Battery pack

Abstract

In this battery pack, a battery holder provided with a plurality of rechargeable cylindrical battery cells is stored in an outer case. The battery holder comprises a plurality of holding tube parts that hold the plurality of rechargeable battery cells in a mutually parallel orientation and a heat capacity part coupled to the outside of the holding tube parts to absorb heat from the rechargeable battery cells. The outer case is provided with a coupling heat capacity part protruding from the inner surface of the outer case, the coupling heat capacity part being formed from a plurality of heat-conducting protrusions that are thermally coupled to the battery holder to absorb heat conducted from the battery holder. The battery holder is provided with a plurality of mating recesses adjacent to the heat capacity part, in which the plurality of mating recesses are coupled to the plurality of heat-conducting protrusions in a mating structure. In the battery pack, the heat-conducting protrusions of the outer case mate with the mating recesses of the battery holder to conduct the heat generated by the rechargeable battery cells from the battery holder to the outer case and dissipate the heat to the outside.

Description

Battery pack

[0001] The present invention relates to a battery pack in which a plurality of secondary battery cells are held by a battery holder and housed in an exterior case.

[0002] Battery packs containing multiple secondary battery cells housed in an exterior case are used as power sources for portable electrical devices such as medical equipment, electric cleaners, and power tools. These battery packs house multiple secondary battery cells housed in a battery holder in a predetermined arrangement within the exterior case. In battery packs with multiple secondary battery cells, if an unsafe event such as an internal short circuit occurs in one of the secondary battery cells, the secondary battery cell may overheat and ignite. This heat may then heat adjacent secondary battery cells, resulting in a chain reaction and fire. In particular, if there is no route for dissipating the generated heat to the outside, the trapped heat may locally concentrate in adjacent secondary battery cells, causing overheating and potentially resulting in a chain reaction and fire. If an unsafe event occurs in one of the secondary battery cells within the battery pack and generates heat, the heat from the abnormal cell may spread to other secondary battery cells, potentially resulting in a fire, creating an extremely dangerous situation.

[0003] JP 2011-159478 A

[0004] The present invention was developed with the aim of preventing a chain reaction of fire spreading to adjacent secondary battery cells due to heat generated from an abnormal battery cell in a battery pack having multiple secondary battery cells, even if an unsafe event occurs in one of the secondary battery cells, such as smoke or fire.

[0005] One objective of one embodiment of the present disclosure is to provide a battery pack that, when a secondary battery cell housed in an exterior case becomes abnormal and generates heat, can effectively dissipate heat generated from the abnormal battery cell to the outside, thereby effectively preventing a chain reaction of fire spreading to adjacent secondary battery cells. Note that the description of this objective and problem of the present disclosure does not preclude the existence of other objectives and problems. Furthermore, one embodiment of the present disclosure does not necessarily solve all of these problems. Furthermore, other problems can be extracted from the description of the specification, drawings, and claims of the present disclosure.

[0006] A battery pack according to one embodiment of the present disclosure includes a plurality of secondary battery cells, a battery holder that houses the plurality of secondary battery cells, and an exterior case that houses the battery holder. The secondary battery cells are cylindrical batteries, and the battery holder includes a plurality of holding tube portions that house the plurality of secondary battery cells and hold them parallel to one another, and a heat capacity portion that is connected to the outside of the holding tube portions and absorbs heat conducted from the secondary battery cells. The exterior case has a connecting heat capacity portion on its inner surface that is thermally coupled to the battery holder and absorbs heat conducted from the battery holder. This connecting heat capacity portion is composed of a plurality of heat conductive protrusions protruding from the inner surface of the exterior case. The battery holder has a plurality of fitting recesses adjacent to the heat capacity portion that connect the plurality of heat conductive protrusions in a fitting structure. With the battery holder housed in the outer case, the battery pack thermally couples the battery holder to the outer case by engaging the heat-conducting convex portion with the mating concave portion, and the heat generated by the secondary battery cells is conducted from the battery holder to the outer case and dissipated to the outside.

[0007] According to the battery pack of the present disclosure, when a secondary battery cell housed in an outer case becomes abnormal and generates heat, the heat generated from the abnormal battery cell can be effectively dissipated to the outside, thereby effectively preventing a chain reaction of fire spreading to adjacent secondary battery cells.

[0008] 1 is a perspective view of a battery pack according to a first embodiment of the present disclosure. FIG. 1 is an exploded perspective view of the battery pack shown in FIG. 2. FIG. 3 is an exploded perspective view of the battery pack shown in FIG. 3, seen from below. FIG. 1 is a vertical cross-sectional view of the battery pack shown in FIG. 1, taken along line V-V. FIG. 5 is a vertical longitudinal cross-sectional view of the battery pack shown in FIG. 5, taken along line VI-VI. FIG. 5 is a vertical longitudinal cross-sectional view of the battery pack shown in FIG. 5, taken along line VII-VII. FIG. 5 is an exploded cross-sectional view corresponding to the cross section of line VIII-VIII of the battery pack shown in FIG. 5. FIG. 5 is an enlarged cross-sectional view of a main part of the battery pack shown in FIG. 5. FIG. 6 is a bottom perspective view showing another example of a heat capacity portion and a fitting recess provided in a battery holder of a battery pack according to a second embodiment. FIG. 7 is a perspective view showing another example of a heat-conducting protrusion provided in an exterior case of a battery pack according to a second embodiment. FIG. 8 is an exploded cross-sectional view of a battery pack according to a third embodiment.

[0009] First, we will explain one of the key features of this disclosure. In a battery pack in which multiple secondary battery cells are housed in a battery holder, and the battery holder is housed in an exterior case, if an unsafe event such as an internal short circuit occurs in one of the secondary battery cells and ignites, the resulting heat can heat nearby secondary battery cells, potentially causing a chain reaction and spreading of the fire. To solve this problem, structures that quickly dissipate heat generated by an abnormal battery cell have been considered. For example, by thermally coupling the battery holder and the exterior case, heat from the abnormal battery cell can be conducted from the battery holder to the exterior case and dissipated to the outside. However, differences in the shapes of conventional battery holders and exterior cases make it difficult to achieve efficient thermal coupling. In particular, in battery packs using cylindrical secondary battery cells, the exterior shape of the battery holder has a curved surface that follows the exterior shape of the cylindrical battery, which easily creates a gap between the battery holder and the interior surface of the exterior case, preventing efficient thermal coupling.

[0010] To solve these problems, a method has been proposed in which potting resin is filled between the battery holder and the exterior case. This structure allows the potting resin to be poured into the gap between the outer surface of the battery holder and the inner surface of the exterior case, filling the gap and thermally bonding the battery holder and the exterior case via the potting resin. Another advantage of the potting resin, which is filled around the periphery of the battery holder, is that it can absorb heat from the secondary battery cells due to its thermal capacity.

[0011] However, the structure of filling the space between the battery holder and the outer case with potting resin requires potting resin, which increases material costs, and also requires processes for filling the potting resin and hardening the filled resin, making manufacturing time-consuming and labor-intensive.

[0012] In light of these problems, the inventors investigated a structure in which a resin heat capacity portion is integrally molded on the outside of the battery holder to absorb heat from the secondary battery cells, while the surface of the heat capacity portion is shaped to fit the inner surface of the exterior case, thermally bonding the battery holder and the exterior case in surface contact, thereby efficiently conducting heat from the battery holder to the exterior case and dissipating it. However, a heat capacity portion integrally molded on the outside of the battery holder from resin suffers from the problem of sink marks occurring during resin molding when the volume is increased to increase the heat capacity. Therefore, it is necessary to provide a gap in the heat capacity portion to prevent sink marks. However, providing this gap prevents the volume of the heat capacity portion from being increased, reduces the thermal coupling efficiency with the exterior case, and reduces the thermal conduction efficiency from the battery holder to the exterior case.

[0013] To solve the above problems, the inventors investigated various structures through repeated trial and error, and eventually discovered that by providing a heat capacity section not only on the outside of the battery holder but also on the inside of the exterior case, and by connecting the heat capacity sections formed on the outside of the battery holder and the inside of the exterior case in a fitted state, it is possible to efficiently thermally couple the battery holder and the exterior case while ensuring the volume of the heat capacity section that absorbs the heat of the secondary battery cells.In other words, by providing heat capacity sections on the outside of the battery holder and the inside of the exterior case and connecting them in a fitted structure, the present invention achieves a battery pack that can efficiently conduct heat from the battery holder to the exterior case while increasing the thermal capacity of the heat capacity section molded from resin, without using a potting resin as in the past, and ensures reliable thermal coupling between the battery holder and the exterior case, thereby enabling efficient heat conduction from the battery holder to the exterior case and heat dissipation.

[0014] A battery pack according to one embodiment of the present disclosure includes a plurality of secondary battery cells, a battery holder that houses the plurality of secondary battery cells, and an exterior case that houses the battery holder. The secondary battery cells are cylindrical batteries, and the battery holder includes a plurality of holding tube portions that house the plurality of secondary battery cells and hold them parallel to one another, and a heat capacity portion that is connected to the outside of the holding tube portions and absorbs heat conducted from the secondary battery cells. The exterior case has a connecting heat capacity portion on its inner surface that is thermally coupled to the battery holder and absorbs heat conducted from the battery holder. This connecting heat capacity portion is composed of a plurality of heat conductive protrusions that are integrally connected to the exterior case and protrude from the inner surface. The battery holder has a plurality of fitting recesses adjacent to the heat capacity portion that connect the plurality of heat conductive protrusions in a fitting structure. With the battery holder housed in the outer case, the battery pack thermally couples the battery holder to the outer case by engaging the heat-conducting convex portion with the mating concave portion, and the heat generated by the secondary battery cells is conducted from the battery holder to the outer case and dissipated to the outside.

[0015] According to the above configuration, the battery holder includes a plurality of holding cylindrical sections that hold a plurality of secondary battery cells in a parallel orientation, and a heat capacity section that is connected to the outside of the holding cylindrical sections and absorbs heat from the secondary battery cells that is conducted from the holding cylindrical sections. The outer case has a plurality of heat conductive protrusions that protrude from the inner surface as connected heat capacity sections that are thermally coupled to the battery holder and absorb heat conducted from the battery holder. Furthermore, the battery holder has mating recesses that connect the heat conductive protrusions with a mating structure and are adjacent to the heat capacity sections. Therefore, when the battery holder is stored in the outer case, the heat conductive protrusions and mating recesses are mated, and heat generated by the cylindrical secondary battery is absorbed by the heat capacity section and connected heat capacity section, while being conducted from the battery holder to the outer case, allowing efficient heat dissipation to the outside. This effectively prevents the heat generated by the secondary battery cells from overheating adjacent secondary battery cells and causing them to catch fire.

[0016] In another embodiment of the battery pack of the present disclosure, the battery holder is made of resin, multiple cylindrical holding portions are integrally molded, and a heat capacity portion is integrally molded with the cylindrical holding portion, and multiple fitting recesses formed adjacent to the heat capacity portion can also be used as recesses to prevent sink marks during resin molding. Also, the battery pack has an outer case made of resin, a connecting heat capacity portion is integrally molded with the outer case, and the connecting heat capacity portion is divided into multiple heat conductive protrusions with gaps between adjacent heat conductive protrusions.

[0017] According to the above configuration, the resin battery holder has multiple fitting recesses adjacent to the heat capacity portion integrally molded into the cylindrical holding portion, and these fitting recesses also serve as sink-preventing recesses, effectively preventing sink marks when the heat capacity portion is molded from the resin. Furthermore, the resin exterior case divides the connecting heat capacity portion integrally molded on the inner surface into multiple heat-conducting protrusions with gaps between adjacent heat-conducting protrusions, effectively preventing sink marks when the connecting heat capacity portion is molded from the resin.

[0018] In a battery pack according to another embodiment of the present disclosure, the heat capacity portion is located in a valley portion formed between adjacent retaining cylindrical portions, and is molded to span the retaining cylindrical portions, and multiple mating recesses can be formed in the valley portions.

[0019] According to the above configuration, the heat capacity portion is provided in the valley portion formed between adjacent cylindrical holding portions, so the space between the valley portions formed between the cylindrical holding portions can be effectively used to form the heat capacity portion, and by providing the heat capacity portion across adjacent cylindrical holding portions, heat can be efficiently conducted from the cylindrical holding portions to the heat conduction portion regardless of the state in which the secondary battery cells housed in either cylindrical holding portion are generating heat. Furthermore, since multiple fitting recesses are provided in the valley portions formed between adjacent cylindrical holding portions, the space between the valley portions can be effectively used to form deep fitting recesses, which effectively prevents sink marks during resin molding and increases the contact area with the heat conduction protrusions, allowing for efficient thermal coupling.

[0020] In another embodiment of the battery pack of the present disclosure, the heat capacity portion is composed of a plurality of connecting ribs arranged in the extension direction of the valley portion and connecting adjacent retaining tube portions, grooves are formed between the adjacent connecting ribs to serve as mating recesses, and the heat conducting protrusions can be rib-shaped and fitted into the grooves.

[0021] According to the above configuration, the heat capacity portion formed on the outer peripheral surface of the battery holder is a plurality of connecting ribs arranged in the extension direction of the valley portions and connecting adjacent peripheral wall portions, which serves as a reinforcing rib to improve the rigidity of the battery holder. Furthermore, the heat capacity portion has grooves formed between adjacent connecting ribs to form mating recesses, and the heat conductive protrusions of the exterior case are rib-shaped and fit into the grooves. This allows the battery holder and exterior case to be accurately positioned and connected via the mating heat conductive protrusions and mating recesses. Furthermore, with this fitting structure, the rib-shaped heat conductive protrusions fit into the grooves formed between the multiple connecting ribs, and the multiple connecting ribs and multiple heat conductive protrusions are fitted together in a stacked state, resulting in a thermal coupling over a wider area and efficient heat conduction.

[0022] In another embodiment of the battery pack of the present disclosure, the surface shape of the heat-conducting convex portion facing the holding cylindrical portion is shaped to conform to the outer peripheral surface of the holding cylindrical portion, and when inserted into the groove, the facing surface can be brought close to or in close contact with the outer surface of the holding cylindrical portion to be thermally bonded.

[0023] With this configuration, the surface shape of both side surfaces of the heat-conducting protrusions is shaped to fit the outer peripheral surface of the cylindrical holding part, so that when the heat-conducting protrusions are fitted into the grooves, the two side surfaces can be brought close to the outer peripheral surfaces of the opposing cylindrical holding part, allowing for effective thermal coupling. With this structure, the outer peripheral surface of the cylindrical holding part can be thermally coupled directly to the heat-conducting protrusions of the outer case, allowing for efficient thermal conduction and dissipation of heat generated by the secondary battery cells from the cylindrical holding part to the outer case.

[0024] In a battery pack according to another embodiment of the present disclosure, the rib-shaped heat-conducting protrusions have a surface gradient such that the thickness gradually decreases in the protruding direction, and the grooves have an inner surface gradient such that the groove width gradually increases toward the opening edge, and when the heat-conducting protrusions are inserted into the grooves, the opposing surfaces of the two can be brought close together or in close contact with each other to fit together.

[0025] According to the above configuration, a rib-shaped heat-conducting convex portion, which is formed so that its thickness decreases toward the tip, is inserted into a groove portion, which is formed so that the groove width increases toward the opening edge.This allows the heat-conducting convex portion to be easily and reliably guided into the groove portion, and when the heat-conducting convex portion is inserted into the groove portion, the inclined surfaces of each other can be brought close to each other to ensure reliable thermal coupling.

[0026] In a battery pack according to another embodiment of the present disclosure, a thermally conductive paste can be disposed between the fitting recess and the thermally conductive protrusion.

[0027] This configuration improves the thermal conductivity between the mating recess and the heat-conducting protrusion, enabling effective heat conduction. In addition, the heat-conducting paste disposed between the mating recess and the heat-conducting protrusion allows the mating recess and the heat-conducting protrusion to be mated more smoothly with low resistance.

[0028] A battery pack according to another embodiment of the present disclosure includes a battery holder that includes a cylindrical holder portion that is open at both ends and holds the middle portion of the secondary battery cell in the longitudinal direction, and a pair of holder lid portions that are connected to the openings at both ends of the cylindrical holder portion and hold both ends of the secondary battery cell, and a heat capacity portion and multiple mating recesses can be provided on the outer surface of the cylindrical holder portion.

[0029] According to the above configuration, the battery holder is composed of a cylindrical holder portion and a pair of holder lids, and the outer peripheral surface of the cylindrical holder portion is provided with a heat capacity portion and multiple mating recesses. This allows heat generated in the middle of the secondary battery cell to be effectively conducted from the cylindrical holder portion to the outer case via the cylindrical holder portion that holds the middle portion of the secondary battery cell. Furthermore, since the heat capacity portion and multiple mating recesses are formed on the outer peripheral surface of the cylindrical holder portion that holds the middle portion of the secondary battery cell without dividing the battery holder at the middle portion, this has the advantage that the heat-conducting protrusions on the inner surface of the outer case can be accurately and smoothly mated with the mating recesses.

[0030] A battery pack according to another embodiment of the present disclosure has an outer case comprising a box-shaped main body case with an upper opening and a lid case that closes the upper opening of the main body case, the main body case comprising a bottom plate portion that faces the underside of the battery holder, side plate portions connected to both sides of the bottom plate portion and facing both side surfaces of the battery holder, and end plate portions connected to both ends of the bottom plate portion and the side plate portion and facing both end surfaces of the battery holder, the battery holder has a plurality of mating recesses that open to the underside, and the outer case can have a plurality of heat-conducting protrusions on the bottom plate portion.

[0031] According to the above configuration, multiple heat-conducting protrusions provided on the bottom plate of the outer case are fitted into multiple fitting recesses opening on the underside of the battery holder. This has the advantage that the fitting direction of the heat-conducting protrusions and fitting recesses is aligned with the direction of gravity acting on the multiple secondary battery cells stored in the battery holder, thereby enabling the fitting state to be maintained stably.

[0032] In a battery pack according to another embodiment of the present disclosure, the battery holder is formed with multiple retaining cylindrical sections arranged in a bale-like shape in cross section so that battery rows in which multiple secondary battery cells are aligned diametrically can be stored in multiple layers in a bale-like position, the side of the battery holder formed by the retaining cylindrical sections stacked one on top of the other forms an undercut surface that is inclined in an undercut shape, and a heat capacity section and a fitting recess are formed on the undercut surface, and the side plate section of the outer case that faces the undercut surface has an inclined section that follows the undercut surface, forming a heat conductive protrusion on the inclined section, and the heat conductive protrusion on the inclined section can be fitted into the fitting recess on the undercut surface.

[0033] According to the above configuration, multiple holding tubes are arranged in a rice bale-like shape, allowing multiple secondary battery cells to be stored efficiently in a space-saving manner in a rice bale-like position, and by fitting the heat-conducting protrusions on the inclined portion of the outer case into the mating recesses on the undercut surface of the battery holder, the battery holder can also be thermally coupled to the outer case from the side, allowing for effective heat dissipation.

[0034] In another embodiment of the battery pack of the present disclosure, the outer case includes a second connecting heat capacity portion that is thermally coupled to the retaining cylinder portion of the battery holder along the boundary between the bottom plate portion and the side plate portion, and the second connecting heat capacity portion is composed of a plurality of opposing ribs that are integrally connected across the bottom plate portion and the side plate portion, and the opposing surfaces of the opposing ribs can be shaped to follow the surface of the retaining cylinder portion.

[0035] According to the above configuration, the exterior case includes a second connecting heat capacity portion on the inner surface of the main case along the boundary between the bottom plate and the side plate, which is thermally coupled to the cylindrical battery holder portion. The second connecting heat capacity portion is composed of multiple opposing ribs integrally connected across the bottom plate and the side plate, and the opposing ribs have surfaces facing the cylindrical battery holder that conform to the surface of the cylindrical battery holder. This allows the multiple opposing ribs to be efficiently thermally coupled to the cylindrical battery holder portion, thereby conducting heat from the cylindrical battery holder portion to the exterior case. Furthermore, dividing the second heat capacity portion into multiple opposing ribs eliminates sink marks during molding of the resin-molded second heat capacity portion. Furthermore, the main case includes multiple opposing ribs integrally connected across the bottom plate and the end plate at the corners between the bottom plate and the end plate, thereby increasing the rigidity and reinforcement of the box-shaped main case.

[0036] Embodiments of the present disclosure will be described below with reference to the drawings. However, the embodiments described below are merely examples for embodying the technical concepts of the present disclosure, and the present disclosure is not limited to the following. Furthermore, this specification does not in any way specify the components set forth in the claims to be those of the embodiments. The dimensions, materials, shapes, relative positions, etc. of components described in the embodiments are not intended to limit the scope of the present disclosure, and are merely illustrative examples, unless otherwise specified. The size and relative positions of components shown in the drawings may be exaggerated for clarity. Furthermore, in the following description, the same names and symbols indicate components that are identical or of the same quality, and detailed descriptions will be omitted as appropriate. Furthermore, the elements constituting the present invention may be configured with the same components, such that multiple elements are served by a single component, or conversely, the functions of a single component may be shared by multiple components.

[0037] The battery pack according to the present disclosure can be suitably used as a battery pack used as a power source for portable medical equipment, electric cleaners, power tools, and other portable electrical equipment. It can also be used as a power source for mobile objects such as power-assisted bicycles and electric carts. Hereinafter, as one embodiment of the present disclosure, a battery pack used as a power source for a pulse oximeter in medical equipment will be described.

[0038] [Embodiment 1] A battery pack according to Embodiment 1 of the present disclosure is shown in Figures 1 to 9. In these figures, Figure 1 is a perspective view showing a battery pack according to Embodiment 1, Figure 2 is an exploded perspective view of the battery pack of Figure 1, Figure 3 is an exploded perspective view further disassembled of the battery pack of Figure 2, Figure 4 is an exploded perspective view of Figure 3 as viewed from below, Figure 5 is a vertical cross-sectional view of the battery pack of Figure 1 taken along line V-V, Figures 6 and 7 are vertical longitudinal cross-sectional views of the battery pack of Figure 5 taken along line VI-VI and line VII-VII, respectively, Figure 8 is an exploded cross-sectional view corresponding to the cross section of the battery pack of Figure 5 taken along line VIII-VIII, and Figure 9 is an enlarged cross-sectional view of a main portion of Figure 5.

[0039] The battery pack 100 shown in these figures includes multiple rechargeable battery cells 1, a battery holder 2 that houses the rechargeable battery cells 1, and an exterior case 3 that houses the battery holder 2. The rechargeable battery cells 1 are cylindrical batteries, and the battery holder 2 includes multiple holding cylindrical sections 21 that house the multiple rechargeable battery cells 1 and hold them parallel to one another, and a heat capacity section 4 that is connected to the outside of the holding cylindrical sections 21 and absorbs heat conducted from the rechargeable battery cells 1. The exterior case 3 has a connecting heat capacity section 6 on its inner surface that is thermally coupled to the battery holder 2 and absorbs heat conducted from the battery holder 2. The connecting heat capacity section 6 is composed of multiple heat conductive protrusions 7 protruding from the interior surface of the exterior case 3. The battery holder 2 has multiple fitting recesses 5 adjacent to the heat capacity section 4 that connect the multiple heat conductive protrusions 7 in a fitting structure. In the battery pack 100, when the battery holder 2 is housed in the outer case 3, the heat-conducting convex portion 7 is fitted into the fitting concave portion 5 to thermally couple the battery holder 2 to the outer case 3, and the heat generated by the secondary battery cell 1 is thermally conducted from the battery holder 2 to the outer case 3 and dissipated to the outside.

[0040] 2 shows a battery pack 100 in which a battery holder 2 containing multiple rechargeable battery cells 1 in a predetermined arrangement is housed in an exterior case 3 as a battery assembly 10. The multiple rechargeable battery cells 1 housed in a predetermined arrangement in the battery holder 2 have lead plates 13 connected to both end faces for a predetermined connection. Furthermore, a circuit board 12 is stacked on the top surface of the battery holder 2, and each lead plate 13 is connected to the circuit board 12 to form the battery assembly 10.

[0041] (Secondary Battery Cell 1) The secondary battery cell 1, which is a cylindrical battery, houses an electrode assembly in a cylindrical metal outer can with a bottom and is filled with an electrolyte. The opening of the outer can is crimped and hermetically sealed with a sealing body. In this secondary battery cell 1, the sealing body and the outer can serve as positive and negative electrodes. The end face of the secondary battery cell 1 sealed by the sealing body is designated as a first end face 1A, and the bottom face of the outer can is designated as a second end face 1B. A highly energy-efficient nonaqueous electrolyte secondary battery, such as a lithium-ion secondary battery, can be suitably used for this secondary battery cell 1. However, the battery pack of the present disclosure does not limit the secondary battery cells to lithium-ion secondary batteries. Any rechargeable battery, such as a nickel-metal hydride battery, a nickel-cadmium battery, or an all-solid-state battery, can also be used for the secondary battery cell.

[0042] The battery pack 100 shown in Figures 3 and 4 contains eight rechargeable battery cells 1. The number of rechargeable battery cells 1 contained in the battery pack 100 is determined to be an optimum number taking into consideration the application and capacity of the battery pack 100, the capacity of each rechargeable battery cell 1, and other factors, and can be, for example, 3 to 20. Furthermore, the battery pack 100 shown in the figures has eight rechargeable battery cells 1 connected in four parallel and two series via lead plates 13. However, the connection state of the multiple rechargeable battery cells 1 can be changed in various ways depending on the application and purpose. The battery pack 100 can increase the output voltage by increasing the number of rechargeable battery cells 1 connected in series, and can increase the maximum current supplied to a load and the charge / discharge capacity of the entire battery pack by increasing the number of rechargeable battery cells 1 connected in parallel.

[0043] (Battery Holder 2) The battery holder 2 holds multiple rechargeable battery cells 1 in a fixed position with a predetermined orientation. The battery holder 2 shown in Figures 2 to 4 holds multiple rechargeable battery cells 1 parallel to one another, with both longitudinal end faces of the rechargeable battery cells 1 aligned flush with one another. The battery holder 2 shown in the figures includes multiple holding tubular sections 21 that house multiple rechargeable battery cells 1 and hold them parallel to one another, and a heat capacity section 4 connected to the outside of the holding tubular sections 21 and absorbing heat conducted from the holding tubular sections 21 to the rechargeable battery cells 1. The battery holder 2 is made of resin, and the multiple holding tubular sections 21 are integrally molded, and the heat capacity section 4 is integrally molded with the holding tubular sections 21. The resin used to form the battery holder 2 is preferably a material with excellent thermal conductivity, insulation, and heat resistance, such as polycarbonate or ABS.

[0044] (Retaining cylindrical portion 21) As shown in Figures 3 and 4, the battery holder 2 has a structure in which multiple retaining cylindrical portions 21 are integrally connected and each accommodates a respective rechargeable battery cell 1 inside. Each retaining cylindrical portion 21 is cylindrical with an inner shape that follows the outer shape of the rechargeable battery cell 1, and forms a battery storage section 20 inside that accommodates the rechargeable battery cell 1. As shown in Figures 6 to 8, the multiple retaining cylindrical portions 21 are integrally connected at the boundaries between adjacent rechargeable battery cells 1 to form partition walls 22. Furthermore, in the outer peripheral region where there are no adjacent rechargeable battery cells 1, an outer peripheral wall portion 23 is formed that follows the outer periphery of the rechargeable battery cell 1.

[0045] The battery holder 2 is provided with multiple integrally molded retaining cylindrical portions 21 so that it can store multiple rechargeable battery cells 1 aligned in the diameter direction (left-right direction in FIGS. 6 to 8 ) in one or more tiers. A battery holder 2 that stores multiple tiers of left-right aligned rechargeable battery cells 1 has multiple retaining cylindrical portions 21 molded in a rice-bale stacking arrangement so that vertically arranged rechargeable battery cells 1 are located in the valleys between the left-right arranged rechargeable battery cells 1. The battery holder 2 shown in the figures has four rechargeable battery cells 1 aligned linearly in the left-right direction to form a battery string 11, and two battery strings 11 stacked in two tiers, storing eight rechargeable battery cells 1 in a rice-bale stacking arrangement with the secondary battery cells 1 of one battery string 11 located in the valleys between the secondary battery cells 1 of the other battery string 11. The battery holder 2 shown in the figure has eight holding tube portions 21 integrally connected together so that it has a generally parallelogram shape in cross section.

[0046] (Holder Tube Portion 2A, Holder Lid Portion 2B) The battery holder 2 shown in Figures 3 to 5 is composed of three components: a holder tube portion 2A that holds the longitudinal middle of the rechargeable battery cell 1, and a pair of holder lid portions 2B connected to both ends of the holder tube portion 2A and holding both ends of the rechargeable battery cell 1. As shown in Figures 4 and 5, the holder tube portion 2A is integrally connected to multiple holding tube portions 21 in a predetermined arrangement. The holder tube portion 2A, which is composed of multiple holding tube portions 21, has openings at both ends, each of which is closed by a pair of holder lid portions 2B. When the battery storage section 20, which is the internal space of each holding tube portion 21, is molded using a mold, a draft angle is provided so that the inner diameter gradually increases from the center toward the opening edge, thereby making the inner diameter at the center the smallest. As a result, the rechargeable battery cell 1 stored in the holding tube portion 21 is held with the center portion closest to the inner surface of the holding tube portion 21. Normally, the central portion of a secondary battery cell 1 is the most likely to expand and generate heat, so a structure that tightly contacts this portion with the inner surface of the holding tube portion 21 has the advantage of being able to efficiently conduct heat from the secondary battery cell 1 to the holding tube portion 21.

[0047] As shown in Figures 3 to 5, the holder lid 2B has an opposing surface shaped to match the end shape of the holder tubular portion 2A, and is structured to cover and hold the ends of the rechargeable battery cells 1 that protrude from the opening of the holder tubular portion 2A. In the example shown in Figure 5, the holder lid 2B has tubular holding portions 41 that hold the ends of the rechargeable battery cells 1. These holding portions 41 hold the ends of the rechargeable battery cells 1 and are inserted inside the edge of the opening of the holder tubular portion 2A to hold the ends of the rechargeable battery cells 1 in place. Furthermore, the holder lid 2B has electrode windows 42 that expose the end surface electrodes of the rechargeable battery cells 1. Lead plates 13 are connected to the first end surface 1A and second end surface 1B exposed through the electrode windows 42, connecting the multiple rechargeable battery cells 1 in series and parallel.

[0048] Although not shown, a battery holder consisting of multiple holding tubes can also be configured as two separate holders split in half at the middle. In this battery holder, the ends of the rechargeable battery cells are inserted into the openings of the two separate holders, and the rechargeable battery cells are stored inside with the two holders sandwiching the rechargeable battery cells from both sides.

[0049] (Heat Capacity Portion 4) As shown in Figures 3 to 7, the heat capacity portion 4 is integrally molded with the holding cylindrical portion 21 and has a heat capacity that absorbs heat from the secondary battery cells 1 that is conducted through the holding cylindrical portion 21. The heat capacity portion 4 is located in the valley portion 24 formed between adjacent holding cylindrical portions 21 and is integrally molded across the holding cylindrical portions 21 so that it can effectively absorb heat conducted from the holding cylindrical portions 21. In this way, a structure in which the heat capacity portion 4 is provided in the valley portion 24 between adjacent holding cylindrical portions 21 allows the heat capacity portion 4 to be provided by effectively utilizing dead space in the battery holder 2. In particular, by forming the heat capacity portion 4 across adjacent holding cylindrical portions 21, heat can be reliably conducted to the heat capacity portion 4 and absorbed regardless of the heat generated by the secondary battery cells 1 housed in either holding cylindrical portion 21. Increasing the volume of the heat capacity portion 4 located in the valley portion 24 between adjacent holding cylindrical portions 21 increases the heat capacity and can effectively absorb heat conducted from the holding cylindrical portions 21. However, a large heat capacity portion 4 with a large volume can cause sink marks during resin molding if it becomes lumpy. To solve this problem, the battery holder 2 shown in the figure has a sink mark prevention recess 25 adjacent to the heat capacity portion 4 to prevent sink marks during molding of the heat capacity portion 4. This sink mark prevention recess 25 also serves as the fitting recess 5 into which the heat conduction protrusion 7 of the exterior case 3, described below, fits.

[0050] (Connecting Ribs 26, Grooves 27) The heat capacity portion 4 shown in Figures 3 to 9 is composed of multiple connecting ribs 26 connecting adjacent holding tubular portions 21. The multiple connecting ribs 26 are arranged in multiple rows parallel to each other at predetermined intervals along the extension direction of the valley portions 24 between adjacent holding tubular portions 21. In this battery holder 2, the heat capacity portion 4 formed in the valley portions 24 is divided into multiple rows, providing gaps between adjacent heat capacity portions 4 and sink mark prevention recesses 25. Each connecting rib has a predetermined thickness and is integrally connected to the holding tubular portion 21 along the valley portions 24, which are generally V-shaped in cross section and formed between adjacent holding tubular portions 21. The connecting ribs 26 in this structure also function as reinforcing ribs that reinforce adjacent holding tubular portions 21. This structure, in which multiple connecting ribs 26 connect adjacent holding tubular portions 21 and reinforce them, increases the rigidity of the battery holder 2 and improves its resistance to impacts such as dropping. 9, the thickness (t) of each connecting rib 26 is a thickness that can maintain sufficient strength while ensuring heat capacity, and is, for example, 3 mm or more, preferably 4 mm or more. The thickness (t) of each connecting rib 26 is a thickness that can prevent sink marks from occurring during resin molding, and is, for example, 10 mm or less, preferably 8 mm or less.

[0051] The heat capacity portion 4, which is made up of a plurality of connecting ribs 26, has grooves 27 with a predetermined width (m) formed between adjacent connecting ribs 26, and these grooves 27 serve as sink mark prevention recesses 25. The grooves 27 formed in the valley portions 24 are formed deep enough to reach the bottom of the valley portions 24, and by making the opposing surfaces between these sink mark prevention recesses 25 and the connecting ribs 26 deep and wide, adjacent connecting ribs 26 are separated over a wider area, reliably preventing sink marks during molding of the heat capacity portion 4. Furthermore, by forming the grooves 27 deep and wide, when the heat conduction protrusions 7 are fitted into the grooves 27 as fitting recesses 5, they can be connected to the heat conduction protrusions 7 over a wider area while maintaining a reliable thermal coupling state. Furthermore, as shown in Figure 8, the groove portion 27 partially exposes the outer peripheral surface of the holding tube portion 21, and as shown in Figure 7, the heat conduction protrusions 7 of the outer case 3 are guided into the groove portion 27, and the heat conduction protrusions 7 are brought close to or in close contact with the holding tube portion 21, thereby achieving thermal coupling.

[0052] The battery holder 2 shown in Figures 3, 4, and 6-8 has multiple cylindrical holding sections 21 stacked in two stages in a bale-like configuration, with the multiple cylindrical holding sections 21 connected to form a roughly parallelogram in cross section. This battery holder 2 has multiple rows of valleys 24 on its underside, with multiple rows of connecting ribs 26 serving as heat capacity sections 4, and grooves 27 between adjacent connecting ribs 26 to form sink-prevention recesses 25. These sink-prevention recesses 25 serve as mating recesses 5 that guide multiple heat-conducting protrusions 7 protruding from the bottom surface of the exterior case 3 in which the battery holder 2 is housed. Furthermore, the battery holder 2 shown in Figures 6 and 7 has an undercut surface 28 on the side of the battery holder 2 formed by stacking vertically stacked retaining cylindrical sections 21. The battery holder 2 has multiple retaining cylindrical sections 21 connected to form a parallelogram in cross section. The undercut-shaped sloped side (the right side in Figures 6 and 7) of the battery holder 2 is also provided with a heat capacity section 4 and a sink mark prevention recess 25. The sink mark prevention recess 25 on the undercut surface 28 serves as a mating recess 5 for guiding multiple heat conduction protrusions 7 protruding from the sloped side of the exterior case 3. Furthermore, the battery holder 2 shown in Figures 3, 6, and 7 has multiple rows of connecting ribs 26 as heat capacity sections 4 in the multiple rows of valleys 24 formed on the top surface, and grooves 27 between adjacent connecting ribs 26 to form sink mark prevention recesses 25. The grooves 27 formed on the top surface do not double as fitting recesses 5 because there are no opposing heat-conducting protrusions 7, and instead function as sink-mark prevention recesses 25. By providing a heat capacity portion 4 on the top surface as well, this structure can absorb heat from the secondary battery cells 1 arranged in the upper tier while increasing rigidity by using the connecting ribs 26 as reinforcing ribs. In particular, by dividing the heat capacity portion 4 into multiple connecting ribs 26 and providing grooves 27 between them, the surface area of ​​the heat capacity portion 4 can be increased, improving heat dissipation characteristics.

[0053] The battery holder 2 described above has multiple connecting ribs 26 formed on the outer periphery of the holder tubular portion 2A, which function as the heat capacity portion 4. This structure, which provides the heat capacity portion 4 on the holder tubular portion 2A, is characterized by its ability to effectively absorb and dissipate heat near the center of the rechargeable battery cell 1, a region prone to heat generation. In particular, grooves 27 formed on the holder tubular portion 2A function as mating recesses 5, which thermally couple to the heat-conducting protrusions 7 on the exterior case 3, thereby more effectively dissipating heat from the rechargeable battery cell 1 to the outside. Furthermore, the battery holder 2 shown in the figure also has connecting ribs 26 formed on the holder lid 2B as the heat capacity portion 4. While the connecting ribs 26 formed on the holder lid 2B are not thermally coupled to the heat-conducting protrusions 7 on the exterior case 3, they reinforce the holder lid 2B, increasing its strength, and their increased surface area allows for more effective dissipation of heat conducted from the holder lid 2B. However, it is also possible to provide a mating recess adjacent to the connecting rib formed on the holder lid, and provide a heat-conducting protrusion on the exterior case that fits into this mating recess. This structure allows the heat from the holder lid to be effectively conducted to the exterior case and dissipated.

[0054] As described above, the heat capacity portion 4 formed on the battery holder 2 is divided into multiple connecting ribs 26, and grooves 27 are provided between adjacent connecting ribs 26. This prevents sink marks during resin molding, but reduces the heat capacity of the heat capacity portion 4 by reducing its volume. To solve this problem, the battery pack 100 of the present disclosure has a connecting heat capacity portion 6 on the inner surface of the exterior case 3 that is thermally coupled to the battery holder 2.

[0055] (External Case 3) As shown in Figures 1 to 6, the external case 3 has a box-shaped exterior and a hollow interior to house the battery assembly 10. The external case 3 shown in the figures is made of resin and includes a box-shaped main case 3A with an opening at the top and a lid case 3B that closes the top opening of the main case 3A. The main case 3A includes a bottom plate 31 that faces the underside of the battery holder 2, side plate portions 32 connected to both sides of the bottom plate 31 and facing the side surfaces of the battery holder 2, and end plate portions 33 connected to both ends of the bottom plate 31 and the side plate portion 32 and facing the end surfaces of the battery holder 2. The lid case 3B includes a top plate 35 and a low peripheral wall portion 36 that runs along the outer periphery of the top plate portion 35. The external cases 3 are connected together with the edge of the opening of the main case 3A facing the leading edge of the peripheral wall portion 36 of the lid case 3B. With the battery assembly 10 housed inside the exterior case 3, the upper opening of the main case 3A is closed by the cover case 3B, and the battery holder 2 is housed inside.

[0056] (Linked Heat Capacity Section 6) The exterior case 3 has a linked heat capacity section 6 on its inner surface that is thermally coupled to the battery holder 2 housed therein and absorbs heat conducted from the battery holder 2. As shown in Figures 3 to 9 , the linked heat capacity section 6 is integrally molded with the exterior case 3 and has the thermal capacity to absorb heat conducted from the secondary battery cells 1 by the battery holder 2. The linked heat capacity section 6 is composed of multiple heat-conducting protrusions 7 protruding from the interior surface of the exterior case 3. The linked heat capacity section 6, which is integrally molded with the exterior case 3, is divided into multiple heat-conducting protrusions 7, providing gaps 34 between adjacent heat-conducting protrusions 7 to prevent sink marks during resin molding of the linked heat capacity section 6. The multiple divided heat-conducting protrusions 7 are fitted into fitting recesses 5 formed in the battery holder 2 and thermally coupled to the battery holder 2 to effectively absorb heat conducted from the battery holder 2.

[0057] The illustrated exterior case 3 has multiple heat-conducting protrusions 7 on the inner surface of the main case 3A, namely, the inner surface of the bottom plate 31 facing the underside of the battery holder 2 housed in the main case 3A, and the inner surface of the side plate 32 facing the undercut surface 28 of the battery holder 2, forming a connected heat capacity section 6. The multiple heat-conducting protrusions 7 on the bottom plate 31 are located in an area facing the valleys 24 between the multiple holding cylindrical sections 21 arranged on the underside of the battery holder 2, and are positioned opposite the multiple fitting recesses 5 formed in the valleys 24. The multiple heat-conducting protrusions 7 on the side plate 32 are located in an area facing the valleys 24 between the holding cylindrical sections 21 arranged above and below the undercut surface 28 of the battery holder 2, and are positioned opposite the multiple fitting recesses 5 formed in the valleys 24. The exterior case 3 shown in the figures has a side plate portion 32 facing the undercut surface 28, which has an inclined portion 32A that follows the undercut surface 28 and a vertical portion 32B that is connected to the upper end of the inclined portion 32A, and a plurality of heat-conducting protrusions 7 are provided on the inclined portion 32A that faces the undercut surface 28.

[0058] (Heat Conduction Protrusions 7) The heat conduction protrusions 7 shown in Figures 3 and 4 are formed in a rib shape that fits into the mating recesses 5, which are the grooves 27 of the battery holder 2. The rib-shaped heat conduction protrusions 7 are arranged in parallel rows along the extension direction of the opposing valleys 24, with gaps 34 of a predetermined width between them. The thickness (w) of the rib-shaped heat conduction protrusions 7, as shown in Figure 9, is a thickness that ensures sufficient strength to maintain an upright position while ensuring heat capacity, and is, for example, 3 mm or more, preferably 4 mm or more. The thickness (w) of the heat conduction protrusions 7 is also a thickness that prevents sink marks during resin molding, and is, for example, 10 mm or less, preferably 8 mm or less.

[0059] As shown in Figure 9, the thickness (w) and width (s) of the gaps 34 of the multiple heat-conducting protrusions 7 are adjusted so that they can fit into the multiple mating recesses 5 formed along the valleys 24 of the battery holder 2. The gaps 34 formed between adjacent heat-conducting protrusions 7 serve as insertion gaps for guiding the connecting ribs 26 of the battery holder 2. The thickness (w) of the heat-conducting protrusions 7 and the width (s) of the gaps 34 are determined so that the heat-conducting protrusions 7 can be fitted into the grooves 27 formed between the connecting ribs 26 and the connecting ribs 26 can be fitted into the gaps 34 formed between the heat-conducting protrusions 7. The thickness (w) of the heat-conducting protrusions 7 is made slightly smaller than or approximately equal to the groove width (m) of the grooves to ensure reliable thermal coupling when smoothly inserted into the grooves 27 that form the mating recesses 5. Similarly, the width (s) of the gap 34 between adjacent heat-conducting protrusions 7 is made slightly larger than or approximately equal to the thickness (t) of the connecting rib 26 so that the connecting rib 26 of the battery holder 2 can be inserted smoothly and thermally bonded reliably.

[0060] Furthermore, the rib-shaped heat-conducting protrusions 7 can have a sloped surface so that their thickness gradually decreases in the direction of protrusion. The inner surface of the grooves 27 of the battery holder 2, which form the mating recesses 5, can have a sloped surface so that the groove width (m) gradually increases toward the opening edge. This structure allows the heat-conducting protrusions 7 to be inserted into the grooves 27, with the sloped opposing surfaces approaching each other for mating. The heat-conducting protrusions 7 can be easily and reliably guided into the grooves 27, and once the heat-conducting protrusions 7 are fitted into the grooves 27, the opposing surfaces can be brought closer together for reliable thermal coupling. Here, a structure in which the grooves 27 formed between the connecting ribs 26 have a gradient on the inner surface so that the groove width (m) gradually increases toward the opening edge results in a structure in which the thickness (t) of adjacent connecting ribs 26 gradually decreases from the bottom of the valley portion 24 toward the opening edge, and a structure in which the surface of the rib-shaped heat conducting protrusions 7 has a gradient so that the thickness gradually decreases in the protruding direction results in a structure in which the width (s) of the gaps 34 formed between the heat conducting protrusions 7 gradually increases from the base side toward the tip side of the heat conducting protrusions 7. Therefore, even when the connecting rib 26 is inserted into the gaps 34 between adjacent heat conducting protrusions 7, the connecting rib 26 can be easily and reliably guided, and when the connecting rib 26 is fitted into the gaps 34, the opposing surfaces of the connecting rib 26 can be brought close together to ensure reliable thermal coupling.

[0061] As described above, a structure in which both the heat-conducting protrusions 7 and the grooves 27 are sloped allows for more effective mating. However, it is also possible to slope only one of the heat-conducting protrusions 7 (or gaps 34) and the grooves 27 (or connecting ribs 26), while leaving the other surface unsloped, e.g., vertical. Even in this case, providing a slope on one of the surfaces simplifies and facilitates the mating of the heat-conducting protrusions 7 and the grooves 27, and the mating of the connecting ribs 26 and the gaps 34, while ensuring reliable thermal coupling. Furthermore, as shown in FIG. 9 , the heat-conducting protrusions 7 can be provided with chamfered portions 7a on both sides of their leading edge, at the boundaries with the side surfaces. This structure allows the heat-conducting protrusions 7 to fit more smoothly into the mating recesses 5.

[0062] 9, the height (H) of the heat-conducting protrusions 7 is preferably smaller than the depth (K) of the grooves 27 so that the tip surfaces of the heat-conducting protrusions 7 do not contact the bottom surface of the grooves when fitted into the recessed fitting portions 5. With this structure, when the heat-conducting protrusions 7 are inserted all the way into the recessed fitting portions 5, the tip surfaces of the connecting ribs 26 can be connected in surface contact with the inner surface of the outer case 3. This allows heat conducted from the retaining tube portion 21 to the connecting ribs 26 to be conducted directly to the outer case 3, allowing it to be effectively dissipated to the outside.

[0063] The rib-shaped heat-conducting protrusions 7 fitted into the grooves 27 have a surface shape that conforms to the outer circumferential surface of the holding tubular portion 21. When fitted into the grooves 27, the heat-conducting protrusions 7 are thermally coupled by bringing both opposing surfaces close to or in close contact with the outer surfaces of the opposing holding tubular portion 21. The heat-conducting protrusions 7 shown in the figure are shaped like Mount Fuji when viewed from the front. The top surface is close to or in close contact with the partition wall 22 of the battery holder 2, and both side surfaces are curved surfaces 7A that conform to the outer circumferential surface of the outer wall 23 of the holding tubular portion 21, also close to or in close contact with the holding tubular portion 21. This structure allows the outer circumferential surface of the holding tubular portion 21 to be thermally coupled directly to the heat-conducting protrusions 7 of the outer case 3, allowing for efficient thermal conduction and dissipation of heat generated by the rechargeable battery cells 1 from the holding tubular portion 21 to the outer case 3. Furthermore, the heat-conducting protrusions on the inclined portion 32A of the side plate 32 have a vertical surface 7B facing the left side in Fig. 8. This structure, in which the facing surface of the heat-conducting protrusions 7 formed on the inclined portion 32A is vertical surface 7B, has the advantage that the battery holder 2 can be inserted smoothly into the main case 3A without contact with the retaining tube portion 21.

[0064] Furthermore, in the fitting structure shown in FIG. 9 , thermally conductive paste 15 is disposed between the fitting recess 5 and the thermally conductive protrusion 7. This structure improves the thermal conductivity between the fitting recess 5 and the thermally conductive protrusion 7, enabling effective heat conduction. In particular, even if the height (H) of the thermally conductive protrusion 7 is smaller than the depth (K) of the groove 27, creating a gap between the tip surface of the thermally conductive protrusion 7 and the bottom surface of the groove 27, applying thermally conductive paste 15 to this gap provides a more effective thermal coupling between the battery holder 2 and the exterior case 3. Silicone oil, thermally conductive grease, or the like can be used as this thermally conductive paste 15. Furthermore, the structure in which thermally conductive paste 15 is disposed between the fitting recess 5 and the thermally conductive protrusion 7 also has the advantage of allowing the fitting recess 5 and the thermally conductive protrusion 7 to fit together more smoothly with low resistance during the assembly process of the battery pack 100.

[0065] (Second Linked Heat Capacity Portion 8) The exterior case 3 also includes a second linked heat capacity portion 8 that is thermally coupled to the holding tube portion 21 of the battery holder 2 along the boundary between the bottom plate portion 31 and the side plate portion 32 of the main case 3A. The second linked heat capacity portion 8 is composed of multiple opposing ribs 38 that are integrally connected across the bottom plate portion 31 and the side plate portion 32. The illustrated second linked heat capacity portion 8 is divided into multiple opposing ribs 38, providing gaps between adjacent opposing ribs 38 to prevent sink marks during resin molding of the second linked heat capacity portion 8. Furthermore, the opposing surface of each opposing rib 38 is shaped to conform to the surface of the holding tube portion 21. The opposing surface of the illustrated opposing rib 38 is an arc-shaped curved surface 8A that conforms to the curved surface of the holding tube portion 21. This allows for close surface contact with the holding tube portion 21, enabling effective heat conduction. In this way, the multiple opposing ribs 38 integrally formed across the bottom plate portion 31 and the side plate portion 32 have the advantage of being able to increase the rigidity and reinforce the corner portions of the box-shaped main body case 3A.

[0066] In the battery pack 100 with the above structure, the heat capacity portion 4 on the battery holder 2 and the connecting heat capacity portion 6 on the exterior case 3 are connected by a fitting structure at the opposing portion between the outer peripheral surface of the battery holder 2 and the inner surface of the exterior case 3. This effectively utilizes the excess space between the battery holder 2 and the exterior case 3 to form a resin mass that would not be possible with either component alone, allowing for efficient heat conduction and dissipation of the heat from the generated secondary battery cells 1 from the battery holder 2 to the exterior case 3. The heat transfer that occurs when the heat from the generated secondary battery cells 1 is conducted from the battery holder 2 to the exterior case 3 for heat dissipation in the above battery pack 100 is described in detail in FIGS. 5 to 7 and 9. Note that FIG. 5 is a cross-sectional view corresponding to the cross section along line V-V in FIGS. 6 and 7, and FIG. 9 is an enlarged cross-sectional view of a key portion of FIG. 5.

[0067] In these figures, arrows a to h indicate the transfer of heat from secondary battery cell A located at the lower left in Figures 6 and 7 when the secondary battery cell A generates heat due to an abnormality such as thermal runaway. A portion of the heat generated in secondary battery cell A is conducted from the holding cylindrical portion 21 to the connecting rib 26, which is the heat capacity portion 4, as shown by arrow a, and then from the connecting rib 26 to the outer case 3 as shown by arrow b, where it is dissipated to the outside. A portion of the heat generated in secondary battery cell A is conducted from the holding cylindrical portion 21 to the heat conductive protrusions 7, which are the connecting heat capacity portion 6, as shown by arrow c, and then from the heat conductive protrusions 7 to the outer case 3 as shown by arrow d, where it is dissipated to the outside. Furthermore, a portion of the heat conducted from the holding cylindrical portion 21 to the connecting rib 26, which is the heat capacity portion 4, as shown by arrow a, is conducted from the connecting rib 26 to the heat conductive protrusions 7 as shown by arrow e, and then from the heat conductive protrusions 7 to the outer case 3 as shown by arrow d, where it is dissipated to the outside. In this way, the structure in which the heat capacity section 4 provided on the battery holder 2 and the connecting heat capacity section 6 provided on the exterior case are thermally coupled by an interlocking structure, as shown in Figure 5, thermally couples the underside of the battery holder 2 and the bottom plate section 31 of the exterior case 3 in a tight, tight contact state, allowing efficient heat conduction from the battery holder 2 to the exterior case 3 and heat dissipation.

[0068] 6 and 7 , where the holding tube portion 21 of the battery holder 2 directly contacts the inner surface of the exterior case 3, some of the heat generated by the secondary battery cells A is thermally conducted from the holding tube portion 21 to the exterior case 3 as shown by arrow f and then radiated to the outside. Also, where the holding tube portion 21 of the battery holder 2 contacts the second connecting heat capacity portion 8 provided at the corner of the exterior case 3, some of the heat generated by the secondary battery cells A is conducted from the holding tube portion 21 to the opposing rib 38, which is the second connecting heat capacity portion 8, as shown by arrow g, and then from the opposing rib 38 to the exterior case 3 as shown by arrow h, where it is radiated to the outside.

[0069] The above battery pack is assembled in the following steps: (1) The rechargeable battery cells 1 are placed in the battery holder 2. The battery holder 2 shown in Figures 3 and 4 is composed of three components. After the holder lid 2B is secured to one opening of the holder tube 2A, the rechargeable battery cells 1 are inserted into the battery storage compartments 20 of each holding tube 21. After the rechargeable battery cells 1 (eight rechargeable battery cells 1 in the figure) are inserted in the correct orientation into all holding tube sections 21 of the holder tube 2A, the holder lid 2B is secured to the opening on the opposite side to close the opening. (2) Lead plates 13 are connected to the electrodes on both ends of the rechargeable battery cells 1 placed in the battery holder 2. The electrodes on both ends of the rechargeable battery cells 1 are connected via the lead plates 13, resulting in a predetermined connection. In the figure, eight rechargeable battery cells 1 are connected via the lead plates 13 in a four-parallel, two-series configuration. (3) Place the circuit board 12 on the top surface of the battery holder 2, and connect the lead plates 13 connected to the rechargeable battery cells 1 to the circuit board 12. In this state, the circuit board 12 is fixed to the battery holder 2 via the lead plates 13, completing the battery assembly 10. (4) Apply thermally conductive paste 15 to the multiple mating recesses 5 formed in the battery holder 2. The battery holder 2 shown in the figure has grooves 27 formed on the underside and grooves 27 formed in the undercut surface 28 as mating recesses 5, so apply thermally conductive paste 15 to these mating recesses. (5) Place the battery assembly 10 inside the main case 3A. At this time, the multiple heat-conducting protrusions 7 on the bottom plate 31 of the main case 3A are guided into the mating recesses 5 on the underside of the battery holder 2, while the multiple heat-conducting protrusions 7 on the inclined portions 32A of the side plate 32 are guided into the mating recesses 5 on the undercut surfaces 28 of the battery holder 2, mating the heat-conducting protrusions 7 with the mating recesses 5. In this state, the battery assembly is placed in its designated position in the main case. (6) The lid case 3B is connected to the opening edge of the main case 3A, and the upper opening of the main case 3A is closed with the lid case 3B.

[0070] In the first embodiment described above, the battery holder 2 and the exterior case 3 are made of resin. However, the battery pack of the present disclosure does not limit the materials of the battery holder 2 and the exterior case 3 to resin. In the battery pack of the present disclosure, materials other than resin, such as metal or heat-softening (phase-change) material, can also be used for either or both of the battery holder and the exterior case. For example, the battery holder can be made of a metal such as aluminum. An aluminum battery holder can be integrally molded using aluminum die-casting, with the cylindrical holding portion and heat capacity portion. The battery holder can also be a hybrid of a metal such as aluminum and resin. For example, the cylindrical holding portion of this battery holder can be made of resin to maintain insulation from the secondary battery cells, while a metal heat capacity portion can be provided on the outside of the cylindrical holding portion to improve heat capacity and thermal conductivity. This battery holder can be manufactured, for example, by inserting a resin member with multiple integrally molded cylindrical retaining sections into the inside of a cylindrical metal heat capacity section with multiple connecting ribs and grooves on its outer periphery. Alternatively, a metal member with multiple connecting ribs and grooves can be inserted into the outside of a resinous cylindrical retaining section to form an integral structure. The exterior case can also be made of a metal, such as aluminum. A metal exterior case can be formed into a predetermined shape by press-molding an aluminum plate. Furthermore, an exterior case manufactured by press-molding an aluminum plate can have multiple inwardly protruding heat-conducting protrusions formed on the inner surface by embossing during press-molding. This structure, which forms multiple heat-conducting protrusions by press-molding, is simple and easy to manufacture, and by forming the protrusions inward, it can increase the rigidity of the exterior case while increasing its surface area and improving its heat dissipation characteristics.

[0071] (Embodiment 2) In the above example, the heat capacity portion 4 formed on the battery holder 2 is configured with multiple rows of connecting ribs 26, the grooves 27 between the connecting ribs 26 serve as mating recesses 5, and the heat conduction protrusions 7 on the exterior case 3 are ribbed. However, the heat capacity portion 4 and the heat conduction protrusions 7 can also have other shapes. The battery holder 2 shown in Figure 10 has a heat capacity portion 4 extending over the entire valley 24 formed between adjacent retaining cylindrical portions 21. Furthermore, this battery holder 2 has multiple recesses extending in the depth direction of the valley 24 at predetermined intervals along the extension direction of the valley 24 in the heat capacity portion 4, forming sink mark prevention recesses 25. The sink mark prevention recesses 25 formed on the underside of the battery holder 2 serve as mating recesses 5 into which the heat conduction protrusions 7 on the exterior case 3 fit. The sink mark prevention recesses 25 shown in the figure have an inverted truncated pyramid shape with a cross-sectional area that gradually decreases in the depth direction.

[0072] Furthermore, the exterior case 3 shown in Figure 11 has a shape that allows the heat-conducting protrusions 7 on the main case 3A to fit into the mating recesses 5 shown in Figure 10. Specifically, the heat-conducting protrusions 7 shown in Figure 11 have a truncated quadrangular pyramid shape with a cross-sectional area that gradually decreases in the direction of protrusion. When fitted into the mating recesses 5 of the battery holder 2, the heat-conducting protrusions 7 are positioned close to or in close contact with the inner surface of the mating recess 5, ensuring reliable thermal coupling. The exterior case 3 shown in the figure has truncated quadrangular pyramid-shaped heat-conducting protrusions 7 and, facing the battery holder 2, inverted truncated quadrangular pyramid-shaped mating recesses 5 into which the heat-conducting protrusions 7 can fit. However, the shape, size, volume, and spacing of the heat-conducting protrusions 7, as well as the shape, depth, volume, and spacing of the mating recesses 5 on the battery holder 2, can be designed in a variety of ways.

[0073] Third Embodiment In the above examples, a battery row 11 is formed by arranging multiple secondary battery cells 1 in a single row in the diameter direction, and two battery rows 11 are arranged one above the other with the rows offset left and right so as to form a stacked posture like a rice bag. However, a battery pack can also be configured with a single battery row 11 consisting of multiple secondary battery cells 1 arranged in a single row in the diameter direction. A battery pack 300 with this structure is shown in FIG. 12 . The battery pack 300 shown in FIG. 12 houses five secondary battery cells 1 in a single row in the diameter direction, parallel to each other, in a battery holder 2, and this battery holder 2 is housed in an exterior case as a battery assembly 10. Note that in this second embodiment, the same components as those in the battery pack of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0074] The battery holder 2 shown in Figure 12 is integrally molded with five diametrically aligned, connected retaining cylindrical sections 21 to accommodate five rechargeable battery cells 1. Similar to the previously described battery holder 2, this battery holder 2 has multiple rows of connecting ribs 26 as heat capacity sections 4 in multiple rows of valleys 24 formed on the underside, and grooves 27 between adjacent connecting ribs 26 to form sink-mark prevention recesses 25. These sink-mark prevention recesses 25 also serve as mating recesses 5 that guide multiple heat-conducting protrusions 7 protruding from the bottom surface of the exterior case 3 that houses the battery holder 2. By fitting the heat-conducting protrusions 7 on the exterior case 3 into the mating recesses 5 on the underside of this battery holder 2, the connecting heat capacity section 6 on the exterior case 3 and the heat capacity section 4 of the battery holder 2 can be thermally coupled without gaps. In this structure, all of the retaining cylindrical portions 21 in which the secondary battery cells 1 are housed in a row housed in the battery holder 2 can be thermally coupled to the outer case 3 via the heat capacity portion 4 and the connecting heat capacity portion 6, so that even when any of the secondary battery cells 1 is generating heat, the heat from the secondary battery cells 1 can be effectively conducted to the outer case 3 and dissipated.

[0075] 12 also has multiple rows of connecting ribs 26 formed as heat capacity sections 4 in multiple rows of valley sections 24 formed on the top surface, and grooves 27 are formed between adjacent connecting ribs 26 to form sink mark prevention recesses 25. Because there are no opposing heat conduction protrusions 7, the grooves 27 formed on the top surface do not also function as fitting recesses 5 but as sink mark prevention recesses 25. By dividing this heat capacity section 4 into multiple connecting ribs 26 and providing grooves 27 between them, the surface area of ​​the heat capacity section 4 can be increased, improving heat dissipation characteristics.

[0076] As described above, battery holders 2 that house a single battery row 11 have multiple cylindrical retaining sections 21 connected in a flush configuration, which can make them vulnerable to impacts. However, the battery holder 2 shown in the figure has connecting ribs 26 on both the top and bottom of the valleys 24 between adjacent cylindrical retaining sections 21. This reinforces the adjacent cylindrical retaining sections 21 with the connecting ribs 26, increasing the rigidity of the battery holder 2 and improving its impact resistance. Furthermore, on the underside of the battery holder 2, the heat capacity section 4 of the battery holder 2 and the connecting heat capacity section 6 of the exterior case 3 are connected by a fitting structure, further reinforcing the battery holder 2 while ensuring thermal coupling between the battery holder 2 and the exterior case 3 for heat dissipation.

[0077] The battery pack according to the present disclosure can be suitably used as a power source for portable medical equipment, electric cleaners, power tools, and other portable electrical equipment, or as a battery pack for mobile objects such as power-assisted bicycles and electric carts.

[0078] DESCRIPTION OF SYMBOLS 100, 300...Battery pack 1...Second battery cell 1A...First end face 1B...Second end face 2...Battery holder 2A...Holder cylindrical portion 2B...Holder lid portion 3...External case 3A...Main body case 3B...Lid case 4...Heat capacity portion 5...Fitting recess 6...Connecting heat capacity portion 7...Heat conductive protrusion 7A...Curved surface 7B...Vertical surface 7a...Chamfered portion 8...Second connecting heat capacity portion 8A...Curved surface 10...Battery assembly 11...Battery string 12...Circuit board 13...Lead plate 15...Heat conductive paste 20...Battery storage portion 21...Retaining cylindrical portion 22...Partition wall portion 23...Outer peripheral wall portion 24...Valve portion 25...Sink mark prevention recess 26...Connecting rib 27...Groove portion 28...Undercut surface 31...Bottom plate portion 32...Side plate portion 32A: Inclined portion; 32B: Vertical portion; 33: End surface plate portion; 34: Gap; 35: Top surface plate portion; 36: Peripheral wall portion; 38: Opposing rib; 41: Holding portion; 42: Electrode window

Claims

1. A battery pack comprising: a plurality of secondary battery cells; a battery holder that houses the plurality of secondary battery cells; and an exterior case that houses the battery holder, wherein each of the plurality of secondary battery cells is a cylindrical battery; the battery holder comprises: a plurality of holding tube sections that house the plurality of secondary battery cells respectively and hold them parallel to each other; and a heat capacity section that is connected to the outside of the plurality of holding tube sections and absorbs heat of the plurality of secondary battery cells that is conducted from the plurality of holding tube sections; the exterior case has a connected heat capacity section on its inner surface that is thermally coupled to the battery holder and absorbs heat conducted from the battery holder, the connected heat capacity section being composed of a plurality of heat conductive protrusions protruding from the inner surface of the exterior case; and the battery holder has a plurality of fitting recesses adjacent to the heat capacity section that connect the plurality of heat conductive protrusions in a fitting structure; With the battery holder housed in the outer case, the multiple heat conductive protrusions are engaged with the multiple mating recesses to thermally couple the battery holder to the outer case, and heat generated by the multiple secondary battery cells is thermally conducted from the battery holder to the outer case and dissipated to the outside.

2. A battery pack as described in claim 1, wherein the battery holder is made of resin, the multiple holding cylindrical parts are integrally molded, and the heat capacity part is integrally molded with the multiple holding cylindrical parts, and further, the multiple fitting recesses formed adjacent to the heat capacity parts also serve as recesses to prevent sink marks during resin molding, and the exterior case is made of resin, the connecting heat capacity part is integrally molded with the exterior case, and the connecting heat capacity part is divided into the multiple heat conductive protrusions with gaps provided between adjacent heat conductive protrusions.

3. A battery pack as described in claim 2, wherein the heat capacity portion is located in a valley portion formed between adjacent retaining cylindrical portions and is molded to straddle the multiple retaining cylindrical portions, and the multiple fitting recesses are formed and located in the valley portions.

4. A battery pack as described in claim 3, wherein the heat capacity portion is composed of a plurality of connecting ribs arranged in the extension direction of the valley portion among the plurality of retaining cylindrical portions and connecting adjacent retaining cylindrical portions, and grooves are formed between adjacent connecting ribs among the plurality of connecting ribs, and each of the plurality of grooves serves as the fitting recess, and the heat conducting protrusion is rib-shaped and fits into the groove.

5. A battery pack as described in claim 4, wherein the surface shape of the heat-conducting convex portion facing the retaining cylindrical portion is shaped to conform to the outer circumferential surface of the retaining cylindrical portion, and when fitted into the groove, the facing surface is brought close to or in intimate contact with the outer surface of the retaining cylindrical portion, thereby achieving thermal coupling.

6. A battery pack as described in claim 4, wherein the rib-shaped heat-conducting protrusions have a surface gradient so that the thickness gradually decreases in the protruding direction, and the grooves have an inner surface gradient so that the groove width gradually increases toward the opening edge, and when the heat-conducting protrusions are inserted into the grooves, the opposing gradient surfaces are brought close to each other and fitted together.

7. A battery pack according to any one of claims 1 to 6, wherein a thermally conductive paste is disposed between said fitting recess and said thermally conductive protrusion.

8. A battery pack as described in any one of claims 1 to 6, wherein the battery holder comprises a holder tubular portion that is open at both ends and holds the longitudinal middle portions of the multiple secondary battery cells, and a pair of holder lid portions that are connected to the openings at both ends of the holder tubular portion and hold both ends of the multiple secondary battery cells, and the heat capacity portion and multiple fitting recesses are provided on the outer peripheral surface of the holder tubular portion.

9. A battery pack as described in any one of claims 1 to 6, wherein the outer case comprises a box-shaped main case with an upper opening, and a lid case closing the upper opening of the main case, the main case comprises a bottom plate portion facing the lower surface of the battery holder, side plate portions connected to both sides of the bottom plate portion and facing both side surfaces of the battery holder, and end plate portions connected to both ends of the bottom plate portion and the side plate portion and facing both end surfaces of the battery holder, the battery holder having a plurality of the fitting recesses opening to the lower surface, and the outer case having a plurality of the heat conductive protrusions on the bottom plate portion.

10. A battery pack as described in claim 9, wherein the battery holder is formed by arranging a plurality of the retaining cylindrical portions in a cross-sectional configuration so that a plurality of the secondary battery cells can be arranged in a diametrically aligned manner in a stacked shape in multiple stages, the side surface of the battery holder formed by the retaining cylindrical portions stacked one on top of the other forms an undercut surface that is inclined in an undercut shape, and the heat capacity portion and the fitting recess are formed on the undercut surface, and the exterior case is configured such that the side plate portion facing the undercut surface has an inclined portion that follows the undercut surface, and the heat conductive protrusion is formed on the inclined portion, and the heat conductive protrusion of the inclined portion is fitted into the fitting recess of the undercut surface.

11. A battery pack as described in claim 9, wherein the outer case has a second connecting heat capacity portion thermally coupled to the retaining tube portion of the battery holder along the boundary between the bottom plate portion and the side plate portion, the second connecting heat capacity portion being composed of a plurality of opposing ribs integrally connected across the bottom plate portion and the side plate portion, and the opposing ribs have a shape such that the surfaces facing the retaining tube portion conform to the surface of the retaining tube portion.

12. A battery pack comprising: a plurality of secondary battery cells; a battery holder that houses the plurality of secondary battery cells; and an exterior case that houses the battery holder, wherein each of the plurality of secondary battery cells is a cylindrical battery, the battery holder comprises: a plurality of holding cylindrical sections that house the plurality of secondary battery cells respectively and hold them parallel to each other, a heat capacity section that is connected to the outside of the plurality of holding cylindrical sections and absorbs heat from the plurality of secondary battery cells conducted from the plurality of holding cylindrical sections, and a plurality of fitting recesses adjacent to the heat capacity section, the exterior case comprises a connected heat capacity section on an inner surface, the connected heat capacity section being composed of a plurality of heat conductive protrusions protruding from the inner surface of the exterior case, the plurality of heat conductive protrusions and the plurality of fitting recesses being connected by a fitting structure, and the battery holder and the exterior case are thermally coupled when the battery holder is housed in the exterior case, and heat generated by the plurality of secondary battery cells is thermally conducted from the battery holder to the exterior case and dissipated to the outside.

13. A battery pack as described in claim 12, wherein the battery holder is made of resin and is integrally molded with the multiple holding cylindrical portions, and the heat capacity portion is integrally molded with the multiple holding cylindrical portions, the heat capacity portion is located in a valley portion formed between adjacent holding cylindrical portions and molded to span the multiple holding cylindrical portions, and the multiple fitting recesses are located in the valley portion, the heat capacity portion is composed of a plurality of connecting ribs that are arranged along the axes of the multiple holding cylindrical portions and connect adjacent holding cylindrical portions among the multiple connecting ribs, and grooves are formed between adjacent connecting ribs among the multiple connecting ribs, each of the multiple grooves serves as the fitting recess, and a space is provided between the adjacent connecting ribs with a depth reaching the bottom of the valley portion, and the exterior case is made of resin, the connecting heat capacity portion is integrally molded with the exterior case, and a gap is provided between adjacent heat conductive protrusions.

14. A battery pack as described in claim 13, wherein the heat-conducting protrusions are rib-shaped and fitted into the grooves.

15. A battery pack as described in claim 14, wherein the surface shape of the heat-conducting convex portion facing the retaining cylindrical portion is shaped to conform to the outer peripheral surface of the retaining cylindrical portion, and when fitted into the groove, the facing surface is brought close to or in intimate contact with the outer surface of the retaining cylindrical portion, thereby thermally bonding the battery pack.

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