Nonaqueous secondary battery and method for manufacturing the same

Abstract

To provide a nonaqueous secondary battery and a method for manufacturing a nonaqueous secondary battery, capable of suppressing a local increase in resistance due to the expansion of a negative electrode active material during charging of a nonaqueous secondary battery, in a curved portion included in an electrode body.SOLUTION: A nonaqueous secondary battery includes an electrode body 20 in which a positive electrode plate 21, a negative electrode plate 24 and a separator 27 that holds a nonaqueous electrolyte are wound while being stacked such that the separator 27 is disposed between the positive electrode plate 21 and the negative electrode plate 24. The electrode body 20 includes a curved portion in which layers constituting the electrode body 20 are curved. The positive electrode plate 21 includes a positive electrode substrate 22 and a positive electrode mixture layer 23. The negative electrode plate 24 includes a foil-shaped negative electrode substrate 25 and a negative electrode mixture layer 26 including a negative electrode active material that absorbs a charge carrier during charging. A coefficient of static friction between the negative electrode mixture layer 26 and the separator 27 is 0.60 or greater, and a coefficient of static friction between the positive electrode mixture layer 23 and the separator 27 is 0.50 or less.SELECTED DRAWING: Figure 4

Description

[Technical field]

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

[0002] Electric vehicles and hybrid vehicles are equipped with nonaqueous secondary batteries as their power source. A lithium ion secondary battery, which is one example of a nonaqueous secondary battery, is equipped with an electrode body in which a positive electrode plate, a negative electrode plate, and a separator are laminated. One example of the electrode body is equipped with a flat portion where each layer constituting the electrode body is pressed, and curved portions located at both ends of the flat portion where each layer constituting the electrode body is curved (for example, Patent Document 1). The electrode body is housed in a case with, for example, the flat portion facing the side wall of the rectangular cylindrical case and the curved portions located above and below the flat portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-161293 A Summary of the Invention [Problem to be solved by the invention]

[0004] When a lithium-ion secondary battery is charged, the negative electrode active material contained in the negative electrode plate expands as it absorbs lithium ions, which act as charge carriers, and the thickness of the negative electrode plate increases. Even if the thickness of the negative electrode plate increases due to the expansion of the negative electrode active material during charging, the flat parts are restrained by the side walls of the case, so that the negative electrode plate and the separator are kept in close contact with each other.

[0005] On the other hand, in the curved portion, when the negative electrode active material expands during charging, the thickness of the negative electrode plate increases toward the outer periphery of the curved portion. At this time, if the static friction coefficient between the negative electrode plate and the separator is small, the negative electrode plate slides against the separator and deforms in a wavy manner, which tends to cause a gap between the negative electrode plate and the separator. The portion where a gap occurs between the negative electrode plate and the separator is in a state where the interelectrode distance, which is the distance between the positive electrode plate and the negative electrode plate, has increased. That is, a portion with high resistance is locally generated in the electrode body, which leads to a decrease in the lithium deposition resistance of the electrode body. Note that even in non-aqueous secondary batteries other than lithium ion secondary batteries, in a configuration in which the negative electrode active material expands during charging, the metal ions that serve as charge carriers are likely to deposit as metals by a similar mechanism. [Means for solving the problem]

[0006] A nonaqueous secondary battery for solving the above problems comprises an electrode body in which a positive electrode plate, a negative electrode plate, and a separator holding a nonaqueous electrolyte are wound in a stacked state such that the separator is disposed between the positive electrode plate and the negative electrode plate, the electrode body has a curved portion in which each layer constituting the electrode body is curved, the positive electrode plate comprises a foil-shaped positive electrode base material and a positive electrode mixture layer provided on two of the surfaces of the positive electrode base material that face in opposite directions, the negative electrode plate comprises a foil-shaped negative electrode base material and a negative electrode mixture layer provided on two of the surfaces of the negative electrode base material that face in opposite directions, the negative electrode mixture layer contains a negative electrode active material that occludes charge carriers during charging, and the static friction coefficient between the negative electrode mixture layer and the separator is 0.60 or more, and the static friction coefficient between the positive electrode mixture layer and the separator is 0.50 or less.

[0007] When the coefficient of static friction between the negative electrode mixture layer and the separator is 0.60 or more, when the thickness of the negative electrode plate increases toward the outer periphery of the curved portion during charging, the separator expands in response to the increase in the thickness of the negative electrode plate while maintaining a state of close contact with the negative electrode mixture layer. This makes it possible to suppress undulation of the negative electrode plate that occurs when the coefficient of static friction between the negative electrode plate and the separator is small at the curved portion, and also to suppress the formation of a gap between the negative electrode plate and the separator.

[0008] In addition, if the static friction coefficient between the positive electrode plate and the separator is large, the frictional force between the positive electrode plate and the separator acts as a resistance force against the deformation of the separator, so that the separator is less likely to expand in response to the increase in the thickness of the negative electrode plate. In this case, the negative electrode plate is more likely to deform so as to slide against the separator, and as a result, a gap is more likely to be formed between the negative electrode plate and the separator. In this respect, if the static friction coefficient between the positive electrode mixture layer and the separator is 0.50 or less, when the separator expands in response to the increase in the thickness of the negative electrode plate, the frictional force between the positive electrode mixture layer and the separator is less likely to inhibit the deformation of the separator. As a result, the formation of a gap between the negative electrode plate and the separator can be suitably suppressed.

[0009] In the nonaqueous secondary battery, the static friction coefficient between the positive electrode mixture layer and the separator is preferably 0.30 or more. If the static friction coefficient between the positive electrode mixture layer and the separator is excessively small, one of the positive electrode plate and the separator may be wound in a meandering state relative to the other during the manufacture of the electrode body. In this regard, by setting the static friction coefficient between the positive electrode mixture layer and the separator to 0.30 or more, the positive electrode plate can be prevented from being wound in a meandering state relative to the separator.

[0010] In the nonaqueous secondary battery, it is preferable that the surface roughness of the positive electrode mixture layer in contact with the separator is 0.5 μm to 0.7 μm, and the surface roughness of the separator in contact with the positive electrode mixture layer is 0.5 μm to 0.7 μm. By setting the surface roughness of the positive electrode mixture layer and the surface roughness of the separator within the above ranges, the static friction coefficient between the positive electrode mixture layer and the separator can be controlled to a range of 0.30 to 0.50.

[0011] In the nonaqueous secondary battery, it is preferable that the surface roughness of the negative electrode mixture layer in contact with the separator is 0.6 μm to 0.8 μm, and the surface roughness of the separator in contact with the negative electrode mixture layer is 0.5 μm to 0.7 μm. By setting the surface roughness of the negative electrode mixture layer and the surface roughness of the separator within the above ranges, the static friction coefficient between the negative electrode mixture layer and the separator can be controlled to 0.60 or more.

[0012] A method for manufacturing a non-aqueous secondary battery to solve the above problems includes an electrode body manufacturing step of manufacturing an electrode body in which a curved portion is formed in each of the stacked layers by winding a positive electrode plate including a positive electrode mixture layer provided on two surfaces of a positive electrode substrate that face in opposite directions, a negative electrode mixture layer provided on two surfaces of a negative electrode substrate that face in opposite directions, the negative electrode mixture layer including a negative electrode active material that occludes charge carriers during charging, and a separator that holds a non-aqueous electrolyte, in a stacked state such that the separator is disposed between the positive electrode plate and the negative electrode plate, and a liquid injection step of injecting a non-aqueous electrolyte into a case that contains the electrode body, and the electrode body manufactured in the electrode body manufacturing step has a static friction coefficient between the negative electrode mixture layer and the separator of 0.60 or more, and a static friction coefficient between the positive electrode mixture layer and the separator of 0.50 or less. Effect of the Invention

[0013] According to the present invention, it is possible to suppress a local increase in resistance in a curved portion of an electrode body that is caused by expansion of a negative electrode active material due to charging of a nonaqueous secondary battery. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of a lithium ion secondary battery. [Diagram 2] FIG. 2 is a perspective view showing the electrode body in an expanded state. [Diagram 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a cross-sectional view that illustrates a layer structure of a curved portion of an electrode body. [Diagram 5] FIG. 5 is a flowchart showing the manufacturing process of a lithium ion secondary battery. [Figure 6] FIG. 6 is a cross-sectional view that illustrates a layer structure of the curved portion during charging. [Figure 7] FIG. 7 is an enlarged cross-sectional view showing the layer structure of the curved portion during charging. [Figure 8] FIG. 8 is a table showing the first static friction coefficient, the second static friction coefficient, and the deposition limit current ratio in the examples and the comparative examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, one embodiment of the present invention will be described with reference to FIGS. [Lithium-ion secondary battery] As shown in FIG. 1, a lithium ion secondary battery 10, which is an example of a non-aqueous secondary battery, includes a case 11 and an electrode assembly 20. The case 11 has a flat, bottomed, rectangular outer shape with an opening on the upper side. The case 11 contains the electrode assembly 20 and a non-aqueous electrolyte. The case 11 includes a pair of side walls 11A disposed opposite each other. The lid 12 closes the opening of the case 11. By attaching the lid 12, the case 11 forms a sealed rectangular parallelepiped battery container.

[0016] The lid 12 is provided with a positive external terminal 13A and a negative external terminal 13B. The positive electrode side current collector 20A, which is the end of the electrode body 20 on the positive electrode side, is electrically connected to the positive electrode external terminal 13A via a positive electrode side current collector 14A. The negative electrode side current collector 20B, which is the end of the electrode body 20 on the negative electrode side, is electrically connected to the negative electrode external terminal 13B via a negative electrode side current collector 14B. The lid 12 is provided with an injection port 15 for injecting a nonaqueous electrolyte. The shapes of the external terminals 13A and 13B are not limited to those shown in FIG. 1 and may be any shape.

[0017] The lithium ion secondary battery 10 is used, for example, in the state of an assembled battery configured by arranging a plurality of lithium ion secondary batteries 10. In the state of the assembled battery, for example, the lithium ion secondary batteries 10 are arranged in a predetermined arrangement direction so that the side walls 11A of adjacent lithium ion secondary batteries 10 face each other, and a restraining load is applied to sandwich the plurality of lithium ion secondary batteries 10 in the arrangement direction. This allows the plurality of lithium ion secondary batteries 10 to be held integrally.

[0018] [Electrode body] 2, the electrode body 20 is a flat wound body formed by winding a laminate in which a positive electrode plate 21 and a negative electrode plate 24 are stacked with a separator 27 interposed therebetween. The positive electrode plate 21, the negative electrode plate 24, and the separator 27 are stacked such that their respective longitudinal directions coincide with the longitudinal direction D1. The electrode body 20 has a structure in which the positive electrode plate 21 and the negative electrode plate 24, which are stacked with the separator 27 sandwiched therebetween, are wound around a winding axis L1 that extends along the width direction D2 of the band shape.

[0019] The electrode body 20 comprises a flat portion 31, an upper curved portion 32, and a lower curved portion 33. The flat portion 31 comprises a pair of flat surfaces 31S facing in opposite directions. The upper curved portion 32 is located at the upper portion of the flat portion 31. The upper curved portion 32 has a shape that bulges upward from the upper end of the flat portion 31. The lower curved portion 33 is located at the lower portion of the flat portion 31. The lower curved portion 33 has a shape that bulges downward from the lower end of the flat portion 31. The upper curved portion 32 and the lower curved portion 33 are each an example of a curved portion that the electrode body 20 comprises.

[0020] The electrode body 20 is housed in the case 11 with the winding axis L1 extending parallel to the bottom surface of the case 11 so that the upper curved portion 32 is located on the lid body 12 side and the lower curved portion 33 is located on the bottom surface side of the case 11. Furthermore, when the electrode body 20 is housed in the case 11, each of the flat surfaces 31S of the flat portion 31 faces the side wall 11A of the case 11.

[0021] 3, the electrode body 20 is stacked in a stacking direction D3 such that the separator 27 is disposed between the positive electrode plate 21 and the negative electrode plate 24. The stacking direction D3 is a direction perpendicular to a plane including the longitudinal direction D1 and the width direction D2.

[0022] [Positive plate] The positive electrode plate 21 includes a positive electrode substrate 22 and a positive electrode mixture layer 23. The positive electrode substrate 22 is a foil-shaped metal made of aluminum or an aluminum alloy. The positive electrode mixture layer 23 is provided on each of two surfaces of the positive electrode substrate 22 that face in opposite directions. The positive electrode substrate 22 includes a positive electrode-side uncoated portion 22A at one end in the width direction D2 where the positive electrode mixture layer 23 is not formed and the positive electrode substrate 22 is exposed. In the positive electrode substrate 22, the positive electrode-side uncoated portion 22A includes opposing portions that are pressed against each other in a wound body state to form a positive electrode-side current collecting portion 20A.

[0023] The positive electrode mixture layer 23 includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode mixture paste, which is a precursor of the positive electrode mixture layer 23, further includes a positive electrode solvent. An example of the positive electrode solvent is an NMP (N-methyl-2-pyrrolidone) solution, which is an example of an organic solvent.

[0024] The positive electrode active material is a lithium-containing composite metal oxide capable of absorbing and releasing lithium ions, which are charge carriers in the lithium-ion secondary battery 10. The positive electrode active material releases lithium ions during charging and absorbs lithium ions during discharging. The lithium-containing composite oxide is an oxide containing lithium and a metal element other than lithium. The metal element other than lithium is at least one selected from the group consisting of nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained in the lithium-containing composite oxide as iron phosphate.

[0025] For example, the lithium-containing complex oxide is lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or lithium manganese oxide (LiMn2O4). For example, the lithium-containing complex oxide is a ternary lithium-containing complex oxide (NCM) containing nickel, cobalt, and manganese, and is lithium nickel cobalt manganese oxide (LiNiCoMnO2). For example, the lithium-containing complex oxide is lithium iron phosphate (LiFePO4). The particle size (median diameter D50) of the positive electrode active material is, for example, 2 μm or more and 6 μm or less.

[0026] The positive electrode conductive agent may be, for example, carbon black such as acetylene black (AB) or Ketjen black, carbon fiber such as carbon nanotube (CNT) or carbon nanofiber, or graphite. The positive electrode binder may be, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and styrene butadiene rubber (SBR).

[0027] The positive electrode plate 21 may have an insulating layer at the boundary between the positive electrode uncoated portion 22A and the positive electrode mixture layer 23. The insulating layer contains an inorganic component having insulating properties and a resin component functioning as a binder. The inorganic component is at least one selected from the group consisting of powdered boehmite, titania, and alumina. The resin component is at least one selected from the group consisting of PVDF, PVA, and acrylic.

[0028] [Negative plate] The negative electrode plate 24 includes a negative electrode substrate 25 and a negative electrode mixture layer 26. The negative electrode substrate 25 is a foil-shaped metal made of copper or a copper alloy. The negative electrode mixture layer 26 is provided on each of two surfaces of the negative electrode substrate 25 that face in opposite directions. The negative electrode substrate 25 includes a negative electrode side uncoated portion 25A in which the negative electrode mixture layer 26 is not formed and the negative electrode substrate 25 is exposed at an end portion located opposite the positive electrode side uncoated portion 22A in the width direction D2. In the negative electrode side uncoated portion 25A in the wound body state, opposing portions are pressed against each other to form the negative electrode side current collecting portion 20B.

[0029] The negative electrode mixture layer 26 includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder. The negative electrode mixture paste, which is a precursor of the negative electrode mixture layer 26, further includes a negative electrode solvent. An example of the negative electrode solvent is water. The negative electrode active material is a material capable of absorbing and releasing lithium ions. The negative electrode active material absorbs lithium ions during charging and releases lithium ions during discharging. For example, carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, and carbon nanotubes are used as the negative electrode active material. The negative electrode active material may be composite particles in which graphite particles are coated with an amorphous carbon layer. The particle size (median diameter D50) of the negative electrode active material is, for example, 5 μm or more and 10 μm or less.

[0030] The negative electrode conductive agent may be, for example, the same as the positive electrode conductive agent. The negative electrode thickener may be, for example, carboxymethyl cellulose (CMC). CMC also functions as a dispersant for dispersing the negative electrode active material in the negative electrode mixture paste. The negative electrode binder is at least one selected from the group consisting of PVDF, PVA, and SBR.

[0031] [Separator] The separator 27 prevents contact between the positive electrode plate 21 and the negative electrode plate 24, and also retains a nonaqueous electrolyte between the positive electrode plate 21 and the negative electrode plate 24. When the electrode body 20 is immersed in the nonaqueous electrolyte, the nonaqueous electrolyte permeates the separator 27 from the ends toward the center.

[0032] The separator 27 is a porous nonwoven fabric made of polypropylene, etc. As the separator 27, for example, a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, a porous polyvinyl chloride membrane, an ion-conductive polymer electrolyte membrane, etc. can be used.

[0033] The porosity ε of the separator 27 is, for example, 50% or more and 60% or less. Note that, when the masses of the constituent materials contained in the separator 27 per unit volume W0 are Wa, Wb, ... Wn, and the true densities of the constituent materials are ρa, ρb, ... ρn, the porosity ε is expressed as ε = {1 - (Wa / ρa + Wb / ρb ... + Wn / ρn) / W0} × 100.

[0034] [Nonaqueous electrolyte] The non-aqueous electrolyte is a composition in which a supporting salt is contained in a non-aqueous solvent. The non-aqueous solvent is, for example, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate. The supporting salt is, for example, one or more lithium compounds selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc.

[0035] A film-forming agent is added to the non-aqueous electrolyte. The film-forming agent is, for example, lithium bis(oxalato)borate (LiBOB). For example, LiBOB is added to the non-aqueous electrolyte so that the concentration of LiBOB in the non-aqueous electrolyte is 0.001 to 0.1 mol / L.

[0036] [Friction coefficient between layers constituting the electrode body] As shown in FIG. 4, the positive electrode plate 21 has a positive electrode contact surface 21S that contacts the separator 27. The positive electrode contact surface 21S is a surface of the positive electrode mixture layer 23. The positive electrode plate 21 has two positive electrode contact surfaces 21S that face in opposite directions. The negative electrode plate 24 has a negative electrode contact surface 24S that contacts the separator 27. The negative electrode contact surface 24S is a surface of the negative electrode mixture layer 26. The negative electrode plate 24 has two negative electrode contact surfaces 24S that face in opposite directions. The separator 27 has a first contact surface 27S1 and a second contact surface 27S2. The first contact surface 27S1 is a surface of the separator 27 that contacts the positive electrode contact surface 21S. The second contact surface 27S2 is a surface of the separator 27 that contacts the negative electrode contact surface 24S.

[0037] The first static friction coefficient μ1 between the positive electrode mixture layer 23 and the separator 27 is configured to be 0.50 or less. The first static friction coefficient μ1 is preferably 0.30 or more. The first static friction coefficient μ1 is the static friction coefficient between the positive electrode contact surface 21S of the positive electrode mixture layer 23 included in the positive electrode plate 21 and the first contact surface 27S1 of the separator 27 in a dry state that does not hold a nonaqueous electrolyte.

[0038] The second static friction coefficient μ2 between the negative electrode mixture layer 26 and the separator 27 is configured to be 0.60 or more. The second static friction coefficient μ2 is the static friction coefficient between the negative electrode contact surface 24S of the negative electrode mixture layer 26 included in the negative electrode plate 24 and the second contact surface 27S2 of the separator 27 in a dry state. The upper limit of the second static friction coefficient μ2 is not particularly limited as long as it is 1.00 or less.

[0039] The first static friction coefficient μ1 is measured by a method conforming to JIS K7125:1999 using the positive electrode plate 21 and the separator 27 in a dry state. For example, the positive electrode plate 21, which is installed so that the positive electrode mixture layer 23 contacts the separator 27 in a dry state, is slid over the separator 27 at a speed of 100 mm / min, and the static friction coefficient can be measured. The second static friction coefficient μ2 is measured by a method similar to that of the first static friction coefficient μ1, using the negative electrode plate 24 and the separator 27 in a dry state.

[0040] For example, during the manufacturing process of the lithium ion secondary battery 10, the first static friction coefficient μ1 and the second static friction coefficient μ2 may be measured using the positive electrode plate 21 and the separator 27, and the negative electrode plate 24 and the separator 27 before being wound into the electrode assembly 20.

[0041] For example, when disassembling and examining the lithium ion secondary battery 10, first, the electrode body 20 is removed from the case 11 so as not to cause unnecessary scratches. Then, the positive electrode plate 21, the negative electrode plate 24, and the two separators 27 are each separated from the electrode body 20. Next, the nonaqueous electrolyte is thoroughly washed from each of the positive electrode plate 21, the negative electrode plate 24, and the separators 27 with an organic solvent, and then the first static friction coefficient μ1 and the second static friction coefficient μ2 are measured in a dried state.

[0042] [Method of manufacturing lithium-ion secondary batteries] As shown in Fig. 5, the method for manufacturing the lithium-ion secondary battery 10 includes steps S1 to S4. Step S1 is a source process including a step of manufacturing a positive electrode plate 21 and a step of manufacturing a negative electrode plate 24. The step of manufacturing the positive electrode plate 21 includes a step of applying a positive electrode mixture paste to a positive electrode substrate 22, a step of drying the positive electrode mixture paste to form a positive electrode mixture layer 23, and a step of pressing the positive electrode mixture layer 23 to adjust the thickness. The step of manufacturing the negative electrode plate 24 includes a step of applying a negative electrode mixture paste to a negative electrode substrate 25, a step of drying the negative electrode mixture paste to form a negative electrode mixture layer 26, and a step of pressing the negative electrode mixture layer 26 to adjust the thickness.

[0043] Step S2 is an electrode assembly manufacturing process in which the electrode assembly 20 is manufactured using the positive electrode plate 21, the negative electrode plate 24, and the separator 27. In step S2, the positive electrode plate 21 and the negative electrode plate 24 are first stacked with the separator 27 interposed therebetween and wound, and then pressed flat. Next, the positive electrode side uncoated portion 22A is pressed to form the positive electrode side current collector 20A. Similarly, the negative electrode side uncoated portion 25A is pressed to form the negative electrode side current collector 20B. Through the above procedure, the electrode assembly 20 is manufactured.

[0044] Step S3 is a process of housing the electrode body 20 in the case 11. In step S3, the positive electrode side current collecting part 20A is electrically connected to the positive electrode external terminal 13A via the positive electrode side current collecting member 14A. The negative electrode side current collecting part 20B is electrically connected to the negative electrode external terminal 13B via the negative electrode side current collecting member 14B. After the electrode body 20 is housed in the case 11, the opening at the top of the case 11 is closed with the lid 12.

[0045] Step S4 includes a step of drying the electrode body 20 housed in the case 11 and a step of injecting a non-aqueous electrolyte. After that, aging and initial charging steps are performed to manufacture the lithium ion secondary battery 10. When the lithium ion secondary battery 10 is used in an assembled battery, a restraining load is applied using restraining bands, an assembled battery case, end plates, etc., in a state where a plurality of lithium ion secondary batteries 10 are arranged in a predetermined arrangement direction so that the side walls 11A face each other.

[0046] [Operation of the embodiment] The operation of this embodiment will be described below with reference to FIGS. As shown in FIG. 6, when the lithium-ion secondary battery 10 is charged, the negative electrode active material absorbs lithium ions, which are charge carriers, causing the negative electrode mixture layer 26 to expand. At this time, in the flat portion 31, even if the negative electrode mixture layer 26 expands, the electrode body 20 is restrained by the side wall 11A. Therefore, in the flat portion 31, an excessive increase in the thickness of the negative electrode plate 24 due to the expansion of the negative electrode mixture layer 26 during charging is suppressed. In particular, when the lithium-ion secondary battery 10 is used in the state of a battery pack, the amount of deformation of the side wall 11A is reduced by the application of a restraining load, and therefore an excessive increase in the thickness of the negative electrode plate 24 in the flat portion 31 is suitably suppressed.

[0047] On the other hand, in the upper curved portion 32 and the lower curved portion 33, the top and bottom of the electrode body 20 are not constrained, and therefore the thickness of the negative electrode plate 24 increases toward the outer periphery as the negative electrode mixture layer 26 expands during charging. That is, during charging, the negative electrode plate 24 stretches in the vertical direction as the negative electrode mixture layer 26 expands.

[0048] As an example, the expansion rate (rate of increase in thickness) of the negative electrode mixture layer 26 when charged from SOC 10% to SOC 90% is 110% or more and 120% or less in the upper curved portion 32 and the lower curved portion 33. That is, in the upper curved portion 32 and the lower curved portion 33, the thickness of the negative electrode mixture layer 26 at SOC 90% is 1.1 times or more and 1.2 times or less the thickness of the negative electrode mixture layer 26 at SOC 10%. The present invention is particularly suitable for a nonaqueous secondary battery in which the thickness of the negative electrode mixture layer 26 increases by 1.1 times or more and 1.2 times or less during charging.

[0049] 7, in the upper curved portion 32 and the lower curved portion 33, as the negative electrode mixture layer 26 expands during charging, an expansion force F1 acts on the negative electrode plate 24, which tends to increase the thickness toward the outer periphery of the electrode body 20. At the same time, a negative electrode side static friction force F2 acts between the negative electrode contact surface 24S of the negative electrode plate 24 and the second contact surface 27S2 of the separator 27. The negative electrode side static friction force F2 is generated between both the separator 27 located on the outer periphery side with respect to the negative electrode plate 24 and the separator 27 located on the inner periphery side with respect to the negative electrode plate 24.

[0050] If the second static friction coefficient μ2 is excessively small, the maximum value of the negative electrode side static friction force F2 may be smaller than the expansion force F1 acting on the negative electrode plate 24. In this case, the negative electrode plate 24 deforms in a undulating manner while sliding against the second contact surface 27S2 of the separator 27, which tends to cause a gap between the negative electrode plate 24 and the separator 27. In the electrode body 20, the portion where a gap occurs between the negative electrode plate 24 and the separator 27 is in a state where the interelectrode distance, which is the distance between the positive electrode plate 21 and the negative electrode plate 24, has increased, and therefore becomes a portion with locally high resistance in the electrode body 20. Lithium is easily precipitated in the locally high resistance portion of the electrode body 20, which reduces the amount of lithium contributing to charging and discharging, resulting in a decrease in battery performance.

[0051] In this regard, by setting the second static friction coefficient μ2 to 0.60 or more, the maximum value of the negative electrode side static friction force F2 becomes large, so that the separator 27 expands in accordance with the increase in the thickness of the negative electrode plate 24 while maintaining a state of close contact with the negative electrode mixture layer 26 during charging. This makes it possible to suppress undulation of the negative electrode plate 24 that occurs when the second static friction coefficient μ2 between the negative electrode plate 24 and the separator 27 is small, and also makes it possible to suppress the formation of a gap between the negative electrode plate 24 and the separator 27.

[0052] Furthermore, when the separator 27 expands in accordance with an increase in the thickness of the negative electrode plate 24 during charging, an extension force F3 that extends the separator 27 toward the outer circumferential direction of the electrode body 20 acts on the separator 27. The extension force F3 that acts on the separator 27 is greater than the positive electrode side static friction force F4 that acts between the positive electrode contact surface 21S of the positive electrode plate 21 and the first contact surface 27S1 of the separator 27. That is, when the separator 27 expands due to the extension force F3, the positive electrode side static friction force F4 acts between the positive electrode contact surface 21S and the first contact surface 27S1, and then the separator 27 expands in a sliding manner relative to the positive electrode contact surface 21S.

[0053] If the first static friction coefficient μ1 is excessively large, the positive electrode side static friction force F4 between the positive electrode plate 21 and the separator 27 acts as a resistance force against the deformation of the separator 27, making it difficult for the separator 27 to stretch in accordance with an increase in the thickness of the negative electrode plate 24. In this case, the deformation of the separator 27 is suppressed by the positive electrode plate 21, making it easier for the negative electrode plate 24 to deform in a sliding manner relative to the separator 27, and as a result, a gap is more likely to be formed between the negative electrode plate 24 and the separator 27.

[0054] In this regard, by setting the first static friction coefficient μ1 to 0.50 or less, the deformation of the separator 27 is less likely to be hindered by the positive electrode side static friction force F4 when the separator 27 expands in response to an increase in the thickness of the negative electrode plate 24. As a result, the formation of a gap between the negative electrode plate 24 and the separator 27 can be suitably suppressed.

[0055] In addition, when the first static friction coefficient μ1 is excessively large and the kinetic friction coefficient between the positive electrode plate 21 and the separator 27 is large, the kinetic friction force between the positive electrode plate 21 and the separator 27 may act as a resistance force against the deformation of the separator 27. In this regard, if the first static friction coefficient μ1 is 0.50 or less, the kinetic friction coefficient between the positive electrode plate 21 and the separator 27 is also less than the first static friction coefficient μ1, so that the deformation of the separator 27 is less likely to be hindered by the kinetic friction force between the positive electrode plate 21 and the separator 27.

[0056] Furthermore, when the first static friction coefficient μ1 is excessively small, during the manufacture of the electrode body 20, the positive electrode plate 21 may be wound in a serpentine state around the separator 27 wound around the inner circumference side, as a result of the positive electrode plate 21 being wound in a sliding manner around the separator 27. Similarly, the separator 27 may be wound in a serpentine state around the positive electrode plate 21 as a result of the separator 27 being wound in a serpentine state around the positive electrode plate 21, as a result of the separator 27 being wound in a serpentine state around the positive electrode plate 21. In this regard, by setting the first static friction coefficient μ1 to 0.30 or more, it is possible to suppress the positive electrode plate 21 from being wound in a serpentine state around the separator 27.

[0057] [Method of controlling the static friction coefficient] The first static friction coefficient μ1 has a positive correlation with the surface roughness Ra1 of the positive electrode contact surface 21S of the positive electrode mixture layer 23 of the positive electrode plate 21. The first static friction coefficient μ1 has a positive correlation with the surface roughness Ra2 of the first contact surface 27S1 of the separator 27. The second static friction coefficient μ2 has a positive correlation with the surface roughness Ra3 of the negative electrode contact surface 24S of the negative electrode mixture layer 26 of the negative electrode plate 24. The second static friction coefficient μ2 has a positive correlation with the surface roughness Ra4 of the second contact surface 27S2 of the separator 27.

[0058] Each of the surface roughnesses Ra1 to Ra4 is measured by a method conforming to the measurement method of arithmetic mean roughness (Ra) specified in JIS B0601:2013. The surface roughness Ra2 of the first contact surface 27S1 of the separator 27 is measured on a portion of the first contact surface 27S1 excluding the hole portions where the openings are located. Similarly, the surface roughness Ra4 of the second contact surface 27S2 of the separator 27 is measured on a portion of the second contact surface 27S2 excluding the hole portions where the openings are located.

[0059] An example of a method for adjusting the surface roughness Ra1 of the positive electrode contact surface 21S is to change the surface roughness of the press roll in the process of pressing the positive electrode mixture layer 23 to adjust the thickness when manufacturing the positive electrode plate 21 in the source process of step S1. For example, the surface roughness Ra1 of the positive electrode contact surface 21S can be increased by pressing the positive electrode mixture layer 23 using a press roll with a large surface roughness value. For example, the surface roughness Ra1 of the positive electrode contact surface 21S can be decreased by pressing the positive electrode mixture layer 23 using a press roll with a small surface roughness value. Similarly, an example of a method for adjusting the surface roughness Ra3 of the negative electrode contact surface 24S is to change the surface roughness of the press roll that presses the negative electrode mixture layer 26 in the source process of step S1.

[0060] The first static friction coefficient μ1 and the second static friction coefficient μ2 can also be changed by changing the manufacturing conditions of the separator 27 so as to change the surface roughness Ra2 of the first contact surface 27S1 and the surface roughness Ra4 of the second contact surface 27S2.

[0061] The surface roughness Ra1 of the positive electrode contact surface 21S is, for example, 0.5 μm or more and 0.7 μm or less. The surface roughness Ra2 of the first contact surface 27S1 is, for example, 0.5 μm or more and 0.7 μm or less. The state in which the surface roughness Ra1 of the positive electrode contact surface 21S and the surface roughness Ra2 of the first contact surface 27S1 are within the above range is an example of a state in which the first static friction coefficient μ1 is 0.30 or more and 0.50 or less.

[0062] The surface roughness Ra3 of the negative electrode contact surface 24S is, for example, 0.6 μm or more and 0.8 μm or less. The surface roughness Ra4 of the second contact surface 27S2 is, for example, 0.5 μm or more and 0.7 μm or less. A state in which the surface roughness Ra3 of the negative electrode contact surface 24S and the surface roughness Ra4 of the second contact surface 27S2 are within the above range is an example of a state in which the second static friction coefficient μ2 is 0.60 or more.

[0063] In addition, the first static friction coefficient μ1 has a positive correlation with the effective contact area between the positive electrode contact surface 21S of the positive electrode plate 21 and the first contact surface 27S1 of the separator 27. Therefore, the first static friction coefficient μ1 can also be changed by changing the manufacturing conditions of the separator 27 so as to change the contact area between the first contact surface 27S1 and the positive electrode contact surface 21S. Similarly, the second static friction coefficient μ2 has a positive correlation with the effective contact area between the negative electrode contact surface 24S of the negative electrode plate 24 and the second contact surface 27S2 of the separator 27. Therefore, the second static friction coefficient μ2 can also be changed by changing the manufacturing conditions of the separator 27 so as to change the contact area between the second contact surface 27S2 and the negative electrode contact surface 24S.

[0064] For example, by increasing the porosity ε of the separator 27, the effective area of ​​the first contact surface 27S1 in contact with the positive electrode contact surface 21S is reduced by the amount of the holes where the openings are located on the first contact surface 27S1. At the same time, the effective area of ​​the second contact surface 27S2 in contact with the negative electrode contact surface 24S is reduced by the amount of the holes where the openings are located on the second contact surface 27S2. Therefore, by increasing the porosity ε of the separator 27, both the first static friction coefficient μ1 and the second static friction coefficient μ2 can be reduced. Conversely, by decreasing the porosity ε of the separator 27, both the first static friction coefficient μ1 and the second static friction coefficient μ2 can be increased.

[0065] [Effects of the embodiment] According to the above embodiment, the following effects can be obtained. (1) By setting the second static friction coefficient μ2 to 0.60 or more, in the upper curved portion 32 and the lower curved portion 33, the separator 27 extends in accordance with an increase in the thickness of the negative electrode plate 24 while maintaining a state in which the separator 27 is in close contact with the negative electrode mixture layer 26 during charging. This makes it possible to prevent a gap from being formed between the negative electrode plate 24 and the separator 27 in the upper curved portion 32 and the lower curved portion 33.

[0066] (2) By setting the first static friction coefficient μ1 to 0.50 or less, the deformation of the separator 27 during charging is less likely to be hindered by the positive electrode side static friction force F4 at the upper curved portion 32 and the lower curved portion 33. This makes it possible to suitably suppress the formation of a gap between the negative electrode plate 24 and the separator 27 at the upper curved portion 32 and the lower curved portion 33.

[0067] (3) By setting the first static friction coefficient μ1 to 0.30 or more, it is possible to prevent one of the positive electrode plate 21 and the separator 27 from being wound in a meandering state relative to the other during the manufacture of the electrode body 20. As a result, the yield of the lithium ion secondary batteries 10 can be improved.

[0068] (4) Since the surface roughness Ra1 of the positive electrode contact surface 21S is 0.5 μm or more and 0.7 μm or less, and the surface roughness Ra2 of the first contact surface 27S1 is 0.5 μm or more and 0.7 μm or less, the first static friction coefficient μ1 can be controlled in the range of 0.30 or more and 0.50 or less.

[0069] (5) Since the surface roughness Ra3 of the negative electrode contact surface 24S is 0.6 μm or more and 0.8 μm or less and the surface roughness Ra4 of the second contact surface 27S2 is 0.5 μm or more and 0.7 μm or less, the second static friction coefficient μ2 can be controlled in the range of 0.60 or more.

[0070] [Example of change] The above embodiment can be modified as follows: The following modified examples can be combined as long as they are not technically inconsistent.

[0071] As long as the second static friction coefficient μ2 is 0.60 or more, the surface roughness Ra3 of the negative electrode contact surface 24S may be less than 0.6 μm or more than 0.8 μm. Also, as long as the second static friction coefficient μ2 is 0.60 or more, the surface roughness Ra4 of the second contact surface 27S2 may be less than 0.5 μm or more than 0.7 μm.

[0072] As long as the first static friction coefficient μ1 is at least 0.50 or less, the surface roughness Ra1 of the positive electrode contact surface 21S may be less than 0.5 μm or more than 0.7 μm. As long as the first static friction coefficient μ1 is at least 0.50 or less, the surface roughness Ra2 of the first contact surface 27S1 may be less than 0.5 μm or more than 0.7 μm.

[0073] During the manufacture of the electrode assembly 20, if it is possible to control the positive electrode plate 21 and the separator 27 so that they are not wound in a meandering state relative to the other, the first static friction coefficient μ1 may be less than 0.30. Even if one of the positive electrode plate 21 and the separator 27 meanders relative to the other, if the degree of meandering does not affect the product function or an electrode assembly 20 without meandering can be selected by visual inspection or the like, the first static friction coefficient μ1 may be less than 0.30.

[0074] Although the lithium ion secondary battery 10 has been exemplified as a nonaqueous secondary battery, the present invention can be applied to any nonaqueous secondary battery in which the negative electrode active material expands during charging. Also, although a graphite-type material has been exemplified as the negative electrode active material, the present invention can also be applied to nonaqueous secondary batteries using silicon-based negative electrode active materials, since the negative electrode active material expands during charging.

[0075] The lithium ion secondary battery 10 may be mounted on an automatic transport vehicle, a special vehicle for loading and unloading, an electric vehicle, a hybrid vehicle, a computer, or other electronic device, or may be part of other systems. For example, it may be mounted on a moving object such as a ship or an aircraft, or may be a power supply system that supplies power from a power plant via a substation to a building or home in which a secondary battery is installed.

[0076] [Example] Examples 1 to 4 and Comparative Examples 1 to 4 will be described below with reference to Fig. 8. Note that the following examples are merely examples for explaining the effects of the above-described embodiment, and do not limit the present invention.

[0077] [Example 1] 8, in Example 1, a lithium ion secondary battery 10 was manufactured using an electrode assembly 20 that was fabricated so that the first static friction coefficient μ1 was 0.30 and the second static friction coefficient μ2 was 0.60. In Example 1, four electrode assemblies 20 were fabricated using the same positive electrode plate 21, negative electrode plate 24, and separator 27, and then four lithium ion secondary batteries 10, Sample 1 to Sample 4, were manufactured (n=4).

[0078] [Example 2] In Example 2, four electrode bodies 20 were fabricated so that the first static friction coefficient μ1 was 0.50 and the second static friction coefficient μ2 was 0.60, and then four lithium ion secondary batteries 10, Sample 1 to Sample 4, were manufactured (n=4).

[0079] [Example 3] In Example 3, four electrode bodies 20 were fabricated so that the first static friction coefficient μ1 was 0.50 and the second static friction coefficient μ2 was 0.90, and then four lithium ion secondary batteries 10, Sample 1 to Sample 4, were manufactured (n=4).

[0080] [Example 4] In Example 4, four electrode assemblies 20 were produced so that the first static friction coefficient μ1 was 0.25 and the second static friction coefficient μ2 was 0.60, and then four lithium ion secondary batteries 10, Sample 1 to Sample 4, were manufactured (n=4). In Example 4, it was confirmed that in Sample 3, the positive electrode plate 21 was wound in a meandering state around the separator 27 during the manufacture of the electrode assembly 20.

[0081] [Comparative Example 1] In Comparative Example 1, four electrode bodies 20 were fabricated so that the first static friction coefficient μ1 was 0.60 and the second static friction coefficient μ2 was 0.90, and then four lithium ion secondary batteries 10, Samples 1 to 4, were manufactured (n=4).

[0082] [Comparative Example 2] In Comparative Example 2, four electrode bodies 20 were produced so that the first static friction coefficient μ1 was 0.60 and the second static friction coefficient μ2 was 0.60, and then four lithium ion secondary batteries 10, Samples 1 to 4, were manufactured (n=4).

[0083] [Comparative Example 3] In Comparative Example 3, four electrode bodies 20 were fabricated so that the first static friction coefficient μ1 was 0.60 and the second static friction coefficient μ2 was 0.40, and then four lithium ion secondary batteries 10, Samples 1 to 4, were manufactured (n=4).

[0084] [Comparative Example 4] In Comparative Example 4, four electrode bodies 20 were fabricated so that the first static friction coefficient μ1 was 0.50 and the second static friction coefficient μ2 was 0.40, and then four lithium ion secondary batteries 10, Sample 1 to Sample 4, were manufactured (n=4).

[0085] [Lithium precipitation resistance evaluation] For each of the samples 1 to 4 manufactured in Examples 1 to 4 and Comparative Examples 1 to 4, the first critical current value I1 at which metallic lithium precipitates in the flat portion 31 during charging, and the second critical current value I2 at which metallic lithium precipitates in the upper curved portion 32 and the lower curved portion 33 during charging were measured. As the second critical current value I2, the current value at which metallic lithium precipitates in at least one of the upper curved portion 32 and the lower curved portion 33 during charging was adopted. Then, the precipitation limit current ratio, which is the ratio of the second critical current value I2 to the first critical current value I1, was calculated as I2 / I1×100(%). In addition, in each of the samples manufactured in Examples 1 to 4 and Comparative Examples 1 to 4, the increase rate of the thickness of the negative electrode mixture layer 26 when charging from SOC 10% to SOC 90% was 1.1 times or more and 1.2 times or less in the upper curved portion 32 and the lower curved portion 33.

[0086] In addition, the closer the deposition limit current ratio is to 100%, the more equivalent the lithium deposition resistance in the upper curved portion 32 and the lower curved portion 33 is to the lithium deposition resistance in the flat portion 31. Therefore, the closer the deposition limit current ratio is to 100%, the more the formation of a gap between the negative electrode plate 24 and the separator 27 in the upper curved portion 32 and the lower curved portion 33 is suppressed.

[0087] [Evaluation Results] 8, in Examples 1 to 3, the deposition limiting current ratio was 100% in all of Samples 1 to 4. Therefore, it was confirmed that when the first static friction coefficient μ1 was 0.30 or more and 0.50 or less and the second static friction coefficient μ2 was 0.60 or more, the formation of a gap between the negative electrode plate 24 and the separator 27 was suppressed.

[0088] On the other hand, in Example 4, the deposition limit current ratios were 100% in Samples 1, 2, and 4, but 97% in Sample 3. The decrease in the second critical current value I2 in Sample 3 of Example 4 is considered to be due to an increase in resistance caused by the positive electrode plate 21 being wound in a meandering state relative to the separator 27 during the manufacture of the electrode body 20. From the above results, it was confirmed that by setting the first static friction coefficient μ1 to 0.30 or more, it is possible to suppress the positive electrode plate 21 and the separator 27 from being wound in a meandering state relative to the other during the manufacture of the electrode body 20, and the associated increase in resistance.

[0089] In Comparative Example 1, the deposition limit current ratio was about 94% to 95%. In Comparative Example 2, the deposition limit current ratio was about 89% to 91%. In Comparative Example 3, the deposition limit current ratio was about 80% to 81%. In Comparative Examples 1 to 3, the first static friction coefficient μ1 was 0.60, so the positive electrode side static friction force F4 was at a relatively high level compared to Examples 1 to 4. Therefore, it is considered that the decrease in the second critical current value I2 in Comparative Examples 1 to 3 is due to the formation of a gap between the negative electrode plate 24 and the separator 27 due to the positive electrode side static friction force F4 hindering the deformation of the separator 27. In addition, it is considered that the deposition limit current ratio became lower in the order of Comparative Examples 1 to 3 because the smaller the second static friction coefficient μ2, the easier it is to form a gap between the negative electrode plate 24 and the separator 27.

[0090] In Comparative Example 4, the deposition limit current ratio was about 96% to 97%. In Comparative Example 4, the second static friction coefficient μ2 was 0.40, and therefore the negative electrode side static friction force F2 was at a relatively small level compared to Examples 1 to 4. Therefore, it is considered that the decrease in the second critical current value I2 in Comparative Example 4 is caused by the separator 27 being unable to follow the deformation of the negative electrode plate 24 during charging, resulting in the generation of a gap between the negative electrode plate 24 and the separator 27. [Explanation of symbols]

[0091] 10...Lithium-ion secondary battery 11. Case 11A…Side wall 20...Electrode body 21…Positive electrode plate 21S…Positive contact surface 22...Positive electrode substrate 23...Positive electrode mixture layer 24…Negative electrode plate 24S…Negative electrode contact surface 25...Negative electrode substrate 26...Negative electrode mixture layer 27…Separator 27S1…1st contact surface 27S2…Second contact surface 31…Flat section 32…Upper curved section 33…Lower curved part

Claims

1. an electrode assembly in which a positive electrode plate, a negative electrode plate, and a separator for holding a non-aqueous electrolyte are stacked and wound together such that the separator is disposed between the positive electrode plate and the negative electrode plate; The electrode body includes a curved portion in which each layer constituting the electrode body is curved, The positive electrode plate includes a foil-shaped positive electrode substrate and a positive electrode mixture layer provided on two surfaces of the positive electrode substrate that face in opposite directions, The negative electrode plate includes a foil-shaped negative electrode base material and a negative electrode mixture layer provided on two surfaces of the negative electrode base material that face in opposite directions, the negative electrode mixture layer contains a negative electrode active material that occludes charge carriers during charging, a static friction coefficient between the negative electrode mixture layer and the separator is 0.60 or more and 1.00 or less; The static friction coefficient between the positive electrode mixture layer and the separator is 0.25 or more and 0.50 or less. Non-aqueous secondary battery.

2. The static friction coefficient between the positive electrode mixture layer and the separator is 0.30 or more. The nonaqueous secondary battery according to claim 1 .

3. The surface roughness of the positive electrode mixture layer on the surface in contact with the separator is 0.5 μm or more and 0.7 μm or less, The surface roughness of the separator surface in contact with the positive electrode mixture layer is 0.5 μm or more and 0.7 μm or less. The nonaqueous secondary battery according to claim 2 .

4. the surface roughness of the negative electrode mixture layer on the surface in contact with the separator is 0.6 μm or more and 0.8 μm or less; The surface roughness of the separator surface in contact with the negative electrode mixture layer is 0.5 μm or more and 0.7 μm or less. The nonaqueous secondary battery according to claim 1 .

5. an electrode assembly manufacturing process in which a positive electrode plate including a positive electrode mixture layer provided on two surfaces of a positive electrode substrate facing in opposite directions, a negative electrode mixture layer provided on two surfaces of a negative electrode substrate facing in opposite directions, the negative electrode mixture layer including a negative electrode active material that occludes charge carriers during charging, and a separator that holds a non-aqueous electrolyte are wound in a stacked state such that the separator is disposed between the positive electrode plate and the negative electrode plate, thereby manufacturing an electrode assembly in which curved portions are formed in the stacked layers; A liquid injection step of injecting a non-aqueous electrolyte into a case containing the electrode body, In the electrode body manufactured in the electrode body manufacturing process, a static friction coefficient between the negative electrode mixture layer and the separator is 0.60 or more and 1.00 or less; The static friction coefficient between the positive electrode mixture layer and the separator is 0.25 or more and 0.50 or less. A method for manufacturing a non-aqueous secondary battery.

Images