Secondary battery, battery pack, and vehicle

Abstract

To provide a secondary battery in which self-discharge failure is reduced by suppressing an internal short circuit.SOLUTION: A secondary battery includes a negative electrode, a positive electrode, and an electrolyte. The negative electrode includes: a negative electrode current collector; and a negative electrode mixture layer laminated on the negative electrode current collector and having a front surface and a back surface. The negative electrode current collector has a thickness of 8 μm or more and 18 μm or less, and has a first current collector end surface extending along a stacking direction of the negative electrode current collector and the negative electrode mixture layer. The negative electrode mixture layer contains a niobium-titanium composite oxide as a negative electrode active material, and has a first projecting portion projecting from the end surface of the first current collector along a first direction perpendicular to the stacking direction. A protrusion length A1 of the first projecting portion satisfies 0 mm<A1≤1.0 mm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a secondary battery, a battery pack, and a vehicle. [Background technology]

[0002] In recent years, research and development of high-energy density secondary batteries, such as nonaqueous electrolyte secondary batteries like lithium-ion secondary batteries, has been actively pursued. Nonaqueous electrolyte secondary batteries are expected to be used as power sources for vehicles like hybrid electric vehicles and electric vehicles, as well as for uninterruptible power supplies in mobile phone base stations. Furthermore, because of the rapidly increasing demand for power sources for mobile services, such as autonomous industrial robots and drones, secondary batteries are required to have not only high energy density but also other excellent performance characteristics, such as rapid charge / discharge capability and long-term reliability.

[0003] When producing an electrode for a secondary battery, for example, a method may be employed in which an electrode composite layer-forming slurry is applied to a metal foil as a current collector, followed by drying to produce a laminate of the current collector and the electrode composite layer, and then the laminate is punched out into a desired shape. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-034009 [Patent Document 2] Patent Publication No. 2021-048005 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a secondary battery in which internal short circuits are suppressed and thereby self-discharge defects are reduced, a battery pack including this secondary battery, and a vehicle including this battery pack. [Means for solving the problem]

[0006] According to an embodiment, a secondary battery is provided. The secondary battery includes a negative electrode, a positive electrode, and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode composite layer laminated on the negative electrode current collector and having a front surface and a back surface. The negative electrode current collector has a thickness of 8 μm to 18 μm, and has a first current collector end surface extending along the lamination direction of the negative electrode current collector and the negative electrode composite layer. The negative electrode composite layer contains niobium titanium composite oxide as a negative electrode active material, and has a first protrusion protruding from the first current collector end surface in a first direction perpendicular to the lamination direction. The protrusion length A1 of the first protrusion is 0 .1 mm ≤ A1≦1.0mm is satisfied.

[0007] According to another embodiment, a battery pack is provided, which includes a secondary battery according to the embodiment.

[0008] According to another embodiment, a vehicle is provided, the vehicle including a battery pack according to an embodiment. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a plan view showing an example of a negative electrode included in the secondary battery according to the embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the negative electrode taken along line II-II in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the negative electrode taken along line III-III in FIG. [Figure 4] 3 is an enlarged cross-sectional view showing the vicinity of a first protrusion in the cross-sectional view of the negative electrode shown in FIG. 2. FIG. [Figure 5] FIG. 10 is an enlarged cross-sectional view showing a modified example of the first protrusion. [Figure 6] FIG. 10 is an enlarged cross-sectional view showing another modified example of the first protrusion. [Figure 7] FIG. 10 is an enlarged cross-sectional view showing another modified example of the first protrusion. [Figure 8] FIG. 10 is an enlarged cross-sectional view showing another modified example of the first protrusion. [Figure 9] FIG. 3 is a plan view showing measurement positions of the width along the short side direction of the negative electrode included in the secondary battery according to the embodiment. [Figure 10] FIG. 3 is a plan view showing measurement positions of the width along the long side direction of the negative electrode included in the secondary battery according to the embodiment. [Figure 11] FIG. 3 is a plan view showing measurement positions of the width along the long side direction of the negative electrode included in the secondary battery according to the embodiment. [Figure 12] 1 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment. [Figure 13] FIG. 13 is an enlarged cross-sectional view of part B of the secondary battery shown in FIG. [Figure 14] FIG. 10 is a cross-sectional view schematically illustrating another example of a secondary battery according to an embodiment. [Figure 15] FIG. 10 is a plan view schematically showing a stack including secondary batteries before initial charging and a restraining jig; [Figure 16] 16 is a cross-sectional view of the laminate shown in FIG. 15 taken along line XVI-XVI. [Figure 17] 17 is a cross-sectional view schematically showing a state after initial charging of a secondary battery included in the stack in FIG. 16. FIG. [Figure 18] 10 is a cross-sectional view schematically showing another method for restraining a secondary battery before initial charging is performed. [Figure 19] FIG. 1 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. [Figure 20] FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. [Figure 21] FIG. 21 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 20. [Figure 22] 1 is a cross-sectional view schematically illustrating an example of a vehicle according to an embodiment. [Figure 23] FIG. 10 is a diagram schematically illustrating another example of a vehicle according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the embodiments, the same reference numerals are assigned to common configurations, and duplicate descriptions are omitted. In addition, each drawing is a schematic diagram for facilitating the explanation and understanding of the embodiments, and there are some parts where the shape, dimensions, ratio, etc. are different from the actual device, but these can be appropriately designed and changed in consideration of the following description and known technologies.

[0011] When punching out a laminate of a current collector and an electrode mixture layer using a mold, stress due to punching is applied to the end of the electrode mixture layer laminated on the surface of the current collector. The end of the electrode mixture layer may break due to this stress and slip off from the current collector. As a result, the vicinity of the end of the current collector is exposed. When the exposed end of the current collector contacts the counter electrode, an internal short circuit occurs, resulting in a problem of an increase in the self-discharge amount.

[0012] (First Embodiment) According to the first embodiment, a secondary battery is provided. The secondary battery includes a negative electrode, a positive electrode, and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer laminated on the negative electrode current collector and having a front surface and a back surface. The negative electrode current collector has a thickness of 8 μm or more and 18 μm or less, and has a first current collector end face extending along the lamination direction of the negative electrode current collector and the negative electrode mixture layer. The negative electrode mixture layer contains a niobium titanium composite oxide as a negative electrode active material, and has a first protruding portion protruding along a first direction orthogonal to the lamination direction from the first current collector end face. The protruding length A1 of the first protruding portion satisfies 0 mm < A1 ≤ 1.0 mm.

[0013] In the negative electrode included in the secondary battery according to the embodiment, the end of the negative electrode mixture layer supported on the negative electrode current collector protrudes from the end face of the negative electrode current collector by a predetermined length. In other words, in the vicinity of the end of the negative electrode current collector, since the front surface or the back surface of the negative electrode current collector is covered by the negative electrode mixture layer, an internal short circuit with the positive electrode is unlikely to occur. As a result, according to the secondary battery according to the embodiment, the frequency of self-discharge defects can be reduced.

[0014] The negative electrode included in the secondary battery according to the embodiment will be described while referring to the drawings.

[0015] FIG. 1 is a plan view schematically illustrating an example of a negative electrode included in a secondary battery according to an embodiment. FIG. 2 is a cross-sectional view of the negative electrode according to FIG. 1 taken along line II-II. FIG. 3 is a cross-sectional view of the negative electrode according to FIG. 1 taken along line III-III. In the following description, the X-axis direction and the Y-axis direction are parallel to the main surface of the negative electrode current collector 3a and are perpendicular to each other. The Z-axis direction is perpendicular to the X-axis direction and the Y-axis direction. In other words, the Z-axis direction is the thickness direction of the electrode (negative electrode). The direction parallel to the X-axis direction and the Y-axis direction is also referred to as the in-plane direction.

[0016] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode composite material layer 3b formed on at least one surface of the negative electrode current collector 3a. FIGS. 1 to 3 show a case in which the negative electrode composite material layer 3b is laminated on both of the two main surfaces of the negative electrode current collector 3a. Although not shown, the negative electrode current collector 3a may further include a strip portion (negative electrode current collector tab) for extracting current to the outside. The negative electrode current collector tab does not support the negative electrode composite material layer 3b.

[0017] The shape of the main surface of the negative electrode 3 is not particularly limited, and may be, for example, a square, a rectangle, a circle, or an ellipse. FIGS. 1 to 3 show a case where the main surface of the negative electrode 3 has a rectangular shape. When the main surface of the negative electrode 3 has a shape with corners such as a square or a rectangle, the corners of the electrode may be chamfered to have a rounded shape, as shown by reference numerals 15a to 15d in FIG. 1. The shapes of the main surface of the negative electrode current collector 3a and the main surface of the negative electrode composite layer 3b may be the same as the shape of the negative electrode 3.

[0018] The cross-sectional view shown in FIG. 2 is a diagram schematically illustrating a state in which the negative electrode shown in FIG. 1 is cut in a first direction perpendicular to the stacking direction (Z-axis direction) of the negative electrode current collector 3a and the negative electrode composite layer 3b. The first direction is any one of the in-plane directions defined by the X-axis direction and the Y-axis direction. In FIGS. 1 to 3, a case in which the first direction is parallel to the X-axis direction is described as an example. In the negative electrode 3 shown in FIG. 1, the first direction 51 is parallel to each of a pair of short sides of the rectangular negative electrode 3. The first direction may also be parallel to the Y-axis direction.

[0019] On the other hand, a direction perpendicular to both the stacking direction (Z-axis direction) and the first direction 51 is defined as a second direction 52. The second direction 52 is a direction parallel to the Y-axis direction.

[0020] The negative electrode current collector 3a is, for example, a sheet-like metal foil having a front surface 53 and a back surface 54. The negative electrode current collector 3a has four side surfaces 3a1, 3a2, 3a3, and 3a4 that are perpendicular to the front surface 53 and the back surface 54. Of the four side surfaces 3a1, 3a2, 3a3, and 3a4, the side surface 3a1 and the side surface 3a3 are opposite to each other. The side surfaces 3a2 and 3a4 are also opposite to each other.

[0021] As shown in FIG. 2, the side surface 3a1 and the side surface 3a3 extend along the stacking direction of the negative electrode current collector 3a and the negative electrode composite layer 3b and correspond to, for example, the long sides of the rectangular negative electrode 3. The side surface 3a1 is also referred to as a first current collector end face, and the side surface 3a3 is also referred to as a third current collector end face. The first current collector end face 3a1 corresponds to one of the pair of long sides of the negative electrode current collector 3a. The third current collector end face 3a3 corresponds to the other of the pair of long sides of the negative electrode current collector 3a.

[0022] As shown in FIG. 3 , the side surface 3a2 and the side surface 3a4 extend along the stacking direction of the negative electrode current collector 3a and the negative electrode composite layer 3b and correspond to, for example, the short sides of the rectangular negative electrode 3. The side surface 3a2 is also referred to as the second current collector end face, and the side surface 3a4 is also referred to as the fourth current collector end face. The second current collector end face 3a2 corresponds to one of the pair of short sides of the negative electrode current collector 3a. The fourth current collector end face 3a4 corresponds to the other of the pair of short sides of the negative electrode current collector 3a.

[0023] The negative electrode mixture layer 3b has a front surface 55 and a back surface 56. One of the two negative electrode mixture layers 3b provided in the negative electrode 3 is supported on a front surface 53 of the negative electrode current collector 3a. The other of the two negative electrode mixture layers 3b provided in the negative electrode 3 is supported on a back surface 54 of the negative electrode current collector 3a. Back surfaces 56 of the two negative electrode mixture layers 3b are both in contact with the negative electrode current collector 3a.

[0024] Unless otherwise specified, the following description of the negative electrode mixture layer 3b applies independently to both the negative electrode mixture layer 3b supported on the surface 53 of the negative electrode current collector 3a and the negative electrode mixture layer 3b supported on the back surface 54 of the negative electrode current collector 3a. At least one of the two negative electrode mixture layers 3b supported on the surface 53 and the back surface 54 of the negative electrode current collector 3a has a protrusion having a predetermined length. Both of the two negative electrode mixture layers 3b supported on the surface 53 and the back surface 54 of the negative electrode current collector 3a may have a protrusion having a predetermined length. One of the two negative electrode mixture layers 3b supported on the surface 53 and the back surface 54 of the negative electrode current collector 3a does not have to have a protrusion of a predetermined length, as described below.

[0025] 2, negative electrode composite material layer 3b has first protruding portion 11 protruding from first current collector end surface 3a1 along first direction 51. Protruding length A1 of first protruding portion 11 satisfies the following formula (1). 0mm <A1≦1.0mm (1)。

[0026] Because the first protrusion 11 protrudes by a length satisfying formula (1), the vicinity of the first current collector end face 3a1 of the negative electrode current collector 3a is likely to be shielded from the outside of the negative electrode 3. For example, the probability of the negative electrode current collector 3a coming into contact with the positive electrode can be reduced. This can suppress internal short circuits and reduce the frequency of self-discharge defects. A protrusion length A1 of the first protrusion 11 of less than 0 mm means that the first protrusion 11 does not protrude from the first current collector end face 3a1. In this case, the first protrusion 11 does not shield the first current collector end face 3a1, and therefore the effect of suppressing internal short circuits is not obtained. On the other hand, if the protrusion length A1 of the first protrusion 11 exceeds 1.0 mm, at least a portion of the negative electrode composite material layer 3b including the protrusion tends to break. If at least a portion of the negative electrode composite material layer 3b breaks, the protrusion length A1 may ultimately become less than 0 mm, which may result in an inability to suppress internal short circuits, as described above. Furthermore, the broken protrusion (part of the composite layer) floats in the electrolyte, which may increase self-discharge.

[0027] The protruding length A1 of the first protruding portion 11 is preferably in the range of 0.1 mm to 0.95 mm, and more preferably in the range of 0.2 mm to 0.8 mm.

[0028] 1, negative electrode composite layer 3b may have first protrusion 11 along the entire long side of negative electrode 3, or may have first protrusion 11 on at least a part of the long side of negative electrode 3. First protrusion 11 may be present on any one of the four sides of rectangular negative electrode 3.

[0029] 2, negative electrode composite material layer 3b may further have third protrusion 13 protruding from third current collector end face 3a3 along first direction 51. Protrusion length A3 of third protrusion 13 satisfies the following formula (3). 0mm <A3≦1.0mm (3)。

[0030] When the third protrusion 13 protrudes further to a length that satisfies formula (3), the same effect as that described above for the first protrusion 11 can be obtained. That is, the vicinity of the third current collector end surface 3a3 of the negative electrode current collector 3a is likely to be shielded from the outside of the negative electrode 3. For example, the probability that the negative electrode current collector 3a will come into contact with the positive electrode can be reduced. This can therefore suppress internal short circuits and reduce the frequency of self-discharge failures.

[0031] 1, negative electrode composite layer 3b may have third protrusion 13 along the entire long side of negative electrode 3, or may have third protrusion 13 on at least a part of the long side of negative electrode 3. Third protrusion 13 may be present on one of the four sides of rectangular negative electrode 3 that faces the side on which first protrusion 11 is present.

[0032] Next, a description will be given of second protrusions 12 and fourth protrusions 14 that may be included on a pair of short sides of negative electrode 3. As shown in Fig. 3, negative electrode mixture layer 3b preferably further includes second protrusions 12 that protrude from fourth current collector end face 3a4 along second direction 52. Protrusion length A2 of second protrusion 12 satisfies the following formula (2). 0mm <A2≦1.0mm (2)。

[0033] When the second protrusion 12 further protrudes by a length satisfying formula (2), the vicinity of the second current collector end surface 3a2 of the negative electrode current collector 3a is likely to be shielded from the outside of the negative electrode 3. For example, the probability of the negative electrode current collector 3a coming into contact with the positive electrode can be reduced. This can suppress internal short circuits and reduce the frequency of self-discharge defects. A protrusion length A2 of the second protrusion 12 of less than 0 mm means that the second protrusion 12 does not protrude from the second current collector end surface 3a2. In this case, the second protrusion 12 does not provide a shielding effect for the second current collector end surface 3a2, and therefore does not suppress internal short circuits. On the other hand, when the protrusion length A2 of the second protrusion 12 exceeds 1.0 mm, at least a portion of the negative electrode composite material layer 3b including the protrusion tends to break. If at least a portion of the negative electrode composite material layer 3b breaks, the protrusion length A2 may ultimately become less than 0 mm. Furthermore, the broken protrusion (part of the composite layer) floats in the electrolyte, which may increase self-discharge.

[0034] The protruding length A2 of the second protruding portion 12 is preferably in the range of 0.1 mm to 0.95 mm, and more preferably in the range of 0.2 mm to 0.8 mm.

[0035] 1, negative electrode composite layer 3b may have second protrusion 12 over the entire short side of negative electrode 3, or may have second protrusion 12 on at least a part of the short side of negative electrode 3. Second protrusion 12 may be present on one of the four sides of rectangular negative electrode 3 that is perpendicular to the side on which first protrusion 11 is present.

[0036] 3, negative electrode mixture layer 3b may further have fourth protrusion 14 protruding from fourth current collector end face 3a4 along second direction 52. Protrusion length A4 of fourth protrusion 14 satisfies the following formula (4). 0mm <A4≦1.0mm (4)。

[0037] When the fourth protrusion 14 protrudes further to a length that satisfies formula (4), the same effect as that described above for the first protrusion 11 can be obtained. That is, the vicinity of the fourth current collector end surface 3a4 of the negative electrode current collector 3a is likely to be shielded from the outside of the negative electrode 3. For example, the probability that the negative electrode current collector 3a will come into contact with the positive electrode can be reduced. This can therefore suppress internal short circuits and reduce the frequency of self-discharge failures.

[0038] The protrusion length A1 and the protrusion length A3 may be the same or approximately the same, but may be different from each other. The protrusion length A2 and the protrusion length A4 may be the same or approximately the same, but may be different from each other. The protrusion length A1 and the protrusion length A2 may be the same or approximately the same, but may be different from each other.

[0039] Negative electrode mixture layer 3b may also have protrusions 15a to 15d protruding from the end face of the current collector at each of the four corners of rectangular negative electrode 3. At least one of protrusions 15a to 15d at the four corners may not be present.

[0040] The negative electrode current collector 3a is provided with a potential at which lithium (Li) is inserted into and extracted from the active material, for example, 1.0 V (vs. Li / Li + ) is used. The material of the negative electrode current collector is not particularly limited, but it is preferably made of, for example, only aluminum or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. Since aluminum is one of the lightest metals, the energy density of the battery can be increased by including aluminum in the negative electrode current collector. Aluminum or an aluminum alloy is also preferred because of its low cost.

[0041] The negative electrode current collector has a thickness of 8 μm or more and 18 μm or less. If the thickness of the negative electrode current collector is less than 8 μm, the negative electrode current collector is prone to fracture, and the fractured current collector is released into the electrolyte, which tends to increase self-discharge, which is undesirable. Furthermore, using an excessively thin current collector makes it difficult to manufacture the negative electrode, which raises concerns about increased manufacturing costs. If the negative electrode current collector is thicker than 18 μm, the area of ​​the end face of the negative electrode current collector becomes large, making it difficult to achieve the effect of suppressing internal short circuits due to the protrusions of the negative electrode composite layer. The thickness of the negative electrode current collector is preferably in the range of 10 μm or more and 15 μm or less.

[0042] The length of each of the first to fourth protrusions 11 to 14 is, for example, within a range of 5 to 100 times, and preferably within a range of 10 to 90 times, the thickness (herein referred to as "tE") of the negative electrode current collector 3a. When the ratio is within this range, the negative electrode composite layer has protrusions of an appropriate length relative to the thickness (end face area) of the negative electrode current collector, thereby reducing the probability of the negative electrode current collector coming into contact with the positive electrode. Therefore, an excellent self-discharge suppression effect can be obtained.

[0043] The ratio A1 / tE of the protrusion length A1 of the first protrusion 11 to the thickness tE of the negative electrode current collector is, for example, within a range of 5 to 100, and preferably within a range of 10 to 90. The ratio A2 / tE of the protrusion length A2 of the second protrusion 12 to the thickness tE of the negative electrode current collector is, for example, within a range of 5 to 100, and preferably within a range of 10 to 90. The ratio A3 / tE of the protrusion length A3 of the third protrusion 13 to the thickness tE of the negative electrode current collector is, for example, within a range of 5 to 100, and preferably within a range of 10 to 90. The ratio A4 / tE of the protrusion length A4 of the fourth protrusion 14 to the thickness tE of the negative electrode current collector is, for example, within a range of 5 to 100, and preferably within a range of 10 to 90.

[0044] The shape of first protruding portion 11 of negative electrode composite material layer 3b will be described with reference to FIGS. 4 to 8. First protruding portion 11 may have any of the shapes shown in FIGS. 4 to 8. FIG. 4 is an enlarged cross-sectional view showing the vicinity of first protruding portion 11 in the cross-sectional view of negative electrode 3 shown in FIG. 2. FIG. 5 is an enlarged cross-sectional view showing a modified example of first protruding portion 11. FIG. 6 is an enlarged cross-sectional view showing another modified example of first protruding portion 11. FIG. 7 is an enlarged cross-sectional view showing another modified example of first protruding portion 11. FIG. 8 is an enlarged cross-sectional view showing another modified example of first protruding portion 11.

[0045] According to one example, second protruding portion 12 to fourth protruding portion 14 of negative electrode composite material layer 3b may have any of the shapes shown in FIGS.

[0046] As shown in FIG. 4 , the negative electrode composite material layer 3b has a first composite material layer end surface 3b1. The first composite material layer end surface 3b1 is an end surface extending parallel or approximately parallel to the stacking direction of the negative electrode current collector 3a and the negative electrode composite material layer 3b. According to one example, the first composite material layer end surface 3b1 may be an end surface extending in a direction parallel or approximately parallel to the first current collector end surface 3a1 of the negative electrode current collector 3a. The first composite material layer end surface 3b1 may be a part of the first protrusion 11.

[0047] Negative electrode mixture layer 3b has corner 550 where surface 55 intersects with first mixture layer end surface 3b1. Negative electrode mixture layer 3b has corner 560 where back surface 56 intersects with first mixture layer end surface 3b1. Although not shown, corner 550 and corner 560 extend in the Y-axis direction.

[0048] As shown in Figures 4 to 6 and 8, at least a portion of the first protrusion 11 may have a rounded shape. In Figure 4, as an example, both corners 550 and 560 have a rounded shape. When the corners have a rounded shape, potential concentration at the corners is alleviated, which has the advantage of making it difficult for metal ions to deposit at the corners. Therefore, when at least a portion of the first protrusion 11 has a rounded shape, the capacity retention rate is excellent.

[0049] The first protrusion 11 may have the configuration shown in Fig. 5 and Fig. 6. In the example shown in Fig. 5, the corner 550 has a rounded shape, but the corner 560 does not have a rounded shape. In the example shown in Fig. 6, the corner 550 does not have a rounded shape, but the corner 560 has a rounded shape. Even in the cases shown in Fig. 5 and Fig. 6, the potential concentration at the corner is alleviated, making it difficult for metal ions to deposit at the corner, and providing the effect of excellent capacity retention.

[0050] The first protrusion 11 does not have to have an R-shape, as shown in Fig. 7. Even in this case, the first protrusion 11 shields the vicinity of the first current collector end face 3a1, thereby preventing an internal short circuit.

[0051] The first protrusion 11 may have a configuration shown in FIG. 8. In the configuration shown in FIG. 8, at least a portion of the first protrusion 11 is warped toward the negative electrode current collector 3a (the back surface 56). For example, at least a portion of the first protrusion 11 covers the first current collector end surface 3a1 of the negative electrode current collector 3a. This can prevent chipping of the corners of the first current collector end surface 3a1. In addition, in this configuration, at least a portion of the first protrusion 11 has an R-shape, which reduces potential concentration at the corners of the composite layer, as described above. This makes it difficult for metal ions to deposit at the corners, resulting in an excellent capacity retention rate.

[0052] <Method for measuring the thickness and protrusion length of each layer> Next, methods for measuring the layer thicknesses of the negative electrode current collector and the negative electrode composite layer, and the protrusion length of each protrusion will be described with reference to Figures 9 to 11. Figures 9 to 11 show plan views of the negative electrode 3 described with reference to Figures 1 to 3. The negative electrode 3 shown in Figures 9 to 11 has the same structure as the negative electrode 3 described with reference to Figures 1 to 3, except that the negative electrode current collector 3a further has a negative electrode current collecting tab 3c.

[0053] First, the secondary battery to be measured is fully discharged. For example, the battery is discharged at a current of 0.1 C in a 25°C environment until the rated end voltage or the battery voltage reaches 1.0 V. This is repeated multiple times until the current value during discharge is 1 / 100 or less of the rated capacity. Even in a discharged state, residual lithium ions may still be present.

[0054] A secondary battery containing electrodes in a fully discharged state (State of Charge: 0%) is disassembled in a glove box filled with argon. The electrode to be measured is removed from the disassembled secondary battery. This electrode is then washed with an appropriate solvent. A good example of a solvent to use for washing is ethyl methyl carbonate. If the washing is insufficient, it may be difficult to observe the particles due to the influence of lithium carbonate or lithium fluoride remaining in the electrode.

[0055] Here, assuming that the extracted electrode (here, the negative electrode) is rectangular or approximately rectangular, a method for measuring the protrusion length of each of the first protrusion 11 and the third protrusion 13 located on the long side will be described with reference to Figure 9.

[0056] The long side length LL of the negative electrode 3 is measured and divided into four equal parts to define sections L1 to L4. Then, widths W1 to W3 along the short side direction of the negative electrode composite material layer 3b are measured at positions corresponding to one-quarter, one-half, and three-quarters of the long side length LL. The positions corresponding to one-quarter, one-half, and three-quarters of the long side length LL correspond to the positions separating sections L1 and L2, the positions separating sections L2 and L3, and the positions separating sections L3 and L4, respectively. This measurement can be performed using a scale such as a ruler. The simple average of the measured widths W1 to W3 is considered to be the width (width along the short side direction) of the negative electrode composite material layer 3b.

[0057] Meanwhile, the negative electrode 3 was cut using an ion milling machine at positions corresponding to one-quarter, one-half, and three-quarters of the long side length LL, and each cross section was observed using a scanning electron microscope (SEM). The SEM observation was performed according to the following procedure.

[0058] The cross section of the cut electrode is attached to the SEM sample stage. At this time, a treatment such as conductive tape is applied to prevent the electrode from peeling or floating from the sample stage. The electrode (composite layer) attached to the SEM sample stage is observed with an SEM to obtain an SEM image. During SEM measurement, observation is performed at a magnification of 10,000x so that the protruding part of the negative electrode composite layer is included in the field of view. It is also preferable to maintain an inert atmosphere when introducing the electrode into the sample chamber.

[0059] By observing the cross section of the negative electrode with an SEM, the shapes of the first projecting portions and the third projecting portions can be observed.

[0060] Thereafter, negative electrode mixture layer 3b is peeled off to expose the surface of negative electrode current collector 3a. Then, the width of negative electrode current collector 3a is measured at each position where widths W1 to W3 along the short side direction of negative electrode mixture layer 3b were measured. The simple average of the three obtained values ​​is regarded as the width along the short side direction of negative electrode current collector 3a.

[0061] The total length of the protrusion length A1 of the first protrusion 11 and the protrusion length A3 of the third protrusion 13 can be calculated by subtracting the width of the negative electrode current collector 3a along the short side from the previously determined width of the negative electrode composite layer 3b along the short side. The value obtained by dividing the calculated total length by 2 is regarded as the protrusion length A1 and the protrusion length A3. Alternatively, the protrusion length A1 of the first protrusion and the protrusion length A3 of the third protrusion may be measured from the SEM image obtained by the above method using the length measurement function of the SEM.

[0062] When measuring the thickness tE of the negative electrode current collector and the thickness of the negative electrode composite layer 3b, the thickness tE of the negative electrode current collector and the thickness of the negative electrode composite layer 3b are measured, for example, at the center position in the width direction of the image including each of the protrusions obtained above.

[0063] Next, a method for measuring the protrusion lengths of the second protrusion 12 and the fourth protrusion 14 located on the short side will be described with reference to FIGS. 10 and 11. FIG. 10 shows a case where the negative electrode current collector tab 3c is located at the center or approximately the center of the short side of the negative electrode 3. FIG. 11 shows a case where the negative electrode current collector tab 3c is located near the end of the short side of the negative electrode 3. The location of the negative electrode current collector tab 3c is not particularly limited. Therefore, depending on the position of the negative electrode current collector tab 3c included in the negative electrode 3 to be measured, the protrusion lengths of the second protrusion 12 and the fourth protrusion 14 can be measured using the method described with reference to either FIG. 10 or FIG. 11.

[0064] Referring to FIG. 10, using a scale such as a ruler, the width wT of the negative electrode current collector tab 3c is subtracted from the length LS of one short side of the negative electrode 3. The obtained value is divided by 2 to determine the lengths LS1 and LS2 of the portions of the short side of the negative electrode 3 that do not have the negative electrode current collector tab 3c. The lengths LS1 and LS2 are approximately the same value. The lengths LS1 and LS2 are each divided in half to define sections S1 and S2 and sections S3 and S4. Then, the width W4 of the negative electrode composite layer 3b along the long side direction is measured at a position separating sections S1 and S2. Furthermore, the width W5 of the negative electrode composite layer 3b along the long side direction is measured at a position separating sections S3 and S4. This measurement can be performed using a scale such as a ruler. The simple average of the measured widths W4 and W5 is considered to be the width (width along the long side direction) of the negative electrode composite layer 3b.

[0065] Referring to FIG. 11, the length LS of one short side of the negative electrode 3 is measured using a scale such as a ruler. The length of the longest part of the short side, excluding the width wT of the negative electrode current collector tab 3c, is defined as LS3. The length LS3 is divided into three equal parts to define sections S5 to S7. A width W6 along the long side of the negative electrode composite layer 3b is measured at a position separating sections S5 and S6. A width W7 along the long side of the negative electrode composite layer 3b is also measured at a position separating sections S6 and S7. This measurement can be performed using a scale such as a ruler. The simple average of the measured widths W6 and W7 is considered to be the width (width along the long side) of the negative electrode composite layer 3b.

[0066] Furthermore, the negative electrode 3 is cut using an ion milling machine at each of the positions where the widths W4 to W7 along the long side direction of the negative electrode composite layer 3b were measured, and each cross section is observed using a scanning electron microscope (SEM). By observing the negative electrode cross section using SEM, the shapes of the second protrusions and the fourth protrusions can be observed.

[0067] Thereafter, the negative electrode composite layer 3b is peeled off to expose the surface of the negative electrode current collector 3a. Then, the width of the negative electrode current collector 3a along the long side direction is measured at each position where the widths W4 and W5 along the long side direction of the negative electrode composite layer 3b were measured, or at each position where the widths W6 and W7 were measured. The simple average of the two obtained values ​​is regarded as the width along the long side direction of the negative electrode current collector 3a.

[0068] The total length of the protrusion length A2 of the second protrusion 12 and the protrusion length A4 of the fourth protrusion 14 can be calculated by subtracting the width of the negative electrode current collector 3a along the long side direction from the previously determined width of the negative electrode composite layer 3b along the long side direction. The value obtained by dividing the calculated total length by 2 is regarded as the protrusion length A2 and the protrusion length A4. Alternatively, the protrusion length A2 of the second protrusion and the protrusion length A4 of the fourth protrusion may be measured from the SEM image obtained by the above method using the length measurement function of the SEM.

[0069] <Details of secondary batteries> The secondary battery will be described in detail below. According to this embodiment, a secondary battery including a negative electrode, a positive electrode, and an electrolyte is provided.

[0070] The secondary battery may further include a separator disposed between the positive electrode and the negative electrode. The negative electrode, the positive electrode, and the separator may constitute an electrode assembly. The electrolyte may be held in the electrode assembly.

[0071] The secondary battery may further include an exterior member that houses the electrode group and the electrolyte.

[0072] Furthermore, the secondary battery may further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

[0073] The secondary battery may be, for example, a lithium secondary battery, or a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0074] The negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal will be described in detail below.

[0075] (1) Negative electrode The negative electrode may include a negative electrode current collector and a negative electrode mixture layer. The negative electrode mixture layer may be formed on one or both sides of the negative electrode current collector. The negative electrode mixture layer may include a negative electrode active material and, optionally, a conductive agent and a binder.

[0076] The thickness of the negative electrode composite layer is not particularly limited, but is, for example, in the range of 3 μm to 250 μm. In particular, from the viewpoint of achieving both excellent energy density and output characteristics, the thickness of the negative electrode composite layer is preferably in the range of 10 μm to 100 μm.

[0077] The negative electrode active material includes a niobium titanium composite oxide. The niobium titanium composite oxide has, for example, a monoclinic crystal structure. The monoclinic niobium titanium composite oxide is, for example, represented by the general formula Li x Ti 1-y M1 y Nb 2-zM2 z O 7+δ and a composite oxide represented by the general formula Li x Ti 1-y M3 y+z Nb 2-z O 7-δ where M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. Each subscript in the composition formula satisfies 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3.

[0078] Specific examples of monoclinic niobium titanium composite oxides include Nb2TiO7, Nb2Ti2O9, and Nb 10 Ti2O 29 , Nb 14 TiO 37 and Nb 24 TiO 62 Examples of the substituted niobium titanium composite oxide include: The monoclinic niobium titanium composite oxide may be a substituted niobium titanium composite oxide in which at least a portion of Nb and / or Ti has been substituted with a different element. Examples of the substituted element include Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, and Al. The substituted niobium titanium composite oxide may contain one type of substituted element, or may contain two or more types of substituted elements.

[0079] The negative electrode active material may contain an active material other than the niobium titanium composite oxide. Examples of the other active material include lithium titanate having a ramsdellite structure (e.g., Li 2+y Ti3O7, 0≦y≦3), lithium titanates with spinel structure (e.g., Li 4+x Ti5O 12, 0≦x≦3), titanium dioxide (TiO2), niobium pentoxide (Nb2O5), anatase type titanium dioxide, rutile type titanium dioxide, hollandite type titanium composite oxide, and orthorhombic titanium-containing composite oxide.

[0080] As an example of orthorhombic titanium-containing composite oxide, Li 2+a M(I) 2-b Ti 6-c M(II) d O 14+σ Examples of compounds represented by the formula (I) include compounds represented by the formula (I) above. Here, M(I) is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M(II) is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. Specific examples of orthorhombic titanium-containing composite oxides include Li 2+a Na2Ti6O 14 (0≦a≦6).

[0081] The proportion of the niobium titanium composite oxide in the negative electrode active material is, for example, 50 mass % or more, and preferably 80 mass % or more.

[0082] The negative electrode active material may be a single primary particle, a secondary particle formed by aggregation of primary particles, or a mixture of primary particles and secondary particles.

[0083] The average particle size (D50) of the negative electrode active material is preferably in the range of 1 μm or more and 10 μm or less. The particle shape may be either granular or fibrous. The average particle size of the active material particles can be measured using, for example, a laser diffraction / scattering particle size distribution analyzer. For example, a laser diffraction / scattering particle size distribution analyzer (model: MT3000-II) manufactured by Microtrackbell Co., Ltd. can be used as the measuring device.

[0084] The conductive material is blended to improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive materials include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive material, or two or more may be used in combination. Alternatively, instead of using a conductive material, the surfaces of the active material particles may be coated with carbon or an electronically conductive inorganic material.

[0085] The binder is blended to fill gaps between the dispersed active materials and to bind the active materials and the negative electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination.

[0086] The blending ratios of the negative electrode active material, conductive material, and binder in the negative electrode mixture layer can be appropriately changed depending on the application of the negative electrode. For example, the negative electrode active material, conductive material, and binder are preferably blended in ratios of 70% by mass or more and 96% by mass or less, 2% by mass or more and 28% by mass or less, and 2% by mass or more and 28% by mass or less, respectively. By setting the amount of conductive material to 2% by mass or more, the current collection performance of the negative electrode mixture layer can be improved. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient binding between the negative electrode mixture layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to set the amounts of conductive material and binder to 28% by mass or less, respectively, in order to achieve high capacity.

[0087] The density of the negative electrode mixture layer (excluding the current collector) is 2.1 g / cm 3 More than 3.0g / cm 3It is preferable that the following conditions are met. A negative electrode with the density of the negative electrode composite material layer within this range is excellent in energy density and electrolyte retention. The electrode density of the negative electrode composite material layer is more preferably 2.4 g / cm 3 or more and 2.8 g / cm 3 or less.

[0088] The negative electrode can be manufactured, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of a composite material layer and a current collector. Then, this laminate is pressed. In this way, a negative electrode before the first charge is manufactured. After assembling a secondary battery using the negative electrode before the first charge, a negative electrode having the above-described first protrusion can be manufactured by performing the first charge according to the method described below.

[0089] (2) Positive electrode The positive electrode can include a positive electrode current collector and a positive electrode composite material layer. The positive electrode composite material layer can be formed on one or both sides of the positive electrode current collector. The positive electrode composite material layer can include a positive electrode active material, and optionally a conductive agent and a binder. A polymer fiber layer described below can be laminated on the positive electrode composite material layer. The positive electrode with the polymer fiber layer laminated thereon can be a positive electrode structure.

[0090] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain one kind of compound alone as the positive electrode active material, or may contain a combination of two or more kinds of compounds. Examples of the oxide and the sulfide include compounds into which Li or Li ions can be inserted and desorbed.

[0091] Such compounds include, for example, manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (for example, Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (for example, Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (for example, Lix CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≤ 1, Li x Fe 1-y Mn y PO4; 0 < x ≤ 1, 0 < y < 1, Li x CoPO4; 0 < x ≤ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) is included.

[0092] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; 0 < x ≤ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≤ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), lithium manganese cobalt composite oxide (e.g., Li x Mny Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; 0 < x ≤ 1), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included. When using these compounds as the positive electrode active material, the positive electrode potential can be increased.

[0093] When using a room temperature molten salt as the electrolyte of the battery, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li x VPO4F (0 ≤ x ≤ 1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof. Since these compounds have low reactivity with the room temperature molten salt, the cycle life can be improved. Details of the room temperature molten salt will be described later.

[0094] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material with a primary particle size of 1 μm or less can smoothly progress the solid-state diffusion of lithium ions.

[0095] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. A positive electrode active material with a specific surface area of 0.1 m 2 / g or more can sufficiently secure the Li ion storage and release sites. A positive electrode active material with a specific surface area of 10 m 2 / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0096] The binder is blended to fill gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0097] The conductive agent is blended to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination as the conductive agent. The conductive agent may also be omitted.

[0098] In the positive electrode mixture layer, the positive electrode active material and the binder are preferably mixed in proportions of 80% by mass to 98% by mass and 2% by mass to 20% by mass, respectively.

[0099] By using a binder amount of 2% by mass or more, sufficient electrode strength can be obtained. Furthermore, the binder can function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

[0100] When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably mixed in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

[0101] By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This low proportion can reduce decomposition of the electrolyte during high-temperature storage.

[0102] The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0103] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0104] The positive electrode current collector may also include a portion on the surface of which no positive electrode mixture layer is formed, and this portion can function as a positive electrode current collecting tab.

[0105] The positive electrode can be produced, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of a composite layer and the current collector. After that, this laminate is pressed. In this manner, the positive electrode is produced.

[0106] Alternatively, the positive electrode may be prepared by the following method: First, an active material, a conductive agent, and a binder are mixed to obtain a mixture, and then the mixture is formed into pellets. The pellets are then placed on a current collector to obtain a positive electrode.

[0107] (3) Electrolyte The electrolyte may be, for example, a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte. The liquid nonaqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0108] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoride (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), and lithium bistrifluoromethylsulfonylimide (LiN(CFSO)), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and LiPF is most preferred.

[0109] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or in combination.

[0110] The gel-like non-aqueous electrolyte is prepared by combining a liquid non-aqueous electrolyte with a polymeric material, such as polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

[0111] Alternatively, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room temperature molten salts containing lithium ions (ionic melts), polymer solid electrolytes, inorganic solid electrolytes, and the like may be used as the nonaqueous electrolyte.

[0112] Room-temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C or higher and 25°C or lower). Room-temperature molten salts include room-temperature molten salts that exist as a liquid on their own, room-temperature molten salts that become liquid when mixed with an electrolyte salt, room-temperature molten salts that become liquid when dissolved in an organic solvent, and mixtures of these. Generally, the melting point of room-temperature molten salts used in secondary batteries is 25°C or lower. Furthermore, organic cations generally have a quaternary ammonium skeleton.

[0113] The solid polymer electrolyte is prepared by dissolving an electrolyte salt in a polymer material and solidifying it.

[0114] The inorganic solid electrolyte is a solid material that has Li-ion conductivity.

[0115] The electrolyte may be an aqueous electrolyte containing water.

[0116] The aqueous electrolyte includes an aqueous solvent and an electrolyte salt. The aqueous electrolyte is, for example, liquid. The liquid aqueous electrolyte is an aqueous solution prepared by dissolving an electrolyte salt as a solute in an aqueous solvent. The aqueous solvent is, for example, a solvent containing 50% or more by volume of water. The aqueous solvent may be pure water.

[0117] The aqueous electrolyte may be a gel-like aqueous electrolyte obtained by combining an aqueous electrolytic solution with a polymeric material, such as polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), or polyethylene oxide (PEO).

[0118] The aqueous electrolyte preferably contains 1 mol or more of aqueous solvent per 1 mol of solute salt, and more preferably 3.5 mol or more of aqueous solvent per 1 mol of solute salt.

[0119] The presence of water in aqueous electrolytes can be confirmed by GC-MS (Gas Chromatography-Mass Spectrometry). The salt concentration and water content in aqueous electrolytes can be calculated using, for example, ICP (Inductively Coupled Plasma) optical emission spectrometry. The molar concentration (mol / L) can be calculated by weighing a specified amount of aqueous electrolyte and calculating the salt concentration. Furthermore, the number of moles of solute and solvent can be calculated by measuring the specific gravity of the aqueous electrolyte.

[0120] The aqueous electrolyte is prepared, for example, by dissolving an electrolyte salt in an aqueous solvent at a concentration of 1 to 12 mol / L.

[0121] To suppress electrolysis of the aqueous electrolyte, LiOH or Li2SO4 can be added to adjust the pH, preferably 3-13, more preferably 4-12.

[0122] (4) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene, because these porous films melt at a certain temperature and can interrupt current.

[0123] (5) Exterior materials The exterior member may be, for example, a container made of a laminate film or a metal container.

[0124] The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0125] The laminate film is a multilayer film containing multiple resin layers and metal layers interposed between the resin layers. The resin layers include polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it by heat fusion.

[0126] The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0127] The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of these metals is preferably 100 mass ppm or less.

[0128] The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be appropriately selected depending on the battery dimensions and the intended use of the battery.

[0129] (6) Negative terminal The negative electrode terminal can be formed from a material that is electrochemically stable at the Li absorption / desorption potential of the above-mentioned negative electrode active material and has electrical conductivity. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum or an aluminum alloy is preferably used as the material for the negative electrode terminal. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0130] (7) Positive terminal The positive electrode terminal has a potential range of 3V to 4.5V relative to the redox potential of lithium (vs. Li / Li + ) and can be formed from a material that is electrically stable and conductive. Examples of materials for the positive electrode terminal include aluminum and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0131] (8) Secondary battery type The secondary battery according to this embodiment can be used in various forms, such as a rectangular, cylindrical, flat, thin, or coin-shaped battery. It may also be a secondary battery having a bipolar structure. A secondary battery having a bipolar structure has the advantage that multiple serially connected cells can be fabricated from a single cell. The secondary battery may be a stacked secondary battery in which sheet-shaped negative electrodes and sheet-shaped positive electrodes are alternately stacked with a separator interposed therebetween.

[0132] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0133] Fig. 12 is a partially cutaway perspective view schematically showing an example of a secondary battery according to an embodiment, and Fig. 13 is an enlarged cross-sectional view of part B of the secondary battery shown in Fig. 12.

[0134] 12 and 13 includes a stacked electrode group 1 shown in Fig. 12 and 13, an exterior member 2 shown in Fig. 12, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 2. The electrolyte is held in the electrode group 1.

[0135] The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0136] The electrode group 1 is a laminated electrode group, as shown in Fig. 13. The laminated electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately laminated with separators 4 interposed therebetween.

[0137] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode composite layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode composite layer 5b supported on both sides of the positive electrode current collector 5a.

[0138] The negative electrode current collector 3a of each negative electrode 3 includes a portion 3c on one side where the negative electrode composite layer 3b is not supported on any surface. This portion 3c serves as a negative electrode current collector tab. As shown in FIG. 13 , the portion 3c serving as the negative electrode current collector tab does not overlap with the positive electrode 5. The multiple negative electrode current collector tabs (portions 3c) are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is pulled out to the outside of the exterior member 2.

[0139] Although not shown, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode composite layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. Like the negative electrode current collector tab (portion 3c), the positive electrode current collector tab does not overlap with the negative electrode 3. The positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab (portion 3c). The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is drawn out to the outside of the exterior member 2.

[0140] Another example of a laminated electrode group is shown in Figure 14. Figure 14 is an exploded perspective view of the electrode group. This electrode group has a zigzag folded separator 4 and a rectangular positive electrode 5 and negative electrode 3. A negative electrode 31 is stacked on the top layer of the separator 4. Furthermore, a positive electrode 51, a negative electrode 32, a positive electrode 52, and a negative electrode 33 are inserted between the folded separators 4 in this order from top to bottom.

[0141] <Secondary battery manufacturing method> The secondary battery according to the embodiment can be manufactured, for example, by the method described below.

[0142] One or more negative electrodes and one or more positive electrodes are fabricated by the method described above. Separately, one or more strip-shaped separators are prepared. For example, as described with reference to FIGS. 12 and 13, the negative electrodes and positive electrodes are alternately stacked with the separators interposed therebetween to fabricate a stacked electrode group.

[0143] The electrode group thus produced is assembled into a housing made of a multilayer film including multiple resin layers and metal layers interposed between the resin layers, and then subjected to a drying process. After that, for example, a liquid electrolyte is injected, and the housing is heat-sealed to produce a secondary battery before initial charging.

[0144] Next, the secondary battery is subjected to initial charging while being restrained before initial charging. An example of the restraining mode of a secondary battery will be described with reference to FIGS. 15 to 17. When the secondary battery is subjected to initial charging, lithium ions are inserted into the niobium-titanium composite oxide contained in the negative electrode active material, causing the negative electrode composite layer to expand. This causes the negative electrode composite layer to expand both in the thickness direction and in the in-plane direction of the layer. However, by restraining the main surfaces of the stacked electrode group from the outside of the exterior member of the secondary battery, the expansion width in the thickness direction can be controlled to a predetermined value or less. In this way, the negative electrode composite layer cannot expand beyond the restrained width in the thickness direction, and the corresponding expansion volume expands in the in-plane direction. In this way, a first protrusion satisfying the above formula (1) can be formed on at least a portion of the end of the negative electrode composite layer.

[0145] Fig. 15 is a plan view schematically showing a stack 70 including a secondary battery before initial charging and a restraining jig 60. Fig. 16 is a cross-sectional view taken along line XVI-XVI of the stack 70 shown in Fig. 15. Fig. 17 is a cross-sectional view schematically showing a state after initial charging of the secondary battery included in the stack of Fig. 16.

[0146] One method for restraining the secondary battery 100 is to restrain the secondary battery 100, which has a flattened rectangular parallelepiped shape, from the outside using two restraining jigs 60a and 60b, as shown in Figures 15 and 16. The secondary battery 100 shown in Figure 16 is a secondary battery including the stacked electrode group 1 described with reference to Figures 12 and 13, for example. However, in Figure 16, the negative electrode terminal 6 and the positive electrode terminal 7 are not shown.

[0147] The stack 70 includes a secondary battery 100, two or more restraining jigs 60a and 60b, two or more bake plates 61a and 61b, two or more restraining means 62, and two or more spacers 63a and 63b.

[0148] 15 to 17, a secondary battery 100 is restrained by restraining jigs 60a and 60b via bake plates 61a and 61b. The secondary battery 100 has a flattened rectangular parallelepiped shape and has two main surfaces, namely, a front surface 101 and a back surface 102. The front surface 101 and the back surface 102 face the bake plates 61a and 61b, respectively.

[0149] Examples of the restraining jigs 60a and 60b include metal plates made of metal such as stainless steel (SUS) or aluminum. In the stack 70 shown in FIGS. 15 to 17, two restraining jigs 60 each sandwich a secondary battery 100 via a bakelite plate 61. The two restraining jigs 60 are fixed to each other by spacers 63a and 63b, maintaining a predetermined distance between them. The method for fixing the restraining jigs 60a and 60b to each other is not particularly limited, but as an example, they are fixed by fastening restraining means 62 such as bolts and nuts. The restraining means 62 fixes the restraining jigs 60a and 60b to each other via the spacers 63a and 63b, etc., toward each other. The spacers may be, for example, rigid bodies such as bakelite made of phenolic resin or elastic bodies such as elastomers. The restraining jigs 60a and 60b may have through-holes at predetermined positions through which the restraining means 62 such as bolts and nuts can be inserted.

[0150] 15 and 16, which show the state before the initial charge, secondary battery 100 is placed on bake plate 61b. Therefore, back surface 102 of secondary battery 100 is in contact with bake plate 61b. Meanwhile, front surface 101 of secondary battery 100 is spaced apart from bake plate 61a. The thickness of secondary battery 100 before the initial charge is defined as the distance tB between front surface 101 and back surface 102. Although not shown in FIG. 16, the total thickness of at least one negative electrode composite layer present in secondary battery 100 before the initial charge is defined as tC.

[0151] In the laminate 70 before the initial charge, the distance between the main surface of one bake plate 61a and the main surface of the other bake plate 61b is set to a value obtained by adding the value tCx (where x is greater than 0% and less than or equal to 25%) obtained when the negative electrode composite layer 3b, having a total thickness tC, expands in the thickness direction at a thickness coefficient x% and the above-mentioned tB, i.e., tB + tCx. The value tB + tCx is also referred to as the "constraint thickness." The thickness coefficient x may be in the range of 5% to 25%, 5% to 20%, or 5% to 15%.

[0152] When the secondary battery 100 is initially charged, at least one negative electrode composite layer present in the secondary battery 100 expands in the thickness direction. Due to this expansion, the thickness tB of the secondary battery 100 increases to a thickness tB' as shown in FIG. 17. The thickness tB' has a value that is the same as or approximately the same as the constrained thickness tB+tCx. In the expanded secondary battery 100, the front surface 101 is in contact with the bake plate 61a, and the back surface 102 may be in contact with the bake plate 61b. However, even if the front surface 101 and the back surface 102 of the secondary battery 100 are not in contact with the bake plate after the initial charge, the negative electrode composite layer may have a first protrusion.

[0153] The thickness tB of secondary battery 100 before the initial charge is, for example, in the range of 400 μm to 60,000 μm. The total thickness tC of at least one negative electrode composite layer present in secondary battery 100 before the initial charge is, for example, in the range of 50 μm to 30,000 μm. If tB and tC are too small, the energy density may become too small, which is not preferable. If tB and tC are too large, the temperature unevenness inside the secondary battery may increase, which may reduce the capacity retention rate, which is not preferable.

[0154] The constraint thickness tB+tCx is, for example, in the range of 400 μm to 67,500 μm. If the thickness coefficient x or the constraint thickness tB+tCx is too small, the secondary battery may be damaged, which is undesirable. In this case, the size of the protrusion of the negative electrode mixture layer from the end surface of the current collector tends to exceed 1 mm, which is also undesirable. If the thickness coefficient x or the constraint thickness tB+tCx is too large, the effect of constraining the secondary battery is unlikely to be achieved. In other words, the margin for expansion of the negative electrode mixture layer in the thickness direction is too large, which may make it difficult for the negative electrode mixture layer to expand in the in-plane direction.

[0155] By adjusting parameters such as the thickness of the negative electrode current collector, the thickness and electrode density of the negative electrode composite layer, and the thickness coefficient x in a composite manner, the protrusion lengths and shapes of the first to fourth protrusions can be controlled.

[0156] For example, by decreasing the value of the thickness coefficient x, it is possible to promote the expansion of the negative electrode mixture layer 3b in the in-plane direction during initial charging, and therefore the protrusion lengths of the first to fourth protrusions can be increased. On the other hand, by increasing the value of the thickness coefficient x, it is possible to suppress the expansion of the negative electrode mixture layer 3b in the in-plane direction during initial charging, and therefore the protrusion lengths of the first to fourth protrusions can be reduced.

[0157] 15 to 17 have described a method of using spacers to restrain the secondary battery 100 at a predetermined restraint thickness, i.e., a restraint method using fixed size restraint. However, the secondary battery 100 according to the embodiment may be restrained by constant pressure restraint as exemplified in Fig. 18. In constant pressure restraint, the fastening torque is controlled using restraint means such as bolts and nuts, rather than using spacers to control the restraint thickness tB+tCx.

[0158] The laminate 70 shown in FIG. 18 has the same configuration as the laminate described with reference to FIGS. 15 and 16, except that it does not include spacers. The laminate 70 shown in FIG. 18 illustrates a case in which the front surface 101 and back surface 102 of the secondary battery 100 before initial charging are in contact with the bake plates 61a and 61b, respectively. In constant pressure restraint, the thickness coefficient x may be 0 as described above. Even if the thickness coefficient x is 0, the restraining force applied to the main surface of the secondary battery (the main surface of the negative electrode composite layer) can be controlled by controlling the magnitude of the fastening torque. In other words, the length of the protrusion generated by the expansion of the negative electrode composite layer can be controlled. An excessively large fastening torque is not preferable because it can damage the secondary battery 100.

[0159] Even in the case of constant pressure restraint, the thickness coefficient x does not have to be 0. In this case, the thickness coefficient x can be in the range of 0%≦x≦25%.

[0160] For example, a plate in which a resin such as phenolic resin is laminated on a base material such as paper or cloth can be used as the bakelite board 61. The thickness of the bakelite board 61 is, for example, 1 mm to 40 mm.

[0161] By interposing the bake plate 61 between the metal plate serving as a restraining jig and the secondary battery, deformation of the metal plates can be suppressed when the metal plates are fastened together, and therefore uniform pressure can be applied to the entire flat portion of the secondary battery 100, and ultimately the stacked electrode group 1 housed in the exterior member 2.

[0162] An example of dimensions will be described for the case where the secondary battery according to the embodiment has a flattened rectangular parallelepiped shape. For example, the width of the secondary battery 100 (exterior member 2) in the X-axis direction shown in Fig. 16 is in the range of 5 cm to 100 cm. The length of the secondary battery 100 (exterior member 2) in the Y-axis direction is in the range of 5 cm to 100 cm.

[0163] The initial charging conditions are not particularly limited. For example, the following conditions are adopted. The secondary battery is charged at a current value of 0.1C to 2.0C at 25°C until the battery voltage reaches 2.0V to 3.0V. Note that the current value during charging is expressed in a unit where the current value at which the SOC (State of Charge) of the secondary battery becomes 0% in 1 hour when the secondary battery is discharged from a state where the SOC is 100% is defined as 1C. After the initial charging, aging may be performed as necessary.

[0164] According to the first embodiment, a secondary battery is provided. The secondary battery includes a negative electrode, a positive electrode, and an electrolyte. The negative electrode includes a negative electrode current collector containing aluminum, and a negative electrode composite material layer laminated on the negative electrode current collector and having a front surface and a back surface. The negative electrode current collector has a thickness of 8 μm or more and 18 μm or less, and has a first current collector end face extending along the lamination direction of the negative electrode current collector and the negative electrode composite material layer. The negative electrode composite material layer contains a niobium titanium composite oxide as a negative electrode active material, and has a first protruding portion protruding along a first direction orthogonal to the lamination direction from the first current collector end face. The protruding length A1 of the first protruding portion satisfies 0 mm < A1 ≤ 1.0 mm. In the negative electrode included in the secondary battery according to the embodiment, in the vicinity of the end of the negative electrode current collector, the front surface or the back surface of the negative electrode current collector is covered with the negative electrode composite material layer. Therefore, an internal short circuit between the negative electrode and the positive electrode is less likely to occur. As a result, according to the secondary battery according to the embodiment, the frequency of defects due to self-discharge can be reduced.

[0165] (Second Embodiment) According to the second embodiment, a battery pack is provided. The battery pack according to the second embodiment includes a plurality of secondary batteries according to the first embodiment.

[0166] In the battery pack according to the embodiment, each single battery may be electrically connected in series or in parallel, or may be arranged in a combination of series connection and parallel connection.

[0167] Next, an example of the battery pack according to the embodiment will be described while referring to the drawings.

[0168] Fig. 19 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. The battery pack 200 shown in Fig. 19 includes five cells 100a-100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five cells 100a-100e is a secondary battery according to the first embodiment.

[0169] The bus bar 21 connects, for example, the negative electrode terminal 6 of one cell 100a to the positive electrode terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four bus bars 21. That is, the battery pack 200 in FIG. 19 is a five-series battery pack. Although an example is not shown, in a battery pack including a plurality of cells electrically connected in parallel, the plurality of cells can be electrically connected by, for example, connecting the negative electrode terminals to each other by a bus bar and connecting the positive electrode terminals to each other by a bus bar.

[0170] The positive terminal 7 of at least one of the five cells 100a-100e is electrically connected to a positive electrode lead 22 for external connection. The negative terminal 6 of at least one of the five cells 100a-100e is electrically connected to a negative electrode lead 23 for external connection.

[0171] The battery pack according to the second embodiment includes the secondary battery according to the first embodiment. Therefore, the battery pack according to the second embodiment can reduce the frequency of defects caused by self-discharge.

[0172] (Third embodiment) According to a third embodiment, a battery pack is provided. This battery pack includes the battery assembly according to the second embodiment. This battery pack may include a single secondary battery according to the first embodiment instead of the battery assembly according to the second embodiment.

[0173] The battery pack according to the embodiment may further include a protection circuit. The protection circuit has a function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device (e.g., electronic device, automobile, etc.) that uses the battery pack as a power source may be used as the protection circuit for the battery pack.

[0174] The battery pack according to the embodiment may further include an external terminal for current supply. The external terminal for current supply is for outputting current from the secondary battery to the outside and / or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminal for current supply. When charging the battery pack, charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminal for current supply.

[0175] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0176] Fig. 20 is an exploded perspective view schematically illustrating an example of a battery pack according to an embodiment, and Fig. 21 is a block diagram illustrating an example of an electric circuit of the battery pack shown in Fig. 20.

[0177] The battery pack 300 shown in FIGS. 20 and 21 includes a container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

[0178] The storage container 31 shown in Fig. 20 is a bottomed, square container having a rectangular bottom. The storage container 31 is configured to be able to accommodate a protective sheet 33, a battery pack 200, a printed wiring board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the storage container 31 to accommodate the battery pack 200 and other components. Although not shown, the storage container 31 and the lid 32 are provided with openings or connection terminals for connection to external devices and the like.

[0179] The battery pack 200 includes a plurality of cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0180] At least one of the plurality of cells 100 is the secondary battery according to the first embodiment. The plurality of cells 100 are electrically connected in series as shown in FIG. 21 . The plurality of cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the plurality of cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0181] The adhesive tape 24 fastens the plurality of cells 100 together. Heat-shrinkable tape may be used to secure the plurality of cells 100 together instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both side surfaces of the battery pack 200, and the heat-shrinkable tape is wrapped around the cells 100, and the heat-shrinkable tape is then thermally shrunk to bind the plurality of cells 100 together.

[0182] One end of the positive electrode lead 22 is connected to the battery pack 200. One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 23 is connected to the battery pack 200. One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more cells 100.

[0183] The printed wiring board 34 is installed along one of the shorter sides of the inner surface of the container 31. The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wires 342a and 343a, an external terminal 350 for supplying current, a positive wire (positive wire) 348a, and a negative wire (negative wire) 348b. One main surface of the printed wiring board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

[0184] The other end 22a of the positive electrode lead 22 is electrically connected to the positive electrode connector 342. The other end 23a of the negative electrode lead 23 is electrically connected to the negative electrode connector 343.

[0185] The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 346.

[0186] The external terminals 350 for applying current are fixed to the other main surface of the printed wiring board 34. The external terminals 350 for applying current are electrically connected to devices located outside the battery pack 300. The external terminals 350 for applying current include a positive terminal 352 and a negative terminal 353.

[0187] The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via a positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via a negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via a wiring 343a. The protection circuit 346 is also electrically connected to each of the plurality of single cells 100 via wiring 35.

[0188] The protective sheet 33 is disposed on both inner surfaces of the long sides of the container 31 and on the inner surface of the short side that faces the printed wiring board 34 across the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0189] The protection circuit 346 controls charging and discharging of the plurality of cells 100. Furthermore, the protection circuit 346 cuts off the electrical connection between the protection circuit 346 and external terminals 350 (positive terminal 352, negative terminal 353) for supplying electricity to an external device, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from each cell 100 or the battery pack 200.

[0190] An example of the detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of the cell 100 is equal to or higher than a predetermined temperature. An example of the detection signal transmitted from each cell 100 or the battery pack 200 is a signal indicating that overcharge, overdischarge, or overcurrent of the cell 100 is detected. When detecting overcharge or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

[0191] The protection circuit 346 may be a circuit included in a device (such as an electronic device or an automobile) that uses the battery pack 300 as a power source.

[0192] As described above, the battery pack 300 is also provided with the external terminals 350 for current application. Therefore, the battery pack 300 can output current from the battery assembly 200 to an external device and input current from the external device to the battery assembly 200 via the external terminals 350 for current application. In other words, when the battery pack 300 is used as a power source, the current from the battery assembly 200 is supplied to the external device via the external terminals 350 for current application. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 via the external terminals 350 for current application. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as the charging current from the external device.

[0193] The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive electrode lead 22 and the negative electrode lead 23 may be used as the positive and negative terminals of the external terminals for supplying current, respectively.

[0194] Such a battery pack is used in applications requiring excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used, for example, as a power source for electronic devices, a stationary battery, or an on-board battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

[0195] The battery pack according to the third embodiment includes the secondary battery according to the first embodiment or the battery assembly according to the second embodiment. Therefore, according to the third embodiment, it is possible to provide a battery pack including a secondary battery or battery assembly that has a low frequency of defects due to self-discharge.

[0196] (Fourth embodiment) According to a fourth embodiment, a vehicle is provided, which is equipped with the battery pack according to the third embodiment.

[0197] In the vehicle according to the fourth embodiment, the battery pack recovers, for example, regenerative energy for powering the vehicle. The vehicle may include a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

[0198] Examples of the vehicle according to the fourth embodiment include two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, power-assisted bicycles, and railcars.

[0199] The mounting position of the battery pack in the vehicle according to the fourth embodiment is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

[0200] The vehicle according to the fourth embodiment may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, in parallel, or in a combination of series and parallel connections. For example, if each battery pack includes a battery assembly, the battery assembly may be electrically connected in series, in parallel, or in a combination of series and parallel connections. Alternatively, if each battery pack includes a single battery, the batteries may be electrically connected in series, in parallel, or in a combination of series and parallel connections.

[0201] Next, an example of a vehicle according to a fourth embodiment will be described with reference to the drawings.

[0202] FIG. 22 is a partial perspective view schematically illustrating an example of a vehicle according to an embodiment.

[0203] A vehicle 400 shown in Fig. 22 includes a vehicle body 40 and a battery pack 300 according to the embodiment. In the example shown in Fig. 22, the vehicle 400 is a four-wheeled automobile.

[0204] The vehicle 400 may be equipped with a plurality of battery packs 300. In this case, the batteries (for example, single cells or assembled batteries) included in the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

[0205] 22 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in the front of the vehicle body 40. As described above, the battery pack 300 may be mounted, for example, at the rear of the vehicle body 40 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for powering the vehicle 400.

[0206] Next, with reference to FIG. 23, an embodiment of a vehicle according to the fourth embodiment will be described.

[0207] Fig. 23 is a diagram that schematically shows an example of a control system related to an electrical system in a vehicle according to Embodiment 4. A vehicle 400 shown in Fig. 23 is an electric vehicle.

[0208] The vehicle 400 shown in Figure 23 comprises a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a higher-level control device of the vehicle power supply 41, an external terminal (terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45.

[0209] Vehicle 400 has vehicle power supply 41 mounted, for example, in the engine compartment, at the rear of the vehicle body, or under the seat. Note that in vehicle 400 shown in Fig. 23, the mounting location of vehicle power supply 41 is shown schematically.

[0210] The vehicle power supply 41 includes a plurality of (for example, three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0211] The battery pack 300a includes an assembled battery 200a and an assembled battery monitoring device 301a (for example, a voltage temperature monitor (VTM)). The battery pack 300b includes an assembled battery 200b and an assembled battery monitoring device 301b. The battery pack 300c includes an assembled battery 200c and an assembled battery monitoring device 301c. The battery packs 300a-300c are the same as the battery pack 300 described above, and the assembled batteries 200a-200c are the same as the assembled battery 200 described above. The assembled batteries 200a-200c are electrically connected in series. The battery packs 300a, 300b, and 300c can each be removed independently and replaced with another battery pack 300.

[0212] Each of the assembled batteries 200a-200c includes a plurality of unit cells connected in series. At least one of the unit cells is the secondary battery according to the first embodiment. Each of the assembled batteries 200a-200c is charged and discharged via a positive terminal 413 and a negative terminal 414.

[0213] The battery management device 411 communicates with the assembled battery monitoring devices 301a-301c and collects information on the voltage, temperature, etc. of each of the cells 100 included in the assembled batteries 200a-200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information on the maintenance of the vehicle power supply 41.

[0214] The battery management unit 411 and the assembled battery monitoring units 301a-301c are connected via a communication bus 412. In the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management unit 411 and one or more assembled battery monitoring units 301a-301c). The communication bus 412 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

[0215] The battery pack monitoring devices 301a-301c measure the voltage and temperature of each of the cells constituting the battery packs 200a-200c based on commands received through communication from the battery management device 411. However, the temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all the cells.

[0216] The vehicle power supply 41 may also have an electromagnetic contactor (e.g., a switch device 415 shown in FIG. 23) that switches between electrical connection and disconnection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that is turned on when the assembled batteries 200a-200c are being charged, and a main switch (not shown) that is turned on when the output from the assembled batteries 200a-200c is being supplied to a load. The pre-charge switch and the main switch each include a relay circuit (not shown) that is switched on or off by a signal supplied to a coil disposed near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

[0217] The inverter 44 converts the input DC voltage into a three-phase alternating current (AC) high voltage for driving the motor. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. The inverter 44 is controlled based on control signals from the battery management unit 411 or the vehicle ECU 42, which controls the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

[0218] The drive motor 45 is rotated by the electric power supplied from the inverter 44. The drive force generated by the rotation of the drive motor 45 is transmitted to the axles and drive wheels W via, for example, a differential gear unit.

[0219] Although not shown, vehicle 400 also includes a regenerative braking mechanism (regenerator). When vehicle 400 is braked, regenerative braking mechanism rotates drive motor 45 and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to inverter 44 and converted into direct current. The converted direct current is input to vehicle power supply 41.

[0220] One terminal of a connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of the connection line L1 is connected to a negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 in the battery management device 411 is provided on the connection line L1 between the negative terminal 414 and the negative input terminal 417.

[0221] One terminal of a connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41. The other terminal of the connection line L2 is connected to a positive input terminal 418 of the inverter 44. A switch device 415 is provided on the connection line L2 between the positive terminal 413 and the positive input terminal 418.

[0222] The external terminal 43 is connected to the battery management unit 411. The external terminal 43 can be connected to, for example, an external power source.

[0223] In response to operational inputs from the driver or the like, the vehicle ECU 42 coordinates with other management devices and control devices including the battery management device 411 to control the vehicle power supply 41, the switch device 415, the inverter 44, etc. Through the coordinated control of the vehicle ECU 42, etc., the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, thereby managing the entire vehicle 400. Data relating to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line.

[0224] The vehicle according to the fourth embodiment is equipped with the battery pack according to the third embodiment. Therefore, according to the fourth embodiment, it is possible to provide a vehicle equipped with a battery pack that has a low frequency of defects due to self-discharge.

[0225] [Example] Examples will be described below, but the embodiments are not limited to the examples described below.

[0226] Example 1 In Example 1, a secondary battery was fabricated according to the following procedure.

[0227] <Preparation of positive electrode> The positive electrode active material is LiNi with an average primary particle size of 2 μm. 0.5 Co 0.2 Mn 0.3 A slurry for forming a positive electrode composite layer was prepared by blending 90% by mass of O2 composite oxide, 5% by mass of graphite powder as a conductive agent, and 5% by mass of PVdF as a binder in an N-methyl-2-pyrrolidone (NMP) solvent. The blending amounts are each the mass relative to the mass of the positive electrode composite layer. The prepared slurry was applied to both sides of a 15 μm-thick aluminum alloy foil (purity 99.3%) and dried to obtain a laminate. This laminate was pressed to obtain a positive electrode composite layer with an electrode density of 3.2 g / cm on one side. 3 A positive electrode was prepared.

[0228] <Preparation of negative electrode> Monoclinic Nb2TiO7 (NTO) powder with an average particle size D50 of 5 μm was prepared as the negative electrode active material. The composite layer materials consisted of these active material particles, acetylene black powder as a conductive agent, carboxymethylcellulose (CMC) sodium salt powder as a thickener, and styrene-butadiene rubber (SBR) as a binder. The mass ratio of these materials was NTO:acetylene black:CMC:SBR = 93:5:1:1. These materials were mixed in the following order with stirring in pure water as the solvent to prepare a slurry: carboxymethylcellulose sodium salt was dissolved in pure water, and then SBR was added to obtain a dispersion. Acetylene black was dispersed in this dispersion, and finally NTO powder was dispersed and stirred to obtain a slurry. The resulting slurry was applied to both sides of a 15 μm-thick aluminum alloy foil (99.3% purity). The coating was dried to obtain a laminate consisting of a current collector and composite layer. This laminate was pressed to obtain an electrode density of 2.6 g / cm 3 A negative electrode was prepared.

[0229] <Preparation of electrolyte> A mixed solvent of propylene carbonate and diethyl carbonate in a volume ratio of 1:2 was prepared. LiPF6 was then dissolved in this mixed solvent to a concentration of 1.2 M to prepare a liquid nonaqueous electrolyte.

[0230] <Preparation of secondary battery> A plurality of positive electrodes and a plurality of negative electrodes prepared by the above procedure were prepared, and these were stacked with a separator made of a nonwoven fabric having a thickness of 20 μm interposed between the positive electrode and the negative electrode to prepare a stacked electrode group.

[0231] The obtained stacked electrode group was incorporated into an exterior member made of a multilayer film including a plurality of resin layers and a metal layer interposed between these resin layers, and vacuum dried for 8 hours in an environment of 120° C. Thereafter, the previously prepared electrolyte solution was poured into the exterior member, and the exterior member was heat-sealed to produce a secondary battery before initial charging.

[0232] <Attaching the restraint jig> A restraining jig was attached to the fabricated secondary battery, which had not yet been charged, by the method described with reference to Fig. 15 and Fig. 16. Specifically, both sides of the secondary battery, which had a flattened rectangular parallelepiped shape, were sandwiched between stainless steel plates via bake plates, and a spacer was further interposed between the stainless steel plates. The stainless steel plates were then fastened together with screws to fabricate a stack including secondary batteries restrained to a fixed size.

[0233] The thickness tB of the secondary battery before the initial charge was 1740 μm. The total thickness tC of the multiple negative electrode composite layers present in the secondary battery before the initial charge was 580 μm. The thickness coefficient x was set to 19.0%, and the constrained thickness tB + tCx was adjusted to 1850 μm.

[0234] <Initial charging / discharging and gas removal process> The laminated body including the restrained secondary battery was placed in a thermostatic chamber set at an internal temperature of 25°C. The battery was charged at a constant current of 0.2C in the thermostatic chamber until the battery voltage reached 3.00V. After the battery voltage reached 3.00V, further constant voltage charging was performed. The total charging time was 10 hours. After charging, the battery was kept in a resting state for 10 minutes. The secondary battery was then discharged at a constant current of 0.2C until the battery voltage reached 1.5V. The battery capacity was 1.5Ah.

[0235] The battery was then charged at a constant current of 1 C, and after the battery voltage reached 2.25 V, constant voltage charging was further performed. Charging was terminated when the charging current reached 0.05 C. The cell was then released from the restraints and subjected to a degassing process. Thus, the secondary battery according to Example 1 was produced.

[0236] Examples 2 and 3 Secondary batteries were fabricated in the same manner as in Example 1, except that the thickness coefficient x when constraining the secondary battery was changed as shown in Table 2 below.

[0237] Examples 4 to 6 The electrode density on one side of the negative electrode mixture layer is 2.8 g / cm 3 A secondary battery was fabricated in the same manner as in Example 1, except that the restraining conditions were changed as shown in Table 2.

[0238] Example 7 The electrode density on one side of the positive electrode mixture layer is 3.4 g / cm 3 A secondary battery was fabricated in the same manner as in Example 1, except that the restraining conditions were changed as shown in Table 2.

[0239] Examples 8 and 9 A secondary battery was fabricated in the same manner as in Example 1, except that the thickness tE of the negative electrode current collector was changed as shown in Table 1 below and the constraint conditions were changed as shown in Table 2.

[0240] Examples 10 and 11 A secondary battery was fabricated in the same manner as in Example 1, except that the electrode density on one side of the negative electrode mixture layer and the restraining conditions were changed as shown in Table 2.

[0241] (Comparative Examples 1 and 2) A secondary battery was fabricated in the same manner as in Example 1, except that the constraint conditions were changed as shown in Table 2.

[0242] (Comparative Examples 3 and 4) A secondary battery was fabricated in the same manner as in Example 1, except that the thickness tE of the negative electrode current collector was changed as shown in Table 1 and the constraint conditions were changed as shown in Table 2.

[0243] <Measurement of ΔOCV failure> Using the method described in each example above, 100 secondary batteries were fabricated, and the open-circuit voltage of each cell was measured 24 hours after the initial charge / discharge. This voltage was defined as V1. The open-circuit voltage of each cell was also measured 120 hours after the initial charge / discharge. This voltage was defined as V2. To determine whether a secondary battery had a ΔOCV defect, a secondary battery for which ΔV = V1 - V2 was -2 mV or less was determined to have a ΔOCV defect. According to this determination criteria, the number of ΔOCV defects among the 100 secondary batteries was counted.

[0244] <Measurement of the protrusion length of each protrusion> For one of the secondary batteries fabricated in each example after the initial charge / discharge, the secondary battery was disassembled according to the method described in the first embodiment, and the protrusion lengths A1 and A2 of the first and second protrusions of the negative electrode composite layer were measured. The first protrusion here means the protrusion on one of the pair of long sides. The second protrusion here means the protrusion on one of the pair of short sides.

[0245] The above results are summarized in Tables 1 and 2. In Tables 1 and 2, for convenience, the first protrusions and second protrusions of the negative electrode composite layer are treated as the long side and short side, respectively. However, this relationship may be reversed. That is, the long side and short side of the negative electrode composite layer may be treated as the second protrusions and the first protrusions, respectively. As described in the first embodiment, the secondary battery according to this embodiment has a protrusion from the current collector end face in at least a part of the end of the negative electrode composite layer.

[0246] In Table 2, the electrode density indicates the electrode density of the composite layer on one side of the negative electrode excluding the current collector.

[0247] [Table 1]

[0248] [Table 2]

[0249] For example, the following can be seen from Tables 1 and 2. As shown in Examples 1 to 11, when the negative electrode current collector had a thickness of 8 μm or more and 18 μm or less and the negative electrode composite layer had first protrusions of 0 mm to 1 mm, the frequency of ΔOCV defects was low.

[0250] In Comparative Example 1, the electrode density was 2.3 g / cm 3 This was a relatively low value, and there was an excessive expansion width (expansion margin) in the thickness direction before the first charge. As a result, the composite layer was difficult to expand in the in-plane direction, so no protrusions were formed on either the long or short side. In this Comparative Example 1, internal short circuits near the end faces of the negative electrode current collector were difficult to suppress, resulting in a large number of ΔOCV defects.

[0251] In Comparative Example 2, the electrode density was 2.9 g / cm 3In addition, the expansion width in the thickness direction (expansion margin) was excessively small before the first charge. As a result, the expansion in the in-plane direction proceeded excessively, and the length of the protrusions of the composite layer on both the long and short sides exceeded 1.0 mm. In Comparative Example 2, the number of ΔOCV defects was high. The reason for this is thought to be that the composite layer tended to break near the end face of the negative electrode current collector.

[0252] As shown in Comparative Example 3, when the thickness tE of the negative electrode current collector was less than 8 μm, the negative electrode current collector was prone to breakage, and the broken current collector was liberated into the electrolyte, which is thought to have resulted in a large number of ΔOCV defects.

[0253] In Comparative Example 4, the current collector thickness exceeded 18 μm. Therefore, it is believed that expansion in the in-plane direction was not promoted even when sizing constraint was performed, controlling the expansion width in the thickness direction (expansion margin) to, for example, the same level as in Example 2. In Comparative Example 4, the exposed portion of the end face of the current collector was large, which is thought to have increased internal short circuits and resulted in a large number of ΔOCV defects.

[0254] As shown in Example 4, by increasing the electrode density to a certain extent and controlling the expansion width (expansion margin) in the thickness direction to be small as a constraint, the composite layer that expands in the in-plane direction can be warped toward the current collector.

[0255] Furthermore, as shown in Examples 5 and 6, by increasing or decreasing the thickness coefficient while keeping the electrode density relatively high, it is possible to make only the corners (upper corners) that intersect with the surface of the negative electrode composite layer or only the corners (lower corners) that intersect with the back surface of the negative electrode composite layer round.

[0256] Electrode density is 2.4g / cm 3 ~2.8g / cm 3 In Examples 1 to 6 in which the ratio A1 / tE of the protrusion length of the primary protrusion to the thickness tE of the negative electrode current collector was within the range of 10 to 90, the frequency of ΔOCV defects was extremely low.

[0257] According to at least one embodiment and example described above, a secondary battery is provided. The secondary battery includes a negative electrode, a positive electrode, and an electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode composite material layer laminated on the negative electrode current collector and having a front surface and a back surface. The negative electrode current collector has a thickness of 8 μm or more and 18 μm or less, and has a first current collector end surface extending along the lamination direction of the negative electrode current collector and the negative electrode composite material layer. The negative electrode composite material layer contains a niobium titanium composite oxide as a negative electrode active material, and has a first protrusion protruding along a first direction orthogonal to the lamination direction from the first current collector end surface. The protrusion length A1 of the first protrusion satisfies 0 mm < A1 ≤ 1.0 mm. According to this secondary battery, the frequency of defects caused by self-discharge can be reduced.

[0258] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope. The invention described in the original claims of the present application is appended below. [1] A negative electrode comprising a negative electrode current collector and a negative electrode composite layer laminated on the negative electrode current collector and having a front surface and a back surface, a positive electrode, and an electrolyte, the secondary battery comprising: the negative electrode current collector has a thickness of 8 μm or more and 18 μm or less, and has a first current collector end face extending along the lamination direction of the negative electrode current collector and the negative electrode composite layer, the negative electrode composite layer contains a niobium titanium composite oxide as a negative electrode active material, and has a first protruding portion protruding along a first direction orthogonal to the lamination direction from the first current collector end face, the secondary battery in which the protruding length A1 of the first protruding portion satisfies 0 mm < A1 ≤ 1.0 mm. [2] The secondary battery according to [1], wherein at least a part of the first protruding portion has an R shape. [3] Both the negative electrode current collector and the negative electrode composite layer have a rectangular shape, the first current collector end face corresponds to one of the long side and the short side of the negative electrode current collector, the negative electrode current collector further has a second current collector end face corresponding to the other of the long side and the short side of the negative electrode current collector, the negative electrode composite layer has a second protruding portion protruding along a second direction orthogonal to the lamination direction from the second current collector end face, the secondary battery according to [1] or [2], in which the protruding length A2 of the second protruding portion satisfies 0 mm < A2 ≤ 1.0 mm. [4] The secondary battery according to any one of [1] to [3], in which the ratio A1 / tE of the protruding length A1 of the first protruding portion to the thickness tE of the negative electrode current collector is within the range of 5 to 100. [5] The electrode density of the negative electrode composite layer is 2.1 g / cm 3 ~3.0 g / cm 3 The secondary battery according to any one of [1] to [4], which is within the range. [6] A battery pack including the secondary battery according to any one of [1] to [5]. [7] An external terminal for energization, and a protection circuit The battery pack according to [6], which further includes. [8] Comprising a plurality of the secondary batteries, the battery pack according to [6] or [7], in which the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. [9] A vehicle equipped with the battery pack according to any one of [6] to [8].

[10] The vehicle described in [9], including a mechanism for converting the kinetic energy of the vehicle into regenerative energy. [Explanation of symbols]

[0259] REFERENCE SIGNS LIST 1...electrode group, 2...exterior member, 3...negative electrode, 3a...negative electrode current collector, 3a1...first current collector end face, 3a2...second current collector end face, 3a3...third current collector end face, 3a4...fourth current collector end face, 3b...negative electrode composite layer, 3b1...first composite layer end face, 3c...negative electrode current collecting tab, 4...separator, 5...positive electrode, 5a...positive electrode current collector, 5b...positive electrode composite layer, 6...negative electrode terminal, 7...positive electrode terminal, 11...first protrusion, 12...second protrusion, 13...third protrusion, 14...fourth protrusion, 15a...protrusion, 15 b...protrusion, 15c...protrusion, 15d...protrusion, 21...bus bar, 22...positive electrode lead, 22a...other end, 23...negative electrode lead, 23a...other end, 24...adhesive tape, 31...container, 32...lid, 33...protective sheet, 34...printed wiring board, 35...wiring, 40...vehicle body, 41...vehicle power supply, 43...external terminal, 44...inverter, 45...drive motor, 51...first direction, 52...second direction, 53...surface, 54...rear face, 55...surface, 56...rear face, 6 0...restraint jig, 60a...restraint jig, 60b...restraint jig, 61...bakelite board, 61a...bakelite board, 61b...bakelite board, 62...restraint means, 63a...spacer, 63b...spacer, 70...laminated body, 100...secondary battery, 101...surface, 102...back surface, 200...battery assembly, 300...battery pack, 301a...battery assembly monitoring device, 301b...battery assembly monitoring device, 301c...battery assembly monitoring device, 342...positive electrode side connector, 342a...wiring, 343...negative electrode side connector, 3 43a...wiring, 345...thermistor, 346...protection circuit, 348a...positive wiring, 348b...negative wiring, 350...external terminal for energizing, 352...positive terminal, 353...negative terminal, 400...vehicle, 411...battery management device, 412...communication bus, 413...positive terminal, 414...negative terminal, 415...switch device, 416...current detection unit (current detection circuit), 417...negative input terminal, 418...positive input terminal, 550...corner, 560...corner, W...drive wheel.

Claims

1. a negative electrode including a negative electrode current collector and a negative electrode mixture layer laminated on the negative electrode current collector and having a front surface and a back surface; A positive electrode and A secondary battery comprising an electrolyte, the negative electrode current collector has a thickness of 8 μm or more and 18 μm or less, and has a first current collector end surface extending along a stacking direction of the negative electrode current collector and the negative electrode composite material layer, the negative electrode mixture layer contains a niobium titanium composite oxide as a negative electrode active material, and has a first protrusion protruding from an end surface of the first current collector along a first direction perpendicular to the stacking direction, A secondary battery in which the protruding length A1 of the first protruding portion satisfies 0.1 mm≦A1≦1.0 mm.

2. The secondary battery according to claim 1 , wherein at least a portion of the first protrusion has an R-shape.

3. A secondary battery as described in claim 1, wherein at least one of the first protrusions, either a corner where the surface of the negative electrode composite layer intersects with the end face of the negative electrode composite layer or a corner where the back surface of the negative electrode composite layer intersects with the end face of the negative electrode composite layer, has an R-shape.

4. Both the negative electrode current collector and the negative electrode mixture layer have a rectangular shape, the end surface of the first current collector corresponds to one of the long sides and the short sides of the negative electrode current collector, the negative electrode current collector further includes a second current collector end surface corresponding to the other of the long side and the short side of the negative electrode current collector, the negative electrode mixture layer has a second protruding portion protruding from the end surface of the second current collector along a second direction perpendicular to the stacking direction, 4. The secondary battery according to claim 1, wherein a protruding length A2 of the second protruding portion satisfies 0 mm<A2≦1.0 mm.

5. The secondary battery according to any one of claims 1 to 4, wherein the ratio A1 / tE of the protrusion length A1 of the first protrusion to the thickness tE of the negative electrode current collector is in the range of (100 / 18) or more and 100 or less.

6. The electrode density of the negative electrode mixture layer is 2.1 g / cm 3 ~3.0 g / cm 3 The secondary battery according to any one of claims 1 to 5, wherein the range is

7. A battery pack comprising the secondary battery according to any one of claims 1 to 6.

8. An external terminal for applying current; Protection circuit and The battery pack according to claim 7, further comprising:

9. A battery includes a plurality of the secondary batteries, 9. The battery pack according to claim 7, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

10. A vehicle equipped with the battery pack according to any one of claims 7 to 9.

11. The vehicle according to claim 10, further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.

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