Lithium ion secondary battery and manufacturing method of lithium ion secondary battery

Abstract

To suppress Li precipitation by optimizing a gap between layers of a lamination body.SOLUTION: A manufacturing method of a lithium ion secondary battery includes: a gap measurement step of measuring a gap between layers of a lamination body wound at the outermost periphery in a curved part R, in which the lithium ion secondary battery has a flat press-shaped flat part and a curved part and is set such that a heat shrinkage ratio XOUT [%] of an outer separator is larger than a heat shrinkage ratio XIN [%] of an inner separator of the lamination body wound at the outermost periphery; and a heating temperature setting step of setting a heating temperature T [°C] so as to reduce the gap between the layers to a set value; and a heating step of heating at the set heating temperature T [°C]. The gap between the layers of the lamination body is optimized to suppress Li deposition.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a lithium ion secondary battery and a method for manufacturing a lithium ion secondary battery, and more particularly to a lithium ion secondary battery and a method for manufacturing a lithium ion secondary battery that can suppress Li deposition. [Background technology]

[0002] Fig. 1 is a perspective view of a lithium ion secondary battery 1 according to the present embodiment, which is an example of a lithium ion secondary battery. Fig. 2 is a perspective view of an electrode body 10 of Fig. 1, in which a part of the electrode body 10 is developed. Conventionally, lithium ion secondary batteries 1, which have a large capacity per volume and are capable of inputting and outputting large currents, have been used as power sources for driving electric vehicles and hybrid vehicles. For this purpose, they are used as assembled batteries (not shown) in which a large number of plate-shaped cell batteries are stacked as shown in Fig. 1. In order to increase the electrical capacity per volume, such lithium ion secondary batteries 1 include an electrode assembly 10, which is formed by winding a laminate 10a in which a positive electrode plate 110 and a negative electrode plate 100 are stacked with a separator 120 interposed therebetween, as shown in Fig. 2, and pressing the laminate into a flat shape.

[0003] Fig. 7 is a schematic diagram showing the winding step of the laminate 10a in which the positive electrode plate 110 and the negative electrode plate 100 are stacked with the separator 120 interposed therebetween as in Fig. 2. Fig. 8 is a schematic diagram showing the state in which the laminate 10a has been cut after the winding step (S3 in Fig. 5) has been completed.

[0004] As shown in Fig. 7, the positive electrode plate 110, the negative electrode plate 100, and the separator 120 are respectively supplied from supply rollers (not shown). IN a negative electrode plate 100 and an outer separator 120 OUT are stacked and supplied as a laminate 10a. The laminate 10a is wound around a winding core 3 and wound up while applying tension with a tension roller 5. At this time, the end E of the wound laminate 10a is pressed down by a pressure roller 4 to prevent the wound laminate 10a from loosening.

[0005] However, as shown in FIG. 8, the length of the outermost periphery to be wound last, L OUT The laminate 10a is cut at the end E. As a result, the laminate is wound tightly up to the point pressed by the pressure roller 4, but the end E of the laminate 10a beyond that point becomes a free end and is not subjected to tension. When the outermost laminate 10a in this state is wound and its end E is fixed with adhesive tape, the tension applied to the winding is weaker than that of the laminate below it, resulting in gaps between the plates.

[0006] FIG. 4 is a schematic diagram showing the wound body pressing step (FIG. 5: S4) after the winding step (FIG. 5: S3). As shown in FIG. 4, in the wound body pressing step (S4) after the winding step (S3), the winding core 3 is pulled out after the winding step (S3) and compressed by the press surface 2a of the press machine 2. At this time, the gaps between the electrode plates are tightly packed and disappear at the flat portion F pressed by the press surface 2a shown in FIG. 3. On the other hand, gaps are formed between the electrode plates at the curved portion R corresponding to the end of the winding direction Z.

[0007] 9 is a diagram showing a curved portion R where a gap is formed between the electrode plates. As shown in FIG. 9, the inner electrode plate 10 of the curved portion R IN and outer electrode 10 OUT The distance G between R However, the inner electrode plate 10 of the flat portion F IN and outer electrode 10 OUT The distance G between F When the resistance between the plates increases, the electrical resistance between the plates becomes larger in the curved part R than in the flat part F. When the resistance between the plates increases, a high voltage is applied, and the negative electrode potential [V vs. Li / Li + ] is 0 [V vs. Li / Li + If the potential exceeds [1 / (1 / 2)], the potential will be lower than that for Li deposition, and deposition of metallic Li may occur.

[0008] Therefore, Patent Document 1 reports a technology for reducing the gaps in the curved R portion by applying a temperature cycle to the cell after the activation process. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2020-53352 Summary of the Invention [Problem to be solved by the invention]

[0010] However, in the invention described in Patent Document 1, when a temperature cycle is applied to eliminate the gap in the curved portion R, the inner separator 120 IN and outer separator 120 OUT Therefore, they all shrink uniformly, and the outer separator 120 OUT If you try to eliminate the gap, the inner separator 120 IN 15 is a schematic diagram showing a problem that can occur in a conventional electrode assembly 10. IN When the positive electrode current collector foil 111 made of Al foil of the positive electrode plate 110 corresponding to the positive electrode plate 110 is cut to a predetermined size, sharp "burrs 111a" may remain on the cut edge. This burr 111a is formed when the inner and outer separators 120 shrink uniformly. IN If the amount of shrinkage becomes excessively large, the positive electrode composite layer 112 may penetrate further into the inner separator 120. IN In such a case, the inner separator 120 IN Stress is concentrated in a part of the inner separator 120 IN There was a problem that excessive stress was applied to the

[0011] The problem to be solved by the lithium ion secondary battery and the method for producing a lithium ion secondary battery of the present invention is to suppress Li deposition by optimizing the gap between layers of the laminate. [Means for solving the problem]

[0012] In order to solve the above-mentioned problems, the lithium ion secondary battery of the present invention is a lithium ion secondary battery including an electrode assembly formed by winding a laminate in which a positive electrode plate and a negative electrode plate are stacked with a separator interposed therebetween and pressing the laminate into a flat shape, and the laminate wound around the outermost periphery of the electrode assembly includes an innermost electrode plate, an inner separator on the outer periphery of the inner electrode plate, an outer electrode plate on the outer periphery of the inner separator, and an outer separator on the outer periphery of the outer electrode plate, and the thermal shrinkage rate X in the winding direction of the inner separator is IN From [%], the thermal shrinkage rate X of the outer separator in the winding direction is OUT It is characterized by being set so that [%] is large.

[0013] Further, in the method for producing a lithium ion secondary battery of the present invention, a laminate obtained by stacking a positive electrode plate and a negative electrode plate with a separator interposed therebetween is wound and the end portions are fixed, and the lithium ion secondary battery is provided with an electrode body that is press-shaped flat so as to form a flat portion and curved portions wound at both ends of the flat portion, and the laminate wound around the outermost periphery of the electrode body comprises an innermost electrode plate, an inner separator on the outer periphery of the inner electrode plate, an outer electrode plate on the outer periphery of the inner separator, and an outer separator on the outer periphery of the outer electrode plate, and the thermal shrinkage rate X in the winding direction of the inner separator is IN From [%], the thermal shrinkage rate X of the outer separator in the winding direction is OUT In a lithium ion secondary battery set so that [%] is large, the battery is characterized by comprising a gap measurement step of measuring the gap between each layer of the laminate wound around the outermost periphery on a center plane S parallel to the flat portion including the winding axis in the curved portion of the electrode body, a heating temperature setting step of setting a heating temperature T [°C] based on the gap between each layer of the laminate measured in the gap measurement step so as to reduce the gap to a set value, and a heating step of heating at the heating temperature T [°C] set in the heating temperature setting step.

[0014] The heating temperature setting step is performed by setting the upper limit temperature T maxThe heating temperature T [°C] can be set with an upper limit of [°C].

[0015] The heating temperature setting step may be configured to set the heating temperature T [°C] within a range of temperatures T [°C] such that the gap between each layer of the laminate measured in the gap measurement step is within a predetermined allowable range.

[0016] In the step of setting the heating temperature, the upper limit temperature T max [°C], in the curved portion R of the electrode body, the thickness in the thickness direction between the opposing inner electrode plates: L [mm], the thickness of the separator: k [mm], the thickness of the outer electrode plate: l [mm], the distance between the inner electrode plate and the outer separator on the central plane S: b [mm], the distance between the inner electrode plate and the inner separator on the central plane S: a [mm], the thermal shrinkage rate of the inner separator: X IN [%], the heat shrinkage rate of the outer separator: X OUT [%], half the circumference of the curved portion R of the inner separator: A IN , half the circumference of the curved portion R of the outer separator: A OUT When A IN is expressed as the following (Equation 1),

[0017]

number

[0018] A OUT is expressed as the following (Equation 2):

[0019]

number

[0020] The heat shrinkage rate [%] of the outer separator at a given temperature T [°C] is expressed as X OUT [%], the heat shrinkage rate [%] of the inner separator is X IN When set to [%],

[0021]

number

[0022] The temperature T [°C] that satisfies the upper limit temperature T max It may also be set as [°C]. The thermal shrinkage rate X of the inner separator in the winding direction is IN From [%], the thermal shrinkage rate X of the outer separator in the winding direction is OUT The difference ΔX [%] between the heat shrinkage rates X [%] set so that the heat shrinkage rate X [%] is larger is set so that the heating temperature T [°C] set in the heating temperature setting step is within the temperature range [°C] that allows heating in advance in the manufacturing process of the lithium ion secondary battery. IN [%] and the thermal shrinkage rate X of the outer separator in the winding direction OUT It is also possible to set [%].

[0023] The heating step can be carried out as a cell drying step for the lithium ion secondary battery. If the gap between the inner electrode plate and the outer electrode plate measured in the gap measurement step is within a predetermined tolerance range, the heating temperature setting step can be omitted, and the cell can be heated at a predetermined heating temperature T0 [°C] in the cell drying process.

[0024] The inner electrode plate may be a positive electrode plate, and the outer electrode plate may be a negative electrode plate. [Effects of the Invention]

[0025] According to the lithium ion secondary battery and the method for manufacturing the lithium ion secondary battery of the present invention, the gap between the layers of the laminate can be optimized to suppress Li deposition. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a perspective view of a lithium ion secondary battery according to an embodiment of the present invention; [Figure 2] FIG. 2 is a perspective view showing a part of the electrode assembly of FIG. 1 in an expanded state. [Figure 3] FIG. 2 is a perspective view of the electrode body of the present embodiment. [Figure 4] FIG. 10 is a schematic diagram showing a wound body pressing step after a winding step. [Figure 5] 2 is a flowchart showing the procedure of a manufacturing process for a lithium ion secondary battery according to the present embodiment. [Figure 6] 10 is a flowchart showing the procedure for heating the electrode assembly according to the present embodiment. [Figure 7] FIG. 2 is a schematic diagram showing a winding process of a laminate in which positive electrode plates and negative electrode plates are stacked with a separator interposed therebetween. [Figure 8] FIG. 10 is a schematic diagram showing a state in which the laminate has been cut after the winding step has been completed. [Figure 9] FIG. 10 is a diagram schematically illustrating a curved portion where a gap is formed between the electrode plates. [Figure 10] 10 is a schematic view of the electrode body after the wound body pressing step (S4) is completed, as viewed from the width direction W. FIG. [Figure 11] 1 is a graph showing the relationship between the heating temperature T [°C] of the inner separator and the outer separator and the corresponding heat shrinkage rate [%]. [Figure 12] 10 is a graph showing the relationship between heating temperature T [°C] and (1-XIN) / (1-XOUT). [Figure 13] 1 is a table showing conditions in an example. [Figure 14] 10 is a table comparing the distance (ba) [mm] between the inner separator and the outer separator after drying the cell and the Li deposition resistance in an example of this embodiment and comparative examples 1 and 2 in which the heating temperature T [°C] was changed. [Figure 15] 1 is a schematic diagram illustrating a problem that may occur in a conventional electrode assembly. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, the lithium ion secondary battery and the method for manufacturing the lithium ion secondary battery of the present invention will be described with reference to FIGS. 1 to 15, taking an embodiment of the method for manufacturing the lithium ion secondary battery 1 as an example.

[0028] (Outline of this embodiment) As described in the background art, in the outermost laminate 10a of the electrode assembly 10 of the lithium ion secondary battery 1, the inner electrode plate 10 at the curved portion R is wound due to the tension of the winding, as shown in FIG. IN The positive electrode plate 110 and the outer electrode plate 10 OUT The distance G of the negative electrode plate 100 is R But the distance G of the flat part F F This causes metallic lithium to deposit, especially at the curved portion R.

[0029] In addition, in the invention disclosed in Patent Document 1, such a distance G F In order to reduce the heat shrinkage, the heat shrinkable separator 120 is shrunk, but one type of separator 120 with the same heat shrinkage rate X [%] is used. IN , inner separator 120 IN , outer plate 10 OUT , outer separator 120 OUT It was difficult to uniformly reduce the gap.

[0030] Therefore, in the lithium ion secondary battery 1 of this embodiment, the inner separator 120 IN Heat shrinkage rate X in winding direction Z IN From [%], outer separator 120 OUT Heat shrinkage rate X in winding direction Z OUT Therefore, even if the same heat treatment is performed, the inner electrode plate 10 of the outermost laminate 10a after the heat treatment is IN , inner separator 120 IN , outer plate 10 OUT , outer separator 120 OUT The gap can be made uniformly small.

[0031] As a result, the gaps between the layers in the flat portion F and the curved portion R of the electrode body 10 can be uniformly reduced, and the resistance [mΩ] of each portion of the electrode body 10 can be uniformed. By uniforming the resistance [mΩ] of each portion of the electrode body 10, it is possible to effectively prevent the potential [V] of the electrode body 10 from locally reaching the potential [V] of metallic lithium deposition, particularly due to overcharging. As a result, even under harsh usage conditions, the generation of dendrites in the lithium-ion secondary battery 1 can be suppressed, and the battery life can be extended.

[0032] (Configuration of this embodiment) The lithium ion secondary battery 1 of this embodiment and a method for manufacturing the same will be described in detail below with reference to FIGS.

[0033] <Lithium-ion secondary battery 1 of this embodiment> First, an example of the configuration of a lithium ion secondary battery 1 that is the premise of this embodiment will be briefly described.

[0034] FIG. 1 is a perspective view of a lithium-ion secondary battery 1. As shown in FIG. 1, the lithium-ion secondary battery 1 is configured as a cell battery. It includes a rectangular parallelepiped battery case 11 with an opening on the upper side. The battery case 11 includes a lid 12 that seals the opening of the battery case 11. An electrode assembly 10 is housed inside the battery case 11. The battery case 11 is filled with a nonaqueous electrolyte 17. The battery case 11 and the lid 12 are made of a metal such as an aluminum alloy. The lithium-ion secondary battery 1 forms a sealed battery container by attaching the lid 12 to the battery case 11. The lid 12 of the lithium-ion secondary battery 1 also includes a negative electrode external terminal 14 and a positive electrode external terminal 16, which are used for charging and discharging power. The negative electrode external terminal 14 and the negative electrode connection portion 103 (see FIG. 2) of the electrode assembly 10 are connected by a negative electrode current collector 13 via the lid 12. The positive electrode external terminal 16 and the positive electrode connection part 113 (see FIG. 2) of the electrode body 10 are connected by the positive electrode current collector 15 via the lid body 12 .

[0035] <Laminate 10a> 2 is a schematic diagram showing the configuration of the laminate 10a of the electrode assembly 10 of the lithium ion secondary battery 1. Here, the laminate 10a is configured by stacking a positive electrode plate 110 on the innermost side, a separator 120 on the outer side thereof, a negative electrode plate 100 on the outer side thereof, and a separator 120 on the outermost side. FIG. 2 shows the outermost laminate 10a of this embodiment in an expanded state. As shown in FIG. 2, the outermost laminate 10a has an inner electrode plate 10 on the innermost side. IN The positive electrode plate 110 is provided on the outer periphery thereof with an inner separator 120. IN Furthermore, an outer electrode plate 10 is provided on the outer periphery thereof. OUT The negative electrode plate 100 is provided on the outermost side as a separator 120. OUT Equipped with.

[0036] This laminate 10a is wound in a winding direction Z around a winding axis C and shaped into a flat electrode body 10. The end E of the laminate 10a is fixed in a wound state as shown in FIG. 3 with adhesive tape (not shown) or the like.

[0037] The negative electrode plate 100 has a negative electrode composite layer 102 on both sides of a negative electrode current collector foil 101. The positive electrode plate 110 has a positive electrode composite layer 112 on both sides of a positive electrode current collector foil 111. The negative electrode plate 100 and the positive electrode plate 110 are stacked with a separator 120 interposed therebetween to form a laminated electrode body 10.

[0038] Negative electrode connector 103 functions as a current collector that extracts electricity from negative electrode composite layer 102 of negative electrode plate 100. Positive electrode connector 113 functions as a current collector that extracts electricity from positive electrode composite layer 112 of positive electrode plate 110.

[0039] <Configuration of electrode body 10> 3 is a perspective view showing the end of the wound electrode body 10 on the negative electrode side in the width direction W. The electrode body 10 stacked in the stacking step (S2 in FIG. 6) is wound while being supported by a winding core 3 centered on a winding axis C in the winding step (S3 in FIG. 5) shown in FIGS.

[0040] Next, after the winding step (S3) is completed, the winding core 3 is removed, and in the wound body pressing step (S4 in FIG. 5), a pair of opposing presses 2 (see FIG. 4) is used to shape the end portion as seen from the width direction W into a flattened shape resembling a racing track. The portion formed flat in this wound body pressing step (S4) is called the flat portion F. At the upper and lower ends of the length direction H of the flat portion F, the electrode body 10 consisting of the stacked negative electrode plate 100, positive electrode plate 110, and separator 120 is curved into a semi-cylindrical shape, forming a curved portion R. This curved portion R has a nearly concentric semi-circular shape as seen from the width direction W.

[0041] Here, the direction parallel to the winding axis C of the electrode body 10 is referred to as the "width direction W." Furthermore, the direction perpendicular to the winding axis C of the electrode body 10 and perpendicular to the surface of the flat portion F is referred to as the "thickness direction D." Furthermore, the direction perpendicular to the width direction W and the thickness direction D is referred to as the "length direction H." Note that on the surface of the flat portion F, the winding direction Z is parallel to the "length direction H."

[0042] 4 is a schematic diagram showing the configuration of the end portion of the electrode assembly 10 as viewed from the width direction W in the wound assembly pressing step (S4). The wound assembly of the electrode assembly 10 is formed by repeatedly stacking negative electrode plates 100 and positive electrode plates 110 with separators 120 interposed therebetween. The central portion of the electrode assembly 10 that has been pressed flat is flat, and a "flat portion F" (see FIG. 3) is formed by the negative electrode plates 100, positive electrode plates 110, and separators 120. Here, the plane that includes the winding axis C and is parallel to the length direction H is referred to as the central plane S.

[0043] The flattened electrode assembly 10 is then housed in a battery case 11 as shown in Fig. 1, and a negative electrode current collector 13 is welded to the negative electrode connection portion 103. A positive electrode current collector 15 is welded to the positive electrode connection portion 113. Methods for welding the connection portions and current collectors include ultrasonic welding, resistance welding, and electric welding. A negative electrode external terminal 14 is then connected to the negative electrode current collector 13, penetrating the lid 12, and a positive electrode external terminal 16 is connected to the positive electrode current collector 15.

[0044] <Negative electrode plate 100> In the negative electrode plate 100, a negative electrode composite layer 102 is formed on both sides of a negative electrode current collector foil 101. In this embodiment, the negative electrode current collector foil 101 is made of Cu foil. The negative electrode current collector foil 101 serves as a base for the aggregate of the negative electrode composite layer 102, and also functions as a current collecting member that collects electricity from the negative electrode composite layer 102. In the negative electrode plate 100, the negative electrode composite layer 102 is formed on the metallic negative electrode current collector foil 101. In the first embodiment, the negative electrode active material is a material that can occlude and release lithium ions, and a powdered carbon material made of graphite or the like is used.

[0045] The negative electrode plate 100 is made, for example, by kneading a negative electrode active material, a solvent, and a binder to form a negative electrode composite paste. The prepared negative electrode composite paste is applied to a negative electrode current collector foil 101 and dried in a drying process. The negative electrode is then pressed to a predetermined thickness and density.

[0046] <Positive electrode plate 110> Positive electrode plate 110 is configured by forming positive electrode composite material layers 112 on both sides of positive electrode current collector foil 111. In this embodiment, positive electrode current collector foil 111 is configured from Al foil or Al alloy foil. Positive electrode current collector foil 111 serves as a base as an aggregate for positive electrode composite material layer 112, and also functions as a current collecting member that collects electricity from positive electrode composite material layer 112.

[0047] The positive electrode plate 110 has a positive electrode composite layer 112 formed on the surface of a positive electrode current collector foil 111. The positive electrode composite layer 112 contains a positive electrode active material. The positive electrode active material is a material capable of absorbing and releasing lithium, and examples of the positive electrode active material include lithium cobalt oxide (LiCoO), lithium manganese oxide (LiMnO), and lithium nickel oxide (LiNiO). Alternatively, a material in which LiCoO, LiMnO, and LiNiO are mixed in any ratio may be used.

[0048] The positive electrode composite layer 112 also contains a conductive material. Examples of the conductive material include carbon black such as acetylene black (AB) and ketjen black, and graphite. In this embodiment, highly conductive carbon nanotubes, carbon nanofibers, and the like are used as the conductive material.

[0049] The positive electrode plate 110 is made by, for example, kneading a positive electrode active material, a conductive material, a solvent, and a binder to form a positive electrode composite paste. The kneaded positive electrode composite paste is applied to the positive electrode current collector foil 111 and then dried. Finally, a positive electrode pressing process is performed to achieve a predetermined thickness and density.

[0050] <Separator 120> The separator 120 is a highly insulating nonwoven fabric made of porous resin or the like that insulates the negative electrode plate 100 and the positive electrode plate 110 and holds the nonaqueous electrolyte solution 17 therebetween. Alternatively, the separator 120 may be a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, or a lithium ion or ion conductive polymer electrolyte membrane, either alone or in combination.

[0051] In this embodiment, a layer made of polyethylene (PE) is provided in the center as a core material. Polyethylene (PE) melts at a certain temperature. Therefore, when the temperature exceeds a certain level, it melts, closing its network structure and interrupting the flow of the non-aqueous electrolyte 17, which is called shutdown. This shutdown allows lithium ions Li + By restricting the passage of the current, the circuit of the lithium ion secondary battery 1 is interrupted, the flow of current is stopped, and overheating is prevented.

[0052] The core is also sandwiched between surface layers made of polypropylene (PP). This surface layer has high mechanical strength and protects the separator 120 from foreign matter such as dendrites of metallic Li precipitates or mixed metal powder, preventing them from penetrating and causing a short circuit. This surface layer also has higher heat resistance than the polyethylene (PE) core, does not melt easily even when overheated, and electrically isolates the electrodes to prevent a short circuit.

[0053] <Separator 120 IN , 120 OUT > The resin separator 120 configured in this manner has a certain degree of elasticity, and even if it is temporarily subjected to stress such as compression or tension, it will return to its original thickness and length once the stress is removed. However, if the stress exceeds a certain level, the material will undergo plastic deformation.

[0054] In the manufacturing method of the separator 120 of this embodiment, a porous sheet is stretched in the winding direction Z to set the thermal shrinkage rate [%] to a target value. IN , outer separator 120 OUT The winding direction Z in this example refers to the longitudinal direction of a separator manufactured in a long shape. In this embodiment, the winding direction Z, which is the longitudinal direction in the manufacture of the separator 120, is the resin flow direction MD (Mold Direction). In the manufacturing process, a stretching step is performed in the winding direction Z, and the thickness, stretchability, porosity, and thermal shrinkage rate of the separator 120 change depending on the stretching rate SR [%]. In other words, when a porous resin sheet, which is the raw material for the separator 120, is stretched along the winding direction Z, the thermal shrinkage rate [%] increases. Therefore, by changing this stretching rate SR [%], two types of separators 120 with different thermal shrinkage rates [%] are produced. Of these, the separator 120 with a higher stretching rate SR [%], i.e., a higher thermal shrinkage rate [%], is referred to as the outer separator 120. OUT On the other hand, the separator 120 having a low elongation rate SR [%], i.e., a low thermal shrinkage rate [%], was used as the inner separator 120. IN It was decided.

[0055] Here, FIG. 11 shows the inner separator 120 IN , outer separator 120 OUT 1 is a graph showing the relationship between the heating temperature T [°C] and the corresponding heat shrinkage rate X [%]. The horizontal axis represents the heating temperature T [°C], and the vertical axis represents the heat shrinkage rate X [%] relative to the heating temperature T [°C]. Here, the heat shrinkage rate X [%] in this embodiment is expressed as a percentage, calculated by the formula: X [%] = 100 × (Lo - L1) / Lo, where Lo is the sample length before heating and L1 is the sample length after heating. The measurement method is, for example, in accordance with JIS K 7133:1999, "Measuring Method for Dimensional Changes in Plastic Films and Sheets Due to Heat." Generally, the shrinkage rate is 1.5 to 4.0% for PE (polyethylene) and 1.0 to 2.5% for PP (polypropylene). Here, the inner separator 120 IN and outer separator 120 OUT As described above, since the inner separator 120 is stretched at a different stretching rate SR [%], even if the heating temperature T1 [°C] is the same, as shown in the graph of FIG. IN Heat shrinkage rate X IN [%] is approximately 2.4[%]. OUT Heat shrinkage rate X OUT The thermal shrinkage rate X [%] is approximately 6.5 [%], which is a large difference. In addition, as the heating temperature T [°C] decreases, the thermal shrinkage rate X IN [%] and heat shrinkage rate X OUT Conversely, as the heating temperature T [°C] increases, the difference between the thermal shrinkage rate X IN [%] and heat shrinkage rate X OUT It can be seen that the difference with [%] becomes larger.

[0056] 11 is merely an example, and the thermal shrinkage rate X [%] can be adjusted by changing the stretch rate SR [%]. Furthermore, the stretch rate SR [%] can also be adjusted by changing the components of the resin material or by adjusting the porosity [%].

[0057] <Nonaqueous electrolyte 17> The nonaqueous electrolyte 17 of the lithium-ion secondary battery 1 of this embodiment shown in FIG. 1 is impregnated in the electrode assembly 10. The nonaqueous electrolyte 17 is a composition in which a lithium salt is dissolved in an organic solvent. Examples of the lithium salt include LiClO4, LiPF6, LiAsF6, LiBF4, and LiSO3CF3. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. The nonaqueous electrolyte 17 may be composed of one or more of these compounds mixed together. However, the composition of the nonaqueous electrolyte 17 is not limited to this example.

[0058] <Method of manufacturing lithium-ion secondary battery 1> FIG. 5 is a flowchart showing an example of a method for manufacturing the lithium ion secondary battery 1 of this embodiment.

[0059] <Source process (S1), lamination process (S2)> The lithium ion secondary battery 1, which is a cell battery, is first assembled in a source step (S1) by assembling a negative electrode plate 100, a positive electrode plate 110, and a separator 120 (inner separator 120) which are power generating elements. IN , outer separator 120 OUT ) respectively.

[0060] After the negative electrode plate 100, the positive electrode plate 110, and the separator 120 are produced in the source step (S1), the negative electrode plate 100 and the positive electrode plate 110 are then stacked with the separator 120 interposed therebetween in the stacking step (S2) to be integrated into a stack 10a.

[0061] <Winding process S3> In the winding step (S3), the laminate 10a thus produced is wound around the winding core 3 in the winding direction Z, as shown in Figures 7 and 8. When winding the laminate 10a around the winding core 3, as shown in Figure 7, the leading end of the laminate 10a is fixed to the winding core 3, and the laminate is wound while applying tension with a tension roller 5. The laminate 10a wound around the winding core 3 is pressed down with a pressure roller 4 to prevent it from loosening.

[0062] After a predetermined length of the laminate 10a has been wound around the winding core 3, the laminate 10a is cut at the end E of the laminate 10a. OUT is the longest, and the outer electrode plate 10 of this embodiment OUT The negative electrode plate 100 corresponding to the inner separator 120 is cut shorter than the negative electrode plate 100. IN The inner electrode plate 10 is cut to be sufficiently longer than the negative electrode plate 100 in order to sufficiently separate the negative electrode plate 100 from the positive electrode plate 110. IN The positive electrode plate 110 corresponding to the negative electrode plate 100 is cut to a length that faces the negative electrode plate 100.

[0063] Because of this cutting, the end portion behind the pressure roller 4 becomes a free end that is not subjected to tension by the tension roller 5. This free end, the laminate 10a, is then wound as the outermost periphery of the electrode assembly 10, and the end E is fixed to the electrode assembly 10 with adhesive tape (not shown) or the like, as shown in FIG. 4. However, compared to the tension applied by the tension roller 5, the winding force on the portion of the laminate 10a wound as the outermost periphery is weaker.

[0064] <Wound body pressing process (S4)> In the winding step (S3), the winding core 3 is pulled out from the laminate 10a wound around the winding core 3. The disk-shaped electrode body 10 from which the winding core 3 has been pulled out is shaped into a flat shape in the winding body pressing step (S4). In the winding body pressing step (S4), the electrode body 10 formed into such a wound body is pressed in the thickness direction D indicated by the arrow by the press surfaces 2a of a pair of opposing presses 2 as shown in FIG. 4. When pressed in the winding body pressing step (S4), the electrode body 10 takes on a shape roughly resembling a track used in athletics when viewed from the width direction W as shown in FIG. 4. In the winding body pressing step (S4), the electrode body 10 is pressed until it reaches a specified thickness [mm] so that it can be housed without gaps in the battery case 11 shown in FIG. 1.

[0065] FIG. 10 is a schematic view of the electrode assembly 10 after the winding press step (S4) has been completed, as viewed from the width direction W. After the winding press step (S4) has been completed, there are no gaps between the layers in the flat portion F by design. Therefore, the outer separator 120 OUT and inner separator 120 IN The separator 120 includes an outer electrode plate 10. OUT a negative electrode plate 100 including an inner electrode plate 10 IN There is no gap between the positive electrode plates 110 including the

[0066] <Configuration of curved section R> On the other hand, even after the winding press process (S4) is completed, there is not enough tension to wind the laminate 10a at its outermost periphery, and the flat portion F cannot absorb the slack, so that the slack affects the curved portion R, causing gaps to form between the layers.

[0067] The details will be described with reference to Fig. 10. The inner electrode plates 10 facing each other at the boundary between the flat portion F and the curved portion R IN The distance in the thickness direction D between the two layers is L [mm]. The separator 120 is located inside the outermost laminate 10a, but sufficient tension is applied up to this layer. Therefore, there are no gaps between the layers. In addition, the inner electrode plate 10 of the outermost laminate 10a that is in contact with this separator 120 IN In this case, the curved portion R can be considered to be roughly semicircular.IN The midpoint of the distance L in the thickness direction D between the curved part R is the center C of the semicircle. R Then, the inner electrode plate 10 IN is this center C R It becomes a semicircle with the center C R The distance in the length direction H along the center plane S is L / 2 [mm].

[0068] Next, the inner electrode plate 10 along this central plane S IN and inner separator 120 IN The distance to the inner electrode plate 10 along this center plane S is a [mm]. IN and outer separator 120 OUT Let the distance to be b [mm].

[0069] Here, the thickness of the separator 120 is k [mm]. In this embodiment, the inner separator 120 IN and outer separator 120 OUT The thickness of the outer electrode plate 10 is the same in k [mm]. OUT The thickness of the negative electrode plate 100 is set to 1 [mm].

[0070] <Adjusting the gap> 6 is a flowchart showing a procedure for equalizing the gaps between the layers of the laminate 10a wound at the outermost periphery on the center plane S. In order to equalize the resistance [Ω] at the flat portion F and the curved portion R, it is necessary to equalize the gaps between the layers of the laminate 10a wound at the outermost periphery on the center plane S at the curved portion R of the electrode body 10. Therefore, in this embodiment, a procedure for equalizing the gaps between the layers of the laminate 10a wound at the outermost periphery on the center plane S is performed.

[0071] First, after the winding pressing step (S4), the gaps between the layers are measured by X-ray inspection of the curved portion R (S10). IN and outer electrode 10 OUT Distance G R [mm], inner plate 10 in the central plane S IN and outer electrode 10 OUT Distance G FIn this embodiment, the outer separator 120 is measured (S11). OUT and inner electrode 10 IN Distance b [mm] and inner separator 120 IN and inner electrode 10 IN The difference (ba) [mm] between the distances a [mm] of the inner electrode plate 10 immediately inside is measured. IN and outer electrode 10 OUT Distance G R This procedure corresponds to the gap measurement step of the present invention. IN The thickness L [mm] of the inner separator 120 in the thickness direction D is also measured. IN and inner electrode 10 IN Distance a [mm], outer separator 120 OUT and inner electrode 10 IN The distance b [mm] between the separator 120 and the outer electrode plate 10 is also measured. OUT The thickness l [mm] of the negative electrode plate 100 has already been measured. This measurement is basically performed by 100% inspection, but if it is determined that the values ​​are sufficiently uniform between production lots, it may be performed by random inspection. In this embodiment, the thickness l [mm] of the inner electrode plate 10 at the curved portion R is measured. IN and outer electrode 10 OUT Distance G R Instead, measure the outer separator 120 [mm]. OUT and inner electrode 10 IN Distance b [mm] and inner separator 120 IN The difference in distance (ba) [mm] between the target and the target is used to determine whether it is within a specified range (S12).

[0072] Next, the inner electrode plate 10 at the curved portion R IN and outer electrode 10 OUT Distance G RThe measured value in the measurement of [mm] (S11) is compared with a preset threshold value and determined to be within a specified range (S12: YES). In this embodiment, the determination is made based on the gap between each layer of the outermost laminate 10a. If the gap between each layer of the outermost laminate 10a is ≦0.12 [mm], it is determined that there is no need to adjust the gap between each layer of the laminate 10a wound at the outermost periphery on the center plane S at the curved portion R of the electrode assembly 10, and the cell drying steps (S15, S6) are performed under normal conditions.

[0073] On the other hand, the inner electrode plate 10 in the curved portion R IN and outer electrode 10 OUT Distance G R If the measured value in the measurement of [mm] (S11) is greater than the threshold value, it is determined to be outside the specified range (S12: NO). In this embodiment, if the gap between each layer of the outermost laminate 10a is greater than 0.12 [mm], it is determined that the gap between each layer of the laminate 10a wound at the outermost periphery on the center plane S at the curved portion R of the electrode assembly 10 needs to be adjusted. Then, the temperature conditions in the cell drying step (S6) are changed to adjust the gap between each layer of the inner electrode plate 10 at the curved portion R. IN and outer electrode 10 OUT Distance G R The distance [mm] is reduced and a heating temperature T [°C] that eliminates the gap is set (S13). This procedure corresponds to the step of setting the heating temperature in this invention. Then, the procedure of heating at this set heating temperature T [°C] in the cell drying process (S14) corresponds to the step of heating in this invention.

[0074] <Cell drying temperature setting> Here, the temperature setting in the cell drying temperature setting (S13) will be explained in detail. The purpose of the cell drying temperature setting (S13) is as follows. The problem to be solved by the lithium ion secondary battery 1 and the method for manufacturing the lithium ion secondary battery 1 of the present invention is to optimize the gap between the layers of the laminate 10a to suppress Li deposition. To achieve this, it is necessary to optimize the gap between the layers of the laminate 10a. Specifically, it is necessary to optimize the gap between the inner separators 120 having different thermal shrinkage rates X [%]. IN and outer separator 120 OUTThe length is adjusted using the difference ΔX [%] in the thermal shrinkage rate X [%] so that there is no gap. The target heating temperature T [°C] at this time is the upper limit temperature T max [°C].

[0075] where: L [mm]: Opposing inner electrode 10 IN The thickness in the thickness direction D between k [mm]: thickness of separator 120, l[mm]: Outer plate 10 OUT (Negative electrode plate 100) thickness, a[mm]: Inner plate 10 IN and inner separator 120 IN Distance to, b[mm]: Inner plate 10 IN and outer separator 120 OUT Distance to, X IN : Inner separator 120 IN Heat shrinkage rate [%], X OUT :Outer separator 120 OUT Heat shrinkage rate [%], A IN [mm]: Inner separator 120 IN Half the circumference of the curved part R of A OUT [mm]:Outer separator 120 OUT Half the circumference of the curved part R of Let's say.

[0076] First, the inner separator 120 IN Half the circumference A of the curved part R IN To find the distance [mm], use the following formula (1).

[0077]

number

[0078] Also, the outer separator 120 OUT Half the circumference A of the curved part R OUT To find the distance [mm], use the following formula (2).

[0079]

number

[0080] Here, when the following (Equation 3) is satisfied, the inner separator 120 after the cell drying step (S6) IN Half the circumference A of the curved part R IN [mm] and outer separator 120 OUT Half the circumference A of the curved part R OUT As a result, the length of the inner separator 120 IN and outer separator 120 OUT Since the laminate 10a has elasticity, the layers are tightly adhered to each other so that there are no gaps between them, thereby optimizing the gaps between the layers of the laminate 10a.

[0081]

number

[0082] This (Equation 3) can be expressed as the following (Equation 4).

[0083]

number

[0084] Therefore, A calculated by (Equation 1) IN [mm] and A calculated using (Equation 2) OUT Substitute [mm] into the left side and find X that satisfies the right side. IN [%], X OUT Calculate the percentage. Next, find X that satisfies the right-hand side. IN [%], X OUT [%] Inner separator 120 IN and outer separator 120 OUT Calculate the heating temperature T [°C].

[0085] Figure 12 shows the change in X with heating temperature T [°C]. IN [%], XOUT Based on [%], (1-X OUT ) / (1-X IN ) is a graph showing the value of the heating temperature T [°C] on the horizontal axis and the value of (1-X OUT ) / (1-X IN ) value. As mentioned above, the right-hand side (1-X OUT ) / (1-X IN ) is calculated using Equation 1. IN [mm] and A calculated using (Equation 2) OUT By substituting [mm] into the left side, you can derive the numerical value.

[0086] Therefore, the vertical axis value is A IN [mm] and A OUT By reading the heating temperature T [°C] corresponding to the value derived from [mm], it is possible to derive the heating temperature T [°C] that satisfies (Equation 3).

[0087] By this procedure, it is possible to derive a heating temperature T [°C] that can optimize the gap between the layers of the laminate 10a. This heating temperature T [°C] is set based on the gap between each layer of the laminate 10a measured in the gap measurement step, so as to reduce the gap to a set value. This procedure is a specific example of the heating temperature setting step of the present invention.

[0088] <Assembly process (S5) to inspection process (S9)> Once the thickness of the electrode body 10 has been adjusted in the wound body pressing step (S4), an assembly step (S5) is performed. In the assembly step (S5), as shown in FIG. 1, a negative electrode current collector 13 and a positive electrode current collector 15 are attached to the electrode body 10, and further, a negative electrode external terminal 14 and a positive electrode external terminal 16 are attached via a lid 12. The electrode body 10 is then housed in a battery case 11. The lid 12 is then welded to the battery case 11 to seal the opening of the battery case 11. At this stage, the liquid injection port 18 of the lid 12 is open, so the cell is heated in a cell drying step (S6) to dry the inside of the cell. In the cell drying step (S6), the distance G RIf it is determined that the distance G is within the specified range (S12: YES), the cell is dried under normal temperature conditions (S15). R If it is determined that the temperature is outside the specified range (S12: NO), the temperature for the cell drying process is set (S13), and the cell drying process is performed so that the cell is heated at the set heating temperature T [°C] (S14, S6).

[0089] After the inside of the cell is dried in the cell drying step (S6), non-aqueous electrolyte 17 is poured in the liquid pouring and sealing step (S7), and the liquid pouring port 18 is sealed. This completes the assembly of the lithium ion secondary battery 1.

[0090] Then, an SEI film is formed by initial charging in the activation step (S8), and micro-short circuits are eliminated by storing the battery at high temperature for a long period of time in the aging step. Once this activation process (S8) is complete, the inspection process (S9) inspects the battery capacity [Ah], internal resistance [Ω], self-discharge [A / h], OCV [V], etc., and only those that pass are shipped as products.

[0091] (Action of this embodiment) <Example> Here, the operation of this embodiment will be described with reference to an example. FIG. 13 is a table showing the conditions used in the example. In the example, the thickness L of the opposing flat portion F in the thickness direction D was 12.00 mm, the thickness k of the separator 120 was 0.02 mm, and the negative electrode plate 100 (outer electrode plate 10 OUT The thickness l of the positive electrode plate 110 (inner electrode plate 10) was set to 0.10 [mm]. IN ) and inner separator 120 IN Distance a = 0.11 [mm], positive electrode plate 110 (inner electrode plate 10 IN ) and outer separator 120 OUT The distance a between the inner separator 120 and the curved portion R was set to 0.11 [mm]. IN Half the circumference of A IN =19.02, (Equation 2) shows that the outer separator 120 at the curved portion R OUT Half the circumference of A OUT =19.77.

[0092] Then, from (Equation 4), A IN / A OUT =0.9621. Next, Figure 12 shows the relationship between the heating temperature T [°C] and (1- XIN ) / (1-X OUT ) is a graph showing the relationship between

[0093] Here, the vertical axis (1- XIN ) / (1-X OUT )=0.9621, it can be seen that the heating temperature T on the horizontal axis at that time is 144 [°C]. Therefore, in this embodiment, if the cell is dried at a heating temperature T=144 [°C] in the cell drying step (S6), the inner separator 120 IN and outer separator 120 OUT In practice, the elasticity of the separator 120 allows the gap between each layer of the laminate 10a to be 0 mm.

[0094] 14 is a table comparing the gaps [mm] between the layers of the outermost layer laminate 10a and the Li deposition resistance of an example of this embodiment, comparative example 1, and comparative example 2, in which the heating temperature T [°C] was changed. In the example, the cell drying temperature (heating temperature T) [°C] was set to 144 [°C], so the inner separator 120 of the curved portion R after the cell drying IN and outer separator 120 OUT As a result, the gap between the layers of the outermost laminate 10a was 0 mm. IN The positive electrode current collecting foil 111 (positive electrode plate 110) and the outer electrode plate 10 made of Cu OUT The negative electrode current collector foil 101 (negative electrode plate) hardly shrinks due to heat. IN and outer separator 120 OUT By reducing the length of the heat shrinkage, the gap [mm] between the layers of the outermost layer laminate 10a is reduced to almost zero. IN and outer separator 120 OUT The inner electrode plate is made of Al. IN(positive electrode plate 110) and an outer electrode plate 10 made of Cu OUT Unlike the negative electrode plate, the negative electrode plate has elasticity, which allows it to absorb slight dimensional differences and make the gaps [mm] between the layers of the outermost laminate 10a close to zero.

[0095] By making the gap [mm] between each layer of the outermost laminate 10a close to zero, the electrical resistance [Ω] in the flat portion F and the curved portion R of the electrode body 10 becomes uniform, and the current density [Ah / mm 2 ] unevenness does not occur. Therefore, it is possible to avoid localized metallic Li deposition potential [V], thereby improving the so-called Li deposition resistance, i.e., the difficulty of metallic Li deposition (in this embodiment, this refers to the height of the critical voltage OCV [V] at which metallic Li does not deposit). Regarding Li deposition resistance, a critical voltage OCV [V] at which metallic Li does not deposit is higher than the standard, a "○" is indicated; a voltage lower than the standard but deemed within a practical range is indicated as a "△," and a voltage lower than the standard but deemed within a practical range is indicated as an "×." The deposition of metallic Li was determined visually using a micrograph. In other words, a battery that did not deposit metallic Li at a predetermined high SOC state, for example, near an SOC of 100 [%], was indicated as an "○." Furthermore, a battery that partially deposited metallic Li but did not pose a practical problem was indicated as a "△," and a battery that caused metallic Li deposition to pose a practical problem was indicated as an "×."

[0096] In Comparative Example 1, the cell drying temperature (heating temperature T) [°C] was set to 130 [°C]. In this case, the gap [mm] between each layer of the outermost laminate 10a after the cell drying was 0.12 [mm]. Therefore, the resistance between the positive electrode plate 110 and the negative electrode plate 100 at the curved portion R was larger than that at the flat portion F, and the Li deposition resistance was reduced, resulting in an evaluation of "Fair."

[0097] In Comparative Example 2, the cell drying temperature (heating temperature T) [°C] was set to 100 [°C]. In this case, the gap [mm] between each layer of the outermost laminate 10a after the cell drying was 0.20 [mm]. Therefore, the resistance between the positive electrode plate 110 and the negative electrode plate 100 at the curved portion R was even larger than that at the flat portion F, and the Li deposition resistance was reduced, resulting in an evaluation of "X".

[0098] Here, as shown in FIG. 11, in this embodiment, when the heating temperature T [°C] is 144 [°C], the outer separator 120 OUT Heat shrinkage rate X OUT and inner separator 120 IN Heat shrinkage rate X IN The difference between 144 Therefore, the inner separator 120 IN Half the circumference of A IN [mm] and outer separator 120 at curved section R OUT Half the circumference of A OUT It was found that the difference in length between [mm] and [mm] could be sufficiently reduced.

[0099] On the other hand, in Comparative Example 1, when the heating temperature T is 130°C, the outer separator 120 OUT Heat shrinkage rate X OUT and inner separator 120 IN Heat shrinkage rate X IN The difference between 130 Therefore, the inner separator 120 at the curved portion R IN Half the circumference of A IN [mm] and outer separator 120 at curved section R OUT Half the circumference of A OUT It was found that the difference in length between [mm] could not be sufficiently reduced.

[0100] Furthermore, in Comparative Example 2, when the heating temperature T is 100°C, the outer separator 120 OUT Heat shrinkage rate X OUT and inner separator 120 IN Heat shrinkage rate X IN The difference between 100 Therefore, the inner separator 120 at the curved portion R IN Half the circumference of A IN [mm] and outer separator 120 at curved section R OUT Half the circumference of A OUTIt was found that the difference in length between [mm] could hardly be reduced.

[0101] From the comparison between the Example, Comparative Example 1, and Comparative Example 2, it was found that by setting an appropriate heating temperature T [°C], the outer separator 120 OUT Heat shrinkage rate X OUT and inner separator 120 IN Heat shrinkage rate X IN By doing so, it is possible to make the gap between each layer of the laminate 10a close to 0 [mm]. On the other hand, if the heating temperature T [°C] is not appropriate, it is not possible to make the gap between each layer of the laminate 10a close to 0 [mm], and it has been found that precipitation of metallic Li occurs.

[0102] (Effects of this embodiment) (1) The lithium ion secondary battery 1 and the method for manufacturing the lithium ion secondary battery 1 according to the present embodiment have the advantage of optimizing the gaps between the layers of the laminate 10a, thereby suppressing Li deposition.

[0103] (2) By utilizing the fact that the separator 120 irreversibly thermally shrinks the gaps between layers of Al foil or Cu foil, which do not irreversibly thermally shrink, it is possible to optimize the gaps between layers of the laminate 10a and suppress Li precipitation.

[0104] (3) Inner separator 120 IN Heat shrinkage rate X in winding direction Z IN From [%], outer separator 120 OUT Heat shrinkage rate X in winding direction Z OUT Therefore, the outer separator 120 at the curved portion R OUT Heat shrink the inner separator 120 IN A more appropriate heating temperature T [°C] reduces the gaps between the layers of the laminate 10a, thereby suppressing Li deposition.

[0105] (4) The method for manufacturing the lithium-ion secondary battery 1 of this embodiment includes a gap measurement step (FIG. 6: S10, S11) for measuring the gap between each layer of the laminate 10a wound at the outermost periphery on the center plane S parallel to the flat portion F including the winding axis C, at the curved portion R of the electrode body 10. This has the effect of enabling an appropriate correction amount to be calculated based on the measurements of the flat portion F and the curved portion R.

[0106] (5) The method further includes a heating temperature setting step (FIG. 6: S13) for setting the heating temperature T [°C] so as to reduce the gap between each layer of the laminate 10a to a set value based on the gap between the layers measured in the gap measurement step (FIG. 6: S10, S11). IN Heat shrinkage rate X IN [%] and outer separator 120 OUT Heat shrinkage rate X OUT By using [%], the gap between the layers of the laminate 10a can be optimized, thereby suppressing Li deposition.

[0107] (6) In the heating temperature setting step (FIG. 6: S13), there is an effect that the appropriate heating temperature T [°C] can be easily calculated based on (Equation 1) to (Equation 4). In these (Equation 1) to (Equation 4), IN and outer electrode 10 OUT The gap between the inner separator 120 and the IN and outer separator 120 OUT The distance (ba) is then considered to be the distance between the inner separator 120 and the inner separator 120. IN and outer separator 120 OUT The difference in distance (ba) between the inner separator 120 and the outer separator 120 is made close to zero. This makes it possible to optimize the gap between the layers of the laminate 10a. IN and outer separator 120 OUT This has the effect that, since it has elasticity, some dimensional errors can be absorbed.

[0108] (7) A heating step (FIG. 6: S14) is provided in which heating is performed at the heating temperature T [°C] set in the heating temperature setting step (FIG. 6: S13). Therefore, simply by heating at the set heating temperature T [°C], it is possible to optimize the gap between the layers of the laminate 10a and suppress Li precipitation.

[0109] (8) The heating step (S14 in Fig. 6) is performed during the cell drying process (S6 in Fig. 5), which has the advantage of being easy to implement without increasing the number of steps in the conventional manufacturing process and without requiring any additional equipment other than a gap or measuring device.

[0110] (Variation) The above embodiment is an example of the implementation of the present invention, and can be implemented with the following modifications.

[0111] In the heating step (S13) of this embodiment, the upper limit temperature T max The procedure is performed at [°C]. However, in the heating step of the present invention, if the gaps between the layers of the laminate 10a are reduced to a certain extent, the effect of suppressing Li precipitation can be expected. Therefore, it is not necessary to inspect every product, and the gap measurement step can be performed for each production lot, or the heating step can be performed uniformly for products of the same type.

[0112] In the gap measurement step (S11) of this embodiment, the outer separator 120 OUT and inner electrode 10 IN Gap b [mm] and inner separator 120 IN and inner electrode 10 IN The difference (ba) [mm] between the distances a [mm] of the inner electrode plate 10 immediately inside is measured. IN and outer electrode 10 OUT Distance G R Of course, the inner electrode plate 10 in the curved portion R is indirectly measured. IN and outer electrode 10 OUT Distance G R[mm], inner plate 10 in the central plane S IN and outer electrode 10 OUT Distance G F [mm] may be measured directly.

[0113] In this embodiment, if the gap between the layers of the laminate 10a is outside the specified range, the target is to reduce the gap to zero. However, if the gap between the layers of the laminate 10a is reduced, the effect of suppressing Li precipitation is achieved. Therefore, it is not necessarily necessary to target zero gap between the layers of the laminate 10a.

[0114] In this embodiment, an X-ray inspection is performed after the winding pressing process (FIG. 6: S10). IN and outer electrode 10 OUT Distance G R The measurement method is not limited as long as it can be measured. IN and outer electrode 10 OUT Distance G R In other words, in the gap measurement step (FIG. 6: S10) of this embodiment, the direct distance G R It is not necessary to measure it, and it can be estimated from previous measurements.

[0115] In the heating step (S13) of this embodiment, the procedure is performed by setting the set temperature in the cell drying step (S6) to the heating temperature T [°C]. This heating step (S13) can also be performed by providing a heating step separate from the cell drying step (S6).

[0116] In this embodiment, the lithium ion secondary battery 1, which is a plate-shaped cell battery for vehicle use, is used as an example of a non-aqueous electrolyte secondary battery. However, the present invention is not limited to this and can be applied to other uses such as stationary use.

[0117] The drawings are for use in explaining the present embodiment, and are not intended to be limiting, as some figures may be omitted or dimensional balance may be exaggerated for clarity.

[0118] The flowcharts shown in FIGS. 5 and 6 are examples of the present invention, and steps can be added, deleted, changed in order, or interchanged. Various numerical values ​​and ranges are merely examples and can be optimized and implemented by those skilled in the art.

[0119] The composition and material properties of the separator 120 are merely examples of the present invention and can be optimized by those skilled in the art. This embodiment is one embodiment of the present invention, and it goes without saying that those skilled in the art can add, delete, or modify the configuration without being limited to the embodiment, as long as it does not deviate from the scope of the claims. [Explanation of symbols]

[0120] C... Winding shaft C R …Center of curved section R Z…winding direction H: Lengthwise direction W…Width direction (winding axis direction) D: Thickness direction F...Flat area R... (a pair of semi-cylindrical curved sections formed by winding both ends of the flat section) S…Central plane E...Terminal G[mm]…Inner electrode plate 10 IN and outer electrode 10 OUT Distance from G R [mm]…Inner electrode plate 10 at curved section R IN and outer electrode 10 OUT Distance from G F [mm]…Inner pole plate 10 at center plane S IN and outer electrode 10 OUT Distance from X...Heat shrinkage rate [%] X IN …Inner separator 120 IN Heat shrinkage rate [%] X OUT …Outer separator 120 OUT Heat shrinkage rate [%] ΔX [%]...(Difference in thermal shrinkage rate X [%]) SR[%]…Stretching rate a [mm]…Inner separator 120 IN and inner electrode 10 IN Distance b [mm]…Outer separator 120 OUT and inner electrode 10 IN Distance L [mm]... Opposing inner pole plate 10 IN Thickness in the thickness direction D between k [mm]…Separator thickness l[mm]…Outer plate 10 OUT Thickness of (negative electrode plate 100) T[°C]…Heating temperature T1[°C]…Heating temperature T max [°C]…Upper temperature limit A IN [mm]…Inner separator 120 IN Half the circumference of the curved part R A OUT [mm]…Outer separator 120 OUT Half the circumference of the curved part R 1...Lithium-ion secondary battery 2...Press machine 2a...Press surface 3...spool core 4...Pressure roller 5...Tension roller 10...Electrode body 10a...Laminate 10 IN …Inner electrode plate 10 OUT …outer plate 120 IN …Inner separator 120 OUT …Outer separator 11...Battery case 12...lid body 13...Negative electrode current collector 14...Negative external terminal 15...Positive electrode current collector 16...Positive external terminal 17...Nonaqueous electrolyte 18...Filling port 100...Negative electrode plate 101...Negative electrode current collecting foil 102...Negative electrode composite material layer 103...Negative electrode connection part 110...Positive electrode plate 111...Positive current collector foil 112...Positive electrode mixture layer 113...Positive electrode connection part 120...Separator

Claims

1. A lithium ion secondary battery including an electrode assembly formed by winding a laminate in which a positive electrode plate and a negative electrode plate are stacked with a separator interposed therebetween and pressing the laminate into a flat shape, the laminate wound around the outermost periphery of the electrode assembly includes an innermost electrode plate, an inner separator on the outer periphery of the inner electrode plate, an outer electrode plate on the outer periphery of the inner separator, and an outer separator on the outer periphery of the outer electrode plate; The thermal shrinkage rate X of the inner separator in the winding direction Z ＩＮ From [%], the thermal shrinkage rate X of the outer separator in the winding direction is ＯＵＴ A lithium-ion secondary battery characterized in that [%] is set to be large.

2. A method for manufacturing a lithium ion secondary battery including an electrode body that is press-shaped into a flat shape so as to form a flat portion and curved portions wound at both ends of the flat portion, the method comprising: winding a laminate in which a positive electrode plate and a negative electrode plate are stacked with a separator interposed therebetween and fixing an end of the laminate; the laminate wound around the outermost periphery of the electrode assembly includes an innermost electrode plate, an inner separator on the outer periphery of the inner electrode plate, an outer electrode plate on the outer periphery of the inner separator, and an outer separator on the outer periphery of the outer electrode plate; The thermal shrinkage rate X of the inner separator in the winding direction ＩＮ From [%], the thermal shrinkage rate X of the outer separator in the winding direction is ＯＵＴ In a lithium-ion secondary battery where [%] is set to be large, a gap measurement step of measuring gaps between layers of the laminate wound on the outermost periphery on a center plane S parallel to the flat portion including a winding axis in the curved portion of the electrode body; a heating temperature setting step of setting a heating temperature T [°C] based on the gap between each layer of the laminate measured in the gap measurement step so as to reduce the gap to a set value; a heating step of heating at the heating temperature T [°C] set in the heating temperature setting step; A method for manufacturing a lithium ion secondary battery, comprising:

3. The heating temperature setting step is performed by setting the upper limit temperature T ｍａｘ 3. The method for manufacturing a lithium ion secondary battery according to claim 2, wherein the heating temperature T [°C] is set with an upper limit of 100°C.

4. The method for manufacturing a lithium ion secondary battery described in claim 2, characterized in that the heating temperature setting step sets the heating temperature T [°C] within a range of temperatures T [°C] such that the gap between each layer of the laminate measured in the gap measurement step is within a predetermined allowable range.

5. In the step of setting the heating temperature, the upper limit temperature T ｍａｘ [°C], In the curved portion R of the electrode body, Thickness in the thickness direction between the opposing inner electrode plates: L [mm], The thickness of the separator: k [mm], The thickness of the outer electrode plate: 1 [mm], The distance between the inner electrode plate and the outer separator on the center plane S: b [mm], The distance between the inner electrode plate and the inner separator on the center plane S: a [mm], The heat shrinkage rate of the inner separator is: X ＩＮ [%], The heat shrinkage rate of the outer separator is: X ＯＵＴ [%], Half the circumference of the curved portion R of the inner separator: A ＩＮ , Half the circumference of the curved portion R of the outer separator: A ＯＵＴ When A ＩＮ is expressed by the following (Equation 1): [Equation 1] A ＯＵＴ is expressed by the following (Equation 2): [Equation 2] When the temperature T is expressed as X, the thermal shrinkage rate [%] of the outer separator at a predetermined temperature T [°C] is ＯＵＴ [%], the heat shrinkage rate [%] of the inner separator is X ＩＮ When set to [%], [Equation 3] The temperature T [°C] that satisfies the upper limit temperature T ｍａｘ 4. The method for manufacturing a lithium ion secondary battery according to claim 3, wherein the temperature is set as [°C].

6. The thermal shrinkage rate X of the inner separator in the winding direction ＩＮ From [%], the thermal shrinkage rate X of the outer separator in the winding direction is ＯＵＴ The difference ΔX [%] between the heat shrinkage rates X [%] set so that the difference ΔX [%] between the heat shrinkage rates X [%] in the winding direction of the inner separator is larger than the difference ΔX [%] between the heat shrinkage rates X [%] in the winding direction of the inner separator so that the heating temperature T [°C] set in the heating temperature setting step is within a temperature range [°C] that allows heating in advance in the manufacturing process of the lithium ion secondary battery. ＩＮ [%] and the thermal shrinkage rate X of the outer separator in the winding direction ＯＵＴ 4. The method for manufacturing a lithium ion secondary battery according to claim 3, wherein the ratio of the total number of lithium ion batteries to the total number of lithium ion batteries is 1 / 2.

7. 3. The method for manufacturing a lithium ion secondary battery according to claim 2, wherein the heating step is a cell drying step for the lithium ion secondary battery.

8. If the gap between the inner electrode plate and the outer electrode plate measured in the gap measurement step is within a preset tolerance range, the heating temperature setting step is omitted, and the cell drying step is performed at a preset heating temperature T ０ 8. The method for producing a lithium ion secondary battery according to claim 7, wherein the heating is performed at a temperature of [°C].

9. 9. The method for producing a lithium ion secondary battery according to claim 2, wherein the inner electrode plate is a positive electrode plate and the outer electrode plate is a negative electrode plate.

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