Secondary battery and separator

Abstract

This secondary battery is provided with: an electrode group which comprises a positive electrode, a negative electrode that faces the positive electrode, and a separator that is disposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte. The separator is divided into a first region that includes the vicinities of both ends in the short-side direction and a second region other than the first region, the second region including the central part in the short-side direction. The width of the second region in the short-side direction is shorter than the width of a positive electrode mixture layer in the short-side direction. A first spacer which has a first linear part that extends substantially parallel to the longitudinal direction is disposed between the first region and at least one of the positive electrode and the negative electrode. A second spacer which has a plurality of second linear parts is disposed between the second region and the one of the positive electrode and the negative electrode. Each of the plurality of second linear parts is not orthogonal to a second direction and extends obliquely in a direction that intersects with the second direction.

Description

Secondary batteries and separators Cross-reference of related applications

[0001] This disclosure claims priority with respect to Japanese Patent Application No. 2024-171110, filed with the Japan Patent Office on 30 September 2024, and the entirety of the said patent application is incorporated herein by reference.

[0002] This disclosure relates to a secondary battery and a separator used in a secondary battery.

[0003] Non-aqueous electrolyte secondary batteries are used in applications such as ICT devices like personal computers and smartphones, automotive applications, and energy storage. In these applications, there is a demand for even higher capacity in non-aqueous electrolyte secondary batteries. Lithium-ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. Increasing the capacity of lithium-ion batteries can be achieved by using, for example, a combination of graphite and an alloy active material such as a silicon compound as the negative electrode active material. However, the capacity of lithium-ion batteries is reaching its limits.

[0004] As a high-capacity non-aqueous electrolyte secondary battery that surpasses lithium-ion batteries, lithium secondary batteries (lithium metal secondary batteries) are promising. In lithium secondary batteries, lithium metal is deposited on the negative electrode during charging, and this lithium metal dissolves into the non-aqueous electrolyte during discharge.

[0005] Patent Document 1 proposes, regarding electrode groups for non-aqueous secondary batteries used in lithium-ion batteries, that a spacer made of resin, which is softened with a non-aqueous electrolyte to relieve stress caused by the expansion and contraction of the electrode plates during charging and discharging, is placed between the positive electrode and the separator or between the negative electrode and the separator, in at least one of these locations, thereby suppressing buckling of the electrode plates due to the expansion of the negative electrode during charging and suppressing heat generation due to internal short circuits caused by buckling of the electrode plates.

[0006] Japanese Patent Publication No. 2011-8929

[0007] When spacers are spaced apart within an electrode group, wavy wrinkles may form on the edges of the separators during electrode group fabrication, requiring careful consideration during the manufacturing process. Furthermore, the position of the spacers may shift between separators located above and below the electrodes, resulting in variations in surface pressure. Consequently, non-uniformity may occur in the charge-discharge reaction, potentially degrading the cycle characteristics.

[0008] One aspect of the present disclosure comprises an electrode group including a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode and the negative electrode are wound around the separator, the positive electrode, the negative electrode and the separator have an elongated shape having a length L1 in a first direction D1 and a length L2 (L1 < L2) in a second direction D2 perpendicular to the first direction, the positive electrode comprises a positive electrode current collector and a positive electrode composite layer disposed on the positive electrode current collector, the spacer layer comprises a first spacer and a second spacer, and at least one member selected from the group consisting of the positive electrode, the negative electrode and the separator has a spacer layer, and the separator is wound around the first direction The present invention relates to a secondary battery, wherein the battery is divided in a direction into a first region including the vicinity of both ends in the first direction and a second region other than the first region including the central part in the first direction, the width of the second region in the first direction is shorter than the width of the positive electrode composite layer in the first direction, a first spacer having a first line-shaped portion extending substantially parallel to the second direction is disposed between at least one electrode of the positive electrode and the negative electrode and the first region, a second spacer having a plurality of second line-shaped portions is disposed between at least one electrode of the positive electrode and the negative electrode and the second region, and each of the plurality of second line-shaped portions extends diagonally in a direction that is not perpendicular to the second direction but intersects the second direction.

[0009] Another aspect of the present disclosure relates to a separator having a long shape with a base layer and a spacer layer, having a length L1 in a first direction D1 and a length L2 (L1 < L2) in a second direction D2 perpendicular to the first direction, wherein the spacer layer comprises a first spacer and a second spacer, and when the first direction is divided into a first region including the vicinity of both ends in the first direction and a second region other than the first region including the central part in the first direction, the first spacer having a first line-shaped portion extending substantially parallel to the second direction is arranged in the first region, and the second spacer having a plurality of second line-shaped portions is arranged in the second region, each of the plurality of second line-shaped portions extending diagonally in a direction that is not perpendicular to the second direction but intersects the second direction.

[0010] According to this disclosure, variations in the surface pressure of the negative electrode in the electrode group can be improved, thereby enhancing the cycle characteristics of the secondary battery. Novel features of the present invention are described in the appended claims, but the present invention, both in terms of structure and content, and in conjunction with other objects and features of the present invention, will be better understood by the following detailed description in conjunction with the drawings.

[0011] This is a schematic plan view showing an example of the arrangement of spacer layers provided on the surface of a separator in a secondary battery according to an embodiment of the present disclosure. This is a diagram illustrating the overlap of the linear portions of the spacer layers in two separators. This is a schematic plan view showing another example of the arrangement of spacer layers provided on the surface of a separator. This is a schematic plan view showing another example of the arrangement of spacer layers provided on the surface of a separator. This is a schematic plan view showing another example of the arrangement of spacer layers provided on the surface of a separator. This is a schematic plan view showing another example of the arrangement of spacer layers provided on the surface of a separator. This is a schematic longitudinal cross-sectional view showing a lithium secondary battery according to one embodiment of the present disclosure. This is a schematic enlarged view showing the main part of the lithium secondary battery of Figure 8.

[0012] The embodiments of this disclosure will be described below with examples, but this disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be given as examples, but other numerical values ​​and materials may be applied as long as the effects of this disclosure are obtained. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be read as "greater than or equal to numerical value A and less than or equal to numerical value B". In the following description, when lower and upper limits are given as examples for numerical values ​​of specific physical properties or conditions, either of the given lower limits and either of the given upper limits can be arbitrarily combined, as long as the lower limit does not exceed the upper limit. When multiple materials are given as examples, one of them may be selected and used alone, or two or more may be used in combination.

[0013] Furthermore, this disclosure encompasses any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims. In other words, any combination of matters described in two or more claims, which may be arbitrarily selected from the multiple claims set forth in the attached claims, is possible, provided that no technical inconsistency arises.

[0014] A secondary battery according to one embodiment of the present disclosure comprises an electrode group including a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The positive and negative electrodes are wound around each other via the separator. The positive electrode, negative electrode, and separator have a length L1 in a first direction D1 and a length L2 in a second direction D2 perpendicular to the first direction, and are elongated in shape such that length L1 is shorter than length L2 (L1 < L2). Hereinafter, the positive and negative electrodes may be collectively referred to as electrodes.

[0015] The shape of the electrode group is not particularly limited. The electrode group may be a wound electrode group in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound in a spiral shape with a separator in between, or it may be a flattened electrode group formed by pressing a wound electrode group radially. The electrode group may be constructed by stacking the positive electrode and the negative electrode with a separator in between, or by stacking the positive electrode and the negative electrode in a zigzag pattern with a separator in between. The electrode group may be a wound electrode group in which the positive electrode and the negative electrode are wound with a separator in between. In that case, the first direction is the axial direction of the winding, and the positive electrode, the negative electrode and the separator are wound in the second direction to form a wound electrode group.

[0016] The positive electrode comprises a positive electrode current collector and a positive electrode composite layer on which the positive electrode current collector is arranged.

[0017] At least one component selected from the group consisting of a positive electrode, a negative electrode, and a separator has a spacer layer. The spacer layer forms a space between the positive electrode and the separator or between the negative electrode and the separator, suppressing the expansion of the negative electrode during charging and discharging.

[0018] Secondary batteries include lithium-ion batteries and lithium secondary batteries (lithium metal secondary batteries). The negative electrode of a lithium-ion battery expands during charging due to the absorption of lithium ions. The negative electrode of a lithium secondary battery expands during charging due to the deposition of lithium metal. Among secondary batteries, lithium secondary batteries exhibit a greater degree of negative electrode expansion due to Li deposition, resulting in a larger volume change of the electrode group.

[0019] In secondary batteries, volume changes in the electrode group during charging and discharging can cause damage to the electrode components, electrode buckling, internal short circuits, and other problems. As a result, cycle characteristics may deteriorate. To address this, in lithium secondary batteries, volume changes in the electrode group during charging and discharging can be suppressed by placing a spacer (protrusion) between the positive and negative electrodes to create a space for accommodating deposited Li. In lithium-ion batteries, volume changes in the electrode group during charging and discharging can be suppressed by placing a flexible spacer between the positive and negative electrodes.

[0020] (Spacer layer) The spacer layer is provided as a convex portion on at least one of the positive electrode, the negative electrode, and the separator. The spacer layer or the convex portion may be provided on the surface of the positive electrode, on the surface of the negative electrode, or on the surface of the separator facing the positive electrode or the negative electrode. The convex portion provided on the surface of the positive electrode and / or the surface of the separator facing the positive electrode forms a space between the positive electrode and the separator, and the convex portion provided on the surface of the negative electrode and / or the surface of the separator facing the negative electrode forms a space between the negative electrode and the separator. Due to the space, the expansion of the negative electrode accompanying charge and discharge is suppressed, and the deterioration of the cycle characteristics is suppressed.

[0021] Here, the surface of the separator is divided in the first direction (the winding axis direction) into a first region including the vicinity of both ends in the first direction and a second region other than the first region including the central portion in the first direction. More specifically, when the width of the separator in the first direction is L1s, the first region is two regions along the second direction where the distance to either end of the separator in the first direction is equal to or less than a predetermined distance (=W / 2), and they are separated with the second region in between. The second region is a region along the second direction with a width of (L1s - W) in the first direction excluding the first region (see FIG. 1).

[0022] A spacer layer is disposed between at least one of the positive electrode and the negative electrode and the separator. The spacer layer includes a first spacer and a second spacer. The first spacer is disposed in the first region including both ends of the separator in the first direction (the winding axis direction). The second spacer is disposed in the second region including the central portion of the separator.

[0023] The first spacer has a first linear portion extending substantially parallel along the second direction. By disposing the first linear portion extending in the second direction (the winding direction) at both ends of the separator in the first direction (the winding axis direction), the first linear portion maintains the shape of the electrode group while holding a space between the separator and the electrode.

[0024] At the end of the electrode group (for example, the end corresponding to the end face of a columnar wound electrode group), the force for maintaining the shape of the electrode group is weak. Therefore, volume changes are likely to occur during charge and discharge, and the negative electrode is likely to elongate. When the negative electrode located at the end of the electrode group elongates, the portion that does not face the positive electrode becomes larger, and accordingly, Li (or Li ions) that does not contribute to the battery reaction increases in the negative electrode, which may cause a deterioration in cycle characteristics.

[0025] The second spacer has a plurality of second linear portions. Each of the plurality of second linear portions extends obliquely in a direction that is not orthogonal to the second direction and intersects the second direction. By arranging a second linear portion that extends obliquely in addition to the second direction (winding direction) at the central portion of the separator in the first direction (winding axis direction), the variation in surface pressure at the central portion can be suppressed, and the deterioration of cycle characteristics can be suppressed.

[0026] The width of the second region in the first direction is made shorter than the width of the positive electrode composite layer in the first direction. That is, in this case, since there is no second linear portion facing the end portion of the positive electrode composite layer along the second direction, bulging due to the deposition of Li that has flowed into the space near the spacer layer (second linear portion) does not occur during charging, and the cycle characteristics are improved. Since there is no adjacent spacer at the positive electrode end, the force for holding the electrode group is weak, and the effect of improving the cycle characteristics is remarkable.

[0027] Also, the plurality of second linear portions (second spacer) are sandwiched between the first linear portions (first spacer) that extend in the second direction. In this case, the first linear portion suppresses the occurrence of wavy wrinkles at the end of the winding of the separator during winding, and a wound electrode group can be easily manufactured without the occurrence of wrinkles.

[0028] The end of the positive electrode in the first direction does not have to face the first spacer. That is, when the separator is placed on top of the positive electrode, the first line-shaped portion does not have to appear at the end of the positive electrode in the first direction (winding axis direction). In this case, because there is no spacer (first line-shaped portion) facing the end of the positive electrode in the first direction (end along the second direction), swelling due to the deposition of Li that has wrapped around the spacer during charging does not occur, and the cycle characteristics are improved. In particular, because there is no spacer adjacent to the end of the positive electrode in the first direction in the first direction, the force holding the electrode group is weak, and the resulting improvement in cycle characteristics is significant.

[0029] The end of the positive electrode in the second direction does not have to face either the first or second spacer. In this case, the absence of spacers (first linear portion and second linear portion) at the end of the positive electrode in the second direction (the end along the first direction) prevents swelling due to the deposition of Li that has wrapped around to the spacer during charging, thus improving the cycle characteristics. Furthermore, because there are no adjacent spacers in the second direction at the end of the positive electrode in the second direction, the force holding the electrode group is weaker, and this effect of improving the cycle characteristics becomes more pronounced.

[0030] It is preferable that the first linear portion and the second linear portion do not intersect each other. In this case, a flow path for the electrolyte can be secured at the boundary between the first and second regions, improving the fluidity of the electrolyte and suppressing a decrease in cycle characteristics.

[0031] Preferably, the first linear portion has a defect so that it is not continuous in the second direction. Although the spacer may reduce the circulation of the electrolyte, the defect forms a flow path for the electrolyte, suppressing the reduction in electrolyte circulation. The electrolyte can circulate through the defect, thereby improving fluid flow and suppressing the deterioration of cycle characteristics. Therefore, the defect allows for maintaining high electrolyte circulation while ensuring the space-forming ability of the spacer, thereby improving the cycle characteristics of the secondary battery.

[0032] The ratio of the length of the missing portion to the total length of the first line-shaped portion including the missing portion may be 5% or more and 40% or less.

[0033] Here, the ratio of the length of the missing portion refers to the ratio of the total length of the missing portion to the total length of the linear convex portions, assuming that the convex portions exist in a linear shape within the missing portion. The first linear portion, if it includes the missing portion, has multiple linear portions extending along a common line (straight, broken, or curved). The multiple linear portions are spaced apart by the missing portion, which also extends along the common line. The total length of the first linear portion is the length of the common line.

[0034] Multiple second line-shaped portions are arranged between at least one of the positive and negative electrodes and the second region of the separator. Preferably, each of the second line-shaped portions intersects with another opposing second line-shaped portion via at least one of the electrodes.

[0035] Multiple second line-shaped sections intersect with multiple other second line-shaped sections at points, thereby maintaining a space between the separator and the electrode, suppressing variations in surface pressure, and improving cycle characteristics.

[0036] Typically, an electrode group is fabricated using a positive electrode, a negative electrode, and two separators. For example, a wound electrode group is fabricated by winding together a first separator, a negative electrode, a second separator, and a positive electrode in that order. In this case, the positive and negative electrodes face the first separator on one surface and the second separator on the opposite surface (back surface). When multiple second line-shaped portions are arranged between one of the positive and negative electrodes and the second region of the first separator, multiple other second line-shaped portions may be arranged between the other electrode and the second region of the second separator. Multiple second line-shaped portions arranged on the second region of the first separator face multiple other second line-shaped portions arranged on the second region of the second separator via one of the electrodes.

[0037] Similarly, when a first line-shaped portion is positioned between one of the positive and negative electrodes and a first region of the first separator, another first line-shaped portion may be positioned between the other electrode and a first region of the second separator. In terms of maintaining the shape of the electrode group, it is preferable that the first line-shaped portion positioned on the first region of the first separator coincides with or overlaps with another first line-shaped portion positioned on the first region of the second separator in the first direction (winding axis direction). However, since the first region is a relatively narrow region at both ends of the separator, it is easy to align the first line-shaped portions. Furthermore, to facilitate alignment, the line width of the first line-shaped portions can be increased.

[0038] Similar to the first linear portion, the second linear portion may have missing parts. The second linear portion may be a straight linear pattern or a curved linear pattern, or it may be part of a mesh-like geometric pattern (for example, a hexagonal honeycomb shape). The shape of the mesh in the mesh-like pattern is not particularly limited, but it may be polygonal, and quadrilaterals or hexagons are preferred.

[0039] From the viewpoint of securing the minimum necessary space between the electrode and the separator, the average height h of the protrusions of the first and second spacers may be 0.01 mm or more and 0.1 mm or less, or 0.015 mm or more and 0.09 mm or less, depending on the battery size. The average height h of the protrusions can be determined by averaging the measurements of any 10 points.

[0040] From the viewpoint of improving the liquid flow of the non-aqueous electrolyte on the negative electrode surface, the height of a portion of the protrusion may differ from the height of the rest of the protrusion, and the heights of adjacent protrusions may differ. Multiple protrusions may include a protrusion of height h1 and a protrusion of height h2 which is smaller than height h1. In this case, the ratio of height h2 to height h1: h2 / h1 may be, for example, 0.8 or more and less than 1.0, or 0.8 or more and 0.95 or less. The width of the protrusion (width of the line-shaped protrusions 401 and 402 in Figure 1) may be, for example, 1 mm or less, or 0.1 mm or more and 1 mm or less.

[0041] From the viewpoint of suppressing the deposition of lithium metal on the surface of the protrusions, the protrusions may be made of a material with lower conductivity than the electrodes, or they may be made of a resin material.

[0042] The material constituting the spacer layer is not particularly limited. The spacer layer may be composed of a conductive material and / or an insulating material. Among these, an insulating material is preferred. Since lithium metal is less likely to deposit on the surface of an insulating material, the effect of suppressing the expansion of the negative electrode can be enhanced.

[0043] As the conductive material, it can be appropriately selected from the materials described later for the negative electrode current collector or the positive electrode current collector. Such a spacer layer may be provided by forming a protrusion on the negative electrode current collector by press working or the like. Alternatively, conductive paint may be applied to the surface of the separator or electrode, or conductive tape may be attached to the surface of the separator or electrode.

[0044] Examples of insulating materials include resin materials. Examples of resin materials include polyolefin resins, acrylic resins, polyamide resins, polyimide resins, silicone resins, fluororesins, urethane resins, melamine resins, and urea resins. Cured products of curable resins such as epoxy resins may also be used as resin materials. In addition, inorganic fillers may be mixed into these resin materials.

[0045] The material constituting the spacer layer is preferably a material having a Young's modulus of 0.01 GPa or more and 10 GPa or less. This makes it easier to relieve stress caused by the expansion and contraction of the negative electrode and to maintain the space for housing the lithium metal. In addition, it makes it easier to suppress damage to the electrode caused by the spacer layer. Examples of insulating materials having a Young's modulus within the above range include the cured products of the curable resins mentioned above.

[0046] The spacer layer can be formed, for example, by attaching a resin adhesive tape to the surface of the separator or electrode. Alternatively, the spacer layer may be formed by applying a solution or dispersion containing a resin material to the surface of the separator or electrode and drying it. The spacer layer may also be formed by applying a curable resin to the surface of the separator or electrode in a desired shape and curing it. Or, the spacer layer may be formed by scattering resin material particles in a desired shape on the surface of the separator or electrode.

[0047] Spacer layers may be provided on both sides of the component. In this case, the spacer layer located on the first surface of the component and the spacer layer located on the second surface opposite to the first surface of the component, having the first and second spacers described above, suppresses the expansion of the negative electrode during charging and discharging, reduces variations in surface pressure, and improves the battery's cycle characteristics.

[0048] The secondary battery may be a lithium secondary battery. A lithium secondary battery is a type of secondary battery in which lithium metal is deposited on the negative electrode during charging and dissolves from the negative electrode during discharge. In a lithium secondary battery, the spacer layer serves to secure a space for lithium metal to be deposited on the surface of the negative electrode. This reduces the volume change of the negative electrode due to the deposition of lithium metal, suppresses the expansion and contraction of the negative electrode, and improves the cycle characteristics.

[0049] In lithium secondary batteries, for example, 70% or more of the rated capacity is due to the deposition and dissolution of lithium metal. The movement of electrons in the negative electrode during charging and discharging is mainly due to the deposition and dissolution of lithium metal in the negative electrode. Specifically, 70-100% (e.g., 80-100% or 90-100%) of the movement of electrons (or current, from another perspective) in the negative electrode during charging and discharging is due to the deposition and dissolution of lithium metal. In other words, the negative electrode of a lithium secondary battery differs from a negative electrode where the movement of electrons in the negative electrode during charging and discharging is mainly due to the intercalation and release of lithium ions by the negative electrode active material (such as graphite).

[0050] A separator according to one embodiment of the present disclosure relates to a separator provided with the above-described spacer layer. The separator has an elongated shape having a length L1 in a first direction D1 and a length L2 (L1 < L2) in a second direction D2 perpendicular to the first direction, and comprises a base layer and a spacer layer. The spacer layer comprises a first spacer and a second spacer. When the first direction is divided into a first region including the vicinity of both ends in the first direction and a second region other than the first region including the central part in the first direction, a first spacer having a first line-shaped portion extending substantially parallel to the second direction is arranged in the first region, and a second spacer having a plurality of second line-shaped portions is arranged in the second region. Each of the plurality of second line-shaped portions extends diagonally in a direction that is not perpendicular to the second direction but intersects with the second direction.

[0051] The arrangement of the spacer layer will be described below with reference to the drawings. In the illustrated example, the spacer layer is provided on the surface of the separator. However, the embodiments of this disclosure are not limited to this, and the spacer layer may be provided on the surface of the electrode.

[0052] Figures 1 to 7 are schematic plan views showing the spacer layer arranged on the surface of the separator.

[0053] In the separator 301 shown in the example of Figure 1, the spacer layer 400 has a convex portion 401 (first spacer) located in two first regions A1 including the vicinity of both ends in a first direction D1 on the surface of the separator 301, and a convex portion 402 (second spacer) located in a second region A2 including the central part in the first direction D1.

[0054] The protrusions 401 consist of one line-shaped protrusion (first line-shaped portion) for each first region A1, extending substantially parallel to the second direction D2 and extending intermittently with a defect. "Substantially parallel" means roughly parallel, and the line-shaped protrusions may intersect at angles, for example, 0° to 10° or 0° to 5°.

[0055] The protrusion 402 consists of a plurality of line-shaped protrusions (second line-shaped portions) that extend diagonally in a direction that is not perpendicular to the second direction D2 but intersects the second direction D2. The plurality of line-shaped protrusions are arranged at equal intervals in the second direction D2 and are arranged in a stripe pattern. Each of the plurality of line-shaped protrusions does not have a defect, but may have a defect.

[0056] In Figure 1, the width of the separator in the first direction D1 is L1s. The first region A1 consists of two regions at both ends of the separator in the first direction D1, with a width of W / 2 in the first direction D1. The width of the second region A2 in the first direction D1 is L1s - W.

[0057] The width of the second region A2 in the first direction D1 is longer than the width of the positive electrode composite layer in the first direction D1. That is, when the separator is placed on top of the positive electrode, the contour of the positive electrode composite layer along the second direction D2 is in the first region A1. In Figure 1, the area occupied by the positive electrode composite layer when the separator is placed on top of the positive electrode is shown as region X enclosed by a dashed line. This means that the protrusion 402 is located in the region opposite to the positive electrode composite layer and does not face the positive electrode end.

[0058] For example, a wound electrode group can be manufactured by using two separators 301 as shown in Figure 1, stacking the separator 301, negative electrode, separator 301, and positive electrode in that order, and then winding the stack. In this case, the two separators 301 are arranged so that the protrusions 401 and 402 of one separator 301 face each other via either the positive or negative electrode. The protrusions 401 and 402 of one separator 301 and the protrusions 401 and 402 of the other separator 301 overlap with either electrode in between. The overlap in this case is shown in Figure 2.

[0059] In Figure 2, the protrusion 402 (solid line) of one separator 301 and the protrusion 402 (dashed line) of the other separator 301 do not extend perpendicular to the second direction D2, but rather diagonally in a direction intersecting the second direction D2, so the protrusions 402 intersect at a single point. In contrast, the protrusion 401 of one separator 301 and the protrusion 401 of the other separator 301 lie on the same straight line parallel to the second direction D2, and either completely overlap or at least partially overlap by a line. This allows for maintaining space between the separator and the electrode and suppressing variations in surface pressure. Furthermore, this suppresses the formation of wavy wrinkles at the end of the winding of the separator during winding, making it easier to manufacture wound electrode groups.

[0060] As shown in the separator 302 of Figure 3, the convex portion 401 (first spacer) positioned in the first region A1 may have a plurality of linear convex portions (first linear portions) extending substantially parallel along the second direction D2. The plurality of first linear portions are positioned at different locations in the first direction D1.

[0061] The separator 303 shown in Figure 4 is an example in which a missing portion 404 is provided in the multiple line-shaped protrusions (second line-shaped portion) that constitute the protrusion 402 in Figure 1.

[0062] The separator 304 shown in Figure 5 is an example in which, in Figure 1, a missing portion is provided in the multiple line-shaped protrusions (second line-shaped portion) that constitute the protrusion 402, and the inclination of the adjacent line-shaped protrusions on either side of the missing portion is made different.

[0063] The separator 305 shown in Figure 6 is an example in which the multiple line-shaped protrusions (second line-shaped parts) constituting the protrusion 402 include multiple types of line-shaped protrusions 402A to 402D with different inclinations.

[0064] The separator 306 shown in Figure 7 is an example in which the convex portion 402 is composed of a geometric pattern of regular hexagons with missing portions.

[0065] Hereinafter, each component of the secondary battery according to the embodiment of this disclosure will be described in more detail, using a lithium secondary battery as an example. [Negative electrode] The negative electrode comprises a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode current collector by charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode current collector by charging and become lithium metal, which is deposited on the surface of the negative electrode current collector. The lithium metal deposited on the surface of the negative electrode current collector dissolves as lithium ions in the non-aqueous electrolyte by discharge. Note that the lithium ions contained in the non-aqueous electrolyte may originate from lithium salts added to the non-aqueous electrolyte, or they may be supplied from the positive electrode active material by charging, or both.

[0066] The negative electrode current collector can be any conductive sheet. Examples of conductive sheets include foil and film.

[0067] The surface of the conductive sheet may be smooth. This makes it easier for lithium metal from the positive electrode to deposit evenly on the conductive sheet during charging. Smoothness means that the maximum height roughness Rz of the conductive sheet is 20 μm or less. The maximum height roughness Rz of the conductive sheet may be 10 μm or less. The maximum height roughness Rz is measured in accordance with JIS B 0601:2013.

[0068] The material of the negative electrode current collector (conductive sheet) may be any conductive material other than lithium metal and lithium alloys. The conductive material may be a metallic material such as a metal or alloy. Preferably, the conductive material is one that does not react with lithium. More specifically, it is preferable that the conductive material does not form any alloys or intermetallic compounds with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metallic elements, or graphite in which the basal surface is preferentially exposed. Examples of alloys include copper alloys and stainless steel (SUS). Among these, copper and / or copper alloys with high conductivity are preferred.

[0069] The thickness of the negative electrode current collector is not particularly limited, but is, for example, 5 μm or more and 300 μm or less.

[0070] A negative electrode composite layer (not shown) may be formed on the surface of the negative electrode current collector. The negative electrode composite layer is formed, for example, by applying a paste containing a negative electrode active material such as graphite to at least a portion of the surface of the negative electrode current collector. However, from the viewpoint of achieving a lithium secondary battery with a capacity exceeding that of a lithium-ion battery, the thickness of the negative electrode composite layer is set to be sufficiently thin so that lithium metal can be deposited at the negative electrode. In this case, the open-circuit potential of the negative electrode at full charge may be 70 mV or less relative to lithium metal (lithium dissolution potential). When the open-circuit potential of the negative electrode at full charge is 70 mV or less relative to lithium metal, lithium metal is present on the surface of the lithium ion storage layer at full charge. That is, the negative electrode exhibits capacity due to the deposition and dissolution of lithium metal.

[0071] The negative electrode composite layer is formed by creating layers of negative electrode composite containing negative electrode active material. In addition to the negative electrode active material, the negative electrode composite may also contain binders, thickeners, conductive agents, etc.

[0072] Examples of negative electrode active materials include carbonaceous materials, Si-containing materials, and Sn-containing materials. The negative electrode may contain one type of negative electrode active material, or a combination of two or more types. When the negative electrode contains a Si-containing material as the negative electrode active material, the expansion rate of the negative electrode during charging is large, and the volume change of the electrode group is large, so the effect of the cylindrical body described above is significantly obtained. Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon).

[0073] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjenblack, carbon nanotubes, and graphite.

[0074] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0075] [Positive Electrode] The positive electrode comprises, for example, a positive electrode current collector and a positive electrode composite layer supported by the positive electrode current collector. The positive electrode composite layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode composite layer may be formed on only one side of the positive electrode current collector or on both sides. The positive electrode can be obtained, for example, by applying a positive electrode composite slurry containing the positive electrode active material, a conductive material, and a binder to both sides of the positive electrode current collector, drying the coating, and then rolling it.

[0076] The positive electrode active material is a material that intercepts and releases lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred because they have low manufacturing costs and a high average discharge voltage.

[0077] Examples of transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one transition metal element or two or more. The transition metal element may be Co, Ni, and / or Mn. Lithium-containing transition metal oxides may optionally contain one or more main group elements. Examples of main group elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The main group element may also be Al.

[0078] Among lithium-containing transition metal oxides, composite oxides containing Co, Ni, and / or Mn as transition metal elements, and possibly containing Al as an optional component, and having a layered rock salt-type crystalline structure, are preferred for obtaining high capacity. In this case, in a lithium secondary battery, the molar ratio of the total amount of lithium (mLi) in the positive and negative electrodes to the amount of metal M other than lithium (mM) in the positive electrode (mLi / mM) is set to, for example, 1.1 or less.

[0079] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjenblack, carbon nanotubes, and graphite.

[0080] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0081] The positive electrode current collector can be any conductive sheet. Examples of conductive sheets include foil and film. The surface of the positive electrode current collector may also be coated with a carbon material.

[0082] Examples of materials for the positive electrode current collector (conductive sheet) include metallic materials containing Al, Ti, Fe, etc. The metallic material may be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy may be stainless steel (SUS).

[0083] The thickness of the positive electrode current collector is not particularly limited, but is, for example, 5 μm or more and 300 μm or less.

[0084] [Separator] A porous sheet having ion permeability and insulating properties is used as the separator. Examples of porous sheets include thin films with microporosity, woven fabrics, nonwoven fabrics, etc. The material of the separator is not particularly limited, but it may be a polymer material. Examples of polymer materials include olefin resins, polyamide resins, cellulose, etc. Examples of olefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The separator may contain additives as needed. Examples of additives include inorganic fillers, etc.

[0085] [Non-aqueous electrolytes] Non-aqueous electrolytes having lithium ion conductivity include, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. Non-aqueous electrolytes may be in liquid or gel form.

[0086] Liquid non-aqueous electrolytes are prepared by dissolving lithium salts in a non-aqueous solvent. The dissolution of lithium salts in the non-aqueous solvent generates lithium ions and anions.

[0087] The gel-like non-aqueous electrolyte contains a lithium salt, a matrix polymer, or a lithium salt, a non-aqueous solvent, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, and the like.

[0088] As the lithium salt or anion, known ones used in the non-aqueous electrolyte of a lithium secondary battery can be used. Specifically, BF ２ｍ＋１ , ３ , － , － , － , ４ , ３ , ４ , ２ , － , ２ , ｙ , ３ , ４ , ２ｎ＋１ , ４ , ｘ , － , ３ , － , ２ , ６ , ２ , ｍ , － , ２ , ２ , ２ , ２ , ２ , ｎ , ２ , － , ２ － , ClO ４ － , PF ６ － , CF ３ SO ３ － , CF ３ CO ２ － , anions of imides, anions of oxalate complexes, and the like. Examples of the anions of imides include N(SO ２ CF ３ )([0000015])([0000016]), N(C ｍ F ２ｍ＋１ )SO \((m\) and \(n\) are each independently an integer of 0 or 1 or more, \(x\) and \(y\) are each independently 0, 1, or 2, and \(x + y = 2\) is satisfied.), and the like. The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalate borate anion, BF ２ (C ２ O ４ )([0000029]), PF ４ (C ２ O ４ )([0000033]), PF ２ (C ２ O ４ )([0000037])([0000038]), and the like.​​​​​​​​​​​​​​​​​​​​​Examples include these. Non-aqueous electrolytes may contain these anions individually or in combination of two or more.

[0089] From the viewpoint of suppressing the dendritic deposition of lithium metal, the non-aqueous electrolyte preferably contains at least an oxalate complex anion. The interaction between the oxalate complex anion and lithium makes it easier for lithium metal to precipitate uniformly in fine particulate form. Therefore, it is easier to suppress localized deposition of lithium metal. The oxalate complex anion may be combined with other anions. Other anions are PF ６ － And / or imide anions.

[0090] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, or halogen-substituted compounds thereof. The non-aqueous electrolyte may contain one of these non-aqueous solvents or two or more of them. Examples of halogen-substituted compounds include fluorides.

[0091] Examples of esters include carbonate esters and carboxylic acid esters. Examples of cyclic carbonate esters include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of linear carbonate esters include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of linear carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0092] Examples of ethers include cyclic ethers and linear ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of linear ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methylphenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diethylene glycol dimethyl ether.

[0093] The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or more and 3.5 mol / L or less. The concentration of anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. Alternatively, the concentration of anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

[0094] The non-aqueous electrolyte may contain additives. The additives may form a film on the negative electrode. The formation of a film derived from the additive on the negative electrode makes it easier to suppress dendrite formation. Examples of such additives include vinylene carbonate, FEC, vinyl ethyl carbonate (VEC), and the like.

[0095] The configuration of the secondary battery relating to this disclosure will be described below with reference to the drawings, using a cylindrical battery equipped with a wound electrode group as an example. However, this disclosure is not limited to the following configuration.

[0096] Figure 8 is a longitudinal cross-sectional view of a lithium secondary battery 10. The lithium secondary battery 10 is a cylindrical battery comprising a cylindrical battery case, a wound electrode group 14 housed within the battery case, and a non-aqueous electrolyte (not shown). The battery case consists of a case body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the case body 15. The case body 15 has an annular stepped portion 21 formed by partially pressing the side wall from the outside near the opening. The sealing body 16 is supported by the opening-side surface of the stepped portion 21. A gasket 27 is placed between the case body 15 and the sealing body 16, thereby ensuring the airtightness of the battery case. Inside the case body 15, insulating plates 17 and 18 are placed at both ends of the electrode group 14 in the direction of the winding axis, respectively.

[0097] The sealing body 16 comprises a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26. The cap 26 is located on the outside of the case body 15, and the filter 22 is located on the inside of the case body 15. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheries. The filter 22 and the lower valve body 23 are connected to each other at their respective peripheries. The upper valve body 25 and the cap 26 are connected to each other at their respective peripheries. A ventilation hole is formed in the lower valve body 23. When the internal pressure of the battery case rises due to abnormal heat generation or the like, the upper valve body 25 bulges towards the cap 26 and separates from the lower valve body 23. This disconnects the electrical connection between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures, and gas is discharged from the opening formed in the cap 26.

[0098] The electrode group 14 consists of a positive electrode 110, a negative electrode (negative electrode current collector) 120, and a separator 300. The positive electrode 110, the negative electrode 120, and the separator 300 interposed between them are all strip-shaped and are wound in a spiral pattern such that their respective width directions are parallel to the winding axis.

[0099] The positive electrode 110 is electrically connected to the cap 26, which also serves as the positive electrode terminal, via a positive electrode lead 19. One end of the positive electrode lead 19 is connected, for example, near the center of the positive electrode 110 in the longitudinal direction. The other end of the positive electrode lead 19, which extends from the positive electrode 110, is welded to the inner surface of the filter 22 through a through hole formed in the insulating plate 17.

[0100] The negative electrode 120 is electrically connected to the case body 15, which also serves as the negative electrode terminal, via the negative electrode lead 20. One end of the negative electrode lead 20 is connected, for example, to the longitudinal end of the negative electrode 120, and the other end is welded to the inner bottom surface of the case body 15.

[0101] Figure 9 is a schematic enlarged view showing the discharge state of region X enclosed by the dashed line in Figure 8. In the illustrated example, the cross-sectional shape of the spacer layer is trapezoidal. However, embodiments of this disclosure are not limited to this. In the illustrated example, the spacer layer is provided between the positive electrode and the separator. However, embodiments of this disclosure are not limited to this, and the spacer layer may be provided between the negative electrode and the separator, or between the positive electrode and the negative electrode and the separator.

[0102] The positive electrode 110 comprises a positive electrode current collector 111 and a positive electrode composite layer 112. A spacer layer 400 is provided between the positive electrode composite layer 112 and the separator 300. The spacer layer 400 comprises a first linear portion located in the first region A1 described above and a second linear portion located in the second region A2. As the separator 300, any of the above-described separators 301 to 306 configurations may be adopted. In the discharge state, lithium metal is not deposited on the surface of the negative electrode current collector 121, and a space is maintained between the positive electrode 110 and the separator 300. On the other hand, in the charge state, lithium metal is deposited on the surface of the negative electrode current collector 121 and is housed in the space between the positive electrode 110 and the separator 300 while receiving the pressing force of the separator 300. That is, the negative electrode 120 comprises a negative electrode current collector 121 in the discharge state and a negative electrode current collector 121 and the lithium metal deposited on its surface in the charge state.

[0103] Since the lithium metal is contained in the space between the positive electrode 110 and the separator 300, the apparent volume change of the electrode group due to the deposition of lithium metal during the charge-discharge cycle is reduced. Therefore, the stress applied to the negative electrode current collector 121 is also suppressed. Furthermore, since pressure is applied from the separator 300 to the lithium metal contained between the positive electrode 110 and the separator 300, the deposition state of the lithium metal is controlled, making it less likely for the lithium metal to become isolated, and suppressing a decrease in charge-discharge efficiency.

[0104] The illustrated example describes a cylindrical lithium secondary battery equipped with a wound electrode group, but the shape of the lithium secondary battery is not limited to this. Depending on the application, various shapes such as coin-shaped, prismatic, sheet-shaped, and flat-shaped batteries can be appropriately selected in addition to the cylindrical shape. The form of the electrode group is also not particularly limited and may be stacked. Furthermore, known components other than the electrode group and non-aqueous electrolyte of the lithium secondary battery can be used without particular restriction.

[0105] (Note) The above description of embodiments discloses the following technologies. (Technology 1) An electrode group comprising a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode, the negative electrode and the separator are elongated in length L1 in a first direction D1 and length L2 (L1 < L2) in a second direction D2 perpendicular to the first direction, the positive electrode comprises a positive electrode current collector and a positive electrode composite layer disposed on the positive electrode current collector, at least one member selected from the group consisting of the positive electrode, the negative electrode and the separator has a spacer layer, the spacer layer comprises a first spacer and a second spacer, the separator is divided in the first direction into a first region including the vicinity of both ends in the first direction and a second region other than the first region including the central part in the first direction A secondary battery wherein the width of the second region in the first direction is shorter than the width of the positive electrode composite layer in the first direction, a first spacer having a first linear portion extending substantially parallel to the second direction is disposed between the positive electrode and the negative electrode and the first region, a second spacer having a plurality of second linear portions is disposed between the positive electrode and the negative electrode and the second region, and each of the plurality of second linear portions extends diagonally in a direction that is not perpendicular to the second direction but intersects the second direction. (Technology 2) The secondary battery according to Technology 1, wherein the end of the positive electrode in the first direction does not face the first spacer. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the end of the positive electrode in the second direction does not face either the first spacer or the second spacer. (Technology 4) The secondary battery according to any one of Technology 1 to 3, wherein the first linear portion and the second linear portion do not intersect each other. (Technical 5) The secondary battery according to any one of Technical 1 to 4, wherein the first linear portion has a defect that is not continuous in the second direction, and the ratio of the length of the defect to the total length of the first linear portion including the defect is 5% or more and 40% or less.(Technical 6) A secondary battery according to any one of Technical 1 to 5, wherein each of the second linear portions intersects with another opposing second linear portion via at least one electrode. (Technical 7) A secondary battery according to any one of Technical 1 to 6, wherein in the electrode group, the positive electrode and the negative electrode are wound in the second direction via the separator. (Technical 8) A secondary battery according to any one of Technical 1 to 7, wherein the negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal dissolves during discharge.

[0106] (Technical 9) A separator having a long shape with a length L1 in a first direction D1 and a length L2 (L1 < L2) in a second direction D2 perpendicular to the first direction, comprising a base layer and a spacer layer, wherein the spacer layer comprises a first spacer and a second spacer, and when the first direction is divided into a first region including the vicinity of both ends in the first direction and a second region other than the first region including the central part in the first direction, the first spacer having a first line-shaped portion extending substantially parallel to the second direction is arranged in the first region, and the second spacer having a plurality of second line-shaped portions is arranged in the second region, and each of the plurality of second line-shaped portions extends diagonally in a direction that is not perpendicular to the second direction but intersects the second direction.

[0107] [Examples] The lithium secondary battery relating to this disclosure will be described in detail below based on examples and comparative examples. This disclosure is not limited to the following examples.

[0108] 《Example 1》 (1) Preparation of the positive electrode A rock salt-type lithium-containing transition metal oxide (NCA; positive electrode active material) having a layered structure and containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al is 1.0), acetylene black (AB; conductive material), and polyvinylidene fluoride (PVdF; binder) were mixed in a mass ratio of NCA:AB:PVdF = 95:2.5:2.5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added and stirred to prepare a positive electrode slurry. Next, the obtained positive electrode slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector), dried, and the coating film of the positive electrode mixture was rolled using a roller. After that, it was cut to a predetermined width.

[0109] (2) A 20 μm thick polyethylene microporous thin film (porous sheet) was prepared as the substrate for the separator.

[0110] Insulating particles (median diameter 3 μm, volume resistivity 10) １４ A dispersion of the spacer material was prepared by mixing 50 parts by volume of (Ω·cm), 50 parts by volume of polyvinylidene fluoride (PVdF), a resin material, and N-methyl-2-pyrrolidone (NMP), a dispersion medium.

[0111] Next, a dispersion of the spacer material was dispensed onto a microporous thin film using a dispenser, and the coating was vacuum-dried to form first line-shaped portions (protrusions 401) (line width 0.40 mm, height 30 μm, repeat length 5 mm (coated portion 4.25 mm, intermittent portion (defective portion) 0.75 mm, defect ratio 15%)) that extend intermittently parallel to the second direction, at a position 2.0 mm from both ends in the first direction of the opposing positive electrode, within a region at least 2.0 mm inward from both ends in the second direction of the positive electrode. Furthermore, a second line-shaped portion (protrusion 402) extending diagonally was formed on one main surface of the microporous thin film, 2.0 mm inward from the first line-shaped portion and 2.0 mm inward from both ends of the positive electrode in the second direction, in a diagonal stripe pattern (line width 0.40 mm, height 30 μm, inclination angle 20° with respect to the first direction, spacing between protrusions in the second direction 3 mm). In this way, a separator having a substrate and a spacer, with the spacer layer arrangement shown in Figure 1, was obtained.

[0112] (3) Fabrication of the negative electrode A strip of electrolytic copper foil (15 μm thick) was prepared as the negative electrode current collector.

[0113] (4) Preparation of non-aqueous electrolyte Ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed in a volume ratio of EC:DMC = 30:70, and LiPF is added to the resulting mixed solvent. ６ 1 mol / L, LiBF ２ (C ２ O ４ The two substances were each dissolved at a concentration of 0.1 mol / L to prepare liquid non-aqueous electrolytes.

[0114] (5) Battery Assembly In an inert gas atmosphere, the positive electrode and the negative electrode current collector were wound in a spiral shape via the separator to create the electrode group. At this time, the separator was positioned so that the spacer faced the positive electrode. The electrode group was housed in a bag-shaped outer casing made of a laminate sheet with an Al layer, a non-aqueous electrolyte was injected, and the outer casing was sealed to complete the lithium secondary battery A1.

[0115] <Example 2> In the preparation of the separator described in (2) above, the ratio of the length of the missing portion in the first line-shaped portion (protrusion 401) that extends intermittently parallel to the second direction was changed, and the repeating length of the first line-shaped portion was set to 5 mm (coated portion 4.75 mm, intermittent portion (missing portion) 0.25 mm, ratio of missing portion 5%). Except for this, the procedure was the same as in Example 1, and a separator having the arrangement of the spacer layer shown in Figure 1 was prepared to complete the lithium secondary battery A2.

[0116] <Example 3> In the fabrication of the separator described in (2) above, the first linear portion (protrusion 401) was arranged to extend continuously parallel to the second direction, and the ratio of the length of the missing portion in the first linear portion (protrusion 401) was set to 0%. Except for this, the procedure was the same as in Example 1, and a separator having a spacer layer arrangement similar to that in Figure 1 was fabricated to complete the lithium secondary battery A3.

[0117] <Example 4> In the preparation of the separator described in (2) above, the ratio of the length of the missing portion in the first line-shaped portion (protrusion 401) that extends intermittently parallel to the second direction was changed to a repeating length of 5 mm for the first line-shaped portion (coated portion 3.0 mm, intermittent portion (missing portion) 2.0 mm, and ratio of missing portion 40%). Except for this, the same procedure as in Example 1 was followed to prepare a separator having the arrangement of spacer layers shown in Figure 1, and the lithium secondary battery A4 was completed.

[0118] <Example 5> In the preparation of the separator described in (2) above, the ratio of the length of the missing portion in the first line-shaped portion (protrusion 401) that extends intermittently parallel to the second direction was changed to a repeating length of 5 mm for the first line-shaped portion (coated portion 2.75 mm, intermittent portion (missing portion) 2.25 mm, and ratio of missing portion 45%). Except for this, the procedure was the same as in Example 1, and a separator having the arrangement of the spacer layer shown in Figure 1 was prepared to complete the lithium secondary battery A5.

[0119] <Comparative Example 1> In the preparation of the separator described in (2) above, the first linear portion (protrusion 401) was not arranged, and the second linear portion (protrusion 402) was formed on one main surface of the microporous thin film in a diagonal stripe pattern (line width 0.40 mm, height 30 μm, inclination angle with respect to the first direction 20°, spacing between protrusions in the second direction 3 mm) in a region 2.0 mm inward from both ends in the first direction of the opposing positive electrode and 2.0 mm inward from both ends in the second direction of the positive electrode. In this way, a separator having a substrate and a spacer was obtained in which only the diagonally extending second linear portion was arranged in the second region. The separator was prepared in the same manner as in Example 1 except for this, and the lithium secondary battery B1 was assembled.

[0120] <Comparative Example 2> In the preparation of the separator described in (2) above, the line-shaped portion was formed on one main surface of the microporous thin film in a diagonal stripe pattern (line width 0.40 mm, height 30 μm, inclination angle 20° with respect to the first direction, and spacing 3 mm in the second direction between protrusions) that extends across both ends of the opposing positive electrode in the first direction within a region including both ends of the separator in the first direction. In this way, a separator having a substrate and a spacer, with diagonally extending line-shaped portions arranged in the first and second regions, was obtained. The separator was prepared in the same manner as in Example 1, and lithium secondary battery B2 was completed.

[0121] 《Comparative Example 3》 In the preparation of the separator described in (2) above, the second line-shaped portion (protrusion 402) was arranged in a stripe pattern that extends intermittently parallel to the second direction, similar to the first line-shaped portion (protrusion 401). Specifically, the second line-shaped portion (protrusion 402) extending parallel to the second direction was arranged in a region 2.0 mm inward from the first line-shaped portion, with a line width of 0.40 mm, a height of 30 μm, and a repeat length of 5 mm (coated portion 4.25 mm, intermittent portion (missing portion) 0.75 mm, and a missing portion ratio of 15%). In the stripe pattern, the spacing of the second line-shaped portions in the first direction was 2 mm. In this way, a separator having a base material and a spacer was obtained, in which line-shaped portions extending parallel to the second direction were arranged in the first and second regions. The separator was prepared in the same manner as in Example 1, and the lithium secondary battery B3 was completed.

[0122] [Evaluation 1] (Evaluation of separator warping) For the electrode group prepared in the battery assembly described in (5) above, the diameters (Ferret diameters) of the upper and lower ends of the electrode group were measured. The diameters were measured using calipers at 16 locations with different angles of circumference. If the difference between the maximum and minimum diameters was 1 mm or more at at least one of the upper and lower ends of the electrode group, it was determined that the separator was warped.

[0123] Ten electrode groups were fabricated and their diameters were measured (N=10). The number of electrode groups n that were determined to have separator warping was then determined. The ratio n / N of electrode groups determined to have separator warping was evaluated.

[0124] [Evaluation 2] (Evaluation of cycle characteristics (durability)) Charge and discharge tests were performed on each of the obtained batteries. In the charge and discharge tests, the batteries were charged in a constant temperature chamber at 25°C under the following conditions, then left to rest for 20 minutes, and then discharged under the following conditions.

[0125] (Charging) Constant current charging was performed at a current of 0.5C until the battery voltage reached 4.2V. Then, constant voltage charging was performed at a voltage of 4.2V until the current value reached 15mA. (Discharging) Constant current discharge was performed at a current of 0.5C until the battery voltage reached 2.5V.

[0126] The above charging and discharging process was repeated, with each cycle considered as one. The charging and discharging cycle was repeated until the discharge capacity fell below 80% of the first cycle's discharge capacity. The number of cycles at which the discharge capacity remained above 80% of the first cycle's discharge capacity was then determined. A high number of cycles (e.g., 500 or more) indicates that the secondary battery exhibits excellent cycle characteristics (durability).

[0127] The evaluation results are shown in Table 1. For battery B1, due to wavy separation of the separator during the fabrication of the electrode group, it was not possible to construct the battery and therefore the cycle characteristics could not be evaluated.

[0128]

[0129] As shown in Table 1, in batteries A1 to A5, where a first linear portion (protrusion 401) extending parallel to the second direction is arranged in the first region and a second linear portion (protrusion 402) extending diagonally is arranged in the second region, separator waviness was suppressed and high cycle characteristics were maintained.

[0130] The lithium secondary battery of this disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet devices, electric vehicles including hybrid and plug-in hybrid vehicles, and home battery storage systems combined with solar cells.

[0131] Although the present invention has been described in relation to preferred embodiments at present, such disclosure should not be interpreted restrictively. Various modifications and alterations will undoubtedly become apparent to those skilled in the art in the field to which the invention pertains by reading the above disclosure. Accordingly, the appended claims should be interpreted as encompassing all modifications and alterations without departing from the true spirit and scope of the invention.

[0132] 10 Lithium secondary battery 14 Electrode group 15 Case body 16 Sealing body 17, 18 Insulating plate 19 Positive electrode lead 20 Negative electrode lead 21 Step section 22 Filter 23 Lower valve body 24 Insulating material 25 Upper valve body 26 Cap 27 Gasket 100 Electrode 110 Positive electrode 111 Positive electrode current collector 112 Positive electrode composite layer 120 Negative electrode 121 Negative electrode current collector 300 Separator 400 Spacer layer 401, 402 Protrusions

Claims

1. An electrode group comprising a positive electrode, a negative electrode facing the positive electrode, and a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the positive electrode, the negative electrode, and the separator are elongated in length L1 in a first direction D1 and length L2 (L1 < L2) in a second direction D2 perpendicular to the first direction; the positive electrode comprises a positive electrode current collector and a positive electrode composite layer disposed on the positive electrode current collector; at least one member selected from the group consisting of the positive electrode, the negative electrode, and the separator has a spacer layer, the spacer layer comprises a first spacer and a second spacer; the separator is divided in the first direction into a first region including the vicinity of both ends in the first direction and a second region other than the first region including the central part in the first direction; the width of the second region in the first direction is shorter than the width of the positive electrode composite layer in the first direction. A secondary battery comprising: a first spacer having a first linear portion extending substantially parallel to the second direction, disposed between at least one electrode of the positive electrode and the negative electrode and the first region; a second spacer having a plurality of second linear portions, disposed between at least one electrode of the positive electrode and the negative electrode and the second region, each of the plurality of second linear portions extending diagonally in a direction not perpendicular to the second direction but intersecting the second direction.

2. The secondary battery according to claim 1, wherein the end of the positive electrode in the first direction does not face the first spacer.

3. The secondary battery according to claim 1, wherein the end of the positive electrode in the second direction does not face either the first spacer or the second spacer.

4. The secondary battery according to claim 1, wherein the first linear portion and the second linear portion do not intersect each other.

5. The secondary battery according to claim 1, wherein the first linear portion has a defect that is not continuous in the second direction, and the ratio of the length of the defect to the total length of the first linear portion including the defect is 5% or more and 40% or less.

6. The secondary battery according to claim 1, wherein each of the second line-shaped portions intersects with another opposing second line-shaped portion via at least one electrode.

7. The secondary battery according to claim 1, wherein in the electrode group, the positive electrode and the negative electrode are wound in the second direction via the separator.

8. The secondary battery according to claim 1, wherein the negative electrode is an electrode in which lithium metal is deposited during charging and the lithium metal is dissolved during discharge.

9. A separator having a long shape with a length L1 in a first direction D1 and a length L2 (L1 < L2) in a second direction D2 perpendicular to the first direction, comprising a base layer and a spacer layer, wherein the spacer layer comprises a first spacer and a second spacer, and when the first direction is divided into a first region including the vicinity of both ends in the first direction and a second region other than the first region including the central part in the first direction, the first spacer having a first line-shaped portion extending substantially parallel to the second direction is arranged in the first region, and the second spacer having a plurality of second line-shaped portions is arranged in the second region, and each of the plurality of second line-shaped portions extends diagonally in a direction that is not perpendicular to the second direction but intersects the second direction.

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