Lithium secondary battery

Abstract

Provided is a lithium secondary battery comprising: a laminate in which positive electrodes and negative electrodes are stacked in a stacking direction with separators interposed between them, one of the positive electrode and the negative electrode including a first current collector formed by sandwiching a resin layer between a pair of conductive layers, the first current collector having a first end extending in a first direction different from the stacking direction; a first electrode tab electrically connected to the first end, the first electrode tab including a first bonding mark formed by bonding with the first end and a first insulating portion that is arranged spaced apart in the first direction from the first bonding mark and is covered with an insulating material; and a sealed container having a sealing portion, the sealed container configured to enclose the laminate inside the sealing portion while sandwiching the first insulating portion of the first electrode tab at the sealing portion to allow a portion of the first electrode tab to be taken out of the sealed container.

Description

[Technical field]

[0001] Exemplary embodiments of the present disclosure relate to lithium secondary batteries. [Background technology]

[0002] Patent Document 1 discloses that the safety of a battery cell is improved by using a current collector in which metal layers are formed on both sides of a resin film. The front and back of the resin film are separated by an insulating resin layer, and electrical conduction is not possible. Therefore, when connecting an electrode tab for drawing wiring to the electrode film, conduction is not possible between the front and back of the electrode, and also between multiple electrodes and the electrode tab. In this regard, Patent Document 2 discloses that the current collector is folded multiple times and laminated on each metal layer in order to connect each metal layer separated by a resin layer to an electrode tab for drawing wiring. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-102711 [Patent Document 2] JP 2013-016321 A Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a technique for suppressing deterioration in output characteristics and productivity of lithium secondary batteries. [Means for solving the problem]

[0005] In one exemplary embodiment of the present disclosure, there is provided a lithium secondary battery comprising: a laminate in which positive electrodes and negative electrodes are stacked in a stacking direction with separators interposed therebetween, one of the positive electrode and the negative electrode including a first current collector formed by sandwiching a resin layer between a pair of conductive layers, the first current collector having a first end portion extending in a first direction different from the stacking direction; a first electrode tab electrically connected to the first end portion, the first electrode tab including a first bonding mark formed by bonding with the first end portion and a first insulating portion that is arranged spaced apart in the first direction from the first bonding mark and is covered with an insulating material; and a sealed container having a sealing portion, the sealed container being configured to enclose the laminate inside the sealing portion while sandwiching the first insulating portion of the first electrode tab at the sealing portion to allow a portion of the first electrode tab to be taken out of the sealed container. Effect of the Invention

[0006] According to one exemplary embodiment of the present disclosure, a technique for suppressing deterioration in output characteristics and productivity of a lithium secondary battery can be provided. [Brief description of the drawings]

[0007] [Figure 1] FIG. 2 is a plan view for explaining a configuration example of a secondary battery 1. [Diagram 2] 2 is an exploded perspective view for explaining a configuration example of a laminate ST. FIG. [Diagram 3] FIG. 2 is a perspective view showing an example of a negative electrode 10. [Figure 4] FIG. 2 is a perspective view showing an example of a positive electrode 30. [Diagram 5] 13 is a diagram for explaining the bonding state of a negative electrode tab 40, a negative electrode end P, and a metal sheet M1. FIG. [Figure 6] 13 is a diagram showing a cross section of a first bonding mark W1. FIG. [Figure 7] 1 is a flow chart showing an example of the present manufacturing method. [Figure 8A] FIG. 11 is a diagram for explaining step ST1. [Figure 8B] FIG. 11 is a diagram for explaining step ST1. [Figure 9A]FIG. 11 is a diagram for explaining step ST2. [Figure 9B] FIG. 11 is a diagram for explaining step ST2. [Figure 9C] FIG. 11 is a diagram for explaining step ST2. [Figure 9D] FIG. 11 is a diagram for explaining step ST2. [Figure 10] FIG. 11 is a diagram for explaining step ST3. [Figure 11A] FIG. 2 is a perspective view showing another example of the negative electrode 10. [Figure 11B] FIG. 2 is a perspective view showing another example of the negative electrode 10. [Figure 11C] FIG. 2 is a perspective view showing another example of the negative electrode 10. [Figure 12] FIG. 2 is a perspective view showing another example of the positive electrode 30. [Figure 13] 10 is a perspective view illustrating another example of lamination of the negative electrode 10. FIG. [Figure 14] 10 is a perspective view illustrating another example of lamination of the negative electrode 10. FIG. [Figure 15] FIG. 1 shows the results of Experiment 1. [Figure 16A] This is an example of a case in which metal material protruded in Experiment 1. [Figure 16B] This is an example of a case in which there was no protrusion of metal material in Experiment 1. [Figure 17] FIG. 13 shows the results of Experiment 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Each embodiment of the present disclosure will be described below.

[0009] In one exemplary embodiment, a lithium secondary battery is provided, comprising: a laminate in which positive electrodes and negative electrodes are stacked in a stacking direction with separators interposed therebetween, one of the positive electrode and the negative electrode including a first current collector formed by sandwiching a resin layer between a pair of conductive layers, the first current collector having a first end extending in a first direction different from the stacking direction; a first electrode tab electrically connected to the first end, the first electrode tab including a first bonding mark formed by bonding with the first end and a first insulating portion that is arranged spaced apart in the first direction from the first bonding mark and is covered with an insulating material; and a sealed container having a sealing portion, the sealed container being configured to enclose the laminate inside the sealing portion while sandwiching the first insulating portion of the first electrode tab at the sealing portion to allow a portion of the first electrode tab to be taken out of the sealed container.

[0010] In one exemplary embodiment, the first bonding mark at the first end portion is provided 2 mm or more inward from the outer edge of the first end portion in the first direction.

[0011] In one exemplary embodiment, the first bonding mark at the first end portion is provided 2.5 mm or more inward from the outer edge of the first end portion in the first direction.

[0012] In one exemplary embodiment, when the total number of first current collectors included in the laminate is X and the distance between the first bonding mark at the first end portion and the outer edge of the first end portion in the first direction is Y, the relationship Y>0.048X+1.3 holds.

[0013] In one exemplary embodiment, X is 10 or greater.

[0014] In one exemplary embodiment, the first bond mark is a weld mark.

[0015] In one exemplary embodiment, the first bonding mark includes a region where a pair of conductive layers are integrated together in a cross section in the stacking direction.

[0016] In one exemplary embodiment, the first end and the first electrode tab are joined to each other via a metal sheet.

[0017] In one exemplary embodiment, the first bond mark is a weld mark.

[0018] In one exemplary embodiment, the first bonding mark includes a region where a pair of conductive layers and the metal sheet are integrated in a cross section in the stacking direction.

[0019] In one exemplary embodiment, the first end portion has a preliminary joining mark formed by joining to a metal sheet, and the preliminary joining mark is provided at a position different from the first joining mark when viewed from the stacking direction.

[0020] In one exemplary embodiment, the first current collector is a negative electrode current collector of a negative electrode, and the first electrode tab is a negative electrode tab connected to the negative electrode current collector.

[0021] In one exemplary embodiment, the sealed container is constructed from an aluminum laminate film.

[0022] In one exemplary embodiment, the other of the positive electrode and the negative electrode includes a second current collector having a resin layer sandwiched between a pair of conductive layers, and the second current collector has a second end extending in a second direction different from the stacking direction.

[0023] In one exemplary embodiment, the device further includes a second electrode tab electrically connected to a second end of the second current collector, the second electrode tab including a second bonding mark formed by bonding with the second end and a second insulating portion arranged away from the second bonding mark in a second direction and covered with an insulating material, and the sealed container is configured to sandwich the second insulating portion of the second electrode tab in the seal portion to extend a portion of the second electrode tab to the outside of the sealed container.

[0024] In one exemplary embodiment, the first direction and the second direction are the same direction.

[0025] In one exemplary embodiment, the first direction and the second direction are different directions.

[0026] Hereinafter, each embodiment of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or similar elements are given the same reference numerals, and duplicated explanations will be omitted. Unless otherwise specified, the positional relationship such as up, down, left, right, etc. will be described based on the positional relationship shown in the drawing. The dimensional ratio of the drawings does not indicate the actual ratio, and the actual ratio is not limited to the illustrated ratio.

[0027] As described above, Patent Document 2 proposes folding the current collector multiple times and stacking it on each metal layer in order to connect each metal layer separated by a resin layer to an electrode tab for drawing out wiring. However, this method requires a new device mechanism for stacking the current collector while folding back the end of the current collector for each metal layer. In addition, it is necessary to fold back the end of the current collector while linking with the stacking, which significantly reduces productivity. In addition, in this method, even if the electrode tab can be mechanically joined to the current collector and each metal layer, the resistance of the joint increases and the output characteristics decrease. In a lithium secondary battery 1 (hereinafter also referred to as "secondary battery 1") according to one embodiment, such problems can be solved.

[0028] <Secondary battery configuration example> Fig. 1 is a plan view for explaining a configuration example of a secondary battery 1. As shown in Fig. 1, the secondary battery 1 includes a sealed container 100, a laminate ST, a negative electrode tab 40, and a positive electrode tab 42. The laminate ST is formed by laminating a plurality of positive electrodes and negative electrodes in a lamination direction (z direction in Fig. 1) with separators interposed therebetween.

[0029] The sealed container 100 includes a sealing portion 102 and a receiving portion 104. The sealing portion 102 is provided along the entire outer periphery of the sealed container 100 and isolates the receiving portion 104 from the outside of the sealed container 100.

[0030] The sealed container 100 is configured to sandwich the insulating portion 40B of the negative electrode tab 40 in the seal portion 102 while the other end portion 40C of the negative electrode tab 40 is taken out to the outside of the sealed container 100. Similarly, the sealed container 100 is configured to sandwich the insulating portion 42B of the positive electrode tab 42 in the seal portion 102 while the other end portion 42C of the positive electrode tab 42 is taken out to the outside of the sealed container 100.

[0031] The storage section 104 of the sealed container 100 provides a sealed space for storing the laminate ST. In one embodiment, the sealed container 100 may be formed by overlapping a pair of sheet members with each other and bonding them around the periphery. The sheet members may be formed of multiple layers, and may be, for example, an aluminum laminate film.

[0032] The negative electrode tab 40 is electrically connected to a negative electrode end P of each negative electrode of the laminate ST. In one embodiment, the negative electrode tab 40 is a strip extending in a first direction (x direction in FIG. 1) different from the stacking direction of the laminate ST.

[0033] The negative electrode tab 40 may have one end 40A, an insulating portion 40B, and the other end 40C along the first direction. The one end 40A is joined to the negative electrode end P of each negative electrode of the stack ST, and a first bonding mark W1 is formed by this joining. The first bonding mark W1 may be one or a plurality of points (spots), or may be a continuous line or surface.

[0034] The insulating portion 40B is covered with an insulating material IL such as a sealant film. The insulating portion 40B is provided at a predetermined distance or more in the first direction from the first joining mark W1. The other end portion 40C extends in the first direction from the insulating portion 40B and is disposed outside the sealed container 100. The other end portion 40C may be connected to an external circuit.

[0035] In one embodiment, the negative electrode tab 40 may be made of at least one selected from the group consisting of Cu, Ni, Ti, Fe, and other metals that do not react with Li, and alloys thereof, and stainless steel (SUS).

[0036] The positive electrode tab 42 is electrically connected to a positive electrode end Q of each positive electrode of the laminate ST. In one embodiment, the positive electrode tab 42 is a strip extending in a second direction different from the stacking direction of the laminate ST (in the example shown in FIG. 1, this is the x direction which is the same as the first direction, but is not limited thereto, and may be a direction different from the first direction, for example, a direction opposite to the first direction). The positive electrode tab 42 may have one end 42A, an insulating portion 42B, and another end 42C along the second direction.

[0037] The one end 42A is joined to the positive electrode end Q of each positive electrode of the laminate ST, and a second bonding mark W2 is formed by this joining. The second bonding mark W2 may be one or a plurality of points (spots), or may be a continuous line or surface.

[0038] The insulating portion 42B is covered with an insulating material IL such as a sealant film. The insulating portion 42B is provided at a distance equal to or greater than a predetermined distance in the second direction from the second bonding mark W2. The other end portion 42C extends in the first direction from the insulating portion 42B and is disposed outside the sealed container 100. The other end portion 42C may be connected to an external circuit.

[0039] In one embodiment, the positive electrode tab 42 may be made of at least one material selected from the group consisting of aluminum, titanium, stainless steel, nickel, and alloys thereof.

[0040] The laminate ST is placed in a sealed space of the storage section 104. In one embodiment, the laminate ST may be placed in the sealed container 100 together with an electrolytic solution. The electrolytic solution is a liquid containing a solvent and an electrolyte, and acts as a conductive path for lithium ions. The electrolytic solution may be impregnated into the separator of the laminate ST, or may be held by a polymer to form a polymer electrolyte or a gel electrolyte.

[0041] Hereinafter, a configuration example of the laminate ST will be described in detail with reference to Figs. 2 to 6. Fig. 2 is an exploded perspective view for explaining a configuration example of the laminate ST. As shown in Fig. 2, the laminate ST is configured by stacking a plurality of negative electrodes 10 and positive electrodes 30 alternately in the stacking direction (z direction in Fig. 2) with separators 20 interposed therebetween. As shown in Fig. 2, each of the plurality of negative electrodes 10 may be configured from a single flat sheet. Also, each of the plurality of positive electrodes 30 may be configured from a single flat sheet. Note that the plurality of negative electrodes 10 and / or the plurality of positive electrodes 30 may be configured as a whole by folding or rolling a single flat sheet (an example of such an embodiment will be described later with reference to Figs. 13 and 14).

[0042] In one embodiment, the number of stacked positive electrodes and negative electrodes in the laminate ST may be 5 or more, 10 or more, or 20 or more. In one embodiment, the number of stacked positive electrodes and negative electrodes in the laminate ST may be 50 or less, 40 or less, or 30 or less. The number of stacked positive electrodes and negative electrodes in the laminate ST may be appropriately set according to the energy density and rated capacity of the secondary battery 1. Here, the energy density of the secondary battery 1 may be, for example, 300 Wh / kg or more. The rated capacity of the secondary battery 1 may be, for example, 1.5 Ah or more, or 5 Ah or more.

[0043] As shown in FIG. 2, the negative electrode tab 40 is arranged to be aligned with the negative electrode end P of each negative electrode 10 in the stacking direction. For example, the negative electrode tab 40 may be arranged above or below the negative electrode end P in the stacking direction. Also, for example, the negative electrode tab 40 may be arranged between a certain negative electrode end P and an adjacent negative electrode end P. Similarly, the positive electrode tab 42 is arranged to be aligned with the positive electrode end Q of each positive electrode 30 in the stacking direction. For example, the positive electrode tab 42 may be arranged above or below the positive electrode end Q in the stacking direction. Also, for example, the positive electrode tab 42 may be arranged between a certain positive electrode end Q and an adjacent positive electrode end Q.

[0044] As shown in FIG. 2, the separator 20 is disposed between the negative electrode 10 and the positive electrode 30 in the stacking direction. The separator 20 physically and / or electrically isolates the negative electrode 10 and the positive electrode 30, and ensures ion conductivity of lithium ions. In one embodiment, the separator 20 may be at least one selected from the group consisting of an insulating porous member, a polymer electrolyte, a gel electrolyte, and an inorganic solid electrolyte. The separator 20 may be one type of member used alone, or two or more types of members may be used in combination.

[0045] (Negative electrode 10) 3 is a perspective view showing an example of the negative electrode 10. In one embodiment, the negative electrode 10 includes a negative electrode current collector 12 and a negative electrode active material layer 14 disposed on the negative electrode current collector 12.

[0046] The negative electrode current collector 12 may be composed of a negative electrode insulating layer 120 and a pair of negative electrode conductive layers 122 arranged so as to sandwich the negative electrode insulating layer 120 therebetween.

[0047] In one embodiment, the negative electrode insulating layer 120 may be made of, for example, a sheet-shaped (film-shaped) or fibrous resin. The resin may be, for example, at least one of polyolefin resins such as polyethylene terephthalate (PET), polyethylene, and polypropylene, and thermoplastic resins such as polystyrene, polyvinyl chloride, and polyamide. The negative electrode insulating layer 120 may be made of at least one of the resins laminated together. In one embodiment, the negative electrode insulating layer 120 is made of a material having a melting point of 150° C. or more and 300° C. or less. In one embodiment, the thickness of the negative electrode insulating layer 120 may be 3 μm or more and 10 μm or less, or may be 4 μm or more and 8 μm or less. By including the negative electrode insulating layer 120 in the negative electrode collector 12, the weight of the negative electrode 10 can be reduced while its rigidity (thickness) can be increased.

[0048] The negative electrode conductive layer 122 is formed on both sides of the negative electrode insulating layer 120 so as to sandwich the negative electrode conductive layer 120. The negative electrode conductive layer 122 is in physical and / or electrical contact with the negative electrode active material layer 14 and functions to give and receive electrons to and from the negative electrode active material layer 14. In one embodiment, the negative electrode conductive layer 122 is formed from at least one selected from the group consisting of metals that do not react with Cu, Ni, Ti, Fe, and Li, alloys thereof, and stainless steel. Here, the "metal that does not react with Li" may be a metal that does not react with lithium ions or lithium metal to form an alloy in the operating state of the secondary battery 1. In one embodiment, the negative electrode conductive layer 122 is Cu. In one embodiment, the negative electrode conductive layer 122 is formed by vapor deposition, sputtering, electrolytic plating, or lamination of the above-mentioned material on the surfaces of both sides of the negative electrode insulating layer 120. In one embodiment, the thickness of the negative electrode conductive layer 122 may be 0.5 μm to 5 μm, 0.7 μm to 3 μm, or 0.8 μm to 2.0 μm.

[0049] The negative electrode active material layer 14 may be disposed on both sides of the negative electrode current collector 12, or may be disposed on only one side of the negative electrode current collector 12. The negative electrode active material layer 14 includes a negative electrode active material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, at the negative electrode. The negative electrode active material may include, for example, lithium metal and an alloy containing lithium metal, a carbon-based material, a metal oxide, and a metal that alloys with lithium and an alloy containing the metal. The carbon-based material may be, for example, graphene, graphite, hard carbon, carbon nanotubes, etc. The metal oxide may be, for example, a titanium oxide-based compound, a cobalt oxide-based compound, etc. The metal that alloys with lithium may be, for example, silicon, silicon oxide, germanium, tin, lead, aluminum, and gallium, and these may be pre-doped with lithium.

[0050] 3, the negative electrode current collector 12 has a negative electrode end P. In one embodiment, the negative electrode end P is configured as a part of the negative electrode current collector 12, extending from a side surface of the negative electrode current collector 12 in a first direction (x direction in FIG. 3) different from the stacking direction. No negative electrode active material layer 14 is disposed on the negative electrode end P.

[0051] In one embodiment, a metal sheet M1 for the negative electrode may be provided on the negative electrode end P. The metal sheet M1 may be bonded to one side of the negative electrode end P as shown in FIG. 3, or may be bonded to both sides of the negative electrode end P. The metal sheet M1 may be provided only on the negative electrode end P of some of the negative electrodes 10, or may be provided on the negative electrode end P of all the negative electrodes 10. The metal sheet M1 may be made of the same material as the negative electrode conductive layer 122, and in one example, is Cu. In one embodiment, the thickness of the metal sheet M1 may be 3 μm or more, 5 μm or more, or 7 μm or more. In one embodiment, the thickness of the metal sheet M1 may be 15 μm or less, 12 μm or less, or 10 μm or less.

[0052] As shown in FIG. 3, the metal sheet M1 and the negative electrode end P have a first joining mark W1 formed by joining the negative electrode tab 40. In one embodiment, the metal sheet M1 and the negative electrode end P may have a preliminary joining mark WP1 formed by joining the two. The preliminary joining mark WP1 is a joining mark formed when the metal sheet M1 and the negative electrode end P are joined together (hereinafter also referred to as "preliminary joining") prior to joining with the negative electrode tab 40. The first joining mark W1 and the preliminary joining mark WP1 may be formed at different positions from each other as viewed from the stacking direction (z direction). The preliminary joining mark WP1 may be formed in a line shape along the negative electrode end P in one row or in multiple rows, or may be formed in a multiple dot shape. Note that, when the metal sheet M1, the negative electrode end P, and the negative electrode tab 40 are joined at one time without performing preliminary joining, only the first joining mark W1 is formed, and the preliminary joining mark WP1 is not formed.

[0053] In one embodiment, the first bonding mark W1 and / or the preliminary bonding mark WP1 may be a bonding mark by welding, i.e., a welding mark. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. In one example, the welding is ultrasonic welding. In one embodiment, the metal sheet M1 and the negative electrode conductive layer 122 of the negative electrode end P may be integrated by being fused partially or entirely by heat or the like at the first bonding mark W1 and / or the preliminary bonding mark WP1. (positive electrode 30) 4 is a perspective view showing an example of the positive electrode 30. In one embodiment, the positive electrode 30 includes a positive electrode current collector 32 and a positive electrode active material layer 34 disposed on the positive electrode current collector 32.

[0054] The positive electrode current collector 32 may be composed of a positive electrode insulating layer 320 and a pair of positive electrode conductive layers 322 arranged so as to sandwich the positive electrode insulating layer 320 therebetween.

[0055] The positive electrode insulating layer 320 may be made of, for example, a sheet-like (film-like) or fibrous resin. The resin may be, for example, at least one of polyolefin resins such as polyethylene terephthalate (PET), polyethylene, and polypropylene, and thermoplastic resins such as polystyrene, polyvinyl chloride, and polyamide. The positive electrode insulating layer 320 may be made of at least one of the resins laminated together. In one embodiment, the positive electrode insulating layer 320 is made of a material having a melting point of 150° C. or more and 300° C. or less. In one embodiment, the thickness of the positive electrode insulating layer 320 may be 3 μm or more and 10 μm or less, or 4 μm or more and 8 μm or less.

[0056] The positive electrode insulating layer 320 can function to melt when abnormal heat is generated due to overcharge or high temperature, to damage the positive electrode 30, and to cut off the short-circuit current inside the battery. This can suppress a sudden temperature rise inside the laminate ST and suppress the ignition of the battery when the secondary battery 1 is used. In other words, the positive electrode insulating layer 320 can contribute to improving the safety of the secondary battery 1.

[0057] The positive electrode conductive layer 322 is formed on both sides of the positive electrode insulating layer 320 so as to sandwich the positive electrode conductive layer 320. The positive electrode conductive layer 322 is in physical and / or electrical contact with the positive electrode active material layer 34 and functions to give and receive electrons to and from the positive electrode active material layer 34. The positive electrode conductive layer 322 is made of a conductor that does not react with lithium ions in the secondary battery 1. In one embodiment, the positive electrode conductive layer 322 is made of at least one material selected from the group consisting of aluminum, titanium, stainless steel, nickel, and alloys thereof. In one example, the positive electrode conductive layer 322 is aluminum or an aluminum alloy. In one embodiment, the positive electrode conductive layer 322 is formed by vapor deposition, sputtering, electrolytic plating, or lamination of the above material on the surfaces of both sides of the positive electrode insulating layer 320. In one embodiment, the thickness of the positive electrode conductive layer 322 may be 0.5 μm to 5 μm, 0.7 μm to 3 μm, or 0.8 μm to 2.0 μm.

[0058] The positive electrode active material layer 34 may include a positive electrode active material for retaining lithium ions, and lithium ions are charged and released from the positive electrode active material by charging and discharging the battery. The positive electrode active material may be a metal oxide or a metal phosphate. The metal oxide may be, for example, a cobalt oxide-based compound, a manganese oxide-based compound, or a nickel oxide-based compound. The metal phosphate may be, for example, an iron phosphate-based compound, or a cobalt phosphate-based compound. In one embodiment, the positive electrode active material is LiCoO2, LiNi x Co y Mn z O(x+y+z=1), LiNi x Co y Al z O(x+y+z=1), LiNi x Mn y The positive electrode active material layer 34 may be at least one selected from the group consisting of O(x+y=1), LiNiO2, LiMn2O4, LiFePO4, LiCoPO4, LiFeOF, LiNiOF, and LiTiS2. The positive electrode active material may be used alone or in combination of two or more. In one embodiment, the positive electrode active material layer 34 may contain one or more components other than the positive electrode active material, such as a sacrificial positive electrode material, a gel electrolyte, a polymer electrolyte, a conductive assistant, and / or a binder.

[0059] As shown in Fig. 4, the positive electrode current collector 32 has a positive electrode end Q. In one embodiment, the positive electrode end Q is configured as a part of the positive electrode current collector 32, extending from a side surface of the positive electrode current collector 32 in a second direction different from the stacking direction (in the example shown in Fig. 4, the x direction is the same as the first direction, but is not limited to this). No positive electrode active material layer 34 is disposed on the positive electrode end Q.

[0060] In one embodiment, a metal sheet M2 for the positive electrode may be provided on the positive electrode end Q. The metal sheet M2 may be bonded to one side of the positive electrode end Q as shown in FIG. 4, or may be bonded to both sides of the positive electrode end Q. The metal sheet M2 may be provided only on the positive electrode ends Q of some of the positive electrodes 30, or may be provided on the positive electrode ends Q of all of the positive electrodes 30. In one embodiment, the metal sheet M2 is made of the same material as the positive electrode conductive layer 322. In one example, the metal sheet M2 is aluminum or an aluminum alloy. In one example, the metal sheet M2 may be a hard aluminum foil or a soft aluminum foil. The soft aluminum foil may be formed by subjecting the hard aluminum foil to a high-temperature (around 400° C.) heat treatment. In one embodiment, the thickness of the metal sheet M2 may be 3 μm or more, 5 μm or more, or 7 μm or more. In one embodiment, the thickness of the metal sheet M2 may be 15 μm or less, 12 μm or less, or 10 μm or less.

[0061] As shown in FIG. 4, the metal sheet M2 and the positive electrode end Q have a second joining mark W2 formed by joining with the positive electrode tab 42. In one embodiment, the metal sheet M2 and the positive electrode end Q may have a preliminary joining mark WP2 formed by joining the two. The preliminary joining mark WP2 is a joining mark formed when the metal sheet M2 and the positive electrode end Q are joined prior to joining with the positive electrode tab 42. The second joining mark W2 and the preliminary joining mark WP2 may be formed at different positions from each other as viewed from the stacking direction (z direction). The preliminary joining mark WP2 may be formed in a line shape along the positive electrode end Q in one row or in multiple rows, or may be formed in a multiple dot shape. Note that, when the metal sheet M2, the positive electrode end Q, and the positive electrode tab 42 are joined at one time without performing preliminary joining, only the second joining mark W2 is formed, and the preliminary joining mark WP2 is not formed.

[0062] In one embodiment, the second bonding mark W2 and / or the preliminary bonding mark WP2 may be a bonding mark by welding, i.e., a welding mark. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. In one example, the welding is ultrasonic welding. In one embodiment, the metal sheet M2 and the positive electrode conductive layer 322 of the positive electrode end Q may be integrated by being fused partially or entirely by heat or the like at the second bonding mark W2 and / or the preliminary bonding mark WP2.

[0063] (First bonding mark W1 and preliminary bonding mark WP1) Fig. 5 is a diagram for explaining the bonding state of the negative electrode tab 40, the negative electrode end P, and the metal sheet M1. Fig. 5 shows a schematic cross section of the negative electrode end P, taken along the xz plane, at a location including the first bonding mark W1 and the preliminary bonding mark WP1.

[0064] As shown in Fig. 5, the first bonding mark W1 and the preliminary bonding mark WP1 are provided at different positions from each other when viewed from the stacking direction. The first bonding mark W1 is formed over the entire negative electrode tab 40, each negative electrode end P, and each metal sheet M1. That is, the first bonding mark W1 is formed continuously in the stacking direction from the negative electrode tab 40 to the negative electrode end P of the lowest layer. In contrast, the preliminary bonding mark WP1 is formed for each negative electrode end P. In other words, one preliminary bonding mark WP1 is not formed across multiple negative electrode ends P.

[0065] As shown in FIG. 5, in the negative electrode end P, the first bonding mark W1 is disposed at a predetermined distance Y or more inward from the outer edge of the negative electrode end P in the first direction. In one embodiment, the distance Y may be 2.0 mm, 2.5 mm, or 3.0 mm. In one embodiment, when the number of stacked negative electrodes 10 in the stack ST (i.e., the total number of negative electrode ends P) is X, the predetermined distance Y may be set so that the relationship Y>0.048X+1.3 holds. In one embodiment, X may be 10 or more, 15 or more, or 20 or more.

[0066] Fig. 6 is a diagram showing a cross section of the first bonding mark W1. Fig. 6 shows a schematic cross section of the first bonding mark W1 cut along the zy plane (AA cross section in Fig. 5). As shown in Fig. 6, the cross section of the first bonding mark W1 includes a first region R1 and a second region R2. In one embodiment, the cross section of the first bonding mark W1 may have a recess recessed on one side in the stacking direction.

[0067] In the first region R1, the negative electrode conductive layer 122 and the metal sheet M1 are laminated integrally and joined to the negative electrode tab 40. Here, being laminated integrally includes a state in which the negative electrode conductive layers 122 and the metal sheet M1 are partially or entirely fused together by heat or the like (a state in which the layers cannot be distinguished from each other).

[0068] In one embodiment, the first region R1 may be substantially free of the negative insulating layer 120 along the stacking direction. The first region R1 provides a physical path for electrical connection between the negative electrode tab 40 and each of the negative conductive layers 122 and the metal sheet M1.

[0069] In one embodiment, the first region R1 may be configured between two second regions R2. In one embodiment, the maximum thickness of the first region R1 may be less than or equal to half the maximum thickness of the second region R2.

[0070] In the second region R2, a pair of negative electrode conductive layers 122 and the metal sheet M1 are laminated, sandwiching the negative electrode insulating layer 120. That is, the second region R2 is a region that includes the negative electrode insulating layer 120 along the lamination direction.

[0071] In one embodiment, the first bonding mark W1 is formed by pressing the negative electrode tab 40, the negative electrode end P, and the metal sheet M1 along the stacking direction. At this time, heat may be applied to the pressed location. For example, the first bonding mark W1 may be formed by welding (in this case, the first bonding mark W1 is a welding mark). As a result, the negative electrode insulating layer 120 is softened at the pressed location and pushed outward in the width direction (left and right direction in FIG. 6) from the pressed location. Also, at the pressed location, each negative electrode conductive layer 122 and the metal sheet M1 are thermally melted and integrated. As a result, the first region R1 and the second region R2 can be formed.

[0072] Here, when the first bonding mark W1 is formed, a part of the metal material constituting the negative electrode conductive layer 122 and / or the metal sheet M1 may be pushed out from the pressing point toward the first direction (x direction in FIGS. 5 and 6). At this time, if the metal material protrudes outward from the negative electrode end P and reaches the insulating material IL (see FIGS. 1 and 5) of the insulating part 40B of the negative electrode tab 40, insulation failure may occur between the negative electrode 10 and the seal part 102 (see FIG. 1) of the sealed container 100. For example, if a crack or the like occurs in the seal part 102 (e.g., an aluminum laminate film) in a state where the metal material protruding from the negative electrode end P is present in the insulating part 40B, the negative electrode end P of the negative electrode 10 and the sealed container 100 are short-circuited. In that case, the seal part 102 may be damaged, which may cause a decrease in the performance or life of the secondary battery 1.

[0073] In this regard, in the secondary battery 1, as described above, the first bonding mark W1 is disposed at least a predetermined distance Y inward from the outer edge of the negative electrode end P. Therefore, even if a part of the metal material is pushed out from the pressed portion in the first direction when the first bonding mark W1 is formed, the metal material is prevented from jumping out from the outer edge of the negative electrode end P and further reaching the insulating part 40B of the negative electrode tab 40. This can prevent insulation failure between the negative electrode 10 and the seal part 102 of the sealed container 100 (see FIG. 1) as described above.

[0074] As described above, in one embodiment, a metal sheet M1 for the negative electrode may be provided on the negative electrode end P. In this case, the metal sheet M1 functions as an additional conductive layer of the negative electrode conductive layer 122 in the first bonding mark W1, and increases the ratio of the conductive layer to the negative electrode insulating layer 120. Therefore, an increase in resistance in the first bonding mark W1 is suppressed, and the output characteristics of the secondary battery 1 can be improved. In addition, when the total number (number of layers) of the negative electrodes 10 is large, it is necessary to press and bond the negative electrode tab 40 and each negative electrode end P with a stronger force, but since the metal sheet M1 functions as a protective layer for the negative electrode conductive layer 122, the negative electrode conductive layer 122 can be suppressed from being damaged or broken. This can improve the production yield of the secondary battery 1. In one embodiment, the resistance of the first bonding mark W1 may be 5.0 mΩ or less, 3.0 mΩ or less, 1.0 mΩ or less, or 0.5 mΩ or less.

[0075] (Second bonding mark W2 and preliminary bonding mark WP2) The positive electrode tab 42, the positive electrode end Q, and the second bonding mark W2 and preliminary bonding mark WP2 of the metal sheet M2 may be configured similarly to the first bonding mark W1 and preliminary bonding mark WP1 described in Figures 5 and 6. For example, in one embodiment, the second bonding mark W2 may be disposed a predetermined distance Y or more inward from the outer edge of the positive electrode end Q. This can suppress insulation failure between the positive electrode 30 and the seal portion 102 of the sealed container 100 (see Figure 1).

[0076] <Manufacturing method of secondary battery 1> Next, an example of a method for manufacturing the secondary battery 1 (hereinafter also referred to as "this manufacturing method") will be described with reference to Figs. 7 to 10. Fig. 7 is a flow chart showing an example of this manufacturing method. Figs. 8A and 8B are views for explaining step ST1 in Fig. 7. Figs. 9A to 9D are views for explaining step ST2 in Fig. 7. Fig. 10 is a view for explaining step ST3 in Fig. 7.

[0077] As shown in FIG. 7 , this manufacturing method may include a step ST1 of preparing a negative electrode sheet S1, a step ST2 of joining a metal sheet M1, a step ST3 of cutting out a plurality of negative electrodes 10, a step S4 of preparing a positive electrode sheet S2, a step ST5 of joining the metal sheet M2, a step ST6 of cutting out a plurality of positive electrodes 30, a step ST7 of forming a laminate ST, a step ST8 of joining the electrode tabs and the current collector, and a step ST9 of sealing the laminate ST in a sealed container 100.

[0078] First, in step ST1, as shown in Fig. 8A and Fig. 8B, a negative electrode sheet S1 is prepared. Fig. 8A is a plan view of the negative electrode sheet S1. Fig. 8B is a cross-sectional view taken along line BB of Fig. 8A. As shown in Fig. 8A, the negative electrode sheet S1 may be a strip-shaped sheet having a longitudinal direction (y direction) and a lateral direction (x direction). In one embodiment, as shown in Fig. 8A and Fig. 8B, the negative electrode sheet S1 may be composed of a negative electrode collector 12 and a negative electrode active material layer 14 applied to both sides of the negative electrode collector 12. At one end of the lateral direction (x direction) of the negative electrode sheet S1, the negative electrode active material layer 14 is not formed, and the negative electrode conductive layer 122 of the negative electrode collector 12 is exposed.

[0079] In one embodiment, the separator 20 may be provided from the beginning on one surface (the surface on which the negative electrode conductive layer 122 is not formed) of the negative electrode active material layer 14. In this case, it is not necessary to align and dispose the separator 20 between the negative electrode 10 and the positive electrode 30 in step ST7.

[0080] Next, in step ST2, as shown in Figures 9A to 9D, a metal sheet M1 is joined to one end in the short side direction of the negative electrode sheet S1. Figure 9A is a plan view of the negative electrode sheet S1 to which the metal sheet M1 is joined. Figures 9B to 9D are examples of a CC cross section of Figure 9A.

[0081] As shown in FIG. 9A, the joining in step ST2 forms a preliminary joining mark WP1 along the longitudinal direction, for example, in a line shape. The metal sheet M1 may be joined to the negative electrode sheet S1 by welding. The welding may be, for example, ultrasonic welding, laser welding, resistance welding, or spot welding. In one example, the welding is ultrasonic welding.

[0082] In one embodiment, the joining in the step ST2 may be performed by pressing the metal sheet M1 against the negative electrode current collector 12. For example, as shown in FIG. 9B and FIG. 9C, the preliminary joining mark WP1 may be formed so that the metal sheet M1 is recessed toward the negative electrode current collector 12. In one embodiment, the preliminary joining mark WP1 may be provided between the metal sheet M1 and one negative electrode conductive layer 122 (with which the metal sheet M1 is in contact) as shown in FIG. 9B. In this case, at the preliminary joining mark WP1, the metal sheet M1 is not electrically connected to the other negative electrode conductive layer 122. In one embodiment, the preliminary joining mark WP1 may be provided between the metal sheet M1 and both negative electrode conductive layers 122 as shown in FIG. 9C. In this case, at the preliminary joining mark WP1, the metal sheet M1 is electrically connected to both negative electrode conductive layers 122.

[0083] In one embodiment, the bonding in step ST2 may be performed by pressing the negative electrode current collector 12 against the metal sheet M1. For example, as shown in Fig. 9D, the preliminary bonding mark WP1 may be formed so that the negative electrode current collector 12 is recessed toward the metal sheet M1 side. In this case, at the preliminary bonding mark WP1, the metal sheet M1 is electrically connected to both negative electrode conductive layers 122.

[0084] Next, in step ST3, a plurality of negative electrodes 10 are cut out from the negative electrode sheet S1. Specifically, a cutting blade, a laser, or the like is used to cut a plurality of negative electrodes 10 having a given shape from the negative electrode sheet S1, as shown in Fig. 10. This results in a plurality of negative electrodes 10 to which the metal sheet M1 is pre-joined.

[0085] Steps ST4 to ST6 may be performed in the same manner as steps ST1 to ST3. That is, a positive electrode sheet S2 including a positive electrode current collector 32 and a positive electrode active material layer 34 may be prepared (step ST4), a metal sheet M2 may be joined to one end in the short side direction of the positive electrode sheet S2 (step ST5), and a plurality of positive electrodes 30 may be cut out from the metal sheet M2 (step ST6).

[0086] Next, in step ST7, a laminate ST is formed. Specifically, the negative electrodes 10 and the positive electrodes 30 prepared in steps ST1 and ST3 are alternately arranged with separators 20 interposed therebetween so as to be spaced apart from each other in the lamination direction, as shown in FIG.

[0087] Next, in step ST8, the electrode tab and the current collector are joined. Specifically, the negative electrode end P of the negative electrode collector 12 and the metal sheet M1 are joined to the negative electrode tab 40 so as to form the first joining mark W1 described above. At this time, the joining point with the negative electrode tab 40 is located at a position at a predetermined distance Y or more inside from the outer edge of the negative electrode end P. Note that this joining point may be located at a position that does not overlap with the preliminary joining mark WP1 in the stacking direction. Also, the positive electrode end Q of the positive electrode collector 32 and the metal sheet M2 are joined to the positive electrode tab 42 so as to form the second joining mark W2 described above. At this time, the joining point with the positive electrode tab 42 is located at a predetermined distance Y or more inside from the outer edge of the positive electrode end Q. Note that this joining point may be located at a position where the second joining mark W2 does not overlap with the preliminary joining mark WP2 in the stacking direction. The joining of the electrode tab and the current collector may be performed by ultrasonic welding, laser welding, resistance welding, or spot welding.

[0088] Next, in step ST9, the laminate ST formed in step ST8 is sealed in a sealed container 100. At this time, as shown in FIG. 1, the insulating portion 40B of the negative electrode tab 40 is placed in the seal portion 102 of the sealed container 100, and the other end portion 40C of the negative electrode tab 40 is taken out to the outside of the sealed container 100. Also, the insulating portion 42B of the positive electrode tab 42 is placed in the seal portion 102 of the sealed container 100, and the other end portion 42C of the positive electrode tab 42 is taken out to the outside of the sealed container 100. In one embodiment, an electrolyte may be sealed in the sealed container 100 together with the laminate ST. In this manner, the secondary battery 1 is manufactured.

[0089] In this manufacturing method, in step ST8, the joining location with the negative electrode tab 40 is located at a position at least a predetermined distance Y inward from the outer edge of the negative electrode end P. This prevents a part of the metal material constituting the negative electrode conductive layer 122 and / or the metal sheet M1 from protruding from the outer edge of the negative electrode end P and reaching the insulating part 40B of the negative electrode tab 40. This can prevent insulation failure between the negative electrode 10 and the seal part 102 of the sealed container 100. In this manufacturing method, in step ST8, the joining location with the positive electrode tab 42 is located at a position at least a predetermined distance Y inward from the outer edge of the positive electrode end Q, so the above points are similarly applicable to the positive electrode 30.

[0090] In this manufacturing method, the metal sheet M1 is previously joined to the negative electrode sheet S1 in step ST2. Therefore, in step ST3, the metal sheet M1 can be simultaneously cut out to match the shape of the negative electrode end P. That is, a separate step of cutting the metal sheet M1 to match the shape of the negative electrode end P is not required. In step ST9, the alignment of the metal sheet M1 and the negative electrode end P is not required, so that the negative electrode tab 40 and the negative electrode end P can be easily joined. Furthermore, in step ST9, it is theoretically possible to provide the first joining mark W1 so as not to overlap with the preliminary joining mark WP1 in the stacking direction. By providing the first joining mark W1 so as not to overlap with the preliminary joining mark WP2 in the stacking direction, the joining state of the first joining mark W1 is improved compared to the case where both are provided overlapping, and an increase in the resistance of the first joining mark W1 can be suppressed. In this manufacturing method, the metal sheet M2 is previously joined to the positive electrode sheet S2 in step ST4, so the above points are also applicable to the positive electrode 30.

[0091] <How to use secondary battery 1> The secondary battery 1 is charged and discharged by connecting the negative electrode tab 40 to one end of an external circuit and the positive electrode tab 42 to the other end of the external circuit. The external circuit may be, for example, a resistor, a power source, an apparatus, a device, another battery, or a potentiostat. The negative electrode ends P of the multiple negative electrodes 10 may be connected to the external circuit at the same potential. The positive electrode ends Q of the multiple positive electrodes 30 may be connected to the external circuit at the same potential.

[0092] When a voltage is applied between the negative electrode tab 40 and the positive electrode tab 42 such that a current flows from the negative electrode tab 40 through an external circuit to the positive electrode tab 42, the secondary battery 1 is charged and lithium metal is deposited on the negative electrode 10. When the negative electrode tab 40 and the positive electrode tab 42 of the charged secondary battery 1 are connected via a desired external circuit, the secondary battery 1 is discharged and the lithium metal in the negative electrode 10 is electrolytically dissolved.

[0093] In one embodiment, the secondary battery 1 may have a solid electrolyte interface layer (SEI layer) formed on the surface of the negative electrode 10 or the surface of the separator 20 (i.e., the interface between the negative electrode 10 and the separator 20) by the first charge (initial charge) after the assembly of the battery. The SEI layer may contain, for example, an inorganic compound containing lithium, or an organic compound containing lithium. In one embodiment, the thickness of the SEI layer is 1.0 nm or more and 10 μm or less. When the secondary battery 1 has an SEI layer formed therein, lithium metal is precipitated or dissolved at the interface between the negative electrode 10 and / or the separator 20 and the SEI layer by charge and discharge.

[0094] According to the secondary battery 1 described above, the output characteristics and productivity of the battery can be improved.

[0095] <Modification> The secondary battery 1 can be modified in various ways without departing from the scope and spirit of the present disclosure.

[0096] (Negative electrode 10) 11A to 11C are perspective views showing other examples of the negative electrode 10. For example, as shown in Fig. 11A and Fig. 11C, a metal sheet does not have to be provided at the negative electrode end P of the negative electrode 10.

[0097] For example, as shown in FIG. 11B and FIG. 11C, the negative electrode 10 may be composed of a negative electrode current collector 12 and may not substantially have a negative electrode active material. Here, the negative electrode 10 "substantially does not have a negative electrode active material" includes, for example, that the layer thickness of the negative electrode active material deposited on the negative electrode 10 at the end of discharge (for example, a state in which the open circuit voltage of the battery is 2.5 V or more and 3.6 V or less) is 25 μm or less. The layer thickness of the negative electrode active material at the end of discharge may be 20 μm or less, 15 μm or less, 10 μm or less, or 5 μm or less, or may be 0 μm. Since the negative electrode 10 does not substantially have a negative electrode active material, the energy density per volume can be improved in addition to the weight energy density. In this case, the secondary battery 1 can also be called an "anode-free lithium battery", a "zero anode lithium battery", or an "anode-less lithium battery".

[0098] In the examples shown in FIG. 11B and FIG. 11C, the negative electrode 10 does not have a negative electrode active material before the initial charge of the battery (the state from the assembly of the battery to the first charge). That is, the secondary battery 1 may be charged and discharged by depositing lithium metal on the negative electrode after the initial charge, and electrolytically dissolving the deposited lithium metal. In this case, the volume and mass occupied by the negative electrode active material are suppressed, the volume and mass of the entire battery are reduced, and the energy density is increased in principle. Note that "lithium metal deposits on the negative electrode" includes not only lithium metal depositing on the surface of the negative electrode, but also lithium metal depositing on the surface of a solid electrolyte interface (SEI) layer or on the surface or inside of a buffer functional layer, which will be described later.

[0099] In the examples shown in FIG. 11B and FIG. 11C, the mass of lithium metal deposited on the negative electrode 10 when the voltage is 4.2 V is M 4.2 The same mass at a voltage of 3.0 V is M 3.0 In this case, M 3.0 / M 4.2 may be 40% or less, or 35% or less. In one embodiment, the ratio M 3.0 / M 4.2 may be 1.0% or more, 2.0% or more, 3.0% or more, or 4.0% or more.

[0100] 11B and 11C, the thickness of the negative electrode 10 may be 1.0 μm or more and 30 μm or less. This can reduce the volume occupied by the negative electrode 10 in the secondary battery 1 and improve the energy density. The thickness of the negative electrode 10 may be 2.0 μm or more and 20 μm or less, 2.0 μm or more and 18 μm or less, or 3.0 μm or more and 15 μm or less.

[0101] (buffer layer) In one embodiment, a porous or fibrous buffer functional layer may be provided between the negative electrode 10 and the separator 20. The buffer functional layer has a solid portion (including a gel portion) having ionic conductivity and electrical conductivity, and a pore portion formed by gaps in the solid portion. In this case, lithium metal may be precipitated on the surface of the negative electrode 10 (the interface between the negative electrode 10 and the buffer functional layer) and / or inside the buffer functional layer (the surface of the solid portion of the buffer functional layer).

[0102] (positive electrode 30) Fig. 12 is a perspective view showing another example of the positive electrode 30. For example, as shown in Fig. 12, the positive electrode end Q of the positive electrode 30 does not necessarily need to be provided with a metal sheet.

[0103] (Laminate ST) 13 and 14 are perspective views for explaining another example of lamination of the plurality of negative electrodes 10. As shown in FIG. 13 and FIG. 14, the plurality of negative electrodes 10 may be configured as a single flat sheet as a whole, rather than as a single flat sheet. For example, as shown in FIG. 13, the plurality of negative electrodes 10 may be configured by winding the negative electrode sheet S1 multiple times. Also, for example, as shown in FIG. 14, the plurality of negative electrodes 10 may be configured by folding the negative electrode sheet S1 alternately at acute angles multiple times. The negative electrode sheet S1 may be configured as shown in FIG. 8A, or may be configured by joining a metal sheet M1 as shown in FIG. 9A.

[0104] Similarly, the multiple positive electrodes 30 may be configured as a single flat sheet as a whole, rather than as a single flat sheet. For example, the multiple positive electrodes 30 may be configured by winding the positive electrode sheet S2 multiple times, as in Fig. 13. Also, for example, the multiple positive electrodes 30 may be configured by folding the positive electrode sheet S2 alternately at acute angles multiple times, as in Fig. 14.

[0105] Hereinafter, an experiment conducted to verify the effects of the present disclosure will be described. The present disclosure is not limited to the following experiment.

[0106] <Experiment 1> Fig. 15 is a diagram showing the results of experiment 1. Fig. 16A is an example of a case where there was protrusion of metal material in experiment 1. Fig. 16B is an example of a case where there was no protrusion of metal material in experiment 1. Figs. 16A and 16B are examples of the electrode tab 40 viewed from the negative electrode end P side (in Fig. 2, the electrode tab 40 viewed from the negative electrode end P at the bottom end in the z direction).

[0107] In experiment 1, multiple laminates ST with the structure shown in Fig. 2 were prepared. Each laminate ST differed in the number X of laminated negative electrodes 10 (11 or 21 sheets), the distance Y from the outer edge of the negative electrode end P to the first bonding mark W1 (see Fig. 5, 0.5 mm to 4.45 mm), and the presence or absence of a metal sheet M1. The common configuration of each laminate ST is as follows.

[0108] In each laminate ST, 6 μm thick polyethylene terephthalate (PET) was used as the negative electrode insulating layer 120. 1.0 μm thick copper foil was used as the negative electrode conductive layer 122. A mixed material was used as the negative electrode active material layer 14, in which 97 parts by mass of graphite, 0.5 parts by mass of carbon black as a conductive aid, and 1.5 parts by mass of carboxymethyl cellulose (CMC) and 1.0 part by mass of styrene-butadiene rubber (SBR) as binders were mixed with water as a solvent. For the laminate in which the metal sheet M1 was arranged, 4 μm thick copper foil was used as the metal sheet M1. For the negative electrode tab 40, 0.2 mm thick nickel-plated copper was used.

[0109] In each laminate ST, the separator 20 used was a sheet whose surface was coated with a mixture of polyvinylidene fluoride (PVDF) and Al2O3.

[0110] In each laminate ST, a 6 μm-thick film of polyethylene terephthalate was used as the positive electrode insulating layer 320. A 1.0 μm-thick aluminum was used as the positive electrode conductive layer 322. A 1.0 μm-thick aluminum alloy was used as the positive electrode active material layer 34. The positive electrode active material layer 34 was made of LiNi in N-methyl-pyrrolidone (NMP) as a solvent. 0.8 Co 0.15 Al 0.05A mixture of 96 parts by mass of O2, 2 parts by mass of carbon black as a conductive assistant, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder was used. Aluminum was used as the metal sheet M2. Aluminum with a thickness of 0.2 mm was used as the positive electrode tab 42.

[0111] Each laminate ST prepared as described above was evaluated for the presence or absence of "protrusion" of the metal material from the negative electrode end P. As shown in Fig. 16A, the case where the metal material from the negative electrode end P contacted the insulating portion 40B of the negative electrode tab 40 was determined as "protrusion present." Also, as shown in Fig. 16B, the case where the metal material from the negative electrode end P did not contact the insulating portion 40B of the negative electrode tab 40 was determined as "no protrusion."

[0112] As shown in FIG. 15, when the number of layers X is 11, no "extrusion" of the metal material occurred in the laminate ST where Y is 2.0 mm or more. When the number of layers X is 21, no "extrusion" of the metal material occurred in the laminate ST where the distance Y is 2.7 mm or more. From the results in FIG. 15, in order to prevent extrusion, it is necessary for the distance Y and the number of layers X to have a relationship of Y>0.048X+1.3. The reason why the distance Y at which extrusion does not occur increases as the number of layers X increases is thought to be that the increase in the number of layers X increases the bonding interface, which increases the pressing force required for bonding, and as a result, the metal material becomes more likely to be extruded.

[0113] <Experiment 2> FIG. 17 is a diagram showing the results of Experiment 2. In Experiment 2, secondary batteries having the structure shown in FIG. 1 were fabricated using a plurality of laminates ST (shown as E1 to E4 and R1 to R3 in FIG. 15) fabricated in Experiment 1, and cycle tests were performed. In the cycle tests, 100 cycles of 0.3 C charge and 0.3 C discharge were repeated while applying a pressure of 50 kPa to the secondary battery 1 in a thermostatic chamber at 25° C. Then, the capacity retention rate (%) after 100 cycles was measured. The capacity retention rate (%) is the ratio (A2 / A1×100) of the capacity (A2) of the secondary battery 1 at the end of 100 cycles to the capacity (A1) at the end of one cycle.

[0114] 17, the secondary batteries formed from the laminates E1 to E4 in which no protrusion of the metal material occurred all had a capacity retention rate of 98% or more, which was extremely good compared to the secondary batteries formed from the laminates R1 to R3 in which protrusion of the metal material occurred. This is believed to be because no insulation failure occurred between the negative electrode 10 and the seal portion 102 of the sealed container 100.

[0115] The embodiments of the present disclosure further include the following aspects.

[0116] (Appendix 1) a laminate in which a plurality of positive electrodes and negative electrodes are laminated in a stacking direction with separators interposed therebetween, one of the positive electrodes and the negative electrodes includes a first current collector having a resin layer sandwiched between a pair of conductive layers, and the first current collector has a first end portion extending in a first direction different from the stacking direction; a first electrode tab electrically connected to the first end portion, the first electrode tab including a first bonding mark formed by bonding with the first end portion, and a first insulating portion disposed apart from the first bonding mark in the first direction and covered with an insulating material; a sealed container including a seal portion, the sealed container being configured to enclose the laminate inside the seal portion while sandwiching the first insulating portion of the first electrode tab in the seal portion and taking out a part of the first electrode tab to the outside of the sealed container; A lithium secondary battery.

[0117] (Appendix 2) 2. The lithium secondary battery according to claim 1, wherein the first bonding mark at the first end portion is provided 2 mm or more inward from an outer edge of the first end portion in the first direction.

[0118] (Appendix 3) 2. The lithium secondary battery according to claim 1, wherein the first bonding mark at the first end portion is provided at least 2.5 mm inward from an outer edge of the first end portion in the first direction.

[0119] (Appendix 4) 2. The lithium secondary battery according to claim 1, wherein when a total number of the first current collectors included in the laminate is X and a distance between the first joining mark at the first end and an outer edge of the first end in the first direction is Y, a relationship of Y>0.048X+1.3 is satisfied.

[0120] (Appendix 5) 5. The lithium secondary battery according to claim 4, wherein X is 10 or more.

[0121] (Appendix 6) 6. The lithium secondary battery according to claim 1, wherein the first joining mark is a welding mark.

[0122] (Appendix 7) 7. The lithium secondary battery according to claim 1, wherein the first bonding mark includes a region where the pair of conductive layers are integrated together in a cross section in the stacking direction.

[0123] (Appendix 8) 6. The lithium secondary battery according to claim 1, wherein the first end and the first electrode tab are joined to each other via a metal sheet.

[0124] (Appendix 9) 9. The lithium secondary battery according to claim 8, wherein the first joining mark is a welding mark.

[0125] (Appendix 10) 10. The lithium secondary battery according to claim 8, wherein the first joining mark includes a region where the pair of conductive layers and the metal sheet are integrated in a cross section in the stacking direction.

[0126] (Appendix 11) 11. The lithium secondary battery of claim 8, wherein the first end has a preliminary joining mark due to joining with the metal sheet, and the preliminary joining mark is provided at a position different from the first joining mark when viewed from the stacking direction.

[0127] (Appendix 12) 12. The lithium secondary battery of claim 1, wherein the first current collector is a negative electrode current collector of the negative electrode, and the first electrode tab is a negative electrode tab connected to the negative electrode current collector.

[0128] (Appendix 13) 13. The lithium secondary battery according to claim 1, wherein the sealed container is made of an aluminum laminate film.

[0129] (Appendix 14) 14. The lithium secondary battery according to any one of Appendix 1 to Appendix 13, wherein the other of the positive electrode and the negative electrode includes a second current collector formed by sandwiching a resin layer between a pair of conductive layers, and the second current collector has a second end extending in a second direction different from the stacking direction.

[0130] (Appendix 15) a second electrode tab electrically connected to the second end of the second current collector, the second electrode tab including a second bonding mark formed by bonding with the second end and a second insulating portion disposed away from the second bonding mark in the second direction and covered with an insulating material; 15. The lithium secondary battery of claim 14, wherein the sealed container is configured to sandwich the second insulating portion of the second electrode tab at the seal portion and to extend a portion of the second electrode tab outside the sealed container.

[0131] (Appendix 16) 16. The lithium secondary battery according to claim 14, wherein the first direction and the second direction are the same direction.

[0132] (Appendix 17) 16. The lithium secondary battery according to claim 14, wherein the first direction and the second direction are different directions. [Explanation of symbols]

[0133] 1...Lithium secondary battery, 10...Negative electrode, 20...Separator, 30...Positive electrode, 40...Negative electrode tab, 40B...Insulating part, 42...Positive electrode tab, 42B...Insulating part, 100...Sealed container, 102...Sealing part, IL...Insulating material, M1, M2...Metal sheet, P...Negative electrode end, Q...Positive electrode end, ST...Laminate, W1...First joining mark, W2...Second joining mark, WP1, WP2...Preliminary joining mark

Claims

1. A laminate in which a plurality of positive electrodes and negative electrodes are laminated in a stacking direction via a separator, wherein one of the positive electrode and the negative electrode includes a first current collector configured by sandwiching a resin layer between a pair of conductive layers, and the first current collector includes a first end portion extending in a first direction different from the stacking direction. A laminate, A first electrode tab electrically connected to the first end portion, the first electrode tab including a first bonding mark formed by bonding to the first end portion and a first insulating portion disposed apart from the first bonding mark in the first direction and covered with an insulating material. A first electrode tab, A sealed container including a seal portion, the sealed container being configured to enclose the laminate inside the seal portion and sandwich the first insulating portion of the first electrode tab at the seal portion to take out a part of the first electrode tab to the outside of the sealed container. A sealed container, Comprising, When the total number of the first current collectors included in the laminate is X and the distance between the first bonding mark and the outer edge of the first end portion in the first direction at the first end portion is Y, a lithium secondary battery in which the relationship Y>0.048X + 1.3 holds.

2. The lithium secondary battery according to claim 1, wherein the first bonding mark at the first end portion is provided at least 2 mm inward from the outer edge of the first end portion in the first direction.

3. The lithium secondary battery according to claim 1, wherein the first bonding mark at the first end portion is provided at least 2.5 mm inward from the outer edge of the first end portion in the first direction.

4. The lithium secondary battery according to claim 1, wherein X is 10 or more.

5. The lithium secondary battery according to any one of claims 1 to 4, wherein the first bonding mark is a welding mark.

6. The lithium secondary battery according to claim 5, wherein the first bonding mark includes a region where the pair of conductive layers are integrated in a cross section in the stacking direction.

7. The lithium secondary battery according to any one of claims 1 to 4, wherein the first end portion and the first electrode tab are joined to each other via a metal sheet.

8. The lithium secondary battery according to claim 7, wherein the first bonding mark is a welding mark.

9. The lithium secondary battery according to claim 8, wherein the first bonding mark includes a region where the pair of conductive layers and the metal sheet are integrated in a plurality of layers in a cross section in the stacking direction.

10. The first end portion has a preliminary bonding mark due to bonding with the metal sheet, and the preliminary bonding mark is provided at a position different from the first bonding mark when viewed in the stacking direction. The lithium secondary battery according to claim 7.

11. The first current collector is the negative electrode current collector of the negative electrode, and the first electrode tab is a negative electrode tab connected to the negative electrode current collector. The lithium secondary battery according to any one of claims 1 to 4.

12. The sealed container is made of an aluminum laminate film. The lithium secondary battery according to claim 11.

13. The other of the positive electrode and the negative electrode includes a second current collector formed by sandwiching a resin layer between a pair of conductive layers. The second current collector includes a second end portion extending in a second direction different from the stacking direction. The lithium secondary battery according to any one of claims 1 to 4.

14. The battery further includes a second electrode tab electrically connected to the second end portion of the second current collector. The second electrode tab includes a second bonding mark formed by bonding with the second end portion, and a second insulating portion disposed at a distance from the second bonding mark in the second direction and covered with an insulating material. The sealed container is configured to sandwich the second insulating portion of the second electrode tab at the seal portion and take out a part of the second electrode tab to the outside of the sealed container. The lithium secondary battery according to claim 13.

15. The first direction and the second direction are the same direction. The lithium secondary battery according to claim 13.

16. The first direction and the second direction are different directions. The lithium secondary battery according to claim 13.

Images