Lithium secondary battery

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. Lithium metal deposits on the negative electrode at the time of charging, and the lithium metal is dissolved from the negative electrode at the time of discharging. A spacer is provided between the separator and the positive electrode and / or the negative electrode. A first length of the separator in a first direction D1 is smaller than a second length thereof in a second direction D2 intersecting with the first direction D1. In a cross section of the spacer taken along the first direction D1 and the thickness direction of the separator, the angle on the spacer side formed by the separator and the spacer, and / or the angle on the spacer side formed by the spacer and an electrode being in contact with the spacer, is more than 90°.

Description

[Technical field]

[0001] The present disclosure relates to a lithium secondary battery that uses lithium metal as a negative electrode active material. [Background technology]

[0002] Lithium ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. The capacity of lithium ion batteries can be increased by using, for example, an alloy active material such as graphite and a silicon compound as a negative electrode active material. However, the capacity of lithium ion batteries is reaching its limit.

[0003] Lithium secondary batteries (lithium metal secondary batteries) are promising non-aqueous electrolyte secondary batteries with a higher capacity than lithium ion batteries. In lithium secondary batteries, lithium metal is precipitated on the negative electrode during charging, and the lithium metal dissolves during discharging and is released as lithium ions into the non-aqueous electrolyte.

[0004] Patent Document 1 proposes providing a spacer to form a gap between the negative electrode or positive electrode and the separator to accommodate lithium deposited on the negative electrode surface. Patent Document 2 proposes providing a spacer to relieve stress caused by expansion and contraction of the negative electrode. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-12279 [Patent Document 2] JP 2011-8929 A Summary of the Invention

[0006] In the methods of Patent Documents 1 and 2, the capacity retention rate is likely to decrease.

[0007] The present disclosure relates to 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, wherein lithium metal precipitates on the negative electrode during charging and dissolves from the negative electrode during discharging, and wherein a spacer is provided between at least one of the positive electrode and the negative electrode and the separator, and a first length of the separator in a first direction D1 is smaller than a second length in a second direction D2 intersecting with the first direction D1, and in a cross section of the spacer cut along a thickness direction of the separator and the first direction D1, at least one of an angle formed between the separator and the spacer on the spacer side and an angle formed between an electrode in contact with the spacer and the spacer on the spacer side is greater than 90°.

[0008] According to the present disclosure, the capacity retention rate can be improved in a lithium secondary battery. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view illustrating a schematic view of a main part of a lithium secondary battery according to an embodiment of the present disclosure. [Figure 2A] FIG. 2A is a cross-sectional view illustrating a schematic view of a main part of another lithium secondary battery according to an embodiment of the present disclosure. [Figure 2B] FIG. 2B is a cross-sectional view that illustrates a schematic view of a main portion of still another lithium secondary battery according to an embodiment of the present disclosure. [Figure 3A] FIG. 3A is a cross-sectional view illustrating a schematic view of a main portion of still another lithium secondary battery according to an embodiment of the present disclosure. [Figure 3B] FIG. 3B is a cross-sectional view that illustrates a schematic view of a main portion of still another lithium secondary battery according to an embodiment of the present disclosure. [Figure 4] FIG. 64 is a cross-sectional view illustrating a schematic view of a main portion of still another lithium secondary battery according to an embodiment of the present disclosure. [Figure 5A] FIG. 5A is a plan view that illustrates a spacer disposed on the surface of a separator. [Figure 5B] FIG. 5B is a plan view that illustrates another spacer disposed on the surface of the separator. [Figure 5C] FIG. 5C is a plan view that illustrates still another spacer disposed on the surface of the separator. [Figure 5D] FIG. 5D is a plan view that illustrates still another spacer disposed on the surface of the separator. [Figure 5E] FIG. 5E is a plan view that illustrates still another spacer disposed on the surface of the separator. [Figure 6] FIG. 6 is a vertical cross-sectional view illustrating a lithium secondary battery according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is an enlarged view that illustrates a schematic view of a main part of the lithium secondary battery of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The lithium secondary battery according to 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. In the lithium secondary battery, lithium metal is deposited on the negative electrode during charging, and lithium metal dissolves from the negative electrode during discharging. A spacer is provided between at least one of the positive electrode and the negative electrode (hereinafter, sometimes collectively referred to as an electrode) and the separator.

[0011] The expansion and contraction of the negative electrode places stress on the spacer. This stress tends to concentrate especially at the corners of the spacer. Therefore, the electrode is easily damaged at the portion where the corners of the spacer come into contact. Also, when the corners of the spacer come into contact with the separator, the separator repels the stress and pushes the spacer back toward the electrode. As a result, the electrode is damaged. The damage to the electrode increases as the charge / discharge cycle progresses, and may reduce the capacity retention rate.

[0012] The spacer according to the present disclosure comes into contact with the electrodes or separators at an angle greater than 90°, which reduces the concentration of stress at the corners and suppresses damage to the electrodes.

[0013] (Spacer) The spacer is provided between the electrode and the separator. The spacer forms a space between the electrode and the separator that can accommodate the deposited lithium metal. The spacer reduces the volume change of the negative electrode that accompanies the deposition of lithium metal.

[0014] In a cross section (hereinafter referred to as a reference cross section) of the spacer cut along the thickness direction of the separator and the first direction D1, at least one of the angle (hereinafter referred to as a first angle θ1) between the electrode in contact with the spacer and the spacer and the angle (hereinafter referred to as a second angle θ2) between the separator and the spacer (hereinafter referred to as an angle θ) is greater than 90°. This reduces the concentration of stress at the corners, suppressing damage to the electrodes. The angle θ is preferably 100° or more, more preferably 130° or more. The angle θ is less than 180°. The angle θ is preferably 175° or less, more preferably 170° or less, and particularly preferably 150° or less. The angle θ is the average value of the angle θ at five different reference cross sections. The first angle θ1 and the second angle θ2 are obtained in the same manner.

[0015] In order to more easily prevent damage to the electrodes, it is preferable that at least one of the first angles θ1 formed between the electrodes and the spacers is greater than 90°. In particular, it is preferable that at least one of the first angles θ1 formed between the positive electrode and the spacer is greater than 90°. Furthermore, it is preferable that all of the first angles θ1 formed between the electrodes and the spacers are greater than 90°. In particular, it is preferable that all of the first angles θ1 formed between the positive electrode and the spacers are greater than 90°.

[0016] The first direction D1 of the separator is a direction along the short side of the separator. That is, a first length of the separator in the first direction D1 is smaller than a second length in a second direction D2 intersecting with the first direction D1. The shape of the separator may be, for example, a long rectangle, that is, a strip shape. The angle between the first direction D1 and the second direction D2 may be approximately 90°, for example, 88 to 92°.

[0017] In the reference cross section, the contact length between the separator and the electrode and the spacer is not particularly limited. The contact length is appropriately set according to the first length. The contact length in the reference cross section is, for example, 500 μm or more and 2000 μm or less. When the contact length is in this range, the stress applied to the spacer is easily uniformly distributed to the separator and the electrode. The contact length is the average value of the contact lengths in five different reference cross sections.

[0018] In the reference cross section, the height of the spacer is not particularly limited. The height of the spacer may be determined according to the amount of lithium metal deposited. The height of the spacer is, for example, 10 μm or more and 60 μm or less. When the height of the spacer is in this range, the effect of absorbing the volume change of the negative electrode caused by the deposition of lithium metal can be further improved. In addition, the lithium metal deposited on the surface of the negative electrode is appropriately pressed by the separator, and the conductivity between the lithium metal and the negative electrode is increased, so that the charge and discharge efficiency can be improved. The height of the spacer is the average value of the maximum height of the spacer in five different reference cross sections.

[0019] The material constituting the spacer is not particularly limited, and the spacer is made of a conductive material and / or an insulating material.

[0020] The conductive material can be appropriately selected from the materials for the negative electrode current collector or the positive electrode current collector described later. Such a spacer may be provided by forming a convex portion on the current collector by pressing or the like. Alternatively, a conductive paint may be applied to the surface of the separator or electrode, or a conductive tape may be attached to the surface of the separator or electrode.

[0021] The insulating material may be a resin material. Examples of the resin material include polyolefin resin, acrylic resin, polyamide resin, polyimide resin, silicone resin, fluorine-based resin, urethane resin, melamine resin, and urea resin. The resin material may be a cured product of a curable resin such as an epoxy resin. In addition, inorganic fillers may be mixed into these resin materials.

[0022] Among these, insulating materials are preferable because lithium metal is less likely to deposit on the surface of insulating materials, which can enhance the effect of suppressing the expansion of the negative electrode.

[0023] The material constituting the spacer 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 alleviate the stress caused by the expansion and contraction of the negative electrode, and makes it easier to maintain the space for accommodating the lithium metal. In addition, it makes it easier to suppress damage to the electrode caused by the spacer. Examples of materials that are insulating and have a Young's modulus in the above range include the cured product of the above-mentioned curable resin.

[0024] The spacer may be formed, for example, by attaching a resin adhesive tape to the surface of the separator or electrode. Alternatively, the spacer 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 may be formed by applying a curable resin to the surface of the separator or electrode in a desired shape and curing it. Alternatively, the spacer may be formed by scattering particles of a resin material on the surface of the separator or electrode in a desired shape. Among these, the method of using a solution containing a resin material or particles of a resin material is preferred because it is easy to form an angle θ larger than 90°.

[0025] It is preferable that the reference cross section of the spacer has a curve that contacts at least one of the separator and the electrode, which makes it easier for the spacer to have a larger contact angle.

[0026] When the reference cross section of the spacer has a curve that contacts the electrode, the first angle θ1 is the angle on the spacer side between the tangent at the intersection of the curve with the electrode and the surface of the electrode. In this case, the first angle θ1 is greater than 90°. The second angle θ2 is not particularly limited. The second angle θ2 may be 90°.

[0027] When the reference section of the spacer has a curve that contacts the separator, the second angle θ2 is the angle on the spacer side between the tangent at the intersection of the curve with the separator and the surface of the separator. In this case, the second angle θ2 is greater than 90°. The first angle θ1 is not particularly limited. The first angle θ1 may be 90°.

[0028] In order to increase the contact angle of the spacer, it is preferable that the radius of curvature at the intersection of the curve with the separator or electrode is large. For example, the radius of curvature may be 1 / 2 or more, 1 or more, or 2 or more times the longer of the contact length between the electrode and the spacer and the contact length between the separator and the spacer.

[0029] In the reference cross section, the contact length between the electrode and the spacer and the contact length between the separator and the spacer may be different. In this case, the contact angle of the spacer is also likely to be larger. Furthermore, in the reference cross section, a slope connecting the electrode and the separator can be formed on the spacer. Therefore, the electrode and the separator are less likely to be misaligned around the spacer, and damage to the electrode is more likely to be suppressed. The contact length between the separator and the spacer is preferably larger than the contact length between the electrode and the spacer. In this case, the contact angle of the spacer with respect to the electrode is larger, and damage to the electrode is more likely to be suppressed.

[0030] One contact length is length L1, and the other contact length longer than length L1 is length L2. The ratio of length L1 to length L2, L1 / L2, is preferably 0.5 to 0.95, more preferably 0.8 to 0.95. In this case, even the member with the shorter contact length can contact the spacer over a certain area. Therefore, the stress from the spacer is dispersed, making it easier to suppress damage to the electrodes.

[0031] In order to further reduce the likelihood of misalignment between the electrodes and the separator, it is preferable that the spacer has a shape that is symmetrical or nearly symmetrical with respect to a straight line along the thickness direction of the separator in the reference cross section.

[0032] The shape of the spacer in the reference cross section is not particularly limited. The shape of the spacer in the reference cross section is, for example, a rectangle having at least one curved corner, a trapezoid, an ellipse, a part of an ellipse, or a shape similar to these. An ellipse includes a perfect circle.

[0033] A preferred shape of the spacer in the reference cross section will be described below with reference to the drawings as appropriate. The illustrated example shows the shape of the spacer in the reference cross section. In the illustrated example, at least one of the first angles θ1 formed between the electrode and the spacer is greater than 90°. However, the embodiment of the present disclosure is not limited thereto, and at least one of the second angles θ2 formed between the separator and the spacer may be greater than 90°.

[0034] [First embodiment] The shape of the spacer in this embodiment in a reference cross section is a rectangle having at least one curved corner, in which case the radius of curvature of the curve is preferably three times or more the longer of the contact length between the electrode and the spacer and the contact length between the separator and the spacer.

[0035] 1 is a cross-sectional view showing a schematic view of a main part of a lithium secondary battery according to an embodiment of the present disclosure. A spacer 400 is provided between an electrode 100 and a separator 300. The shape of the spacer 400 in a reference cross section is a substantially rectangular shape with rounded corners on the electrode 100 side. The spacer 400 has a curved line that contacts the electrode 100. Therefore, the first angle θ1 is larger than 90°. The second angle θ2 is about 90°.

[0036] The contact length L1 between the electrode 100 and the spacer 400 is different from the contact length L2 between the separator 300 and the spacer 400. The contact length L1 is shorter than the contact length L2. The ratio of the length L1 to the length L2: L1 / L2 is 0.5 or more and 0.95 or less. The radius of curvature at the intersection of the above curve with the electrode 100 is three times or more the contact length L2 between the separator 300 and the spacer 400.

[0037] [Second embodiment] The shape of the spacer in this embodiment in the reference cross section is trapezoidal. The contact length L1 between the electrode and the spacer is different from the contact length L2 between the separator and the spacer. The ratio of length L1 to length L2: L1 / L2 is preferably 0.5 or more and 0.95 or less.

[0038] FIG. 2A is a cross-sectional view showing a schematic view of a main part of another lithium secondary battery according to an embodiment of the present disclosure. The spacer 400 is provided between the electrode 100 and the separator 300. The shape of the spacer 400 in the reference cross section is a trapezoid. The contact length L1 between the electrode 100 and the spacer 400 is shorter than the contact length L2 between the separator 300 and the spacer 400. The ratio of the length L1 to the length L2: L1 / L2 is 0.5 or more and 0.95 or less. The spacer 400 has two inclined surfaces connecting the electrode 100 and the separator 300. Therefore, the two first angles θ1 are both greater than 90°. The two second angles θ2 are both less than 90°.

[0039] FIG. 2B is a cross-sectional view showing a schematic view of a main part of another lithium secondary battery according to an embodiment of the present disclosure. The spacer 400 is provided between the electrode 100 and the separator 300. The shape of the spacer 400 in the reference cross section is a trapezoid. The contact length L1 between the electrode 100 and the spacer 400 is shorter than the contact length L2 between the separator 300 and the spacer 400. The ratio of the length L1 to the length L2: L1 / L2 is 0.5 or more and 0.95 or less. The spacer 400 has one inclined surface connecting the electrode 100 and the separator 300. That is, one of the two first angles θ1 is greater than 90°, and the other is 90°. One of the two second angles θ2 is less than 90°, and the other is 90°.

[0040] [Third embodiment] The shape of the spacer according to this embodiment in a reference cross section is a part of an ellipse.

[0041] Of the positive electrode, negative electrode, and separator, the member that contacts the spacer at the arc portion is referred to as the first member, and the member that contacts the spacer at the chord portion is referred to as the second member.

[0042] The angle on the spacer side between the tangent to the arc at the intersection between the arc and the second member and the second member is defined as the contact angle θ, and the angle on the spacer side between the straight line connecting the midpoint at the contact portion between the first member and the spacer and the intersection and the second member is defined as the elevation angle θe. The contact angle θ and the elevation angle θe satisfy the relationship θ≧2×θe, for example. In this case, the angle between the first member and the spacer is sufficiently large.

[0043] (Contact length between the second member and the spacer)×tan θe indicates the height h of the spacer. Therefore, the elevation angle θe is set, for example, in a range such that the height h of the spacer is 10 μm or more and 60 μm or less.

[0044] In the reference cross section, the maximum diameter L3 of the spacer in the plane direction of the separator may be 500 μm or more and 2000 μm or less. This makes it easier to maintain the space for accommodating lithium metal. The maximum diameter L3 may be greater than the contact length between the separator and the spacer and the contact length between the electrode and the spacer.

[0045] 3A is a cross-sectional view showing a schematic diagram of a main part of a lithium secondary battery according to an embodiment of the present disclosure. A spacer 400 is provided between an electrode 100 and a separator 300. The shape of the spacer 400 in a reference cross section is a part of an ellipse having an arc and a chord. The spacer 400 has a cross-sectional shape obtained by dividing an ellipse into two equal parts in the major axis direction. The arc part of the spacer 400 contacts the electrode 100, and the chord part of the spacer 400 contacts the separator 300.

[0046] Since the spacer 400 is in contact with the electrode 100 at the arc portion, the first angle θ1 is greater than 90°. The second angle θ2 is approximately 90°. The contact angle θ and the elevation angle θe satisfy the relationship θ≧2×θe.

[0047] A contact length L1 between the electrode 100 and the spacer 400 is different from a contact length L2 between the separator 300 and the spacer 400. The contact length L1 between the electrode 100 and the spacer 400 is shorter than the contact length L2 between the separator 300 and the spacer 400. The ratio of the length L1 to the length L2: L1 / L2 is 0.5 or more and 0.95 or less. The maximum diameter L3 of the spacer is equal to the length L2.

[0048] 3B is a cross-sectional view showing a schematic diagram of a main part of a lithium secondary battery according to an embodiment of the present disclosure. The spacer 400 is provided between the electrode 100 and the separator 300. The shape of the spacer 400 in the reference cross section is a part of an ellipse having an arc and a chord. The spacer 400 has a shape like an ellipse cut in the major axis direction so as not to pass through the center of the ellipse. The arc part of the spacer 400 contacts the electrode 100, and the chord part of the spacer 400 contacts the separator 300.

[0049] Since the spacer 400 is in contact with the electrode 100 at the arc portion, the first angle θ1 is greater than 90°. The second angle θ2 is also greater than 90°. The contact angle θ and the elevation angle θe satisfy the relationship θ≧2×θe.

[0050] A contact length L1 between the electrode 100 and the spacer 400 is different from a contact length L2 between the separator 300 and the spacer 400. The contact length L1 between the electrode 100 and the spacer 400 is shorter than the contact length L2 between the separator 300 and the spacer 400. The ratio of the length L1 to the length L2: L1 / L2 is 0.5 or more and 0.95 or less. The maximum diameter L3 of the spacer is shorter than the length L2.

[0051] [Fourth embodiment] The shape of the spacer in the reference cross section according to this embodiment is a trapezoid having at least one curved corner. However, this trapezoid is formed by stacking a plurality of particles. The shape and particle size of the particles are not particularly limited. The shape of the plurality of particles in the reference cross section is, for example, an ellipse. The shape and particle size of the plurality of particles may be the same or different. When a spacer is formed by combining a plurality of members in this way, the cross-sectional shape of the spacer is determined by drawing a line surrounding the plurality of members.

[0052] The radius of curvature of the curve is preferably at least three times the longer of the contact length between the electrode and the spacer and the contact length between the separator and the spacer. The contact length L1 between the electrode and the spacer is different from the contact length L2 between the separator and the spacer. The ratio of length L1 to length L2: L1 / L2 is preferably 0.5 or more and 0.95 or less.

[0053] FIG. 4 is a cross-sectional view showing a schematic view of a main part of a lithium secondary battery according to an embodiment of the present disclosure. The spacer 400 is provided between the electrode 100 and the separator 300. The shape of the spacer 400 in the reference cross section is a substantially trapezoid with rounded corners on the electrode 100 side and the separator 300 side. The spacer 400 is formed by stacking a plurality of particles with different particle sizes. The particle shape is generally elliptical. The spacer 400 has a curved line contacting the electrode 100. Therefore, the first angle θ1 is larger than 90°. The spacer 400 has a curved line contacting the separator 300. Therefore, the second angle θ2 is also larger than 90°. The radius of curvature at the intersection of the curved line with the electrode 100 or the separator 300 is three times or more larger than either the contact length L1 between the electrode and the spacer or the contact length L2 between the separator and the spacer, whichever is longer.

[0054] A contact length L1 between the electrode 100 and the spacer 400 is different from a contact length L2 between the separator 300 and the spacer 400. The ratio of the length L1 to the length L2: L1 / L2 is equal to or greater than 0.5 and equal to or less than 0.95.

[0055] The arrangement of the spacer is not particularly limited. In particular, it is preferable that the spacer is arranged so that a straight line SL passing through the spacer at three or more points (preferably four or more points, and further five or more points) along the first direction D1 can be drawn when viewed from the normal direction of the main surface of the separator. In this case, lithium metal is less likely to deposit unevenly or in a dendritic form on the negative electrode. Furthermore, local expansion of the negative electrode is suppressed, so that damage to the electrode is less likely to occur. In addition, the number of fulcrums at which the spacer supports the separator and the electrode increases, and the separator and the electrode receive stress from the spacer relatively evenly. Therefore, damage to the electrode is further suppressed. In addition, a more uniform pressing force can be applied from the separator to the entirety of the deposited lithium metal. Therefore, the deposition direction of the lithium metal is more easily controlled toward the surface direction of the negative electrode.

[0056] When viewed from the normal direction of the main surface of the separator, the ratio of the minimum distance d (μm) between adjacent spacers on the straight line SL to the height h (μm) of the spacer: d / h may be, for example, 10 to 800, or 40 to 400. By controlling the d / h ratio within the above range, it becomes easier to ensure a sufficient space for accommodating lithium metal. Furthermore, a more uniform pressing force can be applied from the separator to the entire precipitated lithium metal. The minimum distance d between adjacent spacers may be determined by measuring one point on each of any 10 straight lines SL and averaging the measurements.

[0057] When viewed from the normal direction of the main surface of the separator, the ratio of the area S of the region where the positive electrode and the negative electrode face each other to the area s of the spacer arranged in the region where the positive electrode and the negative electrode face each other: s / S may be, for example, 0.05 or more and 0.2 or less. By controlling the ratio of the area s within the above range, it is possible to apply a more uniform pressing force from the separator to the entire lithium metal that is deposited. Furthermore, it is possible to reduce resistance to the electrode reaction.

[0058] When viewed from the normal direction of the main surface of the separator, the ratio l / L of the length l of the spacer on the straight line SL to the first length L may be, for example, 0.05 to 0.2. This allows the separator to apply a more uniform pressing force to the entire deposited lithium metal. The length l may be measured for any 10 straight lines SL and calculated as the average value.

[0059] The spacer may be, for example, a plurality of linear protrusions arranged in a stripe pattern on the surface of the electrode or separator along the second direction. For example, one protrusion along the second direction D2 may be provided at each end of the separator surface in the first direction D1, and one protrusion along the second direction D2 may be provided in the center between the two ends (a total of three). In this case, a straight line SL can be drawn so as to pass through the spacer at two points at both ends and one point between the two ends, a total of three points. A spacer consisting of such a plurality of linear protrusions can be formed on the surface of the separator or electrode relatively easily. In addition, parameters such as the height h, the d / h ratio, the s / S ratio, and the l / L ratio can be easily controlled.

[0060] Hereinafter, the arrangement of the spacers will be described with reference to the drawings. In the illustrated example, the spacers are provided on the surface of the separator. However, the embodiment of the present disclosure is not limited thereto, and the spacers may be provided on the surface of the electrode.

[0061] 5A is a plan view showing a spacer arranged on the surface of a separator. The spacer 400 includes linear convex portions 401 arranged along the second direction D2 at both ends of the surface of the separator 300 in the first direction D1, and a linear convex portion 401 arranged along the second direction D2 at the center between the ends. That is, the spacer 400 includes a total of three linear convex portions 401 that are substantially parallel to each other. Therefore, a straight line SL drawn along the first direction D1 passes through the spacer 400 at three points. Note that substantially parallel means roughly parallel, and the linear convex portions 401 may intersect with each other at an angle of, for example, 0° to 20° or 0° to 10°.

[0062] 5B is a plan view showing a schematic diagram of another spacer arranged on the surface of a separator. Spacer 400 is composed of a plurality of linear protrusions 401 arranged in stripes on the surface of separator 300 along second direction D2. In this case, straight lines SL can be drawn along first direction D1 so as to pass through the same number of locations as linear protrusions 401 (seven locations in the illustrated example).

[0063] 5C is a plan view showing a schematic diagram of yet another spacer arranged on the surface of a separator. The spacer 400 is composed of a plurality of spot-shaped protrusions 401 evenly distributed on the surface of the separator 300. In the illustrated example, when a straight line SL is drawn along the first direction D1, the number of spot-shaped protrusions 401 passing through differs depending on the position of the straight line SL. The straight line SL1 passes through four protrusions 401, and the straight line SL2 passes through five protrusions 401. In such a case, it is sufficient that the number of protrusions through which at least one straight line SL passes among the plurality of straight lines SL that can be drawn in different modes is three or more.

[0064] 5D is a plan view showing a schematic diagram of yet another spacer arranged on the surface of a separator. Spacer 400 is a continuous body of honeycomb-shaped ribs evenly distributed on the surface of separator 300. In this case, too, when a straight line SL is drawn along first direction D1, the number of ribs that the straight line SL passes through varies depending on the position of the straight line SL. Straight line SL1 passes through the ribs at five points, and straight line SL2 passes through the ribs at four points.

[0065] 5E is a plan view showing a schematic diagram of still another spacer arranged on the surface of a separator. The spacer 400 is composed of a plurality of linear convex portions 401 arranged so as to be evenly distributed on the surface of the separator 300. The linear convex portions 401 are arranged so as to intersect alternately along the first direction D1. In this case as well, when a straight line is drawn along the first direction D1, the number of linear convex portions 401 passing through differs depending on the position of the straight line SL. For example, the straight line SL1 passes through three or four convex portions 401, the straight line SL2 passes through three convex portions 401, and the straight line SL3 passes through two convex portions 401.

[0066] Each component of the lithium secondary battery will now be described in more detail.

[0067] [Negative electrode] The negative electrode includes a negative electrode current collector. In a lithium secondary battery, lithium metal is deposited on the surface of the negative electrode by charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode by charging, become lithium metal, and deposit on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode is dissolved as lithium ions in the non-aqueous electrolyte by discharging. 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 a positive electrode active material by charging, or may be both of them.

[0068] The negative electrode current collector may be a conductive sheet, such as a foil or a film.

[0069] 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. "Smooth" 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.

[0070] The material of the negative electrode current collector (conductive sheet) may be any conductive material other than lithium metal and lithium alloy. The conductive material may be a metallic material such as a metal or an alloy. The conductive material is preferably a material that does not react with lithium. More specifically, a material that does not form any alloy or intermetallic compound with lithium is preferable. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, or graphite with a basal surface preferentially exposed. Examples of alloys include copper alloys and stainless steel (SUS). Among them, copper and / or copper alloys having high conductivity are preferable.

[0071] The thickness of the negative electrode current collector is not particularly limited and is, for example, 5 μm or more and 300 μm or less.

[0072] A negative electrode mixture layer may be formed on the surface of the negative electrode current collector. The negative electrode mixture layer is formed, for example, by applying a paste containing a negative electrode active material such as graphite to at least a part of the surface of the negative electrode current collector. However, from the viewpoint of achieving a high-capacity lithium secondary battery exceeding that of a lithium ion battery, the thickness of the negative electrode mixture layer is set to be sufficiently thin so that lithium metal can be precipitated in the negative electrode.

[0073] [Positive electrode] The positive electrode includes, for example, a positive electrode current collector and a positive electrode mixture layer supported by the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive material, and a binder. The positive electrode mixture layer may be formed on only one side of the positive electrode current collector, or may be formed on both sides. The positive electrode is obtained, for example, by applying a positive electrode mixture slurry including a 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.

[0074] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. Among them, lithium-containing transition metal oxides are preferred because of their low manufacturing cost and high average discharge voltage.

[0075] The lithium contained in the lithium-containing transition metal oxide is released from the positive electrode as lithium ions during charging and precipitates as lithium metal on the negative electrode or the negative electrode current collector. During discharging, the lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed into the composite oxide of the positive electrode. That is, the lithium ions involved in charging and discharging are generally derived from the solute in the nonaqueous electrolyte and the positive electrode active material.

[0076] Examples of the transition metal element contained in the lithium-containing transition metal oxide include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. The lithium-containing transition metal oxide may contain one or more transition metal elements. The transition metal element may be Co, Ni, and / or Mn. The lithium-containing transition metal oxide may contain one or more typical elements as necessary. Examples of typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. The typical element may be Al, etc.

[0077] Among lithium-containing transition metal oxides, composite oxides containing Co, Ni and / or Mn as transition metal elements, and optionally containing Al, and having a layered rock-salt crystal structure are preferred in terms of obtaining high capacity. In this case, in the lithium secondary battery, the molar ratio mLi of the total amount of lithium in the positive and negative electrodes to the amount mM of metal M other than lithium in the positive electrode is set to, for example, 1.1 or less: mLi / mM.

[0078] The conductive material is, for example, a carbon material, such as carbon black, acetylene black, ketjen black, carbon nanotubes, and graphite.

[0079] Examples of the binder include fluororesins, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, rubber-like polymers, etc. Examples of the fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, etc.

[0080] The maximum height roughness Rz of the surface of the positive electrode mixture layer is controlled to, for example, 10 μm or less so that a spacer can be easily arranged on the positive electrode surface. The maximum height roughness Rz is measured in accordance with JIS B 0601:2013.

[0081] The positive electrode current collector may be a conductive sheet. The conductive sheet may be a foil, a film, etc. The surface of the positive electrode current collector may be coated with a carbon material.

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

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

[0084] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator. Examples of the porous sheet include a thin film having micropores, a woven fabric, and a nonwoven fabric. The material of the separator is not particularly limited, but may be a polymeric material. Examples of the polymeric material include an olefin resin, a polyamide resin, and cellulose. Examples of the olefin resin include polyethylene, polypropylene, and a copolymer of ethylene and propylene. The separator may contain an additive as necessary. Examples of the additive include an inorganic filler.

[0085] [Non-aqueous electrolyte] The non-aqueous electrolyte having lithium ion conductivity contains, 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.

[0086] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent, which generates lithium ions and anions.

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

[0088] The lithium salt or anion may be any known one used in non-aqueous electrolytes for lithium secondary batteries. - , ClO4 - , PF6 - , CF3SO3 - , CF3CO2 - , anions of imides, anions of oxalate complexes, etc. Examples of the anions of imides 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 1 or more, and x and y are each independently 0, 1, or 2, and x+y=2 is satisfied.) The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bisoxalate borate anion, BF2(C2O4) - , PF4(C2O4) - , PF2(C2O4)2 - The non-aqueous electrolyte may contain one of these anions alone or two or more of them.

[0089] From the viewpoint of suppressing lithium metal precipitation in a dendritic form, the non-aqueous electrolyte preferably contains at least an anion of an oxalate complex. The interaction between the anion of the oxalate complex and lithium makes it easier for the lithium metal to be uniformly precipitated in the form of fine particles. This makes it easier to suppress localized precipitation of the lithium metal. The anion of the oxalate complex may be combined with another anion. The other anion may be PF6 - and / or the anion of an imide.

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

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

[0092] Examples of the ether include cyclic ethers and chain ethers. Examples of the cyclic ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of the 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 diethylene glycol dimethyl ether.

[0093] 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. The concentration of the anion of the oxalate complex in the non-aqueous electrolyte may be 0.05 mol / L or more and 1 mol / L or less.

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

[0095] [Lithium secondary battery] Hereinafter, the configuration of a lithium secondary battery according to the present disclosure will be described with reference to the drawings, taking as an example a cylindrical battery including a wound-type electrode group. However, the present disclosure is not limited to the following configuration.

[0096] FIG. 6 is a vertical cross-sectional view of a lithium secondary battery 10. The lithium secondary battery 10 is a cylindrical battery including a cylindrical battery case, a wound electrode group 14, and a nonaqueous electrolyte housed in the battery case. The battery case is composed of a case body 15, which is a cylindrical metal container with a bottom, and a sealing body 16 that seals the opening of the case body 15. The case body 15 has an annular step 21 formed by pressing a part of the side wall from the outside near the opening. The sealing body 16 is supported by the surface of the step 21 on the opening side. A gasket 27 is disposed between the case body 15 and the sealing body 16, thereby ensuring the hermeticity of the battery case. In the case body 15, insulating plates 17 and 18 are disposed at both ends of the electrode group 14 in the winding axis direction, respectively.

[0097] The sealing body 16 includes 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 disposed outside the case body 15, and the filter 22 is disposed inside the case body 15. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central parts, and an insulating member 24 is interposed between each of their peripheral parts. The filter 22 and the lower valve body 23 are connected to each other at their respective peripheral parts. The upper valve body 25 and the cap 26 are connected to each other at their respective peripheral parts. The lower valve body 23 has an air hole. When the internal pressure of the battery case increases due to abnormal heat generation or the like, the upper valve body 25 expands toward the cap 26 and separates from the lower valve body 23. This breaks the electrical connection between the lower valve body 23 and the upper valve body 25. When the internal pressure further increases, the upper valve body 25 breaks, and gas is discharged from an opening formed in the cap 26.

[0098] The electrode group 14 is composed 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 therebetween are all strip-shaped, and are spirally wound so that their width directions are parallel to the winding axis.

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

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

[0101] FIG. 7 is an enlarged view showing a schematic diagram of a discharge state of the region X surrounded by a dashed line in FIG. 6. In the illustrated example, the cross-sectional shape of the spacer is a trapezoid. However, the embodiment of the present disclosure is not limited thereto, and may be, for example, a rectangle, an ellipse, or a part of an ellipse having a curved line at least at one corner. In the illustrated example, the spacer is provided between the positive electrode and the separator. However, the embodiment of the present disclosure is not limited thereto, and the spacer may be provided between the negative electrode and the separator, or between the positive electrode, the negative electrode, and the separator.

[0102] The positive electrode 110 includes a positive electrode current collector 111 and a positive electrode composite layer 112. A spacer 400 is provided between the positive electrode composite layer 112 and the separator 300. The spacer 400 includes linear projections 401 provided along the second direction D2 (longitudinal direction) of the separator 300. In the discharged state (a), lithium metal is not deposited on the surface of the negative electrode current collector 121, and a space is maintained between the positive electrode 110 and the separator 300. On the other hand, in the charged state, lithium metal is deposited on the surface of the negative electrode current collector 121, and is accommodated 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 includes the negative electrode current collector 121 in the discharged state, and includes the negative electrode current collector 121 and lithium metal deposited on its surface in the charged state.

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

[0104] In the illustrated example, a cylindrical lithium secondary battery having a wound electrode group has been described, but the shape of the lithium secondary battery is not limited to this, and can be appropriately selected from various shapes such as cylindrical, coin, square, sheet, flat, etc., depending on the application. The shape of the electrode group is also not particularly limited, and may be a laminated type. In addition, the configuration of the lithium secondary battery other than the electrode group and non-aqueous electrolyte can be any known configuration without any particular limitation.

[0105] [Example] The lithium secondary battery according to the present disclosure will be described in more detail below with reference to examples and comparative examples, although the present disclosure is not limited to the following examples.

[0106] Example 1 (1) Preparation of the positive electrode A rock salt type lithium-containing transition metal oxide (NCA: positive electrode active material) containing Li, Ni, Co and Al (the molar ratio of Li to the total of Ni, Co and Al is 1.0) and having a layered structure, 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 an Al foil (positive electrode current collector), dried, and the coating film of the positive electrode mixture was rolled using a roller. Finally, the obtained laminate of the positive electrode current collector and the positive electrode mixture was cut to a predetermined electrode size, and a positive electrode having a positive electrode mixture layer on both sides of the positive electrode current collector was obtained.

[0107] (2) Formation of spacers A polyethylene separator (microporous film) was prepared. Polyimide ink was applied to both ends in the first direction D1 of both surfaces of the separator and to the center between the ends along the second direction D2, and then dried with hot air to provide spacers that were three parallel linear convex portions made of polyimide resin (Young's modulus 2 GPa). The polyimide ink was applied using a dispenser. The width (length L2) of the convex portion was 800 μm.

[0108] The height h of the protrusion was 15 μm, the minimum distance d between adjacent protrusions in the first direction D1 was 12 mm, the ratio (s / S) of the area s of the positive electrode composite layer covered by the spacer to the opposing area S of the positive electrode and negative electrode was 0.2, and the ratio (l / L) of the length of the spacer to the first length was 0.2.

[0109] (3) Preparation of the negative electrode A rectangular electrolytic copper foil (thickness: 15 μm) was prepared as a negative electrode current collector.

[0110] (4) Preparation of non-aqueous electrolyte Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC = 30:70, and LiPF6 and LiBF2(C2O4) were dissolved in the resulting mixed solvent at concentrations of 1 mol / L and 0.1 mol / L, respectively, to prepare a liquid non-aqueous electrolyte.

[0111] (5) Battery assembly In an inert gas atmosphere, the positive electrode and the negative electrode current collector were spirally wound with the separator interposed therebetween to prepare an electrode group. Since all the lithium contained in the electrode group originates from the positive electrode, the molar ratio of the total amount of lithium mLi possessed by the positive electrode and the negative electrode to the amount mM of metal M (here, Ni, Co, and Al) possessed by the positive electrode: mLi / mM is 1.0.

[0112] The electrode group was housed in a bag-shaped exterior body formed of a laminate sheet having an Al layer, and the nonaqueous electrolyte was injected, and then the exterior body was sealed to complete the lithium secondary battery A1.

[0113] In the reference cross section obtained by cutting the electrode group, the cross-sectional shape of the convex portion was close to a trapezoid. The contact length L2 between the separator and the spacer was longer than the contact length L1 between the positive electrode and the negative electrode and the spacer, and L1 / L2=0.88. The larger of the two first angles θ1 was 137°. The smaller of the two second angles θ2 was 43°.

[0114] Example 2 A battery A2 was fabricated in the same manner as in Example 1, except that a trapezoidal spacer was formed so that the contact length L2 between the separator and the spacer and the contact length L1 between the positive electrode and the spacer and the negative electrode were L1 / L2=0.56. The larger of the two first angles θ1 was 172°. The smaller of the two second angles θ2 was 8°.

[0115] Comparative Example 1 A battery B1 was produced in the same manner as in Example 1, except that in the formation of the spacer (2), a polyethylene tape (thickness about 30 μm) was attached to the separator to form the spacer. In the reference cross section obtained by cutting the electrode group, the cross-sectional shape of the convex portion was a rectangle with no rounded corners. The two first angles θ1 and the two second angles θ2 were all 90°.

[0116] [evaluation] The resulting battery was evaluated by a charge / discharge test.

[0117] In the charge-discharge test, three batteries were charged under the following conditions in a thermostatic chamber at 25°C, then a 20-minute break was given, followed by 100 cycles of discharging under the following conditions. The ratio of the discharge capacity at the 40th cycle to the discharge capacity at the 1st cycle (MR40) was calculated as the capacity retention rate (%).

[0118] (charging) The battery was charged at a constant current of 10 mA per unit area (cm2) of the electrode until the battery voltage reached 4.3 V, and then charged at a constant voltage of 4.3 V until the current value per unit area of ​​the electrode reached 1 mA.

[0119] (discharge) The battery was discharged at a constant current of 10 mA per unit area of ​​the electrode until the battery voltage reached 3.0 V.

[0120] The number of cycles at which the cycle stopped due to a crack in the negative electrode current collector occurred was calculated for the three batteries. If the cycle stopped for some of the batteries, the average MR40 value for the remaining batteries was calculated.

[0121] [Table 1]

[0122] In the batteries A1 and A2, the number of cycles until a cycle stop occurs is large and the capacity retention rate is also high, whereas in the battery B1, the number of cycles until a cycle stop occurs is small and the capacity retention rate is also low. [Industrial Applicability]

[0123] 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 hybrids and plug-in hybrids, and home storage batteries combined with solar cells. [Explanation of symbols]

[0124] 10. Lithium secondary battery 14 electrode group 15 Case body 16 Sealing body 17,18 Insulating plate 19 Positive lead 20 Negative lead 21 Step section 22 Filters 23 Lower valve body 24 Insulating materials 25 Upper valve 26 Cap 27 Gasket 100 electrodes 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 401 Convex

Claims

1. A positive electrode and A negative electrode; a separator disposed between the positive electrode and the negative electrode; A non-aqueous electrolyte having lithium ion conductivity, Lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves from the negative electrode during discharging, a spacer is provided between at least one of the positive electrode and the negative electrode and the separator; a first length of the separator in a first direction D1 is smaller than a second length of the separator in a second direction D2 intersecting the first direction D1; In a cross section of the spacer taken along the thickness direction of the separator and the first direction D1, at least one of an angle formed between the separator and the spacer on the spacer side and an angle formed between the spacer and an electrode in contact with the spacer on the spacer side is greater than 90°; When viewed from a normal direction of the main surface of the separator, The spacers are arranged so that a straight line passing through three or more points of the spacers can be drawn along the first direction D1, a ratio s / S of an area s of the spacer disposed in the region to an area S of the region where the positive electrode and the negative electrode face each other is 0.05 or more and 0.2 or less.

2. 2. The lithium secondary battery of claim 1, wherein the cross section of the spacer comprises a curve that contacts at least one of the separator and the electrode.

3. 3. The lithium secondary battery according to claim 2, wherein a radius of curvature of the curve at an intersection with the separator or the electrode is equal to or greater than half of the longer of a contact length between the electrode and the spacer and a contact length between the separator and the spacer.

4. In the cross section of the spacer, 4. The lithium secondary battery according to claim 1, wherein a contact length between the separator and the spacer, and a contact length between the electrode and the spacer are 500 μm or more and 2000 μm or less.

5. In the cross section of the spacer, 5. The lithium secondary battery according to claim 1, wherein a contact length between the electrode and the spacer is different from a contact length between the separator and the spacer.

6. When one of the contact lengths is length L1 and the other contact length longer than length L1 is length L2, 6. The lithium secondary battery according to claim 5, wherein a ratio of the length L1 to the length L2: L1 / L2 is 0.5 or more and 0.95 or less.

7. 7. The lithium secondary battery according to claim 5, wherein a contact length between the separator and the spacer is greater than a contact length between the electrode and the spacer.

8. 8. The lithium secondary battery according to claim 1, wherein the cross-sectional shape of the spacer is a rectangle, a trapezoid, an ellipse, or a part of an ellipse having a curved edge at least at one corner.

9. the cross-sectional shape of the spacer is a portion of the ellipse; Among the positive electrode, the negative electrode, and the separator, a member that contacts the spacer at an arc portion of the cross-sectional shape is defined as a first member, and a member that contacts the spacer at a chord portion of the cross-sectional shape is defined as a second member, a contact angle θ is an angle formed by a tangent to the arc at an intersection point between the arc and the second member and the second member on the spacer side, When an angle on the spacer side formed by a straight line connecting a midpoint of a contact portion between the first member and the spacer and the intersection point and the second member is defined as an elevation angle θe, The lithium secondary battery according to claim 8 , which satisfies the relationship θ≧2×θe.

10. the cross-sectional shape of the spacer is a portion of the ellipse; 10. The lithium secondary battery according to claim 8, wherein a maximum diameter L3 of the cross section in a plane direction of the separator is 500 μm or more and 2000 μm or less.

11. the cross-sectional shape of the spacer is a portion of the ellipse; The lithium secondary battery according to any one of claims 8 to 10, wherein a maximum diameter L3 of the cross section in a plane direction of the separator is greater than a contact length between the separator and the spacer and a contact length between the electrode and the spacer.

12. the cross-sectional shape of the spacer is rectangular, 9. The lithium secondary battery according to claim 8, wherein the radius of curvature of the curve is at least three times the longer of a contact length between the electrode and the spacer and a contact length between the separator and the spacer.

13. The lithium secondary battery according to any one of claims 1 to 12, wherein the spacer has a height of 15 µm or more and 60 µm or less.

14. The non-aqueous electrolyte contains lithium ions and anions, The lithium secondary battery according to any one of claims 1 to 13, wherein the anion includes at least an anion of an oxalate complex.

15. A positive electrode, A negative electrode; a separator disposed between the positive electrode and the negative electrode; A non-aqueous electrolyte having lithium ion conductivity, Lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves from the negative electrode during discharging, a spacer is provided between at least one of the positive electrode and the negative electrode and the separator; a first length of the separator in a first direction D1 is smaller than a second length of the separator in a second direction D2 intersecting the first direction D1; In a cross section of the spacer taken along the thickness direction of the separator and the first direction D1, at least one of an angle formed between the separator and the spacer on the spacer side and an angle formed between the spacer and an electrode in contact with the spacer on the spacer side is greater than 90°; the cross-sectional shape of the spacer is a portion of an ellipse having at least one curved corner; a maximum diameter L3 of the cross section in a plane direction of the separator is greater than a contact length between the separator and the spacer and a contact length between the electrode and the spacer.

16. A positive electrode, A negative electrode; a separator disposed between the positive electrode and the negative electrode; A non-aqueous electrolyte having lithium ion conductivity, Lithium metal is deposited on the negative electrode during charging, and the lithium metal dissolves from the negative electrode during discharging, a spacer is provided between at least one of the positive electrode and the negative electrode and the separator; a first length of the separator in a first direction D1 is smaller than a second length of the separator in a second direction D2 intersecting the first direction D1; In a cross section of the spacer taken along the thickness direction of the separator and the first direction D1, At least one of an angle formed between the separator and the spacer on the spacer side and an angle formed between the spacer and an electrode in contact with the spacer is greater than 90°. the cross-sectional shape of the spacer is a rectangle having at least one curved corner; a radius of curvature of the curve is three times or more the longer of a contact length between the electrode and the spacer and a contact length between the separator and the spacer.

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