Battery pack

Abstract

Provided is a battery pack capable of suppressing a decrease in a capacity retention rate. The battery pack includes a plurality of single cells. Each single cell includes an electrode body and a case that houses the electrode body and is sealed by a sealing portion. The plurality of single cells are arranged along an arrangement direction that is one direction. The battery pack includes a spacer that is interposed between case side walls of two cases that are adjacent to each other. In the battery pack, the plurality of single cells are restrained in a state in which a load is applied in a direction in which the single cells are close to each other. The electrode body faces the case side walls and includes a pair of opposing flat portions. The spacer includes a base portion and a plurality of protruding portions that are configured to protrude from the base portion toward the case side walls. At least a portion of the plurality of protruding portions is a first protruding portion that presses a position of the case side wall that corresponds to the upper curved portion.

Description

Technical Field

[0001] This invention relates to a battery pack consisting of multiple individual cells arranged with spacers between them. Background Technology

[0002] Non-aqueous secondary batteries, such as lithium-ion batteries, which are widely used in high-output power supplies for vehicle propulsion, are constructed in the form of battery packs. The battery pack is constructed by sandwiching spacers between multiple individual cells whose electrodes are housed in a casing. Furthermore, constraint straps are used to apply a constant load along the arrangement direction of the individual cells. Each individual cell is sealed with a sealing part while its electrodes are housed in the casing (see Patent Document 1).

[0003] Each spacer has multiple protrusions that project toward the sidewall of the housing. These protrusions are configured in a comb-like shape relative to the base plate. The spacer presses against the sidewall of the housing using the front ends of each protrusion. The space between the protrusions is configured as a passage for cooling air to circulate. Existing technical documents Patent documents

[0004] Patent Document 1: Japanese Patent Application Publication No. 2019-128991 Summary of the Invention The problem that the invention aims to solve

[0005] Furthermore, in each individual cell, a seal is formed by closing the opening of the casing with a cover to house the electrodes. However, over time, moisture seeps into this seal. This seeped moisture reacts with charge carriers such as ions in the active material at the upper edge near the seal, causing these charge carriers to be removed from the active material. This results in the shrinkage of the active material and, consequently, the shrinkage of the electrodes. Consequently, the constraint pressure on the upper edge of the electrodes based on the spacer weakens, making it difficult to maintain an appropriate inter-electrode distance. As a result, this may lead to a decrease in capacitance retention.

[0006] In Patent Document 1, the convex portion of the spacer is configured to elastically deform along the arrangement direction. When the convex portion is configured to elastically deform along the arrangement direction, the constraint pressure pressing against the sidewall of the housing is reduced in that portion. Therefore, the infiltrated moisture reacts with lithium ions, making it difficult to maintain an appropriate inter-electrode distance when electrode shrinkage occurs. Methods for solving problems

[0007] One aspect of the battery pack disclosed herein includes a plurality of individual cells arranged in one direction, each comprising an electrode body and a housing containing the electrode body and sealed by a sealing portion, and a spacer sandwiched between the sidewalls of two adjacent housings. The plurality of individual cells are constrained by applying a constraint pressure in a direction of mutual proximity. The electrode body is opposite to the housing sidewall and has a pair of opposing planar portions. The spacer has a base portion and a plurality of protrusions arranged in a direction protruding from the base portion toward the housing sidewall. At least a portion of the plurality of protrusions is an upper protrusion, which presses against the housing sidewall at a position above the corresponding position of the planar portion that is closest to the upper edge of the sealing portion.

[0008] In the aforementioned battery pack, the electrode body can be configured as follows: it is a flat wound body obtained by winding a laminate formed by stacking positive and negative electrode sheets with a separator between them. The opposite sides of the flat wound body are the pair of planar portions. The portion of the flat wound body that connects the upper edges of the pair of planar portions includes an upwardly bulging upper curved portion. The upper protrusion presses against the side wall of the housing at a position corresponding to the upper curved portion.

[0009] In the aforementioned battery pack, the aforementioned upper protrusion may be configured to extend continuously without interruption, parallel to the extending direction of the upper edge of the aforementioned planar portion.

[0010] In the aforementioned battery pack, the aforementioned protrusions may be configured to have the same height relative to the aforementioned substrate portion.

[0011] The battery pack described above can be configured as follows: when the length between the first position corresponding to the upper edge of the flat portion and the second position corresponding to the lower edge of the flat portion on the side wall of the housing is set as A, and the distance from the first position to the pressing position on the side close to the first position where the upper protrusion is pressed is set as B, the ratio C of B to A is 4.5% or more and 13.6% or less.

[0012] The effects of the invention According to the present invention, the decrease in capacitance retention rate can be suppressed. Attached Figure Description

[0013] Figure 1 It is a 3D diagram of the battery pack. Figure 2 It shows the composition Figure 1 A 3D view of a single cell in a battery pack. Figure 3 This is a three-dimensional view showing the electrode body in its unfolded state. Figure 4It is a top view of a battery pack formed by constraining multiple individual cells. Figure 5 It is a three-dimensional view of the spacer sandwiched between individual batteries. Figure 6 This is a schematic diagram showing the positional relationship between a single cell and a spacer. Figure 7 This is a diagram illustrating the manufacturing process of the single cell used in the embodiments and comparative examples. Figure 8 This is a graph showing the resistance distribution of the negative plate in the comparative example. Figure 9 This is a graph showing the average value of the negative plate resistance at each position from position 1 to position 4 in the comparative example. Figure 10 This is a diagram showing the surface pressure distribution in Example 1. Figure 11 This is a graph showing the average surface pressure at each position from position 1 to position 4 in Example 1 and the Comparative Example. Figure 12 This is a graph showing the relationship between the number of cycles and the capacitance retention rate in Examples 1-3 and the Comparative Example. Detailed Implementation

[0014] The following is for reference Figures 1-12 One embodiment of the present invention will be described. [Battery Pack Composition] like Figure 1 As shown, the battery pack 1 includes a plurality of individual cells 10, a plurality of spacers 40, a pair of end plates 50, and a plurality of constraint straps 52. The plurality of individual cells 10 are arranged along an arrangement direction X. The pair of end plates 50 are disposed at both ends of the battery pack 1 in the arrangement direction X. The plurality of constraint straps 52 are installed on the pair of end plates 50 in a manner that bridges the pair of end plates 50. The plurality of spacers 40 are respectively disposed between the plurality of individual cells 10 and between the individual cells 10 and the end plates 50 in the arrangement direction X.

[0015] A pair of end plates 50 clamp a plurality of individual cells 10 and a plurality of spacers 40 along the arrangement direction X. A plurality of constraint straps 52 are fixed to the end plates 50 using a plurality of screws. The constraint straps 52 are installed on the pair of end plates 50 in a manner that applies a predetermined constraint pressure along the arrangement direction X. Thus, constraint pressure is applied to the plurality of individual cells 10 and the plurality of spacers 40 from a direction that is the same as the arrangement direction X and that the plurality of individual cells 10 are close to each other, keeping the battery pack 1 as a single unit. In this embodiment, a constraint mechanism is constituted by a pair of end plates 50 and a plurality of constraint straps 52.

[0016] [Composition of a single battery] like Figure 2As shown, as an example, the single battery 10 is a lithium-ion secondary battery. The single battery 10 includes a casing 11 and a cover 12. The casing 11 houses the electrode body 20. The casing 11 has a flat, bottomed rectangular (cubic prism) shape with an opening on the upper side. The cover 12 closes the opening of the casing 11. The casing 11 and the cover 12 are made of metals such as aluminum or aluminum alloy. In addition, the thickness (plate thickness) of the casing 11 is approximately 1 mm or less, preferably 0.5 mm or less, for example, 0.3 mm or more, or 0.4 mm. It is also conceivable to combine the above upper and lower limits arbitrarily. In the single battery 10, a sealed battery cell is formed by mounting the cover 12 to the casing 11. In the arrangement direction X, a pair of casing sidewalls 11A opposite each other in the casing 11 are formed by planes. When a constraint pressure is applied from the spacer 40, the casing sidewalls 11A bend slightly inward, pressing the electrode body 20.

[0017] The cover 12 has two external terminals 13A and 13B. These external terminals 13A and 13B are used for charging and discharging electricity. The positive-side current collector 20A, the positive end of the electrode body 20, is electrically connected to the positive external terminal 13A via a positive-side current collector 14A. The negative-side current collector 20B, the negative end of the electrode body 20, is electrically connected to the negative external terminal 13B via a negative-side current collector 14B. Current collectors 14A and 14B penetrate the cover 12 and are connected to the external terminals 13A and 13B. An insulating gasket is disposed between the current collectors 14A and 14B and the cover 12. The gasket electrically insulates the current collectors 14A and 14B from the cover 12 and seals the space between them. Additionally, a non-aqueous electrolyte is injected into the housing 11 through the injection port 15. It should be noted that the shape of the external terminals 13A and 13B is not limited to... Figure 2 The shape shown can be any shape. The external terminals 13A and 13B of the positive and negative terminals of adjacent single cells 10 are connected via bus 18 (see reference). Figure 1 The adjacent single cells 10 are electrically connected.

[0018] [Electrode] like Figure 3As shown, the electrode body 20 is a flat, wound body formed by laminating a strip-shaped positive electrode 21 and a negative electrode 24 with a separator 27 in between, and then winding the resulting laminated body. The positive electrode 21, the negative electrode 24, and the separator 27 are laminated in such a way that their respective long sides are aligned with the length direction D1. In the laminated body before winding, the positive electrode 21, the separator 27, the negative electrode 24, and the separator 27 are laminated in this order along the thickness direction. The electrode body 20 has a structure in which the positive and negative sheets 21 and 24, which are laminated with the separator 27 in between, are wound around a winding axis L1 (which extends along the width direction D2 of the strip shape).

[0019] [Positive electrode tablets] The positive electrode 21 includes a positive current collector 22 and a positive composite material layer 23. The positive current collector 22 is an electrode substrate formed into a long strip or foil shape. The positive composite material layer 23 is provided on two opposite surfaces of the positive current collector 22. At one end of the positive current collector 22 in the width direction D2, there is an uncoated portion 22A on the positive electrode side where the positive composite material layer 23 is not formed and the positive current collector 22 is exposed.

[0020] The positive current collector 22 is made of a metal foil composed of aluminum or an alloy with aluminum as the main component. The positive current collector 22 functions as the current collector for the positive electrode. The uncoated portion 22A on the positive side of the positive current collector 22 is pressed together with its opposing surfaces in a wound state to form the positive current collector portion 20A.

[0021] The positive electrode composite layer 23 is a cured form of a liquid positive electrode composite paste. The positive electrode composite paste includes a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder. The positive electrode composite layer 23 is formed by drying the positive electrode composite paste and vaporizing the positive electrode solvent. Therefore, the positive electrode composite layer 23 includes a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0022] The positive electrode active material is a lithium-containing composite metal oxide capable of absorbing and releasing lithium ions, which serve as charge carriers in the single cell 10. The lithium-containing composite metal oxide is an oxide containing lithium and other metal elements besides lithium. Other metal elements besides lithium include, for example, at least one selected from the group consisting of nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained in the lithium-containing composite metal oxide in the form of iron phosphate.

[0023] For example, lithium-containing composite metal oxides include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium manganese oxide (LiMn2O4). For example, lithium-containing composite metal oxides are ternary lithium-containing composite metal oxides containing nickel, cobalt, and manganese, such as lithium nickel cobalt manganese oxide (LiNiCoMnO2). For example, lithium iron phosphate (LiFePO4) is another example of a lithium-containing composite metal oxide.

[0024] The positive electrode solvent is an example of an organic solvent, such as NMP (N-methyl-2-pyrrolidone) solution. The positive electrode conductive material includes, for example, carbon black such as acetylene black and Ketjen black, carbon fibers such as carbon nanotubes and carbon nanofibers, and graphite. The positive electrode binder is an example of a resin component contained in the positive electrode composite paste. Examples of positive electrode binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and styrene-butadiene rubber (SBR).

[0025] It should be noted that the positive electrode sheet 21 may have an insulating layer at the boundary between the uncoated portion 22A on the positive electrode side and the positive electrode composite material layer 23. The insulating layer comprises an inorganic component with insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titanium dioxide, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic acid.

[0026] [Negative electrode plate] The negative electrode 24 includes a negative electrode current collector 25 and a negative electrode composite material layer 26. The negative electrode current collector 25 is a foil-shaped electrode substrate formed in the shape of a strip. The negative electrode composite material layer 26 is respectively provided on two opposite surfaces of the negative electrode current collector 25. At one end of the negative electrode current collector 25 in the width direction D2 and at the end opposite to the uncoated portion 22A on the positive electrode side, there is an uncoated portion 25A on the negative electrode side where the negative electrode composite material layer 26 is not formed and the negative electrode current collector 25 is exposed.

[0027] The negative current collector 25 uses a metal foil made of copper or an alloy with copper as the main component. The negative current collector 25 functions as the current collector for the negative electrode. The uncoated portion 25A on the negative side is formed by pressing the opposing surfaces together in the wound state to form the negative current collector portion 20B.

[0028] The negative electrode composite layer 26 is a cured form of a liquid negative electrode composite paste. The negative electrode composite paste includes a negative electrode active material, a negative electrode solvent, a negative electrode tackifier, and a negative electrode binder. The negative electrode composite layer 26 is formed by drying the negative electrode composite paste and vaporizing the negative electrode solvent. Therefore, the negative electrode composite layer 26 includes a negative electrode active material, as well as a negative electrode tackifier and a negative electrode binder as additives. It should be noted that the negative electrode composite layer 26 may further include additives such as conductive materials.

[0029] The negative electrode active material is a material capable of absorbing and releasing lithium ions. Examples of negative electrode active materials include carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, and carbon nanotubes. Water is used as an example of a negative electrode solvent. Carboxymethyl cellulose (CMC) can be used as an example of a negative electrode dispersion material. The negative electrode binder can be the same material used for the positive electrode binder. SBR is an example of a negative electrode binder material.

[0030] [Spacing] The separator 27 prevents the positive electrode 21 from contacting the negative electrode 24 and maintains a non-aqueous electrolyte between the positive electrode 21 and the negative electrode 24. When the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte permeates from the end of the separator 27 toward the center.

[0031] The spacer 27 is made of nonwoven fabric such as polypropylene. For example, porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, as well as ion-conducting polymer electrolyte membranes, can be used as spacers 27.

[0032] [Non-aqueous electrolyte] A non-aqueous electrolyte is a composition containing a supporting salt in a non-aqueous solvent. As the non-aqueous solvent, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate can be used. Furthermore, as the supporting salt, one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, and LiI can be used.

[0033] In this embodiment, ethylene carbonate is used as the non-aqueous solvent. A lithium salt, lithium bis(oxalato)borate (LiBOB), is added as an additive to the non-aqueous electrolyte. For example, LiBOB is added to the non-aqueous electrolyte in such a way that the concentration of LiBOB in the non-aqueous electrolyte is 0.001 to 0.1 mol / L or higher.

[0034] [Electrode storage status] The electrode body 20 is disposed within the housing 11 with its winding shaft L1 extending parallel to the bottom surface of the housing 11. Furthermore, the electrode body 20 has a flat, wound shape and includes a pair of opposing flat portions 31, an upper curved portion 32 connecting the upper edges of the opposing pair of flat portions 31, and a lower curved portion 33 connecting the lower edges of the flat portions 31. The upper curved portion 32 has an upward bulging shape, and the lower curved portion 33 has a downward bulging shape. The electrode body 20 is housed within the housing 11 with the lower curved portion 33 located on the bottom surface side of the housing 11 and the upper curved portion 32 located on the cover 12 side. The pair of flat portions 31 of the electrode body 20 housed within the housing 11 are respectively opposed to a pair of housing sidewalls 11A.

[0035] When the electrode body 20 is housed in the housing 11, a cover 12 is disposed at the opening of the housing 11, and the opening of the housing 11 is sealed by a fixing method such as laser welding. The welded part that seals the opening of the housing 11 to the cover 12 is a sealing part 12A for sealing the housing 11 (see reference). Figure 2 One example is the gasket disposed between the current collectors 14A and 14B and the cover 12, which is an example of the sealing part 12A. Then, via the injection port 15 provided in the cover 12 (see reference...) Figure 2 Electrolyte is injected into the casing 11 of the single cell 10. Afterwards, the injection port 15 is sealed by laser welding or the like. The welded portion that seals the injection port 15 is an example of the sealing portion 12A. The upper curved portion 32 becomes the upper edge of the electrode body 20, which is close to the sealing portion 12A.

[0036] [Spacer] like Figure 4 As shown, the battery pack 1 includes a predetermined number of individual cells 10 and a plurality of spacers 40 sandwiched between these individual cells 10. In the battery pack 1 of this embodiment, these individual cells 10 are arranged such that the spacers 40 are sandwiched between parallel housing sidewalls 11A in the arrangement direction X. Furthermore, the alternately arranged individual cells 10 and spacers 40 are sandwiched between a pair of end plates 50 located at both ends of the arrangement direction X. The battery pack 1 of this embodiment uses each spacer 40 and each end plate 50 as constraint members to form a configuration for bundling together a plurality of individual cells 10. As an example, a surface pressure of 1 MPa or more and 5 MPa or less is applied to the housing sidewalls 11A of each individual cell 10 as a constraint pressure. Alternatively, a surface pressure of 2 MPa or more and about 3 MPa may be applied. It is also conceivable to arbitrarily combine the above-mentioned upper and lower limits.

[0037] like Figure 5As shown, each spacer 40 includes a base plate portion 41 formed of a rectangular flat plate and a plurality of protrusions 42 provided on one side of the base plate portion 41. One side of the base plate portion 41 is an abutting surface that abuts against the side wall 11A of the housing. The plurality of protrusions 42 are rib-shaped and arranged in a comb-like pattern on one side of the base plate portion 41. The plurality of protrusions 42 are at the same height from one side of the base plate portion 41. The plurality of protrusions 42 form a ventilation path for cooling each individual battery 10. The front end face of each protrusion 42 is formed as a plane so as to make surface contact with the side wall 11A of the housing. Regarding the ventilation path, as an example, cooling air flows from the lower end upwards.

[0038] The first protrusion 43 among the plurality of protrusions 42 is a rib extending along the upper edge of the substrate portion 41 in the direction of the winding axis L1, and is an upper protrusion. In other examples, the first protrusion 43 among the plurality of protrusions 42 may be a rib extending parallel to the upper edge of the substrate portion 41 in the direction of the winding axis L1 near the upper edge of the substrate portion 41. The first protrusion 43 extends above the corresponding position of the housing sidewall 11A corresponding to the upper edge of the planar portion 31 of the electrode body 20, in other words, at a position of the housing sidewall 11A above the corresponding position of the housing sidewall 11A. That is, the first protrusion 43 extends at a position of the housing sidewall 11A corresponding to the upper curved portion 32 of the electrode body 20. Furthermore, the first protrusion 43 presses the upper curved portion 32 via the housing sidewall 11A. The first protrusion 43 is a straight-shaped rib that is continuously and uninterruptedly provided. As an example, the first protrusion 43 is the uppermost one located on the substrate portion 41.

[0039] The remaining protrusions 42, other than the first protrusion 43, are mainly second protrusions 44 that press against the position of the side wall 11A of the housing corresponding to the flat portion 31 of the electrode body 20, and are mainly protrusions for the flat portion. The second protrusion 44 has a parallel portion 44A that is parallel to the winding shaft L1, a vertical portion 44B that is perpendicular to the winding shaft L1, and a connecting bend portion 44C that connects the parallel portion 44A and the vertical portion 44B.

[0040] The second protrusion 44 of the odd-numbered segments following the third segment from the top is a continuous rib consisting of a parallel portion 44A and a connecting curved portion 44C and a vertical portion 44B. For the multiple vertical portions 44B of the multiple second protrusions 44 in the odd-numbered segments, the ribs that connect more closely to the lower parallel portion 44A extend further away from the central line L2. Furthermore, the second protrusions 44 of the even-numbered segments are composed of the parallel portion 44A.

[0041] [The function of the battery pack] like Figure 6As shown, multiple protrusions 42 press the electrode body 20 with a predetermined constraint pressure via the housing sidewall 11A. This suppresses the expansion of the electrode body 20. Simultaneously, the multiple protrusions 42 function to maintain a constant inter-electrode distance within the electrode body 20. At this time, the second protrusion 44, occupying the majority of the multiple protrusions 42, presses the corresponding position on the housing sidewall 11A corresponding to the flat portion 31 of the electrode body 20 using constraint pressure. In contrast, the first protrusion 43 is separated from the flat portion 31 by a gap between the housing sidewall 11A and the upper curved portion 32, thus naturally tilting. Consequently, the first protrusion 43 generates a load concentration relative to the housing sidewall 11A, causing the second protrusion 44 to press with a higher surface pressure than when pressing the housing sidewall 11A. As a result, the constraint pressure in this portion increases, and the displacement of the housing sidewall 11A is greater than in other areas.

[0042] Over time, even in minute quantities, moisture seeps from the sealing portion 12A of the single cell 10 into the interior of the casing 11. This seeped moisture reacts with lithium ions in the active material near the sealing portion 12A, specifically in and around the upper curved portion 32. As a result, lithium ions are removed from the active material, causing shrinkage of the active material and consequently, shrinkage of the electrode. Even under these conditions, the first protrusion 43 presses against the upper curved portion 32 with a higher constraint pressure than the second protrusion 44 via the casing sidewall 11A. This maintains the inter-electrode distance, thereby suppressing lithium deposition and preventing a decrease in capacitance retention.

[0043] [Example] In an embodiment, the single cell 10 is manufactured as shown below. Figure 7 As shown, process 101 is the process of assembling a single cell 10. Specifically, positive and negative electrode sheets 21 and 24 are manufactured. Then, the positive electrode sheet 21 and the negative electrode sheet 24 are layered with a separator 27 in between and wound together, and further pressed into a flattened shape. Subsequently, the uncoated portion 22A on the positive electrode side is pressed to form the positive electrode side current collector 20A, and the uncoated portion 25A on the negative electrode side is pressed to form the negative electrode side current collector 20B. The electrode body 20 is manufactured through the above process. Next, the electrode body 20 is housed in the housing 11. At this time, the positive electrode side current collector 20A is electrically connected to the external terminal 13A of the positive electrode via the positive electrode side current collector 14A. The negative electrode side current collector 20B is electrically connected to the external terminal 13B of the negative electrode via the negative electrode side current collector 14B. The upper opening of the housing 11 is closed by the cover 12. Here, the cover 12 used in the embodiment is different from the product, etc., and has a through hole formed for the purpose of conducting experiments. Due to the effect of the external atmosphere, the state of the electrical tank inside the housing 11 is easily affected by the external environment.

[0044] Here, before the opening of the housing 11 is closed with the cover 12, multiple sensors for measuring pressure and negative electrode resistance are arranged between the housing sidewall 11A and the electrode body 20. These sensors cannot be stably arranged on the upper curved portion 32 and the lower curved portion 33 of the electrode body 20. Therefore, these sensors are arranged in the flat portion 31.

[0045] In step 102, the electrode body 20 is dried. For example, the electrode body 20 is dried at 105°C under reduced pressure for at least one hour. In step 103, for example, the electrode body 20 is dehumidified. For example, dehumidification is performed for 12 hours at 25°C and 65% humidity.

[0046] In step 104, a non-aqueous electrolyte is injected into the casing 11 through the injection port 15. After injection, the injection port 15 is sealed. In the single cell 10 configured in this way, initial charging is performed in step 105, followed by activation. A lithium deposition test is performed in step 106.

[0047] [Example 1] like Figure 6 As shown, in the planar portion 31, the boundary position between the planar portion 31, which is the upper edge of the planar portion 31, and the upper curved portion 32 is defined as position 1 (first position). The second position from the top, separated from position 1 by a certain interval, is defined as position 2. The third position from the top, separated from position 2 by a certain interval, is defined as position 3. The boundary position between the planar portion 31, which is the lower edge of the planar portion 31, and the lower curved portion 33 is defined as position 4 (second position). The intervals between positions 1 and 2, positions 2 and 3, and positions 3 and 4 are equal.

[0048] Furthermore, the distance between the upper edge (position 1) and the lower edge (position 4) of the planar portion 31, i.e., the height of the planar portion 31, is defined as "A". Additionally, the distance from the upper edge (position 1) of the planar portion 31 to the corner (edge) of the first protrusion 43 near position 1, i.e., the distance from the first protrusion 43 to the planar portion 31, is defined as "B". In other words, B is the amount by which the first protrusion 43 extends from the upper edge of the planar portion 31. In Embodiment 1, the ratio C of B to A, i.e., the extension ratio C from position 1 upwards towards the curved portion 32, is set to 13.6%.

[0049] [Example 2] In Example 2, the ratio C of B to A, i.e. the amount of protrusion from position 1 upwards to the side of the curved portion 32, is set to 7.8%.

[0050] [Example 3] In Example 3, the ratio C of B to A, i.e. the amount of protrusion from position 1 to the side of the upward bending portion 32, is set to 4.5%.

[0051] [Comparative Example] In the comparative example, the ratio C of B to A, i.e., the amount of protrusion from position 1 to the upward curved portion 32, is set to -2.9%. That is, the protrusion 42 is only located above the flat portion 31, and not above the upper curved portion 32. In the comparative example, the spacer 40 does not have a rib that can be defined as the first protrusion 43.

[0052] In Examples 1, 2, 3 and the Comparative Example, the following settings were made: A was increased by increasing the core diameter when winding the laminate formed by stacking the positive electrode 21 and the negative electrode 24 with the spacer 27 in between, while B was decreased.

[0053] [Table 1]

[0054] Figure 8 This is a graph showing the resistance distribution of the negative plate in the comparative example. Figure 8 In the middle, the upper side is the upper curved portion 32, and the lower side is the lower curved portion 33. Additionally, Figure 9 The average value of the negative electrode resistance at each position from position 1 to position 4 is shown. Figure 8 In the diagram, the darker the color of a region, the higher its resistance.

[0055] In the comparative example, it can be confirmed that the negative electrode resistance around position 1 is higher than that of positions 2, 3, and 4 (refer to...). Figure 8 and Figure 9 This is believed to be due to moisture seeping into the electrode body 20 through the sealing part 12A. If continued use continues, the seeped-in moisture reacts with the charge carriers such as ions of the active material, causing the active material to shrink, which in turn causes the electrode body 20 to shrink, resulting in lithium deposition. It should be noted that the area with high negative electrode resistance in the center of the left-right direction and in the up-down direction is not due to the upper curved part 32 reacting with the seeped-in moisture, causing an increase in negative electrode resistance.

[0056] Figure 10 The surface pressure distribution of the constraint pressure in Example 1 is shown. Figure 10 In the diagram, the darker the color of the area, the higher the pressure. Additionally, Figure 11 The average value of the constraint pressure at positions 1, 2, 3, and 4 in Embodiment 1 is shown. In Embodiment 1, the spacer 40 has a first protrusion 43. Therefore, it can be confirmed that the constraint pressure at position 1 is higher than that at positions 2, 3, and 4. Figure 11As shown, in the comparative example, since the first protrusion 43 is not present, the constraint pressure at position 1 is lower than that in Example 1. Furthermore, in the comparative example, it can be confirmed that the constraint pressure applied to positions 1 through 4 is approximately equal.

[0057] [Table 2]

[0058] Table 2 above shows the capacitor maintenance rates in Examples 1 to 3. The capacitor maintenance rate was calculated for charge-discharge cycle numbers of “0”, “50”, “100”, “150”, “200”, “250”, “300”, and “350”, respectively. At this time, the charging current value (A) also increased sequentially to “0”, “210”, “220”, “230”, “240”, “250”, “260”, and “280”. Figure 12 The capacitance retention rate relative to the number of cycles is shown. It can be confirmed that in Examples 1 to 3, even with an increase in the number of cycles compared to the comparative example, the decrease in capacitance retention rate is minimal.

[0059] That is, in Embodiments 1 to 3, the first protrusion 43 is separated from the flat portion 31, thus naturally tilting. Therefore, the position where the first protrusion 43 presses against the sidewall is subjected to a higher constraint pressure than the position where the second protrusion 44 presses against the housing sidewall 11A. Therefore, even if electrode contraction occurs in the upper curved portion 32 and its periphery, the inter-electrode distance can be maintained, resulting in the suppression of lithium deposition and the suppression of the decrease in capacitance retention rate.

[0060] [Effects of the Implementation Method] According to the above implementation method, the following effects can be obtained. (1) Over time, even in minute quantities, moisture seeps from the sealing portion 12A of each individual cell 10 into the interior of the casing 11. This seeped moisture reacts with lithium ions near the sealing portion 12A, specifically at and around the upper curved portion 32 of the electrode body 20. As a result, lithium ions are removed from the active material, causing the active material to shrink, and consequently, the electrode body 20 to shrink. Consequently, the constraint pressure based on the spacer 40 on the upper curved portion 32 and its surrounding area weakens, making it difficult to maintain an appropriate inter-electrode distance in this area, potentially leading to a decrease in capacitance retention.

[0061] In this regard, by pressing the position of the housing sidewall 11A corresponding to the upper curved portion 32 using the first protrusion 43, the constraint pressure of this portion is increased, and the displacement of the housing sidewall 11A is greater than that of other areas. Therefore, even if the electrode body 20 contracts, the inter-electrode distance can be maintained. As a result, lithium deposition and the decrease in capacitance retention rate can be suppressed.

[0062] (2) Even with a gap between the housing sidewall 11A and the upper curved portion 32, the first protrusion 43 is separated from the flat portion 31, thus naturally tilting. As a result, the position of the housing sidewall 11A corresponding to the upper curved portion 32 can be pressed with a concentrated load. Consequently, even if the electrode body 20 contracts, the inter-electrode distance can be maintained.

[0063] (3) The first protrusion 43 is configured to extend continuously without interruption in the direction of extension of the upper edge. Therefore, it is possible to press the position of the housing sidewall 11A corresponding to the upper curved portion 32 continuously without interruption in the direction of extension of the upper edge.

[0064] (4) The multiple protrusions 42 are at the same height relative to the base plate portion 41. Therefore, the flat housing sidewall 11A can be pressed as a whole using the first protrusion 43 and the second protrusion 44. Furthermore, by tilting the first protrusion 43 at the position of the housing sidewall 11A corresponding to the upper curved portion 32, the constraint pressure can be increased.

[0065] (5) By making the pressing position of the first protrusion 43 extend from the upper edge of the flat part 31 by an extension ratio, i.e., “C”, of 4.5% or more and 13.6% or less, lithium deposition can be suppressed and the decrease in capacitance retention rate can be suppressed.

[0066] [Variation Example] It should be noted that the above implementation method can be modified as follows. • As long as the upper curved portion 32 can be pressed via the housing sidewall 11A using the first protrusion 43, the proportion of the first protrusion 43 extending from the upper edge of the flat portion 31, i.e., "C", is not limited to 4.5% or more and 13.6% or less. That is, the proportion C can be less than 4.5% or greater than 13.6%.

[0067] • The multiple protrusions 42 may not be at the same height relative to the base plate portion 41. For example, if the housing sidewall 11A is easily bent, the first protrusion 43 may be higher than the second protrusion 44. This allows for pressing the position corresponding to the upper curved portion 32 with a higher constraint pressure.

[0068] • The first protrusion 43 may not be a continuous rib in the extending direction of the upper curved portion 32. As an example, a portion of the continuous rib in the first protrusion 43 may be interrupted. Alternatively, the first protrusion 43 may be a rib with a dashed shape in the extending direction of the upper curved portion 32.

[0069] • The electrode body 20 may also be a laminated body, formed by stacking the positive electrode 21 and the negative electrode 24 with a spacer 27, rather than a wound body, and housed in the housing 11. In this case, the electrode body 20 does not have the upper bend 32 and the lower bend 33. The first protrusion 43 presses against the housing sidewall 11A at a position above the corresponding position of the upper edge of the flat part 31, in a state separated from the flat part 31.

[0070] • The first protrusion 43 is not limited to the uppermost one; it can also be two or three protrusions, as long as it extends at the position corresponding to the upper curved part 32. The configuration of the protrusion 42 of the spacer 40 is not limited to Figure 5 , Figure 6 The structure is as follows. As an example, multiple protrusions 42 can all be provided at equal intervals on ribs extending at the same height in a direction parallel to the winding shaft L1. In a spacer 40 with ribs arranged in a horizontal line like this, the uppermost section extending at a position corresponding to the upper curved section 32, or several protrusions extending from the uppermost section, are called first protrusions 43, and the remaining protrusions extending at a position corresponding to the flat section 31 are called second protrusions 44.

[0071] Furthermore, multiple protrusions 42 may extend vertically, be parallel to the direction perpendicular to the winding shaft L1, and be provided at equal intervals. In this case, the portion that presses against the side wall 11A of the housing at the position corresponding to the upper curved portion 32 is the first protrusion 43.

[0072] • The first protrusion 43 may not be a flat surface but may be composed of a single arcuate surface or a concave-convex surface with multiple protrusions. Additionally, each front end face may be composed of an inclined surface that slopes from one end to the other. Furthermore, each front end face may be constructed by combining various shapes.

[0073] The multiple protrusions 42 can also be arranged at unequal intervals. That is, the intervals between the multiple protrusions 42 can be partially narrowed or widened. • The single cell 10 is not limited to a lithium-ion secondary battery. As long as it has a positive electrode 21, a negative electrode 24 and a non-aqueous electrolyte, it can also be a nickel-metal hydride secondary battery, etc.

[0074] • In addition to being installed in automatic conveyors, special vehicles for loading and unloading, electric vehicles, and hybrid vehicles, the single battery 10, as a lithium-ion secondary battery, can also be installed in computers, other electronic devices, and can form other systems. For example, it can be installed in mobile bodies such as ships and aircraft, or in power supply systems that supply power from power plants to buildings or homes equipped with secondary batteries via substations.

Claims

1. A battery pack comprising a plurality of individual cells arranged in an arrangement direction, each containing an electrode body and a housing containing the electrode body and sealed by a sealing portion, and a spacer sandwiched between the sidewalls of two adjacent housings, wherein the battery pack is formed by constraining the plurality of individual cells with a constraint pressure applied in a direction of mutual approach, wherein, The electrode body is a flat wound body obtained by winding a laminate formed by stacking positive and negative electrode sheets with spacers in between. The electrode body is opposite to the side wall of the housing, and has a pair of opposing planar portions and an upwardly curved portion that bulges upward at the portion connecting the upper edges of the pair of planar portions. The spacer includes a base plate portion and a plurality of protrusions that project at the same height from the base plate portion toward the sidewall of the housing, and the plurality of protrusions form a ventilation passage. At least a portion of the plurality of protrusions is a first protrusion serving as an upper protrusion. The first protrusion is configured to extend continuously without interruption in the extending direction of the upper edge of the planar portion. The first protrusion presses against the housing sidewall at a position higher than the corresponding position of the upper edge of the planar portion closest to the upper edge of the sealing portion and at a position corresponding to the upper curved portion. The protrusions other than the first protrusion among the plurality of protrusions are second protrusions that press against the position of the sidewall of the housing corresponding to the planar portion. The second protrusion includes: a protrusion having a parallel portion parallel to the winding axis of the electrode body, a vertical portion perpendicular to the winding axis, and a connecting bend portion connecting the parallel portion and the vertical portion; and a protrusion having only the parallel portion.

2. The battery pack according to claim 1, wherein, Let A be the length between the first position on the sidewall of the housing corresponding to the upper edge of the planar portion and the second position corresponding to the lower edge of the planar portion. When B is defined as the distance from the first position to the pressing position on the side closest to the first position where the first protrusion is pressed, The ratio of B to A is between 4.5% and 13.6%.

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