Secondary battery

Abstract

The present application provides a technology capable of inhibiting generation of drying unevenness in the inside of an electrode body. A secondary battery (100) disclosed herein is provided with at least an electrode body having a pair of rectangular faces, and a battery case accommodating the electrode body. The battery case (10) is formed in a hexahedron shape having a pair of rectangular wide faces and four rectangular side faces between the pair of wide faces. The electrode body (20) is accommodated in the battery case (10) in a manner that the rectangular faces of the electrode body oppose the wide faces of the battery case (10). Here, the battery case (10) is provided with a protruding portion (13) in the inside, and the protruding portion (13) contacts at least a portion of a central region of the electrode body (20) accommodated in the battery case (10), including a center line in a long side direction of the rectangular faces.

Description

Technical Field

[0001] The present invention relates to a secondary battery. Background Art

[0002] Currently, secondary batteries such as lithium-ion secondary batteries and nickel-metal hydride batteries are widely used in various fields such as vehicles and mobile terminals. A typical example of such a secondary battery is a battery case comprising an electrode body and a battery case for accommodating the electrode body. The electrode body comprises a positive electrode, a negative electrode, and a separator for separating the positive electrode from the negative electrode.

[0003] As a method for manufacturing a secondary battery having the above-described structure, for example, the method described in Patent Document 1 can be cited. Patent Document 1 describes a process for housing an electrode body in a battery case and drying the interior of a battery assembly that has not been filled with electrolyte. The manufacturing method disclosed in this document includes the following steps: a placement step of placing the battery assembly, with the electrode body housed in the battery case, inside a vacuum drying oven; a drying step of drying the battery assembly by heating and reducing the pressure inside the vacuum drying oven; and a pressure-increasing step of increasing the pressure inside the vacuum drying oven after drying the battery assembly.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2018-6261

[0005] However, in the drying of the battery assembly described above, if there is uneven drying inside the electrode body, it may become a major factor causing uneven current distribution and potential distribution, which is not preferable. Summary of the Invention

[0006] The present invention has been made to solve this problem, and an object of the present invention is to provide a technique capable of suppressing the occurrence of drying unevenness inside an electrode body.

[0007] The secondary battery disclosed herein comprises: an electrode body having a positive electrode, a negative electrode, and a separator for isolating the positive electrode from the negative electrode, and having at least a pair of rectangular surfaces; and a battery case for housing the electrode body. The battery case is formed in the shape of a six-sided box having a pair of rectangular wide surfaces and four rectangular side surfaces between the pair of wide surfaces. The electrode body is housed in the battery case in such a manner that the rectangular surfaces of the electrode body face the wide surfaces of the battery case. Here, the battery case has a protrusion inside, and the protrusion contacts at least a portion of the central area of ​​the electrode body housed in the battery case, including the center line of the long side direction of the rectangular surface.

[0008] According to the research by the present inventor, it has been found that in the drying process of the battery assembly, there is a tendency that moisture remains in the central region of the electrode body. The secondary battery according to the present application has a protruding portion in contact with at least a portion of the central region inside the battery case. Thus, in the drying process of the battery assembly, the heat transfer efficiency to the central region can be improved. Therefore, the removal of moisture from the central region can be promoted to suppress the generation of drying unevenness in the inside of the electrode body.

[0009] In a preferred embodiment of the secondary battery disclosed herein, the ratio (L2 / L1) of the length L2 of the central region in the electrode body in the long side direction to the length L1 of the rectangular face in the long side direction is 1 / 8 or more and 1 / 2 or less. By configuring the ratio (L2 / L1) to be in the above range, the technical effects disclosed herein can be appropriately achieved.

[0010] In another preferred embodiment of the secondary battery disclosed herein, the length L1 is 100 mm or more. When drying the battery assembly having an electrode body with a length L1 of 100 mm or more, the technical effects disclosed herein can be favorably achieved.

[0011] In another preferred embodiment of the secondary battery disclosed herein, the positive electrode is a long strip-shaped positive electrode sheet, and the negative electrode is a long strip-shaped negative electrode sheet. The electrode body is a wound electrode body in which the positive electrode sheet and the negative electrode sheet are wound around a winding axis orthogonal to the sheet long side direction with the separator interposed therebetween. Here, the laminated surface of the positive electrode sheet, the negative electrode sheet, and the separator is open to the outside of the electrode body from both ends in the direction of the winding axis. In the drying of the wound electrode body having the above structure, moisture in the electrode body overflows from the open laminated surface to the outside, and thus drying unevenness is likely to occur in the wound electrode body. When drying the battery assembly having the wound electrode body, the technical effects disclosed herein can be favorably achieved.

[0012] In another preferred embodiment of the secondary battery disclosed herein, a plurality of the electrode bodies are provided. The plurality of the electrode bodies are housed in the battery case in a state of being arranged in a predetermined direction. The protruding portion is in contact with the electrode bodies at both ends in the arrangement direction. When drying the battery assembly having a plurality of the electrode bodies, the technical effects disclosed herein can be appropriately achieved.

[0013] In another preferred embodiment of the secondary battery disclosed herein, an insertion member is provided between the electrode bodies. The insertion member is in contact with at least a portion of the central region of the electrode body adjacent to the insertion member. According to this structure, by providing the insertion member between the electrode bodies, the heat transfer efficiency to the central region of the electrode body can be further improved. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a perspective view schematically showing the secondary battery according to the first embodiment.

[0015] Figure 2 It is along Figure 1 Schematic transverse cross-sectional view along line II-II.

[0016] Figure 3 It is a perspective view showing a state in which the case body of the secondary battery according to the first embodiment is unfolded.

[0017] Figure 4 It is a perspective view schematically showing an electrode assembly of the secondary battery according to the first embodiment.

[0018] Figure 5 It is a schematic diagram showing the structure of an electrode body of a secondary battery according to the first embodiment.

[0019] Figure 6 It is a transverse cross-sectional view showing the structure of a secondary battery according to the second embodiment.

[0020] Figure 7 It is a transverse cross-sectional view showing the structure of a secondary battery according to a third embodiment.

[0021] Description of Reference Numerals

[0022] 10…battery box; 11…plate; 12…box body; 14…cover; 15…injection hole; 16…sealing plug; 17…safety valve; 20…electrode body; 22…positive electrode (positive electrode sheet); 23…positive electrode tab group; 24…negative electrode (negative electrode sheet); 25…negative electrode tab group; 26…isolation member; 30…positive electrode external terminal; 40…negative electrode external terminal; 50…positive electrode internal terminal; 60…negative electrode internal terminal; 70…electrode body bracket; 80…insertion component; 100…secondary battery. DETAILED DESCRIPTION

[0023] Below, several preferred embodiments of the technology disclosed herein are described with reference to the accompanying drawings. In addition, matters required for the implementation of the present invention other than those specifically mentioned in this specification (for example, the general structure and manufacturing process of secondary batteries that do not characterize the technology disclosed herein) can be understood as design matters based on the prior art by those skilled in the art in this field. The technology disclosed herein can be implemented based on the content disclosed in this specification and technical common sense in this field.

[0024] In this specification, the term "secondary battery" refers to a general term for electrical storage devices that can be repeatedly charged and discharged, and is a concept that includes so-called storage batteries (chemical batteries) such as lithium-ion secondary batteries and nickel-metal hydride batteries, and capacitors (physical batteries) such as electric double-layer capacitors.

[0025] In the drawings referenced in this specification, the reference symbol X indicates the depth direction, the reference symbol Y indicates the width direction, and the reference symbol Z indicates the height direction. Furthermore, F in the depth direction X indicates "front," and Rr indicates "rear." L in the width direction Y indicates "left," and R indicates "right." Furthermore, U in the height direction Z indicates "up," and D indicates "down." However, these directions are merely for ease of explanation and do not in any way limit the arrangement of the secondary batteries.

[0026] <First embodiment>

[0027] An example of a secondary battery disclosed herein is Figure 1 、 2 shown. Figure 1 It is a perspective view schematically showing the secondary battery according to the first embodiment. Figure 2 It is along Figure 1 A schematic transverse cross-sectional view taken along line II-II is shown. The secondary battery 100 includes an electrode body 20, an electrode body holder 70 covering the electrode body 20, an electrolyte (not shown), and a battery case 10 containing the electrode body, the electrode body holder, and the electrolyte. The secondary battery 100 is a lithium-ion secondary battery. Any electrolyte that can be used in other secondary batteries can be used without particular limitation. Since this electrolyte does not contribute to the characteristics of the technology disclosed herein, a detailed description thereof will be omitted.

[0028] The battery case 10 includes a case body 12 having an opening and a cover body 14 that blocks the opening. The battery case 10 is integrated and hermetically sealed (closed) by joining the cover body 14 to the periphery of the opening of the case body 12. The cover body 14 is provided with an injection hole 15, a safety valve 17, a positive external terminal 30, and a negative external terminal 40. The injection hole 15 is a hole for injecting electrolyte into the battery case 10 and is sealed by a sealing plug 16. The safety valve 17 is a thin-walled portion that is configured to break when the pressure in the battery case 10 becomes higher than a specified value to discharge the gas in the battery case 10 to the outside. The positive external terminal 30 and the negative external terminal 40 are electrically connected to the electrode body contained in the battery case 10.

[0029] The battery case 10 is formed into a six-sided box shape having a pair of rectangular wide width surfaces 12b and four rectangular side surfaces between the pair of wide width surfaces 12b. In addition to the pair of rectangular wide width surfaces 12b, the battery case 10 also has a rectangular bottom surface 12a and a pair of rectangular narrow width surfaces 12c. Figure 1In the embodiment, three of the four rectangular side surfaces are composed of the bottom surface 12 a and a pair of narrow width surfaces 12 c , and the remaining one is composed of the cover body 14 .

[0030] like Figure 2 As shown, the battery case 10 has a protrusion 13 inside. The protrusion 13 contacts the electrode body 20 (specifically, at least a portion of the central region described later) housed in the battery case 10. The protrusion 13 is arranged on both the F side and the Rr side in the depth direction X, sandwiching the electrode body 20, and contacts the electrode body 20 from both sides. Note that "contacting the electrode body 20" includes contacting the electrode body 20 while it is covered by the electrode body holder 70.

[0031] The battery case 10 is made of metal, for example. Examples of the metal material constituting the battery case 10 include aluminum, aluminum alloys, iron, and iron alloys.

[0032] exist Figure 3 FIG. 1 shows an example of the structure of the box body 12. This figure is a perspective view of the box body of the secondary battery according to the first embodiment after it is unfolded. The box body 12 is composed of Figure 3 The plate 11 is formed as shown. The plate 11 has a bottom portion 11a, two wide portions 11b, and two narrow portions 11c. The two wide portions 11b are adjacent to the bottom portion 11a on the long side of the bottom portion 11a. The two narrow portions 11c are adjacent to the narrow portions 11c on the short side of the bottom portion 11a. The bottom portion 11a is a component of the bottom surface 12a of the box body 12 and is rectangular. Figure 1 、 3 As shown, by bending the wide surface 11b along the long sides of the bottom surface 11a, a wide surface 12b is formed, which rises from the bottom surface 12a of the box body 12. By bending the narrow surface 11c along the short sides of the bottom surface 11a, a narrow surface 12c is formed, which rises from the bottom surface 12a of the box body 12. After the bending, the short sides of the wide surface 11b and the long sides of the narrow surface 11c are welded to form the box body 12.

[0033] The protrusion 13 is formed on the wide surface 11b of the plate 11. For example, the protrusion 13 is separate from the plate 11, and the protrusion 13 and the plate 11 can be integrated by joining a member (e.g., plate) constituting the protrusion 13 to the wide surface 11b. When the wide surface 11b is bent as described above, a protrusion is formed on the wide surface 12b of the box body 12 (see FIG. Figure 2The protrusions 13 are, for example, made of metal. The protrusions 13 can be made of the same material as the plate 11 or a different material. The method of joining the plate 11 and the protrusions 13 is not particularly limited and can be a method known in the art such as laser welding, ultrasonic joining, resistance welding, or the like. The thickness of the protrusions 13 can be appropriately set so as to be in contact with the electrode body 20.

[0034] The area of the protrusions 13 in the wide surface portion 11b can be set to a contact area that is in contact with the central region of the electrode body 20 within a prescribed range. Here, when the area of the central region is 100%, the contact area can be 40% or more, for example, 50% or more, preferably 60% or more, more preferably 70% or more, further preferably 80% or more, and it is more desirable that the contact area be closer to 100% (for example, 90% or more, or 95% or more).

[0035] The protrusions 13 can have any shape as long as the contact area described above is achieved. The protrusions 13 can be, for example, planar rectangular shapes as shown in FIG. 1, or other shapes such as dots, rib structures, or the like. Figure 3

[0036] The electrode body 20 is a power generating element of the secondary battery 100 and includes a positive electrode, a negative electrode, and a separator that separates the positive electrode and the negative electrode. Figure 4 FIG. 1 is a perspective view schematically showing an electrode body of a secondary battery according to a first embodiment. Figure 5 FIG. 2 is a schematic view showing the structure of the electrode body of the secondary battery according to the first embodiment. As shown in FIG. 2, the electrode body 20 is a flat wound electrode body in which a long strip-shaped positive electrode sheet 22 and a long strip-shaped negative electrode sheet 24 are stacked with a long strip-shaped separator 26 interposed therebetween and wound around a winding axis WL that is orthogonal to the sheet longitudinal direction. Figure 2 4 As shown in FIG. 1, the electrode body 20 is provided with a positive internal terminal 50 and a negative internal terminal 60. The positive internal terminal 50 is connected to the positive external terminal 30 (see FIG. 3). The negative internal terminal 60 is connected to the negative external terminal 40 (see FIG. 4). Figure 1 Figure 1

[0037] As shown in FIG. 2, the electrode body 20 has the positive electrode sheet 22 and the negative electrode sheet 24. Here, the electrode body 20 is a flat wound electrode body in which the long strip-shaped positive electrode sheet 22 and the long strip-shaped negative electrode sheet 24 are stacked with the long strip-shaped separator 26 interposed therebetween and wound around the winding axis WL that is orthogonal to the sheet longitudinal direction. Figure 5 Figure 4 As shown in FIG. 2, the electrode body 20 has a pair of rectangular faces 20a and a pair of end faces 20b in the width direction Y. The end faces 20b are the stacked faces of the positive electrode sheet 22, the negative electrode sheet 24, and the separator 26 and are open to the outside of the electrode body 20.

[0038] ​​​​​Although detailed illustration is omitted, the electrode assembly 20 is arranged inside the box body 12 as an outer body with the winding axis WL parallel to the width direction Y. Figure 1 、 2 In the state of being inside the battery case 10, the pair of rectangular surfaces 20a of the electrode body 20 faces the wide surface 12b of the battery case 10. In addition, the pair of end surfaces 20b faces the narrow surface 12c.

[0039] The positive electrode sheet 22 comprises a long, strip-shaped positive electrode current collector foil 22c (e.g., aluminum foil) and a positive electrode active material layer 22a fixed to at least one surface of the positive electrode current collector foil 22c. Although not particularly limited, a positive electrode protective layer 22p may be provided as needed on one side edge of the positive electrode sheet 22 in the width direction Y. The materials constituting the positive electrode active material layer 22a and the positive electrode protective layer 22p can be any materials used in such secondary batteries without particular limitation. These materials do not contribute to the characteristics of the technology disclosed herein, and therefore a detailed description thereof will be omitted.

[0040] At one end portion ( Figure 4 A plurality of positive electrode tabs 22t are provided at the left end portion of the positive electrode. The plurality of positive electrode tabs 22t are respectively oriented to one side in the width direction Y ( Figure 4 The plurality of positive electrode tabs 22t are provided at intervals (intermittently) along the longitudinal direction of the positive electrode sheet 22. The positive electrode tab 22t is a portion of the positive electrode current collector foil 22c, and is a portion (current collector foil exposed portion) where the positive electrode active material layer 22a and the positive electrode protective layer 22p are not formed. The plurality of positive electrode tabs 22t are provided at one end portion ( Figure 4 The positive electrode tab group 23 is stacked to form a positive electrode tab group 23. The positive electrode internal terminal 50 (see Figure 2 、 4 ).

[0041] The negative electrode sheet 24 includes a long, strip-shaped negative electrode current collector foil 24 c (e.g., copper foil) and a negative electrode active material layer 24 a fixed to at least one surface of the negative electrode current collector foil 24 c. The negative electrode active material layer 24 a can be made of any material that can be used in such secondary batteries without particular limitation. Since this material does not contribute to the characteristics of the technology disclosed herein, a detailed description thereof will be omitted.

[0042] At one end portion ( Figure 4 A plurality of negative electrode tabs 24t are provided on the right end portion of the negative electrode. The plurality of negative electrode tabs 24t face one side in the width direction Y ( Figure 4The plurality of negative electrode tabs 24t are provided at intervals (intermittently) along the longitudinal direction of the negative electrode sheet 24. Here, the negative electrode tab 24t is a portion of the negative electrode current collector foil 24c, which is a portion of the negative electrode active material layer 24a where the negative electrode current collector foil 24c is not formed (the current collector foil exposed portion). The plurality of negative electrode tabs 24t are provided at one end portion ( Figure 4 The negative electrode tab group 25 is stacked to form a negative electrode tab group 25. The negative electrode internal terminal 60 (see Figure 2 、 4 ).

[0043] like Figure 4 As shown, the central region 201 of the electrode body 20 is a region that includes the center line C of the longitudinal direction Y (hereinafter, "width direction Y" will also be referred to as "longitudinal direction Y" as appropriate) of the rectangular surface 20a of the electrode body 20. Here, "including the center line C" means that the central region 201 only includes the center line C, and includes both cases where the center line of the region is the center line C and where the center line of the region is not the center line C. In the case where the center line of the central region 201 is not the center line C, the distance between the center line of the central region 201 and the center line C can be set to be less than or equal to 1 / 4 of L2 (the length L2 will be described later).

[0044] The ratio (L2 / L1) of the length L2 in the same direction of the central region 201 of the electrode body 20 to the length L1 in the longitudinal direction Y of the rectangular surface 20a can be, for example, 1 / 8 or greater. From the perspective of reducing drying unevenness, it is preferably 1 / 6 or greater, and more preferably 1 / 4 or greater. Furthermore, the ratio (L2 / L1) can be, for example, 1 / 2 or less. From the perspective of reducing drying unevenness, it is preferably 2 / 5 or less, and more preferably 1 / 3 or less.

[0045] According to the research of the present inventors, the greater the length L1, the more uneven drying occurs. The technical effects disclosed herein can be well achieved in the manufacture of secondary batteries having electrode bodies with a length L1 of 100 mm or more. In addition, even if the length L1 is 200 mm or more, 250 mm or more, or 300 mm or more, the technical effects disclosed herein can be well achieved. The length L1 is not particularly limited, but can be, for example, 1000 mm or less.

[0046] The manufacturing method of the secondary battery 100 includes at least the following steps (1) and (2):

[0047] (1) Battery assembly manufacturing process; and

[0048] (2) Drying process.

[0049] (1) In the battery assembly manufacturing process, the electrode body is housed in a battery box to manufacture a battery assembly. This process can include manufacturing a combination of the electrode body 20 and the cover body 14, housing the combination in the box body 12, and sealing the box body 12. Although there is no intention to limit this process, the electrode body 20 can first be manufactured using a conventionally known method. Next, the positive internal terminal 50 is mounted on the positive electrode tab group 23 of the electrode body 20, and the negative internal terminal 60 is mounted on the negative electrode tab group 25 to prepare a combination of the electrode body and the internal terminal (first combination). Next, the first combination is integrated with the cover body 14 to prepare a second combination. Specifically, for example, the positive external terminal 30 pre-installed on the cover body 14 is joined to the positive internal terminal 50 of the first combination. Similarly, the negative external terminal 40 pre-installed on the cover body 14 is joined to the negative internal terminal 60 of the first combination. As the joining means, for example, ultrasonic joining, resistance welding, laser welding, etc. can be used.

[0050] Next, the second assembly is housed in the box body 12. Specifically, for example, the electrode body 20 is housed in an electrode body holder 70 made by bending an insulating resin sheet (e.g., a polyolefin such as polyethylene (PE)) into a bag or box shape. Furthermore, the electrode body 20 covered by the electrode body holder 70 is inserted into the box body. In this state, the cover 14 is overlapped with the opening of the box body 12, and the box body 12 and the cover 14 are welded. In this way, the box body 12 is sealed, and the battery assembly is completed.

[0051] (2) In the drying process, the interior of the battery assembly is dried. Although not particularly limited, as a method for drying the battery assembly, for example, a drying chamber can be used. Specifically, for example, the battery assembly and a heating element (a plate heater, an electric heater, etc.) are first placed in a drying chamber, and the switch of the heating element is turned on to heat the drying chamber. The temperature in the drying chamber is heated until it reaches a predetermined temperature, and after reaching the temperature, it is maintained for a predetermined time (for example, 10 minutes to 4 hours). The temperature is not particularly limited as long as it is a temperature that can sufficiently remove moisture from the interior of the battery assembly, but for example, it can also be set to 100°C or more and 150°C or less.

[0052] At this time, the drying chamber can be decompressed. For example, a vacuum pump is connected to the drying chamber and the vacuum pump is switched on to decompress the drying chamber. The pressure in the drying chamber is reduced to a predetermined pressure and maintained for a predetermined time (for example, 1 to 3 hours) after reaching the predetermined pressure. The pressure is not particularly limited, but can be, for example, below -0.05 MPa, below -0.08 MPa, or below -0.09 MPa relative to atmospheric pressure (0.1 MPa). The lower the pressure, the better.

[0053] After the drying process, the heating element is turned off to lower the temperature inside the drying chamber and the battery assembly. Alternatively, to reduce the pressure inside the drying chamber, the vacuum pump is turned off to raise the pressure inside the drying chamber to approximately the same level as atmospheric pressure.

[0054] The battery assembly is removed from the drying chamber, and the electrolyte is injected into the battery case 10 through the injection hole 15 using a conventionally known method. The injection hole 15 is then sealed with a sealing plug 16 to obtain the secondary battery 100. Furthermore, the secondary battery 100 is initially charged and aged under predetermined conditions to be ready for use.

[0055] The secondary battery 100 can be used for various purposes. Preferred applications include driving power sources installed in vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Furthermore, the secondary battery 100 can be used as a storage battery for small power storage devices, etc. The secondary battery 100 can typically be used in the form of a battery pack consisting of multiple batteries connected in series and / or in parallel.

[0056] Hereinafter, test examples conducted by the present inventors will be described.

[0057] <Construction of battery assembly>

[0058] NCM (positive electrode active material), PVdF (binder), and acetylene black (conductive member) were weighed in a mass ratio of 98:1:1 and mixed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. This slurry was applied to both sides of a long strip of positive electrode current collector (aluminum foil) and allowed to dry. This was cut to a specified size and rolled using a roller to obtain a positive electrode sheet with a positive electrode active material layer on both sides of the positive electrode current collector.

[0059] Graphite powder as the negative electrode active material, styrene-butadiene rubber as the binder, and carboxymethyl cellulose as the thickener are weighed in a mass ratio of 98:1:1 and mixed in water to prepare a negative electrode slurry. The negative electrode slurry is applied to both sides of a long strip of negative electrode collector (copper foil) and dried. It is cut into a specified size and rolled by rolling to obtain a negative electrode sheet having a negative electrode active material layer on both sides of the negative electrode collector. Next, the positive electrode sheet and the negative electrode sheet prepared above are placed opposite each other and stacked with a polyethylene separator. It is made by winding it in the direction of the long side of the sheet. Figure 4 The wound electrode body is shown.

[0060] Next, the aluminum wire, which serves as the internal terminal of the positive electrode, is welded to the positive electrode sheet (positive electrode tab group), and the nickel wire, which serves as the internal terminal of the negative electrode, is welded to the negative electrode sheet (negative electrode tab group). In addition, the dimensional relationship of the electrode body is as follows:

[0061] W: 11.6mm±0.2mm; L1: 332mm±1.6mm; H1: 94mm±0.25mm; and H2: 81mm.

[0062] In addition, the reference numerals Figure 4 Specifically, W is the thickness of the electrode body 20. L1 is the width of the electrode body 20. H1 is the height of the electrode body 20. H2 is the height of the rectangular surface 20a of the electrode body 20. The above-mentioned dimensional relationship is the average value obtained by manufacturing three electrode bodies.

[0063] Next, the electrode assembly was connected to the battery case lid via the positive and negative internal terminals. This was then inserted into the case body, and the case body and lid were welded together. This completed the test battery assembly.

[0064] <Drying of battery assemblies>

[0065] Next, the above-mentioned test battery assembly is placed in a drying chamber equipped with a plate heater. In the drying chamber, the test battery assembly is placed on the plate heater. Next, the switch of the vacuum pump connected to the drying chamber and the switch of the plate heater are turned on, the pressure in the drying chamber is reduced to a specified pressure, and the temperature is heated to a specified temperature. Thereafter, the reduced pressure state and the heating state are maintained for a specified time. After the above-mentioned specified time has passed, the switch of the vacuum pump and the switch of the plate heater are turned off, the pressure in the drying chamber is increased, and the temperature is cooled. Thereafter, the test battery assembly is removed from the drying chamber.

[0066] <Moisture measurement>

[0067] The moisture content in the test battery assembly before and after drying was measured to evaluate the drying state of the test battery assembly. Specifically, first, in a drying room, a 2 cm × 2 cm test piece was cut out from the positive electrode sheet of the test battery assembly before and after drying. For the preparation of the test piece, the rectangular surface 20a of the electrode body 20 was divided into three areas (left end area 202, central area 201 and right end area 203) in the longitudinal direction Y (refer to Figure 4 ), three test pieces were cut out from each region. In addition, the length of the three regions in the same direction was 1 / 3 of L1.

[0068] Next, the amount of moisture in the above test piece was measured using a Karl Fischer moisture meter. The heating temperature at the time of measurement was 150°C. The amount of moisture before and after drying was compared in each region, and it was confirmed that a certain amount of moisture was removed from the electrode body by drying. The relative value when the amount of moisture remaining in the right end region was set to 1 is shown in the "amount of moisture remaining" column of Table 1 as the amount of moisture remaining in each region (i.e., the amount of moisture after drying). Furthermore, the average value obtained using the measured values in the three test pieces cut out from each of the above regions was applied to calculate the values described in Table 1.

[0069] [Table 1]

[0070] Measurement area Moisture residue Left end area 1 Central area 1.2 Right end area 1

[0071] From the results shown in Table 1, it was found that the amount of moisture remaining in the central region of the electrode body after drying was more than in the other regions (i.e., the end regions) except for the central region. That is, it was found that uneven drying occurred in the electrode body of the above test battery assembly.

[0072] In the secondary battery disclosed herein, the battery case 10 has the protruding portion 13 inside. The protruding portion 13 contacts at least a part of the central region 201 of the electrode body 20 housed in the battery case 10, including the center line C in the long side direction Y of the rectangular face 20a. By the battery case 10 having the protruding portion 13 as described above, it is possible to selectively improve the heat transfer efficiency to the central region 201 of the electrode body 20 in the drying process of the battery assembly at the time of manufacturing the secondary battery. Therefore, it is possible to promote the removal of moisture from the region to suppress the occurrence of uneven drying in the electrode body 20.

[0073] For drying the wound electrode body, moisture in the wound electrode body is removed from the end face 20b (which is an open face of the electrode body to the outside of the electrode body) Figure 4 In the wound electrode body, as also shown in the research example of the present inventor, moisture remains in the central region, and uneven drying is likely to occur. By applying the technology disclosed herein to the manufacturing of a secondary battery having a wound electrode body, it is possible to suppress the occurrence of uneven drying in the wound electrode body.

[0074] The above-described first embodiment is only one example of the secondary battery disclosed herein. The technology disclosed herein can be implemented in other ways. Hereinafter, other embodiments of the technology disclosed herein will be described.

[0075] <Second Embodiment>

[0076] In the above-described first embodiment, as Figure 2As shown, the secondary battery 100 includes one electrode body 20. However, the number of electrode bodies included in the secondary battery disclosed herein is not limited to one. That is, the secondary battery disclosed herein may include a plurality (two or more) of electrode bodies. Figure 6 1 is a transverse cross-sectional view showing the structure of a secondary battery according to the second embodiment. Figure 6 As shown, the secondary battery 200 according to the second embodiment includes a plurality of electrode bodies 20. The plurality of electrode bodies 20 are arranged along a predetermined direction (in Figure 6 The plurality of electrode bodies 20 are housed in the battery box 10 (box body 12) in a state of being arranged in the above-mentioned direction and being housed in the electrode body holder 70. The protrusion 13 contacts the electrode bodies 20 at both ends in the arrangement direction (depth direction X). In this structure, in the drying process of the battery assembly, the heat conduction efficiency to the central area of ​​each electrode body 20 can also be selectively improved. Therefore, the occurrence of uneven drying can be suppressed. In addition, in Figure 6 In the embodiment, for convenience, the number of electrode bodies 20 is set to three, but the present invention is not limited thereto. The secondary battery 200 according to the second embodiment may be the same as the secondary battery 100 according to the first embodiment except for the above-mentioned points. Figure 6 The reference numeral 22t in the figure denotes a “positive electrode tab”, the reference numeral 24t denotes a “negative electrode tab”, the reference numeral 50 denotes a “positive electrode internal terminal”, and the reference numeral 60 denotes a “negative electrode internal terminal”.

[0077] <Third embodiment>

[0078] In the second embodiment described above, the protrusions 13 are in contact only with the electrode bodies 20 at both ends in the arrangement direction (depth direction X) among the plurality of electrode bodies 20 housed in the battery case 10. However, the present invention is not limited thereto. Figure 7 : is a transverse cross-sectional view showing the structure of a secondary battery according to the third embodiment. Figure 7 As shown, the secondary battery 300 according to the third embodiment includes a plurality of electrode bodies 20, and an insertion member 80 is provided between each electrode body 20. The insertion member 80 is connected to the central region 201 (see FIG. Figure 4 ) at least a portion of the electrode bodies 20 are in contact with each other with an inserting member 80 sandwiched therebetween and in a predetermined direction (in Figure 7 The electrodes 20 are arranged in the depth direction (X) and housed in the electrode body holder 70 in the battery case 10. The protrusions 13 are in contact with the electrode bodies 20 at both ends in the arrangement direction (depth direction X).

[0079] Although not particularly limited, the insertion component 80 is made of metal, for example. Examples of the metal material constituting the insertion component 80 include aluminum, aluminum alloy, iron, and iron alloy. The constituent material of the insertion component 80 may be the same as or different from the constituent material of the battery case 10 and the protrusion 13. By using the insertion component 80, the selective heat conduction efficiency to the central area of ​​each electrode body 20 in the drying process of the battery assembly can be further improved. Therefore, the occurrence of uneven drying can be suppressed to a greater extent. In addition, Figure 7 In the embodiment, for convenience, the number of electrode bodies 20 is set to three, but the present invention is not limited thereto. The secondary battery 300 according to the third embodiment may be the same as the secondary battery 100 according to the first embodiment except for the above-mentioned points. Figure 7 The reference numeral 22t in the figure denotes a “positive electrode tab”, the reference numeral 24t denotes a “negative electrode tab”, the reference numeral 50 denotes a “positive electrode internal terminal”, and the reference numeral 60 denotes a “negative electrode internal terminal”.

[0080] Other Modifications

[0081] The protrusion 13 in the above embodiment is formed on the wide surface 11b of the plate 11 (see Figure 3 ). However, as long as the protrusion 13 is provided in a manner that contacts the central area 201 of the electrode body 20, it is not limited to the above structure. For example, it can also be formed on the bottom portion 11a of the plate 11. In addition, in the above embodiment, the protrusions 13 that are separate from each other are joined to the plate 11 to make them integrated, but this is not limited to this, and it is not necessarily necessary to make them integrated. In addition, in the above embodiment, the box body 12 is made by punching a sheet of plate 11 into a prescribed shape. However, this is not limited to this, and a plurality of plates can be combined to make the box body 12. Alternatively, the box body 12 can be made by deep drawing.

[0082] While specific examples of the technology disclosed herein have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technology disclosed herein includes various modifications and variations of the aforementioned specific examples. For example, the technology disclosed herein can also be applied to sodium-ion secondary batteries. Furthermore, the technology disclosed herein can also be applied to secondary batteries having a stacked electrode assembly.

Claims

1. A secondary battery comprising: an electrode body having a positive electrode, a negative electrode, and a separator for separating the positive electrode from the negative electrode, and having at least a pair of rectangular faces; an electrode body holder covering the electrode body; and a metal battery case accommodating the electrode body, wherein: The battery box is formed into a six-sided box shape having a pair of rectangular wide surfaces and four rectangular side surfaces between the pair of rectangular wide surfaces. The electrode body is housed in the battery case in a state covered by the electrode body holder so that the rectangular surface of the electrode body faces the rectangular wide surface of the battery case. Here, the battery box has a protrusion inside. The protrusion is a metal plate having a flat rectangular shape that is separate from the battery box. is joined to the rectangular wide surface, The electrode body holder contacts at least a portion of a central region of the electrode body, which is contained in the battery case and covered by the electrode body holder, including a center line in the longitudinal direction of the rectangular surface.

2. The secondary battery according to claim 1, wherein A ratio of a length L2 of the central region in the electrode body in the longitudinal direction to a length L1 of the rectangular surface in the longitudinal direction, that is, L2 / L1 is not less than 1 / 8 and not more than 1 / 2.

3. The secondary battery according to claim 2, wherein The length L1 is greater than 100 mm.

4. The secondary battery according to claim 1, wherein The positive electrode is a long strip of positive electrode sheet. The negative electrode is a long strip-shaped negative electrode sheet. The electrode body is a wound electrode body in which the positive electrode sheet and the negative electrode sheet are stacked with the separator interposed therebetween and wound around a winding axis perpendicular to the longitudinal direction of the sheet. Here, the stacked surface of the positive electrode sheet, the negative electrode sheet, and the separator is open to the outside of the electrode assembly from both ends in the winding axis direction.

5. The secondary battery according to any one of claims 1 to 4, wherein comprising a plurality of the electrode bodies, The plurality of electrode bodies are housed in the battery case in a state of being arranged in a predetermined direction. The protrusions are in contact with the electrode bodies at both ends in the arrangement direction.

6. The secondary battery according to claim 5, wherein An insertion member is provided between each electrode body, The insertion member is in contact with at least a portion of the central region of the electrode body adjacent to the insertion member.

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