Lithium secondary battery and separator

Abstract

A lithium secondary battery is provided with a positive electrode, a negative electrode facing the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode are wound with a separator therebetween to constitute an electrode group having a plurality of turns. At least one member selected from the positive electrode, the negative electrode, and the separator has a spacer layer. The spacer layer is configured from a plurality of protrusions so as to be discontinuous in both a first direction parallel to the winding axis and a second direction perpendicular to the first direction. When the electrode group is viewed from the direction of the winding axis, the plurality of convex portions are divided into a plurality of groups, and the convex portions included in each group are arranged in the radial direction to form a plurality of radially arranged rows.

Description

Technical Field

[0001] The present disclosure relates to a lithium secondary battery having a non-aqueous electrolyte with lithium ion conductivity. Background Art

[0002] Non-aqueous electrolyte secondary batteries are used for applications such as ICT use (e.g., personal computers and smartphones), vehicle use, and power storage use. In such applications, further high-capacity non-aqueous electrolyte secondary batteries are required. As a high-capacity non-aqueous electrolyte secondary battery, a lithium ion battery is known. High-capacity lithium ion batteries can be achieved, for example, by using an alloy active material such as graphite and a silicon compound as a negative electrode active material. However, the high-capacity of lithium ion batteries is reaching its limit.

[0003] As a non-aqueous electrolyte secondary battery with a higher capacity than a lithium ion battery, a lithium secondary battery (lithium metal secondary battery) is highly expected. In a lithium secondary battery, during charging, lithium metal is deposited on the negative electrode, and this lithium metal dissolves in the non-aqueous electrolyte during discharging.

[0004] Patent Document 1 proposes to ensure a space for lithium metal deposition during charging by providing a spacer (protrusion) between the positive electrode and the separator, thereby improving charge-discharge efficiency and suppressing cracking of the negative electrode current collector caused by local swelling of the negative electrode. When drawing a straight line in the width direction (short side direction) of the positive electrode current collector, the spacer is arranged between the positive electrode and the separator in such a way that the straight line passes through the spacer at three or more points.

[0005] Prior Art Documents

[0006] Patent Document 1: International Publication No. 2020 / 0066254 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] In Patent Document 1, when observed from the length direction of the positive electrode current collector, a plurality of spacers (protrusions) can be arranged discontinuously. In this case, when the positive electrode and the negative electrode are wound around a separator to form an electrode group, in a certain cross-section of the electrode group perpendicular to the winding axis, the position (phase) of the protrusion in the circumferential direction may vary depending on the number of windings. In this case, the protrusion of a certain winding may sometimes be located between the protrusions existing in the inner or outer circle of that winding, and sometimes the protrusion may sink into the space formed between the protrusions existing in the inner or outer circle of that winding, resulting in a reduction in the amount of space formed by the protrusions. As a result, the improvement effect of the cycle characteristics brought about by the formation of the space may sometimes not be obtained sufficiently.

[0009] Means for Solving the Problems

[0010] One aspect of the present disclosure relates to a lithium secondary battery, which includes a positive electrode, a negative electrode opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode are wound with the separator therebetween to form an electrode group having a plurality of turns. The positive electrode, the negative electrode, and the separator are in a strip shape and have a length L1 in a first direction D1 parallel to the winding axis and a length L2 in a second direction D2 perpendicular to the first direction (L1 < L2). In the negative electrode, lithium metal is deposited during charging and dissolved during discharging. At least one component selected from the positive electrode, the negative electrode, and the separator has a spacer layer, and the spacer layer is composed of a plurality of convex portions in a discontinuous manner in both the first direction and the second direction. When the electrode group is viewed from the direction of the winding axis, the plurality of convex portions are divided into a plurality of groups, and the convex portions included in each group are arranged radially to form a plurality of radially arranged columns.

[0011] Another aspect of the present disclosure relates to a separator, which is in a strip shape and has a length L1 in a first direction D1 and a length L2 in a second direction D2 perpendicular to the first direction (L1 < L2). The separator has a base material layer and a spacer layer, and the spacer layer is composed of a plurality of convex portions in a discontinuous manner in both the first direction and the second direction. When a positive electrode and a negative electrode are wound with the separator therebetween to form an electrode group having a plurality of turns and having a winding axis parallel to the first direction, when the electrode group is viewed from the direction of the winding axis, the plurality of convex portions are divided into a plurality of groups, and the convex portions included in each group are arranged radially to form a plurality of radially arranged columns.

[0012] Effects of the Invention

[0013] According to the present disclosure, a decrease in the cycle characteristics of the lithium secondary battery can be suppressed.

[0014] The novel features of the present invention are described in the appended claims. However, with respect to both the structure and the content, the present invention can be better understood by the following detailed description with reference to the drawings in combination with other objects and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 FIG. is a plan view schematically showing an example of the arrangement of the spacer layer provided on the surface of the separator in the lithium secondary battery according to the embodiment of the present disclosure.

[0016] Figure 2A It shows the use of Figure 1 A conceptual diagram of the state of a cross-section perpendicular to the winding axis when an electrode group is formed using the separator.

[0017] Figure 2B It shows the use of Figure 1Conceptual diagram of the state of a cross-section perpendicular to the winding axis when a separator forms an electrode group.

[0018] Figure 3 It is a top view schematically showing another example of the configuration of the spacer layer provided on the surface of the separator.

[0019] Figure 4 It is a top view schematically showing another example of the configuration of the spacer layer provided on the surface of the separator.

[0020] Figure 5 It is a longitudinal sectional view schematically showing a lithium secondary battery according to an embodiment of the present disclosure.

[0021] Figure 6 It schematically shows Figure 5 an enlarged view of the main part of the lithium secondary battery. Detailed Embodiments

[0022] Hereinafter, embodiments of the present disclosure will be described by way of examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values, materials, etc. may be exemplified, but other numerical values, materials, etc. may also be applied as long as the effects of the present disclosure can be obtained. In addition, components other than the characteristic parts in the present disclosure can be components of known secondary batteries. In this specification, the description "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be replaced with "numerical value A or more and numerical value B or less". In the following description, when the lower limit and the upper limit of a numerical value related to a specific physical property or condition, etc. are exemplified, any one of the exemplified lower limits and any one of the exemplified upper limits can be arbitrarily combined as long as the lower limit is not above the upper limit. When multiple materials are exemplified, one of them can be selected and used alone, or two or more of them can be used in combination.

[0023] In addition, the present disclosure includes combinations of matters recited in two or more claims arbitrarily selected from the multiple claims recited in the appended claims. That is, as long as there is no technical contradiction, matters recited in two or more claims arbitrarily selected from the multiple claims recited in the appended claims can be combined.

[0024] One embodiment of the present disclosure relates to a lithium secondary battery, which includes a positive electrode, a negative electrode opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode are wound with the separator therebetween to form an electrode group having a plurality of turns. The positive electrode, the negative electrode, and the separator are in a strip shape, having a length L1 in a first direction D1 parallel to the winding axis and a length L2 in a second direction D2 perpendicular to the first direction, and the length L1 is shorter than the length L2 (L1 < L2). The lithium secondary battery is a secondary battery of a type in which lithium metal is deposited on the negative electrode during charging and lithium metal is dissolved from the negative electrode during discharging. Hereinafter, the positive electrode and the negative electrode may be collectively referred to as electrodes.

[0025] In the lithium secondary battery, for example, 70% or more of the rated capacity is exhibited by the deposition and dissolution of lithium metal. The movement of electrons in the negative electrode during charging and discharging is mainly due to the deposition and dissolution of lithium metal in the negative electrode. Specifically, 70 to 100% (for example, 80 to 100% or 90 to 100%) of the movement of electrons (current in other viewpoints) in the negative electrode during charging and discharging is caused by the deposition and dissolution of lithium metal. That is, the negative electrode of the lithium secondary battery is different from the negative electrode in which the movement of electrons in the negative electrode during charging and discharging is mainly caused by the occlusion and release of lithium ions by a negative electrode active material (such as graphite).

[0026] At least one component selected from the positive electrode, the negative electrode, and the separator has a spacer layer. The spacer layer forms a space between the positive electrode and the separator or between the negative electrode and the separator, and suppresses the expansion of the negative electrode accompanying charge and discharge.

[0027] (Spacer layer)

[0028] Through the spacer layer, a space for depositing lithium metal on the surface of the negative electrode is ensured, and the volume change of the negative electrode accompanying the deposition of lithium metal is reduced. The spacer layer is provided in the form of protrusions on at least one of the positive electrode, the negative electrode, and the separator. The spacer layer or the protrusions may be provided on the surface of the positive electrode, may be provided on the surface of the negative electrode, or may be provided on the surface of the separator opposite to the positive electrode or the negative electrode. The protrusions provided on the surface of the positive electrode and / or the surface of the separator opposite to the positive electrode form a space between the positive electrode and the separator, and the protrusions provided on the surface of the negative electrode and / or the surface of the separator opposite to the negative electrode form a space between the negative electrode and the separator. Through the space, the expansion of the negative electrode accompanying charge and discharge is suppressed, and the deterioration of the cycle characteristics is suppressed.

[0029] The spacer layer may be composed of a plurality of protrusions in a manner that is discontinuous in both the first direction and the second direction. The electrolyte can circulate in the gaps between the plurality of protrusions, thereby improving the liquid circulation property and further suppressing the deterioration of the cycle characteristics.

[0030] In addition, in any cross-section perpendicular to the winding axis of the electrode group, the cross-sections of the convex portions belonging to different turns are arranged radially to form a plurality of radially arranged columns. In an embodiment having a plurality of convex portions, when the electrode group is viewed from the direction of the winding axis, the plurality of convex portions are separately arranged into a plurality of groups (convex portion groups). The convex portions included in each convex portion group are arranged radially to form a plurality of radially arranged columns.

[0031] In this case, since there are no other convex portions between the convex portion groups forming the radial columns, the convex portions in a certain turn of the winding do not lie between the convex portions existing in the inner turn or the outer turn of that turn. As a result, it is possible to suppress the convex portions from falling into the space formed between the convex portions existing in the inner turn or the outer turn of that turn, which may cause a reduction in the amount of space formed by the convex portions. Consequently, the effect of suppressing the degradation of the cycle characteristics can be sufficiently improved.

[0032] A plurality of convex portions belonging to the same convex portion group overlap at least partially in the second direction in a cross-section of the electrode group perpendicular to the winding axis, forming a radial column. When the electrode group is viewed from the direction of the winding axis, it is preferable that the convex portions of adjacent turns included in the same group overlap each other in the second direction with a length of 50% or more.

[0033] Furthermore, it is preferable that all the convex portions belonging to the same convex portion group have a common overlapping portion in the second direction when the electrode group is viewed from the direction of the winding axis. More preferably, when the electrode group is viewed from the direction of the winding axis, a radial straight line passing through the center in the second direction of a specific convex portion passes through all the convex portions included in the same convex portion group.

[0034] At this time, since the circumference of the turns closer to the outer circle side in the electrode group is longer, in order to ensure that the convex portions of adjacent turns overlap each other, the length or width of any convex portion in the second direction can be set to be equal to or less than the length or width of the convex portion arranged on the more outer circle side in the second direction. Here, there may be a plurality of convex portions belonging to different convex portion groups among the convex portions arranged on the more outer circle side. It is sufficient that the length or width of the convex portion in the second direction is at least equal to or less than the length or width of the convex portion belonging to the same convex portion group and arranged on the more outer circle side in the second direction. The length or width of the plurality of convex portions (belonging to the same convex portion group) in the second direction can gradually increase from the inner circle side to the outer circle side.

[0035] Here, the width of the convex portion in the second direction means, when the convex portion is not a linear shape parallel to the second direction, the difference in the position in the second direction between the portion on the side closest to the second direction (the inner winding side) within the convex portion and the portion on the other side closest to the second direction (the outer winding side) within the convex portion. Similarly, the width of the convex portion in the first direction means the difference in the position in the first direction between the portion on the side closest to the first direction within the convex portion and the portion on the other side closest to the first direction within the convex portion. When the convex portion is a linear shape parallel to the second direction, the width of the convex portion in the second direction is equal to the length of the convex portion in the second direction.

[0036] For any turn in the electrode group, let the diameter approximated by a circle be D. Let the total thickness of the positive electrode, negative electrode, two separator films, and the spacer layer be T. The thicknesses of the positive electrode, negative electrode, and separator films are the thicknesses of the base portions without considering the spacer layer. At this time, in a cross-section perpendicular to the winding axis of the electrode group, let the length of the convex portion of this turn in the second direction be Li. Let the length of the convex portion of the turn on the outer winding side that is adjacent to this turn and belongs to the same convex portion group in the second direction be Lo. When considering the cross-section of the electrode group perpendicular to the winding axis, if the angle occupied by the convex portion of this turn in the circumferential direction is set to θi (rad), then Li = (D / 2) × θi. Similarly, if the angle occupied by the convex portion of the turn on the outer winding side adjacent to this turn in the circumferential direction is set to θo, then Lo = ((D + 2T) / 2) × θo.

[0037] From the viewpoint of ensuring that the convex portions of adjacent turns overlap with each other and ensuring sufficient space, it is preferable that θi = θo. In this case, Li and Lo satisfy the following formula.

[0038] Lo = Li × (D + 2T) / D

[0039] By arranging the convex portions on the surface of the component in a manner that satisfies the above formula, it is possible to effectively ensure the space for lithium metal precipitation and suppress the degradation of the cycle characteristics.

[0040] Here, the turn on the outer winding side adjacent to a turn means the turn corresponding to the (n + 1)-th turn when this turn corresponds to the n-th turn of winding the positive electrode, negative electrode, and separator films. The turn on the inner winding side adjacent to a turn means the turn corresponding to the (n - 1)-th turn when this turn corresponds to the n-th turn of winding the positive electrode, negative electrode, and separator films.

[0041] Consider an arbitrary cross-section of the electrode group perpendicular to the winding axis. In any loop, let the center position of the convex portion in the cross-section be P, and let the center position of the convex portion of the loop on the outer ring side adjacent to this loop and belonging to the same convex portion group be Po. Similarly, let the center position of the convex portion of the loop on the inner ring side adjacent to this loop and belonging to the same convex portion group as the convex portion having point P be Pi. In the component in the state before winding, the distance Ci in the second direction between P and Pi is obtained by substituting the distance from position P to the center of winding as D / 2 into the formula for Li and setting θi = 2π. Similarly, the distance Co in the second direction between P and Po is obtained by substituting θo = 2π into the formula for Lo. Thus, the distances Ci and Co approximately satisfy the relationship Co - Ci = 2πT.

[0042] Therefore, by arranging the convex portion groups composed of multiple convex portions along the second direction on the component and increasing the center pitch between the convex portions belonging to the same convex portion group by 2πT each time, when forming the electrode group, the convex portions belonging to the same convex portion group are arranged radially with respect to each other, and a radially arranged column can be formed.

[0043] When observing the electrode group from the direction of the winding axis, it is preferable that in all loops, a plurality of convex portions (belonging to different convex portion groups) are uniformly distributed. In an arbitrary cross-section perpendicular to the winding axis of the electrode group and crossing the convex portion, it is preferable that the existence ratio of the crossed convex portions is substantially equal in all loops. The existence ratio of the crossed convex portions is the value obtained by dividing the length of the convex portions existing in each loop in the second direction (the sum of the lengths when there are multiple convex portions on the same loop) by the circumference. The fact that the existence ratio of the convex portions is substantially equal in all loops means that when calculating the existence ratio using the above method in all loops, the ratio of the difference between the maximum value and the minimum value of the existence ratio to the maximum value is 10% or less. Thereby, the non-uniformity of the space for lithium metal precipitation is reduced, and the cycle characteristics are improved.

[0044] In addition, when a virtual line parallel to the first direction is drawn at an arbitrary position of the component provided with the spacer layer, it is preferable that the virtual line passes through the spacer layer at two or more positions. In this case, at any position in the second direction, there are two convex portions opposed to each other in the first direction, so that the space for precipitating lithium metal can be reliably ensured. On the contrary, when the virtual line parallel to the first direction does not pass through the spacer layer or passes through only one spacer layer at a certain position in the second direction, in the region around the virtual line, due to the increase in the internal pressure of the electrode group accompanying the precipitation of lithium metal, the space is squeezed, and it may be impossible to ensure sufficient space. By making the virtual line pass through the spacer layer at two or more positions at an arbitrary position in the second direction, the space for lithium metal precipitation can be more reliably ensured, and the reduction of the cycle characteristics can be suppressed.

[0045] From the viewpoint of ensuring space for lithium metal precipitation, in any cross-section perpendicular to the winding axis of the electrode group and passing through the convex portion, there may be two or more regions where the convex portion does not exist.

[0046] When drawing an imaginary line along the second direction from a point on any convex portion, the length Ly passing through the convex portion and the length Ln not passing through the convex portion may satisfy 0.1 ≤ Ln / (Ly + Ln) ≤ 0.75. In this case, it is possible to ensure both the space for lithium metal precipitation and the liquid circulation property, and it is easy to achieve excellent cycle characteristics.

[0047] The plurality of convex portions may be linear convex portions. The plurality of convex portions may be linear convex portions parallel to the second direction. The linear convex portion may be a straight convex portion, a curved convex portion, or a convex portion including a straight portion and a curved portion.

[0048] The plurality of convex portions may be arranged in a staggered manner. A polygon (e.g., a hexagon) mesh may be formed by a plurality of straight convex portions. From the viewpoint of suppressing the non-uniformity of the space between the negative electrode and the separator, the interior angle of the polygon may be 120° or less.

[0049] From the viewpoint of ensuring the necessary minimum space between the negative electrode and the separator, depending on the battery size, the average height h of the convex portion may be 0.02 mm or more and 0.09 mm or less, or may be 0.015 mm or more and 0.01 mm or less. The average height h of the convex portion is obtained by averaging the measured values of any 10 points.

[0050] From the viewpoint of improving the liquid circulation property of the non-aqueous electrolyte on the surface of the negative electrode, the height of a part of the convex portion may be different from the height of the remaining part of the convex portion, and the heights of adjacent convex portions may be different. The plurality of convex portions may include a convex portion with a height of h1 and a convex portion with a height of h2 smaller than the height h1. In this case, the ratio h2 / h1 of the height h2 to the height h1 may be, for example, 0.8 or more and less than 1.0, or may be 0.8 or more and 0.95 or less. The width of the convex portion (e.g., Figure 1 the width W of the linear convex portion 401 in

[0051] From the viewpoint of suppressing the precipitation of lithium metal on the surface of the convex portion, the plurality of convex portions may be made of a material having a lower conductivity than the electrode, and may be made of a resin material.

[0052] There is no particular limitation on the material constituting the spacer layer. The spacer layer may be made of a conductive material and / or an insulating material. Among them, an insulating material is preferred. Since lithium metal is not easily precipitated on the surface of the insulating material, the effect of suppressing the swelling of the negative electrode can be improved.

[0053] As the conductive material, it can be appropriately selected from the materials for the negative electrode current collector or the positive electrode current collector and the materials described later. Such a spacer layer can be provided by forming convex portions on the negative electrode current collector by stamping or the like. Further, a conductive coating can be applied to the surface of the separator or the electrode, or a conductive tape can be adhered to the surface of the separator or the electrode.

[0054] Examples of the insulating material include resin materials. Examples of the resin materials include polyolefin resins, acrylic resins, polyamide resins, polyimide resins, silicone resins, fluorine-based resins, polyurethane resins, melamine resins, urea resins, etc. As the resin material, a cured product of a curable resin such as an epoxy resin can be used. Further, inorganic fillers or the like can be mixed in these resin materials.

[0055] The material constituting the spacer layer is preferably a material having a Young's modulus of 0.01 GPa or more and 10 GPa or less. Thereby, it is easy to relieve the stress caused by the expansion and contraction of the negative electrode, and it is easy to maintain the space for accommodating the lithium metal. In addition, it is easy to suppress damage to the electrode caused by the spacer layer. Examples of the insulating material having a Young's modulus in the above range include cured products of the above curable resins.

[0056] The spacer layer can be formed, for example, by adhering a resin adhesive tape to the surface of the separator or the electrode. Further, the spacer layer can be formed by applying a solution or dispersion containing a resin material to the surface of the separator or the electrode and drying it. The spacer layer can be formed by applying a curable resin in a desired shape to the surface of the separator or the electrode and curing it. Alternatively, the spacer layer can be formed by dispersing particles of the resin material in a desired shape on the surface of the separator or the electrode.

[0057] The spacer layer can be provided on the surfaces on both sides of the component. In this case, the spacer layer includes a first spacer layer disposed on the first surface of the component and a second spacer layer disposed on the second surface of the component. By the convex portions formed by the first spacer layer and the convex portions formed by the second spacer layer respectively satisfying the above relationships, the space for lithium metal precipitation can be reliably ensured, and the deterioration of the cycle characteristics can be suppressed.

[0058] The lithium secondary battery can include a laminated electrode group formed by laminating a positive electrode and a negative electrode with a separator interposed therebetween, or can include a wound electrode group formed by winding a positive electrode and a negative electrode with a separator into a spiral shape.

[0059] One embodiment of the present disclosure relates to a separator provided with the above-described spacer layer. The separator has a strip shape with a length L1 in a first direction D1 and a length L2 (L1 < L2) in a second direction D2 perpendicular to the first direction, and includes a base material layer and a spacer layer. The spacer layer is composed of a plurality of convex portions in a manner that is discontinuous in both the first direction and the second direction. When a positive electrode and a negative electrode are wound with the separator interposed therebetween to form an electrode group having a plurality of turns and a winding axis parallel to the first direction, when the electrode group is viewed from the direction of the winding axis, the plurality of convex portions are divided into a plurality of groups, and the convex portions included in each group are arranged radially to form a plurality of radially arranged columns. When an imaginary line parallel to the first direction is drawn at any position of the separator, it is preferable that the imaginary line passes through the spacer layer at two or more positions.

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

[0061] Figure 1 It is a top view schematically showing the spacer layer disposed on the surface of the separator. Figure 2A and Figure 2B is a schematic representation of Figure 1 When the separator 300 is wound together with the positive electrode and the negative electrode to form an electrode group, it is a conceptual diagram showing the state of a cross section perpendicular to the winding axis.

[0062] In Figure 1 In the example, the spacer layer 400 is composed of a plurality of linear convex portions extending substantially parallel along the second direction D2. In addition, substantially parallel means substantially parallel, and the linear convex portions may cross each other at an angle of, for example, 0° to 20° or 0° to 10°.

[0063] More specifically, the spacer layer 400 includes a plurality of linear convex portions 401 and 402 along the second direction D2. The linear convex portion 402 is different from the linear convex portion 401 in position in the first direction D1 and the second direction. When viewed from the first direction D1, the linear convex portion 401 extends along the second direction D2 at a position in the first direction D1 between adjacent linear convex portions 402, and the linear convex portion 402 extends along the second direction D2 at a position in the first direction D1 between adjacent linear convex portions 401. When viewed from the second direction D2, the linear convex portion 402 is disposed in a region in the second direction D2 that is an intermittent portion where the linear convex portion 401 is not disposed, and the linear convex portion 401 is disposed in a region in the second direction D2 that is an intermittent portion where the linear convex portion 402 is not disposed. That is, as a whole, the plurality of linear convex portions 401 and 402 are arranged in a staggered manner on the surface of the separator 300.

[0064] Thus, when a straight line parallel to the first direction D1 is drawn at any position on the separator 300, the straight line passes through the linear protrusion 401 ( Figure 1 dashed line SL1) at three points, or passes through the linear protrusion 402 ( Figure 1 dashed line SL2) at two points.

[0065] The plurality of linear protrusions 401 are arranged such that the length (width in the second direction) thereof becomes longer as it approaches the outer circumferential side of the winding in the second direction D2, and the interval (center distance) between adjacent protrusions in the second direction becomes longer. In Figure 1 the example of, the plurality of linear protrusions 401 include a plurality of linear protrusions 401a, a plurality of linear protrusions 401b located closer to the inner circumferential side of the winding than the linear protrusions 401a, and a plurality of linear protrusions 401c located closer to the outer circumferential side of the winding than the linear protrusions 401a. The width of the linear protrusion 401a in the second direction D2 is longer than the width of the linear protrusion 401b in the second direction D2 and shorter than the width of the linear protrusion 401c in the second direction D2. In addition, the interval (center distance) between adjacent linear protrusions 401a in the second direction is longer than the interval between adjacent linear protrusions 401b in the second direction and shorter than the interval (center distance) between adjacent linear protrusions 401c in the second direction.

[0066] Similarly, in Figure 1 the example of, the plurality of linear protrusions 402 include a plurality of linear protrusions 402a, a plurality of linear protrusions 402b located closer to the inner circumferential side of the winding than the linear protrusions 402a, and a plurality of linear protrusions 402c located closer to the outer circumferential side of the winding than the linear protrusions 402a. The width of the linear protrusion 402a in the second direction D2 is longer than the width of the linear protrusion 402b in the second direction D2 and shorter than the width of the linear protrusion 402c in the second direction D2. In addition, the interval (center distance) between adjacent linear protrusions 402a in the second direction is longer than the interval between adjacent linear protrusions 402b in the second direction and shorter than the interval (center distance) between adjacent linear protrusions 402c in the second direction.

[0067] In this way, by forming the widths and the arrangement intervals of the linear protrusions 401 and 402 in the second direction D2 to gradually increase as it approaches the outer circumferential side of the winding, when the electrode group is formed, the linear protrusions 401 (401a, 401b, 401c) are arranged neatly in the radial direction to form a radial column, and the linear protrusions 402 (402a, 402b, 402c) are arranged neatly in the radial direction to form a radial column.

[0068] Regarding linear protrusions 401a, 401b, and 401c, if the length of linear protrusion 401a is Lo and the length of linear protrusion 401b is Li, the above-mentioned formula Lo = Li × (D + 2T) / D can be satisfied. Furthermore, if the length of linear protrusion 401c is Lo and the length of linear protrusion 401a is Li, the above-mentioned formula Lo = Li × (D + 2T) / D can be satisfied. Similarly, regarding linear protrusions 402a, 402b, and 402c, if the length of linear protrusion 402a is Lo and the length of linear protrusion 402b is Li, the above-mentioned formula Lo = Li × (D + 2T) / D can be satisfied. Furthermore, if the length of linear protrusion 402c is Lo and the length of linear protrusion 402a is Li, the above-mentioned formula Lo = Li × (D + 2T) / D can be satisfied.

[0069] Figure 2A and Figure 2B It means using 2 Figure 1 A conceptual diagram of a state of a cross section perpendicular to the winding axis when a separator 300 of FIG. 1 is used to form an electrode group. Figure 2A is a cross-sectional view of a section passing through the linear protrusion 401, Figure 2B is a cross-sectional view of a cross section of the linear protrusion 402. Figure 2A and Figure 2B In the figure, for convenience of explanation, the separator 300, the positive electrode 110, and the negative electrode 120 are depicted as concentric circles, but they are actually spiral.

[0070] The spacer layer is set in Figure 1 The separator 300a and the separator 300b are arranged on one side of each of the two separators 300a and 300b. The separator 300a faces one side of the positive electrode 110 via a separator provided on the separator 300a, and the separator 300b faces the other side of the positive electrode 110 via a separator provided on the separator 300b.

[0071] exist Figure 2A In the embodiment, the linear protrusions 401 are arranged in a regular pattern in the radial direction to form two radial rows. The two radial rows are arranged at equal angles in the circle (i.e., at positions 180° apart in the circumferential angle) to form radial rows. Similarly, in Figure 2B In the embodiment, the linear protrusions 402 are arranged neatly in the radial direction to form two radial columns. The two radial columns are arranged at equal angular positions in the circle (i.e., positions offset by 180° from the circumferential angle) to form radial columns. The radial columns formed by the linear protrusions 402 exist between the radial columns formed by the linear protrusions 401 (i.e., positions offset by 90° relative to the linear protrusions 401). Therefore, the electrode group has four radial columns formed by a plurality of protrusions (protrusion groups). However, the present disclosure does not limit the number of radial columns.

[0072] exist Figure 2Aand Figure 2B In the example of Figure 2B , there are two regions in each turn where the linear convex portions 401 or 402 are not interposed in the cross section. In other words, in each turn of the cross section, the space for lithium metal precipitation is divided into two by the linear convex portions 401 or 402. In each turn of the cross section, the proportion of the region where the linear convex portions 401 or 402 are interposed is approximately 50% in all turns and is substantially equal.

[0073] In Figure 2A in, the length of the linear convex portion 401 (401a, 401b, 401c) in the second direction is longer for the convex portions located on the outer ring side. Thus, at least a part (preferably more than 50% of the length of the linear convex portion 401a in the second direction) of the linear convex portion 401c overlaps with the linear convex portion 401a which is in the same column in the radial direction and located on the inner ring side of the same separator in the circumferential direction and covers the linear convex portion 401a. At least a part (preferably more than 50% of the length of the linear convex portion 401b in the second direction) of the linear convex portion 401a overlaps with the linear convex portion 401b which is in the same column in the radial direction and located on the inner ring side of the same separator in the circumferential direction and covers the linear convex portion 401b.

[0074] Similarly, in Figure 2B in, the length of the linear convex portion 402 (402a, 402b, 402c) in the second direction is longer for the convex portions located on the outer ring side. Thus, at least a part (preferably more than 50% of the length of the linear convex portion 402a in the second direction) of the linear convex portion 402c overlaps with the linear convex portion 402a which is in the same column in the radial direction and located on the inner ring side of the same separator in the circumferential direction and covers the linear convex portion 402a. At least a part (preferably more than 50% of the length of the linear convex portion 402b in the second direction) of the linear convex portion 402a overlaps with the linear convex portion 402b which is in the same column in the radial direction and located on the inner ring side of the same separator in the circumferential direction and covers the linear convex portion 402b.

[0075] For each of the linear convex portions 401 (401a, 401b, 401c) and the linear convex portions 402 (402a, 402b, 402c), a straight line in the radial direction passing through the center of the convex portion in the second direction passes through other convex portions in the same column in the radial direction. In Figure 2A and Figure 2B in the example, the straight line in the radial direction passing through the center of the convex portion in the second direction is the same for all convex portions in the same column in the radial direction.

[0076] Figure 3 is a top view schematically showing another example of the configuration of the spacer layer provided on the surface of the separator. In Figure 3In this case, the spacer layer 400 is provided with a plurality of linear protrusions 403 (403a, 403b, 403c) that extend obliquely in a direction that is not orthogonal to the first direction and the second direction D2. The linear protrusions 403 (403a, 403b, 403c) have the same width in the first direction D1, and the width of the protrusions located closer to the outer winding side is longer in the second direction D2, and the widths increase in the order of the protrusions 403c, 403b, 403a. Therefore, the closer to the outer winding side, the more the extending direction of the linear protrusions approaches being inclined parallel to the second direction D2.

[0077] Figure 4 FIG. is a plan view schematically showing another example of the configuration of the spacer layer provided on the surface of the separator, and is an example in which the spacer layer 400 is a hexagonal mesh-like protrusion 404. Defects 405 for facilitating the circulation of the electrolyte can be provided on the mesh-like protrusion 404. The mesh-like protrusion 404 forms a pattern in which the hexagons constituting the mesh are stretched more in the second direction D2 as it approaches the outer winding side.

[0078] Hereinafter, each component of the lithium secondary battery will be described in more detail.

[0079] [Negative electrode]

[0080] The negative electrode includes a negative electrode current collector. In the lithium secondary battery, lithium metal is deposited on the surface of the negative electrode current collector during charging. More specifically, lithium ions contained in the non-aqueous electrolyte receive electrons on the negative electrode current collector during charging to become lithium metal and are deposited on the surface of the negative electrode current collector. The lithium metal deposited on the surface of the negative electrode current collector dissolves in the non-aqueous electrolyte in the form of lithium ions during discharging. In addition, the lithium ions contained in the non-aqueous electrolyte can be derived from a lithium salt added to the non-aqueous electrolyte, can be supplied by the positive electrode active material during charging, or can be both.

[0081] The negative electrode current collector can be any conductive sheet material. As the conductive sheet material, foils, thin films, etc. can be used.

[0082] The surface of the conductive sheet material can be smooth. Thereby, during charging, lithium metal from the positive electrode is likely to be deposited uniformly on the conductive sheet material. Smooth means that the maximum height roughness Rz of the conductive sheet material is 20 μm or less. The maximum height roughness Rz of the conductive sheet material can be 10 μm or less. The maximum height roughness Rz is measured in accordance with JIS B 0601:2013.

[0083] 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 metal 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 either an alloy or an intermetallic compound with lithium is preferred. Such conductive materials may include, for example, copper (Cu), nickel (Ni), iron (Fe), and alloys containing these metal elements, or graphite with a preferentially exposed basal plane. As the alloy, copper alloy, stainless steel (SUS), etc. may be mentioned. Among them, copper and / or copper alloy having high conductivity is preferred.

[0084] 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.

[0085] A negative electrode mixture layer (not shown) may be formed on the surface of the negative electrode current collector. The negative electrode mixture layer is formed, for example, by coating a slurry containing a negative electrode active material such as graphite on at least a part of the surface of the negative electrode current collector. However, from the viewpoint of realizing a lithium secondary battery with a higher capacity than a lithium ion battery, the thickness of the negative electrode mixture layer is set thin enough to allow lithium metal to precipitate in the negative electrode. In this case, the open circuit potential of the negative electrode at full charge with respect to lithium metal (lithium dissolution-precipitation potential) may be 70 mV or less. When the open circuit potential of the negative electrode at full charge with respect to lithium metal is 70 mV or less, lithium metal exists on the surface of the lithium ion storage layer at full charge. That is, the negative electrode exhibits capacity due to the precipitation and dissolution of lithium metal.

[0086] [Positive Electrode]

[0087] 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 contains, for example, a positive electrode active material, a conductive material, and a binder material. The positive electrode mixture layer may be formed only on one side of the positive electrode current collector or on both sides. The positive electrode can be obtained, for example, by coating a positive electrode mixture slurry containing a positive electrode active material, a conductive material, and a binder material on both sides of the positive electrode current collector, drying the coating film, and then calendering.

[0088] The positive electrode active material is a material that stores and releases lithium ions. As the positive electrode active material, for example, lithium-containing transition metal oxides, transition metal fluorides, polyanions, fluorinated polyanions, transition metal sulfides, etc. may be mentioned. Among them, lithium-containing transition metal oxides are preferred from the viewpoints of low manufacturing cost and high average discharge voltage.

[0089] As the transition metal elements contained in the lithium-containing transition metal oxide, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, W, etc. can be cited. The lithium-containing transition metal oxide may contain one transition metal element or may contain two or more. 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 needed. As the typical elements, Mg, Al, Ca, Zn, Ga, Ge, Sn, Sb, Pb, Bi, etc. can be cited. The typical element may be Al, etc.

[0090] In the lithium-containing transition metal oxide, a composite oxide having a layered structure and a rock salt-type crystal structure, which contains Co, Ni, and / or Mn as the transition metal element and sometimes contains Al as an optional component, is preferable for obtaining a high capacity. In this case, in the lithium secondary battery, the molar ratio mLi / mM of the total amount mLi of lithium possessed by the positive electrode and the negative electrode to the amount mM of the metal M other than lithium possessed by the positive electrode is set to 1.1 or less, for example.

[0091] The conductive material is, for example, a carbon material. As the carbon material, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphite, etc. can be cited.

[0092] As the binder material, for example, fluororesin, polyacrylonitrile, polyimide resin, acrylic resin, polyolefin resin, rubber-like polymer, etc. can be cited. As the fluororesin, polytetrafluoroethylene, polyvinylidene fluoride, etc. can be cited.

[0093] The positive electrode current collector only needs to be a conductive sheet. As the conductive sheet, foil, film, etc. can be used. A carbon material can be coated on the surface of the positive electrode current collector.

[0094] As the material of the positive electrode current collector (conductive sheet), for example, metal materials containing Al, Ti, Fe, etc. can be cited. The metal material can be Al, Al alloy, Ti, Ti alloy, Fe alloy, etc. The Fe alloy can be stainless steel (SUS).

[0095] 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.

[0096] [Separator]

[0097] The separator uses a porous sheet having ion permeability and insulation properties. Examples of the porous sheet include microporous films, spunbonded fabrics, non-woven fabrics, etc. The material of the porous sheet is not particularly limited and may be a polymer material. Examples of the polymer material include olefin resins, polyamide resins, cellulose, etc. Examples of the olefin resin include polyethylene, polypropylene, and copolymers of ethylene and propylene. The separator may contain additives as needed. Examples of the additives include inorganic fillers, etc.

[0098] [Non-aqueous electrolyte]

[0099] A non-aqueous electrolyte having lithium ion conductivity contains, for example, a non-aqueous solvent, lithium ions and anions dissolved in the non-aqueous solvent. The non-aqueous electrolyte may be liquid or gel-like.

[0100] The liquid non-aqueous electrolyte is prepared by dissolving a lithium salt in a non-aqueous solvent. By dissolving the lithium salt in the non-aqueous solvent, lithium ions and anions are generated.

[0101] The gel-like non-aqueous electrolyte contains a lithium salt and a matrix polymer, or contains a lithium salt, a non-aqueous solvent and a matrix polymer. As the matrix polymer, for example, a polymer material that gels by absorbing a non-aqueous solvent is used. Examples of the polymer material include fluororesins, acrylic resins, polyether resins, etc.

[0102] As the lithium salt or anion, known substances used in the non-aqueous electrolyte of a lithium secondary battery can be used. Specifically, BF4 - , ClO4 - , PF6 - , CF3SO3 - , CF3CO2 - , anions of imide compounds, anions of oxalate complexes, etc. Examples of the anions of imide compounds 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 more, x and y are each independently 0, 1 or 2, and x + y = 2), etc. The anion of the oxalate complex may contain boron and / or phosphorus. Examples of the anion of the oxalate complex include bis(oxalato)borate anion, BF2(C2O4) - , PF4(C2O4) - , PF2(C2O4)2 - , etc. The non-aqueous electrolyte may contain these anions alone or may contain two or more kinds.

[0103] From the viewpoint of suppressing the dendritic precipitation of lithium metal, it is preferable that the non-aqueous electrolyte contains at least an anion of an oxalate complex. Due to the interaction between the anion of the oxalate complex and lithium, lithium metal is likely to precipitate uniformly in the form of fine particles. Therefore, the local precipitation of lithium metal is easily suppressed. The anion of the oxalate complex can be combined with other anions. The other anion can be PF6 - and / or an anion of imide type.

[0104] As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, or their halogenated derivatives can be cited. The non-aqueous electrolyte can contain these non-aqueous solvents alone or can contain two or more kinds. As the halogenated derivative, fluorides etc. can be cited.

[0105] As the ester, for example, carbonate esters, carboxylate esters etc. can be cited. As the cyclic carbonate ester, ethylene carbonate, propylene carbonate, fluoroethylene carbonate (FEC), etc. can be cited. As the chain carbonate ester, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, etc. can be cited. As the cyclic carboxylate ester, γ-butyrolactone, γ-valerolactone, etc. can be cited. As the chain carboxylate ester, ethyl acetate, methyl propionate, methyl fluoropropionate, etc. can be cited.

[0106] As the ether, cyclic ethers and chain ethers can be cited. As the cyclic ether, 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, etc. can be cited. As the chain ether, 1,2-dimethoxyethane, diethyl ether, ethyl vinyl ether, methyl phenyl ether, benzyl ethyl ether, diphenyl ether, dibenzyl ether, 1,2-diethoxyethane, diglyme, etc. can be cited.

[0107] 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 can be set to 0.5 mol / L or more and 3.5 mol / L or less. In addition, the concentration of the anion of the oxalate complex in the non-aqueous electrolyte can be set to 0.05 mol / L or more and 1 mol / L or less.

[0108] The non-aqueous electrolyte can contain an additive. The additive can be a substance that forms a film on the negative electrode. By forming a film from the additive on the negative electrode, the generation of dendrites is easily suppressed. As such an additive, for example, vinylene carbonate, FEC, ethylene ethyl carbonate (VEC), etc. can be cited.

[0109] Hereinafter, taking a cylindrical battery having a wound electrode group as an example, the structure of the lithium secondary battery of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following structure.

[0110] Figure 5 is a longitudinal sectional view of a lithium secondary battery 10. The lithium secondary battery 10 is a cylindrical battery having a cylindrical battery case, a wound electrode group 14 housed in the battery case, and a non-aqueous electrolyte (not shown). The battery case is composed of a case body 15 which is a bottomed cylindrical metal container and a sealing body 16 which seals the opening of the case body 15. The case body 15 has an annular stepped portion 21 formed by locally stamping the side wall from the outside near the opening. The sealing body 16 is supported by the surface on the opening side of the stepped portion 21. A gasket 27 is disposed between the case body 15 and the sealing body 16, thereby ensuring the airtightness of the battery case. Inside the case body 15, insulating plates 17 and 18 are respectively disposed at both end portions in the winding axis direction of the electrode group 14.

[0111] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a lid 26. The lid 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 central portions, and an insulating member 24 is interposed between their peripheral portions. The filter 22 and the lower valve body 23 are connected to each other at their peripheral portions. The upper valve body 25 and the lid 26 are connected to each other at their peripheral portions. A vent hole is formed in the lower valve body 23. When the internal pressure of the battery case rises due to abnormal heat generation or the like, the upper valve body 25 expands toward the lid 26 side and separates from the lower valve body 23. As a result, the electrical connection between the lower valve body 23 and the upper valve body 25 is cut off. When the internal pressure further rises, the upper valve body 25 ruptures, and gas is discharged from the opening formed in the lid 26.

[0112] 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 wound in a spiral shape with their width directions parallel to the winding axis.

[0113] The positive electrode 110 is electrically connected to the lid 26 which also serves as a positive terminal via a positive electrode lead 19. One end of the positive electrode lead 19 is connected, for example, near the center in the length direction of the positive electrode 110. The other end of the positive electrode lead 19 extending from the positive electrode 110 passes through a through hole formed in the insulating plate 17 and is welded to the inner side surface of the filter 22.

[0114] The negative electrode 120 is electrically connected to the case body 15 which also serves as a negative terminal via a negative electrode lead 20. One end of the negative electrode lead 20 is connected, for example, to the end portion in the length direction of the negative electrode 120, and the other end is welded to the inner bottom surface of the case body 15.

[0115] Figure 6 schematically shows Figure 5An enlarged view of the discharge state of the region X surrounded by the dashed line in []. In the illustrated example, the cross-sectional shape of the spacer is trapezoidal. However, the embodiments of the present disclosure are not limited thereto. In the illustrated example, the spacer layer is provided between the positive electrode and the separator. However, the embodiments of the present disclosure are not limited thereto, and the spacer layer may be provided between the negative electrode and the separator, or between the positive electrode and the negative electrode and the separator.

[0116] The positive electrode 110 includes a positive electrode current collector 111 and a positive electrode mixture layer 112. A spacer layer 400 is provided between the positive electrode mixture layer 112 and the separator 300. The spacer layer 400 is composed of linear protrusions 401 provided along the second direction D2 (length direction) of the separator 300. In the discharge state (a), no lithium metal is deposited on the surface of the negative electrode current collector 121, and a space is maintained between the positive electrode 110 and the separator 300. On the other hand, in the charged state, lithium metal is deposited on the surface of the negative electrode current collector 121 and is received in the space between the positive electrode 110 and the separator 300 while being pressed by the separator 300. That is, the negative electrode 120 includes the negative electrode current collector 121 in the discharge state, and the negative electrode current collector 121 and the lithium metal deposited on its surface in the charged state.

[0117] Since the lithium metal is received in the space between the positive electrode 110 and the separator 300, the apparent volume change of the electrode group associated with the deposition of lithium metal in the charge-discharge cycle is reduced. Accordingly, the stress applied to the negative electrode current collector 121 is also suppressed. In addition, since pressure is applied to the lithium metal received between the positive electrode 110 and the separator 300 from the separator 300, the deposition state of the lithium metal is controlled, the lithium metal is not easily isolated, and a decrease in charge-discharge efficiency is suppressed.

[0118] In the illustrated example, a cylindrical lithium secondary battery having a wound electrode group has been described. However, the shape of the lithium secondary battery and the like are not limited thereto, and depending on its use and the like, in addition to the cylindrical shape, it may be appropriately selected from various shapes such as coin type, square type, thin film type, and flat type. The form of the electrode group is not particularly limited and may be a stacked type. In addition, regarding the configuration other than the electrode group and the non-aqueous electrolyte of the lithium secondary battery, a known configuration may be used without particular limitation.

[0119] (Supplementary Note)

[0120] Based on the description of the above embodiments, the following technical solutions are disclosed.

[0121] (Technical Solution 1)

[0122] A lithium secondary battery, comprising a positive electrode, a negative electrode opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte,

[0123] The positive electrode and the negative electrode are wound with the separator therebetween to form an electrode group having a plurality of turns.

[0124] The positive electrode, the negative electrode, and the separator are in strip shape and have a length L1 in a first direction D1 parallel to the winding axis and a length L2 in a second direction D2 perpendicular to the first direction (L1 < L2).

[0125] In the negative electrode, lithium metal is deposited during charging and dissolved during discharging.

[0126] At least one component selected from the positive electrode, the negative electrode, and the separator has a spacer layer.

[0127] The spacer layer is composed of a plurality of convex portions in a manner discontinuous in both the first direction and the second direction.

[0128] When observing the electrode group in the direction of the winding axis, the plurality of convex portions are divided into a plurality of groups, and the convex portions included in each group are arranged radially to form a plurality of radially arranged columns.

[0129] (Technical solution 2)

[0130] In the lithium secondary battery according to Technical solution 1, the width of any of the convex portions in the second direction is less than or equal to the width of the convex portion disposed on the more outer circumferential side in the second direction.

[0131] (Technical solution 3)

[0132] In the lithium secondary battery according to Technical solution 2, the width of the convex portion in the second direction gradually increases from the inner circumferential side to the outer circumferential side.

[0133] (Technical solution 4)

[0134] In the lithium secondary battery according to Technical solution 3, when the diameter of any of the turns is set as D and the total thickness of the positive electrode, the negative electrode, the separator, and the spacer layer is set as T, the length Li of the convex portion of this turn in the second direction and the length Lo of the convex portion of the turn adjacent to this turn and disposed on the more outer circumferential side in the second direction satisfy Lo = Li×(D + 2T) / D.

[0135] (Technical solution 5)

[0136] In the lithium secondary battery according to any one of Technical solutions 1 to 4, when observing the electrode group in the direction of the winding axis, the convex portions of the adjacent turns included in the same group overlap each other in the second direction by 50% or more in length.

[0137] (Technical solution 6)

[0138] In the lithium secondary battery according to Technical Solution 5, when observing the electrode assembly from the direction of the winding shaft, a radial straight line passing through the center in the second direction of a specific convex portion passes through all the convex portions included in the same assembly.

[0139] (Technical Solution 7)

[0140] In the lithium secondary battery according to any one of Technical Solutions 1 to 6, in any cross-section of the electrode assembly that is perpendicular to the winding shaft and crosses the convex portion, the proportion of the presence of the crossed convex portion is substantially equal in all the turns.

[0141] (Technical Solution 8)

[0142] In the lithium secondary battery according to any one of Technical Solutions 1 to 7, when a hypothetical line parallel to the first direction is drawn at any position of the component, the hypothetical line crosses the spacer layer at two or more positions.

[0143] (Technical Solution 9)

[0144] In the lithium secondary battery according to any one of Technical Solutions 1 to 8, in any cross-section of the electrode assembly that is perpendicular to the winding shaft and crosses the convex portion, there are regions where the convex portion does not exist at two or more positions.

[0145] (Technical Solution 10)

[0146] In the lithium secondary battery according to any one of Technical Solutions 1 to 9, when a hypothetical line is drawn along the second direction from a point on any convex portion, the length Ly of crossing the convex portion and the length Ln of not crossing the convex portion satisfy 0.1 ≤ Ln / (Ly + Ln) ≤ 0.75.

[0147] (Technical Solution 11)

[0148] In the lithium secondary battery according to any one of Technical Solutions 1 to 10, the plurality of convex portions are all linear convex portions parallel to the second direction.

[0149] (Technical Solution 12)

[0150] In the lithium secondary battery according to any one of Technical Solutions 1 to 11, the plurality of convex portions are arranged in a staggered manner.

[0151] (Technical Solution 13)

[0152] A separator is in a long strip shape and has a length L1 in a first direction D1 and a length L2 in a second direction D2 perpendicular to the first direction (L1 < L2),

[0153] The separator has a base material layer and a spacer layer,

[0154] The spacer layer is composed of a plurality of convex portions in a discontinuous manner in both the first direction and the second direction.

[0155] When a positive electrode and a negative electrode are wound with the separator interposed therebetween to form an electrode group having a plurality of turns and a winding axis parallel to the first direction,

[0156] When the electrode group is viewed from the direction of the winding axis, the plurality of convex portions are divided into a plurality of groups, and the convex portions included in each group are arranged in the radial direction to form a plurality of radially arranged columns.

[0157] [Embodiment]

[0158] Hereinafter, the lithium secondary battery of the present disclosure will be specifically described based on embodiments and comparative examples. The present disclosure is not limited to the following embodiments.

[0159] <<Embodiment 1>>

[0160] (1) Fabrication of positive electrode

[0161] A lithium-containing transition metal oxide (NCA; positive electrode active material) having a layered rock salt structure containing Li, Ni, Co, and Al (the molar ratio of Li to the total of Ni, Co, and Al is 1.0), acetylene black (AB; conductive material), and polyvinylidene fluoride (PVdF; binder material) were mixed at 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 paste. Then, the obtained positive electrode mixture paste was coated on both sides of an Al foil (positive electrode current collector) and dried, and the coating film of the positive electrode mixture was calendered using a roller. Finally, the obtained laminate of the positive electrode current collector and the positive electrode mixture was cut into a predetermined electrode size to fabricate a positive electrode having positive electrode mixture layers on both sides of the positive electrode current collector.

[0162] (2) Formation of spacer

[0163] A polyethylene separator (microporous membrane) was prepared. Polyimide ink was coated on a predetermined area of the separator surface and then dried by hot air to provide a spacer layer formed of polyimide resin (Young's modulus: 2 GPa). The polyimide ink was coated using a dispenser. The spacer layer was formed in a pattern similar to Figure 1 a pattern in which linear convex portions were intermittently formed along six straight lines parallel to the second direction D2. The intervals between the six straight lines parallel to the second direction D2 in the first direction D1 were 5 mm. The width of the convex portion (width in the direction perpendicular to the extending direction of the convex portion) was 1 mm. The height h of the convex portion was 50 μm.

[0164] The length of the linear convex portion (the extension length in the extension direction of the convex portion) and the arrangement interval (center distance) in the second direction satisfy the above relational expression Lo = Li×(D + 2T) / D. The linear convex portions of the circles located on the outermost side have larger lengths and arrangement intervals.

[0165] The length of the linear convex portion (the extension length in the extension direction of the convex portion) is set to 1 / 4 of the circumference of the circle where the linear convex portion is located, and two linear convex portions are arranged on the same circle. In addition, when a hypothetical line is drawn along the second direction D2 from a point on an arbitrary linear convex portion, and the length of the line crossing the convex portion is set to Ly and the length of the line not crossing the convex portion is set to Ln, then Ln / (Ly + Ln) = 0.5.

[0166] (3) Fabrication of the negative electrode

[0167] A rectangular electrolytic copper foil (thickness 12 μm) is prepared as the negative electrode current collector.

[0168] (4) Preparation of the non-aqueous electrolyte

[0169] Ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at a volume ratio of EC:DMC = 30:70. In the resulting mixed solvent, LiPF6 is dissolved at a concentration of 1 mol / L and LiBF2(C2O4) is dissolved at a concentration of 0.1 mol / L to prepare a liquid non-aqueous electrolyte.

[0170] (5) Assembly of the battery

[0171] In an inert gas atmosphere, the positive electrode and the negative electrode current collector are wound spirally with the above-mentioned separator in between to fabricate an electrode assembly. Since all the lithium contained in the electrode assembly comes from the positive electrode, the molar ratio mLi / mM of the total amount of lithium mLi in the positive electrode and the negative electrode to the amount mM of the metal M (here Ni, Co, and Al) in the positive electrode is 1.0.

[0172] The electrode assembly is housed in a bag-shaped exterior body formed of a laminated sheet having an Al layer. After injecting the above-mentioned non-aqueous electrolyte, the exterior body is sealed to complete the lithium secondary battery A1.

[0173] 《Example 2》

[0174] In the formation of the spacer in the above-mentioned (2), in the same manner as in Example 1, the arrangement pattern of the spacer layer is formed as a pattern in which linear convex portions are intermittently formed along six straight lines parallel to the second direction D2. The intervals between the six straight lines parallel to the second direction D2 in the first direction D1 are 5 mm.

[0175] In such a manner that the length of the linear convex portion (the extension length in the convex portion extension direction) and the arrangement interval (center pitch) in the second direction satisfy the above relational expression Lo = Li×(D + 2T) / D, the length and the arrangement interval of the linear convex portions of the more outer ring are larger.

[0176] The length of the linear convex portion (the extension length in the convex portion extension direction) is set to 1 / 8 of the circumference of the ring where the linear convex portion is located, and two linear convex portions are arranged on the same ring. The linear convex portions are convex portions arranged along four adjacent straight lines parallel to the second direction D2, and are arranged so that the linear convex portions do not overlap in the first direction. Further, when a virtual line is drawn along the second direction D2 from a point on an arbitrary linear convex portion, and the length of crossing the convex portion is set to Ly and the length of not crossing the convex portion is set to Ln, then Ln / (Ly + Ln) = 0.75.

[0177] In other respects, it is the same as in Example 1, and the lithium secondary battery A2 is completed.

[0178] <<Example 3>>

[0179] In the formation of the spacer in the above (2), in the same manner as in Example 1, the arrangement pattern of the spacer layer is a pattern in which linear convex portions are intermittently formed along six straight lines parallel to the second direction D2, and the length of the linear convex portion (the extension length in the convex portion extension direction) is changed based on Example 1.

[0180] The length of the linear convex portion (the extension length in the convex portion extension direction) is set to 1 / 10 of the circumference of the ring where the linear convex portion is located, and nine linear convex portions are arranged on the same ring. Further, when a virtual line is drawn along the second direction D2 from a point on an arbitrary linear convex portion, and the length of crossing the convex portion is set to Ly and the length of not crossing the convex portion is set to Ln, then Ln / (Ly + Ln) = 0.1.

[0181] In other respects, it is the same as in Example 1, and the lithium secondary battery A3 is completed.

[0182] <<Comparative Example 1>>

[0183] In the formation of the spacer in the above (2), the arrangement pattern of the spacer layer is a pattern in which linear convex portions are continuously formed along six straight lines parallel to the second direction D2 at the central portion and both end portions in the first direction of the separator. Thus, when a virtual line is drawn along the second direction D2 from a point on an arbitrary linear convex portion, and the length of crossing the convex portion is set to Ly and the length of not crossing the convex portion is set to Ln, since Ln = 0, then Ln / (Ly + Ln) = 0.

[0184] Except for this, it is the same as in Example 1, and the lithium secondary battery B1 is completed.

[0185] <<Comparative Example 2>>

[0186] In the formation of the spacer in the above (2), similar to Example 1, the arrangement pattern of the spacer layer is a pattern in which linear protrusions are intermittently formed along six straight lines parallel to the second direction D2. On the other hand, the length of the linear protrusion (the extension length in the protrusion extension direction) and the arrangement interval (center pitch) in the second direction are constant regardless of the circle in which the linear protrusion is located.

[0187] The length of the linear protrusion (the extension length in the protrusion extension direction) is set to 10 mm regardless of the circumference of the circle in which the linear protrusion is located, and the arrangement interval (center pitch) of the linear protrusion in the second direction is the same as the length of the linear protrusion. In addition, when a hypothetical line is drawn along the second direction D2 from a point on an arbitrary linear protrusion, and the length of the part that crosses the protrusion is set to Ly and the length of the part that does not cross the protrusion is set to Ln, then Ln / (Ly + Ln) = 0.5.

[0188] The other steps are the same as in Example 1, and the lithium secondary battery B2 is completed.

[0189] [Evaluation 1]

[0190] Charge-discharge tests were performed on each of the obtained batteries. In the charge-discharge test, in a thermostat at 25°C, after charging the battery under the following conditions, it was stopped for 20 minutes, and then discharged under the following conditions.

[0191] Constant current charging was performed at a current of 10 mA per unit area (square centimeter) of the electrode until the battery voltage reached 4.3 V, and then constant voltage charging was performed at a voltage of 4.3 V until the current value per unit area of the electrode reached 1 mA.

[0192] (Discharge)

[0193] Constant current discharge was performed at a current of 10 mA per unit area of the electrode until the battery voltage reached 3.0 V.

[0194] The above charging and discharging were regarded as one cycle, and the charge-discharge cycle was repeated. The ratio (%) of the discharge capacity in the 50th cycle to the discharge capacity in the first cycle was obtained as the capacity retention rate.

[0195] In addition, the number of cycles at which the cycle stopped was obtained, and it was speculated that the cycle stop was caused by cracking of the negative electrode current collector accompanying the swelling of the negative electrode. The evaluation results are shown in Table 1.

[0196] Table 1

[0197]

[0198] Among batteries A1 to A3, the number of cycles until cycle stop occurs is more than that of batteries B1 and B2, and the capacity retention rate is also higher than that of batteries B1 and B2. On the other hand, although the number of cycles of battery B1 until cycle stop occurs is large, the capacity retention rate is low. Although battery B2 can obtain a capacity retention rate equivalent to that of batteries A1 to A3, the number of cycles until cycle stop occurs is small.

[0199] Industrial applicability

[0200] The lithium secondary battery of the present disclosure can be used for electronic devices such as mobile phones, smartphones, and tablet terminals, electric vehicles including hybrid and plug-in hybrid vehicles, and home storage batteries combined with solar cells.

[0201] The present invention has been described in connection with presently preferred embodiments, but such disclosure should not be construed as restrictive. By reading the above disclosure, those of ordinary skill in the technical field to which the present invention pertains can know various changes and modifications. Therefore, the appended claims should be construed to include all changes and modifications without departing from the gist and scope of the present invention.

[0202] Explanation of reference numerals

[0203] 10 Lithium secondary battery

[0204] 14 Electrode group

[0205] 15 Housing main body

[0206] 16 Sealing body

[0207] 17, 18 Insulating plates

[0208] 19 Positive electrode lead

[0209] 20 Negative electrode lead

[0210] 21 Step portion

[0211] 22 Filter

[0212] 23 Lower valve body

[0213] 24 Insulating member

[0214] 25 Upper valve body

[0215] 26 Cover

[0216] 27 Gasket

[0217] 100 Electrode

[0218] 110 Positive electrode

[0219] 111 Positive electrode current collector

[0220] 112 Positive electrode mixture layer

[0221] 120 Negative electrode

[0222] 121 Negative electrode current collector

[0223] 300 Separator

[0224] 400 Spacer layer

[0225] 401, 401a, 401b, 401c, 402, 402a, 402b, 402c, 403, 403a, 403b, 403c Linear protrusions

[0226] 404 Mesh-like protrusion

[0227] 405 Defect part

Claims

1. A lithium secondary battery includes a positive electrode, a negative electrode opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode are wound with the separator therebetween to form an electrode group having a plurality of turns. The positive electrode, the negative electrode, and the separator are in a strip shape, having a length L1 in a first direction D1 parallel to the winding axis and a length L2 in a second direction D2 perpendicular to the first direction, and L1 < L2. In the negative electrode, lithium metal is deposited during charging and dissolved during discharging. At least one component selected from the positive electrode, the negative electrode, and the separator has a spacer layer. The spacer layer is composed of a plurality of convex portions in a manner discontinuous in both the first direction and the second direction. When the electrode group is viewed from the direction of the winding axis, the plurality of convex portions are divided into a plurality of groups, and the convex portions included in each group are arranged radially to form a plurality of radially arranged columns.

2. The lithium secondary battery according to claim 1. The width of any of the convex portions in the second direction is equal to or less than the width of the convex portion disposed on the outer ring side in the second direction.

3. The lithium secondary battery according to claim 2. The width of the convex portion in the second direction gradually increases from the inner ring side to the outer ring side.

4. The lithium secondary battery according to claim 3. When the diameter of any of the turns is set to D and the total thickness of the positive electrode, the negative electrode, the separator, and the spacer layer is set to T, the length Li of the convex portion of the turn in the second direction and the length Lo of the convex portion of the turn adjacent to the outer ring side of the turn in the second direction satisfy Lo = Li × (D + 2T) / D.

5. The lithium secondary battery according to any one of claims 1 to 4. When the electrode group is viewed from the direction of the winding axis, the convex portions of the adjacent turns included in the same group overlap each other in the second direction by 50% or more in length.

6. The lithium secondary battery according to claim 5. When the electrode group is viewed from the direction of the winding axis, a radial straight line passing through the center of a specific convex portion in the second direction passes through all the convex portions included in the same group.

7. The lithium secondary battery according to any one of claims 1 to 4. In any cross section of the electrode group perpendicular to the winding axis and passing through the convex portion, the proportion of the presence of the convex portion passing through is substantially equal in all the turns.

8. The lithium secondary battery according to any one of claims 1 to 4. When an imaginary line parallel to the first direction is drawn at any position of the component, the imaginary line passes through the spacer layer at two or more positions.

9. The lithium secondary battery according to any one of claims 1 to 4. In any cross section of the electrode group perpendicular to the winding axis and passing through the convex portion, there are two or more regions where the convex portion does not exist.

10. The lithium secondary battery according to any one of claims 1 to 4. When a hypothetical line is drawn along the second direction from a point on any of the convex portions, the length Ly that crosses the convex portion and the length Ln that does not cross the convex portion satisfy 0.1 ≤ Ln / (Ly + Ln) ≤ 0.

75.

11. The lithium secondary battery according to any one of claims 1 to 4, The plurality of convex portions are all linear convex portions parallel to the second direction.

12. The lithium secondary battery according to any one of claims 1 to 4, The plurality of convex portions are arranged in a staggered manner.

13. A separator, which is in a long strip shape, has a length L1 in a first direction D1 and a length L2 in a second direction D2 perpendicular to the first direction, and L1 < L2, The separator has a base material layer and a spacer layer, The spacer layer is composed of a plurality of convex portions in a discontinuous manner in both the first direction and the second direction, When a positive electrode and a negative electrode are wound with the separator interposed therebetween to form an electrode group having a plurality of turns and a winding axis parallel to the first direction, When the electrode group is observed from the direction of the winding axis, the plurality of convex portions are divided into a plurality of groups, and the convex portions included in each group are arranged radially to form a plurality of radially arranged columns.

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