Battery pack and method for manufacturing same

Abstract

A battery pack 100 includes: one or more secondary battery cells 1 each including an outer can having a cylindrical cell side surface 1b and a pair of cell end surfaces 1c forming the end surfaces of the cell side surface, with a gas discharge portion that opens in response to an increase in the internal pressure of the outer can being provided in at least one of the cell end surfaces; and a battery holder 20 having one or more accommodating cylinders 25 that respectively accommodate the one or more secondary battery cells 1. The battery holder 20 comprises: a first holder 21 including first accommodating cylinders 26 for accommodating a portion of each of the secondary battery cells 1; and a second holder 22 including second accommodating cylinders 27 for accommodating another portion of each of the secondary battery cells 1. The battery holder 20 is configured so as to cover the cell side faces 1b in a state in which the first holder 21 and the second holder 22 are joined so that each first accommodating cylinder 26 and each second accommodating cylinder 27 constituting portions of each accommodating cylinder 25 are aligned with one another, and the first holder 21 and the second holder 22 are molded from a thermosetting resin.

Description

Battery Pack and Method for Manufacturing the Same

[0001] The present disclosure relates to a battery pack and a method for manufacturing a battery pack.

[0002] A battery pack in which a plurality of rechargeable secondary battery cells such as lithium-ion secondary battery cells are connected in series or in parallel is used as a power source for electrical equipment. With the recent demands for higher output and higher capacity of power supply devices, the capacity per secondary battery cell tends to increase. Also, the number of secondary battery cells used in a power supply device tends to increase.

[0003] On the other hand, the interior of the outer can of a secondary battery cell may become high-pressure due to some abnormality. Therefore, a gas discharge portion that opens in response to an increase in internal pressure is provided in the outer can, and when the internal pressure rises, the gas discharge portion is opened to discharge the high-temperature and high-pressure gas inside the outer can from the outer can. In the case of a cylindrical secondary battery cell having a cylindrical outer can, such a gas discharge portion is generally provided on one of the pair of end faces on the side surface of the cylindrical cell.

[0004] However, for example, if the internal pressure of the outer can rises rapidly, the gas discharge portion does not operate normally, or there is a blockage at the opening of the gas discharge portion, etc., and the decompression is insufficient for some reason, before the gas discharge portion operates, the side surface of the cell of the outer can may rupture, and a phenomenon called side rupture may occur, such as ignition occurring from there. Generally, a battery pack is provided with measures to safely discharge the high-temperature and high-pressure gas discharged from the gas discharge portion from the battery pack to the outside on the premise that the gas discharge portion operates correctly. However, when side rupture occurs, such a premise does not hold good. As a result, it has been difficult to take measures assuming from which part the high-temperature and high-pressure gas is discharged in which direction.

[0005] Japanese Patent Publication No. 6685003, Japanese Patent Publication No. 6934617

[0006] One objective of this disclosure is to provide a battery pack and a method for manufacturing the same that suppresses side rupture of secondary battery cells. Another objective is to provide a battery pack and a method for manufacturing the same that enhances safety by restricting the discharge of high-temperature, high-pressure gas from the cell end face side even if the internal pressure of the secondary battery cell rises for any reason. The description of these objectives and objectives in this disclosure does not preclude the existence of other objectives and objectives. Furthermore, one aspect of this disclosure is not required to solve all of these objectives. In addition, it is possible to extract other objectives from the description, drawings, and claims of this disclosure.

[0007] A battery pack according to one embodiment of the present disclosure comprises one or more secondary battery cells, each having an outer casing with a cylindrical cell side surface and a pair of cell end surfaces that form the end surfaces of the cell side surface, and at least one of the cell end surfaces having a gas discharge section that opens in response to an increase in the internal pressure of the outer casing; and a battery holder having one or more storage cylinders for housing each of the one or more secondary battery cells, wherein the battery holder comprises a first holder having a first storage cylinder for housing a part of the secondary battery cell, and a second holder having a second storage cylinder for housing another part of the secondary battery cell, and the battery holder is configured to cover the cell side surface with the first holder and the second holder joined together so that the first and second storage cylinders that constitute a part of each storage cylinder coincide, respectively, and the first holder and the second holder are molded from a thermosetting resin.

[0008] Furthermore, a method for manufacturing a battery pack according to another embodiment of the present disclosure comprises one or more secondary battery cells, each having a cylindrical cell side surface and a pair of cell end surfaces that form the end surfaces of the cell side surface, and at least one of the cell end surfaces being provided with a gas discharge section that opens in response to an increase in the internal pressure of the outer casing; and a battery holder having one or more storage cylinders for housing each of the one or more secondary battery cells, the battery holder comprising the steps of: preparing a battery holder having a first storage cylinder for housing a part of the secondary battery cells and a second storage cylinder for housing the other part of the secondary battery cells, wherein the first holder and the second holder are molded from a thermosetting resin; and joining the first holder and the second holder to form each storage cylinder by aligning the first and second storage cylinders, respectively, and inserting the battery holder into the storage cylinders. As a result, even if the battery holder becomes hot and the cell sides of the outer casing expand, a thermoplastic resin would melt and disappear or break, but by using a thermosetting resin, it can be maintained. In particular, by holding the cell sides, expansion is suppressed, reducing the risk of breakage, and the release of high-temperature, high-pressure gas from the gas discharge port on the cell end face can be promoted, thereby improving safety.

[0009] According to the battery pack and its manufacturing method described above, if the battery holder becomes hot and the cell sides of the outer casing expand, a thermoplastic resin would melt and disappear or be damaged, but by using a thermosetting resin, the shape can be maintained. Furthermore, by covering the cell sides, which tend to swell when the internal pressure of the outer casing rises, the battery holder can press against the cell sides that are trying to expand, reducing the risk of the cell sides rupturing.

[0010] This is a perspective view showing a battery pack according to Embodiment 1. This is an exploded perspective view of the battery pack in Figure 1. This is a cross-sectional view of the battery pack in Figure 1 along the line III-III. This is a cross-sectional view showing the expansion of secondary battery cells in the battery pack according to Comparative Example 1. This is a cross-sectional view showing the expansion of secondary battery cells in the battery pack according to Embodiment 1. This is a cross-sectional view showing a battery pack according to Embodiment 2. This is a cross-sectional view showing the expansion of secondary battery cells in the battery pack according to Embodiment 2. This is a cross-sectional view showing a battery pack according to Embodiment 3. This is a cross-sectional view showing a battery pack according to Embodiment 4. This is a horizontal cross-sectional view showing a battery pack according to Embodiment 5. This is a cross-sectional view showing a battery pack according to Embodiment 6.

[0011] The form of this disclosure may be specified by the following configurations and features.

[0012] In other embodiments of the present disclosure, the battery pack is such that the thermosetting resin is an unsaturated polyester or a phenolic resin.

[0013] Furthermore, in other embodiments of the present disclosure, the battery pack, in any of the above embodiments, includes reinforcing fibers in the thermosetting resin of the first holder and the second holder. This configuration increases the rigidity of the battery holder.

[0014] Furthermore, in any of the above embodiments, the battery packs relating to other embodiments of the present disclosure are such that the reinforcing fibers are at least one of carbon fiber, glass fiber, rock wool, silica fiber, alkali earth silicate (AES), and alumina fiber.

[0015] Furthermore, in other embodiments of the present disclosure, the battery pack is configured such that the joint interface between the first holder and the second holder does not overlap with the central region in the longitudinal direction of the cell side surface of one or more secondary battery cells. This configuration enhances safety by covering the joint surface with a single component so that the joint surface of the battery holder does not come into contact with the center of the cell side surface, which is most prone to expansion, thereby preventing breakage from the joint surface.

[0016] Furthermore, in any of the above embodiments, the battery pack has an engagement structure at the joining interface between the first holder and the second holder in which the end faces of the first storage cylinder and the second storage cylinder engage with each other. This configuration prevents the engagement interface from opening during expansion and maintains the pressing state on the side surface of the secondary battery cell, thereby suppressing expansion.

[0017] Furthermore, in any of the above embodiments, the battery pack is skirt-shaped, with one edge of the first holder and the second holder extending inward and the other extending outward.

[0018] Furthermore, in any of the above embodiments, the battery pack according to other embodiments of the present disclosure comprises a pin and a hole in the engagement structure.

[0019] Furthermore, in any of the above embodiments, a battery pack is provided in which the one or more secondary battery cells include a plurality of secondary battery cells, the one or more storage cylinders include a plurality of storage cylinders, and the battery holder is formed by adjacently arranging the plurality of storage cylinders.

[0020] Furthermore, in any of the above embodiments, the battery pack has a battery holder in which the plurality of storage cylinders are arranged in a staggered pattern with adjacent storage cylinders.

[0021] Furthermore, in any of the above embodiments of the battery pack, the battery holder is formed such that the thickness defining the storage cylinder for housing the outermost secondary battery cell among the plurality of secondary battery cells is thicker than the thickness defining the other storage cylinders.

[0022] Furthermore, in other embodiments of the present disclosure, the battery pack is configured such that, in any of the above embodiments, the inner diameter of the storage cylinder decreases as it approaches the central region in the longitudinal direction of the cell side surface. This configuration increases rigidity by reducing the inner diameter and increasing the wall thickness in the central region in the longitudinal direction of the storage cylinder, allowing it to withstand stress applied to the central region of the storage cylinder when the secondary battery cell expands.

[0023] Furthermore, in any of the above embodiments, the battery pack is configured such that the first storage cylinder and the second storage cylinder are joined together to form the storage cylinder.

[0024] Furthermore, in any of the above embodiments, the battery pack further comprises a third holder having a third storage cylinder for housing another part of the secondary battery cell, and the battery holder is constructed by joining the first holder, the second holder and the third holder such that the first, second, and third storage cylinders, which constitute a part of each storage cylinder, are aligned with each other.

[0025] 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 otherwise specifically stated, 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 numeral indicate the same or similar members, and detailed explanations will be 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.

[0026] The battery pack disclosed herein can be used as a power source for mobile devices such as electric assist bicycles, electric carts, and electric scooters; as a power source for portable electrical equipment such as wireless devices, electric cleaners, and power tools; or as a power source for stationary energy storage applications, such as a backup power source for servers or a power supply for homes, offices, and factories; and even as a power source for vehicles such as hybrid cars and electric vehicles. Hereinafter, an embodiment of the present invention will be described, specifically a battery pack used as a power source for an electric assist bicycle. [Embodiment 1]

[0027] Figures 1 to 3 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 Embodiment 1, Figure 2 is an exploded perspective view of the battery pack 100 of Figure 1, and Figure 3 is a cross-sectional view of the battery pack 100 of Figure 1 along line III-III. The battery pack 100 shown in these figures comprises a battery holder 20, a plurality of secondary battery cells 1, and a plurality of lead plates 10. As shown in Figure 1, the battery holder 20 has an external shape consisting of a plurality of cylinders arranged in a row, and as shown in Figure 2, it is provided with a plurality of storage cylinders 25 inside for housing a plurality of secondary battery cells 1. The external shape of the battery holder is not limited to this shape, and any shape such as a box shape can be used as appropriate. Each secondary battery cell 1 has an external shape that is cylindrical, and each has a cylindrical cell side surface 1b and a pair of cell end faces 1c. Cell electrodes are provided on the cell end faces 1c. Each lead plate 10 is connected to the cell electrodes provided on the cell end faces 1c of multiple secondary battery cells 1 housed in the battery holder 20, and is electrically connected in series or parallel. At least a portion of the lead plates 10 is also connected to a circuit board or the like. One or more such battery packs may be prepared as needed, and some of the lead plates 10 may be used to connect them to other core blocks or circuit boards (not shown), and then housed in an outer case (not shown). (Secondary battery cell 1)

[0028] Multiple secondary battery cells 1 are arranged by a battery holder 20 in a position where the cell end faces 1c of each secondary battery cell 1 are on the same plane. Each secondary battery cell 1 can be a cylindrical secondary battery cell. In the examples shown in Figures 2 and 3, cylindrical secondary battery cells 1 are arranged in a staggered pattern in a vertical position. The number and arrangement of secondary battery cells are not limited to this example, and any number and arrangement can be used as appropriate. For example, cylindrical secondary battery cells may be arranged in a grid pattern.

[0029] Each secondary battery cell 1 has positive and negative electrodes. Preferably, one positive electrode is provided on one end face of the secondary battery cell 1, and the other on the other end face. In the example shown in Figure 2, the positive electrode is provided on one end face 1c of the secondary battery cell 1, while the outer casing serves as the negative electrode. Such a secondary battery cell 1 can appropriately utilize known secondary batteries such as lithium-ion batteries, nickel-metal hydride batteries, and nickel-cadmium batteries. (Gas discharge section 1c)

[0030] Furthermore, each secondary battery cell 1 is provided with a gas outlet 1c on its outer casing. The gas outlet 1c releases gas from inside the outer casing to the outside when the internal pressure of the outer casing rises. The gas outlet 1c is provided on one of the cell end faces 1c of the secondary battery cell 1. In the example shown in Figure 2, the gas outlet 1c is provided on the positive electrode side cell end face 1c of the secondary battery cell 1. Such a gas outlet 1c can be a returnable member, such as a gas outlet valve that opens in response to an increase in the internal pressure of the outer casing and closes when the pressure falls below a specified level, or a non-returnable member that ruptures and opens due to internal pressure, as appropriate. Although the gas outlet is generally provided on the positive electrode side, this disclosure does not specify that the gas outlet should be provided on the positive electrode side, but may be provided at other locations, such as the negative electrode side. (Battery holder 20)

[0031] The battery holder 20 houses and holds multiple secondary battery cells 1. The battery holder 20 shown in Figures 2 and 3 is divided into two parts, upper and lower, and consists of an upper first holder 21 and a lower second holder 22. However, this disclosure does not limit the number of divisions of the battery holder 20, i.e., the number of divided sub-holders, to two, but may be three or more. (Storage cylinder 25)

[0032] The battery holder 20 is provided with multiple storage cylinders 25 for individually housing multiple secondary battery cells 1. Each storage cylinder 25 has a partially open window 24 at its end face, and is configured to connect the cell electrodes on the cell end face 1c to the lead plate 10 through the opening window 24. The multiple storage cylinders 25 are arranged adjacent to each other. The inside of each storage cylinder 25 is formed in a cylindrical shape that allows the cylindrical outer casing of the secondary battery cell 1 to be inserted, so that the cylindrical secondary battery cell 1 can be housed inside.

[0033] The multiple storage cylinders 25 are stacked horizontally in a vertical orientation as shown in Figure 1, etc. This allows the battery holder 20 to stack and hold multiple secondary battery cells 1 in a vertical orientation. In the example shown in Figures 1 and 2, a total of 10 storage cylinders 25 are stacked, but the number and layout of the stacked storage cylinders 25 are not limited to this configuration. Furthermore, the aforementioned vertical and horizontal orientations are merely for the convenience of explaining the state shown in the drawings, and it goes without saying that a different explanation would be required if, for example, the storage cylinders were rotated 90°. Also, in the battery pack 100 of Embodiment 1, an example is described in which the multiple storage cylinders 25 provided on the battery holder 20 are arranged in a staggered pattern, but this disclosure is not limited to this configuration, and the multiple storage cylinders may be arranged in a grid pattern. (First holder 21, second holder 22)

[0034] The first holder 21 has a first storage cylinder 26 that houses a portion of the secondary battery cell 1. The second holder 22 has a second storage cylinder 27 that houses the other portion of the secondary battery cell 1. As shown in Figure 2, the first holder 21 and the second holder 22 are joined together so that the first storage cylinder 26 and the second storage cylinder 27, which constitute a portion of each storage cylinder 25, are aligned, thereby forming the battery holder 20. Here, the first storage cylinder 26 of the first holder 21 and the second storage cylinder 27 of the second holder 22 are combined so that one secondary battery cell 1 can be housed, and the combined length of the first storage cylinder 26 and the second storage cylinder 27 is approximately the length of the secondary battery cell 1. In this disclosure, "joining" means connecting or fixing the first holder 21 and the second holder 22 so that they do not come apart. Even if a partial gap is formed at the joining interface between the first holder 21 and the second holder 22 when they are connected or fixed, i.e., joined, they are treated as "joined" in this disclosure. (Opening window 24)

[0035] Opening windows 24 are formed in the upper surface of the first holder 21 and the lower surface of the second holder 22, which are located at both ends of the storage cylinder 25. The cell end face 1c of the secondary battery cell 1 is partially exposed through each opening window 24. The opening area of ​​the opening window 24 is smaller than the cell end face 1c of the secondary battery cell 1. The cell end face 1c of the secondary battery cell 1 is connected to one of the multiple lead plates 10 via the opening window 24.

[0036] Each storage cylinder 25 has an open end that is on the same plane. Furthermore, the first holder 21 and the second holder 22, which house multiple storage cylinders 25, are molded integrally. These first and second holders 21 and 22 are molded from thermosetting resin. With this configuration, if the battery holder 20 becomes hot and the cell side surface 1b of the outer casing expands, a thermoplastic resin would melt and disappear, causing damage. However, by using thermosetting resin, the shape can be maintained. In particular, by holding the cell side surface 1b, expansion is suppressed, reducing the risk of breakage, and the release of high-temperature, high-pressure gas from the gas discharge section of the cell end surface 1c can be promoted, thereby improving safety. [Comparative Example]

[0037] Secondary battery cells are configured to open a gas vent valve and release high-temperature, high-pressure gas from the casing if the internal pressure inside the casing becomes high due to some abnormality. However, for some reason, such as a rapid increase in the internal pressure of the casing, a malfunction of the gas vent valve, or a blockage in the opening of the gas vent valve preventing sufficient pressure reduction, the side of the cell in the casing may rupture, known as a side rupture, before the gas vent valve activates, potentially leading to ignition. Generally, battery packs are designed with the assumption that the gas vent valve operates correctly and measures are taken to safely release the high-temperature, high-pressure gas released from the gas vent valve to the outside of the battery pack. However, if a side rupture occurs, this assumption does not hold true. As a result, it becomes difficult to anticipate which part will release the high-temperature, high-pressure gas and in which direction, and to take countermeasures accordingly. Therefore, the inventors of the present invention have investigated measures to avoid side rupture and have come up with the present invention.

[0038] Specifically, when a secondary battery cell undergoes side rupture, the inside of the outer casing becomes under high pressure and begins to bulge. In particular, as in the battery pack 900 in the comparative example shown in Figure 4, the central part of the outer casing bulges the most. Each secondary battery cell 901 is held in place by the storage cylinder 925 of the battery holder 920, covering the sides of the outer casing. However, since such battery holders 920 are generally made of thermoplastic resin, when the secondary battery cell 901 is at a high temperature, the heat melts the resin of the battery holder 920, and it cannot maintain sufficient strength.

[0039] In contrast, in the battery pack 100 according to this embodiment, the battery holder 20 is molded from a thermosetting resin, which allows it to maintain its shape without melting even at high temperatures, thereby suppressing the expansion of the outer casing of the secondary battery cell 1. As a result, the timing of the occurrence of side rupture can be delayed, and during this time the gas discharge section can be activated to reduce the pressure inside the outer casing, thereby avoiding side rupture.

[0040] The thermosetting resin that constitutes the battery holder 20, such as the first holder 21 and the second holder 22, can be unsaturated polyester, phenolic resin, or glass epoxy resin. Preferably, it is unsaturated polyester or phenolic resin. The thermosetting resin may also contain reinforcing fibers. This can increase the rigidity of the battery holder 20. Suitable reinforcing fibers include carbon fiber, glass fiber, rock wool, silica fiber, alkali earth silicate (AES), alumina fiber, and the like.

[0041] The battery holder 20 is divided into a first holder 21 and a second holder 22. The first holder 21 and the second holder 22 are joined together and configured to cover the cell side surface 1b. By covering the cell side surface 1b, which tends to bulge when the internal pressure of the outer casing rises, the battery holder 20 can press down on the cell side surface 1b that is trying to bulge, thereby reducing the risk of the cell side surface 1b rupturing.

[0042] Furthermore, the battery holder 20 positions the joint interface between the first holder 21 and the second holder 22 so as not to overlap with the central region in the longitudinal direction of the cell side surface 1b of the secondary battery cell 1. By doing so, the mating surface of the battery holder 20 is not positioned at the center of the cell side surface 1b, which has the greatest tendency to expand. By covering it with an integral member, the situation of breaking from the mating surface can be avoided and the safety can be enhanced. As in the battery pack 900 according to Comparative Example 1 in FIG. 4, if the joint interface between the first holder 921 and the second holder 922 is at the center in the longitudinal direction of the cell side surface 901b of the secondary battery cell 901, it becomes easy to break from the mating surface when the secondary battery cell 901 expands, and the expansion cannot be suppressed.

[0043] In contrast, in the battery pack 100 according to the present embodiment, as shown in FIG. 5, the joint interface between the first holder 21 and the second holder 22 is shifted downward from the center in the length direction of the cell side surface 1b. In other words, the first holder 21 and the second holder 22 do not bisect the battery holder 20 so as to have the same length, but one is made longer and the split position is unevenly distributed from the center. Thereby, when the secondary battery cell 1 expands, the central region where stress is likely to be applied can be covered with an integral member to prevent breakage and make it easy to apply a pressing force for suppressing expansion.

[0044] In the examples shown in FIGS. 3 and 5, the upper first holder 21 is formed long and the lower second holder 22 is formed short. However, the present disclosure is not limited to this configuration. For example, the same effect can be obtained by forming the first holder 21 short and the second holder 22 long. [Embodiment 2]

[0045] In the above examples, an example in which the battery holder 20 is divided into two parts, the first holder 21 and the second holder 22, has been described. However, the present disclosure is not limited to this configuration, and the battery holder may be divided into three or more parts. Such an example is shown in FIG. 6 as the battery pack 200 according to Embodiment 2. In this figure, the same members as those in the above-described Embodiment 1 are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0046] The battery holder 20B shown in Figure 6 includes a first holder 21B, a second holder 22B, and a third holder 23B. The third holder 23B has a third storage cylinder 28B that houses a portion of the secondary battery cell 1. The battery holder 20B is constructed by joining the first holder 21B, the second holder 22B, and the third holder 23B so that the first storage cylinders 26B, the second storage cylinder 27B, and the third storage cylinder 28B, which each constitute a portion of the respective storage cylinders 25B, are aligned. With this configuration, even if the battery holder 20B is divided into roughly three equal parts, as shown in Figure 7, the dividing line is not located in the central part of the cell side surface 1b. Therefore, while avoiding the situation where the secondary battery cell 1 ruptures at the interface when it expands, the strength of each divided sub-holder is made uniform, ensuring stable molding and strength maintenance. [Embodiment 3]

[0047] Furthermore, the joining interface between the first holder 21 and the second holder 22 may be an engaging structure 30C in which the end faces of the first storage cylinder 26 and the second storage cylinder 27 engage with each other. By providing a fitting structure in which the end faces of the first storage cylinder 26 and the second storage cylinder 27 interlock, the situation in which they are forcibly released from the engaging interface during expansion can be further suppressed, and the pressing state of the side surface of the secondary battery cell 1 can be maintained to suppress expansion. An example of such an engaging structure 30C is shown in the schematic cross-sectional view of Figure 8 as a battery pack 300 according to Embodiment 3. In this figure, the same reference numerals are used for members similar to those in Embodiment 1 and the like described above, and detailed explanations are omitted as appropriate. In the example of Figure 8, the end face of the first storage cylinder 26C, which constitutes the storage cylinder 25C, is provided with a stepped shape, and the end face of the second storage cylinder 27C is formed with a step that matches this step. Here, one edge of the first holder 21C and the second holder 22C is extended inward, and the other is extended outward, forming a skirt shape. However, the engagement structure is not limited to this configuration; any known joining structure capable of joining the edges of cylindrical members can be used as appropriate. Furthermore, claws, protrusions, or hooks may be provided on the stepped portion to maintain the engaged state. Alternatively, the members may be connected by screwing them together with special precision screws. In this disclosure, the term "engagement structure" is used to include such known connecting structures. [Embodiment 4]

[0048] As another engagement structure 30D, pins and holes may be provided at the joining interface between the first holder 21 and the second holder 22. Such an example is shown in the schematic cross-sectional view of FIG. 9 as the battery pack 400 according to Embodiment 4. In this figure, members similar to those in the above-described Embodiment 1 and the like are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate. In the example of FIG. 9, a plurality of pins are protruded from the end face of the second storage cylinder 27D of the second holder 22D so as to be spaced apart from each other. Further, a plurality of holes into which these pins can be inserted are formed at positions corresponding to the pins on the end face of the first storage cylinder 26D of the first holder 21D. Even with such a configuration, the first storage cylinder 26D of the first holder 21D and the second storage cylinder 27D of the second holder 22D can be maintained in an engaged state. On the other hand, in order to facilitate disassembling the first holder 21D and the second holder 22D, instead of the entire joining surface between the first holder 21D and the second holder 22D, positions that are spaced apart may be spot-fixed. [Embodiment 5]

[0049] Further, the battery holder 20 may be formed such that the wall thickness defining the storage cylinder 25E for storing the secondary battery cell 1out located at the outermost periphery among the plurality of secondary battery cells 1 is thicker than the wall thickness defining the other storage cylinders. In a battery pack in which a plurality of secondary battery cells 1 are stacked, the secondary battery cell 1in located in the middle, that is, the secondary battery cell 1in surrounded by other secondary battery cells around it, is suppressed from expanding when it tries to expand because it is pressed by the surrounding secondary battery cells. Conversely, the secondary battery cell 1out located at the outermost periphery has fewer or no secondary battery cells around it, so such pressing by other secondary battery cells cannot be expected. As a result, it can be said that the position has relatively weak resistance to expansion compared to other secondary battery cells. Therefore, for the secondary battery cell 1out located at the outermost periphery, by making the wall thickness of the storage cylinder 25E thicker than that of the other storage cylinders, the pressing force by the storage cylinder itself can be relatively increased to exhibit an expansion suppression effect similar to that of other secondary battery cells. Such an example is shown in the horizontal cross-sectional view of FIG. 10 as the battery pack 500 according to Embodiment 5. Also in this figure, members similar to those in the above-described Embodiment 1 and the like are denoted by the same reference numerals, and detailed description thereof will be omitted as appropriate.

[0050] The battery pack 500 shown in the horizontal cross-sectional view of Figure 10 has a battery holder 20E that is thicker along its outer circumference. In this example, the thickness d2 of the portion where the secondary battery cells 1out do not face each other is thicker than the thickness d1 of the portion where the secondary battery cells 1 face each other. This increases the resistance force that presses the cell side surface 1b from the outer surface of the battery holder 20E against the expansion of the outermost secondary battery cell 1out, thereby enhancing the effect of suppressing expansion. In the example of Figure 10, the inner thickness d1 is shown with a dashed line relative to the outer thickness d2. Here, the outer thickness d2 is approximately twice that of the inner thickness d1, but this disclosure is not limited to this. [Embodiment 6]

[0051] Furthermore, the battery holder 20 may be formed such that the inner diameter of the storage cylinder 25 decreases as it approaches the central region in the longitudinal direction of the cell side surface 1b. By reducing the inner diameter and increasing the wall thickness in the central region in the longitudinal direction of the storage cylinder 25, rigidity can be increased, and the storage cylinder 25 can withstand stress applied to the central region when the secondary battery cell 1 expands. An example of this is shown in Figure 11 as a battery pack 600 according to Embodiment 6. In this figure as well, the same reference numerals are used for components as in Embodiment 1 and the others described above, and detailed explanations are omitted as appropriate.

[0052] As shown in the vertical cross-sectional view of Figure 11, the battery pack 600 is formed such that the inner diameter of the storage cylinder 25F gradually narrows towards the middle, so that it protrudes in a V-shape in cross-section toward the middle of the length direction of the battery holder 20F. Here, of the first holder 21F, second holder 22F, and third holder 23F that make up the battery holder 20F, the third holder 23F is formed in a V-shape in cross-section and is configured to protrude toward the middle of the height direction of the secondary battery cell 1. By adopting this configuration, the strength of the central part of the storage cylinder 25F, where the most stress is applied when the secondary battery cell 1 expands, can be increased, thereby enhancing the effect of suppressing expansion. [Battery pack manufacturing method]

[0053] Next, the manufacturing method of the battery pack 100 will be described. This battery pack 100 comprises a plurality of secondary battery cells 1 and a battery holder 20. The plurality of secondary battery cells 1 are provided with an outer casing having a cylindrical cell side surface 1b and a pair of cell end surfaces 1c that form the end faces of the cell side surface 1b. The outer casing is provided with a gas discharge valve on at least one of the cell end surfaces 1c that opens in response to an increase in the internal pressure of the outer casing. The battery holder 20 houses the plurality of secondary battery cells 1.

[0054] First, prepare the battery holder 20. The battery holder 20 has multiple storage cylinders 25 for individually housing multiple secondary battery cells 1. This battery holder 20 includes a first holder 21 and a second holder 22. The first holder 21 has a first storage cylinder 26 for housing a portion of the secondary battery cell 1. The second holder 22 has a second storage cylinder 27 for housing the remaining portion of the secondary battery cell 1. Furthermore, the first holder 21 and the second holder 22 are molded from thermosetting resin.

[0055] Next, the first holder 21 and the second holder 22 are joined together, and the first storage cylinder 26 and the second storage cylinder 27 are aligned to form each storage cylinder 25, into which the battery holder 20 is inserted.

[0056] As a result, even if the battery holder 20 becomes hot and the cell side surface 1b of the outer casing expands, a thermoplastic resin would melt and disappear or break, but by being made of a thermosetting resin, it can be maintained. In particular, by holding the cell side surface 1b, expansion is suppressed and the risk of breakage is reduced, and the release of high-temperature, high-pressure gas from the gas discharge section of the cell end surface 1c can be promoted, thereby improving safety.

[0057] 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 is low or the battery pack deteriorates over time, the battery pack can be replaced, and the electrical device can be used continuously. However, this disclosure 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 one in which secondary battery cells are housed within a case, and also includes those in which the secondary battery cells for driving are built into the casing of the electrical device itself. In other words, this disclosure is not limited to replaceable battery packs, but can also be applied to electrical devices that have built-in secondary battery cells.

[0058] The battery pack and its manufacturing method described herein are suitably usable as a power source for mobile devices such as electric carts and electric scooters. They can also be appropriately used as power sources for wireless devices, electric vacuums, power tools, and other portable electrical equipment.

[0059] 100, 200, 300, 400, 500, 600, 900... Battery pack 1... Secondary battery cell; 1b... Cell side; 1c... Cell end face 1out... Secondary battery cell located on the outermost periphery 1in... Secondary battery cell located in the middle 10... Lead plate 20, 20B, 20C, 20D, 20E, 20F... Battery holder 21, 21B, 21C, 21D, 21F... First holder 22, 22B, 22C, 22D, 22F... Second holder 23B, 23F... Third holder 24... Opening window 25, 25B, 25C, 25E... Storage cylinder 26, 26B, 26C, 26D... First storage cylinder 27, 27B, 27C, 27D... Second storage cylinder 28B... Third storage cylinder 30C, 30D... Engagement structure 900...Battery pack 901...Secondary battery cell 901b...Cell side 920...Battery holder 921...First holder 922...Second holder 925...Storage tube d1...Inner wall thickness d2...Outer wall thickness

Claims

1. A battery pack comprising: one or more secondary battery cells, each having an outer casing with a cylindrical cell side surface and a pair of cell end surfaces that form the end faces of the cell side surface, and a gas discharge section that opens in response to an increase in the internal pressure of the outer casing, provided on at least one of the cell end surfaces; and a battery holder having one or more storage cylinders for housing each of the one or more secondary battery cells, wherein the battery holder comprises: a first holder having a first storage cylinder for housing a part of the secondary battery cell; and a second holder having a second storage cylinder for housing another part of the secondary battery cell, and the battery holder is configured to cover the cell side surface with the first holder and the second holder joined together such that the first and second storage cylinders that constitute a part of each storage cylinder coincide, and the first holder and the second holder are molded from a thermosetting resin.

2. A battery pack according to claim 1, wherein the thermosetting resin is an unsaturated polyester or a phenolic resin.

3. A battery pack according to claim 1, wherein the first holder and the second holder are made of the thermosetting resin containing reinforcing fibers.

4. A battery pack according to claim 3, wherein the reinforcing fiber is at least one of carbon fiber, glass fiber, rock wool, silica fiber, alkali earth silicate (AES), and alumina fiber.

5. A battery pack according to claim 1, wherein the battery holder is positioned such that the bonding interface between the first holder and the second holder does not overlap with the central region in the longitudinal direction of the side surface of the one or more secondary battery cells.

6. A battery pack according to claim 1, wherein the joining interface between the first holder and the second holder has an engaging structure that engages the end faces of the first storage cylinder and the second storage cylinder with each other.

7. A battery pack according to claim 6, wherein the engaging structure is skirt-shaped, with one edge of the first holder and the second holder extending inward and the other edge extending outward.

8. A battery pack according to claim 6, wherein the engagement structure is composed of a pin and a hole.

9. A battery pack according to any one of claims 1 to 8, wherein the one or more secondary battery cells include a plurality of secondary battery cells, the one or more storage cylinders include a plurality of storage cylinders, and the battery holder is formed by adjacently arranging the plurality of storage cylinders.

10. A battery pack according to claim 9, wherein the battery holder is a battery pack in which the plurality of storage cylinders are arranged in a staggered pattern with adjacent storage cylinders.

11. A battery pack according to claim 9, wherein the battery holder is formed such that the thickness defining the storage cylinder for housing the outermost secondary battery cell among the plurality of secondary battery cells is thicker than the thickness defining the other storage cylinders.

12. A battery pack according to claim 9, wherein the battery holder is formed such that the inner diameter of the storage cylinder becomes smaller as it approaches the central region in the longitudinal direction of the cell side surface.

13. A battery pack according to any one of claims 1 to 8, wherein the first storage cylinder and the second storage cylinder are joined together to form the storage cylinder.

14. A battery pack according to any one of claims 1 to 8, wherein the battery holder further comprises a third holder having a third storage cylinder for storing another part of the secondary battery cell, and the battery holder is constructed by joining the first holder, the second holder and the third holder such that the first, second, and third storage cylinders, which constitute a part of each storage cylinder, are aligned.

15. A method for manufacturing a battery pack comprising: one or more secondary battery cells, each comprising an outer can having a cylindrical cell side surface and a pair of cell end surfaces that form the end surfaces of the cell side surface, and having a gas discharge section on at least one of the cell end surfaces that opens in response to an increase in the internal pressure of the outer can; and a battery holder having one or more storage cylinders for housing each of the one or more secondary battery cells, the method comprising: preparing a battery holder comprising: a first holder having a first storage cylinder for housing a part of the secondary battery cells; and a second holder having a second storage cylinder for housing another part of the secondary battery cells, wherein the first holder and the second holder are molded from a thermosetting resin; and joining the first holder and the second holder to form each storage cylinder by aligning the first and second storage cylinders, respectively, and inserting the battery holder into the storage cylinders.

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