Battery pack

Abstract

The present invention makes it possible to safely discharge gas to the outside even when the gas is discharged from a secondary battery cell. This battery pack 100 comprises: a battery block 20 composed of a plurality of secondary battery cells 1 in which a gas discharge part 1c is provided on a cell end surface 1a; and an exterior case 10 that stores the battery block 20 in an internal storage space and comprises a cylindrical case body, which is open in at least one direction, and a case lid part 12 for closing the open end of the case body. The case lid part 12 comprises: a gas discharge port 13 opened in order to discharge gas to the outside when the gas is discharged from the gas discharge part 1c; and a plate-like refractory material 30 having heat resistance and disposed, on the inner surface of the case lid part 12, between the battery block 20 and the case lid part 12. The refractory material 30 is installed on a central part of the inner surface of the case lid part 12 such that there is a gap between the refractory material and the inner surface, and forms a gas discharge path 18 through which gas discharged from the gas discharge part 1c flows from the vicinity of the refractory material 30 to the gas discharge port 13 via the gap.

Description

Battery Pack

[0001] The present disclosure relates to a battery pack.

[0002] Battery packs using rechargeable secondary battery cells such as lithium-ion secondary cells are used in a wide range of applications, including battery packs for supplying electric power to drive electric bicycles and electric motorcycles. Such a battery pack is configured by inserting a battery block called a core pack, in which a plurality of secondary battery cells are connected in series or in parallel, into an outer case. In recent years, in order to meet the demand for higher capacity and higher output of battery packs, secondary battery cells with high energy density have been used in such battery packs. As a result, high safety measures structures are required in preparation for the event that any one of the plurality of secondary battery cells undergoes thermal runaway. When a secondary battery cell undergoes thermal runaway, gas is released from the outer can of the secondary battery cell. Such gas is at high temperature and can cause ignition. Against this background, in order to avoid ignition outside the battery pack, configurations using a metal case for the outer case and designing a long gas exhaust passage have been considered.

[0003] However, the use of a metal case increases the weight of the battery pack. Furthermore, lengthening the gas exhaust passage increases the overall length of the battery pack. As a result, there are constraints on the allowable weight and size of the battery pack, and the increase in size of the battery pack leads to a problem that the energy density of the battery pack itself decreases.

[0004] Japanese Unexamined Patent Application Publication No. 2019-029086

[0005] One object of an embodiment of the present disclosure is to provide a battery pack that can safely discharge gas to the outside if gas is released. Another object of another embodiment is to provide a battery pack with improved safety while avoiding structural complication. The description of these objects and problems in the present disclosure does not preclude the existence of other objects and problems. In addition, it is not necessary for one aspect of the present disclosure to solve all of these problems. Furthermore, other problems can be extracted from the descriptions of the specification, drawings, and claims of the present disclosure.

[0006] A battery pack according to one embodiment of the present disclosure comprises a battery block composed of a plurality of secondary battery cells, each having a gas discharge section on its end face for discharging gas when the internal pressure rises; and an outer case that houses the battery block in an internal storage space, the outer case comprising a cylindrical case body with at least one end open and a case lid that closes the open end of the case body, wherein the case lid has a gas outlet that is opened to release gas to the outside when gas is discharged from the gas discharge section, and a heat-resistant plate-shaped fire-resistant material positioned on the inner surface of the case lid between it and the battery block, the fire-resistant material being installed in the center of the inner surface of the case lid with a gap between it and the inner surface, forming a gas discharge path that directs the gas discharged from the gas discharge section from around the fire-resistant material through the gap to the gas discharge section.

[0007] According to one embodiment of the battery pack described herein, when gas is emitted from a portion of the secondary battery cells, the fire-resistant material placed in the storage space prevents the gas from directly irradiating the case lid. Furthermore, by having multiple sections of the case wall intersect with the gas moving from around the fire-resistant material towards the gas outlet, the force of the gas is weakened, the temperature is reduced, and the gas can be safely released from the internal space to the outside of the outer case.

[0008] This is a perspective view showing a battery pack according to an embodiment. This is a cross-sectional view of the battery pack in Figure 1 along line II-II. This is a cross-sectional view of the battery pack in Figure 1 along line III-III. This is an exploded perspective view of the battery pack in Figure 1. This is an exploded perspective view of the battery pack in Figure 4 viewed from the rear side. This is a cross-sectional view of the first lid along line VI-VI in Figure 4. This is a plan view showing a cross-section along line VII-VII in Figure 6. This is a plan view showing a cross-section along line VIII-VIII in Figure 6. This is a cross-sectional view of the case lid along line IX-IX in Figure 1.

[0009] The form of this disclosure may be specified by the following configurations and features.

[0010] In another embodiment of the present disclosure, a battery pack is provided in which, in the above embodiment, a plurality of case walls are formed on the inner surface of the case lid, projecting in a direction opposite to the battery block, the gap is formed by the fire-resistant material being supported by the plurality of case walls, and the plurality of case walls are arranged to surround the gas outlet. With this configuration, the gas released from the secondary battery cell is interfered with by the plurality of case walls before being discharged from the gas outlet, and the temperature of the gas is reduced each time, thereby improving safety in the event of runaway overheating.

[0011] In addition, in any of the above embodiments, the battery packs relating to other embodiments of this disclosure have the plurality of case walls arranged in an annular manner around the gas outlet.

[0012] Furthermore, in any of the above embodiments, the battery packs relating to other embodiments of this disclosure have the plurality of case walls arranged concentrically around the gas outlet.

[0013] Furthermore, in other embodiments of the present disclosure, the battery pack in any of the above embodiments has an uneven surface formed on at least a portion of each of the plurality of case walls. With this configuration, when the gas released from the secondary battery cell flows over the surface of the case wall, powders and other particles contained in the gas are trapped in the uneven surface, and the amount of powder contained in the gas is reduced when it is discharged from the outer case, thereby suppressing the generation of flames due to the combustion of such powders and enhancing safety.

[0014] Furthermore, in other embodiments of the present disclosure, the battery pack is configured such that, in any of the above embodiments, the fire-resistant material is positioned on the block end face of the battery block, covering the gas discharge portion provided on the cell end face of the secondary battery cell located on the block end face of the battery block. With this configuration, even if gas is released from any of the secondary battery cells located on the block end face of the battery block, the fire-resistant material positioned to cover the gas discharge portion provided on the cell end face prevents the gas from directly irradiating the cell end face. The heat-resistant fire-resistant material weakens the force of the gas and guides it to the cell end face, thereby preventing damage to the cell end face and enhancing safety.

[0015] Furthermore, in other embodiments of the present disclosure, the outer shape of the fire-resistant material is formed to be slightly smaller than the inner surface of the case lid, thereby creating a gap between the inner surface of the case lid and the periphery of the fire-resistant material. With this configuration, when gas is discharged from a part of the secondary battery cell, the gas is first dispersed around the fire-resistant material, then allowed to flow around to the back side of the fire-resistant material through the gap, and then discharged from the gas outlet. This increases the distance the gas released from the secondary battery cell travels before being discharged from the outer case, reducing its temperature as it travels, preventing the discharge of high-temperature metal powder, and improving safety.

[0016] Furthermore, in any of the above embodiments, the battery pack is a mica sheet material in which the fire-resistant material is.

[0017] Furthermore, in any of the above embodiments, the battery pack is made of resin.

[0018] Furthermore, in other embodiments of the present disclosure, the battery pack, in any of the above embodiments, comprises an outer case comprising a pair of case lids and a cylindrical case body connecting the pair of case lids, wherein the case body is made of metal. With this configuration, it is possible to increase rigidity by making the case body constituting the side portion of the outer case out of metal, while reducing weight by making the case lids out of resin, and maintaining safety when gas is released.

[0019] Furthermore, in any of the above embodiments, the battery pack comprises an outer casing comprising: a cylindrical case body with at least one opening; a first lid portion having a first lid surface facing the block end face of the battery block and closing the open end of the case body, and a first lid second surface opposite to the first lid surface, and having a first gas outlet opening; and a second lid portion having a second lid surface that overlaps with the first lid portion and facing the first lid second surface of the first lid portion, and a second lid second surface opposite to the second lid surface, and having a second gas outlet opening that communicates with the first gas outlet, wherein the second lid portion forms part of the gas discharge path, and a gas discharge path is defined between the second lid surface and the first lid surface for guiding the gas discharged from the first gas outlet to the second gas outlet, and the gas discharge path is provided with a gas flow obstruction structure that changes the direction of gas flow from the first gas outlet to the second gas outlet. With the above configuration, the case lid of the outer casing is doubled up into a first lid and a second lid, and a gas discharge path is defined between these first and second lids. By inhibiting the force of the gas moving through this gas discharge path with a gas flow inhibiting structure, the gas can be discharged to the outside of the battery pack under reduced pressure, thereby enhancing safety.

[0020] Furthermore, in any of the above embodiments, the battery pack according to other embodiments of the present disclosure comprises a gas flow inhibiting structure defined by a first lid wall portion protruding from the second surface of the first lid of the first lid and a second lid wall portion protruding from the first surface of the second lid of the second lid.

[0021] Furthermore, in any of the above embodiments, the battery pack is configured such that the first lid wall and the second lid wall surround the first gas outlet.

[0022] The embodiments of this disclosure will be described below with reference to the drawings. However, the embodiments shown below are examples for concretizing the technical concept of this disclosure, and this disclosure is not limited to the following. Furthermore, this specification does not limit the members shown in the claims to the members of the embodiments. In particular, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments are not intended to limit the scope of this disclosure to those, unless specifically stated otherwise, but are merely illustrative examples. Note that the size and positional relationships of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, in the following description, the same name and reference numerals indicate the same or similar members, and detailed explanations are omitted as appropriate. Furthermore, each element constituting this disclosure may be configured such that multiple elements are made of the same member, with one member serving multiple elements, or conversely, the function of one member may be shared among multiple members.

[0023] The battery pack disclosed herein can be used as a power source for portable electrical equipment such as power tools and electric cleaners, as a power source for mobile devices such as electric carts, electric scooters, and electric assist bicycles, as a backup power source for servers or as a battery pack for home, business, and factory use in stationary energy storage applications, and as a power source for vehicles such as hybrid cars and electric vehicles. Hereinafter, an embodiment of the present invention will be described as a battery pack used as a power source for power tools. [Embodiment 1]

[0024] Figures 1 to 8 show a battery pack 100 according to Embodiment 1 of the present disclosure. In these figures, Figure 1 is a perspective view showing the battery pack 100 according to the embodiment, Figure 2 is a cross-sectional view of the battery pack 100 in Figure 1 along line II-II, Figure 3 is a cross-sectional view of the battery pack 100 in Figure 1 along line III-III, Figure 4 is an exploded perspective view of the battery pack 100 in Figure 1, Figure 5 is an exploded perspective view of the battery pack 100 in Figure 4 viewed from the rear side, Figure 6 is a cross-sectional view of the first lid along line VI-VI in Figure 4, Figure 7 is a plan view showing the cross-section along line VII-VII in Figure 6, and Figure 8 is a plan view showing the cross-section along line VIII-VIII in Figure 6. The battery pack 100 shown in these figures comprises an outer case 10, a battery module 2, a fire-resistant material 30, and a circuit board 3. (Outer case 10)

[0025] The outer casing 10 is a component for housing the battery module 2. The outer casing 10 can have any shape that provides internal storage space. The outer casing 10 may also house other components, such as a circuit board 3, within its storage space. In the examples shown in Figures 1 to 4, the outer casing 10 is formed in a box shape with its exterior extended in one direction. The box-shaped outer casing 10 comprises a cylindrical case body 11 and case lids 12 that close the cylindrical end faces of the case body 11. However, this disclosure is not limited to this configuration. For example, the outer casing may be a bottomed cylinder, divided into two sections with only one open end closed by a case lid, or divided into four or more sections. The case body may also be divided vertically or horizontally. The divided outer casings are waterproofed by a waterproof structure. (Case body 11)

[0026] The case body 11 is formed in a cylindrical shape with at least one end open. Preferably, this case body 11 is made of a metal such as aluminum or an alloy thereof. This allows for increased rigidity by using a metal case body 11 that constitutes the side portion of the outer case 10, while maintaining safety when gas is released, and reducing weight by using a resin case lid 12. However, the outer case 10 may also be made of a material with excellent insulating properties, such as polycarbonate or a resin such as PC-ABS alloy. Furthermore, the inside of the outer case 10 is provided with an internal space for housing the battery module 2 and the circuit board 3, as shown in Figures 2 and 3. (Case lid 12)

[0027] The case lid 12 closes the open end of the case body 11. The case lid 12 is preferably made of a resin such as polycarbonate or PC-ABS alloy. (Gas outlet 13)

[0028] Furthermore, the outer casing 10 has a gas outlet 13 in at least one of its lid portions 12 to release gas to the outside of the outer casing 10 in the event that gas is discharged from the gas discharge portion 1c of either of the secondary battery cells 1. The gas outlet 13 is preferably located in the central region of the lid portion 12.

[0029] In the examples shown in Figures 4 and 5, the left-side case lid 12' is formed integrally, while the left-side case lid 12 is composed of a first lid 12A and a second lid 12B. However, this disclosure is not limited to this configuration, and the case lid 12 may be composed of only the first lid 12A. (First lid 12A)

[0030] The first lid portion 12A and the second lid portion 12B are superimposed to form the case lid portion 12. As shown in the cross-sectional view of Figure 6, the first lid portion 12A has a first lid surface 12A1 that closes the open end of the case body 11 and faces the block end surface 21 of the battery block 20, and a first lid second surface 12A2 that is opposite to the first lid surface 12A1. At the interface between the first lid portion 12A and the case body 11, members such as connectors and gaskets may be interposed as needed. In the example of Figure 6, the fitting wall portion of the first lid portion 12A that faces the periphery of the open end of the case body 11 is formed to protrude in a frame shape from the outer circumference of the first lid surface 12A1, and a frame-shaped sealing member 40 is installed on the outer circumference of the fitting wall portion of the first lid portion 12A. The open end of the case body 11 is then liquid-tightly closed by the sealing member 40. The first lid portion 12A also has an opening for the first gas outlet 13A. If the case lid 12 is composed only of the first lid 12A, the first gas outlet 13A becomes the gas outlet 13. (Second lid 12B)

[0031] The second lid 12B is superimposed on the first lid 12A and comprises a first surface 12B1 of the second lid facing the second surface 12A2 of the first lid 12A, and a second surface 12B2 of the second lid opposite to the first surface 12B1. The second lid 12B also has an opening for a second gas outlet 13B that communicates with the first gas outlet 13A. (Battery module 2)

[0032] The battery module 2, also called a core pack, houses multiple secondary battery cells 1. Alternatively, the battery module 2 may be composed of one or more battery blocks 20, with each battery block 20 housing multiple secondary battery cells 1. In the examples in Figures 2 and 4, the battery module 2 is constructed by connecting four battery blocks 20, each housing seven secondary battery cells 1 in a stacked configuration, in a horizontal direction. A circuit board 3 is placed on the bottom surface of the battery module 2.

[0033] Furthermore, within the storage space of the outer case 10, the battery module 2 has its end face facing the inner surface of the case lid 12. Specifically, among the multiple battery blocks 20 that make up the battery module 2, the end face 21 of the battery block 20 located at the end faces the inner surface of the case lid 12. (Battery holder 22)

[0034] Each battery block 20 comprises a battery holder 22, a secondary battery cell 1, and a lead plate 5. As shown in Figures 4 and 5, the battery holder 22 has multiple cylindrical holder sections 23, into which the secondary battery cell 1 is inserted and held. The battery holder 22 can house all the secondary battery cells 1 as a single unit, or it may be divided into multiple sub-holders, with some of the secondary battery cells housed in the sub-holders. Alternatively, the battery holder may be divided along the length of the secondary battery cell. In the example shown in Figures 4 and 5, the secondary battery cell 1 is housed in the holder section 23 by a sub-holder divided into two along the length of the secondary battery cell 1, sandwiching it from each cell end face 1a. Such a battery holder 22 is made of a material with excellent insulating properties. Preferably, it is made of a resin such as polycarbonate or PC-ABS alloy. (Lead plate 5)

[0035] The battery block 20 also includes lead plates 5 for electrically connecting the secondary battery cells 1 to each other. The lead plates 5 are preferably arranged on the outer side of the battery holder 22. The lead plates 5 are electrically connected to the terminals of the secondary battery cells 1 that are exposed through electrode windows opened in the battery holder 22. Each lead plate 5 connects the electrodes on the cell end faces 1a of the secondary battery cells 1, thereby connecting multiple secondary battery cells 1 together. The lead plates 5 are made of metal plates with excellent conductivity, such as aluminum plates, nickel plates, or copper plates. Multiple secondary battery cells 1 are connected in series or parallel via the lead plates 5. The number of series connections and parallel connections can be arbitrarily set according to the required specifications. In the example shown in Figure 4, each lead plate 5 mainly connects the end faces of 28 secondary battery cells 1, and the four battery blocks 20 as a whole connect the secondary battery cells 1 in 4 series x 7 parallel configurations. However, the number of secondary battery cells and the connection configuration, i.e., the number of series and parallel connections, are not limited to this configuration.

[0036] In addition to lead plates, busbars can also be used. In the example shown in Figure 5, a busbar 6 is provided to connect the total output of the battery module 2 to the case lid 12. (Circuit board 3)

[0037] The battery block 20 is connected to the circuit board 3 via lead plates 5. The circuit board 3 implements a charge / discharge circuit for charging and discharging the secondary battery cell 1, and a protection circuit that monitors the voltage and temperature of the secondary battery cell 1 and cuts off the current in case of abnormalities. The circuit board 3 is made of a glass epoxy substrate or the like. A substrate holder may also be provided as a component to hold the circuit board 3.

[0038] In the examples shown in Figures 2 and 3, the circuit board 3 is placed on the bottom surface of the battery module 2. However, the disclosure is not limited to this configuration, and a single circuit board may be placed on the top or side surface of the battery module. Furthermore, multiple circuit boards may be provided, or the circuit board may be divided for each battery block. (Secondary battery cell 1)

[0039] Each battery block 20 houses a secondary battery cell 1 within a battery holder 22, as shown in Figures 2 to 4. The secondary battery cell 1 can be a cylindrical or rectangular cell. In the examples shown in Figures 2 to 3, a secondary battery cell 1 with a cylindrical outer casing is used, arranged horizontally in a staggered pattern. The number and arrangement of the secondary battery cells 1 are not limited to this example; any number and arrangement can be used as appropriate. For example, cylindrical secondary battery cells may be arranged in a matrix. The secondary battery cell 1 can be any known secondary battery, such as a lithium-ion battery, nickel-metal hydride battery, or nickel-cadmium battery.

[0040] Each secondary battery cell 1 has a positive electrode and a negative electrode. The terminals of the positive or negative electrode are preferably provided on one cell end face 1a of the secondary battery cell 1. In the example shown in Figure 2, the positive electrode terminal is provided on one cell end face 1a of the secondary battery cell 1, and the other side of the outer casing is used as the negative electrode.

[0041] Furthermore, each secondary battery cell 1 is provided with a gas discharge section 1c on its outer casing. The gas discharge section 1c releases gas from inside the outer casing to the outside when the internal pressure of the outer casing rises. The gas discharge section 1c is provided on one of the cell end faces 1a of the secondary battery cell 1. In the example shown in Figure 2, the gas discharge section 1c is provided on the first cell end face, which is the positive electrode side of the secondary battery cell 1. Such a gas discharge section 1c can be configured as a gas discharge valve that opens in response to an increase in the internal pressure of the outer casing.

[0042] The battery holder 22 stacks a plurality of secondary battery cells 1 in a plurality of stages in the vertical direction in a posture where the end face 1a of each cell is coplanar. Further, in the vertical direction of the plurality of stages, the cell end faces 1a of adjacent secondary battery cells 1 are arranged in an offset manner with their circular centers shifted from each other. As a result, the assembly of the plurality of secondary battery cells 1 housed in the battery block 20 is arranged flat on the upper and lower surfaces, while has an uneven shape on the side surface where the centers of the respective cell end faces 1a are shifted. For this reason, as shown in Fig. 3, the side surface of the battery holder 22 is curved along the outer shape of the outer can of the secondary battery cell 1. (Refractory material 30)

[0043] The refractory material 30 is disposed between the inner surface of the case lid portion 12 and the block end face 21 of the battery block 20 as shown in Fig. 5 in the housing space of the outer case 10. The refractory material 30 is made of a material having heat resistance that does not melt even when exposed to high-temperature gas. Further, the refractory material 30 is formed in a plate shape. An inorganic material can be used for such a refractory material 30. Preferably, a sheet material made of mica can be used. In addition, a metal plate, ceramic, enamel, etc. can also be used as the refractory material 30. Further, the thickness of the refractory material 30 is 0.5 mm to 2.0 mm, preferably 0.8 mm to 1.0 mm.

[0044] The refractory material 30 is disposed to face the block end face 21 of the battery block 20, and is arranged in a posture to cover the gas discharge portion 1c provided on the cell end face 1a of the secondary battery cell 1 located on the block end face 21 of the battery block 20. With such a configuration, even if gas is discharged from any of the secondary battery cells 1 located on the block end face 21 of the battery block 20, the refractory material 30 arranged to cover the gas discharge portion 1c provided on the cell end face 1a can avoid a situation where the gas directly irradiates the cell end face, and guides the gas to the cell end face 1a in a state where the momentum of the gas is weakened by the heat-resistant refractory material 30, thereby avoiding damage to the cell end face 1a and improving safety.

[0045] As shown in Figure 5, the fire-resistant material 30 is provided with multiple positioning holes 32 for positioning. The first lid portion 12A is provided with guide pins 16 for insertion into the positioning holes 32. Furthermore, in the example shown in Figure 5, a busbar connection portion 17 for connecting a busbar 6 that brings the output of the battery module 2 to the outside is provided on the first surface 12A1 of the first lid portion 12A of the case lid portion 12. To connect this busbar connection portion 17 to the busbar 6, the fire-resistant material 30 has an opening for connection holes 33. These connection holes 33 can also be used for positioning the fire-resistant material 30. (Gap space 35)

[0046] Furthermore, the fire-resistant material 30 is installed in the center of the first surface 12A1 of the first lid, which is the inner surface of the first lid 12A of the case lid 12, with a gap between it and the first surface 12A1. By forming the outer shape of the fire-resistant material 30 to be slightly smaller than the inner surface of the case lid 12, a gap space 35 can be created between the inner surface of the case lid 12 and the periphery of the fire-resistant material 30, as shown in Figures 6 and 7. With this configuration, as shown in Figure 6, if gas is discharged from a part of the secondary battery cell 1, the fire-resistant material 30 placed in the storage space prevents the gas from being directly released to the outside at high temperature and pressure through the gas outlet 13 of the case lid 12. In addition, by first dispersing the gas around the fire-resistant material 30 and allowing it to flow through the gap space 35 into the gap between the inner surface of the case lid 12 on the back side of the fire-resistant material 30 and the fire-resistant material 30, and then discharging it from the gas outlet 13, the distance over which the gas discharged from the secondary battery cell 1 is discharged from the outer case 10 can be increased. As a result, by diverting the gas through the gap space 35 and then discharging it from the gas outlet 13, the pressure and temperature of the gas can be reduced as it progresses, and the risk of ignition is reduced when the gas is discharged from the gas outlet 13, thereby improving safety. In particular, when the case lid is made of resin, if the high temperature and pressure of the gas are blown directly onto the case lid, the possibility of damage increases. Therefore, by protecting the case lid 12 with fire-resistant material 30 and further increasing the path length to the gas discharge, the temperature and pressure of the gas can be reduced to a level that prevents damage even to resin cases.

[0047] Furthermore, in the present disclosure, when gas is discharged from the gas discharge portion 1c from some of the plurality of secondary battery cells 1 included in the battery pack 100, it is intended to suppress a situation in which flame erupts from the outer case 10. It is desirable to design the specification such that flame does not leak from the outer case 10 even when gas is discharged from a secondary battery cell located on the block end face 21 side facing the inner surface of the case lid 12, where the pressure and temperature of the gas are considered to be highest. This is because with such a specification, even if gas is discharged from a secondary battery cell not facing the block end face 21, it is assumed that the pressure and temperature of the gas will be relatively low. (Case wall portion 14)

[0048] Furthermore, the case lid portion 12 is formed with a plurality of spaced apart case wall portions 14 protruding from the inner surface toward the battery block 20 in an orientation intersecting the direction from the periphery of the refractory material 30 toward the gas discharge port 13. The plurality of case wall portions 14 support the refractory material 30, and a gap is formed between the inner surface of the case lid portion 12 and the refractory material 30. In addition, the refractory material 30 is disposed at the central portion of the inner surface of the case lid portion 12, and a gap space 35 is formed around the refractory material 30. With such a configuration, when gas is discharged from a part of the secondary battery cells 1, in addition to avoiding a situation where the gas is directly blown onto the case lid portion 12 by the refractory material 30 disposed in the accommodation space, a gas discharge path 18 from the periphery of the refractory material 30 toward the gas discharge port 13 is formed. By the labyrinth structure formed by the plurality of case wall portions 14 in the middle of the gas discharge path 18, intersecting the plurality of case wall portions 14 with respect to the gas passing through the gas discharge path 18 lengthens the flow path of the gas, weakens the momentum of the gas, lowers the temperature, and achieves a safer state. Note that the thick arrows shown in FIGS. 6 to 8 indicate the flow of gas traveling along the gas discharge path 18.

[0049] Furthermore, as shown in FIGS. 5 and 8, it is preferable that the plurality of case wall portions 14 are arranged so as to surround the periphery of the gas discharge port 13. As a result, before the gas discharged from the secondary battery cell 1 is discharged from the gas discharge port 13, the gas is interfered with by the plurality of case wall portions 14, its momentum is weakened each time, and the gas is discharged from the gas discharge port 13 in a state where the pressure is reduced, thereby improving safety during thermal runaway.

[0050] It is preferable that multiple case wall portions 14 are arranged in a ring around the gas outlet 13. More preferably, multiple case wall portions 14 are arranged concentrically around the gas outlet 13. As shown in Figures 5 to 8, the multiple case wall portions 14 are formed in a partial arc shape that constitutes concentric circles of different radii. By making them partial arc shapes, the case wall portions 14 of different radii are arranged so that they overlap the area where the ring is cut out. This causes the gas to be obstructed by the case wall portions 14, and the gas that passes over these case wall portions 14 through the cut-out area is further obstructed by other case wall portions 14, resulting in the gas traveling around multiple case wall portions 14. This causes a pressure loss in the gas, simultaneously lowers the temperature, lengthens the path the gas travels to the outlet, and reduces the gas's force and temperature to a safe level.

[0051] In addition, it is preferable to form irregularities 15 on the surface of each of the multiple case wall portions 14. This allows flammable materials such as powder contained in the gas to be trapped in the irregularities 15 as the gas released from the secondary battery cell 1 flows over the surface of the case wall portion 14, thereby reducing the amount of powder contained in the gas when it is discharged from the outer case 10. This suppresses the generation of flames due to the combustion of such powder and enhances safety. (Gas flow inhibiting structure 19)

[0052] In the event that gas is discharged from the gas discharge port 1c of any of the secondary battery cells 1, the outer casing 10 allows the gas to be discharged through the first gas discharge port 13A of the first lid 12A and then through the second gas discharge port 13B of the second lid 12B, as shown in the cross-sectional view of Figure 9. The second lid 12B also defines a gas discharge path 18 between the first surface 12B1 of the second lid and the second surface 12A2 of the first lid, which guides the gas discharged from the first gas discharge port 13A to the second gas discharge port 13B. The gas discharge path 18 is provided with a gas flow obstruction structure 19 that changes the direction of gas flow from the first gas discharge port 13A to the second gas discharge port 13B. This allows for the creation of a gas discharge path 18 between the first lid 12A and the second lid 12B by utilizing the space created when the case lid 12 of the outer case 10 is doubled up, and by inhibiting the force of the gas moving through this gas discharge path 18 with the gas progress inhibiting structure 19, the gas can be discharged to the outside of the battery pack 100 in a reduced pressure state, thereby enhancing safety.

[0053] Furthermore, the gas advance obstruction structure 19 is defined by a first lid wall portion protruding from the second surface 12A2 of the first lid portion 12A, and a second lid wall portion protruding from the first surface 12B1 of the second lid portion 12B. It is preferable to arrange the first lid wall portion and the second lid wall portion so as to surround the first gas outlet 13A.

[0054] In the above example, for illustrative purposes, the fire-resistant material 30 and case wall 14 near the gas outlet 13 on the left case lid 12 in Figure 1 have been described. However, it goes without saying that a similar gas outlet may be provided on the right case lid 12, and fire-resistant material and case wall may also be provided near it. In particular, it is preferable to provide such fire-resistant material 30 and case wall 14 on the case lid 12 that faces the cell end face 1a of the secondary battery cell that has the gas outlet 1c. In other words, for example, in the case lid 12 on the right side of Figure 1, if only the cell end face of a secondary battery cell without a gas outlet faces the block end face that faces the inner surface of this case lid 12, then it is not necessary to provide such fire-resistant material or case wall.

[0055] In the above example, the battery pack is attached to the electrical device to be powered, and power is supplied to the electrical device. When the remaining capacity of the battery pack becomes low or the battery pack deteriorates over time, the battery pack can be replaced, allowing the electrical device to continue to be used. However, the present invention is not limited to replaceable battery packs that mainly house secondary battery cells, but can also be applied to configurations in which secondary battery cells are housed within the casing of the electrical device. In this disclosure, a battery pack is defined as a device in which secondary battery cells are housed within a case, and also includes devices in which the secondary battery cells for driving are built into the casing of the electrical device itself. In other words, the present invention is not limited to replaceable battery packs, but can also be applied to electrical devices that have built-in secondary battery cells.

[0056] The battery pack disclosed herein can be suitably used as a power source for electric assist bicycles, as well as for self-propelled delivery robots, electric carts for delivery and golf courses, electric scooters, construction machinery, hybrid vehicles, and electric vehicles. It can also be used as a power source for portable electrical equipment such as wireless devices, electric cleaners, and power tools. Furthermore, it can be applied not only to power sources but also to cooling mechanisms for electrical equipment containing heat-generating elements. Alternatively, it can be used for stationary energy storage devices, such as battery packs for homes, businesses, and factories, or as backup power sources for servers.

[0057] 100...Battery pack 1...Secondary battery cell; 1a...Cell end face; 1c...Gas outlet 2...Battery module 3...Circuit board 5...Lead board 6...Bus bar 10...Outer case 11...Case body 12, 12'...Case lid; 12A...First lid; 12A1...First surface of first lid; 12A2...Second surface of first lid 12B...Second lid; 12B1...First surface of second lid; 12B2...Second surface of second lid 13...Gas outlet; 13A...First gas outlet; 13B...Second gas outlet 14...Case wall 15...Rubbered part 16...Guide pin 17...Bus bar connection part 18...Gas outlet path 19...Gas flow obstruction structure 20...Battery block 21...Block end face 22...Battery holder 23...Holder cylinder part 30...Fireproof material 32...Positioning hole 33...Connection hole 35... Gap space 40... Sealing material

Claims

1. A battery pack comprising: a battery block composed of a plurality of secondary battery cells, each having a gas discharge section on its end face for discharging gas when the internal pressure rises; and an outer case that houses the battery block in an internal storage space, the outer case comprising a cylindrical case body with at least one end open and a case lid that closes the open end of the case body, wherein the case lid has a gas outlet that is opened to release gas to the outside when gas is discharged from the gas discharge section; and a heat-resistant plate-shaped fire-resistant material positioned between the case lid and the battery block on the inner surface of the case lid, the fire-resistant material being installed in the center of the inner surface of the case lid with a gap between it and the inner surface, forming a gas discharge path that directs the gas discharged from the gas discharge section from around the fire-resistant material through the gap to the gas discharge section.

2. A battery pack according to claim 1, wherein a plurality of case walls are formed on the inner surface of the case lid, projecting in a direction opposite to the battery block, the gap is formed by the fire-resistant material being supported by the plurality of case walls, and the plurality of case walls are arranged to surround the gas outlet.

3. A battery pack according to claim 2, wherein the plurality of case walls are arranged in an annular manner around the gas outlet.

4. A battery pack according to claim 2, wherein the plurality of case walls are arranged concentrically around the gas outlet.

5. A battery pack according to any one of claims 2 to 4, wherein each of the plurality of case walls has an uneven surface formed on at least a part of its surface.

6. A battery pack according to any one of claims 2 to 4, wherein the fire-resistant material is arranged in a manner that covers the gas discharge portion provided on the cell end face of a secondary battery cell located on the block end face of the battery block, while being positioned on the block end face of the battery block.

7. A battery pack according to claim 6, wherein the outer shape of the fire-resistant material is formed to be slightly smaller than the inner surface of the case lid, and a gap is provided between the inner surface of the case lid and the periphery of the fire-resistant material.

8. A battery pack according to any one of claims 1 to 4, wherein the fire-resistant material is a mica sheet material.

9. A battery pack according to any one of claims 1 to 4, wherein the case lid is made of resin.

10. A battery pack according to claim 9, wherein the outer case comprises a pair of case lids and a cylindrical case body connecting the pair of case lids, and the case body is made of metal.

11. A battery pack according to any one of claims 1 to 4, wherein the outer case comprises: a cylindrical case body with at least one end open; a first lid portion having a first lid first surface facing the block end surface of the battery block and closing the open end of the case body, and a first lid second surface opposite to the first lid first surface, and having a first gas outlet open; a second lid portion having a second lid first surface facing the first lid second surface of the first lid portion and a second lid second surface opposite to the second lid first surface, which overlaps with the first lid portion, and having a second gas outlet open that communicates with the first gas outlet, wherein the second lid portion forms part of the gas discharge path, and a gas discharge path is defined between the second lid first surface and the first lid second surface for guiding the gas discharged from the first gas outlet to the second gas outlet, and the gas discharge path is provided with a gas flow obstruction structure that changes the direction of gas flow from the first gas outlet to the second gas outlet.

12. A battery pack according to claim 11, wherein the gas advance inhibiting structure is defined by a first lid wall portion protruding from the second surface of the first lid of the first lid, and a second lid wall portion protruding from the first surface of the second lid of the second lid.

13. A battery pack according to claim 12, wherein the first lid wall and the second lid wall are arranged to surround the first gas outlet.

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