Lithium secondary battery

Abstract

A lithium-ion secondary battery includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte with lithium-ion conductivity. During charging, lithium metal is deposited at the negative electrode, and during discharging, the lithium metal dissolves from the negative electrode. A spacer is provided between at least one of the positive and negative electrodes and the separator. The first length of the separator in a first direction (D1) is smaller than its second length in a second direction (D2) intersecting the first direction (D1). At least one of the angles formed by the separator and the spacer side, and the angle formed by the electrode in contact with the spacer and the spacer side, in a cross-section cut along the thickness direction of the separator and the first direction (D1), is greater than 90°.

Description

Technical Field

[0001] This disclosure relates to lithium secondary batteries that use lithium metal as the negative electrode active material. Background Technology

[0002] Lithium-ion batteries are known as high-capacity non-aqueous electrolyte secondary batteries. The increased capacity of lithium-ion batteries can be achieved by using alloyed active materials such as graphite and silicon compounds together as the negative electrode active material. However, the potential for increasing the capacity of lithium-ion batteries is gradually reaching its limit.

[0003] Lithium-ion batteries (lithium metal batteries) hold promise as high-capacity non-aqueous electrolyte secondary batteries that surpass lithium-ion batteries. In lithium-ion batteries, lithium metal is deposited at the negative electrode during charging, and during discharging, the lithium metal dissolves and is released as lithium ions into the non-aqueous electrolyte.

[0004] Patent Document 1 proposes to provide spacers to form a void between the negative or positive electrode and the spacer for accommodating lithium deposited on the surface of the negative electrode. Patent Document 2 proposes to provide spacers to mitigate stress caused by the expansion and contraction of the negative electrode.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 10-12279

[0008] Patent Document 2: Japanese Patent Application Publication No. 2011-8929 Summary of the Invention

[0009] In the methods of patent documents 1 and 2, the capacity retention rate is prone to decrease.

[0010] This 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. During charging, lithium metal is deposited at the negative electrode, and during discharging, the lithium metal dissolves from the negative electrode. A spacer is provided between at least one of the positive electrode and the negative electrode and the separator. The first length of the separator in a first direction D1 is smaller than a second length in a second direction D2 intersecting the first direction D1. At least one of the angle between the separator and the spacer on the spacer side, and the angle between the electrode in contact with the spacer and the spacer on the spacer side, is greater than 90° in a cross-section cut along the thickness direction of the separator and the first direction D1.

[0011] According to public information, it can improve the capacity retention rate of lithium secondary batteries. Attached Figure Description

[0012] Figure 1 This is a cross-sectional view schematically showing the main parts of a lithium secondary battery according to one embodiment of the present disclosure.

[0013] Figure 2A This is a schematic cross-sectional view showing the main part of another lithium secondary battery according to one embodiment of the present disclosure.

[0014] Figure 2B This is a cross-sectional view schematically showing the main parts of another lithium secondary battery according to one embodiment of the present disclosure.

[0015] Figure 3A This is a cross-sectional view schematically showing the main parts of another lithium secondary battery according to one embodiment of the present disclosure.

[0016] Figure 3B This is a cross-sectional view schematically showing the main parts of another lithium secondary battery according to one embodiment of the present disclosure.

[0017] Figure 4 This is a cross-sectional view schematically showing the main parts of another lithium secondary battery according to one embodiment of the present disclosure.

[0018] Figure 5A It is a top view schematically showing the spacers arranged on the surface of the separator.

[0019] Figure 5B It is a top view schematically showing another spacer disposed on the surface of the separator.

[0020] Figure 5C It is a top view schematically showing another spacer disposed on the surface of the separator.

[0021] Figure 5D It is a top view schematically showing another spacer disposed on the surface of the separator.

[0022] Figure 5E It is a top view schematically showing another spacer disposed on the surface of the separator.

[0023] Figure 6 This is a schematic longitudinal sectional view of a lithium secondary battery according to one embodiment of the present disclosure.

[0024] Figure 7 It is a schematic representation Figure 6 An enlarged view of the main components of a lithium secondary battery. Detailed Implementation

[0025] The lithium secondary battery disclosed herein includes a positive electrode, a negative electrode, a separator disposed between the positive and negative electrodes, and a non-aqueous electrolyte with lithium-ion conductivity. In the lithium secondary battery, lithium metal is deposited at the negative electrode during charging and dissolves from the negative electrode during discharging. A spacer is provided between at least one of the positive and negative electrodes (hereinafter, sometimes collectively referred to as electrodes) and the separator.

[0026] The expansion and contraction of the negative electrode exerts stress on the spacer. This stress tends to concentrate particularly at the corners of the spacer. Therefore, the portion of the electrode that contacts the corner of the spacer is prone to damage. Furthermore, when the corner of the spacer contacts the separator, the separator generates a reaction force against this stress, pushing the spacer back towards the electrode. This results in electrode damage. Electrode damage increases with charge-discharge cycles, sometimes reducing capacity retention.

[0027] The spacer disclosed herein contacts the electrode or separator at an angle greater than 90°. Therefore, stress concentration at the corners is mitigated, suppressing damage to the electrode.

[0028] (spacer)

[0029] A spacer is disposed between the electrode and the separator. The spacer creates a space between the electrode and the separator capable of accommodating deposited lithium metal. The spacer reduces the volume change of the negative electrode caused by lithium metal deposition.

[0030] On a cross-section (hereinafter referred to as the reference cross-section) cut along the thickness direction of the spacer and the first direction D1, at least one of the angles formed by the electrode in contact with the spacer on the spacer side (hereinafter referred to as the first angle θ1) and the angle formed by the spacer on the spacer side (hereinafter referred to as the second angle θ2) is greater than 90°. This reduces stress concentration at the corners and suppresses damage to the electrodes. Angle θ is preferably 100° or more, more preferably 130° or more. Angle θ is less than 180°. Angle θ is preferably 175° or less, more preferably 170° or less, and particularly preferably 150° or less. Angle θ is the average of the angles θ of the reference cross-section at five different locations. The first angle θ1 and the second angle θ2 are also calculated similarly.

[0031] In order to more easily suppress electrode damage, it is preferable that at least one of the first angles θ1 formed by the electrode and the spacer is greater than 90°. Particularly preferred is that at least one of the first angles θ1 formed by the positive electrode and the spacer is greater than 90°. Furthermore, it is preferable that all the first angles θ1 formed by the electrode and the spacer are greater than 90°. Among these, it is preferable that all the first angles θ1 formed by the positive electrode and the spacer are greater than 90°.

[0032] The first direction D1 of the separator is along the shorter side of the separator. That is, the first length of the separator in the first direction D1 is smaller than the second length in the second direction D2, which intersects the first direction D1. The shape of the separator can be, for example, a long rectangle, i.e., a strip. The angle between the first direction D1 and the second direction D2 can be approximately 90°, for example, it can be 88° to 92°.

[0033] On the reference cross section, the contact length between the spacer and the electrode and the spacer is not particularly limited. The contact length is appropriately set according to the first length. The contact length on the reference cross section is, for example, 500 μm or more and 2000 μm or less. When the contact length is within this range, the stress applied to the spacer is easily distributed uniformly on the spacer and the electrode. The contact length is the average of the contact lengths on the reference cross section at five different locations.

[0034] The height of the spacers on the reference cross-section is not particularly limited. The height of the spacers can be determined based on the amount of lithium metal deposited. For example, the height of the spacers is between 10 μm and 60 μm. When the height of the spacers is within this range, the absorption effect of the volume change of the negative electrode caused by the deposition of lithium metal can be further improved. Furthermore, the lithium metal deposited on the surface of the negative electrode is moderately compressed by the spacers, increasing the conductivity between the lithium metal and the negative electrode, thus improving charge and discharge efficiency. The height of the spacers is the average of the maximum heights of the spacers on the reference cross-section at five different locations.

[0035] There are no particular restrictions on the materials used to make the spacers. The spacers are made of conductive and / or insulating materials.

[0036] As a conductive material, it can be appropriately selected from materials used as negative or positive current collectors, as described later. Such spacers can also be provided by forming protrusions on the current collector using stamping or similar processes. Alternatively, conductive coatings can be applied to the surface of the spacer or electrode, or conductive strips can be adhered to the surface of the spacer or electrode.

[0037] Resin materials are listed as insulating materials. Examples of resin materials include polyolefin resins, acrylic resins, polyamide resins, polyimide resins, silicone resins, fluorinated resins, polyurethane resins, melamine resins, and urea resins. Cured products of curable resins such as epoxy resins can also be used as resin materials. Furthermore, inorganic fillers can be mixed into these resin materials.

[0038] Preferably, the material is an insulating material. Lithium metal is less likely to deposit on the surface of the insulating material. Therefore, it can improve the effect of suppressing the expansion of the negative electrode.

[0039] 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 facilitates the mitigation of stress caused by the expansion and contraction of the negative electrode and maintains space for accommodating lithium metal. Furthermore, it effectively suppresses electrode damage caused by the spacer. Cured products of the aforementioned curable resin are examples of materials that provide insulation and have a Young's modulus within the aforementioned range.

[0040] Spacers can be formed, for example, by attaching a resin-based adhesive tape to the surface of a spacer or electrode. Alternatively, spacers can be formed by coating the surface of a spacer or electrode with a solution or dispersion containing a resin material and allowing it to dry. Spacers can also be formed by coating the surface of a spacer or electrode with a curable resin in a desired shape and allowing it to cure. Alternatively, spacers can be formed by dispersing resin material particles in a desired shape on the surface of a spacer or electrode. In this regard, methods using a solution containing a resin material or resin material particles are preferred, as they facilitate the formation of angles θ larger than 90°.

[0041] The reference cross-section of the spacer is preferably a curve that contacts at least one of the spacer and the electrode. This allows the contact angle of the spacer to be further increased.

[0042] 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 formed by the tangent at the intersection of the curve and 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 can also be 90°.

[0043] When the reference cross-section of the spacer has a curve that contacts the partition, the second angle θ2 is the angle formed by the tangent at the intersection of the curve and the partition and the surface of the partition on the spacer side. In this case, the second angle θ2 is greater than 90°. The first angle θ1 is not particularly limited. The first angle θ1 can also be 90°.

[0044] Regarding the tendency for the contact angle of the spacer to increase further, the radius of curvature at the intersection of the curve with the spacer or the electrode is preferably larger. For example, the radius of curvature can be more than half, more than one time, or more than two times the longer of the contact length between the electrode and the spacer and the contact length between the spacer and the spacer.

[0045] On the reference cross-section, the contact length between the electrode and the spacer and the separator can also be different. In this case, the contact angle of the spacer can easily become larger. Moreover, on the reference cross-section, the spacer can form an inclined surface connecting the electrode and the separator. Therefore, it is less likely for an offset centered on the spacer to occur between the electrode and the separator, which further suppresses electrode damage. Preferably, the contact length between the separator and the spacer is larger than the contact length between the electrode and the spacer. In this case, the contact angle of the spacer relative to the electrode becomes larger, making it easier to suppress electrode damage.

[0046] Let one contact length be defined as length L1, and a contact length larger than length L1 be defined as length L2. The ratio of length L1 to length L2, L1 / L2, is preferably 0.5 or more and 0.95 or less, more preferably 0.8 or more and 0.95 or less. In this case, even components with smaller contact lengths can make contact with the spacer to a certain extent. Therefore, stress dispersion from the spacer makes it easier to suppress electrode damage.

[0047] In order to make it less likely for the electrode and the spacer to misalign, it is preferable that the spacer has a shape that is linearly symmetrical or nearly linearly symmetrical with respect to a straight line along the thickness direction of the spacer on the reference cross section.

[0048] The shape of the reference cross section of the spacer is not particularly limited. The shape of the reference cross section of the spacer may be, for example, a rectangle, trapezoid, ellipse, a portion of an ellipse, or a shape similar to them, having a curve at at least one corner. An ellipse includes a perfect circle.

[0049] Hereinafter, with appropriate reference to the accompanying drawings, a preferred shape of the reference cross-section of the spacer will be described. The drawings illustrate the shape of the spacer in the reference cross-section. In the drawings, at least one of the first angles θ1 formed by the electrode and the spacer is greater than 90°. However, embodiments of this disclosure are not limited thereto, and it is also possible that at least one of the second angles θ2 formed by the separator and the spacer is greater than 90°.

[0050] [First Implementation]

[0051] In this embodiment, the reference cross-section of the spacer is a rectangle with a curve at at least one corner. In this case, the radius of curvature of the curve is preferably more than three times the longer of the contact length between the electrode and the spacer and the contact length between the separator and the spacer.

[0052] Figure 1This is a schematic cross-sectional view showing the main parts of a lithium secondary battery according to one embodiment of the present disclosure. A spacer 400 is disposed between the electrode 100 and the separator 300. The reference cross-sectional shape of the spacer 400 is a generally rectangular shape with rounded corners on the electrode 100 side. The spacer 400 has a curve that contacts the electrode 100. Therefore, the first angle θ1 is larger than 90°. The second angle θ2 is approximately 90°.

[0053] The contact length L1 between electrode 100 and spacer 400 is different from the contact length L2 between spacer 300 and spacer 400. Contact length L1 is shorter than contact length L2. The ratio of length L1 to 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 and electrode 100 is more than three times the contact length L2 between spacer 300 and spacer 400.

[0054] [Second Implementation]

[0055] In this embodiment, the reference cross-section of the spacer 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.

[0056] Figure 2A This is a schematic cross-sectional view illustrating the main components of another lithium secondary battery according to one embodiment of the present disclosure. A spacer 400 is disposed between the electrode 100 and the separator 300. The reference cross-sectional shape of the spacer 400 is trapezoidal. 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 length L1 to 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, both first angles θ1 are greater than 90°. Both second angles θ2 are smaller than 90°.

[0057] Figure 2B This is a schematic cross-sectional view illustrating the main components of another lithium secondary battery according to one embodiment of the present disclosure. A spacer 400 is disposed between the electrode 100 and the separator 300. The reference cross-sectional shape of the spacer 400 is trapezoidal. 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 length L1 to length L2, L1 / L2, is 0.5 or more and 0.95 or less. The spacer 400 has an 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°.

[0058] [Third Implementation]

[0059] In this embodiment, the reference cross-section of the spacer is partially elliptical.

[0060] Among the positive electrode, negative electrode, and separator, the component that contacts the spacer on the arc portion is called the first component, and the component that contacts the spacer on the chord portion is called the second component.

[0061] The contact angle θ is defined as the angle between the tangent of the arc at the intersection of the arc and the second member and the spacer side formed by the second member. The angle θe is defined as the angle between the line connecting the midpoint of the contact portion of the first member and the spacer and the aforementioned intersection point and the spacer side formed by the second member. The contact angle θ and the angle θe, for example, satisfy the relationship θ ≥ 2 × θe. In this case, the angle between the first member and the spacer is sufficiently large.

[0062] (Contact length between the second component and the spacer) × tanθe represents the height h of the spacer. Therefore, the elevation angle θe is set, for example, in the range where the height h of the spacer is 10 μm or more and 60 μm or less.

[0063] On the reference cross-section, the maximum diameter L3 of the spacer in the direction of the separator can be greater than 500 μm and less than 2000 μm. This makes it easy to maintain space for accommodating lithium metal. The maximum diameter L3 can also be larger than both the contact length between the spacer and the separator and the contact length between the electrode and the spacer.

[0064] Figure 3A This is a schematic cross-sectional view illustrating the main components of a lithium secondary battery according to one embodiment of the present disclosure. A spacer 400 is disposed between the electrode 100 and the separator 300. The reference cross-sectional shape of the spacer 400 is a portion of an ellipse having arcs and chords. The spacer 400 has a cross-sectional shape that bisects the ellipse along its major axis. The arc portion of the spacer 400 contacts the electrode 100, and the chord portion of the spacer 400 contacts the separator 300.

[0065] The spacer 400 contacts the electrode 100 in the arc portion, therefore 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.

[0066] The contact length L1 between electrode 100 and spacer 400 is different from the contact length L2 between spacer 300 and spacer 400. The contact length L1 between electrode 100 and spacer 400 is shorter than the contact length L2 between spacer 300 and spacer 400. The ratio of length L1 to length L2 is greater than 0.5 and less than 0.95. The maximum diameter L3 of the spacer is equal to its length L2.

[0067] Figure 3B This is a schematic cross-sectional view illustrating the main components of a lithium secondary battery according to one embodiment of the present disclosure. A spacer 400 is disposed between the electrode 100 and the separator 300. The reference cross-sectional shape of the spacer 400 is a portion of an ellipse having arcs and chords. The spacer 400 has a shape that cuts the ellipse along its major axis without passing through the center of the ellipse. The arc portion of the spacer 400 contacts the electrode 100, and the chord portion of the spacer 400 contacts the separator 300.

[0068] The spacer 400 contacts the electrode 100 in the arc portion, therefore the first angle θ1 is larger than 90°. The second angle θ2 is also larger than 90°. The contact angle θ and the elevation angle θe satisfy the relationship θ ≥ 2 × θe.

[0069] The contact length L1 between electrode 100 and spacer 400 is different from the contact length L2 between spacer 300 and spacer 400. The contact length L1 between electrode 100 and spacer 400 is shorter than the contact length L2 between spacer 300 and spacer 400. The ratio of length L1 to length L2 is greater than 0.5 and less than 0.95. The maximum diameter L3 of the spacer is longer than its length L2.

[0070] [Fourth Implementation]

[0071] In this embodiment, the reference cross-sectional shape of the spacer is a trapezoid with a curve at at least one corner. However, this trapezoid is formed by stacking multiple particles. The shape and size of the particles are not particularly limited. The shape of the reference cross-section of the multiple particles is, for example, elliptical. The shape and size of the multiple particles can be the same or different. In this way, when a spacer is formed by combining multiple components, the cross-sectional shape of the spacer is determined by drawing lines surrounding the multiple components.

[0072] 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 and the contact length L2 between the separator and the spacer are different. The ratio of length L1 to length L2, L1 / L2, is preferably 0.5 or more and 0.95 or less.

[0073] Figure 4This is a schematic cross-sectional view illustrating the main parts of a lithium secondary battery according to one embodiment of the present disclosure. A spacer 400 is disposed between the electrode 100 and the separator 300. The reference cross-sectional shape of the spacer 400 is approximately trapezoidal, having rounded corners on both the electrode 100 and separator 300 sides. The spacer 400 is formed by stacking multiple particles of different sizes. The particles are approximately elliptical in shape. The spacer 400 has a curve in contact with the electrode 100. Therefore, the first angle θ1 is larger than 90°. The spacer 400 also has a curve in contact with the separator 300. Therefore, the second angle θ2 is also larger than 90°. The radius of curvature at the intersection of the aforementioned curves with the electrode 100 or the separator 300 is more than three times the longer of the contact length L1 between the electrode and the spacer and the contact length L2 between the separator and the spacer.

[0074] The contact length L1 between electrode 100 and spacer 400 is different from the contact length L2 between separator 300 and spacer 400. The ratio of length L1 to length L2 is 0.5 or more and 0.95 or less.

[0075] The arrangement of the spacers is not particularly limited. However, when viewed from the normal direction of the main surface of the spacer, it is preferable to arrange the spacers in such a way that a straight line SL along the first direction D1 is drawn passing through three or more (preferably four or more, more preferably five or more) points through the spacers. In this case, lithium metal is less likely to precipitate unevenly or dendritively on the negative electrode. Moreover, local expansion of the negative electrode is suppressed, thus reducing the risk of electrode damage. Furthermore, the spacers provide more support points for the spacers and electrodes, resulting in more uniform stress on the spacers and electrodes. Therefore, electrode damage is further suppressed. In addition, a more uniform compressive force can be applied from the spacers to the entire deposited lithium metal. Therefore, the lithium metal precipitation direction is more easily controlled in the surface direction of the negative electrode.

[0076] When viewed from the normal direction of the main surface of the spacer, the ratio of the minimum distance d (μm) between adjacent spacers to the height h (μm) of the spacer on the aforementioned straight line SL, d / h, can be, for example, 10 or more and 800 or less, or 40 or more and 400 or less. By controlling the d / h ratio within the above range, it is easy to ensure sufficient space for accommodating lithium metal. Moreover, a more uniform extrusion pressure can be applied to the entire deposited lithium metal from the spacer. The minimum distance d between adjacent spacers can be obtained by measuring one location on each of any 10 straight lines SL and taking the average value.

[0077] When viewed from the normal direction of the main surface of the separator, the ratio of the area S of the region opposite the positive and negative electrodes to the area s of the spacers disposed in the region opposite the positive and negative electrodes, s / S, should be, for example, 0.05 or more and 0.2 or less. By controlling the ratio of area s within the above range, a more uniform extrusion pressure can be applied to the entire deposited lithium metal from the separator. Furthermore, it can reduce the obstruction to the electrode reaction.

[0078] When viewed from the normal direction of the main surface of the separator, the ratio of the length l occupied by the spacers on the aforementioned straight line SL to the first length L, l / L, should be, for example, 0.05 or more and 0.2 or less. This allows for a more uniform extrusion pressure to be applied to the entire deposited lithium metal from the separator. The length l can be obtained by measuring each of any 10 straight lines SL and averaging the measurements.

[0079] The spacer can be, for example, a plurality of linear protrusions arranged in a stripe pattern on the surface of the electrode or spacer along the second direction. For instance, it could be that each end of the spacer surface in the first direction D1 has a protrusion along the second direction D2, and a third protrusion (a total of three) along the second direction D2 is provided at the center between the two ends. In this case, a straight line SL can be drawn through a total of three locations: the two ends and the location between the two ends. Such spacers, composed of multiple linear protrusions, can be easily formed on the surface of the spacer or electrode. Furthermore, parameters such as height h, d / h ratio, s / S ratio, and l / L ratio are easily controlled.

[0080] The arrangement of the spacers will now be described with reference to the accompanying drawings. In the example drawings, the spacers are disposed on the surface of the separator. However, the embodiments of this disclosure are not limited thereto, and the spacers may also be disposed on the surface of the electrodes.

[0081] Figure 5A This is a schematic top view showing a spacer disposed on the surface of a separator. The spacer 400 includes: linear protrusions 401 respectively located at both ends on the surface of the separator 300 in a first direction D1 and along a second direction D2; and a linear protrusion 401 located at the center between the two ends and along the second direction D2. That is, the spacer 400 is composed of a total of three substantially parallel linear protrusions 401. Therefore, a straight line SL drawn along the first direction D1 passes through the spacer 400 at three locations. Furthermore, "substantially parallel" means approximately parallel, and the linear protrusions 401 may intersect each other, for example, at angles of 0° to 20° or 0° to 10°.

[0082] Figure 5BThis is a schematic top view showing another spacer disposed on the surface of the separator 300. The spacer 400 is composed of a plurality of linear protrusions 401 arranged in a stripe pattern on the surface of the separator 300 in a manner along the second direction D2. In this case, a straight line SL can be drawn along the first direction D1, passing through the same number of locations as the linear protrusions 401 (7 in the example).

[0083] Figure 5C This is a schematic top view showing another spacer disposed on the surface of the separator 300. The spacer 400 is composed of a plurality of dot-shaped protrusions 401 arranged in a manner uniformly distributed on the surface of the separator 300. In the example shown, when a straight line SL is drawn along the first direction D1, the number of dot-shaped protrusions 401 that the straight line SL passes through varies depending on the position of the straight line SL. Straight line SL1 passes through 4 protrusions 401, and straight line SL2 passes through 5 protrusions 401. In such cases, it is sufficient that at least one of the plurality of straight lines SL drawn in different ways can pass through more than 3 protrusions.

[0084] Figure 5D This is a schematic top view showing another spacer arranged on the surface of the separator 300. The spacer 400 is a continuum of honeycomb-shaped ribs arranged uniformly on the surface of the separator 300. In this case, when the straight line SL is drawn along the first direction D1, the number of ribs it passes through varies depending on the position of the straight line SL. Straight line SL1 passes through the ribs at 5 locations, and straight line SL2 passes through the ribs at 4 locations.

[0085] Figure 5E This is a schematic top view showing another spacer disposed on the surface of the separator 300. The spacer 400 is composed of a plurality of line segment-shaped protrusions 401 arranged in a manner uniformly distributed on the surface of the separator 300. The line segment-shaped protrusions 401 are arranged in a manner that alternately intersects along the first direction D1. In this case, when a straight line is drawn along the first direction D1, the number of line segment-shaped protrusions 401 that the line SL passes through varies depending on the position of the line SL. For example, the line SL1 passes through 3 or 4 protrusions 401, the line SL2 passes through 3 protrusions 401, and the line SL3 passes through 2 protrusions 401.

[0086] The following section provides a more detailed explanation of the structural elements of a lithium secondary battery.

[0087] [negative electrode]

[0088] The negative electrode has a negative current collector. In a lithium-ion secondary battery, lithium metal is deposited on the surface of the negative electrode during charging. More specifically, lithium ions contained in the non-aqueous electrolyte accept electrons at the negative electrode during charging to become lithium metal, which is then deposited on the surface of the negative electrode. The lithium metal deposited on the surface of the negative electrode dissolves into the non-aqueous electrolyte as lithium ions during discharge. Furthermore, the lithium ions contained in the non-aqueous electrolyte can come from lithium salts added to the non-aqueous electrolyte, or can be supplied by the positive electrode active material during charging, or both.

[0089] The negative current collector can be a conductive sheet. Foil, film, etc., can be used as the conductive sheet.

[0090] The surface of the conductive sheet can also be smooth. This allows lithium metal from the positive electrode to easily and uniformly deposit on the conductive sheet during charging. Smoothness refers to a maximum vertical roughness Rz of 20 μm or less for the conductive sheet. The maximum vertical roughness Rz can also be 10 μm or less. The maximum vertical roughness Rz is measured according to JIS B 0601:2013.

[0091] The negative electrode current collector (conductive sheet) can be made of any conductive material other than lithium metal and lithium alloys. The conductive material can also be a metal, alloy, or other metallic material. Preferably, the conductive material is a material that does not react with lithium. More specifically, it is preferably a material that neither forms an alloy nor an intermetallic compound with lithium. Examples of such conductive materials include copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metallic elements, or graphite with a predominantly exposed base. Examples of alloys include copper alloys and stainless steel (SUS). Copper and / or copper alloys, which have high conductivity, are preferred.

[0092] There are no particular restrictions on the thickness of the negative current collector, for example, it can be above 5μm and below 300μm.

[0093] A negative electrode composite material layer can also be formed on the surface of the negative electrode current collector. This 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 viewpoint of achieving lithium secondary batteries with capacities exceeding those of lithium-ion batteries, the thickness of the negative electrode composite material layer is set to be sufficiently thin to allow lithium metal to be deposited at the negative electrode.

[0094] [positive electrode]

[0095] The positive electrode, for example, comprises a positive current collector and a positive electrode composite material layer supported on the positive current collector. The positive electrode composite material layer, for example, includes a positive electrode active material, a conductive material, and a binder material. The positive electrode composite material layer may be formed on only one side of the positive current collector or on both sides. The positive electrode is obtained, for example, by coating both sides of the positive current collector with a positive electrode composite material slurry comprising a positive electrode active material, a conductive material, and a binder material, and then rolling the coating after it has dried.

[0096] The positive electrode active material is a material that absorbs and releases lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, and transition metal sulfides. Among these, lithium-containing transition metal oxides are preferred due to their low manufacturing cost and high average discharge voltage.

[0097] Lithium contained in lithium-containing transition metal oxides is released as lithium ions from the positive electrode during charging and deposited as lithium metal at the negative electrode or negative electrode current collector. During discharging, lithium metal dissolves from the negative electrode, releasing lithium ions, which are then absorbed by the composite oxide of the positive electrode. In other words, the lithium ions participating in charging and discharging primarily originate from the solute in the non-aqueous electrolyte and the positive electrode active material.

[0098] Transition metal elements included in lithium-containing transition metal oxides include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, and W. Lithium-containing transition metal oxides may contain one or more transition metal elements. The transition metal element may also be Co, Ni, and / or Mn. Lithium-containing transition metal oxides may contain more than one typical element as needed. Typical elements include Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, and Bi. Al may also be a typical element.

[0099] In lithium-containing transition metal oxides, for the purpose of obtaining high capacity, it is preferable to have a composite oxide containing Co, Ni, and / or Mn as transition metal elements, Al as an arbitrary component, and having a rock-salt-type crystal structure with a layered structure. In this case, in the lithium secondary battery, the molar ratio of the total amount of lithium (mLi) in the positive and negative electrodes to the amount of metal M other than lithium (mM) in the positive electrode, mLi / mM, is set, for example, to 1.1 or less.

[0100] Conductive materials include, for example, carbon materials. Examples of carbon materials include carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphite.

[0101] Examples of adhesive materials include fluoropolymers, polyacrylonitrile, polyimide resins, acrylic resins, polyolefin resins, and rubber-like polymers. Examples of fluoropolymers include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

[0102] To facilitate the placement of spacers on the cathode surface, the maximum vertical roughness Rz of the cathode composite layer is controlled, for example, to be below 10 μm. The maximum vertical roughness Rz is measured according to JIS B 0601:2013.

[0103] The positive current collector can be any conductive sheet. Foil, film, etc., can be used as the conductive sheet. Alternatively, carbon material can be coated onto the surface of the positive current collector.

[0104] Materials used as positive current collectors (conductive sheets) include, for example, metallic materials containing Al, Ti, and Fe. These metallic materials can also be Al, Al alloys, Ti, Ti alloys, Fe alloys, etc. Fe alloys can also be stainless steel (SUS).

[0105] There are no particular restrictions on the thickness of the positive current collector, for example, it can be above 5μm and below 300μm.

[0106] [Separator]

[0107] The separator uses a porous sheet material with ion permeability and insulation properties. Examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the separator is not particularly limited and can also be a polymer material. Examples of polymer materials include polyolefin resins, polyamide resins, and cellulose. Examples of polyolefin resins include polyethylene, polypropylene, and copolymers of ethylene and propylene. The separator may also contain additives as needed. Examples of additives include inorganic fillers.

[0108] [Non-aqueous electrolytes]

[0109] Non-aqueous electrolytes with lithium-ion conductivity include, for example, a non-aqueous solvent and lithium ions and anions dissolved in the non-aqueous solvent. Non-aqueous electrolytes can be in liquid or gel form.

[0110] Liquid non-aqueous electrolytes are prepared by dissolving lithium salts in a non-aqueous solvent. The dissolution of the lithium salt in the non-aqueous solvent generates lithium ions and anions.

[0111] Gel-like non-aqueous electrolytes may contain lithium salts and matrix polymers, or lithium salts, non-aqueous solvents, and matrix polymers. For example, a polymer material that gels by absorbing a non-aqueous solvent may be used. Examples of polymer materials include fluoropolymers, acrylic resins, and polyether resins.

[0112] As lithium salts or anions, known lithium salts or anions that can be used in non-aqueous electrolytes of lithium secondary batteries are listed. Specifically, BF4 is mentioned. - ClO4 - PF6 - CF3SO3 - CF3CO2 - Anions of imides, anions of oxalate complexes, etc. Examples of imide anions include N(SO₂CF₃)₂. - 、N(C m F 2m+1 SO2) x (C n F 2n+1 SO2) y - (m and n are independent integers greater than or equal to 0 or 1, x and y are independent integers of 0, 1, or 2, satisfying x + y = 2), etc. The anions of oxalate complexes may also contain boron and / or phosphorus. Examples of anions in oxalate complexes include dioxaloborate anion and BF2(C2O4). - PF4(C2O4) - PF2(C2O4)2 - Non-aqueous electrolytes can contain these anions individually or in combination with more than one type.

[0113] From the viewpoint of suppressing the dendritic precipitation of lithium metal, the non-aqueous electrolyte is preferably an anion containing at least an oxalate complex. Utilizing the interaction between the oxalate complex anion and lithium, lithium metal readily precipitates uniformly in fine particles. Therefore, localized precipitation of lithium metal is easily suppressed. The oxalate complex anion can also be combined with other anions. Other anions can also be PF6. - And / or imide anions.

[0114] Examples of non-aqueous solvents include esters, ethers, nitriles, amides, or their halogenated derivatives. Non-aqueous electrolytes may contain only one of these non-aqueous solvents or two or more. Examples of halogenated derivatives include fluorides.

[0115] Examples of esters include carbonates and carboxylic acid esters. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate (FEC). Examples of chain carbonates include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate. Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Examples of chain carboxylic acid esters include ethyl acetate, methyl propionate, and methyl fluoropropionate.

[0116] 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 diethylene glycol dimethyl ether.

[0117] The concentration of lithium salt in the non-aqueous electrolyte is, for example, 0.5 mol / L or higher and 3.5 mol / L or lower. Alternatively, the concentration of anion in the non-aqueous electrolyte can be set to 0.5 mol / L or higher and 3.5 mol / L or lower. Furthermore, the concentration of anion of oxalate complex in the non-aqueous electrolyte can be set to 0.05 mol / L or higher and 1 mol / L or lower.

[0118] Non-aqueous electrolytes may also contain additives. These additives can also form a coating on the negative electrode. The formation of dendrites is easily suppressed by the coating from the additives on the negative electrode. Examples of such additives include vinylene carbonate, FEC, and ethylene ethylene carbonate (VEC).

[0119] [Lithium-ion rechargeable battery]

[0120] The structure of the lithium secondary battery of this disclosure will now be described with reference to the accompanying drawings, using a cylindrical battery with a wound electrode assembly as an example. However, this disclosure is not limited to the following structure.

[0121] Figure 6 This is a longitudinal sectional view of a lithium secondary battery 10. The lithium secondary battery 10 is a cylindrical battery comprising a cylindrical battery casing and a wound electrode assembly 14 housed within the battery casing, and a non-aqueous electrolyte. The battery casing consists of a casing body 15, which is a bottomed cylindrical metal container, and a sealing body 16 that seals the opening of the casing body 15. The casing body 15 has an annular step portion 21 near the opening, formed by partially pressing the sidewall from the outside. The sealing body 16 is supported by the opening side surface of the step portion 21. A gasket 27 is disposed between the casing body 15 and the sealing body 16, thereby ensuring the airtightness of the battery casing. Inside the casing body 15, insulating plates 17 and 18 are respectively disposed at both ends in the winding axis direction of the electrode assembly 14.

[0122] The sealing body 16 includes a filter 22, a lower valve core 23, an insulating member 24, an upper valve core 25, and a cover 26. The cover 26 is disposed on the outside of the housing body 15, and the filter 22 is disposed on the inside of the housing body 15. The lower valve core 23 and the upper valve core 25 are connected to each other at their respective central portions, and the insulating member 24 is located between the peripheral portions of the lower valve core 23 and the upper valve core 25. The filter 22 and the lower valve core 23 are connected to each other at their respective peripheral portions. The upper valve core 25 and the cover 26 are connected to each other at their respective peripheral portions. A vent hole is formed in the lower valve core 23. When the internal pressure of the battery housing rises due to abnormal heating, the upper valve core 25 expands toward the cover 26 and moves away from the lower valve core 23. As a result, the electrical connection between the lower valve core 23 and the upper valve core 25 is blocked. When the internal pressure rises further, the upper valve core 25 breaks, and gas is discharged from the opening formed in the cover 26.

[0123] The electrode assembly 14 consists of a positive electrode 110, a negative electrode (negative current collector) 120, and a separator 300. The positive electrode 110, the negative electrode 120, and the separator 300 between them are all strip-shaped and wound into a spiral shape with their respective width directions parallel to the winding axis.

[0124] The positive electrode 110 is electrically connected to the cover 26, which also serves as the positive terminal, via the positive electrode lead 19. One end of the positive electrode lead 19 is connected, for example, near the center along the long side 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 via a through hole formed in the insulating plate 17.

[0125] The negative electrode 120 is electrically connected to the housing body 15, which also serves as the negative terminal, via the negative electrode lead 20. One end of the negative electrode lead 20 is connected to the end of the negative electrode 120 along its long side, and the other end is soldered to the inner bottom surface of the housing body 15.

[0126] Figure 7 It is a schematic representation. Figure 6 The diagram shows an enlarged view of the discharge state of region X, enclosed by the dashed line. In the example diagram, the cross-sectional shape of the spacer is trapezoidal. However, the embodiments of this disclosure are not limited to this; for example, it may also be a rectangle, ellipse, or a partial ellipse with a curve at at least one corner. In the example diagram, the spacer is disposed between the positive electrode and the separator. However, the embodiments of this disclosure are not limited to this; the spacer may also be disposed between the negative electrode and the separator, or between the positive electrode and the separator, and between the negative electrode and the separator.

[0127] The positive electrode 110 includes a positive electrode current collector 111 and a positive electrode composite material layer 112. A spacer 400 is provided between the positive electrode composite material layer 112 and the separator 300. The spacer 400 is composed of a linear protrusion 401 arranged along the second direction D2 (long side direction) of the separator 300. In the discharge state (a), lithium metal does not deposit on the surface of the negative electrode current collector 121, and a space is maintained between the positive electrode 110 and the separator 300. On the other hand, in the charging state, lithium metal is deposited on the surface of the negative electrode current collector 121, and is contained in the space between the positive electrode 110 and the separator 300 while being squeezed by the separator 300. That is, the negative electrode 120 has a negative electrode current collector 121 in the discharge state and has a negative electrode current collector 121 and lithium metal deposited on its surface in the charging state.

[0128] Lithium metal is contained within the space between the positive electrode 110 and the separator 300, thus reducing the apparent volume change of the electrode assembly caused by lithium metal deposition during charge-discharge cycles. Consequently, the stress imposed on the negative electrode current collector 121 is also suppressed. Furthermore, pressure is applied from the separator 300 to the lithium metal contained between the positive electrode 110 and the separator 300, thereby controlling the deposition state of the lithium metal, preventing it from becoming isolated, and suppressing a decrease in charge-discharge efficiency.

[0129] In the illustrated example, a cylindrical lithium secondary battery with a wound electrode assembly is described. However, the shape of the lithium secondary battery is not limited to this, and various shapes such as cylindrical, coin-shaped, square, sheet-shaped, and flat can be appropriately selected depending on its application. The shape of the electrode assembly is also not particularly limited and can also be stacked. Furthermore, known structures can be used without particular restrictions for the electrode assembly and the non-aqueous electrolyte in the lithium secondary battery.

[0130] [Example]

[0131] The lithium secondary battery of this disclosure will be further described in detail below based on embodiments and comparative examples. However, this disclosure is not limited to the following embodiments.

[0132] Example 1

[0133] (1) Production of the positive electrode

[0134] A layered, rock-salt-type lithium-containing transition metal oxide (NCA: positive electrode active material), acetylene black (AB: conductive material), and polyvinylidene fluoride (PVdF: binder material) containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al is 1.0) with a layered structure are mixed at a mass ratio of NCA:AB:PVdF = 95:2.5:2.5. Then, an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added and the mixture is stirred to prepare a positive electrode composite slurry. The obtained positive electrode composite slurry is coated on both sides of an Al foil (positive electrode current collector), dried, and then rolled using rollers to form a coating of the positive electrode composite material. Finally, the resulting laminate of the positive electrode current collector and the positive electrode composite material is cut to a predetermined electrode size, thereby obtaining a positive electrode with positive electrode composite material layers on both sides of the positive electrode current collector.

[0135] (2) Formation of spacers

[0136] A polyethylene spacer (microporous membrane) was prepared. Polyimide ink was applied along the second direction D2 to both ends and the center between the two ends on the two surfaces of the spacer in the first direction D1. After hot air drying, three parallel linear protrusions (spacers) formed of polyimide resin (Young's modulus of 2 GPa) were created. The polyimide ink was applied using a distributor. The width (length L2) of the protrusions was 800 μm.

[0137] The height h of the protrusion is 15 μm, the minimum distance d between adjacent protrusions in the first direction D1 is 12 mm, the ratio of the area s of the positive electrode composite material layer covered by the spacer to the relative area S of the positive and negative electrodes (s / S) is 0.2, and the ratio of the length of the spacer to the first length (l / L) is 0.2.

[0138] (3) Fabrication of the negative electrode

[0139] A rectangular electrolytic copper foil (15 μm thick) was prepared as the negative electrode current collector.

[0140] (4) Modulation of non-aqueous electrolytes

[0141] Ethyl carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of EC:DMC = 30:70. LiPF6 was dissolved in the resulting mixed solvent at a concentration of 1 mol / L and LiBF2 (C2O4) was dissolved at a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte.

[0142] (5) Battery assembly

[0143] In an inactive gas atmosphere, the positive and negative current collectors are wound into a spiral shape with the aforementioned separator in between to form an electrode assembly. All the lithium contained in the electrode assembly comes from the positive electrode, so the molar ratio of the total amount of lithium (mLi) in the positive and negative electrodes to the amount of metal M (in this case, Ni, Co, and Al) in the positive electrode (mM) is 1.0.

[0144] The electrode assembly is housed in a bag-shaped outer packaging formed by a laminate with an Al layer. After the non-aqueous electrolyte is injected, the outer packaging is sealed to complete the lithium secondary battery A1.

[0145] On the reference cross-section obtained by cutting the electrode assembly, the cross-sectional shape of the protrusion is close to a trapezoid. The contact length L2 between the separator and the spacer is longer than the contact length L1 between the positive and negative electrodes and the spacer, L1 / L2 = 0.88. The larger of the two first angles θ1 is 137°. The smaller of the two second angles θ2 is 43°.

[0146] Example 2

[0147] Except that the spacer is formed in a trapezoidal shape such that the contact length L2 between the spacer and the spacer, and the contact length L1 between the positive and negative electrodes and the spacer are L1 / L2 = 0.56, the battery A2 is manufactured in the same manner as in Example 1. The larger of the two first angles θ1 is 172°. The smaller of the two second angles θ2 is 8°.

[0148] Comparative Example 1

[0149] In the formation of the spacer (2), the battery B1 is manufactured in the same manner as in Example 1, except that a polyethylene strip (approximately 30 μm thick) is adhered to the spacer to form the spacer. In the reference cross-section obtained by cutting the electrode assembly, the cross-sectional shape of the protrusion is a rectangle with unrounded corners. Both first angles θ1 and both second angles θ2 are 90°.

[0150] [evaluate]

[0151] The obtained batteries were subjected to charge-discharge tests and evaluated.

[0152] In the charge-discharge test, three batteries were charged in a constant temperature bath at 25°C under the following conditions, then left to stand for 20 minutes, and then discharged under the following conditions. This cycle was repeated 100 times. The ratio of the discharge capacity of the 40th cycle to the discharge capacity of the 1st cycle (MR40) was used as the capacity retention rate (%).

[0153] (Charge)

[0154] The battery is charged with a constant current of 10 mA per unit area (square centimeters) of the electrode until the battery voltage reaches 4.3V. Then, it is charged with a constant voltage of 4.3V until the current per unit area of ​​the electrode reaches 1 mA.

[0155] (Discharge)

[0156] A constant current discharge is applied at a current of 10mA per unit area of ​​the electrode until the battery voltage reaches 3.0V.

[0157] Calculate the number of cycles required to stop cycling in the three cells, presumably due to cracking of the negative electrode current collector. Furthermore, calculate the average MR40 for the remaining cells after some cells have stopped cycling.

[0158] [Table 1]

[0159]

[0160] In batteries A1 and A2, the number of cycles until cycle cessation is higher, and the capacity retention rate is also higher. On the other hand, battery B1 has fewer cycles until cycle cessation is higher, and the capacity retention rate is also lower.

[0161] Industrial availability

[0162] The lithium secondary battery disclosed herein can be used in electronic devices such as mobile phones, smartphones, and tablets, electric vehicles including hybrid and plug-in hybrid electric vehicles, and household batteries combined with solar cells.

[0163] Explanation of reference numerals in the attached figures

[0164] 10. Lithium secondary battery; 14. Electrode assembly; 15. Casing body; 16. Sealing body; 17, 18. Insulating plate; 19. Positive lead; 20. Negative lead; 21. Stepped portion; 22. Filter; 23. Lower valve core; 24. Insulating component; 25. Upper valve core; 26. Cover; 27. Gasket; 100. Electrode; 110. Positive electrode; 111. Positive current collector; 112. Positive composite material layer; 120. Negative electrode; 121. Negative current collector; 300. Separator; 400. Spacer; 401. Protrusion.

Claims

1. A lithium secondary battery, wherein, This lithium secondary battery has the following features: positive electrode; negative electrode; A separator disposed between the positive electrode and the negative electrode; and It is a non-aqueous electrolyte that exhibits lithium-ion conductivity. During charging, lithium metal is deposited at the negative electrode; during discharging, the lithium metal dissolves from the negative electrode. A spacer is provided between at least one of the positive electrode and the negative electrode and the separator. The first length of the separator in the first direction (D1) is smaller than the second length in the second direction (D2) intersecting the first direction (D1). On the cross-section of the spacer cut along the thickness direction of the separator and the first direction (D1), At least one of the following angles is greater than 90°: the angle between the separator and the spacer on the spacer side, and the angle between the electrode in contact with the spacer and the spacer on the spacer side. When viewed from the normal direction of the main surface of the spacer, the spacer is arranged in such a way that a straight line along the first direction can be drawn passing through three or more parts of the spacer. The ratio of the area of ​​the spacer disposed in the region to the area of ​​the region opposite the positive electrode and the negative electrode is 0.05 or more and 0.2 or less. On the cross section of the spacer, The contact length between the separator and the spacer and the contact length between the electrode and the spacer are greater than 500 μm and less than 2000 μm.

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

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

4. The lithium secondary battery according to any one of claims 1 to 3, wherein, On the cross section of the spacer, The contact length between the electrode and the spacer is different from the contact length between the separator and the spacer.

5. The lithium secondary battery according to claim 4, wherein, When one of the contact lengths is defined as length L1, and a contact length larger than length L1 is defined as length L2, The ratio of the length L1 to the length L2 is L1 / L2, which is greater than 0.5 and less than 0.

95.

6. The lithium secondary battery according to claim 4, wherein, The contact length between the separator and the spacer is greater than the contact length between the electrode and the spacer.

7. The lithium secondary battery according to any one of claims 1 to 3, wherein, The shape of the cross section of the spacer is a rectangle, trapezoid, ellipse, or elliptical section with a curve at at least one corner.

8. The lithium secondary battery according to claim 7, wherein, The shape of the cross-section of the spacer is a portion of the ellipse. In the positive electrode, the negative electrode, and the separator, the component that contacts the arc portion of the spacer's cross-sectional shape is designated as the first component, and the component that contacts the chord portion of the spacer's cross-sectional shape is designated as the second component. The contact angle θ is defined as the angle between the tangent of the arc at the intersection of the arc and the second component and the spacer side formed by the second component. Let the angle between the straight line connecting the midpoint of the contact portion of the first component and the spacer and the intersection point with the spacer side formed by the second component be the elevation angle θe. At this time, The relationship θ≥2×θe is satisfied.

9. The lithium secondary battery according to claim 7, wherein, The shape of the cross-section of the spacer is a portion of the ellipse. The maximum diameter (L3) of the cross section in the direction of the surface of the separator is more than 500 μm and less than 2000 μm.

10. The lithium secondary battery according to claim 7, wherein, The shape of the cross-section of the spacer is a portion of the ellipse. The maximum diameter (L3) of the cross section in the direction of the face of the separator is greater than both the contact length between the separator and the spacer and the contact length between the electrode and the spacer.

11. The lithium secondary battery according to claim 7, wherein, The shape of the cross-section of the spacer is rectangular. The radius of curvature of the curve is more than three times the longer of the contact length between the electrode and the spacer and the contact length between the separator and the spacer.

12. The lithium secondary battery according to any one of claims 1 to 3, wherein, The height of the spacer is 15 μm or more and 60 μm or less.

13. The lithium secondary battery according to any one of claims 1 to 3, wherein, The non-aqueous electrolyte contains lithium ions and anions. The anion contains at least an anion of an oxalate complex.

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