Method for manufacturing a non-aqueous secondary battery

Abstract

To suppress unevenness in resistance in an anode sheet.SOLUTION: In a method for manufacturing a nonaqueous secondary battery having a cathode sheet, an anode sheet and a nonaqueous electrolyte solution containing a lithium salt-containing film-forming material, the anode sheet 24 has an anode collector 25, an anode mixture layer 26, and an uncoated part 25A at an end of the anode sheet, where the anode collector is exposed; the anode mixture layer 26 contains a negative electrode active material, SBR and CMC; the nonaqueous electrolyte solution contains LiBOB; and coating regions of an anode mixture material paste 26X applied to the anode collector 25 are defined as first regions 41, 42 and a second region 43. The method comprises a dry step of drying the anode mixture material paste 26X, in which the anode mixture material paste 26X is dried in such a way that the first regions 41, 42 is larger than the second region 43 in SBR migration index.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a non-aqueous secondary battery.

Background Art

[0002] Non-aqueous secondary batteries such as lithium-ion secondary batteries have a so-called SEI film (Solid Electrolyte Interface) on the surface of the negative electrode composite material. The SEI film exists between the negative electrode composite material and the non-aqueous electrolyte, has a function of facilitating the occlusion and release of lithium ions into the negative electrode and suppressing further decomposition of the non-aqueous electrolyte, and is essential for maintaining good battery characteristics. The SEI film is formed by decomposition products of the non-aqueous electrolyte and additives, and the decomposition products incorporate lithium ions during the formation process. Therefore, repeated charging and discharging of the battery or long-term storage of the battery may cause the SEI film to thicken, leading to a decrease in battery capacity.

[0003] In response to this problem, it has already been proposed to previously add a film-forming material containing lithium to the non-aqueous electrolyte. The film-forming material is a compound having a lithium salt, for example, lithium bisoxalate borate (LiBOB, LiB(C2O4)2). According to this method, at the first charge, bisoxalate borate ions (BOB - , BOB ions, B(C2O4)2 - ) can be decomposed and polymerized to form a stable film derived from BOB ions on the particle surface of the negative electrode active material particles. Thereby, the growth of the SEI film can be suppressed (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, the members constituting the electrode body used in the lithium-ion secondary battery may contain a sodium salt. For example, the negative electrode material is composed of a negative electrode composite material, a binder, a thickener, etc. In some cases, SBR (styrene-butadiene copolymer) is used as the binder and CMC (carboxymethyl cellulose) is used as the thickener. SBR and CMC contain a sodium salt. Therefore, the BOB ions ionized from LiBOB also react with the sodium ions ionized from the sodium salt to form a NaBOB film. And the NaBOB film becomes a part of the film on the negative electrode sheet.

[0006] Incidentally, in the negative electrode forming step, a negative electrode composite material layer is formed on the negative electrode current collector by applying and drying a negative electrode composite material paste to the negative electrode current collector. In the drying step of drying the negative electrode composite material paste on the negative electrode current collector, drying air is blown uniformly in the width direction of the negative electrode current collector. Therefore, migration, which is a phenomenon in which a binder or the like floats from the inside to the surface layer of the negative electrode composite material paste as the solvent volatilizes, also becomes uniform.

[0007] When the non-aqueous electrolyte is injected into the battery case, it penetrates from the end of the negative electrode sheet. The sodium ions dissolved in the non-aqueous electrolyte have a faster ion diffusion rate than the BOB ions. Therefore, the NaBOB film is more likely to be formed in the central part of the negative electrode sheet. The central part of the negative electrode sheet with an excessive film amount has a higher resistance than the surrounding area, and resistance unevenness is formed in the negative electrode sheet. Such a negative electrode sheet will deposit metallic lithium in the high-resistance part during repeated charge and discharge, resulting in deterioration of battery performance. Means for Solving the Problems

[0008] A method for manufacturing a non-aqueous secondary battery for solving the above problems is a method for manufacturing a non-aqueous secondary battery having a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte containing a film-forming material containing a lithium salt. The negative electrode sheet includes a negative electrode current collector, a negative electrode mixture layer, and an uncoated portion where the negative electrode current collector is exposed at an end of the negative electrode sheet. The negative electrode mixture layer includes at least a negative electrode active material and an additive containing a sodium salt. The non-aqueous electrolyte contains a lithium salt as the film-forming material. A coating region of the negative electrode mixture paste applied to the negative electrode current collector is defined as a first region adjacent to the uncoated portion and a second region adjacent to the center side of the first region. In a drying step of drying the negative electrode mixture paste, the negative electrode mixture paste is dried such that the migration index of the additive is larger in the first region than in the second region.

[0009] According to the above configuration, the migration index of the binder is larger in the first region adjacent to the uncoated portion than in the second region, and in the first region, the binder is more distributed in the surface layer portion than in the second region. As a result, the first region has lower electrolyte permeability than the second region. Therefore, when the non-aqueous electrolyte penetrates the negative electrode sheet, it is more difficult for the non-aqueous electrolyte to penetrate the first region than the second region.

[0010] Anions ionized from the lithium salt also react with sodium ions (Na + ) ionized from the sodium salt contained in the negative electrode mixture layer. As a result, in the negative electrode sheet, a sodium salt-containing film in which anions and sodium ions have reacted is formed. At this time, since the sodium ions have a faster ion diffusion rate than the anions, they tend to gather at the central portion of the negative electrode sheet, and at the central portion, the sodium ions and the anions react actively, and the sodium salt-containing film is formed intensively. Then, in the negative electrode sheet, unevenness of the film occurs, resulting in uneven resistance.

[0011] In this regard, in the present invention, the non-aqueous electrolyte penetrates less easily into the first region than into the second region. As a result, sodium ions can be prevented from diffusing in the width direction of the negative electrode sheet and concentrating to form a sodium salt-containing film at the center. Thereby, coating unevenness can be suppressed in the negative electrode sheet, and resistance unevenness can be suppressed.

[0012] In the method for manufacturing the non-aqueous secondary battery, the negative electrode sheet includes the uncoated portions at opposite both ends, and includes the negative electrode composite material layer between the uncoated portions. The first region may be defined to be adjacent to the uncoated portions at both ends, and the second region may be defined between the first regions.

[0013] According to the above configuration, by cutting at the center in the width direction where the second region is located, two negative electrode sheets can be manufactured at once. In this case, in each negative electrode sheet, the non-aqueous electrolyte penetrates less easily into the first region than into the second region that is divided into two. As a result, sodium ions can be prevented from diffusing in the width direction of each negative electrode sheet and concentrating to form a sodium salt-containing film at the center.

[0014] In the method for manufacturing the non-aqueous secondary battery, the negative electrode sheet includes uncoated portions at opposite both ends, and includes the negative electrode composite material layer between the uncoated portions. The first region is defined to be adjacent to the uncoated portions at both ends. Further, a third region that partitions the negative electrode composite material layer is defined at the center in the width direction between the uncoated portions at both ends. The second region is defined between the first region and the third region. In the drying step, the negative electrode composite material paste may be dried such that the migration index of the additive is larger in the first region and the third region than in the second region.

[0015] According to the above configuration, by cutting the negative electrode sheet at the center in the width direction where the third region is defined, two negative electrode sheets can be manufactured at once. In this case, the two end portions of each negative electrode sheet have the second region located between the first region and the third region divided into two. And in each negative electrode sheet, the non-aqueous electrolyte penetrates less easily into the first region and the third region than into the second region. As a result, it is possible to suppress the formation of a sodium salt-containing film concentratedly in the central portion by the diffusion of sodium ions in the width direction of each negative electrode sheet.

[0016] In the method for manufacturing the non-aqueous secondary battery, the film-forming material may be LiBOB (lithium bis(oxalato)borate). According to the above configuration, LiBOB can form a relatively highly stable film on the negative electrode sheet that can extend the battery life.

[0017] In the method for manufacturing the non-aqueous secondary battery, the additive may be SBR (styrene-butadiene copolymer). According to the above configuration, SBR can be used as a binder.

[0018] In the method for manufacturing the non-aqueous secondary battery, the additive may be CMC (carboxymethyl cellulose). According to the above configuration, CMC can be used as a thickening agent.

[0019] In the drying step of the method for manufacturing the non-aqueous secondary battery, the drying air volume may be made larger in the first region than in the second region. According to the above configuration, the drying air volume in the first region is made larger than the drying air volume in the second region. Thereby, the migration index of the additive in the first region can be made larger than the migration index in the second region.

[0020] In the method for manufacturing the non-aqueous secondary battery, in the drying step, the drying air volume may be made larger in the first region and the third region than in the second region. According to the above configuration, the drying air volume in the first region and the third region is made larger than the drying air volume in the second region. Thereby, the migration index in the first region and the third region can be made larger than the migration index in the second region.

Advantages of the Invention

[0021] According to the present invention, in the negative electrode sheet, uneven resistance can be suppressed.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

[0023] Hereinafter, one embodiment of the present invention will be described with reference to FIGS. [Lithium-ion secondary battery] 1, a lithium-ion secondary battery 10, which is an example of a non-aqueous secondary battery, is a cell battery that is combined with a plurality of lithium-ion secondary batteries 10 and sealed in a resin or metal case to form a battery pack. The battery pack is used in hybrid vehicles and electric vehicles.

[0024] The lithium-ion secondary battery 10 includes a battery case 11 and a lid 12. The battery case 11 has a rectangular parallelepiped shape with an opening on the upper side. The lid 12 seals the opening of the battery case 11. The battery case 11 and the lid 12 are made of a metal such as aluminum or an aluminum alloy. The lithium-ion secondary battery 10 forms a sealed battery container by attaching the lid 12 to the battery case 11.

[0025] The lid body 12 is provided with two external terminals 13A and 13B. The external terminals 13A and 13B are used for charging and discharging electric power. Inside the battery case 11, an electrode body 20 is accommodated. The positive electrode current collector part 20A, which is the end part on the positive electrode side of the electrode body 20, is electrically connected to the external terminal 13A of the positive electrode through the positive electrode current collector member 14A. The negative electrode current collector part 20B, which is the end part on the negative electrode side of the electrode body 20, is electrically connected to the external terminal 13B of the negative electrode through the negative electrode current collector member 14B. Also, a non-aqueous electrolyte is injected into the battery case 11 through a liquid injection hole (not shown). Note that the shapes of the external terminals 13A and 13B are not limited to the shapes shown in FIG. 1 and may be any shape.

[0026] [Electrode body] As shown in FIGS. 2 and 3, the electrode body 20 is a flat wound body obtained by winding a laminate in which a long positive electrode sheet 21 and a negative electrode sheet 24 are laminated with a separator 27 interposed therebetween. The positive electrode sheet 21, the negative electrode sheet 24, and the separator 27 are laminated so that the longitudinal direction of each coincides with the longitudinal direction D1 (see FIG. 2). Before winding, the laminate is laminated in the thickness direction D3 (see FIG. 3) in the order of the positive electrode sheet 21, the separator 27, the negative electrode sheet 24, and the separator 27.

[0027] [Positive electrode sheet] As shown in FIG. 3, the positive electrode sheet 21 includes a positive electrode current collector 22 and a positive electrode composite layer 23. The positive electrode current collector 22 is a foil-shaped electrode base material formed in a long shape. The positive electrode composite layer 23 is provided on each of the two opposite surfaces of the positive electrode current collector 22. The positive electrode current collector 22 includes a positive electrode side non-coated part 22A where the positive electrode composite layer 23 is not formed and the positive electrode current collector 22 is exposed at one end in the width direction D2.

[0028] The positive electrode current collector 22 is made of a metal foil composed of aluminum or an alloy mainly composed of aluminum. The positive electrode current collector 22 functions as a current collector in the positive electrode. The positive electrode side non-coated part 22A provided in the positive electrode current collector 22 forms the positive electrode side current collector part 20A with the facing surfaces being pressed against each other in the state of the wound body.

[0029] The positive electrode composite material layer 23 is a cured body of a liquid positive electrode composite material paste. The positive electrode composite material paste contains a positive electrode active material, a positive electrode solvent, a positive electrode conductive material, and a positive electrode binder. The positive electrode composite material layer 23 is formed by drying the positive electrode composite material paste and vaporizing the positive electrode solvent. Therefore, the positive electrode composite material layer 23 contains a positive electrode active material, a positive electrode conductive material, and a positive electrode binder.

[0030] As the positive electrode active material, a lithium-containing composite metal oxide capable of occluding and releasing lithium ions, which are charge carriers in the lithium-ion secondary battery 10, is used. The lithium-containing composite oxide is an oxide containing lithium and another metal element other than lithium. The other metal element other than lithium is at least one selected from the group consisting of, for example, nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained as iron phosphate in the lithium-containing composite oxide.

[0031] For example, the lithium-containing composite oxide is lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or lithium manganate (LiMn2O4). For example, the lithium-containing composite oxide is a ternary lithium-containing composite oxide containing nickel, cobalt, and manganese, and is lithium nickel cobalt manganese oxide (LiNiCoMnO2). For example, the lithium-containing composite oxide is lithium iron phosphate (LiFePO4).

[0032] As the positive electrode solvent, an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent, is used. As the positive electrode conductive material, for example, carbon black such as acetylene black and ketjen black, carbon fibers such as carbon nanotubes and carbon nanofibers, and graphite are used. The positive electrode binder is an example of the resin component contained in the positive electrode composite material paste. As the positive electrode binder, for example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), styrene butadiene rubber (SBR), etc. are used.

[0033] Note that the positive electrode sheet 21 may be provided with an insulating layer at the boundary between the uncoated portion 22A on the positive electrode side and the positive electrode composite material layer 23. The insulating layer includes an inorganic component having insulating properties and a resin component that functions as a binder. The inorganic component is at least one selected from the group consisting of powdery boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0034] [Negative electrode sheet] The negative electrode sheet 24 includes a negative electrode current collector 25 and a negative electrode composite material layer 26. The negative electrode current collector 25 is a foil-shaped electrode base material formed in a long shape. The negative electrode composite material layer 26 is provided on each of the two opposing surfaces of the negative electrode current collector 25. The negative electrode current collector 25 includes a negative electrode side uncoated portion 25A where the negative electrode composite material layer 26 is not formed and the negative electrode current collector 25 is exposed at one end in the width direction D2 and at an end portion located opposite to the uncoated portion 22A on the positive electrode side.

[0035] The negative electrode current collector 25 is made of a metal foil composed of copper or an alloy mainly composed of copper. The negative electrode current collector 25 functions as a current collector in the negative electrode. In the state of the wound body, the opposing surfaces of the negative electrode side uncoated portion 25A are pressed against each other to form the negative electrode side current collecting portion 20B.

[0036] The negative electrode composite material layer 26 is a cured body of a liquid negative electrode composite material paste. The negative electrode composite material paste includes a negative electrode active material, a negative electrode solvent, a negative electrode thickening material, and a negative electrode binder. The negative electrode composite material layer 26 is formed by drying the negative electrode composite material paste and vaporizing the negative electrode solvent. Therefore, the negative electrode composite material layer 26 includes the negative electrode active material and, further, as an additive, a negative electrode thickening material and a negative electrode binder. Note that the negative electrode composite material layer 26 may further include an additive such as a conductive material.

[0037] The negative electrode active material is a material capable of occluding and releasing lithium ions. As the negative electrode active material, for example, carbon materials such as graphite, graphitizable carbon, non-graphitizable carbon, and carbon nanotubes are used. The negative electrode solvent is, for example, water. As the negative electrode thickener, as an example, CMC (carboxymethyl cellulose) can be used as a thickener containing a sodium salt. As the negative electrode binder, the same one as the positive electrode binder can be used. As the negative electrode binder, as an example, SBR (styrene-butadiene copolymer) can be used as a binder containing a sodium salt.

[0038] The negative electrode composite material layer 26 includes a facing portion 26A and a non-facing portion 26B. The facing portion 26A is located at the center of the negative electrode composite material layer 26 in the width direction D2. The facing portion 26A is the portion of the negative electrode composite material layer 26 that faces the positive electrode composite material layer 23 through the separator 27 in the state of the electrode body 20. The width of the facing portion 26A is substantially equal to the width of the positive electrode composite material layer 23 in the width direction D2.

[0039] The non-facing portions 26B are each located at both ends of the facing portion 26A in the width direction D2. The non-facing portion 26B is the portion of the negative electrode composite material layer 26 that extends outward in the width direction D2 from the positive electrode composite material layer 23 in the state of the electrode body 20. In other words, the non-facing portion 26B is the portion of the negative electrode composite material layer 26 that does not face the positive electrode composite material layer 23 through the separator 27 in the state of the electrode body 20. In the width direction D2, the width of the negative electrode composite material layer 26 is larger than the width of the positive electrode composite material layer 23 by the amount of the non-facing portion 26B.

[0040] [Separator] The separator 27 prevents contact between the positive electrode sheet 21 and the negative electrode sheet 24 and holds the non-aqueous electrolyte between the positive electrode sheet 21 and the negative electrode sheet 24. When the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte penetrates from the end portion to the central portion of the separator 27.

[0041] The separator 27 is a non-woven fabric made of polypropylene or the like. As the separator 27, for example, a porous polymer film such as a porous polyethylene film, a porous polyolefin film, or a porous polyvinyl chloride film, and an ion-conductive polymer electrolyte film or the like can be used.

[0042] [Non-aqueous electrolyte] The non-aqueous electrolyte is a composition in which a supporting salt is contained in a non-aqueous solvent. As the non-aqueous solvent, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc. can be used. Further, as the supporting salt, one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc. can be used.

[0043] In this embodiment, ethylene carbonate is employed as the non-aqueous solvent. LiBOB (lithium bisoxalate borate) as a lithium salt as an additive is added to the non-aqueous electrolyte. For example, LiBOB is added to the non-aqueous electrolyte so that the concentration of LiBOB in the non-aqueous electrolyte is 0.001 or more and 0.1 or less [mol / L].

[0044] [Manufacturing process of the positive electrode sheet] In the manufacturing process of the positive electrode sheet 21, first, the positive electrode mixture paste is applied to the positive electrode current collector 22 and then dried. Next, the positive electrode mixture layers 23 are formed one by one on two opposite surfaces of the positive electrode current collector 22 so as to form one positive electrode side non-coated portion 22A at each of both ends in the width direction D2 of the positive electrode current collector 22. Next, the thickness of the positive electrode mixture layer 23 is adjusted by pressing the positive electrode mixture layers 23 formed on both surfaces of the positive electrode current collector 22. Next, the positive electrode current collector 22 with the positive electrode mixture layer 23 applied is cut at the center in the width direction D2 and divided into two along the longitudinal direction D1. Thereby, two positive electrode sheets 21 are manufactured at once.

[0045] [Manufacturing Process of Negative Electrode Sheet] As shown in Fig. 4, the manufacturing process of the negative electrode sheet 24 includes the steps of S1 to S4. In step S1, the negative electrode composite paste 26X is applied to the negative electrode current collector 25 (see Fig. 5). In step S2, the negative electrode composite paste 26X is dried by a drying device to form a negative electrode composite layer 26 on the negative electrode current collector 25.

[0046] In step S3, the negative electrode composite layer 26 is formed on each of the two opposite surfaces of the negative electrode current collector 25 so that one negative electrode non-coated portion 25A is formed at each of both ends in the width direction D2 of the negative electrode current collector 25. In step S1, the negative electrode current collector 25 used has a width approximately twice that based on the state of the electrode body 20 shown in Fig. 2. Also, in step S1, the negative electrode composite layer 26 is applied so as to have a width approximately twice that based on the state of the electrode body 20 shown in Fig. 2. Therefore, in step S1, it is divided into two along the center line CL shown by the dashed-dotted line in Fig. 5, and two negative electrode sheets 24X are formed.

[0047] In step S3, the thickness of the negative electrode composite layer 26 is adjusted by pressing the negative electrode composite layers 26 formed on both surfaces of the negative electrode current collector 25. In step S4, the negative electrode sheet 24 coated with the negative electrode composite layer 26 is cut at the center in the width direction D2 and divided into two along the longitudinal direction D1. Through the steps S1 to S4 above, two negative electrode sheets 24X are manufactured at a time.

[0048] [Manufacturing Process of Electrode Body] The manufacturing process of the electrode body 20 first laminates the positive electrode sheet 21 and the negative electrode sheet 24 with a separator 27 interposed therebetween. In the lamination process, the opposing portion 26A of the negative electrode composite layer 26 provided in the negative electrode sheet 24 is arranged to face the positive electrode composite layer 23 provided in the positive electrode sheet 21 through the separator 27. The laminate of the positive electrode sheet 21 and the negative electrode sheet 24 laminated through the separator 27 is wound along the longitudinal direction D1.

[0049] Next, the wound body in which the positive electrode sheet 21, the negative electrode sheet 24, and the separator 27 are laminated and wound is pressed flat. By going through this process, an outer shape as the electrode body 20 is formed in the wound body composed of the positive electrode sheet 21, the negative electrode sheet 24, and the separator 27.

[0050] Then, the uncoated portion 22A on the positive electrode side is pressed into contact to form the positive electrode current collector portion 20A, and the uncoated portion 25A on the negative electrode side is pressed into contact to form the negative electrode current collector portion 20B. The positive electrode current collector portion 20A is electrically connected to the external terminal 13A of the positive electrode via the positive electrode current collector member 14A. The negative electrode current collector portion 20B is electrically connected to the external terminal 13B of the negative electrode via the negative electrode current collector member 14B. Through the above steps, the electrode body 20 is manufactured.

[0051] [Surface layer portion of the negative electrode sheet] With reference to FIGS. 6 to 11, the state of the surface layer portion of the negative electrode sheet 24 will be described. FIGS. 6(a) and (b) show the relationship between the air outlet 31 of the drying air and the negative electrode sheet 24 when heating and drying the negative electrode mixture layer 26 in the conventional drying device 30. FIG. 6(c) shows the divided negative electrode sheet 24X, and FIG. 6(d) shows the amount of BOB ions and the amount of sodium ions in the width direction D2 of the negative electrode sheet 24X divided in step S4.

[0052] As shown in FIG. 6(a), the air outlet 31 of the drying air in the conventional drying device 30 has a rectangular shape, and the dimension L1 in the long side direction is substantially the same as the width direction D2 of the negative electrode mixture layer 26. Also, the width W1 in the short side direction is a constant dimension from end to end in the long side direction. That is, the air outlet 31 blows the drying air uniformly with respect to the width direction D2 of the negative electrode mixture paste 26X. Therefore, the negative electrode mixture paste 26X dries uniformly in the width direction D2. Therefore, as the solvent volatilizes, the migration index of the negative electrode binder and the like in the negative electrode mixture layer 26 also becomes uniform.

[0053] Here, migration is a phenomenon in which a negative electrode binder such as SBR rises from the inside to the surface layer in the thickness direction D3 of the negative electrode composite layer 26. And the bias in the thickness direction D3 of the negative electrode binder in the thickness direction D3 of the negative electrode composite layer 26 can be represented by a migration index.

[0054] As shown in FIG. 7, the migration index is represented by (the amount of binder in the upper part 26U) / (the amount of binder in the lower part 26D) when the negative electrode composite layer 26 is divided into two in the thickness direction D3. Therefore, the larger the migration index, the more the negative electrode binder is distributed on the surface layer of the negative electrode composite layer 26.

[0055] Since the negative electrode binder has low permeability to the electrolytic solution, the higher the migration index, the lower the permeability in the surface layer part. As shown in FIG. 8(a), the lower the permeability, the larger the contact angle, and the less likely the non-aqueous electrolytic solution is to penetrate into the negative electrode composite layer 26. Also, as shown in FIG. 8(b), the higher the permeability, the smaller the contact angle, and the easier the non-aqueous electrolytic solution is to penetrate into the negative electrode composite layer 26.

[0056] As shown in FIG. 6(b), the negative electrode sheet 24 is cut at the center in the width direction D2 and divided into two along the longitudinal direction D1 to become the negative electrode sheet 24X. The divided negative electrode sheets 24X shown in FIG. 6(c) also have a substantially uniform migration index from the end E1 on the negative electrode side uncoated part 25A side to the opposite cut end E2 (the position of the center line CL).

[0057] When the non-aqueous electrolytic solution is injected into the battery case 11, the non-aqueous electrolytic solution penetrates from the end E1 and the cut end E2 on the negative electrode side uncoated part 25A side of the negative electrode composite layer 26 toward the central part. In FIG. 6(c), the arrow indicates the penetration direction of the non-aqueous electrolytic solution.

[0058] Here, as shown in FIG. 9, in the negative electrode composite layer 26, the first measurement region 36, the second measurement region 37, and the third measurement region 38 are regions for measuring the amounts of sodium ions and BOB ions. The first measurement region 36 is a region adjacent to the end E1 on the side of the non-coated portion 25A on the negative electrode side. The second measurement region 37 is a region adjacent to the cut end E2. The third measurement region 38 is a region between the first measurement region 36 and the second measurement region 37. And FIG. 6(d) is a diagram schematically showing the measurement results of the amounts of sodium ions and BOB ions in each of the first measurement region 36, the second measurement region 37, and the third measurement region 38. Note that the first measurement region 36 and the second measurement region 37 are regions corresponding to the first regions 41 and 42 described later, and the third measurement region 38 is a region corresponding to the second region 43.

[0059] As shown in FIG. 6(d), sodium ions (Na + ) dissolved in the non-aqueous electrolyte have a faster ion diffusion rate than BOB ions (BOB - ), which are anions. For this reason, the NaBOB film, which is a sodium salt-containing film derived from sodium ions, is likely to be formed in a large amount at the central portion in the width direction D2 of the negative electrode composite layer 26. The central portion in the width direction D2 of the negative electrode sheet 24X with an excessively large amount of the NaBOB film has a higher resistance than the surroundings, and resistance unevenness is formed in the negative electrode sheet 24X. Such a negative electrode sheet 24X will deposit metallic lithium at the high-resistance portion during repeated charge and discharge, deteriorating the battery performance.

[0060] On the other hand, FIGS. 10(a) and (b) show the relationship between the air outlet 33 of the drying air when drying the negative electrode composite layer 26 and the negative electrode sheet 24 in the drying device 32 used for the negative electrode sheet 24 in the present embodiment. FIG. 10(c) shows the split negative electrode sheet 24X, and FIG. 10(d) shows the amounts of BOB ions and sodium ions in the negative electrode sheet 24X in the width direction D2 split in step S4.

[0061] As shown in FIG. 10(a), in the drying device 32 used for the negative electrode sheet 24 in the present embodiment, the air outlet 33 of the drying air has a dimension L1 in the long side direction that is substantially the same as the width direction D2 of the negative electrode composite material layer 26. The air outlet 33 includes a narrow portion 33A having a rectangular shape as a basic shape, and widened portions 33B on both sides of the narrow portion 33A. The narrow portion 33A has a constant width W2, and the widened portion 33B has a width W3 at its widest part that is larger than the width W2. And the widened portion 33B gradually narrows in width until it becomes width W2 toward the center.

[0062] With such an air outlet 33, the amount of drying air is larger in the widened portion 33B than in the narrow portion 33A. As a result, the drying of the negative electrode composite paste 26X also proceeds faster in the first regions 41 and 42 at both ends E1 and E2 in the width direction D2 than in the second region 43. Thereby, as shown in FIG. 10(b), the migration index of the negative electrode composite material layer 26 is also higher in the first regions 41 and 42, which are the peripheral portions at both ends of the negative electrode composite material layer 26 in the width direction D2, than in the second region 43, which is the central portion, and the permeability is lower. That is, the contact angle of the non-aqueous electrolyte with respect to the negative electrode composite material layer 26 is larger in the first regions 41 and 42 than in the second region 43.

[0063] Note that the width of the first regions 41 and 42 where the drying air hits is preferably wider than the opposing portion 26A of about 20 mm from both ends of the negative electrode composite material layer 26 in the width direction D2 toward the center line CL, more preferably 30 mm or more, and even more preferably 30 mm or more and 45 mm or less.

[0064] As shown in FIG. 10(c), the negative electrode sheet 24 is cut at the center in the width direction D2 and divided into two along the longitudinal direction D1 to become the negative electrode sheet 24X. For the two divided negative electrode sheets 24X, the migration index is also higher in the first regions 41 and 42 on the E1 side at both ends in the width direction D2 than in the second region 43A on the E2 side of the cut end. As a result, the permeability is lower in the first regions 41 and 42 than in the second region 43A on the E2 side of the cut end. Note that the first regions 41 and 42 are wider than the non-opposing portion 26B (see FIG. 3).

[0065] When a non-aqueous electrolyte is injected into the battery case 11, the non-aqueous electrolyte penetrates from each end E1, E2 of the negative electrode composite layer 26 in the negative electrode sheet 24X. That is, the non-aqueous electrolyte penetrates from the end E1 on the non-coated part 25A side of the negative electrode side of the negative electrode composite layer 26 and the cut end E2 toward the central part. In FIG. 10(c), the arrows indicate the penetration direction of the non-aqueous electrolyte. At this time, it becomes more difficult for the non-aqueous electrolyte to penetrate into the first regions 41, 42 than into the second region 43A which is divided into two. As a result, as shown in FIG. 10(d), the sodium ions diffuse in the D1 direction of the negative electrode sheet 24, and the NaBOB film is formed in a wide range from the first regions 41, 42 to the second region 43A. Thereby, it is possible to suppress the formation of the NaBOB film concentratedly at the central part in the width direction D2 of the negative electrode composite layer 26. As a result, in the negative electrode sheet 24, the unevenness of the film can be suppressed, and the unevenness of the resistance can be suppressed.

[0066] Also, FIGS. 11(a) and (b) show the relationship between the air outlet 35 of the drying air when drying the negative electrode composite layer 26 and the negative electrode sheet 24 in another example of the drying device 34 used for the negative electrode sheet 24 in the present embodiment. FIG. 11(c) shows the divided negative electrode sheet 24X, and FIG. 11(d) shows the amount of BOB ions and the amount of sodium ions in the negative electrode sheet 24X in the width direction D2 divided in step S4.

[0067] As shown in FIG. 11(a), the air outlet 35 of the drying air in the drying device 34 used for the negative electrode sheet 24 in the present embodiment has a dimension L1 in the long side direction that is substantially the same as the width direction D2 of the negative electrode composite layer 26. The air outlet 35 includes narrow-width portions 35A, 35B having a constant width with a rectangular shape as a basic shape, and widened portions 35C, 35D, 35E on both sides of the narrow-width portions 35A, 35B. The narrow-width portion 35A has widened portions 35C, 35D positioned on both sides thereof, and the narrow-width portion 35B has widened portions 35D, 35E positioned on both sides thereof. The narrow-width portions 35A, 35B have a width W2, and the widths of the widened portions 35C, 35D, 35E are such that the widest part has a width W3 that is larger than the width W2. And the widened portions 35C, 35E gradually become narrower in width until they reach the width W2 toward the center. The widened portion 35D gradually becomes narrower in width until it reaches the width W2 from the center toward both ends.

[0068] In such a blower outlet 35, the air volume of the drying air is larger in the widened portions 35C, 35D, 35E than in the narrowed portions 35A, 35B. As a result, the drying of the negative electrode composite layer 26 also progresses faster in the first regions 45, 46 which are the peripheral portions at both ends of the negative electrode composite layer 26 in the width direction D2 and the third region 47 which is the peripheral portion of the center line CL than in the second regions 48, 49. The second regions 48, 49 are the regions between the first regions 45, 46 and the third region 47. Thereby, as shown in FIG. 11(b), the migration index of the negative electrode composite layer 26 is also higher in the first regions 45, 46 and the third region 47 than in the second regions 48, 49, and the permeability is lower. That is, the contact angle of the non-aqueous electrolyte with respect to the negative electrode composite layer 26 is larger in the first regions 45, 46 and the third region 47 in the width direction D2 than in the second regions 48, 49.

[0069] As shown in FIG. 11(c), the negative electrode sheet 24 is cut at the center in the width direction D2 and divided into two along the longitudinal direction D1 to become the negative electrode sheet 24X. At this time, the third region 47 which is the peripheral portion of the center line CL is divided into two. Also in the divided negative electrode sheets 24X, the migration is higher in the first regions 45, 46 and the third region 47A than in the second regions 48, 49, and as a result, the permeability is lower in the first regions 45, 46 and the third region 47A than in the second regions 48, 49. Note that the first regions 45, 46 and the third region 47A are wider than the non-opposing portion 26B (see FIG. 3).

[0070] When the non-aqueous electrolyte is injected into the battery case 11, the non-aqueous electrolyte penetrates from each end E1, E2 of the negative electrode composite material layer 26. That is, the non-aqueous electrolyte penetrates from the end E1 on the uncoated portion 25A side of the negative electrode side of the negative electrode composite material layer 26 and the cut end E2 toward the central portion. In FIG. 11(c), the arrow indicates the penetration direction of the non-aqueous electrolyte. At this time, the non-aqueous electrolyte penetrates less easily into the first regions 45, 46 and the third region 47A than into the second regions 48, 49. As a result, as shown in FIG. 11(d), the sodium ions diffuse in the D1 direction of the negative electrode sheet 24, and the NaBOB film is formed entirely on the negative electrode composite material layer 26. Thereby, it is possible to suppress the formation of the NaBOB film concentratedly in the central portion in the width direction D2 of the negative electrode composite material layer 26. As a result, in the negative electrode sheet 24, unevenness of the film can be suppressed, and unevenness of resistance can be suppressed.

[0071] [Effects of the Embodiment] According to the above embodiment, the following effects can be obtained. (1) The migration index of the negative electrode binder is larger in the first regions 41, 42 adjacent to the uncoated portion 25A on the negative electrode side than in the second region 43A (see FIG. 10(c)). In the first regions 41, 42, the negative electrode binder is distributed more in the surface layer portion than in the second region 43A. As a result, the first regions 41, 42 have lower permeability than the second region 43A. Therefore, when the non-aqueous electrolyte penetrates into the negative electrode sheet 24, the non-aqueous electrolyte penetrates less easily into the first regions 41, 42 than into the second region 43A.

[0072] Also, the migration index of the negative electrode binder is larger in the first regions 45, 46 and the third region 47A adjacent to the uncoated portion 25A on the negative electrode side than in the second regions 48, 49 (see FIG. 11(c)). In the first regions 45, 46 and the third region 47A, the negative electrode binder is distributed more in the surface layer portion than in the second regions 48, 49. As a result, the first regions 45, 46 and the third region 47A have lower permeability than the second regions 48, 49. Therefore, when the non-aqueous electrolyte penetrates into the negative electrode sheet 24, the non-aqueous electrolyte penetrates less easily into the first regions 45, 46 and the third region 47A than into the second regions 48, 49.

[0073] In any of the cases of FIGS. 10 and 11, the sodium ions can be diffused in the width direction D2 of the negative electrode sheet 24X, thereby suppressing the concentrated formation of the NaBOB film in the central portion. As a result, in the negative electrode sheet 24X, the unevenness of the film can be suppressed, and the unevenness of the resistance can be suppressed.

[0074] (2) By cutting at the center in the width direction located in the second region 43 in FIGS. 10(a) to (d) and FIGS. 11(a) to (d), two negative electrode sheets 24X can be manufactured at once.

[0075] (3) LiBOB can form a relatively highly stable film on the negative electrode sheet 24 that can extend the battery life. (4) SBR can be used as the negative electrode binder in the negative electrode composite layer 26.

[0076] (5) CMC can be used as the negative electrode thickener in the negative electrode composite layer 26. (6) In FIGS. 10(a) to (d), the drying air volume in the first regions 41 and 42 is made larger than the drying air volume in the second region 43. Thereby, the migration index of the binder in the first regions 41 and 42 can be made larger than that in the second region 43.

[0077] (7) The first regions 41 and 42 are regions wider than the non-opposing portion 26B. Therefore, the control of the drying air such as the distance between the air outlets 33 and 35 and the negative electrode composite paste 26X, the wind direction, the air volume, and the temperature is easier than the case where the drying air is locally applied to the negative electrode composite layer 26 such as only the non-opposing portion 26B.

[0078] (9) In FIGS. 11(a) to (d), the drying air volume in the first regions 45 and 46 and the third region 47 is made larger than the drying air volume in the second regions 48 and 49. Thereby, the migration index of the binder in the first regions 45 and 46 and the third region 47 can be made larger than that in the second regions 48 and 49.

[0079] (10) The first regions 45, 46 and the third region 47 are regions wider than the non-opposing portion 26B. Therefore, the control of the drying air is easier than in the case where the drying air is locally applied to the negative electrode composite layer 26 such as only to the non-opposing portion 26B.

[0080] [Modified Example] Note that the above embodiment can be implemented with the following modifications. · The shapes of the drying air outlets 33, 35 are not limited to the shapes shown in FIGS. 10(a) and 11(a). For example, the widened portions 33B, 35C, 35D, 35E may be rectangular shapes wider than the narrow portions 33A, 35A, 35B. Also, the widened portions 33B, 35C, 35D, 35E may be shaped to curve and narrow toward the narrow portions 33A, 35A, 35B.

[0081] · As a method of making the migration index of the binder larger in the first regions 45, 46 and the third region 47 than in the second regions 48, 49, the temperature of the drying air may be made the same and the air volume may be changed, or the air volume may be made the same and the temperature may be changed, or the temperature and the air volume may be adjusted in a combined manner.

[0082] · The negative electrode thickening material added to the negative electrode composite material is not limited to CMC as long as it contains a sodium salt. · LiBOB as the film-forming material added to the non-aqueous electrolyte is not particularly limited as long as it contains a lithium salt.

[0083] · The negative electrode binder added to the negative electrode composite material is not limited to SBR as long as it has low permeability to the electrolyte and contains a sodium salt. · In the manufacturing process of the positive electrode sheet 21 and the negative electrode sheet 24, the process of bisecting at the center line CL may be omitted.

[0084] · Although the electrode body 20 was exemplified as a wound body obtained by winding a laminate in which a positive electrode sheet 21 and a negative electrode sheet 24 were laminated via a separator 27, for example, a laminate in which a plurality of positive electrode sheets 21 and a plurality of negative electrode sheets 24 are alternately laminated via a separator 27 may be used.

[0085] · The lithium ion secondary battery 10 may be mounted on a computer, other electronic devices, in addition to an automatic transporter, a special vehicle for cargo handling, an electric vehicle, a hybrid vehicle, etc., and may also be a component constituting other systems. For example, it may be provided in a moving body such as a ship or an aircraft, or may be a power supply system that supplies power to a building or a home where a secondary battery is installed via a substation from a power plant.

Description of Signs

[0086] D2…Width direction D3…Thickness direction E1…End E2…Cut end 10…Lithium ion secondary battery 20…Electrode body 20B…Negative electrode current collector 24…Negative electrode sheet 24X…Negative electrode sheet 25…Negative electrode current collector 25A…Negative electrode non-coated part 26…Negative electrode composite layer 26X…Negative electrode composite paste 27…Separator 32…Drying device 33…Air outlet 33A…Narrow part 33B…Wide part 41…First region 42…First region 43…Second region 43A…Second region

Claims

1. A method for manufacturing a non-aqueous secondary battery having a non-aqueous electrolyte containing a positive electrode sheet, a negative electrode sheet, and a film-forming material containing a lithium salt, wherein the negative electrode sheet includes a negative electrode current collector, a negative electrode mixture layer, and an uncoated portion where the negative electrode current collector is exposed at an end of the negative electrode sheet, the negative electrode mixture layer includes at least a negative electrode active material and an additive containing a sodium salt, the non-aqueous electrolyte contains a lithium salt as the film-forming material, a coating region of the negative electrode mixture paste applied to the negative electrode current collector is defined as a first region adjacent to the uncoated portion and a second region adjacent to the center side of the first region, in the drying step of drying the negative electrode mixture paste, the negative electrode mixture paste is dried such that the migration index of the additive is greater in the first region than in the second region, A method for manufacturing a non-aqueous secondary battery.

2. the negative electrode sheet includes the uncoated portions at opposite ends, and includes the negative electrode mixture layer between the uncoated portions, the first region is defined to be adjacent to the uncoated portions at both ends, and the second region is defined between the first regions, The method for manufacturing a non-aqueous secondary battery according to Claim 1. [[ID= twelve]]

3. the negative electrode sheet includes the uncoated portions at opposite ends, and includes the negative electrode mixture layer between the uncoated portions, the first region is defined to be adjacent to the uncoated portions at both ends, further, a third region that partitions the negative electrode mixture layer is defined at the center in the width direction between the uncoated portions at both ends, the second region is defined between the first region and the third region, in the drying step, the negative electrode mixture paste is dried such that the migration index of the additive is greater in the first region and the third region than in the second region, The method for manufacturing a non-aqueous secondary battery according to Claim 1.

4. The film-forming material is LiBOB (lithium bisoxalate borate). The method for manufacturing a non-aqueous secondary battery according to any one of Claims 1 to 3.

5. The additive is SBR (styrene-butadiene copolymer). The method for manufacturing a non-aqueous secondary battery according to any one of Claims 1 to 3.

6. The additive is CMC (carboxymethyl cellulose). The method for manufacturing a non-aqueous secondary battery according to Claim 5.

7. In the drying step, the drying air volume is made larger in the first region than in the second region. The method for manufacturing a non-aqueous secondary battery according to any one of claims 1 to 6.

8. In the drying step, the drying air volume is made larger in the first region and the third region than in the second region. The method for manufacturing a non-aqueous secondary battery according to claim 3.

Images