Manufacturing method of secondary battery

Abstract

To provide a manufacturing method of a secondary battery, capable of preferably suppressing increase of resistance due to an uneven distribution of an insolubility Na salt in which an additive agent in an electrolyte and a Na ion dissolved in the electrolyte are coupled, in an opposite part of an electrode body.SOLUTION: A manufacturing method of a secondary battery, includes: an electrode preparation step of preparing a positive electrode and a negative electrode; a trap layer formation step of forming a trap layer onto at least one of an end part of a positive electrode collector excluding a positive electrode exposure part in which a positive electrode collector exposes and an end part of a negative electrode collector excluding a negative electrode exposure part of which a negative electrode collector exposes; an electrode body manufacturing step of manufacturing an electrode body containing the positive electrode and the negative electrode via a separator; an electrode body housing step of housing the electrode body into an outer casing; an impregnation step of impregnating the electrolyte containing an additive agent in the electrode body toward the other end of the trap layer side from one end on the side opposite to the trap layer side. The trap layer contains a sodium trap agent coupled to a Na ion dissolved from the electrode body to the electrolyte.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a secondary battery. [Background technology]

[0002] A non-aqueous electrolyte secondary battery such as a lithium ion secondary battery contains, for example, an electrode body including a positive electrode and a negative electrode via a separator, and an electrolyte in an exterior body. When manufacturing such a secondary battery, a process of permeating the electrolyte into the electrode body is performed. When an electrolyte containing an additive is used, the additive may concentrate at the tip in the permeation direction of the electrolyte. After the electrolyte is permeated, in a portion where the additive is concentrated and the concentration of the additive is high, there is a risk that the resistance to lithium precipitation will decrease and the resistance will increase. Therefore, a technology has been proposed to suppress the increase in resistance caused by the uneven distribution of the additive at a high concentration in the electrode body.

[0003] Patent Document 1 discloses a method for producing a laminated lithium ion secondary battery, comprising: (A) assembling a stacked electrode group including a positive electrode, a negative electrode, and a separator, wherein at least one of the positive electrode and the negative electrode contains sodium; (B) preparing an electrolyte solution containing lithium bis(oxalato)borate; (C) immersing one end of the stacked electrode group in a direction perpendicular to the stacking direction in the electrolyte solution, wherein the electrolyte solution permeates from the one end toward the other end opposite to the one end; and (D) removing a predetermined region including the other end from the stacked electrode group after the electrolyte solution has permeated to the other end.

[0004] Patent Document 2 discloses a negative electrode plate of a nonaqueous electrolyte secondary battery having a wound body in which a positive electrode plate and a negative electrode plate are wound with a separator sandwiched therebetween, a nonaqueous electrolyte secondary battery, a manufacturing method for a nonaqueous electrolyte secondary battery, and a positive electrode plate of a nonaqueous electrolyte secondary battery. Patent Document 2 discloses that the negative electrode plate has a negative electrode mixture layer on the surface of a negative electrode substrate, the negative electrode mixture layer has an opposing portion that faces the positive electrode mixture layer of the positive electrode plate with the separator sandwiched therebetween, and a non-opposing portion that does not face the positive electrode mixture layer of the positive electrode plate, with respect to the winding axis direction of the electrode body, and the negative electrode mixture layer has permeability from the end of the opposing portion and permeability from the end of the non-opposing portion set so that at least a part of the uneven distribution range of the additive formed by the joining of the electrolyte permeating from the end of the opposing portion and the electrolyte permeating from the end of the non-opposing portion is located in the non-opposing portion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2018-26297 A [Patent Document 2] JP 2019-192333 A Summary of the Invention [Problem to be solved by the invention]

[0006] For example, the electrolyte contains LiBOB (lithium bis(oxalato)borate) as an additive, which forms a coating called a SEI (Solid Electrolyte Interface) film on the surface of the negative electrode. Here, the electrode body inevitably contains a sodium (Na) component. Therefore, when the electrolyte containing LiBOB penetrates into the electrode body, sodium (Na) ions are dissolved from the electrode body into the electrolyte. Since the electrolyte containing LiBOB penetrates from the end of the electrode body toward the center, the Na ions dissolved in the electrolyte also move from the end of the electrode body toward the center. At this time, the Na ions dissolved from the electrode body into the electrolyte and the BOB ions contained in the electrolyte that move following the Na ions combine to generate sodium bis(oxalato)borate (NaBOB), which is a poorly soluble Na salt.

[0007] As described in Patent Document 1, when an electrolyte is permeated into a laminated electrode body (laminated electrode group) from one end thereof, Na ions dissolved in the electrolyte can be unevenly distributed at the other end of the electrode body. Therefore, by removing a predetermined region including the other end after the electrolyte is permeated into the electrode body, an increase in resistance due to uneven distribution of poorly soluble Na salts in the electrode body can be suppressed. However, since the technology described in Patent Document 1 requires the removal of a predetermined region including the other end, there is a problem that although it can be applied to a laminated electrode body, it cannot be applied to a wound electrode body.

[0008] The technique described in Patent Document 2 can create a difference between the permeation speed of the electrolyte permeating from one end side (opposing part side) of a wound-type electrode body (wound body) and the permeation speed of the electrolyte permeating from the other end side (non-opposing part side). However, the longer the width of the electrode body, the longer the movement distance of the electrolyte, so that the flow of the electrolyte permeating from both ends in the width direction of the electrode body stops at the opposing part, and Na ions are likely to be unevenly distributed in the opposing part. Therefore, the technique described in Patent Document 2 has a problem that it may not be possible to sufficiently suppress an increase in resistance due to uneven distribution of poorly soluble Na salt in the wound-type electrode body.

[0009] The present disclosure has been made to solve such problems, and aims to provide a method for manufacturing a secondary battery in which an increase in resistance caused by the uneven distribution of poorly soluble Na salt formed by combining an additive in an electrolyte with Na ions dissolved in the electrolyte in a portion where a positive electrode mixture layer and a negative electrode mixture layer of an electrode body face each other is suitably suppressed. [Means for solving the problem]

[0010] A method for manufacturing a secondary battery according to one embodiment includes an electrode preparation step of preparing a positive electrode having a positive electrode mixture layer formed on a surface of a positive electrode current collector excluding an end of the positive electrode current collector, and a negative electrode having a negative electrode mixture layer formed on a surface of a negative electrode current collector excluding an end of the negative electrode current collector; a trap layer formation step of forming a trap layer on at least one surface of an end of the positive electrode current collector excluding a positive electrode exposed portion where the positive electrode current collector is exposed and an end of the negative electrode current collector excluding a negative electrode exposed portion where the negative electrode current collector is exposed; an electrode body preparation step of preparing an electrode body including a positive electrode and a negative electrode via a separator; an electrode body accommodation step of accommodating the electrode body in an exterior body; and a permeation step of permeating an electrolyte solution containing an additive into the electrode body from one end opposite to the trap layer side toward the other end of the trap layer side, wherein the trap layer includes a sodium trapping agent that bonds with sodium ions dissolved from the electrode body into the electrolyte. Effect of the Invention

[0011] The present disclosure can provide a method for manufacturing a secondary battery in which an increase in resistance caused by uneven distribution of poorly soluble Na salts formed by combining an additive in an electrolyte with Na ions dissolved in the electrolyte in a portion where a positive electrode mixture layer and a negative electrode mixture layer of an electrode body face each other is suitably suppressed. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is an external view showing an example of a secondary battery. [Diagram 2] 4 is a flowchart showing a method for manufacturing the secondary battery according to the first embodiment. [Diagram 3] FIG. 2 is a diagram illustrating an electrode preparation step to an electrode body fabrication step. [Figure 4] FIG. 2 is a diagram illustrating an electrode assembly accommodation step to a permeation step. [Diagram 5] 4 is a diagram showing the distribution of Na ions and resistance in the width direction of a negative electrode mixture layer of the secondary battery produced by the method for producing a secondary battery according to the first embodiment. FIG. [Figure 6] 1 is a flowchart showing a method for manufacturing a secondary battery of a comparative example. [Figure 7] FIG. 11 is a diagram showing the distribution of Na ions and resistance in the width direction of a negative electrode mixture layer of a secondary battery produced by a method for producing a secondary battery of a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] First embodiment Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiment. In addition, in order to clarify the description, the following description and drawings are appropriately simplified. What is shown in the drawings is a part of the whole, and many other configurations that are not shown are actually included. The width direction shown in the drawings is the width direction of the positive electrode 30, the negative electrode 40, and the separator 50, and indicates the width direction of the electrode body 20. The stacking direction shown in the drawings indicates the stacking direction of the positive electrode 30, the negative electrode 40, and the separator 50 included in the electrode body 20. In the following description, when the structures and members on the positive electrode 30 side and the negative electrode 40 side of the secondary battery 10 are collectively indicated, they may be expressed as "positive and negative electrodes".

[0014] With reference to FIG. 1, an outline of a secondary battery 10 manufactured by the manufacturing method of a secondary battery 10 according to the present embodiment will be described. FIG. 1 is an external view showing an example of a secondary battery. As shown in FIG. 1, the secondary battery 10 is a prismatic battery having a battery case 11 having, for example, a flattened rectangular parallelepiped shape and a power generating element housed in the battery case 11. The battery case 11 is a specific example of an exterior body. However, the exterior body is not limited to a prismatic shape and may be, for example, cylindrical. The exterior body may be, for example, a pouch made of an aluminum laminate film.

[0015] A chargeable and dischargeable secondary battery such as a lithium ion secondary battery, an electric double layer capacitor, etc. can be used as the secondary battery 10. In this embodiment, a specific example will be described in which the secondary battery 10 is a lithium ion secondary battery.

[0016] In a lithium ion secondary battery, charging and discharging are realized during an electrochemical reaction by the conduction of lithium ions, which are charge carriers, through the electrolyte L between the positive electrode 30 and the negative electrode 40. Lithium ion secondary batteries, which are lightweight and can provide high energy density, are suitable for use as high-output power sources for driving vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs).

[0017] The battery case 11 is made of a metal material such as aluminum, an aluminum alloy, or stainless steel. The battery case 11 has a case body 12 in the shape of a rectangular cylinder with an open top and a lid 13 in the shape of a rectangular plate. The lid 13 is provided so as to close the opening of the case body 12 and is joined to the case body 12. The lid 13 seals the inside of the battery case 11 with the power generating element housed inside the case body 12.

[0018] The lid 13 is provided with an injection port 14, a sealing member 15, a positive electrode terminal 16, and a negative electrode terminal 17. The injection port 14 is used when injecting the electrolyte L into the battery case 11, and is a hole penetrating the lid 13. The injection port 14 is airtightly sealed by the sealing member 15. In addition, the lid 13 is provided with a safety valve that opens when the inside of the battery case 11 reaches a predetermined pressure, and discharges gas generated in the battery case 11.

[0019] The power generating element has an electrode body 20 and an electrolyte L. The electrode body 20 has a positive electrode 30, a negative electrode 40, and a separator 50 interposed between the positive and negative electrodes 30, 40. As the electrode body 20, a wound electrode body in which long sheet-like positive electrodes 30 and negative electrodes 40 are stacked and wound with long sheet-like separators 50 interposed therebetween can be suitably used.

[0020] The electrode body 20 has a positive electrode current collector 22 and a negative electrode current collector 23 that protrude outward from both ends in the width direction of a separator 50 that is layered together with positive and negative electrode composite layers 32, 42. The positive electrode current collector 22 is formed by laminating positive electrode exposed parts where the positive electrode current collector 31 is exposed. The negative electrode current collector 23 is formed by laminating negative electrode exposed parts where the negative electrode current collector 41 is exposed.

[0021] The positive electrode terminal 16 is electrically connected to the positive electrode 30 via a positive electrode current collector plate 18 attached to the positive electrode current collector 22. The negative electrode terminal 17 is electrically connected to the negative electrode 40 via a negative electrode current collector plate 19 attached to the negative electrode current collector 23.

[0022] In this embodiment, the positive electrode 30 has a trap layer 33 adjacent to the positive electrode composite layer 32. A method for manufacturing the secondary battery 10 according to this embodiment will now be described with reference to Fig. 2. As shown in Fig. 2, the method for manufacturing the secondary battery 10 according to this embodiment includes an electrode preparation step (step S1), a trap layer formation step (step S2), an electrode body fabrication step (step S3), an electrode body accommodation step (step S4), and a penetration step (step S5). First, the electrode preparation step, the trap layer formation step, and the electrode body fabrication step will be described in detail with reference to Fig. 3.

[0023] [Electrode preparation process (step S1)] Step S1 is an electrode preparation process for preparing a positive electrode 30 in which a positive electrode composite layer 32 is formed on the surface of a positive electrode current collector 31 excluding the end 31a of the positive electrode current collector 31, and a negative electrode 40 in which a negative electrode composite layer 42 is formed on the surface of a negative electrode current collector 41 excluding the end 41a of the negative electrode current collector 41.

[0024] (positive electrode 30) The positive electrode 30 can be produced, for example, by the following procedure. First, a positive electrode active material, and if necessary, a conductive material, a binder, etc. are mixed in a solvent capable of dispersing or dissolving the binder to prepare a paste or slurry-like composition for forming a positive electrode composite layer. The composition for forming a positive electrode composite layer thus prepared is applied to at least one surface of the positive electrode collector 31, except for the end 31a of the positive electrode collector 31 along one edge in the width direction, dried, and then pressed as necessary. This makes it possible to obtain a positive electrode 30 in which a positive electrode composite layer 32 is formed on the surface of the positive electrode collector 31, except for the end 31a of the positive electrode collector 31.

[0025] As a means for applying the positive electrode composite layer forming composition, various coating devices such as a die coater, a slit coater, a comma coater, a gravure coater, a blade coater, etc. can be used. As a means for drying the positive electrode composite layer forming composition, natural drying, drying by hot air, low humidity air, vacuum, infrared rays, far infrared rays, electron beams, etc. can be used alone or in combination. As a means for pressing the positive electrode composite layer 32, various pressing devices such as a roll pressing device and a plate pressing device can be used.

[0026] The positive electrode current collector 31 is made of a metal with good electrical conductivity (e.g., aluminum, an aluminum alloy, etc.). When the electrode body 20 is a wound electrode body, a long sheet-like positive electrode current collector 31 is preferably used. However, the shape of the positive electrode current collector 31 is not limited to a sheet shape and can be appropriately changed depending on the shape of the secondary battery 10, etc.

[0027] As the positive electrode active material, any positive electrode active material that can absorb and release lithium ions and can be used in a lithium ion secondary battery can be used without any particular limitation. As the positive electrode active material, for example, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganese oxide (NCM), etc. can be used alone or in combination. In addition, other metal elements may be added to the positive electrode active material.

[0028] The average particle size (D50) of the positive electrode active material is not particularly limited, but is preferably 3.0 μm to 8.0 μm, and more preferably 4.0 μm to 6.0 μm. The average particle size (D50) of the positive electrode active material can be measured, for example, by particle size distribution measurement.

[0029] As the conductive material, any conductive material that can be used for the positive electrode of a lithium ion secondary battery can be used without any particular limitation. As the conductive material, for example, carbon black such as acetylene black, activated carbon, graphite, carbon materials such as carbon nanotubes, etc. can be used alone or in combination.

[0030] As the binder, any binder that can be used for the positive electrode of a lithium ion secondary battery can be used without any particular limitation. As the binder, for example, a vinyl halide resin such as polyvinylidene fluoride (PVDF) or a polyalkylene oxide such as polyethylene oxide (PEO) is preferably used.

[0031] The solvent is appropriately selected depending on the binder used. Examples of the solvent include non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone (MEK), dimethylformamide (DMF), and toluene, mixed solvents of non-aqueous solvents, and aqueous solvents such as water or mixed solvents mainly composed of water.

[0032] (Negative electrode 40) The negative electrode 40 can be produced, for example, in the same procedure as in the case of producing the positive electrode 30. First, a paste or slurry-like composition for forming a negative electrode composite layer is prepared by mixing a negative electrode active material and, if necessary, a binder, a thickener, etc. in a solvent capable of dispersing or dissolving the binder. The composition for forming a negative electrode composite layer thus prepared is applied to at least one surface of the negative electrode current collector 41, except for the end 41a of the negative electrode current collector 41 along one edge in the width direction, dried, and then pressed as necessary. This makes it possible to obtain a negative electrode 40 in which a negative electrode composite layer 42 is formed on the surface of the negative electrode current collector 41, except for the end 41a of the negative electrode current collector 41.

[0033] The negative electrode current collector 41 is made of a metal with good electrical conductivity (e.g., copper, a copper alloy, etc.). When the electrode body 20 is a wound electrode body, a long sheet-like negative electrode current collector 41 is preferably used. However, the shape of the negative electrode current collector 41 is not limited to a sheet shape and can be appropriately changed depending on the shape of the secondary battery 10, etc.

[0034] As the negative electrode active material, any material capable of absorbing and releasing lithium ions and usable in a lithium ion secondary battery can be used without any particular limitation. Examples of the negative electrode active material include carbon materials such as natural graphite, artificial graphite, hard carbon, and soft carbon, Li4Ti5O 12 Lithium transition metal composite oxides, lithium transition metal composite nitrides, etc., can be used alone or in combination. The surface of the negative electrode active material may be coated with an amorphous carbon film.

[0035] The average particle size (D50) of the negative electrode active material is not particularly limited, but is preferably, for example, 7.0 μm to 14 μm. The average particle size (D50) of the negative electrode active material can be measured, for example, by particle size distribution measurement.

[0036] As the binder, any binder that can be used for the negative electrode of a lithium ion secondary battery can be used without any particular limitation. As the binder, for example, rubbers such as styrene butadiene rubber (SBR), polyethylene oxide (PEO), styrene acrylic acid ester (St-Ac), vinyl acetate copolymer, etc. can be suitably used.

[0037] As the thickener, any thickener that can be used for the negative electrode of a lithium ion secondary battery can be used without any particular limitation. As the thickener, for example, cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), polyvinyl alcohol (PVA), etc. can be used.

[0038] The solvent is appropriately selected depending on the binder used, and the non-aqueous solvents exemplified above, mixed solvents combining non-aqueous solvents, and aqueous solvents such as water or mixed solvents mainly composed of water can be used.

[0039] In this embodiment, the width direction length of the negative electrode mixture layer 42 formed on the surface of the negative electrode current collector 41 is longer than the width direction length of the positive electrode mixture layer 32 formed on the surface of the positive electrode current collector 31.

[0040] [Trapping layer formation process (step S2)] Step S2 is a trap layer formation step in which the trap layer 33 is formed on at least one surface of the end 31a of the positive electrode current collector 31 and the end 41a of the negative electrode current collector 41. In this embodiment, the trap layer formation step will be described using the case in which the trap layer 33 is formed on the end 31a of the positive electrode current collector 31 as an example.

[0041] The trap layer 33 contains a sodium trapping agent that bonds with sodium ions eluted from the electrode body 20 into the electrolyte L. As the sodium trapping agent, a compound that bonds with Na ions to form a salt, a compound that bonds with Na ions to form a complex, or the like can be used.

[0042] A specific example of a compound that bonds with Na ions to form a salt is LiBOB (lithium bis(oxalato)borate). A specific example of a compound that bonds with Na ions to form a complex is crown ether. These can be used alone or in combination of two or more. LiBOB can be suitably used as a sodium trapping agent because it can quickly and selectively capture (trap) Na ions dissolved in the electrolyte L.

[0043] In the trap layer forming step, first, a paste or slurry-like trap layer forming composition is prepared by dispersing or dissolving a sodium trapping agent in a solvent. The trap layer forming composition preferably contains a binder in addition to the sodium trapping agent. As the binder contained in the trap layer forming composition, for example, a binder that can be used for the positive electrode mixture layer 32 can be preferably used. As the binder, a vinyl halide resin such as PVDF is preferable because it can form a trap layer 33 of an appropriate thickness while imparting flexibility to the trap when compressing a plurality of positive electrode exposed parts to bundle and collect current.

[0044] The content of the binder in the total solid content of the trap layer forming composition is, for example, typically 1 mass % or more, may be 5 mass % or more, preferably 10 mass % or more or 15 mass %, and may be, for example, 20±3 mass % or more. The content of the binder in the total solid content of the trap layer forming composition is, for example, typically 40 mass % or less, may be 35 mass % or less, and preferably 30 mass % or less or 25 mass % or less.

[0045] In the trap layer 33 formed using the trap layer-forming composition containing a binder, the sodium trapping agent is suitably bound to the positive electrode current collector 31 by the binder, so that the sodium trapping agent can more reliably trap Na ions that have dissolved into the electrolyte solution L that permeates into the electrode body 20.

[0046] The trap layer forming composition may further contain any component other than the sodium trapping agent and the binder. The trap layer forming composition may contain, for example, an insulating material. As the insulating material, for example, an inorganic filler can be used. When the trap layer 33 formed using the trap layer forming composition containing such an insulating material is disposed adjacent to the positive electrode mixture layer 32 on the surface of the positive electrode current collector 31, a short circuit between the positive electrode 30 and the negative electrode 40 can be suppressed.

[0047] The trapping layer-forming composition may contain, for example, a compound that serves as a lithium source. As the compound that serves as a lithium source, for example, the positive electrode active material contained in the positive electrode mixture layer 32 can be used. When the trapping layer 33 is formed using a trapping layer-forming composition that contains such a compound that serves as a lithium source, the energy density of the positive electrode 30 can be increased.

[0048] The composition for forming the trapping layer can be prepared, for example, by mixing the sodium trapping agent and the binder in a solvent that the binder can be dispersed or dissolved in. As the solvent, for example, the solvent contained in the composition for forming the positive electrode mixture layer can be preferably used.

[0049] The trap layer forming composition thus prepared is applied to at least one surface of the end 31a of the positive electrode current collector 31, except for the positive electrode exposed portion along one edge in the width direction, and then dried and pressed as necessary to form the trap layer 33. As a means for applying the trap layer forming composition, a coating means used for coating the positive electrode composite layer forming composition can be preferably used. As a means for drying the trap layer forming composition, a drying means used for drying the positive electrode composite layer forming composition can be preferably used. As a means for pressing the trap layer 33, a pressing device used for pressing the positive electrode composite layer 32 can be preferably used.

[0050] The trap layer 33 is disposed between the positive electrode mixture layer 32 and the positive electrode exposed portion in the width direction. That is, the trap layer 33 is disposed on the outer side of the positive electrode mixture layer 32 in the width direction. In this embodiment, the trap layer 33 is disposed adjacent to the positive electrode mixture layer 32, but may be disposed with a gap in the width direction from the positive electrode mixture layer 32. The closer the trap layer 33 is to the positive electrode mixture layer 32, the more efficiently it can trap the Na ions dissolved in the electrolyte L in the permeation step. Therefore, it is preferable that the trap layer 33 is disposed adjacent to the positive electrode mixture layer 32. In this embodiment, the trap layer 33 is provided on one surface (one side) of the positive electrode current collector 31, but may be provided on both surfaces (both sides) of the positive electrode current collector 31. The thickness of the trap layer 33 is not particularly limited, but is preferably equal to or less than the thickness of the positive electrode mixture layer 32.

[0051] The trap layer forming step may be performed after the electrode preparation step, before the electrode preparation step, or simultaneously with the electrode preparation step. From the viewpoint of improving the manufacturing efficiency, it is preferable to perform the electrode preparation step and the trap layer forming step simultaneously. When the electrode preparation step and the trap layer forming step are performed simultaneously, for example, the positive electrode composite layer forming composition and the trap layer forming composition are simultaneously applied from the same die head using a die coater to at least one surface of the positive electrode current collector 31, dried, and then pressed as necessary.

[0052] [Electrode body preparation process (step S3)] Step S3 is an electrode assembly preparation step in which an electrode assembly 20 including a positive electrode 30 and a negative electrode 40 is prepared via a separator 50. The separator 50 is composed of a porous insulating oil sheet such as polyethylene (PE) or polypropylene (PP). Such a porous resin sheet may have a single layer structure or a laminated structure of two or more layers. In addition, the resin sheet may have a porous heat-resistant layer on a part of its surface.

[0053] In this embodiment, the electrode body 20 is a wound electrode body produced using a positive electrode 30 provided with a trap layer 33, a negative electrode 40, and a separator 50. In producing the electrode body 20, the positive electrode 30, the negative electrode 40, and the separator 50 are first stacked together such that the positive electrode mixture layer 32 and the negative electrode mixture layer 42 face each other via the separator 50. At this time, the positive electrode 30 and the negative electrode 40 are stacked with a slight shift in the width direction so that the exposed portions of the positive and negative electrodes that become the current collecting parts 22 and 23 of the positive and negative electrodes protrude outward from both ends of the separator 50 in the width direction, as shown in FIG.

[0054] The positive and negative electrodes 30, 40 are overlapped such that both ends in the width direction of the positive electrode mixture layer 32 are located inside both ends in the width direction of the negative electrode mixture layer 42. As a result, an opposing portion 42a that faces the positive electrode mixture layer 32 is formed in the center of the negative electrode mixture layer 42, and non-opposing portions 42b, 42c that do not face the positive electrode mixture layer 32 are formed at both ends of the negative electrode mixture layer 42.

[0055] Next, the stacked positive electrode 30, negative electrode 40, and separator 50 are wound around a winding axis extending in their width direction, and compressed into a flat shape having a predetermined thickness to produce a flat tubular electrode body 20 (wound electrode body). In this embodiment, in the electrode body 20, a part of the trap layer 33 provided on the positive electrode 30 is disposed in a region facing the unfacing portion 42c formed at the end on the other end side in the width direction of the negative electrode mixture layer 42, with the separator 50 interposed therebetween.

[0056] Here, the electrode body 20 produced in the electrode body production process contains Na components as unavoidable impurities. In this embodiment, the Na components include Na components that exist as compounds containing Na as a constituent element. Examples of such Na components include Na ions and various Na salts. In this embodiment, the Na components are contained in the negative electrode mixture layer 42.

[0057] Next, the electrode assembly accommodating step and the permeation step will be described in detail with reference to Fig. 4. Fig. 4 is a diagram for explaining the electrode assembly accommodating step to the permeation step.

[0058] [Electrode body accommodation step (step S4)] Step S4 is an electrode assembly accommodating step in which the electrode assembly 20 is accommodated in the battery case 11 as an exterior body. In the electrode assembly accommodating step, the positive electrode current collector 18 connected to the positive electrode terminal 16 is joined to the compressed portion of the positive electrode current collector 22, and the negative electrode current collector 19 connected to the negative electrode terminal 17 is joined to the compressed portion of the negative electrode current collector 23. This electrically connects the positive and negative electrodes 30, 40 of the electrode assembly 20 to the positive and negative electrode terminals 16, 17. Note that for joining the positive and negative electrodes 30, 40 to the positive and negative electrode terminals 16, 17, for example, ultrasonic welding, resistance welding, or other methods can be used.

[0059] Then, the electrode body 20 is accommodated inside the case body 12 through the prepared opening of the case body 12. The electrode body 20 is accommodated in the case body 12 with the winding axis extending in the width direction of the electrode body 20 aligned along the width direction of the case body 12. Thereafter, the opening of the case body 12 is closed with the lid 13, and these are joined together to construct the battery case 11. The electrode body 20 accommodated in the battery case 11 has a negative electrode current collector 23 at one end in the width direction, and a positive electrode current collector 22 at the other end in the width direction.

[0060] [Penetration process (step S5)] Step S5 is a permeation step in which electrolyte solution L containing an additive is permeated into electrode body 20 from one end of electrode body 20 opposite to trap layer 33 side toward the other end of trap layer 33 side. In the permeation step, electrolyte solution L containing an additive is first prepared. As electrolyte solution L, a nonaqueous electrolyte solution in which a Li salt as a supporting salt is dissolved in an organic solvent (nonaqueous solvent) can be used.

[0061] As the Li salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSO3CF3, etc. can be used alone or in combination. As the organic solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, trifluoropropylene carbonate, etc., chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, etc., ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, etc., sulfur compounds such as ethyl methyl sulfone, butane sultone, etc., or phosphorus compounds such as triethyl phosphate, trioctyl phosphate, etc. can be used alone or in combination as the electrolyte L.

[0062] The concentration of the supporting salt is not particularly limited, but if it is lower than necessary, the amount of Li ions contained in the electrolyte L will be insufficient, and the ionic conductivity will tend to decrease. On the other hand, if the concentration of the supporting salt is higher than necessary, the viscosity of the electrolyte L will increase in a temperature range below room temperature (e.g., 0 to 30°C), and the ionic conductivity will tend to decrease. Therefore, the concentration of the supporting salt is preferably, for example, 0.1 mol / L to 2 mol / L, and more preferably 0.8 mol / L to 1.5 mol / L.

[0063] The electrolyte L contains, for example, an additive that forms a coating called a solid electrolyte interface (SEI) film on the surface of the negative electrode 40. LiBOB can be suitably used as such an additive. By using LiBOB, a coating having preferable properties can be formed on the surface of the negative electrode 40.

[0064] As shown in Fig. 4, the electrolyte L is injected through a liquid injection port into the battery case 11 in which the electrode body 20 is housed. When the electrolyte L is injected into the battery case 11, the electrolyte L permeates in one direction from one end of the electrode body 20 to the other end. The electrolyte L that has entered the electrode body 20 from one end thereof passes through the trapping layer 33 and then reaches the other end of the electrode body 20. At this time, Na ions that have dissolved from the electrode body 20 into the electrolyte L are trapped by the trapping layer 33 by binding with the sodium trapping agent before binding with an additive that has a slower permeation rate than Na ions.

[0065] Here, when the electrode body 20 is a wound electrode body, the permeation of the electrolyte L into the electrode body 20 is limited to both end faces in the width direction of the electrode body 20. Therefore, in the permeation step, by immersing at least a part of the end face on one end side of the electrode body 20 in the electrolyte L so that the electrolyte L does not contact the end face on the other end side of the electrode body 20, the electrolyte L can be permeated into the electrode body 20 from one end to the other end of the electrode body 20.

[0066] The method of permeating the electrolyte L into the electrode body 20 from one end to the other end of the electrode body 20 is not particularly limited, but an example of such a method is to inject the electrolyte L in a state in which the battery case 11 is tilted relative to the horizontal direction so that one end of the electrode body 20 is positioned lower than the other end. After the electrolyte L has permeated into the electrode body 20, the injection port 14 is airtightly sealed using the sealing member 15.

[0067] The method for manufacturing the secondary battery 10 according to this embodiment may include an initial charging step of initially charging the electrode body 20 after the infiltration step. In the initial charging step, the electrode body 20 is charged to a predetermined charging voltage, and then discharged to a predetermined discharging voltage, thereby forming a coating on the surface of the negative electrode 40. This charging and discharging may be repeated multiple times.

[0068] Here, Fig. 6 is a flowchart showing a method for manufacturing a secondary battery of the comparative example. As shown in Fig. 6, the method for manufacturing a secondary battery of the comparative example includes an electrode preparation step (step S1), an electrode body fabrication step (step S3), and an electrode accommodation step (step S4) similar to the method for manufacturing a secondary battery 10 according to the first embodiment, but does not include a trap layer formation step (step S2). Moreover, the method for manufacturing a secondary battery of the comparative example includes a penetration step (step S50) in which an electrolyte solution L containing an additive is permeated into the electrode body 20 from both ends in the width direction of the electrode body 20 on which the trap layer 33 is not provided toward the center, instead of the penetration step (step S5).

[0069] Fig. 7 is a diagram showing the distribution of Na ions and resistance in the width direction of the negative electrode mixture layer of a secondary battery manufactured by the manufacturing method of a secondary battery of the comparative example. The upper side of Fig. 7 shows a graph showing the relationship between the position in the width direction of the negative electrode mixture layer 42 constituting the secondary battery manufactured by the manufacturing method of a secondary battery of the comparative example and the amount of Na ions. The lower side of Fig. 7 shows a graph showing the relationship between the position in the width direction of the negative electrode mixture layer 42 constituting the secondary battery and the resistance.

[0070] In the penetration step (step S50), as the electrolyte L penetrates into the negative electrode mixture layer 42 from both ends in the width direction of the negative electrode mixture layer 42, the Na ions dissolved from the negative electrode mixture layer 42 into the electrolyte L move toward the center in the width direction of the negative electrode mixture layer 42. Therefore, as shown in FIG. 7, the amount of Na ions increases in the center of the negative electrode mixture layer 42. Then, the additives in the electrolyte L, which have a slower penetration speed than the Na ions, move from both ends of the negative electrode mixture layer 42 toward the center so as to follow the Na ions, and bond with the Na ions. As a result, the amount of poorly soluble Na salts generated by the reaction of the additives with the Na ions increases at a position slightly outside the center of the negative electrode mixture layer 42 in the width direction.

[0071] When the poorly soluble Na salt is unevenly distributed in the facing portion 42a in this way, there is a problem that the resistance increases in a part of the facing portion 42a (a position slightly outside the center of the negative electrode mixture layer 42 in the width direction) where the poorly soluble Na salt is concentrated and the concentration becomes high. Since the facing portion 42a has a large contribution to charge and discharge, if the lithium deposition resistance of the facing portion 42a decreases and the resistance increases, the battery performance of the secondary battery decreases.

[0072] To address this problem, the method for manufacturing the secondary battery 10 according to this embodiment involves permeating an electrolyte solution L containing an additive into the electrode body 20, which includes a positive electrode 30 and a negative electrode 40 having a trap layer 33 provided thereon, from one end opposite the trap layer 33 side of the electrode body 20 toward the other end on the trap layer 33 side, via a separator 50.

[0073] Here, Fig. 5 is a diagram showing the distribution of Na ions and resistance in the width direction of the negative electrode mixture layer of the secondary battery manufactured by the manufacturing method for a secondary battery according to embodiment 1. The upper side of Fig. 5 shows a graph showing the relationship between the position in the width direction of the negative electrode mixture layer 42 and the amount of Na ions. The lower side of Fig. 5 shows a graph showing the relationship between the position in the width direction of the negative electrode mixture layer 42 and the resistance.

[0074] As the electrolyte L penetrates into the negative electrode mixture layer 42 from one end in the width direction of the negative electrode mixture layer 42, the Na ions dissolved from the negative electrode mixture layer 42 into the electrolyte L move toward the other end in the width direction of the negative electrode mixture layer 42. Then, the Na ions pass through the separator 50 while moving toward the other end of the negative electrode mixture layer 42 and are trapped by the sodium trapping agent of the trap layer 33. Therefore, as shown in FIG. 5, the amount of Na ions and the resistance increase in the non-facing portion 42c on the other end side facing the trap layer 33. On the other hand, since the Na ions can be uniformly distributed in the facing portion 42a, the uneven distribution of poorly soluble Na salts generated by the reaction of the additive and the Na ions in the facing portion 42a is suppressed. As a result, the increase in resistance due to the decrease in lithium precipitation resistance in the facing portion 42a is suppressed.

[0075] In this way, according to the present embodiment, a method for manufacturing a secondary battery 10 can be provided in which an increase in resistance due to uneven distribution of poorly soluble Na salt in the facing portion 42a, which is formed by combining an additive in the electrolyte solution L with Na ions dissolved in the electrolyte solution L, is suitably suppressed.

[0076] The present disclosure is not limited to the above embodiment, and can be modified as appropriate without departing from the spirit of the present disclosure. In the above embodiment, the method for manufacturing the secondary battery 10 having the wound electrode body as the electrode body 20 has been described, but is not limited thereto. For example, the electrode body 20 of the secondary battery 10 may be a laminated electrode body in which a plurality of positive electrodes 30 and a plurality of negative electrodes 40 are alternately stacked with a separator 50 interposed therebetween. [Explanation of symbols]

[0077] 10 Secondary battery 11 Battery case 12 Case body 13 Lid 14 Inlet 15 Sealing member 16 Positive terminal 17 Negative terminal 18 Positive current collector 19 Negative current collector 20 Electrode body 22 Positive electrode current collector 23 Negative electrode current collector 30 positive electrode 31 Positive electrode current collector 31a End 32 Positive electrode mixture layer 33 Trap Layer 40 negative electrode 41 Negative electrode current collector 41a End 42 Negative electrode composite layer 42a Opposing part 42b, 42c Unopposed parts 50 Separator L Electrolyte

Claims

1. an electrode preparation step of preparing a positive electrode in which a positive electrode mixture layer is formed on a surface of the positive electrode current collector excluding the end portion of the positive electrode current collector, and a negative electrode in which a negative electrode mixture layer is formed on a surface of the negative electrode current collector excluding the end portion of the negative electrode current collector; a trap layer forming step of forming a trap layer on at least one of a surface of an end portion of a positive electrode current collector excluding a positive electrode exposed portion where the positive electrode current collector is exposed and a surface of an end portion of a negative electrode current collector excluding a negative electrode exposed portion where the negative electrode current collector is exposed; an electrode assembly preparation step of preparing an electrode assembly including the positive electrode and the negative electrode with a separator therebetween; an electrode assembly housing step of housing the electrode assembly in an outer casing; a permeation step of permeating an electrolyte solution containing an additive into the electrode body from one end of the electrode body opposite to the trap layer side toward the other end of the electrode body on the trap layer side; having The trap layer includes a sodium trapping agent that bonds with sodium ions dissolved from the electrode body into the electrolyte.

2. The method for producing a secondary battery according to claim 1 , wherein the trap layer is disposed adjacent to at least one of the positive electrode mixture layer and the negative electrode mixture layer.

3. 2. The method for producing a secondary battery according to claim 1, wherein the sodium trapping agent is lithium bis(oxalato)borate.

4. 2. The method for producing a secondary battery according to claim 1, wherein the electrode body is a wound electrode body in which the positive electrode and the negative electrode, each of which is in the form of a long sheet, are stacked and wound with the separator, also in the form of a long sheet, interposed therebetween.

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