Lithium secondary battery and composite member

Abstract

This lithium secondary battery is provided with a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity, the negative electrode being an electrode in which lithium metal is precipitated during charging and dissolved during discharging, a first separator being provided between the negative electrode and the separator, and a second separator being provided between the negative electrode and the separator. A second separator is provided between the positive electrode and the separator.

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery and a composite component. Background Art

[0002] Non-aqueous electrolyte secondary batteries are used for ICT, vehicle-mounted, and power storage applications such as personal computers and smart phones. In such applications, non-aqueous electrolyte secondary batteries are required to be further high-capacity. As high-capacity non-aqueous electrolyte secondary batteries, lithium-ion batteries are known. The high-capacity of lithium-ion batteries can be achieved by, for example, using alloy active materials such as graphite and silicon compounds as negative electrode active materials. However, the high-capacity of lithium-ion batteries is reaching its limit.

[0003] As a non-aqueous electrolyte secondary battery with a higher capacity than a lithium-ion battery, a lithium secondary battery (lithium metal secondary battery) is promising. In a lithium secondary battery, lithium metal is deposited at the negative electrode during charging, and the lithium metal is dissolved in the non-aqueous electrolyte during discharge. Various proposals have been made in the past regarding lithium secondary batteries.

[0004] Patent document 1 discloses a secondary battery comprising a positive electrode containing a lithium-containing positive electrode active material, a negative electrode opposite to the positive electrode and having a negative electrode collector, a separator arranged between the positive electrode and the negative electrode, and a non-aqueous electrolyte with lithium ion conductivity, wherein the negative electrode collector has a layer including a first surface and a second surface opposite to the first surface, a plurality of first protrusions protruding from the first surface, and a second protrusion protruding from the second surface, lithium metal is precipitated on the first surface and the second surface during charging, and when observed from the normal direction of the above-mentioned first surface, the total area of ​​the overlapping parts of the above-mentioned plurality of first protrusions and the above-mentioned plurality of second protrusions is less than 1 / 2 of the total area of ​​the above-mentioned plurality of first protrusions.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-212603 Summary of the invention

[0008] Problems to be solved by the invention

[0009] Lithium secondary batteries are required to have improved cycle characteristics.

[0010] Solution

[0011] One aspect of the present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and a non-aqueous electrolyte with lithium ion conductivity, wherein the negative electrode is an electrode in which lithium metal is precipitated during charging and the lithium metal is dissolved during discharging, a first separator is arranged between the negative electrode and the separator, and a second separator is arranged between the positive electrode and the separator.

[0012] In addition, another aspect of the present invention relates to a composite component, the composite component comprising: a diaphragm having a second main surface opposite to a first main surface and the first main surface; a first spacer disposed on the first main surface; and a second spacer disposed on the second main surface. A ratio of a thickness T1 of the first spacer to a thickness T2 of the second spacer: T1 / T2 is greater than 1.

[0013] Effects of the Invention

[0014] According to the present invention, the cycle characteristics of a lithium secondary battery can be improved.

[0015] Although the novel features of the present invention are described in the attached claims, the present invention will be more clearly understood with respect to both the composition and content of the present invention through the following detailed description in conjunction with other objects and features of the present invention and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a longitudinal sectional view schematically showing an example of a lithium secondary battery according to an embodiment of the present disclosure.

[0017] Figure 2 It is a cross-sectional view schematically showing a main part of an electrode group in a lithium secondary battery according to an embodiment of the present disclosure. Figure 2 (a) and (b) show the main parts of the electrode group during discharge and charge, respectively.

[0018] Figure 3 It is a top view of an example of the pattern of the first spacer.

[0019] Figure 4 yes Figure 3 A partial enlarged view of .

[0020] Figure 5 It is a plan view showing another example of the pattern of the first spacer.

[0021] Figure 6 This is a cross-sectional view schematically showing a main part of an electrode group in a case where a first separator is disposed but a second separator is not disposed. Figure 6 (a) and (b) respectively represent the main parts of the electrode group during discharge and charge.

[0022] Figure 7 This is a cross-sectional view schematically showing a main part of an electrode group in a case where the second separator is disposed but the first separator is not disposed. Figure 7 (a) and (b) respectively represent the main parts of the electrode group during discharge and charge.

[0023] Figure 8 This is a cross-sectional view schematically showing a main part of an example of a composite component composed of a diaphragm, a first spacer, and a second spacer. DETAILED DESCRIPTION

[0024] The following will illustrate the embodiments of the present disclosure, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. are sometimes illustrated, but other numerical values, materials, etc. can also be applied as long as the effects of the present disclosure can be obtained. In addition, the constituent elements other than the characteristic parts of the present disclosure can also be applied to the constituent elements of known secondary batteries. In this specification, when it is referred to as "a range of numerical values ​​A to numerical values ​​B", the range includes numerical values ​​A and numerical values ​​B. In the following description, when the lower limit and upper limit are illustrated with respect to the numerical values ​​of specific physical properties or conditions, as long as the lower limit is not above the upper limit, any one of the illustrated lower limits and any one of the illustrated upper limits can be arbitrarily combined. When multiple materials are illustrated, one can be selected and used alone, or two or more can be used in combination.

[0025] The present invention includes a combination of features described in two or more claims selected from a plurality of claims described in the attached claims, that is, as long as no technical contradiction occurs, the features described in two or more claims selected from a plurality of claims described in the attached claims can be combined. In addition, each figure of the accompanying drawings is a schematic diagram, and in each figure, the shape or feature of each constituent molded product does not necessarily reflect the actual size, nor is it necessarily represented by the same scale.

[0026] The lithium secondary battery according to the embodiment of the present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity. The negative electrode is an electrode where lithium metal is precipitated during charging and dissolved during discharging.

[0027] In a lithium secondary battery, more than 70% of the rated capacity, for example, is expressed by the precipitation and dissolution of lithium metal. The migration of electrons in the negative electrode during charging and discharging is mainly carried out by the precipitation and dissolution of lithium metal in the negative electrode. Specifically, 70 to 100% (for example, 80 to 100% or 90 to 100%) of the movement of electrons in the negative electrode during charging and discharging (current from another point of view) is carried out by the precipitation and dissolution of lithium metal. That is, the movement of electrons in the negative electrode involved in the present disclosure during charging and discharging is different from that of the negative electrode in which lithium ions are mainly absorbed and released by the negative electrode active material (graphite, etc.).

[0028] Hereinafter, the positive electrode, the negative electrode and the separator are collectively referred to as an "electrode group". The electrode group may be a wound electrode group or a stacked electrode group. The wound electrode group is formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator located between the positive electrode and the negative electrode. The stacked electrode group is formed by stacking a sheet-shaped positive electrode and a sheet-shaped negative electrode with a separator located between the positive electrode and the negative electrode.

[0029] In the lithium secondary battery of the embodiment of the present disclosure, a first separator is provided between the negative electrode and the separator, and a second separator is provided between the positive electrode and the separator. Hereinafter, the first separator and the second separator may be collectively referred to as "separators".

[0030] here, Figure 2 This is a cross-sectional view schematically showing a main part of an electrode group in an example of a lithium secondary battery according to an embodiment of the present disclosure. Figure 2 (a) and (b) show the main parts of the electrode group during discharge and charge, respectively. Figure 2 In the case of a stacked electrode group, a cross section in the stacking direction is shown, and in the case of a wound electrode group, a cross section in the winding axis direction is shown.

[0031] like Figure 2 As shown in (a), the electrode group includes a positive electrode 11, a negative electrode 12, and a separator 13. A first separator 51 is provided between the negative electrode 12 and the separator 13, and a second separator 52 is provided between the positive electrode 11 and the separator 13. The first separator 51 forms a first space 51s on the surface of the negative electrode 12 (the surface opposite to the positive electrode 11). The second separator 52 forms a second space 52s on the surface of the positive electrode 11 (the surface opposite to the negative electrode 12).

[0032] like Figure 2As shown in (b), during charging, lithium metal 12a is deposited on the negative electrode 12. At this time, lithium metal 12a is first deposited in the first space 51s. As the deposition of lithium metal 12a further proceeds, the portion of the separator 13 that is not in contact with the second separator 52 is pushed up to the positive electrode 11 side. Since the second space 52s is formed in the portion where the second separator 52 does not exist, the separator 13 in this portion can move to the positive electrode 11 side. Therefore, during repeated charge and discharge, the expansion of the electrode group is suppressed.

[0033] On the other hand, in the portion of the separator 13 in contact with the second separator 52, the movement of the separator 13 toward the positive electrode 11 side is suppressed during charging (when the lithium metal 12a is precipitated), and a part of the second space 52s remains as a space 53 near the second separator 52. The precipitated lithium metal 12a presses the separator 13, and the non-aqueous electrolyte is squeezed out of the separator 13, but the non-aqueous electrolyte is accommodated in the space 53. This can suppress the non-aqueous electrolyte from being squeezed out of the electrode group (depletion of the non-aqueous electrolyte in the electrode group) due to the precipitation of the lithium metal 12a.

[0034] In summary, in the lithium secondary battery disclosed herein, by providing the first separator and the second separator, the expansion of the electrode group can be suppressed during repeated charge and discharge, and the depletion of the non-aqueous electrolyte in the electrode group can be suppressed. As a result, the cycle characteristics (discharge capacity maintenance rate) of the lithium secondary battery can be improved.

[0035] Below, refer to Figure 6 A case where the first spacer is disposed but the second spacer is not disposed will be described. Figure 6 It is a cross-sectional view schematically showing a main part of an electrode group in a case where a first separator is disposed but a second separator is not disposed. Figure 6 (a) and (b) respectively represent the main parts of the electrode group during discharge and charge.

[0036] like Figure 6 As shown in (a), when the first separator 51 is disposed and the second separator is not disposed, the first space 51s is formed on the surface of the negative electrode 12, but the second space is not formed on the surface of the positive electrode 11. Figure 6 As shown in (b), during charging, lithium metal 12a is precipitated in the first space 51s, which can suppress the expansion of the electrode group, but it is difficult to ensure a storage space for the non-aqueous electrolyte squeezed out of the separator as the lithium metal is precipitated. Therefore, the non-aqueous electrolyte is squeezed out of the electrode group, and the non-aqueous electrolyte in the electrode group is easily exhausted.

[0037] In addition, refer to Figure 7 , a case where the second spacer is configured but the first spacer is not configured will be described. Figure 7This is a cross-sectional view schematically showing a main part of an electrode group in a case where the second separator is disposed but the first separator is not disposed. Figure 7 (a) and (b) respectively represent the main parts of the electrode group during discharge and charge.

[0038] like Figure 7 As shown in (a), when the second separator 52 is disposed and the first separator is not disposed, the second space 52s is formed on the surface of the positive electrode 11, but the first space is not formed on the surface of the negative electrode 12. Figure 7 As shown in (b), during charging, the precipitated lithium metal 12a pushes the second separator 52 together with the separator 13 toward the positive electrode 11. As a result, the distance between the negative electrode 12 and the positive electrode 11 increases, and the electrode group may expand.

[0039] (Spacer)

[0040] From the viewpoint of easily suppressing the expansion of the electrode group, the ratio of the thickness T1 of the first separator to the thickness T2 of the second separator: T1 / T2 can be 1 / 3 or more, preferably 1 or more, and more preferably 2 or more. From the viewpoint of easily suppressing the depletion of the non-aqueous electrolyte in the electrode group, T1 / T2 can be 7 or less, preferably 5 or less, and more preferably 3 or less. The thickness T1 of the first separator is, for example, 10 μm or more and 35 μm or less. In addition, the thickness of the separator is synonymous with the height of the convex portion constituting the separator.

[0041] When the first separator and the second separator are used together, the thickness of the first separator can be reduced compared to the case where only the first separator is used, and the separator is arranged near the negative electrode, which can suppress the precipitation of lithium metal in a rough state. That is, the precipitation morphology of lithium metal can be controlled, and the generation of dendrites (isolation of lithium metal, short circuit, etc. caused by the generation of dendrites) can be suppressed.

[0042] From the viewpoint of fully ensuring the first space and easily obtaining a high initial charge capacity, the ratio of the area S1 of one surface of the negative electrode in contact with the first separator in the region relative to the area S0 of the region opposite to the positive electrode: S1 / S0 can be 0.2 or less, or 0.15 or less. In addition, from the viewpoint of easily stably forming the first space through the first separator, S1 / S0 can be 0.03 or more, or 0.05 or more. When the negative electrode has regions opposite to the positive electrode on both sides thereof, and the first separator (first space) is provided on both sides of the negative electrode, it is preferred that S1 / S0 is within the above range on both sides of the negative electrode.

[0043] From the viewpoint of fully ensuring the second space and easily obtaining a high initial charge capacity, the ratio of the area S2 of one surface of the positive electrode in contact with the second separator in the region relative to the area S0 of the region opposite to the negative electrode in one surface of the positive electrode: S2 / S0 can be less than 0.2, or less than 0.15. In addition, from the viewpoint of easily stably forming the second space through the second separator, S2 / S0 can be greater than 0.03, or greater than 0.05. When the positive electrode has a region opposite to the negative electrode on both sides thereof, and the second separator (second space) is provided on both sides of the positive electrode, it is preferred that S2 / S0 on both sides of the positive electrode are within the above range.

[0044] The ratio of the area S1 to the area S2: S1 / S2 may be, for example, not less than 0.3 and not more than 3.

[0045] The spacer is composed of, for example, a plurality of convex portions. The shape of the convex portion may be linear, dotted, etc. The linear shape may be a straight line or a curved line. The spacer may be composed of a plurality of linear convex portions, or may be composed by dispersing a plurality of dotted convex portions. The linear convex portions adjacent to each other may be connected to each other or may be separated. The width of the linear convex portion may be greater than 100 μm (or greater than 200 μm) and less than 2000 μm (or less than 1000 μm).

[0046] From the viewpoint that the first space and the second space are easily and stably formed, it is preferred that the first spacer and the second spacer (the convex portions constituting the first spacer and the second spacer) overlap in whole or in part via the separator. In the case where the first spacer and the second spacer are respectively constituted by linear convex portions, it is also possible to appropriately form a portion where the linear convex portions of the first spacer and the second spacer intersect each other via the separator when the electrode group is formed.

[0047] When the first spacer and the second spacer are respectively composed of linear protrusions, the ratio of the width W1 of the linear protrusion of the first spacer to the width W2 of the linear protrusion of the second spacer: W1 / W2 may be, for example, 0.3 or more and 3 or less (or 1.5 or less).

[0048] The spacer preferably has a prescribed pattern shape. As the shape of the pattern, mesh, stripe, dot, etc. can be listed. At least one of the first spacer and the second spacer can have a mesh pattern. In the case of a mesh pattern, it is easy to form a space between the electrode and the diaphragm uniformly and stably through the spacer, and the precipitation of lithium metal is easy to be uniformly precipitated, and it is easy to suppress the application of large stress to the electrode locally.

[0049] The mesh pattern may be a collection of polygons. An example of a mesh pattern includes a shape formed by combining polygons in a shared edge manner. Polygons include triangles, quadrilaterals, hexagons, etc. Different types of polygons may also be combined. The mesh pattern may also be a honeycomb shape.

[0050] The stripe-shaped pattern can also be formed by, for example, arranging a plurality of linear protrusions spaced apart from each other in the width direction of a strip-shaped electrode (separator) and arranging them in parallel along the longitudinal direction.

[0051] The first separator and the second separator may have different pattern shapes from each other. By appropriately selecting different pattern shapes for the first separator and the second separator, the overlapping portion of the first separator and the second separator can be stably formed when the electrode group is formed (especially in the case of a winding type). For example, the portion where the linear protrusions constituting the first separator and the second separator intersect with each other through the separator can be stably formed. For example, one of the first separator and the second separator may have a mesh pattern, while the other of the first separator and the second separator may have a stripe pattern. In this case, when the electrode group is formed, the overlapping portion (intersection portion) of the first separator and the second separator through the separator can be appropriately distributed and formed. Thus, the first space and the second space can be stably formed when the electrode group is formed.

[0052] From the viewpoints of productivity, manufacturing cost, etc., the first spacer and the second spacer may also have the same pattern shape as each other. For example, the first spacer and the second spacer may have a mesh pattern, respectively. In this case, the first spacer and the second spacer may be arranged to overlap as a whole via the diaphragm, or may be arranged to be partially overlapped and staggered via the diaphragm. When the electrode group is formed (especially in the case of a winding type), the overlapping portion (cross portion) of the first spacer and the second spacer via the diaphragm can be appropriately distributed and formed. Thus, the first space and the second space can be stably formed when the electrode group is formed.

[0053] The first separator may be disposed on the surface of the negative electrode (the surface opposite to the positive electrode) or on the surface of the separator (the surface on the negative electrode side, and the region where the positive electrode and the negative electrode are opposite). The second separator may be disposed on the surface of the positive electrode (the surface opposite to the negative electrode) or on the surface of the separator (the surface on the positive electrode side, and the region where the positive electrode and the negative electrode are opposite).

[0054] The first separator may be provided on one surface (first main surface) of the separator, and the second separator may be provided on the other surface (second main surface) of the separator. That is, a composite component including the separator, the first separator and the second separator may be formed. When forming the electrode group, the composite component is arranged in such a manner that the first main surface is the negative electrode side and the second main surface is the positive electrode side. In the composite component, T1 / T2 is preferably in the above range (e.g., greater than 1).

[0055] When a spacer is formed on one side of the diaphragm, the diaphragm (substrate) will warp toward the side formed by the spacer due to the stress when the spacer is formed. The warping of the diaphragm may cause manufacturing defects (wrinkles or meandering during transportation, misalignment of the end face of the diaphragm during winding (winding deviation), etc.). In contrast, when the spacer is formed on both sides of the diaphragm, the warping of the above-mentioned diaphragm is suppressed. When the pattern shape of the spacer is a mesh shape, it is easier to suppress the above-mentioned warping.

[0056] here, Figure 8 It is a cross-sectional view schematically showing a main part of a composite component. Figure 8 Indicates the cross section in the thickness direction of the diaphragm. Figure 8 This is an example of a composite component, but the composite component is not limited to this.

[0057] The composite component 70 includes a diaphragm 13, a first separator 51, and a second separator 52. The diaphragm 13 includes a first main surface S1 and a second main surface S2 on the opposite side of the first main surface S1. When forming an electrode group, the first main surface S1 is opposite to the negative electrode, and the second main surface S2 is opposite to the positive electrode. The first separator 51 is provided on the first main surface S1 of the diaphragm 13. The second separator 52 is provided on the second main surface S2 of the diaphragm 13. The ratio of the thickness T1 of the first separator 51 to the thickness T2 of the second separator 52: T1 / T2 is preferably greater than 1. Figure 8 In the diagram, when the diaphragm 13 is viewed from the normal direction of the first main surface S1 (the second main surface S2), the first spacer 51 and the second spacer 52 are arranged at substantially the same position so as to overlap each other, but may be arranged at different positions.

[0058] There is no particular restriction on the material constituting the separator. The separator may be composed of a conductive material and / or an insulating material. As the conductive material, for example, it may be appropriately selected from the materials exemplified as the material of the negative electrode collector. The first separator may also be provided, for example, by forming a convex portion by pressing the negative electrode collector. In addition, a conductive coating may be applied to the surface of the negative electrode, or a conductive tape may be attached to the surface of the negative electrode.

[0059] As insulating materials, resin materials can be cited. As resin materials, for example, polyolefin resins, acrylic resins, polyamide resins, polyimide resins, silicone resins, fluorine resins, polyurethane resins, melamine resins, urea resins, etc. can be cited. Cured materials of curable resins such as epoxy resins can also be used. As spacers, resin materials such as polyimide, polyvinylidene fluoride, acrylonitrile-acrylate copolymers that are difficult for lithium ions to penetrate can also be used.

[0060] In addition, as a spacer, a spacer obtained by mixing an inorganic filler in a resin material can also be used. As the inorganic filler, inorganic particles such as insulating metal oxides can be listed. As the insulating metal oxide, aluminum oxide (aluminum oxide or boehmite), magnesium oxide, titanium oxide (titania), zirconium oxide, silicon oxide (silicon dioxide) and the like can be listed.

[0061] The spacer can also be formed by, for example, attaching a resin adhesive tape to the surface of an electrode or a separator. The spacer can be formed by applying a solution (or dispersion) containing a resin material (or a resin material and an inorganic filler) to the surface of an electrode or a separator and drying it. The spacer can also be formed by applying a curable resin to the surface of an electrode or a separator in a desired shape and curing it.

[0062] Hereinafter, examples of the components of the lithium secondary battery will be specifically described. In addition, the components described below are only examples, and the components of the lithium secondary battery of this embodiment are not limited to the following components. As components other than the characteristic parts of this embodiment, known components may also be used.

[0063] [negative electrode]

[0064] The negative electrode includes a negative electrode collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode collector by charging. More specifically, the lithium ions contained in the non-aqueous electrolyte receive electrons from the negative electrode collector by charging and become lithium metal, which is deposited on the surface of the negative electrode collector. The lithium metal deposited on the surface of the negative electrode collector is dissolved in the non-aqueous electrolyte as lithium ions by discharging. In addition, the lithium ions contained in the non-aqueous electrolyte may be derived from a lithium salt added to the non-aqueous electrolyte, may be supplied from the positive electrode active material by charging, or may be both.

[0065] A conductive sheet can be used as the negative electrode current collector. When the electrode group is a wound type, a strip-shaped conductive sheet is used. Examples of the conductive sheet include conductive films, metal foils, and the like.

[0066] The surface of the conductive sheet may be smooth. Thus, during charging, lithium metal from the positive electrode is easily deposited evenly on the conductive sheet. Smooth means that the maximum height roughness Rz of the conductive sheet is less than 20 μm. The maximum height roughness Rz of the conductive sheet may also be less than 10 μm. The maximum height roughness Rz is measured according to JIS B 0601:2013.

[0067] The material of the negative electrode collector (conductive sheet) can be any conductive material other than lithium metal and lithium alloy. The conductive material can also be a metal material such as a metal or an alloy. The conductive material is preferably a material that does not react with lithium. More specifically, it is preferred that the material does not form any of alloys and intermetallic compounds with lithium. These conductive materials include, for example, copper (Cu), nickel (Ni), iron (Fe) and alloys containing these metal elements, or graphite with the substrate surface (basal surface) preferentially exposed. As alloys, copper alloys, stainless steel (SUS) and the like can be listed. From the viewpoint of having high conductivity, copper and / or copper alloys are preferred. The thickness of the negative electrode collector is not particularly limited and can be in the range of 5 to 300 μm.

[0068] A negative electrode composite material layer may also be formed on the surface of the negative electrode current collector. The negative electrode composite material layer is formed, for example, by coating at least a portion of the surface of the negative electrode current collector with a paste containing a negative electrode active material such as graphite. However, from the perspective of realizing a lithium secondary battery with a high capacity exceeding that of a lithium ion battery, the thickness of the negative electrode composite material layer is set to be thin enough so that lithium metal can be precipitated in the negative electrode.

[0069] The negative electrode may include a negative electrode current collector and a sheet of lithium metal or lithium alloy disposed on the negative electrode current collector. That is, a base layer (a layer of lithium metal or lithium alloy) containing lithium metal may also be pre-set in the negative electrode current collector. In addition to lithium, lithium alloys may also contain elements such as aluminum, magnesium, indium, and zinc. By pre-setting the base layer, lithium metal is precipitated thereon during charging, thereby more effectively suppressing dendritic precipitation. The thickness of the base layer is not particularly limited, and for example, it may be in the range of 5 μm to 25 μm.

[0070] [positive electrode]

[0071] The positive electrode, for example, comprises a positive electrode current collector and a positive electrode composite material layer supported by the positive electrode current collector. The positive electrode composite material layer, for example, comprises a positive electrode active material, a conductive material, and a binding material. The positive electrode composite material layer may be formed only on one side of the positive electrode current collector or may be formed on both sides. The positive electrode is obtained, for example, by coating a positive electrode composite material slurry containing a positive electrode active material, a conductive material, and a binding material on both sides of the positive electrode current collector, and rolling the coating after drying.

[0072] The positive electrode active material is a material that absorbs and releases lithium ions. As the positive electrode active material, for example, lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. can be listed. Among them, lithium-containing transition metal oxides are preferred from the viewpoint of low manufacturing cost and high average discharge voltage.

[0073] As transition metal elements contained in the lithium-containing transition metal oxide, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc. can be listed. The lithium-containing transition metal oxide can contain one transition metal element, or it can contain two or more. The transition metal element can be Co, Ni and / or Mn. The lithium-containing transition metal oxide can contain one or more typical elements as needed. As typical elements, Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, etc. can be listed. The typical element can be Al, etc.

[0074] Among lithium-containing transition metal oxides, composite oxides containing Co, Ni and / or Mn as transition metal elements, sometimes containing Al as an arbitrary component, and having a rock salt type crystal structure with a layered structure are preferred from the viewpoint of obtaining a high capacity. At this time, in a lithium secondary battery, the molar ratio of the total amount mLi of lithium possessed by the positive electrode and the negative electrode to the amount mM of metal M other than lithium possessed by the positive electrode: mLi / mM is set to, for example, 1.1 or less.

[0075] The conductive material is, for example, a carbon material, and examples of the carbon material include carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0076] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber polymers, etc. Examples of the fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, and the like.

[0077] The positive electrode current collector may be any conductive sheet. A foil, a film, etc. may be used as the conductive sheet. A carbon material may be coated on the surface of the positive electrode current collector.

[0078] As the material of the positive electrode collector (conductive sheet), metal materials such as Al, Ti, and Fe can be listed. The metal material can be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy can be stainless steel (SUS). The thickness of the positive electrode collector is not particularly limited and can also be in the range of 5 to 300 μm.

[0079] [Diaphragm]

[0080] The base material of the diaphragm uses a porous sheet with ion permeability and insulation. Examples of porous sheets include porous membranes, woven fabrics, non-woven fabrics, etc. There is no particular limitation on the material of the diaphragm, but it can also be a polymer material. Examples of polymer materials include polyolefin resins, polyamide resins, cellulose, etc. Examples of polyolefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene, etc. The base material may contain additives as needed. As additives, inorganic fillers, etc. can be listed. As the base material, a sheet used as a diaphragm for a lithium secondary battery can also be used.

[0081] [Non-aqueous electrolyte]

[0082] The non-aqueous electrolyte having lithium ion conductivity includes, for example, a non-aqueous solvent, and lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be in a liquid state or a gel state.

[0083] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. The lithium salt dissolves in the non-aqueous solvent to generate lithium ions and anions.

[0084] The gel-like non-aqueous electrolyte comprises a lithium salt and 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 can be used. As the polymer material, fluororesins, acrylic resins, polyether resins, etc. can be cited.

[0085] As the lithium salt or anion, known non-aqueous electrolytes used in lithium secondary batteries can be used. Specifically, BF4 － 、ClO4 － PF6 － CF3SO3 － CF3CO2 － , anions of imide, anions of oxalic acid complex, etc. Examples of anions of imide include N(SO2CF3)2 － 、N(C m F 2m+1 SO2) x (C n F 2n+1 SO2) y － (m and n are each independently an integer of 0 or greater than 1, x and y are each independently 0, 1 or 2, and x+y=2) etc. The anion of the oxalic acid complex may contain boron and / or phosphorus. Examples of the anion of the oxalic acid complex include bis(oxalatoborate) anion, BF2(C2O4) － PF4(C2O4) － PF2(C2O4)2 －The non-aqueous electrolyte may contain these anions alone or in combination of two or more.

[0086] From the viewpoint of suppressing the precipitation of lithium metal in the form of dendrites, the non-aqueous electrolyte preferably contains at least anions of the oxalic acid complex. Through the interaction between the anions of the oxalic acid complex and lithium, lithium metal is easily precipitated uniformly in the form of fine particles. Therefore, it is easy to suppress the local precipitation of lithium metal. The anions of the oxalic acid complex and other anions can be combined. The other anions can be PF6 - and / or imide anions.

[0087] The nonaqueous electrolyte may contain LiBF2(C2O4) (lithium difluorooxalatoborate) as a solute (lithium salt).

[0088] Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, or halogen-substituted products thereof. The non-aqueous electrolyte may contain these non-aqueous solvents alone or in combination of two or more. Examples of the halogen-substituted product include fluorides and the like.

[0089] As esters, for example, carbonates, carboxylates, etc. can be listed. As cyclic carbonates, ethylene carbonate, propylene carbonate, fluoroethylene carbonate (FEC), etc. can be listed. As chain carbonates, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, etc. can be listed. As cyclic carboxylates, γ-butyrolactone, γ-valerolactone, etc. can be listed. As chain carboxylates, ethyl acetate, methyl propionate, methyl fluoropropionate, etc. can be listed.

[0090] Examples of ethers include cyclic ethers and chain ethers. Examples of cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of chain ethers include 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, and diglyme.

[0091] The concentration of the 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 the anion in the non-aqueous electrolyte may be 0.5 mol / L or more and 3.5 mol / L or less. In addition, the concentration of the anion of the oxalic acid complex in the non-aqueous electrolyte may also be 0.05 mol / L or more and 1 mol / L or less.

[0092] The non-aqueous electrolyte may contain an additive. The additive may also be an additive that forms a film on the negative electrode. By forming a film from the additive on the negative electrode, the formation of dendrites is easily suppressed. Examples of such additives include vinylene carbonate, FEC, and vinyl ethylene carbonate (VEC).

[0093] Hereinafter, an example of a lithium secondary battery of the present embodiment will be described in detail with reference to the accompanying drawings. In the constituent elements of the example of a lithium secondary battery described below, the above constituent elements can be applied. In addition, the constituent elements of the example described below can be changed according to the above description. In addition, the matters described below can also be applied to the aforementioned embodiment. In addition, in the lithium secondary battery described below, non-essential constituent elements of the lithium secondary battery disclosed herein can also be omitted. In addition, in the following drawings, the scales of the constituent elements are changed for easy understanding.

[0094] Figure 1 FIG. 1 is a longitudinal sectional view schematically showing an example of a lithium secondary battery according to the present embodiment. Figure 1 In the figure, for convenience, the first spacer and the second spacer are omitted. Figure 1 The cylindrical lithium secondary battery 10 shown includes a cylindrical battery case, and a wound electrode group 14 and a non-aqueous electrolyte (not shown) contained in the battery case. The battery case includes a case body 15 which is a bottomed cylindrical metal container and a sealing body 16 which seals the opening of the case body 15. A sealing ring 27 is arranged between the case body 15 and the sealing body 16. The sealing of the battery case is ensured by the sealing ring 27. In the case body 15, an upper insulating plate 17 and a lower insulating plate 18 are respectively arranged at both ends of the electrode group 14 in the winding axis direction.

[0095] The housing body 15 has a step portion 21 formed by partially pressing the side wall of the housing body 15 from the outside, for example. The step portion 21 may be formed annularly on the side wall of the housing body 15 along the circumferential direction of the housing body 15. In this case, the sealing body 16 is supported by the surface of the step portion 21 on the opening side.

[0096] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating component 24, an upper valve body 25 and a cover 26. In the sealing body 16, these components are stacked in this order. The sealing body 16 is installed in the opening portion of the shell body 15 so that the cover 26 is located on the outside of the shell body 15 and the filter 22 is located on the inside of the shell body 15. The above-mentioned components constituting the sealing body 16 are, for example, in the shape of a circular plate or a ring. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central portions, and an insulating component 24 is sandwiched between their respective peripheral portions. The filter 22 and the lower valve body 23 are connected to each other at their respective central portions. The upper valve body 25 and the cover 26 are connected to each other at their respective central portions. That is, the components except the insulating component 24 are electrically connected to each other.

[0097] A vent hole (not shown) is formed in the lower valve body 23. Therefore, when the internal pressure of the battery case rises due to abnormal heat or the like, the upper valve body 25 expands toward the cover 26 and separates from the lower valve body 23. As a result, the electrical connection between the lower valve body 23 and the upper valve body 25 is cut off. When the internal pressure rises further, the upper valve body 25 breaks, and gas is discharged from an opening (not shown) formed in the cover 26.

[0098] The electrode group 14 has a positive electrode 11, a negative electrode 12 and a separator 13. The positive electrode 11, the negative electrode 12 and the separator 13 are all in a strip shape. The positive electrode 11 and the negative electrode 12 are wound into a spiral shape with the separator 13 sandwiched between them in a manner that the width direction of the strip-shaped positive electrode 11 and the negative electrode 12 is parallel to the winding axis. In a cross section perpendicular to the winding axis of the electrode group 14, the positive electrode 11 and the negative electrode 12 are alternately stacked in the radial direction of the electrode group 14 with the separator 13 sandwiched between them. That is, the length direction of each electrode is the winding direction, and the width direction of each electrode is the axial direction.

[0099] The positive electrode 11 includes a positive electrode collector and a positive electrode composite material layer carried on both sides of the positive electrode collector. The positive electrode collector of the positive electrode 11 is electrically connected to a cover 26 that functions as a positive electrode terminal via a positive electrode lead 19. As the negative electrode 12, a negative electrode (negative electrode collector) in a state where no lithium metal is precipitated is shown. The negative electrode 12 is electrically connected to a housing body 15 that functions as a negative electrode terminal via a negative electrode lead 20.

[0100] Figure 2 yes Figure 1 An enlarged view of the main part of the electrode group. Figure 2 (a) and (b) schematically show the main parts of the electrode group during discharge and charge, respectively.

[0101] like Figure 2 As shown in (a), a first separator 51 is provided between the negative electrode 12 and the separator 13, and a second separator 52 is provided between the positive electrode 11 and the separator 13. A first space 51s is formed on the surface of the negative electrode 12 (the surface opposite to the positive electrode 11) by the first separator 51. A second space 52s is formed on the surface of the positive electrode 11 (the surface opposite to the negative electrode 12) by the second separator 52.

[0102] like Figure 2 As shown in (b), during charging, lithium metal 12a is precipitated on the surface of negative electrode 12. By means of first separator 51 (first space 51s) and second separator 52 (second space 52s), during charging, the distance between positive electrode 11 and negative electrode 12 is suppressed from increasing, and a part of second space 52s remains as space 53 capable of accommodating non-aqueous electrolyte. Therefore, expansion of electrode group 14 during repeated charge and discharge is suppressed, and depletion of non-aqueous electrolyte in electrode group 14 is suppressed.

[0103] Figure 3 An example of the pattern shape of the first spacer 51 is shown. Figure 4 express Figure 3 A magnified view of a portion of the Figure 3 In one example, the first spacer 51 is composed of linear protrusions 51a. The linear protrusions 51a are arranged in a mesh, and more specifically, are uniformly formed in a honeycomb pattern. The honeycomb pattern is a pattern in which a plurality of hexagons are arranged in a manner that shares edges with each other. The first space 51s is formed in an area where the linear protrusions 51a are not arranged. Figure 4 denoted by the width W of the linear protrusion 51 a.

[0104] like Figure 3 As shown, the first separator 51 can be formed on the separator 13 (the surface on the negative electrode 12 side, and the area where the positive electrode 11 and the negative electrode 12 are opposite), and the separator 13 and the first separator 51 constitute the composite separator 30. In addition, the first separator 51 can also be formed on the negative electrode 12 (the surface opposite to the positive electrode 11).

[0105] The first spacer 51 has Figure 3 The pattern shape shown in FIG. 1 is not limited to this. For example, the first spacer 51 may also have Figure 5 The shape of the pattern shown. Figure 5 Another example of the pattern shape of the first spacer is shown. The plurality of linear protrusions 61a constituting the first spacer 51 are separated from each other in the width direction of the strip-shaped diaphragm 13 and are arranged in parallel along the length direction of the diaphragm 13. That is, the linear protrusions 61a are arranged in a stripe shape. In the example shown in the figure, six linear protrusions 61a are arranged, but the number of linear protrusions is not limited to this.

[0106] The second separator 52 is composed of linear protrusions similarly to the first separator 51, and has the same pattern shape as the first separator 51. The second separator 52 can be formed on the separator 13 (the surface on the positive electrode 11 side, and the region where the positive electrode 11 and the negative electrode 12 face each other), or on the positive electrode 11 (the surface facing the negative electrode 12).

[0107] The pattern shape of the second spacer 52 is Figure 3 The pattern shape shown in FIG. 1 is the same as that shown in FIG. 1 , but is not limited thereto. The pattern shape of the second spacer may also be the same as that of FIG. Figure 5 The patterns shown are of the same shape.

[0108] The first separator 51 and the second separator 52 are arranged to overlap each other. That is, the first separator 51 and the second separator 52 are provided at substantially the same position between the positive electrode 11 and the negative electrode 12 with the separator 13 interposed therebetween.

[0109] exist Figure 2 In the embodiment, the first spacer 51 and the second spacer 52 have the same pattern shape and are arranged in an overlapping manner, but the arrangement of the first spacer and the second spacer is not limited to this. The first spacer and the second spacer may also have the same pattern shape but be arranged in staggered positions. The first spacer and the second spacer may have different pattern shapes (for example, one is honeycomb-shaped and the other is stripe-shaped). Figure 2 The diaphragm 13, the first spacer 51 and the second spacer 52 form Figure 8 The composite component 70.

[0110] In the illustrated example, a cylindrical lithium secondary battery with a wound electrode group is described, but it is not limited to this case, and the present embodiment can be applied. The shape of the lithium secondary battery can be appropriately selected from various shapes such as coin-shaped, square-shaped, sheet-shaped, flat-shaped, etc., depending on its use, etc., in addition to the cylindrical shape. The shape of the electrode group is not particularly limited, and it can also be a stacked type. In addition, for the structure other than the electrode group and the non-aqueous electrolyte of the lithium secondary battery, a known structure can be used without particular restrictions.

[0111] Postscript

[0112] According to the description of the above embodiments, the following technology is disclosed.

[0113] (Technique 1) A lithium secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity,

[0114] The negative electrode is an electrode from which lithium metal is deposited during charging and dissolved during discharging.

[0115] A first separator is provided between the negative electrode and the separator,

[0116] A second separator is provided between the positive electrode and the separator.

[0117] (Technique 2) In the lithium secondary battery according to Technique 1, a ratio of a thickness T1 of the first separator to a thickness T2 of the second separator: T1 / T2 is 1 or more.

[0118] (Technique 3) In the lithium secondary battery as described in Technique 2, T1 / T2 is 2 or more.

[0119] (Technique 4) In the lithium secondary battery according to any one of Techniques 1 to 3, the first separator and the second separator have mutually different pattern shapes.

[0120] (Technique 5) In the lithium secondary battery according to any one of Techniques 1 to 3, at least one of the first separator and the second separator has a mesh pattern.

[0121] (Technique 6) In the lithium secondary battery according to Technique 5, the mesh pattern is an aggregate of polygons.

[0122] (Technique 7) In the lithium secondary battery as described in Technique 6, the mesh pattern is a honeycomb shape.

[0123] (Technique 8) In the lithium secondary battery according to any one of Techniques 1 to 7, the nonaqueous electrolyte contains lithium ions and anions, and the anions contain at least anions of an oxalic acid complex.

[0124] (Technique 9) A composite component comprising:

[0125] a diaphragm having a first main surface and a second main surface located on the opposite side of the first main surface,

[0126] a first spacer disposed on the first main surface, and

[0127] a second spacer disposed on the second main surface,

[0128] A ratio of a thickness T1 of the first spacer to a thickness T2 of the second spacer: T1 / T2 is 1 or more.

[0129] (Technique 10) In the composite component according to Technique 9, T1 / T2 is 2 or more.

[0130] (Technique 11) In the composite component according to Technique 9 or 10, the first spacer and the second spacer have different pattern shapes from each other.

[0131] (Technique 12) In the composite member according to Technique 9 or 10, at least one of the first spacer and the second spacer has a mesh pattern.

[0132] (Technique 13) In the composite component according to Technique 12, the mesh pattern is an aggregate of polygons.

[0133] (Technique 14) In the composite component described in Technique 13, the mesh pattern is a honeycomb shape.

[0134] [Example]

[0135] Hereinafter, the lithium secondary battery of the present disclosure will be specifically described based on Examples and Comparative Examples. The present disclosure is not limited to the following Examples.

[0136] 《Example 1》

[0137] (Production of positive electrode)

[0138] Prepare a rock salt type lithium-containing transition metal oxide (NCA; positive electrode active material) with a layered structure containing Li, Ni, Co and Al (the molar ratio of Li to the total amount of Ni, Co and Al is 1.0). The lithium-containing transition metal oxide (NCA), acetylene black (AB; conductive material) and polyvinylidene fluoride (PVdF; binder) are mixed in a mass ratio of NCA:AB:PVdF=95:2.5:2.5, and then an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added and stirred to prepare a positive electrode composite material slurry. Then, the obtained positive electrode mixture slurry is applied to both sides of a strip of Al foil (positive electrode collector), and then dried to form a coating of the positive electrode mixture. Then, the coating is rolled using a roller. Finally, the obtained stack of the positive electrode collector and the positive electrode composite material is cut into a specified electrode size to produce a positive electrode having a positive electrode composite material layer on both sides of the positive electrode collector.

[0139] (Preparation of negative electrode)

[0140] As the negative electrode, a negative electrode having a rolled lithium metal layer (25 μm thick) provided on both surfaces of a strip-shaped copper foil (12 μm thick) was used.

[0141] (Preparation of diaphragm)

[0142] As a separator, a belt-shaped porous film (average thickness 10 μm) made of polyethylene was prepared.

[0143] (Formation of the First Spacer)

[0144] Using a paint dispenser, one surface of the separator (the surface on the negative electrode side) was coated with Figure 3 A coating liquid containing polyvinylidene fluoride and alumina particles (inorganic filler) is discharged in the pattern shown. Then, the coating liquid is vacuum dried. This forms a Figure 3 The honeycomb-shaped first spacer is shown.

[0145] The mesh shape of the first spacer is a regular hexagon. The height of the linear protrusion constituting the first spacer is set to 30 μm (the thickness T1 of the first spacer: 30 μm). Among the sides constituting the regular hexagonal mesh, the interval between the two opposite sides is about 4.5 mm. The width of the linear protrusion is 0.25 mm. In the opposing region of the positive electrode and the negative electrode of the separator, the area S1 of the first spacer is 10% of the area S0 of the opposing region.

[0146] (Formation of the Second Spacer)

[0147] Use a paint dispenser to coat both sides of the positive electrode with Figure 3The coating liquid containing polyvinylidene fluoride and alumina particles (inorganic filler) is discharged in the pattern shown in the figure. Then, the coating liquid is vacuum dried. Figure 3 The honeycomb-shaped second spacer is shown.

[0148] The mesh shape of the second spacer is a regular hexagon. The height of the linear protrusion constituting the second spacer is set to 10μm (the thickness T2 of the second spacer: 10μm). Among the sides constituting the regular hexagonal mesh, the interval between the two opposite sides is about 4.5mm. The width of the linear protrusion is 0.25mm. The area S2 of the second spacer is 10% of the area S0 of the region of the positive electrode facing the negative electrode.

[0149] (Preparation of non-aqueous electrolyte)

[0150] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of EC:DMC=30:70. LiPF6 and LiBF2(C2O4) were dissolved in the obtained mixed solvent to make LiPF6 1 mol / L and LiBF2(C2O4) 0.1 mol / L to prepare a liquid non-aqueous electrolyte.

[0151] (Battery production)

[0152] The positive electrode obtained above was provided with an Al tab. The negative electrode was provided with a Ni tab. In an inert gas atmosphere, the positive electrode and the negative electrode separator were wound in a spiral shape to prepare a wound electrode group.

[0153] Specifically, the first separator, the negative electrode prepared as described above, the second separator and the positive electrode are stacked in sequence to form a stack. The stack is wound on a core in such a manner that the first separator becomes the inside (the positive electrode becomes the outside). After winding, the core is removed. The positive electrode uses the positive electrode having the second separator on both sides obtained as described above. The first separator and the second separator respectively use the separators having the first separator on one surface obtained as described above. The separators are arranged in such a manner that the surface having the first separator is the negative electrode side. The length direction dimension of the negative electrode is appropriately adjusted so that all the positive electrode mixture layers on both sides of the positive electrode are opposite to the negative electrode when winding. The length direction dimensions of the first separator and the second separator are appropriately adjusted in such a manner that the first separator and the second separator are arranged at the outermost periphery when winding.

[0154] The obtained electrode group was housed in a bag-shaped outer casing formed of a laminate sheet having an Al layer, and the nonaqueous electrolyte was injected into the outer casing housing the electrode group, and then the outer casing was sealed. In this way, a lithium secondary battery A1 was manufactured.

[0155] 《Examples 2 to 4》

[0156] Batteries A2 to A4 were prepared in the same manner as the battery A1 of Example 1 except that the thickness T1 of the first separator and the thickness T2 of the second separator were set to the values ​​shown in Table 1.

[0157] 《Example 5》

[0158] In addition to setting the pattern of the second separator formed on both sides of the positive electrode to Figure 5 Battery A5 was produced in the same manner as Battery A1 of Example 1 except for the shown pattern (striped shape).

[0159] The linear protrusions constituting the second separator are separated from each other in the width direction of the positive electrode and arranged in parallel along the length direction of the positive electrode. The number of linear protrusions is 6. The height and width of the linear protrusions are 10 μm and 0.25 mm, respectively. The spacing of the linear protrusions is appropriately adjusted so that the area S2 of the second separator is 10% of the area S0 of the region of the positive electrode facing the negative electrode.

[0160] Comparative Example 1

[0161] Battery B1 was produced in the same manner as Battery A1 of Example 1, except that the thickness of the first separator was set to 40 μm and the second separator was not formed.

[0162] Comparative Example 2

[0163] Battery B2 was produced in the same manner as Battery A1 of Example 1, except that the thickness of the second separator was set to 40 μm and the first separator was not formed.

[0164] [evaluate]

[0165] The batteries produced above were evaluated as follows.

[0166] (Charge and discharge test)

[0167] The obtained batteries were subjected to a charge and discharge test. In the charge and discharge test, the batteries were charged in a thermostatic chamber at 25° C. under the following conditions, then stopped for 20 minutes and discharged under the following conditions.

[0168] (Charge)

[0169] The battery was charged at a constant current of 2.15 mA per unit area (cm2) of the electrode until the battery voltage reached 4.1 V, and then charged at a constant voltage of 4.1 V until the current value per unit area of ​​the electrode reached 0.54 mA.

[0170] (Discharge)

[0171] The battery was discharged at a constant current of 2.15 mA per unit area of ​​the electrode until the battery voltage reached 3.75 V.

[0172] (Expansion rate of electrode group)

[0173] The above-mentioned charge and discharge is set as one cycle, and the manufactured battery is charged to the second cycle. Then, the battery before charge and discharge and the battery charged for the second cycle are disassembled separately. Take out the stack of the positive electrode with the second separator on both sides, the negative electrode and the two separators on both sides of the negative electrode (the first separator and the second separator having the first separator on the surface of the negative electrode side). Disassembly is carried out in an inert gas atmosphere. The taken out stack is washed with dimethyl carbonate and then dried.

[0174] The thickness Xd of the stack before charge and discharge is calculated. The thickness Xd of the stack before charge and discharge is the total thickness of each component of the stack before charge and discharge. That is, the thickness Xd is the total thickness of the positive electrode, the negative electrode, the two separators, the first separator respectively arranged on the surface of the negative electrode side of the two separators, and the second separator respectively arranged on one surface and the other surface of the positive electrode.

[0175] The thickness Xc of the laminate at the second cycle charge was determined. The thickness Xc of the laminate at the second cycle charge was the total thickness of the positive electrode, the negative electrode, the two separators, and the lithium metal deposited on one surface and the other surface of the negative electrode.

[0176] The thickness was measured using a Peacock digital thickness gauge G2-205M. The arithmetic mean of the thickness values ​​measured at any five points was calculated as the thickness.

[0177] Using the obtained Xd and Xc, the expansion ratio (%) of the electrode group was calculated according to the following formula.

[0178] Electrode group expansion rate = (Xc / Xd) × 100

[0179] (Discharge capacity maintenance rate)

[0180] The above charge and discharge were defined as one cycle, and the charge and discharge were repeated up to 200 cycles. The ratio (%) of the discharge capacity at the 200th cycle to the discharge capacity at the 1st cycle was determined as the discharge capacity retention rate.

[0181] (Initial charge capacity)

[0182] In addition, the charge capacity at the first cycle was determined as the initial charge capacity.

[0183] The evaluation results are shown in Table 1.

[0184] Table 1

[0185]

[0186] In batteries A1 to A5, the initial charge capacity and discharge capacity retention rates were high, and the expansion rates of the electrode groups were low.

[0187] In the battery B1 provided with the first separator, the expansion rate of the electrode group is reduced, but since the second separator is not provided, the non-aqueous electrolyte in the electrode group is depleted, and the discharge capacity retention rate is reduced. In the battery B2 provided with the second separator, since the first separator is not provided, the expansion rate of the electrode group is increased, and the discharge capacity retention rate is reduced. In addition, the battery B1 and the battery B2 have Figure 6 and Figure 7 The electrode set shown.

[0188] Industrial Availability

[0189] The lithium secondary battery of the present disclosure can be used in electronic devices such as mobile phones, smartphones, and tablet terminals, electric vehicles including hybrid and plug-in hybrid vehicles, and household storage batteries combined with solar cells.

[0190] Although the present invention has been described in conjunction with the currently preferred embodiments, the present disclosure should not be construed restrictively accordingly. By reading the above disclosure, those skilled in the art can clearly see various changes and modifications. Therefore, the appended claims should be interpreted as including all modifications and changes, as long as they do not deviate from the true spirit and scope of the present invention.

[0191] Description of the accompanying drawings

[0192] 10: lithium secondary battery, 11: positive electrode, 12: negative electrode, 12a: lithium metal, 13: diaphragm, 14: electrode group, 15: shell body, 16: sealing body, 17: upper insulating plate, 18: lower insulating plate, 19: positive electrode lead, 20: negative electrode lead, 21: step portion, 22: filter, 23: lower valve body, 24: insulating component, 25: upper valve body, 26: cover, 27: sealing ring, 30: composite diaphragm, 40: negative electrode, 51: first separator, 51s: first space, 51a: linear protrusion, 52: second separator, 52s: second space, 53: space, 61a: linear protrusion, 70: composite component

Claims

1. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having lithium ion conductivity, The negative electrode is an electrode from which lithium metal is deposited during charging and dissolved during discharging. A first separator is provided between the negative electrode and the separator, A second separator is provided between the positive electrode and the separator. 2 . The lithium secondary battery according to claim 1 , wherein a ratio of a thickness T1 of the first separator to a thickness T2 of the second separator ( T1 / T2 ) is 1 or more. 3 . The lithium secondary battery according to claim 2 , wherein T1 / T2 is greater than or equal to 2. 4 . The lithium secondary battery according to claim 1 , wherein the first separator and the second separator have different pattern shapes. 5 . The lithium secondary battery according to claim 1 , wherein at least one of the first separator and the second separator has a mesh pattern. 6 . The lithium secondary battery according to claim 5 , wherein the mesh pattern is an aggregate of polygons. 7 . The lithium secondary battery according to claim 6 , wherein the mesh pattern is a honeycomb shape. 8 . The lithium secondary battery according to claim 1 , wherein the nonaqueous electrolyte contains lithium ions and anions, and the anions contain at least anions of an oxalic acid complex.

9. A composite component comprising: a diaphragm having a first main surface and a second main surface located on the opposite side of the first main surface, a first spacer disposed on the first main surface, and a second spacer disposed on the second main surface, A ratio of a thickness T1 of the first spacer to a thickness T2 of the second spacer: T1 / T2 is 1 or more. 10 . The composite component according to claim 9 , wherein T1 / T2 is 2 or more. 11 . The composite member according to claim 9 , wherein the first spacer and the second spacer have different pattern shapes from each other. 12 . The composite member according to claim 9 , wherein at least one of the first spacer and the second spacer has a mesh pattern.

13. The composite member according to claim 12, wherein the mesh-like pattern is an aggregate of polygons. The composite component according to claim 13 , wherein the mesh pattern is a honeycomb pattern.

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