Secondary battery

Abstract

Provided is a secondary battery including an electrode stack in which a plurality of electrodes are stacked with a separator interposed therebetween, each of the electrodes having an electrode active material layer applied to at least one face of a sheet-shaped current collector, each of the electrodes including a current collector tab that is not provided with the electrode active material layer and that protrudes in a second direction that intersects the first direction, the current collector tab being provided with an insulating layer on a face that faces the first direction, the insulating layer including a protruding portion that protrudes toward the separator, the insulating layer including the protruding portion having a thickness that is less than a thickness of the electrode active material layer.

Description

Technical Field

[0001] The technology disclosed in this specification relates to secondary batteries. Background Technology

[0002] Japanese Patent Application Publication No. 2023-530514 discloses an electrode comprising an electrode current collector coated with an electrode active material, an electrode tab protruding from the electrode current collector, and an insulating layer coated on the electrode tab, the other side of the electrode tab coated with the insulating layer being soldered to an electrode lead.

[0003] Japanese Patent Application Publication No. 2018-45952 discloses a method for manufacturing an electrode having a coated portion on which an active material layer is formed and an uncoated portion on which no active material layer is formed. This manufacturing method includes the step of forming an insulating resin layer across the coated portion and the uncoated portion. Summary of the Invention

[0004] Secondary batteries include an electrode stack consisting of alternating layers of electrodes and a separator, on which an electrode active material layer is coated on a current collector. Conventionally, in such electrode stacks, a problem arises where the relative position of the separator and electrodes shifts in a direction intersecting the stacking directions of the electrodes and separator. Neither Japanese Patent Application Publication No. 2023-530514 nor Japanese Patent Application Publication No. 2018-45952 discloses a method for suppressing such positional shift.

[0005] In view of this problem, this specification provides techniques useful for suppressing the aforementioned positional shifts.

[0006] This specification discloses a secondary battery. The secondary battery includes an electrode stack formed by stacking multiple electrodes along a first direction with a separator sandwiched between them. At least one side of each electrode has an electrode active material layer coated with it. Each electrode has a current collector tab that protrudes in a second direction intersecting the first direction, without the electrode active material layer coated on it. The current collector tab has an insulating layer on its side facing the first direction. The insulating layer has a protrusion protruding toward the separator. The thickness of the insulating layer including the protrusion is less than the thickness of the electrode active material layer.

[0007] According to the aforementioned structure, the protrusions in the insulating layer formed on the collector tab hook or sink into the diaphragm. This suppresses the aforementioned positional shift. Attached Figure Description

[0008] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same elements, and wherein:

[0009] Figure 1This is a cross-sectional view of a secondary battery;

[0010] Figure 2 This is an exploded three-dimensional view of the electrode stack;

[0011] Figure 3 This is a cross-sectional view showing a portion of an electrode stack containing a positive current collector tab;

[0012] Figure 4 This is a diagram showing the positive collector tab and its surroundings from a viewpoint parallel to the Z-axis; and

[0013] Figure 5 This is a cross-sectional view showing a portion of an electrode stack including a positive current collector tab, and it shows the relationship with... Figure 3 Diagrams showing different examples. Detailed Implementation

[0014] The main features of the embodiments described below are listed. These features can be combined arbitrarily.

[0015] According to the secondary battery disclosed in this specification, the aforementioned protrusion may also be formed at the end of the aforementioned insulating layer in the aforementioned second direction on the side away from the aforementioned electrode active material layer.

[0016] According to the aforementioned structure, by utilizing the protrusion formed at the aforementioned end when forming an insulating layer on the collector ear, the aforementioned positional shift can be suppressed.

[0017] According to the secondary battery disclosed in this specification, the aforementioned protrusion may also be formed continuously along the width direction of the aforementioned collector tab that intersects the aforementioned first direction and the aforementioned second direction.

[0018] According to the aforementioned structure, the hooking of the protrusion relative to the diaphragm can be further enhanced, and the aforementioned positional displacement can be further suppressed.

[0019] According to the secondary battery disclosed in this specification, the aforementioned protrusion may also be a shape that tapers towards the top.

[0020] According to the aforementioned structure, the protrusion can easily bite into the diaphragm, which can further suppress the aforementioned positional displacement.

[0021] According to the secondary battery disclosed in this specification, the aforementioned electrode stack may also be formed by alternately stacking the aforementioned positive electrode and the aforementioned negative electrode in the aforementioned first direction with the aforementioned separator sandwiched between them. The aforementioned positive electrode has a positive current collector tab as the aforementioned current collector tab, and the aforementioned negative electrode has a negative current collector tab as the aforementioned current collector tab. Furthermore, the aforementioned positive current collector tab may also have the aforementioned insulating layer.

[0022] According to the aforementioned structure, the insulating layer of the positive collector tab can prevent short circuits between the positive collector tab and the negative electrode caused by foreign objects.

[0023] The embodiments will be described with reference to the accompanying drawings. The drawings are merely illustrative, and the embodiments are not limited to the content shown. Furthermore, since the drawings are illustrative, some parts have been omitted.

[0024] Figure 1 A cross-section of the secondary battery 10 is shown in a simplified manner. The secondary battery 10 is, for example, a rechargeable lithium-ion battery. The secondary battery 10 includes an electrode stack 16, which is formed by stacking a plurality of electrodes 12 along a first direction with a separator 14 sandwiched between them. Figure 2 The electrode stack 16 is simply shown in an exploded perspective view. Electrode 12 is the positive electrode 20 and the negative electrode 30.

[0025] The secondary battery 10 has a flexible outer casing (not shown), and an electrode stack 16 is sealed inside the casing. An electrolyte (not shown) is sealed inside the casing. The outer casing is, for example, a laminate. In the figures, for ease of explanation, mutually orthogonal X-axis, Y-axis, and Z-axis are shown. The Z-axis direction (Z-axis + direction and Z-axis - direction) corresponds to the first direction. The first direction may also be referred to as the stacking direction. Figure 1 It is a cross-sectional view of a section orthogonal to the Y-axis.

[0026] like Figure 1 and Figure 2 As shown, the electrode stack 16 is formed by alternately stacking generally rectangular positive electrodes 20 and generally rectangular negative electrodes 30 between a zigzag strip-shaped diaphragm 14 that repeatedly undergoes folds and bends. In this case, multiple positive electrodes 20 are sandwiched between one of the two sides of the diaphragm 14, and multiple negative electrodes 30 are sandwiched between the other two sides of the diaphragm 14. The positive electrodes 20 and negative electrodes 30 extend along the X-axis and Y-axis directions, respectively.

[0027] The separator 14 is formed of a material that combines the permeability to allow the movement of charge carriers (in this case, lithium ions) during charging and discharging, with the insulating properties to prevent short circuits caused by the contact between the positive electrode 20 and the negative electrode 30. Examples of materials for the separator 14 include polypropylene and polyethylene. Figure 1 , Figure 2 As shown, the structure in which the tortuous, continuous diaphragm 14 is sandwiched between the electrodes 12 is just one example. The diaphragms 14 sandwiched between the electrodes 12 can also be separated from each other. In any case, the electrode stack 16 is formed by alternately stacking the positive electrode 20 and the negative electrode 30 in the first direction with the diaphragms 14 sandwiched between them.

[0028] Electrode 12 has a sheet-like current collector and an electrode active material layer coated on at least one side of the current collector. According to... Figure 2 The positive electrode 20 includes a positive current collector 22 and a positive active material layer 24 coated on the positive current collector 22. The positive active material layer 24 is coated on both sides of the positive current collector 22, for example. The positive current collector 22 is, for example, aluminum foil. The positive active material layer 24 contains a positive active material. Examples of positive active materials include lithium nickel composite oxides, lithium cobalt composite oxides, and lithium manganese composite oxides.

[0029] The negative electrode 30 includes a negative current collector 32 and a negative active material layer 34 coated on the negative current collector 32. The negative active material layer 34 is coated on both sides of the negative current collector 32, for example. The negative current collector 32 is, for example, copper foil. The negative active material layer 34 contains a negative active material. Examples of negative active materials include carbon materials such as graphite, hard carbon, and soft carbon; materials that form alloys with lithium, such as silicon (Si); and lithium alloys. The electrode active material can be composed of a single type of material or multiple materials. The electrode active material layer may contain conductive additives, binders, etc.

[0030] The area of ​​the electrodes 12 (positive electrode 20, negative electrode 30) on which electrode active material layers (positive electrode active material layer 24, negative electrode active material layer 34) are coated on the current collector is called the coated area, and the area on the current collector on which no electrode active material layer is coated is called the uncoated area. Each electrode 12 has a current collector tab 18 protruding in a second direction intersecting the first direction. The Y-axis direction (Y-axis + direction and Y-axis - direction) corresponds to an example of the second direction.

[0031] according to Figure 2 The uncoated portion of the positive current collector 22 protrudes in the Y-axis + direction. This protruding uncoated portion is the current collector tab 18 of the positive electrode 20, i.e., the positive current collector tab 26. Furthermore, according to... Figure 2 The uncoated portion of the negative current collector 32 protrudes in the Y-axis direction. This protruding uncoated portion is the current collector tab 18 of the negative electrode 30, i.e., the negative current collector tab 36. The positive current collector tab 26 and the negative current collector tab 36 protrude outward from each other in opposite directions, to a position further outward than the area sandwiched by the diaphragm 14.

[0032] The positive electrode current collector 26 can be an extension of the positive electrode current collector 22, or it can be a tab-shaped metal foil joined to the uncoated portion of the positive electrode current collector 22 by welding or the like. Similarly, the negative electrode current collector 36 can be an extension of the negative electrode current collector 32, or it can be a tab-shaped metal foil joined to the uncoated portion of the negative electrode current collector 32 by welding or the like. The positive electrode current collector 26 of each of the plurality of positive electrodes 20 is electrically connected to a positive terminal (not shown). The negative electrode current collector 36 of each of the plurality of negative electrodes 30 is electrically connected to a negative terminal (not shown).

[0033] Figure 3 A portion of the electrode stack 16, including the positive current collector tab 26, is shown in a cross-section orthogonal to the X-axis. Positive active material layers 24 are formed on both sides of the positive current collector 22. The positive active material layers 24 are in contact with the separator 14. Negative active material layers 34 are formed on both sides of the negative current collector 32. The negative active material layers 34 are in contact with the separator 14. The current collector tab 18 has an insulating layer 40 on its surface facing the first direction. Figure 3 In this diagram, for ease of observation, the shading line representing the cross-section of the insulating layer 40 is omitted. According to... Figure 3 An insulating layer 40 is formed on both sides of the positive electrode current collector 26, specifically on each side of the positive electrode current collector 26 facing the Z-axis + direction and the Z-axis - direction. The insulating layer 40 is formed of an insulating material such as resin. For example, the insulating layer 40 is formed by coating an insulating material onto the current collector 18 in a step following the process of coating an electrode active material layer onto the current collector, or in parallel with the process of coating an electrode active material layer onto the current collector. The insulating layer 40 and the side surface of the positive electrode active material layer 24 (on Figure 3 The middle part (facing the Y-axis + direction) is connected to the side, and there is no gap between the insulating layer 40 and the positive electrode active material layer 24.

[0034] Figure 4 The positive collector tab 26 and its surroundings are shown from a viewpoint parallel to the Z-axis. Figure 4 In the diagram, the membrane 14, stacked together with the electrodes 12 (positive electrode 20, negative electrode 30), is shown with a double-dotted line; the negative electrode 30 is shown with a single-dotted line; and the positive electrode 20 is shown with a solid line. Additionally, in... Figure 4 In the text, the insulation layer 40 is marked in easily understandable gray. According to... Figure 3 , Figure 4 The forming range A of the insulating layer 40 in the Y-axis direction relative to the positive electrode collector tab 26 converges to the range overlapping with the diaphragm 14. In other words, the insulating layer 40 is not formed in the range of the positive electrode collector tab 26 that protrudes outward from the diaphragm 14. Figure 4 The insulating layer 40 formed in the width direction (X-axis direction) of the positive electrode collector 26 is the entire range of the collector.

[0035] The insulating layer 40 has a protrusion 42 protruding toward the diaphragm 14. The thickness of the insulating layer 40 including the protrusion 42 is less than that of the electrode active material layer. Figure 3The thickness of the positive electrode active material layer 24 is shown in the figure. In this embodiment, the thickness refers to the thickness in the Z-axis direction. On one side of the positive electrode current collector 22, for example, when the thickness of the positive electrode active material layer 24 is set to 50 μm to 60 μm, the thickness of the insulating layer 40 including the protrusion 42 is 8 to 10 μm, and the thickness of the insulating layer 40 other than the protrusion 42 is about 4 μm.

[0036] according to Figure 3 , Figure 4 The protrusion 42 of the insulating layer 40 is formed at the end 44 of the insulating layer 40 in the second direction (Y-axis direction), on the side away from the electrode active material layer (positive electrode active material layer 24). Furthermore, according to... Figure 4 The protrusion 42 is continuously formed along the width direction (X-axis direction) of the positive electrode collector ear 26.

[0037] exist Figure 3 In the shown state, the tip of the protrusion 42 is separated from the separator 14. However, since the separator 14 and the current collector are flexible, when the electrode 12 and the separator 14 are alternately stacked to form the electrode stack 16, the portions of the insulating layer 40 and the separator 14 opposite to the insulating layer 40 approach each other, or one approaches the other, and the tip of the protrusion 42 can contact the separator 14. Therefore, according to this embodiment, the protrusion 42 of the insulating layer 40 formed on the current collector tab 18 hooks or gets stuck in the separator 14. As a result, the relative positional shift between the separator 14 and the electrode 12 can be suppressed. As a result, the positional shift between the electrodes 12, i.e., the positive electrode 20 and the negative electrode 30, is also suppressed, and the performance of the secondary battery 10 is improved.

[0038] The thickness of the insulating layer 40, including the protrusion 42, is smaller than the thickness of the electrode active material layer, so the contact between the electrode active material layer and the diaphragm 14 is not hindered by the protrusion 42.

[0039] When an insulating material is applied to the collector tab 18 to form an insulating layer 40, due to the interfacial tension of the material, a bulge is formed at the end 44 of the insulating layer 40, which becomes a protrusion 42. Therefore, this specification includes the idea of ​​using the protrusion 42 formed at the end 44 to suppress the positional displacement of the diaphragm 14 and the electrode 12 during the formation of the insulating layer 40.

[0040] like Figure 3 As shown, the protrusion 42 can also be tapered towards the tip. By making the protrusion 42 tapered towards the tip, the protrusion 42 can easily engage with the diaphragm 14, further suppressing the aforementioned positional shift.

[0041] according to Figure 3 , Figure 4 The insulating layer 40, in the Y-axis direction relative to the positive electrode collector tab 26, extends outwards than the negative electrode 30. According to... Figure 1 , Figure 3 , Figure 4 In both the X and Y axes, the size of the positive electrode 20, excluding the positive collector tab 26, is smaller than the size of the negative electrode 30, excluding the negative collector tab 36. Figure 2 , Figure 3 As can be seen, in the negative electrode 30, the negative electrode collector tab 36 protrudes from the end facing the Y-axis, and in the positive electrode 20, the positive electrode collector tab 26 protrudes from the end facing the Y-axis. In this structure, the forming range A of the insulating layer 40 extends outward from the end of the negative electrode 30 facing the Y-axis. Furthermore, the end 44 and the protrusion 42 of the insulating layer 40 are located further outward than the end of the negative electrode 30 facing the Y-axis. By forming the insulating layer 40 on the positive electrode collector tab 26, short circuits between the positive electrode collector tab 26 and the negative electrode 30 via foreign objects can be prevented.

[0042] The shape of the protrusion 42 in the insulating layer 40 is not limited to the shape described above. For example, the protrusion 42 may also be formed in the insulating layer 40 at a position other than the end 44. The protrusion 42 may also be formed at multiple positions in the insulating layer 40. For example, the protrusion 42 may also be formed discontinuously in the width direction (X-axis direction) of the positive electrode collector tab 26.

[0043] Figure 5 and Figure 3 Similarly, a portion of the electrode stack 16 containing the positive current collector tab 26 is shown using a section orthogonal to the X-axis. Regarding Figure 5 , omission and Figure 3 Common explanation. According to Figure 5 The insulating layer 40 has a plurality of protrusions 42 protruding toward the diaphragm 14. The plurality of protrusions 42 are separated from each other in the X-axis direction and / or Y-axis direction. In the process of forming the insulating layer 40 on the collector tab 18, for example, by performing a process to roughen the surface of the insulating layer 40 to make the surface uneven, a plurality of hook-shaped protrusions 42 can be formed.

[0044] In this embodiment, an insulating layer 40 including the protrusion 42 can be formed only on the positive electrode collector 26 of the positive electrode collector 26 and the negative electrode collector 36. Alternatively, an insulating layer 40 including the protrusion 42 can be formed on both the positive electrode collector 26 and the negative electrode collector 36. The description of the insulating layer 40 and the protrusion 42 formed on the negative electrode collector 36 also applies to the description of the insulating layer 40 and the protrusion 42 formed on the positive electrode collector 26.

[0045] The above provides a detailed description of specific examples of the technology disclosed in this specification, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes technologies obtained by various modifications and alterations to the specific examples described above. Furthermore, the technical elements illustrated in this specification or drawings exert their technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of application. Additionally, the technology illustrated in this specification or drawings may simultaneously achieve multiple objectives, and achieving even one of these objectives is itself technically useful.

Claims

1. A secondary battery comprising an electrode stack, the electrode stack being formed by stacking a plurality of electrodes along a first direction with a separator sandwiched between them, wherein at least one side of a sheet-like current collector is coated with an electrode active material layer. The electrode has a collector tab that protrudes in a second direction intersecting the first direction without being coated with the electrode active material layer. The current collector has an insulating layer on the surface facing the first direction. The insulating layer has protrusions that project toward the diaphragm. The thickness of the insulating layer including the protrusion is less than the thickness of the electrode active material layer.

2. The secondary battery according to claim 1, wherein, The protrusion is formed at the end of the insulating layer in the second direction on the side away from the electrode active material layer.

3. The secondary battery according to claim 2, wherein, The protrusion is continuously formed throughout the width direction of the collector ear that intersects the first direction and the second direction.

4. The secondary battery according to claim 1, wherein the protrusion has a shape that tapers towards the top.

5. The secondary battery according to any one of claims 1 to 4, wherein, The electrode stack is formed by alternately stacking the positive electrode and the negative electrode in the first direction with a membrane sandwiched between them. The positive electrode has a positive current collector tab that serves as the current collector tab. The negative electrode has a negative current collector tab that serves as the current collector tab. The positive current collector tab has the insulating layer.

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