Method for manufacturing non-aqueous secondary battery

Abstract

To provide a nonaqueous secondary battery that can suppress performance deterioration, an electrode plate for the nonaqueous secondary battery, and a manufacturing method of the nonaqueous secondary battery.SOLUTION: A positive electrode composite material layer 32 is formed by drying a positive electrode composite material paste 34 in a state where the positive electrode composite material paste 34 containing at least a positive electrode active material and an organic solvent is coated on a positive electrode base material 31. The positive electrode composite material layer 32 is formed such that the organic solvent remains. Charging is performed with an electrode body and a non-aqueous electrolyte housed in a battery case.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a non-aqueous secondary battery, an electrode plate for a non-aqueous secondary battery, and a method for manufacturing a non-aqueous secondary battery, and more particularly to a non-aqueous secondary battery, an electrode plate for a non-aqueous secondary battery, and a method for manufacturing a non-aqueous secondary battery that can suppress performance degradation. [Background technology]

[0002] Conventionally, nonaqueous secondary batteries have been disclosed that have an electrode assembly in which a negative electrode plate, a positive electrode plate, and a separator are stacked in a stacking direction and wound in a winding direction, as in Patent Document 1. The electrode assembly in a wound state is housed in a battery case together with a nonaqueous electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-099725 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the invention described in Patent Document 1, repeated charging and discharging of a nonaqueous secondary battery increases the DC internal resistance in the electrode assembly, which may result in performance degradation, such as deterioration of high-rate characteristics. [Means for solving the problem]

[0005] A non-aqueous secondary battery that solves the above problems includes an electrode assembly having a negative electrode plate, a positive electrode plate, and a separator provided between the negative electrode plate and the positive electrode plate, a non-aqueous electrolyte, and a battery case that accommodates the electrode assembly and the non-aqueous electrolyte, wherein the positive electrode plate has a positive electrode base material and a positive electrode composite layer provided on the positive electrode base material, and the positive electrode composite layer is formed by drying a positive electrode composite paste containing at least a positive electrode active material and an organic solvent in a state in which the positive electrode base material is coated with the positive electrode base material, so that the organic solvent remains, and charging is performed with the electrode assembly and the non-aqueous electrolyte contained in the battery case.

[0006] According to this configuration, the positive electrode mixture paste containing at least the positive electrode active material and the organic solvent is dried to form a positive electrode mixture layer so that the organic solvent remains. Then, charging is performed in a state in which the electrode body and the nonaqueous electrolyte are accommodated in the battery case, and the organic solvent remaining as the positive electrode mixture layer is vaporized. In this way, by intentionally drying the positive electrode mixture paste so that the organic solvent remains, the organic solvent remaining in the positive electrode mixture layer can be vaporized inside the battery case during charging. This makes it possible to improve the pressure inside the battery case. Therefore, the nonaqueous electrolyte inside the electrode body is less likely to be pushed out to the outside of the electrode body. Therefore, it is possible to suppress the deterioration of high-rate characteristics caused by an increase in the DC internal resistance in the electrode body.

[0007] Furthermore, the electrode body may be formed such that the positive electrode plate, the negative electrode plate, and the separator are stacked in the stacking direction and wound in a longitudinal direction intersecting the stacking direction, and the positive electrode mixture layer is formed such that a greater amount of the organic solvent remains in an end region in a width direction intersecting the stacking direction and the longitudinal direction than in a central region in the width direction.

[0008] According to this configuration, by performing charging with the electrode body and the nonaqueous electrolyte contained in the battery case, a larger amount of organic solvent is evaporated in the end region in the width direction of the positive electrode mixture layer than in the central region in the width direction of the positive electrode mixture layer. Therefore, bubbles are less likely to be formed due to evaporation of the organic solvent in the central region in the width direction of the positive electrode mixture layer than in the end region in the width direction of the positive electrode mixture layer. As a result, bubbles are less likely to remain inside the electrode body. In this way, it is possible to suppress excessive widening of the distance between the positive electrode plate and the negative electrode plate due to the remaining bubbles formed with the evaporation of the organic solvent. Therefore, it is possible to suppress performance deterioration of the nonaqueous secondary battery, specifically, an increase in resistance.

[0009] Furthermore, when the nonaqueous secondary battery is charged, the organic solvent may evaporate to form bubbles, and the end region may be configured to be a region that is away from an end of the positive electrode mixture layer in the width direction by a distance equal to or less than a radius of the bubbles.

[0010] According to this configuration, the end region where bubbles are likely to form as the organic solvent evaporates is separated from the end in the width direction of the positive electrode mixture layer by a distance equal to or less than the radius of the bubbles. This makes it possible for bubbles formed in the end region as the organic solvent evaporates to be easily discharged to the outside of the electrode body without remaining inside the electrode body. In this way, it is possible to prevent the distance between the positive electrode plate and the negative electrode plate from being excessively increased due to the remaining bubbles formed as the organic solvent evaporates. Therefore, it is possible to prevent performance deterioration of the nonaqueous secondary battery.

[0011] The organic solvent may also be N-methylpyrrolidone. The electrode plate for a non-aqueous secondary battery that solves the above problems includes an electrode base material and a composite layer provided on the electrode base material, and the composite layer is formed by applying a composite paste containing at least an active material and an organic solvent to the electrode base material and drying the composite paste in a state in which the organic solvent remains.

[0012] The mixture layer may be formed such that a larger amount of the organic solvent remains in edge regions in the width direction than in a central region in the width direction. A method for manufacturing a non-aqueous secondary battery that solves the above-mentioned problems is a method for manufacturing a non-aqueous secondary battery including an electrode assembly having a negative electrode plate, a positive electrode plate, and a separator provided between the negative electrode plate and the positive electrode plate, a non-aqueous electrolyte, and a battery case that accommodates the electrode assembly and the non-aqueous electrolyte, the method including: applying a positive electrode composite paste containing at least a positive electrode active material and an organic solvent to a positive electrode base material; drying the positive electrode composite paste to form a positive electrode composite layer such that the organic solvent remains; and charging with the electrode assembly and the non-aqueous electrolyte accommodated in the battery case. Effect of the Invention

[0013] According to the present invention, it is possible to suppress performance degradation. [Brief description of the drawings]

[0014] [Figure 1] 1 is a perspective view of a lithium-ion secondary battery according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of a laminate of an electrode body of a lithium ion secondary battery. [Diagram 3] 1 is a flowchart showing a manufacturing process of a lithium ion secondary battery. [Figure 4] 4 is a schematic diagram showing a positive electrode plate viewed from the longitudinal direction Z in a drying process. FIG. [Diagram 5] 4 is a schematic diagram showing a positive electrode plate viewed from the longitudinal direction Z in a slitting process. FIG. [Figure 6] FIG. 2 is a schematic diagram showing the relationship between the internal pressure of a battery case, the number of charge / discharge cycles, and the rate of increase in direct current internal resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] [First embodiment] An embodiment of the secondary battery will be described below. <Lithium-ion secondary battery 10> The configuration of the lithium ion secondary battery of this embodiment will be described.

[0016] As shown in FIG. 1, the lithium ion secondary battery 10 is configured as a cell battery. The lithium ion secondary battery 10 includes a battery case 11. The battery case 11 includes a lid body 12. The battery case 11 includes an opening (not shown) on the upper side. The lid body 12 seals the opening. The battery case 11 is made of a metal such as an aluminum alloy. The lid body 12 includes a negative electrode external terminal 13 and a positive electrode external terminal 14 used for charging and discharging power. The negative electrode external terminal 13 and the positive electrode external terminal 14 may have any shape.

[0017] The lithium ion secondary battery 10 includes an electrode assembly 15. The lithium ion secondary battery 10 includes a negative electrode current collector 16 and a positive electrode current collector 17. The negative electrode current collector 16 connects the negative electrode of the electrode assembly 15 to a negative electrode external terminal 13. The positive electrode current collector 17 connects the positive electrode of the electrode assembly 15 to a positive electrode external terminal 14. The electrode assembly 15 is accommodated inside a battery case 11.

[0018] The lithium ion secondary battery 10 includes a nonaqueous electrolyte 18. The nonaqueous electrolyte 18 is injected into the battery case 11 through an injection hole (not shown). The lithium ion secondary battery 10 is configured as a sealed battery container by attaching a lid 12 to an opening in the battery case 11. In this manner, the battery case 11 contains the electrode assembly 15 and the nonaqueous electrolyte 18.

[0019] <Nonaqueous electrolyte 18> The non-aqueous electrolyte 18 is a composition in which a supporting salt is contained in a non-aqueous solvent. In this embodiment, ethylene carbonate (EC) can be used as the non-aqueous solvent. The non-aqueous solvent may be one or more materials selected from the group consisting of propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like.

[0020] In addition, as the supporting salt, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc. can be used. In addition, one or more lithium compounds (lithium salts) selected from these can be used. Thus, the nonaqueous electrolyte 18 contains a lithium compound.

[0021] <Electrode body 15> As shown in FIG. 2, the electrode body 15 includes a negative electrode plate 20, a positive electrode plate 30, and a separator 40. The longitudinal direction of the electrode body 15 is referred to as the "length direction Z". The thickness direction of the electrode body 15 is referred to as the "thickness direction D". The direction intersecting the length direction Z and the thickness direction D of the electrode body 15 is referred to as the "width direction W". One direction of the width directions W is referred to as the "first width direction W1", and the other direction of the width directions W is referred to as the "second width direction W2". In other words, the second width direction W2 is the opposite direction to the first width direction W1.

[0022] The electrode body 15 is formed by stacking a negative electrode plate 20, a positive electrode plate 30, and a separator 40 in the thickness direction D. In the electrode body 15, the separator 40 is stacked between the negative electrode plate 20 and the positive electrode plate 30. In detail, the electrode body 15 is stacked in the following order: the separator 40, the positive electrode plate 30, the separator 40, and the negative electrode plate 20.

[0023] The electrode assembly 15 is formed by stacking the negative electrode plate 20, the positive electrode plate 30, and the separator 40 in the thickness direction D and winding them in the length direction Z. The electrode assembly 15 has a flat shape in the thickness direction D at the center in the length direction Z.

[0024] In this way, the thickness direction D in which the negative electrode plate 20, the positive electrode plate 30, and the separator 40 are stacked can also be referred to as the stacking direction. Also, the length direction Z in which the negative electrode plate 20, the positive electrode plate 30, and the separator 40 are wound can also be referred to as the winding direction.

[0025] <Negative electrode plate 20> The negative electrode plate 20 functions as an example of a negative electrode of the lithium ion secondary battery 10. The negative electrode plate 20 includes a negative electrode substrate 21 and a negative electrode mixture layer 22. The negative electrode mixture layer 22 is provided on both sides of the negative electrode substrate 21.

[0026] The negative electrode substrate 21 includes a negative electrode connection portion 23. The negative electrode connection portion 23 is a region where the negative electrode composite layer 22 is not provided on either side of the negative electrode substrate 21. The negative electrode connection portion 23 is provided at an end portion in the first width direction W1 of the electrode body 15. The negative electrode connection portion 23 is exposed from the separator 40 in the first width direction W1.

[0027] In this embodiment, the negative electrode substrate 21 is made of Cu foil. The negative electrode substrate 21 serves as a base for the aggregate of the negative electrode mixture layer 22. The negative electrode substrate 21 functions as a current collecting member that collects electricity from the negative electrode mixture layer 22.

[0028] Negative electrode mixture layer 22 contains a negative electrode active material. In this embodiment, the negative electrode active material is a material capable of absorbing and releasing lithium ions, and a powdered carbon material made of graphite or the like is used.

[0029] The negative electrode plate 20 is produced, for example, by kneading a negative electrode active material, a solvent, and a binder, and drying the kneaded negative electrode composite paste in a state in which it is applied to the negative electrode substrate 21. In other words, the negative electrode composite layer 22 is formed by drying the negative electrode composite paste in a state in which the negative electrode composite paste containing at least the negative electrode active material and the solvent is applied to the negative electrode substrate 21. The solvent for the negative electrode composite layer 22 is, for example, water, but is not limited thereto, and an organic solvent (non-aqueous solvent) may also be used.

[0030] <Positive electrode plate 30> The positive electrode plate 30 functions as an example of a positive electrode of the lithium ion secondary battery 10. The positive electrode plate 30 includes a positive electrode substrate 31 and a positive electrode mixture layer 32. The positive electrode mixture layer 32 is provided on both sides of the positive electrode substrate 31.

[0031] The positive electrode substrate 31 includes a positive electrode connection portion 33. The positive electrode connection portion 33 is a region where the positive electrode composite layer 32 is not provided on either side of the positive electrode substrate 31. The positive electrode connection portion 33 is provided at an end portion in the second width direction W2 of the electrode body 15. The positive electrode connection portion 33 is exposed from the separator 40 in the second width direction W2.

[0032] In this embodiment, the positive electrode substrate 31 is made of an Al foil or an Al alloy foil. The positive electrode substrate 31 serves as a base for the aggregate of the positive electrode mixture layer 32. The positive electrode substrate 31 functions as a current collecting member that collects electricity from the positive electrode mixture layer 32.

[0033] The positive electrode mixture layer 32 has a positive electrode active material. The positive electrode active material is a material capable of absorbing and releasing lithium, and for example, lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), etc. may be used. A material in which LiCoO2, LiMn2O4, and LiNiO2 are mixed in any ratio may also be used. The positive electrode mixture layer 32 contains a conductive material. As the conductive material, for example, carbon black such as acetylene black (AB) and ketjen black, and graphite may be used.

[0034] The positive electrode plate 30 is produced, for example, by kneading a positive electrode active material, a conductive material, a solvent, and a binding agent (binder), applying the kneaded positive electrode composite paste to the positive electrode substrate 31, and drying the paste. In other words, the positive electrode composite layer 32 is formed by drying a positive electrode composite paste containing at least a positive electrode active material and a non-aqueous solvent, which is applied to the positive electrode substrate 31. As the solvent for the positive electrode composite layer 32, for example, N-methylpyrrolidone (NMP), such as N-methyl-2-pyrrolidone, is used, but another organic solvent (non-aqueous solvent) may also be used.

[0035] <Separator 40> The separator 40 is provided between the negative electrode plate 20 and the positive electrode plate 30. The separator 40 holds the non-aqueous electrolyte 18. The separator 40 is a non-woven fabric made of polypropylene or the like, which is a porous resin. As the separator 40, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, and a porous polyvinyl chloride membrane, or a lithium ion or ion conductive polymer electrolyte membrane can be used alone or in combination. When the electrode body 15 is immersed in the non-aqueous electrolyte 18, the non-aqueous electrolyte 18 permeates the separator 40 from the end toward the center.

[0036] <Manufacturing process of lithium ion secondary battery 10> Here, a manufacturing process of the lithium ion secondary battery 10 of this embodiment will be described with reference to Fig. 3. The manufacturing process of the lithium ion secondary battery 10 of this embodiment includes steps S10 to S18. That is, the manufacturing method of the lithium ion secondary battery 10 of this embodiment includes steps S10 to S18.

[0037] 3, in this embodiment, a source process is performed in step S10. The source process is a process for producing a battery element of the lithium-ion secondary battery 10. Specifically, the source process is a process for producing the negative electrode plate 20 and the positive electrode plate 30 that constitute the battery element of the lithium-ion secondary battery 10.

[0038] Specifically, the source process includes a kneading process, a coating process, a drying process, a pressing process, and a slitting process. In the source process, the kneading process is first performed in step S11. The kneading process includes a process of kneading a positive electrode composite paste and a process of kneading a negative electrode composite paste.

[0039] After the kneading process is completed, a coating process is performed in step S12. In the coating process, the negative electrode composite paste is applied to both sides of the negative electrode substrate 21 so as to form the negative electrode connecting portions 23 at both ends in the width direction W. In the coating process, the positive electrode composite paste is applied to both sides of the positive electrode substrate 31 so as to form the positive electrode connecting portions 33 at both ends in the width direction W.

[0040] After the coating process is completed, a drying process is performed in step S13. In the drying process, the negative electrode composite paste coated on the negative electrode substrate 21 is dried to form a negative electrode composite layer 22. In the drying process, the positive electrode composite paste coated on the positive electrode substrate 31 is dried to form a positive electrode composite layer 32.

[0041] After the drying process is completed, a pressing process is performed in step S14. In the pressing process, the negative electrode mixture layer 22 formed on both sides of the negative electrode substrate 21 is pressed to adjust the thickness of the negative electrode mixture layer 22. In the pressing process, the positive electrode mixture layer 32 formed on both sides of the positive electrode substrate 31 is pressed to adjust the thickness of the positive electrode mixture layer 32.

[0042] After the pressing process is completed, a slitting process is performed in step S15. In the slitting process, the negative electrode plate 20 is cut at the center in the width direction W. Through the above process, two strips of negative electrode plates 20 are manufactured at once. In the slitting process, the positive electrode plate 30 is cut at the center in the width direction W. Through the above process, two strips of positive electrode plates 30 are manufactured at once.

[0043] After the assembly process is completed, an assembly process is performed in step S16. The assembly process is a process for assembling the lithium-ion secondary battery 10. In the assembly process, the electrode body 15 is first manufactured. Specifically, the positive electrode plate 30 and the negative electrode plate 20 are first stacked with the separator 40 interposed therebetween, then wound and pressed flat. Thereafter, the negative electrode connection portion 23 is pressure-welded, and the positive electrode connection portion 33 is pressure-welded. Through the above procedure, the electrode body 15 is manufactured.

[0044] Next, the electrode body 15 is housed in the battery case 11. At this time, the positive electrode connection part 33 is electrically connected to the positive electrode external terminal 14 via the positive electrode current collector 17. The negative electrode connection part 23 is electrically connected to the negative electrode external terminal 13 via the negative electrode current collector 16. The opening of the battery case 11 is closed by the lid body 12. Then, the nonaqueous electrolyte 18 is injected into the battery case 11. After the injection of the nonaqueous electrolyte 18 into the battery case 11 is completed, the battery case 11 is sealed. Through the above procedures, the lithium ion secondary battery 10 is assembled.

[0045] When the assembly process is completed, a charging process is performed in step S17. The charging process is a process of charging the lithium ion secondary battery 10 assembled in the assembly process. The charging performed in the charging process is, for example, an initial charge of the lithium ion secondary battery 10 assembled in the assembly process.

[0046] After the charging process is completed, an aging process is performed in step S18. In the aging process, the lithium ion secondary battery 10 that has been through the charging process and the determination process is left at high temperature for a certain period of time. The aging process dissolves metallic foreign matter in the lithium ion secondary battery 10 and stabilizes the SEI coating.

[0047] <Drying process of lithium ion secondary battery 10> Here, the drying process of the lithium ion secondary battery 10 of this embodiment will be described with reference to Fig. 4 and Fig. 5. In order to facilitate understanding of the invention, Fig. 4 and Fig. 5 show a state in which the positive electrode composite paste 34 is applied to one surface of the positive electrode substrate 31.

[0048] 4, in the drying step, the positive electrode composite paste 34 applied to the positive electrode substrate 31 is dried by a drying device 50. The drying device 50 dries the positive electrode composite paste 34 applied to the positive electrode substrate 31.

[0049] The drying device 50 includes a main body 51 and a drying nozzle 52. The drying nozzle 52 is provided in the main body 51. The drying nozzle 52 is a nozzle for drying the positive electrode composite paste applied to the positive electrode substrate 31.

[0050] The drying nozzle 52 includes a first drying nozzle 53. The first drying nozzle 53 includes a first drying nozzle surface 54. The first drying nozzle surface 54 is provided so as to face the positive electrode composite paste 34 applied to the positive electrode substrate 31. The first drying nozzle surface 54 blows hot air toward the positive electrode plate 30 in order to dry the positive electrode composite paste 34 applied to the positive electrode substrate 31.

[0051] The first drying nozzle surface 54 has a first end 54A in the first width direction W1 and a second end 54B in the second width direction W2. The first drying nozzle surface 54 has a width of a distance D1 in the width direction W. In other words, the first drying nozzle surface 54 is configured such that the first end 54A and the second end 54B are separated by the distance D1 in the width direction W.

[0052] The first drying nozzle surface 54 is provided such that the first end 54A and the first position 34A face each other in the thickness direction D. The first position 34A is a position that is a distance D2 away in the second width direction W2 from an end 34B in the first width direction W1 of the positive electrode composite paste 34 as a reference. The distance D1 is about 13 times longer than the distance D2, but is not limited to this. As a specific example, the distance D1 may be 40 mm, and the distance D2 may be 3 mm.

[0053] The drying nozzle 52 includes a second drying nozzle 55. The second drying nozzle 55 includes a second drying nozzle surface 56. The second drying nozzle surface 56 is provided so as to face the positive electrode composite paste 34 applied to the positive electrode substrate 31. The second drying nozzle surface 56 blows hot air toward the positive electrode plate 30 in order to dry the positive electrode composite paste 34 applied to the positive electrode substrate 31.

[0054] The second drying nozzle surface 56 has a first end 56A in the second width direction W2 and a second end 56B in the first width direction W1. The second drying nozzle surface 56 has a width of a distance D1 in the width direction W. In other words, the second drying nozzle surface 56 is configured such that the first end 56A and the second end 56B are separated by the distance D1 in the width direction W.

[0055] The second drying nozzle surface 56 is provided such that the first end 56A and the second position 34C face each other in the thickness direction D. The second position 34C is a position spaced a distance D2 in the first width direction W1 from an end 34D of the positive electrode composite paste 34 in the second width direction W2.

[0056] The first drying nozzle 53 and the second drying nozzle 55 are arranged to be aligned in the width direction W of the positive electrode plate 30. The first drying nozzle 53 is arranged further in the first width direction W1 than the second drying nozzle 55. The first drying nozzle surface 54 and the second drying nozzle surface 56 are separated by a distance D3. In other words, the second end 54B of the first drying nozzle surface 54 and the second end 56B of the second drying nozzle surface 56 are separated by the distance D3.

[0057] The distance D3 corresponds to, for example, twice the distance D2. As a specific example, the distance D3 may be 6 mm. Therefore, the second end 54B of the first drying nozzle surface 54 faces a position that is separated by the distance D2 in the first width direction W1 from the center position 34E of the positive electrode composite paste 34 in the thickness direction D. The second end 56B of the second drying nozzle surface 56 faces a position that is separated by the distance D2 in the second width direction W2 from the center position 34E of the positive electrode composite paste 34 in the thickness direction D.

[0058] That is, the first drying nozzle surface 54 is provided such that the second end 54B and the third position 34F face each other in the thickness direction D. The third position 34F is a position separated from the center position 34E of the positive electrode composite paste 34 by a distance D2 in the first width direction W1.

[0059] The second drying nozzle surface 56 is provided such that the second end 56B and the fourth position 34G face each other in the thickness direction D. The fourth position 34G is a position separated from the center position 34E of the positive electrode composite paste 34 by a distance D2 in the second width direction W2.

[0060] In this manner, the positive electrode mixture paste 34 is dried by the air blown from the drying nozzle 52. In particular, the positive electrode mixture paste 34 is heated less in the second region R2, which does not face the drying nozzle 52, than in the first region R1, which faces the drying nozzle 52 in the thickness direction D. For this reason, the organic solvent contained in the positive electrode mixture paste 34 is heated less in the second region R2 than in the first region R1. Therefore, in the second region R2, the organic solvent contained in the positive electrode mixture paste 34 is not vaporized, and the amount of the organic solvent remaining as the positive electrode mixture layer 32 is greater than in the first region R1.

[0061] As a specific example, in the second region R2, the amount of organic solvent remaining in the positive electrode mixture layer 32 is 1000 to 1200 ppm. In the first region R1, the amount of organic solvent remaining in the positive electrode mixture layer 32 is 450 ppm or less. As a result, in the first region R1 and the second region R2, the amount of organic solvent remaining in the positive electrode mixture layer 32 is 550 ppm or less on average.

[0062] In this embodiment, the drying method for the negative electrode plate 20 is different from the drying method for the positive electrode plate 30. In detail, hot air is blown uniformly toward the entire area of ​​the negative electrode plate 20 in order to dry the negative electrode composite paste applied to the negative electrode substrate 21.

[0063] 5, the positive electrode mixture layer 32 is formed by drying the positive electrode mixture paste 34. In Fig. 5, the reference characters 34A to 34G in the positive electrode mixture paste 34 are shown as the reference characters 32A to 32G in the positive electrode mixture layer 32. The first region R1 and the second region R2 indicate the same regions in the positive electrode mixture paste 34 and the positive electrode mixture layer 32.

[0064] In the slitting process, the positive electrode plates 30 are cut at the center position 32E of the positive electrode mixture layer 32. Therefore, in each of the two positive electrode plates 30, the first region R1 is located in the center in the width direction W, and the second regions R2 are located at both ends in the width direction W.

[0065] Specifically, in each of the two positive electrode plates 30, the first region R1 is a central region in the width direction W of the positive electrode mixture layer 32. In addition, in each of the two positive electrode plates 30, the second region R2 is an end region in the width direction W of the positive electrode mixture layer 32. In particular, in each of the two positive electrode plates 30, the second region R2 is an end region that is a distance D1 away from both ends in the width direction W.

[0066] That is, in the positive electrode plate 30 cut in the slitting process, the amount of remaining organic solvent is greater in the end regions in the width direction W of the positive electrode mixture layer 32 than in the central region in the width direction W of the positive electrode mixture layer 32. In other words, in the positive electrode plate 30 cut in the slitting process, the amount of remaining organic solvent is less in the central region in the width direction W of the positive electrode mixture layer 32 than in the end regions in the width direction W of the positive electrode mixture layer 32.

[0067] The positive electrode plate 30 thus manufactured is used for the electrode body 15. The electrode body 15 is housed in the battery case 11. The battery case 11 is sealed in a state in which the non-aqueous electrolyte 18 is injected. The lithium-ion secondary battery 10 thus manufactured is charged in a charging process. In the charging process, the organic solvent remaining as the positive electrode mixture layer 32 is vaporized, for example, by chemical decomposition and heating. In this way, the organic solvent remaining as the positive electrode mixture layer 32 inside the battery case 11 is vaporized, and the pressure inside the battery case 11 increases.

[0068] In particular, the second region R2 is an end region of the positive electrode mixture layer 32. For this reason, bubbles formed when the organic solvent in the positive electrode mixture layer 32 evaporates tend to be discharged from the end of the electrode body 15 to the outside of the electrode body 15 without remaining inside the electrode body 15.

[0069] Furthermore, the distance D2 is preferably equal to or less than the radius of the bubbles formed when the organic solvent evaporates. As a specific example, when the radius of the bubbles is 6 mm, the distance D2 is preferably equal to or less than 3 mm. This allows the bubbles formed when the organic solvent evaporates in the positive electrode mixture layer 32 to be easily discharged from the end of the electrode body 15 to the outside of the electrode body 15 without remaining inside the electrode body 15.

[0070] <Example> An example of the lithium-ion secondary battery 10 of this embodiment will now be described with reference to Fig. 6. As this example, the relationship between the internal pressure of the battery case 11, the number of charge / discharge cycles, and the rate of increase in DC internal resistance will be described.

[0071] 6, in a graph 60, the increase rate of the DC internal resistance is plotted on the vertical axis, and the number of charge / discharge cycles is plotted on the horizontal axis. In the graph 60, a first curve 61 and a second curve 62 are shown. The second curve 62 is a curve when the pressure inside the battery case 11 is higher than that of the first curve 61.

[0072] In this way, when the pressure inside the battery case 11 is high, the rate of increase in the DC internal resistance tends to be less likely to increase as the number of charge / discharge cycles increases than when the pressure inside the battery case 11 is low. Furthermore, in the first curve 61 and the second curve 62, the rate of increase in the DC internal resistance is roughly proportional to the number of charge / discharge cycles as long as it is within an expected range of the number of charge / discharge cycles.

[0073] As a specific example, when the pressure inside the battery case 11 is doubled, the rate of increase in the DC internal resistance decreases by 15% when the number of cycles becomes 400. In other words, when the pressure inside the battery case 11 is doubled, the number of cycles at which the DC internal resistance increases by 5% increases from 200 to 400.

[0074] In addition, in this embodiment, the pressure inside the battery case 11 is 1.2 times higher than in the conventional technology. As a result, the rate of increase in DC internal resistance is reduced by 1.5% when the number of cycles reaches 400. In other words, in this embodiment, the pressure inside the battery case 11 is 1.2 times higher than in the conventional technology, and the number of cycles at which the DC internal resistance increases by 5% is also 1.2 times higher.

[0075] <Action of this embodiment> The operation of this embodiment will be described. 4, in the source process, the mixed positive electrode composite paste 34 is applied to both sides of the positive electrode substrate 31. Then, the positive electrode composite paste 34 is dried in the second region R2 so as to be heated less than in the first region R1. As a result, the positive electrode composite layer 32 is formed in the second region R2 such that the organic solvent remains without being vaporized, as compared to the first region R1.

[0076] The positive electrode plate 30 thus manufactured is accommodated in the battery case 11 together with the nonaqueous electrolyte solution 18 as the electrode body 15. As the lithium-ion secondary battery 10 is charged, the organic solvent remaining as the positive electrode mixture layer 32 evaporates, causing the pressure inside the battery case 11 to increase.

[0077] Conventionally, as the lithium ion secondary battery 10 is discharged, the concentration of the supporting salt in the nonaqueous electrolyte 18 becomes higher on the positive electrode plate 30 side than on the negative electrode plate 20 side. In other words, the concentration of the supporting salt becomes biased in the thickness direction D of the electrode body 15. This tendency becomes particularly noticeable when high-rate charging and discharging are performed.

[0078] When the lithium-ion secondary battery 10 is repeatedly charged and discharged, the electrode body 15 repeatedly expands and contracts, and the nonaqueous electrolyte 18, which has a low concentration of the supporting salt, is pushed out of the electrode body 15. This causes a bias in the concentration of the supporting salt between the center and both ends in the width direction W of the electrode body 15. This increases the DC internal resistance of the electrode body 15. This could result in performance degradation of the lithium-ion secondary battery 10, such as degradation of the high-rate characteristics.

[0079] In order to solve such technical problems, the positive electrode composite layer 32 is formed so that the organic solvent intentionally remains, and the organic solvent remaining as the positive electrode composite layer 32 during charging is evaporated, thereby increasing the pressure inside the battery case 11. This makes it possible to suppress the nonaqueous electrolyte 18, which has a low concentration of the supporting salt, from being pushed out of the electrode body 15. This makes it difficult for the concentration of the supporting salt to be biased between the center and both ends in the width direction W of the electrode body 15. Therefore, the DC internal resistance of the electrode body 15 is unlikely to increase, and deterioration of the performance of the lithium-ion secondary battery 10, such as deterioration of high-rate characteristics, can be suppressed.

[0080] In addition, the second region R2, which is an end region of the positive electrode mixture layer 32, has a larger amount of residual organic solvent than the first region R1, which is a central region of the positive electrode mixture layer 32. Therefore, the amount of organic solvent that evaporates with charging of the lithium ion secondary battery 10 is larger in the second region R2 than in the first region R1. Therefore, bubbles formed when the organic solvent evaporates with charging of the lithium ion secondary battery 10 do not remain inside the electrode body 15, but are easily discharged from the end of the electrode body 15 to the outside of the electrode body 15.

[0081] Further, the second region R2 is a region extending from both ends of the positive electrode mixture layer 32 to a distance D2. The distance D2 is equal to or less than the radius of the bubbles formed when the organic solvent evaporates. This allows the bubbles formed when the organic solvent evaporates in the positive electrode plate 30 to be easily discharged from the ends of the electrode body 15 to the outside of the electrode body 15 without remaining inside the electrode body 15.

[0082] <Effects of this embodiment> The effects of this embodiment will be described. (1) According to the lithium ion secondary battery 10 of the present embodiment, the positive electrode mixture paste 34 containing at least a positive electrode active material and an organic solvent is dried to form the positive electrode mixture layer 32 so that the organic solvent remains. Then, charging is performed in a state in which the electrode body 15 and the nonaqueous electrolyte 18 are accommodated in the battery case 11, so that the organic solvent remaining as the positive electrode mixture layer 32 is vaporized. In this way, by intentionally drying the positive electrode mixture paste 34 so that the organic solvent remains, the organic solvent remaining in the positive electrode mixture layer 32 can be vaporized inside the battery case 11 during charging. This can improve the pressure inside the battery case 11. Therefore, the nonaqueous electrolyte 18 inside the electrode body 15 is less likely to be pushed out to the outside of the electrode body 15. Therefore, it is possible to suppress deterioration of the high-rate characteristics of the lithium ion secondary battery 10 caused by an increase in the DC internal resistance of the electrode body 15.

[0083] (2) Charging is performed in a state in which the electrode assembly 15 and the nonaqueous electrolyte 18 are accommodated in the battery case 11. As a result, a larger amount of organic solvent is evaporated in the second region R2, which is an end portion in the width direction W of the positive electrode mixture layer 32, than in the first region R1, which is the center portion in the width direction W of the positive electrode mixture layer 32. Therefore, in the first region R1, bubbles are less likely to be formed due to the evaporation of the organic solvent than in the second region R2. As a result, bubbles are less likely to remain inside the electrode assembly 15. In this way, it is possible to suppress excessive widening of the distance between the positive electrode plate 30 and the negative electrode plate 20 due to the remaining bubbles formed with the evaporation of the organic solvent. Therefore, it is possible to suppress performance deterioration of the lithium ion secondary battery 10.

[0084] (3) The second region R2, where bubbles are likely to form as the organic solvent evaporates, is separated from each end of the positive electrode mixture layer 32 in the width direction W by a distance D2 that is equal to or less than the radius of the bubbles. This allows bubbles formed in the second region R2 as the organic solvent evaporates to be easily discharged to the outside of the electrode body 15 without remaining inside the electrode body 15. In this way, it is possible to prevent the distance between the positive electrode plate 30 and the negative electrode plate 20 from being excessively increased due to the remaining bubbles formed as the organic solvent evaporates. This makes it possible to prevent performance deterioration of the lithium-ion secondary battery 10.

[0085] (4) Moreover, the positive electrode mixture layer 32 is formed such that the average amount of the organic solvent remaining as the positive electrode mixture layer 32 in the first region R1 and the second region R2 is equal to or less than a predetermined value. This makes it possible to intentionally leave the organic solvent as the positive electrode mixture layer while suppressing the organic solvent from remaining in excess. This suppresses the organic solvent from remaining in excess, thereby suppressing the chemical reaction of the excess organic solvent with the positive electrode substrate 31. Therefore, it is possible to suppress the performance degradation of the lithium ion secondary battery 10.

[0086] [Example of change] This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other to the extent that there is no technical contradiction.

[0087] In this embodiment, for example, as long as the second region R2 and the first region R1 of the positive electrode composite paste 34 are appropriately allocated, the size of the drying nozzle 52 may be arbitrary. In this embodiment, the drying of the organic solvent is not limited to blowing hot air, and may be, for example, natural drying, drying by blowing low-humidity air, drying by placing in a vacuum, drying by irradiating with infrared or far-infrared rays, or a combination of these.

[0088] In this embodiment, for example, the negative electrode plate 20 may be manufactured in the same manner as the positive electrode plate 30. In particular, the negative electrode mixture layer 22 may be formed by drying a negative electrode mixture paste containing at least a negative electrode active material and an organic solvent so that the organic solvent remains. In this manner, the present invention may be adopted in an electrode plate for a non-aqueous secondary battery including an electrode base material and a mixture layer provided on the electrode base material. In this manner, in the electrode plate for a non-aqueous secondary battery, a mixture layer is formed by drying a mixture paste containing at least an active material and an organic solvent so that the organic solvent remains.

[0089] In the present embodiment, the present invention has been described taking the lithium ion secondary battery 10 as an example. However, the present invention can be applied to other secondary batteries. In the present embodiment, the lithium ion secondary battery 10 is a thin plate-shaped battery for vehicle use, but the present invention can also be applied to cylindrical batteries. In addition, the present invention can also be applied to batteries for ships, aircraft, and stationary use, in addition to vehicle use.

[0090] It goes without saying that those skilled in the art may add, delete, or modify the components of the present invention, and change the order of the components, without departing from the scope of the claims. [Explanation of symbols]

[0091] D: Thickness direction R1…first area R2…Second area W…Width direction Z: Length direction 10...Lithium-ion secondary battery 11…Battery case 12…Lid body 13...Negative external terminal 14…Positive external terminal 15...Electrode body 16...Negative electrode current collector 17...Positive electrode current collector 18...Nonaqueous electrolyte 20...Negative electrode plate 21...Negative electrode substrate 22...Negative electrode composite material layer 23…Negative electrode connection part 30…Positive electrode plate 31...Positive electrode substrate 32...Positive electrode mixture layer 33…Positive electrode connection 34…Positive electrode mixture paste 40…Separator

Claims

1. A method for manufacturing a non-aqueous secondary battery including an electrode assembly having a negative electrode plate, a positive electrode plate, and a separator provided between the negative electrode plate and the positive electrode plate, a non-aqueous electrolyte, and a battery case that accommodates the electrode assembly and the non-aqueous electrolyte, Coating a positive electrode composite paste containing at least a positive electrode active material and an organic solvent onto a positive electrode substrate; forming a positive electrode mixture layer by drying the positive electrode mixture paste so that the organic solvent remains; winding the electrode assembly in a length direction intersecting with the stacking direction with the positive electrode plate, the negative electrode plate, and the separator stacked in the stacking direction; and performing charging in a state in which the electrode assembly and the nonaqueous electrolyte are contained in the battery case, forming the positive electrode mixture layer includes forming the positive electrode mixture layer such that a larger amount of the organic solvent remains in an end region in a width direction intersecting the stacking direction and the length direction than in a central region in the width direction; the end region is a region separated from an end in the width direction of the positive electrode mixture layer by a distance equal to or less than a radius of a bubble formed by evaporation of the organic solvent when the nonaqueous secondary battery is charged. A method for manufacturing a non-aqueous secondary battery.

2. The nonaqueous secondary battery according to claim 1, The organic solvent is N-methylpyrrolidone. A method for manufacturing a non-aqueous secondary battery.

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