electrode

Abstract

An electrode in which an electrode active material layer is coated on at least one surface of a sheet-like current collector, the electrode comprising: a coated portion in which the electrode active material layer is coated on the current collector; an uncoated portion in which the electrode active material layer is not coated on the current collector; and a current collector tab engaged with the uncoated portion, wherein a slit is formed in the uncoated portion, and the current collector tab engages with the uncoated portion between the coated portion and the slit.

Description

Technical Field

[0001] The technology disclosed in this specification relates to an electrode. Background Technology

[0002] Japanese Patent Application Publication No. 2013-98026 discloses an electrode plate, which is a strip-shaped electrode plate wound and housed within a battery. The electrode plate has: a strip-shaped electrode portion on which an electrode active material layer is formed; and a current collector portion on which no electrode active material layer is formed, and which is formed in contact with the width-direction end of the electrode portion. According to Japanese Patent Application Publication No. 2013-98026, a plurality of slits are intermittently formed on or parallel to the boundary line between the electrode portion and the current collector portion.

[0003] Furthermore, Japanese Patent Application Publication No. 11-354103 discloses an electrode plate for a secondary battery, wherein the uncoated portion of the current collector, which is not coated with an active material layer, has multiple cuts that intersect the flow direction (the direction in which the coated portion, where the active material layer is formed during calendering, extends) and are arranged laterally to each other. Summary of the Invention

[0004] As shown in Japanese Patent Application Publication No. 2013-98026, an electrode lead is connected to a current collector (uncoated portion) where no electrode active material layer has been formed. If the electrode lead is connected to an uncoated portion where a slit has been formed, the current will not easily flow from the uncoated portion to the electrode lead due to the presence of the slit.

[0005] This specification provides a technique that is useful for solving the problem of current flow being obstructed due to the presence of slits in such uncoated areas.

[0006] This specification discloses an electrode in which an electrode active material layer is coated on at least one surface of a sheet-like current collector. The electrode includes: a coated portion in which the electrode active material layer is coated on the current collector; an uncoated portion in which the electrode active material layer is not coated on the current collector; and a current collector tab engaged with the uncoated portion. A slit is formed in the uncoated portion, and the current collector tab engages with the uncoated portion between the coated portion and the slit.

[0007] According to the structure described above, a slit is formed in the uncoated portion, and on the other hand, the collector tab engages with the uncoated portion between the coated portion and the slit. Therefore, the slit does not impede the flow of current between the uncoated portion and the collector tab, allowing current to flow easily between them. Furthermore, the slit formed in the uncoated portion functions to eliminate ripples or wrinkles (hereinafter referred to as ripples, etc.) caused by the difference in extension between the coated and uncoated portions during the calendering of the electrode. Thus, the generation of ripples, etc., in the uncoated portion caused by the aforementioned calendering is suppressed. Attached Figure Description

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

[0009] Figure 1 This is a simplified diagram of the rolled electrode sheet, shown from a viewpoint opposite one side of the electrode sheet.

[0010] Figure 2 This is a magnified view showing the slits formed in the uncoated area.

[0011] Figure 3 This is a simplified diagram showing the state where the collector tabs are joined in the uncoated area.

[0012] Figure 4 It means along Figure 3 A sectional view of the section cut along line IV-IV.

[0013] Figure 5 It simply indicates the state where the collector tab is attached to the uncoated portion and is different from... Figure 3 An example diagram.

[0014] Figure 6 It means along Figure 5 A sectional view of the section cut along line VI-VI.

[0015] Figure 7 This is a cross-sectional view of a secondary battery.

[0016] Figure 8 This is an exploded perspective view of the electrode stack. Detailed Implementation

[0017] The following lists the main features of the illustrated embodiments. These features can be combined in any way.

[0018] According to the electrode disclosed in this specification, it can be configured as follows: the slit has a straight portion and slit ends respectively disposed at both ends of the straight portion, and the slit ends are formed by cutting off the current collector in a shape whose width in a direction intersecting the length direction of the straight portion is greater than the width of the straight portion.

[0019] According to the structure described above, ripples and other defects in the uncoated areas are further suppressed. Furthermore, damage to the slit ends is also suppressed.

[0020] According to the electrodes disclosed in this specification, the end of the slit can be set to be circular.

[0021] The structure described above further suppresses damage to the slit end.

[0022] According to the electrode disclosed in this specification, it can be configured such that the ratio of the length of the uncoated portion to the length of the coated portion in the direction in which the uncoated portion extends from the coated portion is 2.5% or less.

[0023] According to the structure, by setting the ratio to a low value of 2.5% or less, the uncoated portion itself can be reduced, thereby suppressing ripples and the like in the uncoated portion.

[0024] According to the electrode disclosed in this specification, it can be configured such that the collector ear further engages with the uncoated portion at a position farther away from the coated portion than the slit.

[0025] According to the structure described above, the bonding strength between the collector ear and the uncoated portion can be improved.

[0026] The embodiments will be described with reference to the accompanying drawings. The drawings are for illustrative purposes only, and the embodiments are not limited to the content shown. Furthermore, since the drawings are illustrative, some details have been omitted.

[0027] Figure 1 The electrode sheet 2 being rolled is simply shown from a viewpoint facing one side of the electrode sheet 2. The electrode sheet 2 includes a strip-shaped current collector 4 and an electrode active material layer 6 coated on at least one side of the current collector 4. The current collector 4 is a metal foil. The area of ​​the current collector 4 coated with the electrode active material layer 6 is referred to as the coated portion 40. The area of ​​the current collector 4 without the electrode active material layer 6 is referred to as the uncoated portion 42. Figure 1 In the diagram, symbol D1 represents the length direction D1 of electrode sheet 2, and symbol D2 represents the width direction D2 of electrode sheet 2, which is orthogonal to the length direction D1. One end and the other end of the width direction D2 of electrode sheet 2 are the uncoated portions 42.

[0028] according to Figure 1 The electrode sheet 2, conveyed along the length direction D1, contacts the roller 8, which extends along the width direction D2. To achieve high density or uniform thickness of the electrode active material layer 6, the electrode sheet 2 is subjected to rolling pressure based on a predetermined calendering pressure using the roller 8. Differences in elongation during calendering occur between the coated section 40 and the uncoated section 42, and due to these differences in elongation, problems such as ripples occur in the uncoated section 42.

[0029] To address this issue, a slit 44 is formed in the uncoated portion 42. The slit 44 is a cut that penetrates the current collector 4. According to... Figure 1 In the uncoated portion 42, slits 44 are intermittently formed along the length direction D1. In the uncoated portion 42, the slits 44 are formed at a position away from the boundary between the coated portion 40 and the uncoated portion 42.

[0030] Figure 2 In the middle, with Figure 1 The same magnified view shows the slit 44 formed in the uncoated portion 42. A slit 44 includes a straight portion 44a and slit ends 44b respectively disposed at both ends of the straight portion 44a. Figure 2 In the example, the length direction of the straight section 44a is parallel to the length direction D1. The length direction of the straight section 44a may be inclined relative to the length direction D1. The ratio of the length of one slit 44 in the length direction D1 to the unformed slit range A between the slits 44 in the length direction D1 is, for example, 1:1. In another example, the ratio of the length of one slit 44 in the length direction D1 to the unformed slit range A in the length direction D1 may be a ratio different from 1:1.

[0031] like Figure 2 As shown, the slit end 44b can also be formed by cutting away the current collector 4 in a shape whose width in the direction intersecting the length direction of the straight portion 44a is greater than the width of the straight portion 44a. That is, the slit end 44b is wider than the straight portion 44a. Figure 2 In this context, the direction intersecting the length direction of the straight section 44a corresponds to the width direction D2. For example... Figure 2 As shown, the slit end 44b is, for example, circular. The slit end 44b can be an oblong or elliptical. Alternatively, the slit end 44b can be a polygon.

[0032] The slit 44 formed in the uncoated portion 42 serves to eliminate ripples and the like caused by the difference in extension between the coated portion 40 and the uncoated portion 42 during the rolling of the electrode sheet 2. Thus, ripples and the like generated in the uncoated portion 42 are suppressed. Furthermore, since the width of the slit end 44b is formed into a shape larger than the width of the straight portion 44a, such as a circle, ripples and the like near the slit end 44b, or damage to the slit end 44b, are suppressed.

[0033] In this embodiment, the size of the uncoated portion 42 is set to be smaller than before. Figure 1 In the diagram, the dimensions of one electrode 12 are illustrated by enclosing it with a double-dotted line. The electrode sheet 2, after being rolled, is cut, for example, separated into... Figure 1 Multiple electrodes 12 of the dimensions shown. In Figure 2 A portion of electrode sheet 2 is shown, but it can also be considered as part of a single electrode 12. If we are interested in a single electrode 12, then, for example, in the direction in which the uncoated portion 42 extends from the coated portion 40 (in... Figure 1 , Figure 2The ratio of the length of the uncoated portion 42 to the length of the coated portion 40 in the width direction D2 of the electrode 12 is 2.5% or less. For example, the length of the coated portion 40 in the width direction D2 of the electrode 12 is 200 mm or more, and the length of the uncoated portion 42 in the width direction D2 of the electrode 12 is 5 mm or less. In this way, by reducing the uncoated portion 42 itself, for example by setting the ratio to a low value of 2.5% or less, ripples and the like in the uncoated portion 42 can be suppressed.

[0034] Corresponding to the reduction of the uncoated portion 42 itself, in this embodiment, a metal current collector tab is joined to the uncoated portion 42. That is, the current collector tab is joined to the uncoated portion 42 after the electrode sheet 2 is rolled using the roller 8. The timing of joining the current collector tab to the uncoated portion 42 is either before or after the rolled electrode sheet 2 is cut into a plurality of electrodes 12.

[0035] Figure 3 In the middle, with Figure 1 , Figure 2 The same viewpoint shows the state in which the collector ear 18 is engaged with the range of one electrode 12 or the electrode sheet 2 equivalent to one electrode 12. Figure 4 Indicates along Figure 3 The cross-section cut along line IV-IV. According to Figure 4 In the coating portion 40 of electrode 12, electrode active material layers 6 are formed on both sides of the current collector 4. Figure 3 , Figure 4 In the diagram, the engagement position P between the coated portion 40 and the slit 44 is shown by a double-dotted line. The collector ear 18 engages with the uncoated portion 42 at engagement position P. That is, the collector ear 18 engages with the uncoated portion 42 between the coated portion 40 and the slit 44. The collector ear 18 is engaged with the uncoated portion 42 at engagement position P, for example, by welding or bonding with an adhesive. The collector ear 18 engaged with the uncoated portion 42 is electrically connected to an electrode terminal (not shown).

[0036] Thus, in this embodiment, a slit 44 is formed in the uncoated portion 42 of the electrode 12, and the collector ear 18 is engaged with the uncoated portion 42 between the coated portion 40 and the slit 44. Therefore, the slit 44 does not become a factor that hinders the flow of current between the uncoated portion 42 and the collector ear 18 (the current flowing between the coated portion 40 and the collector ear 18 through the uncoated portion 42), and the current can easily flow between the uncoated portion 42 and the collector ear 18.

[0037] Figure 5 In the middle, with Figure 3 The same manner shows the state in which the collector ear 18 is engaged with the range of one electrode 12 or the electrode sheet 2 equivalent to one electrode 12. Figure 6 Indicates along Figure 5The cross-section cut along line VI-VI. Regarding Figure 5 , Figure 6 Only for Figure 3 , Figure 4 Explain the different points. Figure 5 , Figure 6 The diagram shows a contact position Q that is further away from the coating portion 40 than the slit 44. That is, contact position Q is located on the opposite side of contact position P, separated by the slit 44. The collector ear 18 engages with the uncoated portion 42 not only at contact position P but also at contact position Q. In other words, the collector ear 18 can be configured to further engage with the uncoated portion 42 at a position further away from the coating portion 40 than the slit 44. This improves the bonding strength between the collector ear 18 and the uncoated portion 42. Contact position P can also be referred to as the first contact position P, and contact position Q as the second contact position Q.

[0038] For example, such as Figure 7 and Figure 8 As shown, electrode 12 is used as part of the structure of secondary battery 10. Figure 7 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 multiple electrodes 12 together along a first direction, with a separator 14 sandwiched between them. Figure 8 The electrode stack 16 is simply shown in an exploded perspective view. Electrode 12 is the positive electrode 20 and the negative electrode 30.

[0039] The secondary battery 10 has a flexible outer casing (not shown), and an electrode laminate 16 is sealed inside the casing. An electrolyte (not shown) is sealed inside the casing. The outer casing is, for example, a laminate. Figure 7 , Figure 8 For ease of explanation, the X, Y, and Z axes are shown as mutually orthogonal. The Z-axis direction corresponds to the first direction. The first direction can also be referred to as the stacking direction. Figure 7 It is a sectional view based on a section orthogonal to the Y-axis.

[0040] like Figure 7 , Figure 8 As shown, the electrode stack 16 is formed by alternately stacking generally rectangular positive electrodes 20 and generally rectangular negative electrodes 30 via a diaphragm 14, which is a strip-shaped structure with alternating zigzag bends and folds. In this case, each of the plurality of positive electrodes 20 is sandwiched between one of the two sides of the diaphragm 14, and each of the plurality of negative electrodes 30 is sandwiched between the other side of the diaphragm 14. The positive electrodes 20 and negative electrodes 30 extend along the X-axis and Y-axis directions, respectively. Furthermore, regarding electrode 12, the Y-axis direction can be understood as being parallel to the X-axis. Figures 1-6The width direction D2 corresponds to.

[0041] The separator 14 is formed of a material that combines the properties of permeability (allowing the movement of charge carriers (lithium ions in this case) during charging and discharging) with insulation (preventing short circuits caused by contact between the positive electrode 20 and the negative electrode 30). Examples of materials for the separator 14 include polypropylene and polyethylene. Figure 7 , Figure 8 As shown, the structure in which a continuous, zigzag-shaped diaphragm 14 is sandwiched between electrodes 12 is only one example. The diaphragms 14 sandwiched between electrodes 12 can be separated from each other. In any case, the electrode stack 16 is formed by alternating layers in the first direction, with the positive electrode 20 and the negative electrode 30 sandwiching the diaphragms 14 between each other.

[0042] according to Figure 8 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 current collector 22 is an example of the current collector 4, and the positive active material layer 24 is an example of the electrode active material layer 6. 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, an 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.

[0043] 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 current collector 32 is an example of the current collector 4, and the negative active material layer 34 is an example of the electrode active material layer 6. 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, for example, carbon materials such as graphite, hard carbon, and soft carbon, materials that can form alloys with lithium such as silicon (Si), and lithium alloys. The electrode active material can be composed of a single material or multiple materials. The electrode active material layer can contain conductive additives, binders, etc.

[0044] Each electrode 12 (positive electrode 20, negative electrode 30) has a collector tab 18 protruding in a second direction intersecting the first direction. Here, the Y-axis direction (Y-axis + direction and Y-axis - direction) corresponds to the second direction. Figure 8 The uncoated portion 42 of the positive electrode 20 protrudes in the Y-axis + direction, and a current collector tab 18, i.e., a positive electrode current collector tab 26, is attached to this uncoated portion 42. Furthermore, according to... Figure 8The uncoated portion 42 of the negative electrode 30 protrudes in the Y-axis direction, and a current collector 18, i.e., a negative current collector 36, of the negative electrode 30 is attached to this uncoated portion 42. The positive current collector 26 and the negative current collector 36 are respectively oriented in opposite directions and protrude outwards from the area held by the diaphragm 14. The positive current collector 26 of each of the plurality of positive electrodes 20 is electrically connected to a positive terminal (not shown). The negative current collector 36 of each of the plurality of negative electrodes 30 is electrically connected to a negative terminal (not shown). Reference Figures 1-6 The features of the electrode 12, which includes a collector tab 18, can be applied to a positive electrode 20 including a positive collector tab 26 and a negative electrode 30 including a negative collector tab 36, respectively.

[0045] The above provides a detailed description of specific examples of the technology disclosed in this specification. However, these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes techniques that modify or alter the specific examples described above. Furthermore, the technical elements described in this specification or drawings are technical elements that exert their technical effect individually or in various combinations, and are not limited to the combinations described in the claims at the time of application. Moreover, the technology illustrated in this specification or drawings is a technology that simultaneously achieves multiple objectives, and achieving even one of these objectives is technically useful.

Claims

1. An electrode, wherein an electrode active material layer is coated on at least one surface of a sheet-like current collector, the electrode being characterized by comprising: A coating section, wherein the electrode active material layer is coated on the current collector; Uncoated portions, wherein the electrode active material layer is not coated on the current collector; and Collector tab, wherein the collector tab is engaged with the uncoated portion. A slit is formed in the uncoated area. The current collector engages with the uncoated portion between the coated portion and the slit.

2. The electrode according to claim 1, characterized in that, The slit has a straight portion and slit ends respectively disposed at both ends of the straight portion. The slit end is formed by cutting off the current collector in a shape whose width is greater than the width of the straight portion in a direction intersecting the length direction of the straight portion.

3. The electrode according to claim 2, characterized in that, The ends of the slit are rounded.

4. The electrode according to claim 1, characterized in that, In the direction in which the uncoated portion extends from the coated portion, the ratio of the length of the uncoated portion to the length of the coated portion is 2.5% or less.

5. The electrode according to claim 1, characterized in that, The current collector further engages with the uncoated portion at a position further away from the coated portion than the slit.

Images