 22, the surface plates 21 have electrode windows 24 that expose the end electrodes 1a, 1b of the battery cells 1, and the lead plates 3 are welded to the end electrodes 1a, 1b that are exposed through the electrode windows 24.

[0042] 2 and 6 has recesses 25 formed on its outer surface into which the lead plates 3 are fitted and positioned. The recesses 25 in the figures are regions in which multiple lead plates 3 are positioned, and are formed over almost the entire outer surface of the surface plate 21 except for the upper end. Furthermore, the surface plate 21 in the figures has positioning recesses 26 in the bottom surface of the recesses 25 into which the lead plates 3 are fitted. The positioning recesses 26 position the multiple lead plates 3 on the same plane at their bottom surfaces. The positioning recesses 26 are shaped to be one step lower, and insulating ribs 27 are provided at the boundaries between adjacent positioning recesses 26. The surface plate 21 positions the lead plates 3 in their fixed positions by fitting them into the positioning recesses 26.

[0043] 6 has a pair of surface plates 21 protruding upward from both ends of the holding section 22, and a board storage space 28 for storing a circuit board 6 is provided between the pair of surface plates 21. The surface plates 21 have connection windows 29 for connecting the connection parts 35 of the lead-plates 3 to the circuit board 6. The connection windows 29 are opened at the positions of the connection parts 35 of the lead-plates 3 that are disposed in the positioning recesses 26, exposing the connection parts 35 to the storage space 28. The connection parts 35 of the lead-plates 3 are disposed in the connection windows 29, and are connected to the circuit board 6 that is disposed in the storage space 28.

[0044] In the above battery holder 2, half of the holding portion 22 and the surface plate 21 are integrally molded to form holder units 2A, 2B, but the battery holder of the battery pack 100 is not limited to the above structure. The battery holder can have any other structure that can hold multiple batteries in place. (Lead plate 3)

[0045] The lead plate 3 is placed in a fixed position in a fitting structure on the bottom surface of a recess 25 provided in the surface plate 21, and is connected to the end electrodes 1a, 1b of the multiple battery cells 1. The lead plate 3 has electrode connection pieces 31 that are welded to the end electrodes 1a, 1b of the battery cells 1 exposed through the electrode window 24 of the surface plate 21 by a method such as spot welding or laser welding. A material with good electrical and thermal conductivity is used for the lead plate 3, and metal plates such as iron plates, nickel plates, copper plates, and aluminum plates with nickel or other plating on the surface are preferably used. In the battery pack 100 shown in the figures, multiple lead plates 3 are placed in the recesses 25 on both side surfaces of the battery holder 2 and connected to the end electrodes 1a, 1b of the battery cells 1.

[0046] The lead plate 3 is disposed on the surface plate 21 of the battery holder 2, and the electrode connection pieces 31 are disposed in positions facing the end electrodes 1a, 1b of the battery cell 1. One lead plate 3 is provided with multiple electrode connection pieces 31 for connection to multiple battery cells 1. As shown in the exploded perspective view of FIG. 6, the lead plate 3 is provided with electrode connection pieces 31 that protrude from a planar plate-like portion 30 toward the end electrodes 1a, 1b of the battery cell 1. The electrode connection pieces 31 protruding from the plate-like portion 30 are guided by electrode windows 24 in the surface plate 21 of the battery holder 2, and connected to the end electrodes 1a, 1b of the battery cell 1. The lead plate 3 connects the plate-like portion 30 and the electrode connection pieces 31 at connecting portions 32, and a gas permeable gap 33 is provided between the plate-like portion 30 and the electrode connection pieces 31.

[0047] The connecting portions 32 can be made thin and serve as fuses that melt when a short-circuit current flows through the battery cell 1. The lead-plate 3, with the connecting portions 32 as fuses, can melt when a short-circuit current flows through the battery cell 1, protecting the battery cell 1 from overcurrent. It is not necessary for all connecting portions 32 of the lead-plate 3 to be fuses; only the connecting portions 32 that connect the electrode connection pieces 31 connected to one of the positive and negative end surface electrodes 1a, 1b to the plate-shaped portion 30 can be used as fuses to protect the battery cell 1 from short-circuit current.

[0048] The gas permeation gap 33 in the lead plate 3 allows exhaust gas sprayed out from the exhaust valve of the battery cell 1 to pass through. The gas permeation gap 33 shown in Figures 4 and 6 is an annular slit opening 33A that runs along the outer periphery of the electrode connection piece 31. The gas permeation gap 33 allows exhaust gas sprayed out from the exhaust valve of a battery cell 1 that has experienced thermal runaway to pass smoothly through the lead plate 3 and flow into the inside of the exterior case 4.

[0049] The battery pack 100 shown in FIG. 2 has a backflow limiting layer 5 between the lead plate 3 and the inner surface of the exterior case 4 to control the flow of exhaust gas. However, in a conventional battery pack without the backflow limiting layer 5, the high-temperature exhaust gas that passes through the lead plate causes thermal runaway in battery cells located away from the thermal runaway battery cell. When the high-temperature exhaust gas passes through the gas permeable gap and flows between the lead plate and the exterior case, the exhaust gas flows along the inner surface of the exterior case and overheats the battery cells located away from the thermal runaway battery cell. The battery cells heated by the exhaust gas melt the insulating material that insulates the positive and negative electrodes of the battery cells, causing a short circuit. In a battery cell with a melted insulating material, the positive and negative electrodes are short-circuited, causing an excessive short circuit current to flow due to its own voltage, and heat is generated by the Joule heat of this short circuit current.

[0050] To prevent exhaust gas that passes through the gas permeable gaps 33 of the lead plates 3 and is ejected onto the inner surface of the exterior case 4 from causing thermal runaway in other battery cells 1, the battery pack 100 in Fig. 2 has a backflow limiting layer 5 disposed on the non-welded surface 3A of the lead plates 3 inside the exterior case 4. The lead plates 3 allow exhaust gas discharged from the exhaust valve to pass through the gas permeable gaps 33 and in the discharge direction from the battery cell 1 side to the backflow limiting layer 5. The backflow limiting layer 5 allows exhaust gas that passes through the gas permeable gaps 33 to pass in the discharge direction, but is provided with resistance sections 7 that suppress or block exhaust gas passing in the opposite direction to the discharge direction, preventing burning of battery cells 1 in distant positions.

[0051] When a battery cell 1 experiences thermal runaway, the backflow limiting layer 5 prevents the spread of fire to a distant battery cell 1 for the following reason. The high-temperature exhaust gas emitted from a thermal runaway battery cell 1 passes through the gas permeable gap 33 in the lead plate 3 in the exhaust direction by the backflow limiting layer 5. The exhaust gas discharged to the inside of the exterior case 4 then diffuses on the inner surface of the exterior case 4, attenuating its energy. The exhaust gas then diffuses on the inner surface of the exterior case 4, attenuating its energy, and flows in the reverse direction toward other battery cells 1, but is suppressed by the resistance section 7, further attenuating its energy. This makes it possible to prevent overheating of distant battery cells 1 from which the exhaust gas has reached. In battery cells 1 with a small temperature rise due to exhaust gas, the insulating material insulating the positive and negative electrodes does not melt, so the positive and negative electrodes do not short-circuit, and thermal runaway due to short-circuit current can be prevented.

[0052] 2 has lead plates 3 arranged in fixed positions on the surface plate 21 of a battery holder 2 in which multiple battery cells 1 are arranged in fixed positions, with electrode windows 24 opened in the surface plate 21 to expose the end electrodes 1a, 1b of the battery cells 1. Furthermore, this battery pack 100 connects the electrode connection pieces 31 of the lead plates 3 to the end electrodes 1a, 1b through the electrode windows 24, preventing exhaust gas emitted from a thermally runaway battery cell 1 from passing between the lead plates 3 and the battery cell 1 and flowing toward an adjacent battery cell 1, thereby preventing the spread of fire to the adjacent battery cell 1. This structure makes it possible to tightly contact the lead plates 3 with the surface plate 21 of the battery holder 2 and prevent gas leakage between them.

[0053] Furthermore, in the battery pack 100 shown in Fig. 2, the battery assembly 10 includes multiple battery cells 1, and the lead plate 3 set on the surface plate 21 has electrode connection pieces 31 that connect to the end electrodes 1a, 1b of each battery cell 1, and has gas permeable gaps 33 around each electrode connection piece 31. As shown in Fig. 6, the lead plate 3 is disposed around each electrode connection piece 31, and has multiple gas permeable gaps 33. The lead plate 3 with multiple gas permeable gaps 33 can attenuate the energy of exhaust gas that is ejected from a specific battery cell 1 and passes through the gas permeable gaps 33 in the reverse direction, thereby more effectively preventing the induction of thermal runaway.

[0054] Furthermore, the backflow limiting layer 5 shown in Figs. 2 to 5 has multiple through holes 51 that allow exhaust gas to pass smoothly in the exhaust direction. The through holes 51 are opened at a position opposite the exhaust valve side to allow exhaust gas ejected from a battery cell 1 that has experienced thermal runaway to pass through. As shown in Figs. 4 and 7, the through holes 51 are opened at a position opposite the center of the annular slit opening 33A, and a resistance portion 7 is provided that blocks the opposing position of the gas permeation gap 33 so that exhaust gas flowing in the reverse direction does not pass directly into the gas permeation gap 33. In other words, exhaust gas flowing in the reverse direction through the through holes 51 collides with the lead plate 3 and the end electrode 1a, as shown in the enlarged cross-sectional view of Fig. 8, and changes its flow direction so as to be dispersed to the surroundings before passing through the gas permeation gap 33.

[0055] The backflow limiting layer 5 shown in Figures 4 and 8 has a through hole 51 that opens facing the inside of the annular slit opening 33A, and serves as a resistance portion 7 that prevents exhaust gas flowing in the reverse direction through the through hole 51 from directly flowing into the gas permeation gap 33. The through hole 51 and the slit opening 33A in Figure 4 are circular, and the inner diameter of the through hole 51 is smaller than the inner edge of the slit opening 33A. The inner diameter of the through hole 51 is preferably 1 mm or more smaller than the inner edge of the slit opening 33A, so that it can serve as a resistance portion 7 that suppresses the passage of exhaust gas in the reverse direction.

[0056] 3 and 4, the backflow limiting layer 5 has cuts 52 extending radially from the through hole 51 so that the through hole 51 can suppress the reverse flow of exhaust gas and smoothly exhaust exhaust gas passing in the exhaust direction from the thermal runaway battery cell 1. This backflow limiting layer 5 has the feature that the inner periphery of the through hole 51 is deformed as shown in Figure 7 (the through hole 51 at the left end in the figure) by the high-temperature exhaust gas forcefully ejected from the thermal runaway battery cell 1, allowing the exhaust gas to be discharged more smoothly.

[0057] Furthermore, the backflow limiting layer 5 formed by providing cuts 52 in the through holes 51 can act as a resistance section 7 that prevents exhaust gas from passing in the reverse direction by deforming the inner periphery of the through holes 51 toward the end electrode 1a of the battery cell 1 due to the exhaust gas flowing in the reverse direction through the through holes 51, closing off the gas permeation gap 33 in the lead plate 3 or narrowing the gap, as shown by the dashed line in Figure 8. With this structure, the inner periphery of the through holes 51 deforms toward the end electrode 1a due to the pressure of the exhaust gas trying to pass through the through holes 51 in the reverse direction, closing off the gas permeation gap 33 in the lead plate 3 or narrowing the gap, thereby preventing exhaust gas flowing in the reverse direction from flowing in through the gas permeation gap 33 and preventing other battery cells 1 from burning.

[0058] As described above, the backflow limiting layer 5 with the cuts 52 in the through holes 51 allows the exhaust gas passing through the gas permeation gap 33 to pass smoothly in the exhaust direction, and suppresses or blocks the exhaust gas passing in the opposite direction to the exhaust direction, thereby preventing the spread of fire to other battery cells 1. However, the backflow limiting layer does not necessarily need to have radial cuts in the through holes. For example, even in a through hole without a cut, the gas permeation gap can be blocked or narrowed by deforming the inner periphery of the through hole toward the end surface electrode of the battery cell by the exhaust gas passing through the through hole in the opposite direction. In addition, the through holes are not necessarily required, and only radial cuts may be provided without the through holes. Even in this case, the radial cuts can be deformed by the high-temperature exhaust gas ejected from the battery cell to discharge the exhaust gas. Furthermore, in the case of the cuts, the passage of the exhaust gas from the opposite direction can be reliably suppressed.

[0059] Furthermore, the backflow limiting layer 5 is made of a rubber material with a predetermined thickness, which allows exhaust gas ejected from a thermally runaway battery cell 1 to pass through more smoothly in the exhaust direction. This is because the backflow limiting layer 5 made of a rubber material is partially burned or melted by the ejected high-temperature exhaust gas, expanding the through-holes 51 and allowing the exhaust gas to pass through more smoothly. In addition, the backflow limiting layer 5 made of a rubber material with cuts in the through-holes 51 has the characteristic of increasing deformation due to high-temperature exhaust gas, allowing the exhaust gas to pass through more smoothly in the exhaust direction.

[0060] Furthermore, the backflow limiting layer 5 made of a rubber material is melted by the high-temperature exhaust gas flowing in the reverse direction through the through-holes 51, and the molten pieces or molten debris block the gas permeation gap 33 in the lead plate 3 or narrow the gap, thereby forming the resistance portion 7 that prevents the exhaust gas from passing in the reverse direction. In this way, the backflow limiting layer 5 melted by the high-temperature exhaust gas is burned or melted by the exhaust gas passing through the gas permeation gap 33, allowing the exhaust gas to pass in the exhaust direction efficiently, and is melted by the exhaust gas passing in the opposite direction to the exhaust direction, blocking or narrowing the gas permeation gap 33 with the molten pieces or molten debris, thereby preventing the exhaust gas from flowing in through the gas permeation gap 33 and preventing the other battery cells 1 from burning.

[0061] In addition, the foamed backflow limiting layer 5 has a small heat capacity relative to its volume, so it is easily overheated and burned by the exhaust gas, and the large through holes 51 allow the exhaust gas to be discharged smoothly in the exhaust direction. The backflow limiting layer 5 made of rubber can be made of a foamed chloroprene rubber material, for example. However, the backflow limiting layer 5 made of rubber can also be made of a rubber material other than chloroprene, such as a silicone rubber foam.

[0062] The backflow limiting layer 5 is preferably bonded to the surface of the lead plate 3 via a bonding layer such as an adhesive, a pressure sensitive adhesive, or a double-sided tape. The battery pack 100 in which the backflow limiting layer 5 is bonded closely to the surface of the lead plate 3 without any gaps has the feature that exhaust gas does not leak through the gap between the lead plate 3 and the backflow limiting layer 5, and a thermal runaway battery cell 1 can reliably prevent the thermal runaway of an adjacent battery cell 1. The backflow limiting layer 5, which is bonded closely to the surfaces of the multiple lead plates 3 via a bonding layer, preferably has a non-bonded area between the lead plates 3 having a potential difference, so that the insulation resistance of the lead plates 3 having a potential difference can be kept high. This is because when the lead plates 3 having a potential difference are connected by the backflow limiting layer 5 via a bonding layer, the insulation resistance is reduced by moisture absorbed by the backflow limiting layer 5. In particular, the backflow limiting layer 5 having fine voids such as a foam is prone to absorbing moisture and decreasing electrical resistance, so it is particularly effective to provide a non-bonded area at the boundary between the lead plates 3 having a potential difference to increase the insulation resistance. [Industrial Applicability]

[0063] The battery pack according to the present invention can be suitably used as a rechargeable battery pack for battery-driven devices such as assisted bicycles, electric motorcycles, electric wheelchairs, electric carts, cleaners, and power tools. [Explanation of symbols]

[0064] 100…Battery pack 1. Battery cell 1a, 1b...end electrode 2…Battery holder 2A, 2B...Holder unit 3...Lead plate 3A: Non-welding surface 3B…Welding surface 4…Outer case 5…Reflux restriction layer 6…Circuit board 7...Resistance part 10…Battery assembly 21…Surface plate 22...Holding part 23…Battery compartment 24…Electrode window 25…Recess 26...Positioning recess 27…Insulating rib 28…Storage space 29...Connection window 30…Plate-shaped part 31...Electrode connection piece 32...Connection part 33...Gas permeation gap 33A…Slit opening 35…Connection 51...Through hole 52…Notch 101...Cylindrical battery 102...Cylinder 103…Heat conductive plate

Claims

1. a plurality of battery cells having exhaust valves on their end faces; The electrodes are parallel to each other and arranged on the same plane. a battery assembly including a lead plate and a welded surface connected to the end electrodes arranged in the same plane; a battery pack including an outer case housing the battery assembly, a backflow limiting layer disposed on the inside of the outer case and on a non-welded surface of the lead plate; The lead plate is The exhaust gas discharged from the exhaust valve, a gas permeable gap that allows gas to pass from the battery cell side in the discharge direction of the backflow limiting layer; The backflow limiting layer is The exhaust gas passing through the gas permeable gap is passed in a discharge direction, A resistance portion is provided for suppressing or preventing exhaust gas passing in a direction opposite to the exhaust direction, The backflow limiting layer is Forming a through hole for passing exhaust gas, a resistance portion for blocking a position facing the gas permeation gap around the through hole, the resistance portion being disposed adjacent the through hole;

2. 2. The battery pack according to claim 1, The battery assembly further comprises: a battery holder in which a plurality of the battery cells are arranged in fixed positions; The battery holder is a surface plate for placing the lead plate in a fixed position; The surface plate is The battery cell has an electrode window that exposes an end surface electrode of the battery cell arranged at a fixed position, a lead plate connected to the end surface electrode of the battery cell in the electrode window;

3. 3. The battery pack according to claim 2, a lead plate disposed at a fixed position on the surface plate, the lead plate having a plurality of the gas permeation gaps;

4. 4. The battery pack according to claim 3, The gas permeable gap of the lead plate is an annular slit opening, The through holes of the backflow limiting layer are The opening is opened facing the inner side of the annular slit opening, A battery pack comprising the resistor portion.

5. 5. The battery pack according to claim 3 or 4, The backflow limiting layer is The battery pack has cuts extending radially from the through hole.

6. 4. The battery pack according to claim 1, The backflow limiting layer is having radially extending cuts for allowing exhaust gas to pass therethrough; The incision is The battery pack further comprises a resistor portion that closes the gas permeable gap at a position opposite the gas permeable gap.

7. 7. The battery pack according to claim 1, The backflow limiting layer is A battery pack made of a rubber material.

8. 8. The battery pack according to claim 1, The battery pack, wherein the backflow limiting layer is made of a foam.

9. 9. A battery pack according to claim 1, The battery cell is A protruding electrode is provided on the end surface. On the outer periphery of the protruding electrode, The battery pack is characterized in that the exhaust port of the exhaust valve is open.

10. 10. The battery pack according to claim 9, The battery pack, wherein the battery cells are cylindrical batteries.

11. 11. The battery pack according to claim 1, The lead plate is A flat plate-shaped portion constituting the non-welding surface; an electrode connection piece that constitutes the welding surface and is connected to the end surface electrode of the battery cell; a slit opening that constitutes the gas permeable gap is provided along an outer periphery of the electrode connection piece.

12. 12. A battery pack according to any one of claims 1 to 11, The backflow limiting layer is A battery pack characterized in that the lead plate is joined to a surface of the lead plate.

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