Secondary battery and separator

Abstract

This secondary battery comprises: an electrode group including a positive electrode, a negative electrode on the opposite of the positive electrode, and a separator disposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte. A spacer layer having a line-shaped protrusion extending in the shape of a line is disposed between the separator and at least one of the positive electrode and the negative electrode. The line-shaped protrusion has a length D1 in a lengthwise direction in which the line-shaped protrusion extends, and a length D2 in a width direction perpendicular to the lengthwise direction, and satisfies the relationship D1≥D2. The edge of the line-shaped protrusion in the width direction has a contour having a wave line shape.

Description

Secondary batteries and separators Cross-reference of related applications

[0001] This disclosure claims priority rights to Japanese Patent Application No. 2024-168734, filed with the Japan Patent Office on 27 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 that by providing a spacer (protrusion) between the positive electrode and the separator, a space for lithium metal to be deposited during charging is secured, thereby improving charge and discharge efficiency and suppressing cracking of the negative electrode current collector due to localized expansion of the negative electrode.

[0006] Patent Document 2 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 plate 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 plate.

[0007] International Publication No. 2020 / 0066254, Japanese Patent Publication No. 2011-8929

[0008] However, during the fabrication of the electrode group and during charging and discharging, stress applied to the electrodes and spacers can cause spacers to detach or spacer patterns to shift. Spacer detachment reduces the function of space formation and leads to a decrease in cycle characteristics, so it is necessary to eliminate this problem.

[0009] One aspect of the present disclosure relates to a secondary battery comprising 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 a spacer layer having a linearly extending linear protrusion is disposed between at least one of the positive electrode and the negative electrode and the separator, the linear protrusion having a length D1 in the longitudinal direction in which the linear protrusion extends and a length D2 in the width direction perpendicular to the longitudinal direction, D1 ≥ D2, and the edge of the linear protrusion in the width direction has a wavy contour.

[0010] Another aspect of the present disclosure relates to a separator having a base layer and a spacer layer, wherein the spacer layer has linearly extending linear protrusions, the linear protrusions having a length D1 in the longitudinal direction in which the linear protrusions extend and a length D2 in the width direction perpendicular to the longitudinal direction, such that D1 ≥ D2, and the edge of the linear protrusions in the width direction has a wavy contour.

[0011] According to this disclosure, the cycle characteristics of secondary batteries can be improved. 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.

[0012] Figure 3 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. Figure 4 is an enlarged view showing the shape of the linear protrusions of the spacer layers. Figure 5 is a schematic longitudinal cross-sectional view showing a lithium secondary battery according to one embodiment of the present disclosure. Figure 6 is an enlarged view showing the main parts of the lithium secondary battery of Figure 3.

[0013] 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.

[0014] 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.

[0015] 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 electrode and the negative electrode, and a non-aqueous electrolyte. A spacer layer having linearly extending linear protrusions is disposed between at least one of the positive electrode and the negative electrode and the separator. The linear protrusions have a length D1 in the longitudinal direction in which the linear protrusions extend and a length D2 in the width direction perpendicular to the longitudinal direction, where D1 is greater than or equal to D2 (D1 ≥ D2).

[0016] 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 in which a wound electrode group is pressed 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.

[0017] The spacer layer is provided on at least one component selected from the group consisting of a positive electrode, a negative electrode, and a separator. Hereinafter, the positive electrode and negative electrode together may be referred to as the electrode. The spacer layer forms a space between the positive electrode and the separator or between the negative electrode and the separator (between the electrode and the separator), suppressing the expansion of the negative electrode during charging and discharging. It also maintains the shape of the electrode group while maintaining a space between the spacer layer, separator, and electrode.

[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, negative electrode, and 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. By means of this space, the expansion of the negative electrode accompanying charge and discharge is suppressed, and the deterioration of the cycle characteristics is suppressed.

[0021] In the spacer layer, the edge portion of the linear convex portion in the width direction (that is, the edge portion along the direction in which the linear convex portion extends linearly) has a wavy contour. By forming the contour of the linear convex portion in a wavy shape, the stress applied to the spacer layer during charge and discharge is suppressed from concentrating at the corner portions, and the stress is dispersed. As a result, peeling and displacement of the spacer layer are suppressed, and the cycle characteristics are improved.

[0022] The wavy contour has a shape in which peaks and valleys are alternately connected. When the linear convex portion is viewed from the surface of the separator or the electrode, the portion protruding outward in the wavy contour is defined as a peak, and the portion recessed inward is defined as a valley.

[0023] For example, when the spacer layer is arranged in a linear convex portion pattern extending linearly, conventionally, a spacer layer having a linear convex portion with a rectangular contour has been used. In this case, the contour of the linear convex portion is a rectangle having a long side along the straight line along which the linear convex portion extends and a short side along the width direction perpendicular to the straight line. In this case, the stress applied to the spacer layer (linear convex portion) during the production of the electrode group or during charge and discharge concentrates at the corner portions of the rectangle, making the spacer layer liable to peel off, and the peeling of the spacer layer is likely to progress from the corner portions to the whole along the contour of the linear convex portion consisting of straight lines.

[0024] In contrast, according to one embodiment of the present disclosure, by forming the contour of the linear convex portion in a wavy shape, stress is dispersed and peeling is also difficult to spread. Therefore, peeling of the spacer layer and displacement of the spacer layer accompanying the peeling are suppressed, and cycle characteristics as battery performance can be improved.

[0025] In terms of enhancing the stress dispersion effect applied to the spacer layer and enhancing the suppression effect of peeling of the spacer layer, it is preferable that the peak or valley of the wavy shape has no corner portion and the apex of the peak or valley is rounded.

[0026] The wavy shape preferably has a regular shape. The regular shape may be, for example, a periodic shape. It is sufficient that the interval between the peaks or valleys of the wavy shape and / or the height at the apex of the peak or valley is constant or has periodicity. The peaks and valleys of the wavy shape may have a symmetrical shape with respect to each other.

[0027] The minimum value of the height difference of the wavy shape is, for example, 8 μm or more, preferably 10 μm or more. The minimum value of the height difference of the wavy shape is more preferably 25 μm or more. The maximum value of the height difference of the wavy shape may be, for example, 200 μm or less, or may be 1 / 5 times or less of D2.

[0028] The height difference of the wavy shape means the difference between the distance from the center line at the apex of the peak farthest from the center line and the distance from the center line at the apex of the valley closest to the center line when a center line is drawn along the direction in which the linear convex portion extends with respect to the linear convex portion. When there are a plurality of peaks or valleys, the minimum value of the height difference of the wavy shape is the difference between the minimum value of the distance from the center line at the apex of each peak and the maximum value of the distance from the center line at the apex of each valley. Similarly, the maximum value of the height difference of the wavy shape is the difference between the maximum value of the distance from the center line at the apex of each peak and the minimum value of the distance from the center line at the apex of each valley.

[0029] The minimum value of the wavelength of the wavy shape is, for example, 15 μm or more, preferably 25 μm or more. The minimum value of the wavelength of the wavy shape is more preferably 50 μm or more. The maximum value of the wavelength of the wavy shape may be, for example, 1 mm or less.

[0030] The wavelength of a waveform refers to the distance between adjacent peaks or valleys in the contour of a linear convex section, separated by a valley. If there are multiple peaks or valleys, the minimum wavelength of the waveform is the smallest of the distances between peaks and valleys. The maximum wavelength of the waveform is the largest of the distances between peaks and valleys.

[0031] Linear protrusions having a wavy contour can be formed, for example, by applying a coating solution containing a spacer layer component and a liquid component to a predetermined location on the substrate of an electrode or separator, and then drying the coating film. Examples of liquid components include N-methyl-2-pyrrolidone. Coating may be performed using a dispenser or other known printing methods such as gravure printing, inkjet printing, and screen printing. Drying may be performed by known methods such as heating or natural drying.

[0032] The arrangement pattern of the linear protrusions in the spacer layer is not particularly limited and may be a straight line pattern, a curved line pattern, a polygonal line pattern (e.g., rectangle or regular hexagon), or a mesh-like geometric pattern (e.g., a hexagonal honeycomb shape). The shape of the mesh in the mesh-like pattern is not particularly limited, but may be polygonal, with quadrilaterals or hexagons being preferred.

[0033] To suppress the decrease in electrolyte circulation due to the placement of the spacer layer, it is preferable that the linear protrusions have defects that are not continuous in a predetermined direction (for example, in a wound electrode group, in a direction intersecting the winding axis). The spacer layer may reduce the circulation of the electrolyte, but the defects form a flow path for the electrolyte, suppressing the decrease in electrolyte circulation. The electrolyte can circulate through the defects, thereby improving circulation and suppressing the decrease in cycle characteristics. Therefore, the defects allow for maintaining high electrolyte circulation while ensuring the space-forming ability of the spacer layer, improving the cycle characteristics of the secondary battery.

[0034] The ratio of the length of the missing portion to the total length of the linear protrusion including the missing portion may be 5% or more and 40% or less. Here, the ratio of the length of the missing portion means the ratio of the total length of the missing portion to the total length of the linear protrusion assuming that the protrusion exists in a linear shape in the missing portion.

[0035] 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.

[0036] 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 (the width of the line-shaped protrusion 401 in Figures 1 and 2, i.e., the length of D2) may be, for example, 1 mm or less, or 0.1 mm or more and 1 mm or less.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] A separator according to one embodiment of the present disclosure relates to a separator provided with the above-described spacer layer. The separator comprises a base layer and a spacer layer, wherein the spacer layer has linearly extending linear protrusions. The linear protrusions have a length D1 in the longitudinal direction in which the linear protrusions extend and a length D2 in the width direction perpendicular to the longitudinal direction, where D1 ≥ D2. The edges of the linear protrusions in the width direction have a wavy contour.

[0044] 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.

[0045] Figure 1 is a schematic plan view showing the spacer layer (linear protrusions) arranged on the surface of the separator. Figure 2 is an enlarged view showing the shape of the linear protrusions in Figure 1. Note that in Figure 1, the linear protrusions are exaggerated, and the ratio of the dimensions of each part of the linear protrusions to the dimensions of the separator rod does not necessarily match reality.

[0046] The separator 300 shown in the example in Figure 1 has a spacer layer 400.

[0047] The spacer layer 400 consists of a plurality of linear protrusions 401 arranged on the surface of the separator 300 in a regular hexagonal mesh (honeycomb) pattern. Each of the plurality of linear protrusions 401 is positioned at a location corresponding to the side of the regular hexagon and has a defect at a location corresponding to the vertex of the regular hexagon.

[0048] As shown in Figure 2, the linear projection 401 has a roughly rectangular shape and has a length D1 in the longitudinal direction in which the linear projection 401 extends, and a length D2 in the width direction perpendicular to the longitudinal direction. However, the contour of the linear projection is not a straight line corresponding to each side of the rectangle, but has a wavy shape along the straight line. The edge of the linear projection in the width direction (the edge of the linear projection along the D2 direction) has a wavy contour.

[0049] In the example shown in Figure 2, the wavy line shape has a periodic shape in which waves with wavelength W and height (difference between the highest and lowest values) X are repeated.

[0050] During the transport of components with spacers, during the fabrication of electrode groups, and during charging and discharging, stress is applied to the spacer layer (linear protrusions). If the linear protrusions have a shape with corners, such as the vertices of a rectangle, this stress concentrates at the corners, and peeling progresses from the corners along each side of the rectangle to the entire structure.

[0051] However, the linear protrusions 401 have rounded corners, which reduces stress concentration at the corners, making them less prone to peeling under stress. In addition, the wavy contour helps to distribute stress even if peeling occurs, preventing the peeling from spreading. As a result, the reduction in space-forming ability due to peeling of the spacer layer is suppressed, and the cycle characteristics of the secondary battery can be maintained at a high level.

[0052] 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.

[0053] Lithium-ion batteries are 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 lithium-ion batteries, the spacer layer serves to secure space on the negative electrode surface for the deposition of lithium metal. 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.

[0054] 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).

[0055] [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 during charging. More specifically, lithium ions contained in the non-aqueous electrolyte accept electrons on the negative electrode current collector during charging, becoming lithium metal, and depositing 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 during discharge. 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 during charging, or both. The negative electrode may consist only of the negative electrode current collector, or it may include a thin lithium metal foil that has been pre-pressed onto the negative electrode current collector.

[0056] The negative electrode current collector can be any conductive sheet. Examples of conductive sheets include foil and film.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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).

[0063] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjenblack, carbon nanotubes, and graphite.

[0064] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0065] [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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjenblack, carbon nanotubes, and graphite.

[0070] Examples of binders include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubbery polymers. Examples of fluororesins include polytetrafluoroethylene and polyvinylidene fluoride.

[0071] 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.

[0072] 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).

[0073] 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.

[0074] [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.

[0075] [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.

[0076] 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.

[0077] 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.

[0078] As the lithium salt or anion, known ones used in the non-aqueous electrolyte of a lithium secondary battery can be used. Specifically, BF ４ － , ClO ４ － , PF ６ － , CF ３ SO ３ － , CF ３ CO ２ － , anions of imides, anions of oxalate complexes, and the like can be mentioned. As the anions of imides, N(SO ２ CF ３ ), N(C ２ － ), N(C ｍ F ２ｍ＋１ SO ２ ), N(C ｘ F ｎ SO ２ｎ＋１ ), N(C ２ F ｙ － (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 can be mentioned. The anion of the oxalate complex may contain boron and / or phosphorus. As the anion of the oxalate complex, bisoxalate borate anion, BF ２ (C ２ O ４ ), PF － (C ４ O ２ ), PF [[ID=F]] ４ － , PF ２ (C ２ O ４ ), PF ２ － ​Examples include these. Non-aqueous electrolytes may contain these anions individually or in combination of two or more.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] Figure 3 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] Figure 4 is a schematic enlarged view showing the discharge state of region X enclosed by the dashed line in Figure 3. 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.

[0092] 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. In the discharge state, no lithium metal is 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 charging 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 the negative electrode current collector 121 and the lithium metal deposited on its surface in the charging state.

[0093] 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.

[0094] 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.

[0095] (Note) The above description of embodiments discloses the following technologies. (Technology 1) A secondary battery comprising: 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 a spacer layer having linearly extending linear protrusions is disposed between at least one of the positive electrode and the negative electrode and the separator, the linear protrusions having a length D1 in the length direction in which the linear protrusions extend and a length D2 in the width direction perpendicular to the length direction, where D1 ≥ D2, and the edge of the linear protrusions in the width direction having a wavy contour. (Technology 2) The secondary battery according to Technology 1, wherein the peaks or valleys of the wavy shape are rounded. (Technology 3) The secondary battery according to Technology 1 or 2, wherein the wavy shape has a regular shape. (Technology 4) A secondary battery according to any one of Technology 1 to 3, wherein the minimum value of the height difference of the wave-shaped form is 10 μm or more. (Technology 5) A secondary battery according to any one of Technology 1 to 3, wherein the minimum value of the height difference of the wave-shaped form is 25 μm or more. (Technology 6) A secondary battery according to any one of Technology 1 to 5, wherein the minimum value of the wavelength of the wave-shaped form is 25 μm or more. (Technology 7) A secondary battery according to any one of Technology 1 to 5, wherein the minimum value of the wavelength of the wave-shaped form is 50 μm or more. (Technology 8) A separator having a base layer and a spacer layer, wherein the spacer layer has a linear projection extending in a line shape, the linear projection has a length D1 in the length direction in which the linear projection extends and a length D2 in the width direction perpendicular to the length direction, D1 ≥ D2, and the edge of the linear projection in the width direction has a wave-shaped contour.

[0096] [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.

[0097] Examples 1-9 (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 mixture slurry. The obtained positive electrode mixture slurry was applied to both sides of a strip-shaped Al foil (positive electrode current collector), dried, and the coating of the positive electrode mixture was rolled using a roller. Finally, the resulting laminate of positive electrode current collector and positive electrode composite material was cut to a predetermined electrode size, and a positive electrode having positive electrode composite material layers on both sides of the positive electrode current collector was obtained.

[0098] (2) Fabrication of the negative electrode A strip of electrolytic copper foil (thickness 15 μm) was prepared as the negative electrode current collector.

[0099] (3) Separator preparation A microporous thin film made of polyethylene with a thickness of 20 μm was prepared as a separator.

[0100] Insulating particles (median diameter 3 μm, volume resistivity 10) １４ A dispersion of the spacer material was prepared by mixing 60 volumes of (Ω·cm), 39 volumes of alkyd resin (a binder resin), 1 volume of CMC (sodium salt), and water (a dispersion medium).

[0101] Next, using a dispenser, a dispersion of the spacer material was dispensed onto one side of each of the pair of microporous thin films in a predetermined pattern, and the coating film was vacuum-dried to form the linear protrusions of a regular hexagonal mesh pattern shown in Figure 1. The length of each side of the regular hexagons constituting the mesh was 1.5 mm. The length of the linear protrusions (length D1 along each side of the regular hexagon) was 1 mm, the width D2 was 0.5 mm, and the thickness was 40 μm.

[0102] The edges of the linear protrusions were formed to have a wavy contour. The wavy shape was a periodic shape with a constant wavelength W and height (difference between the highest and lowest values) X. The wavelength W and height X were as shown in Table 1. In this way, a separator was fabricated having a base material and a spacer, with the arrangement of the spacer layer (linear protrusions) shown in Figure 1.

[0103] (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.

[0104] (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 separators were arranged so that the spacers formed on one side of each separator faced the negative electrode. The electrode group was housed in a bag-shaped outer casing made of a laminate sheet having an Al layer, a non-aqueous electrolyte was injected, and the outer casing was sealed to complete the lithium secondary batteries A1 to A9 according to Examples 1 to 9.

[0105] <Comparative Example 1> In the preparation of the separator described in (3) above, the linear protrusions were formed in a shape that did not have a wavy contour at their edges. That is, linear protrusions having a rectangular contour of 1 mm in length and 0.5 mm in width were arranged in a regular hexagonal mesh pattern similar to that in Figure 1, and the separator was obtained in the same manner as in Example 1.

[0106] Using the obtained separator, a lithium secondary battery B1 according to Comparative Example 1 was completed in the same manner as in Example 1.

[0107] [Evaluation 1] (Separator peel test) The separator prepared in (3) above was cut to a width of 15 mm and a length of 60 to 100 mm. With the side of the separator facing outwards, the ends of the separator in the longitudinal direction were overlapped and the ends were pressed together to form a ring. After inserting a 3 mm diameter pin into the ring, the pin was moved to the opposite side of the ends and the separator was pulled. The state in which tensile stress was applied to the separator was maintained for several seconds.

[0108] Subsequently, the separator was opened, and the appearance of the linear protrusions formed in the bent portion of the separator by the pins was visually inspected to check for cracks and peeling of the linear protrusions.

[0109] The pin diameter was changed to 2 mm, and the presence or absence of cracks and peeling in the linear protrusions was checked using the same method.

[0110] In both cases, when using a 3 mm diameter pin and when using a 2 mm diameter pin, if no cracks or peeling were observed in the linear protrusions, the peel test result was considered very good and was evaluated with "◎".

[0111] When a 3 mm diameter pin was used, no cracks or peeling were observed in the linear protrusions. However, when a 2 mm diameter pin was used, cracks and peeling were observed in the linear protrusions. In such cases, the peel test result was considered good (Good) and evaluated with a "○".

[0112] [Evaluation 2] (Capacity retention rate) For each battery, a charge-discharge test was performed in a constant temperature chamber at 25°C under the following conditions. The rest period between charging and discharging was 20 minutes.

[0113] (Charging) Constant current charging was performed at a current of 2.15 mA per unit area (square centimeter) of the electrodes until the battery voltage reached 4.1 V. Then, constant voltage charging was performed at a voltage of 4.1 V until the current value per unit area of ​​the electrodes reached 0.54 mA.

[0114] (Discharge) A constant current discharge was performed at a current of 2.15 mA per unit area of ​​the electrodes until the battery voltage reached 3.75 V.

[0115] The above charging and discharging process was considered one cycle, and charging and discharging was performed up to 200 cycles. The ratio (%) of the discharge capacity at cycle 200 to the discharge capacity at cycle 1 was calculated as the capacity retention rate.

[0116] The evaluation results are shown in Table 1. Batteries A1 to A9, which used a spacer layer having a wavy contour at the edge of the linear protrusion, showed suppressed peeling of the linear protrusion and improved cycle characteristics compared to battery B1, which used a spacer layer without a wavy shape.

[0117]

[0118] The 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.

[0119] 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.

[0120] 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 Linear protrusion

Claims

1. A secondary battery comprising: 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 a spacer layer having a linearly extending linear protrusion is disposed between at least one of the positive electrode and the negative electrode and the separator, the linear protrusion having a length D1 in the longitudinal direction in which the linear protrusion extends and a length D2 in the width direction perpendicular to the longitudinal direction, where D1 ≥ D2, and the edge of the linear protrusion in the width direction having a wavy contour.

2. The secondary battery according to claim 1, wherein the peaks of the wavy peaks or valleys are rounded.

3. The secondary battery according to claim 1, wherein the wavy shape has a regular shape.

4. The secondary battery according to any one of claims 1 to 3, wherein the minimum value of the height difference of the wave-shaped pattern is 10 μm or more.

5. The secondary battery according to any one of claims 1 to 3, wherein the minimum value of the height difference of the wave-shaped pattern is 25 μm or more.

6. The secondary battery according to any one of claims 1 to 3, wherein the minimum value of the wavelength of the waveform is 25 μm or more.

7. The secondary battery according to any one of claims 1 to 3, wherein the minimum value of the wavelength of the waveform is 50 μm or more.

8. A separator comprising a base layer and a spacer layer, wherein the spacer layer has linearly extending linear protrusions, the linear protrusions have a length D1 in the longitudinal direction in which the linear protrusions extend and a length D2 in the width direction perpendicular to the longitudinal direction, such that D1 ≥ D2, and the edge of the linear protrusions in the width direction has a wavy contour.

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