Electrodes, secondary batteries, battery packs, and vehicles

Abstract

To provide an electrode which can realize a secondary battery that has high flexibility and shows excellent rate characteristics.SOLUTION: An electrode 3 comprises: a current collector 3a which has a first surface 51 and a second surface 52 that is opposed to the first surface 51; and a first active material-containing layer 3b1 which is laminated on one of the first surface 51 and the second surface 52 of the current collector 3a and contains a plurality of first active material particles. The first active material-containing layer 3b1 includes a first rear surface 61 that is in contact with the current collector 3a, and a first surface 62 that is located on the opposite side to the first rear surface 61. A volume reference average particle diameter D50 of the plurality of first active material particles is within a range of 1.1 μm to 2.5 μm. In a cross section image obtained by observing at a magnification of 5,000 using a scanning electron microscope for a cross section of the electrode 3, a number proportion of particles whose cross-sectional area is within a range of 0.1 μm2 to 0.2 μm2 of the plurality of first active material particles is lower in a specific region A than in a specific region B.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to electrodes, secondary batteries, battery packs, and vehicles. [Background technology]

[0002] In recent years, research and development of secondary batteries, such as lithium-ion batteries and other non-aqueous electrolyte secondary batteries, has been actively pursued as high-energy-density batteries. Secondary batteries, including non-aqueous electrolyte secondary batteries, are expected to be used as power sources for vehicles such as hybrid electric vehicles and electric vehicles, and for uninterruptible power supplies in mobile phone base stations. Therefore, secondary batteries are required to excel not only in high energy density but also in other performance aspects such as rapid charge / discharge performance and long-term reliability. For example, secondary batteries capable of rapid charge / discharge not only significantly reduce charging time but also enable improved power performance in vehicles such as hybrid electric vehicles and efficient recovery of regenerative energy. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-102260 [Patent Document 2] Japanese Patent Publication No. 2017-084769 [Non-patent literature]

[0004] [Non-Patent Document 1] Dr. Michael et al., Image Processing with ImageJ, Reprinted from the July 2004 issue of Biophotonics International copyrighted by Laurin Publishing Co. INC. [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide an electrode capable of realizing a secondary battery that has high flexibility and excellent rate characteristics, a secondary battery equipped with this electrode, a battery pack equipped with this secondary battery, and a vehicle equipped with this battery pack. [Means for solving the problem]

[0006] According to the embodiment, an electrode is provided. The electrode comprises a current collector having a first surface and a second surface facing the first surface, and a first active material containing layer laminated on one of the first and second surfaces of the current collector and containing a plurality of first active material particles. The first active material containing layer has a first back surface in contact with the current collector and a first front surface located on the opposite side of the first back surface. The volume-based average particle diameter D50 of the plurality of first active material particles is in the range of 1.1 μm to 2.5 μm. The first active material containing layer includes a region A defined from the first back surface to a position 10% of the total thickness, and a region B defined from the position 10% of the total thickness to the first surface, when the total thickness from the first back surface to the first front surface is 100%. In the cross-sectional image obtained by observing the cross-section of the electrode along the stacking direction of the current collector and the first active material-containing layer at 5,000x magnification using a scanning electron microscope, among the multiple first active material particles, those with a cross-sectional area of ​​0.1 μm² 2 The proportion of particles within the range of ~0.2 μm² is lower in region A compared to region B. The average particle size D50 of the first active material particles contained in region A is larger than that of the first active material particles contained in region B. The density of the first electrode in the first active material-containing layer is 2.2 g / cm³. 3 -2.9 g / cm³ 3 It is within the range.

[0007] According to another embodiment, a secondary battery is provided. The secondary battery comprises a positive electrode, a negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode is an electrode according to the embodiment.

[0008] According to another embodiment, a battery pack is provided. The battery pack includes a secondary battery according to the embodiment.

[0009] According to other embodiments, a vehicle is provided. The vehicle includes a battery pack according to an embodiment. [Brief explanation of the drawing]

[0010] [Figure 1] A schematic cross-sectional view showing an example of an electrode according to the embodiment. [Figure 2] Scanning electron microscope image of the cross-section of the electrode according to Example 1. [Figure 3] An image processed from the image shown in Figure 2. [Figure 4] A schematic diagram illustrating one step in the manufacturing process of electrodes. [Figure 5] A schematic diagram illustrating one step in the manufacturing process of electrodes. [Figure 6] A schematic cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 7] An enlarged cross-sectional view of section A of the secondary battery shown in Figure 6. [Figure 8] A schematic partial cutaway perspective view showing another example of a secondary battery according to the embodiment. [Figure 9] Figure 8 shows an enlarged cross-sectional view of section B of the secondary battery. [Figure 10] A schematic perspective view showing an example of a battery pack according to this embodiment. [Figure 11] An exploded perspective view schematically showing an example of a battery pack according to this embodiment. [Figure 12] A block diagram showing an example of the electrical circuit of the battery pack shown in Figure 11. [Figure 13] A partially transparent view schematically showing an example of a vehicle according to the embodiment. [Figure 14] A schematic diagram showing an example of a control system for the electrical system in a vehicle according to this embodiment. [Figure 15] Scanning electron microscope image of the cross-section of the electrode according to Comparative Example 1. [Figure 16] An image processed from the image shown in Figure 15. [Modes for carrying out the invention]

[0011] The embodiments will be described below with reference to the drawings as appropriate. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each figure is a schematic diagram intended to illustrate the embodiments and facilitate understanding; their shapes, dimensions, ratios, etc., may differ from those of the actual device. These can be appropriately modified in accordance with the following description and known technology.

[0012] When manufacturing batteries, it is necessary to house an electrode group, such as a sheet-like positive electrode and a negative electrode, within the storage space of the outer casing. To increase energy density, it is necessary to house more active material within the casing while suppressing short circuits between the positive and negative electrodes. For this purpose, examples of electrode groups include wound electrode groups and laminated electrode groups. In either embodiment, the electrodes (positive or negative electrode) are required to have high flexibility. In electrodes with poor flexibility, pressing the electrode group containing the electrode may cause cracks in the active material-containing layer or peeling of the active material-containing layer from the current collector.

[0013] Because the electrode according to this embodiment has high flexibility, cracks in the active material-containing layer and peeling of the active material-containing layer from the current collector can be suppressed. Therefore, the electrode can suppress an increase in battery resistance and exhibits excellent rate characteristics.

[0014] (First Embodiment) According to the first embodiment, an electrode is provided. The electrode comprises a current collector having a first surface and a second surface facing the first surface, and a first active material containing layer laminated on one of the first and second surfaces of the current collector and containing a plurality of first active material particles. The first active material containing layer has a first back surface in contact with the current collector and a first front surface located on the opposite side of the first back surface. The volume-based average particle diameter D50 of the plurality of first active material particles is in the range of 1.1 μm to 2.5 μm. The first active material containing layer includes a region A defined from the first back surface to a position 10% of the total thickness, and a region B defined from the position 10% of the total thickness to the first surface, when the total thickness from the first back surface to the first front surface is 100%. In the cross-sectional image obtained by observing the cross-section of the electrode along the stacking direction of the current collector and the first active material-containing layer at 5,000x magnification using a scanning electron microscope, among the multiple first active material particles, those with a cross-sectional area of ​​0.1 μm² 2 ~0.2μm 2 The proportion of particles within this range is lower in region A compared to region B.

[0015] An example of an electrode according to the embodiment will be described with reference to the drawings. Figure 1 is a schematic cross-sectional view showing an example of an electrode 3 according to the embodiment. The X-axis direction and the Y-axis direction are mutually orthogonal directions. The Z-axis direction is orthogonal to both the X-axis direction and the Y-axis direction. The Z-axis direction is, for example, parallel to the stacking direction of the current collector 3a and the active material-containing layer 3b.

[0016] The electrode 3 comprises a current collector 3a, a first active material containing layer 3b1, and a second active material containing layer 3b2. One of the first active material containing layer 3b1 and the second active material containing layer 3b2 may be omitted.

[0017] The current collector 3a has a first surface 51 and a second surface 52 facing the first surface 51. The current collector 3a has a sheet shape that extends along the X-axis and Y-axis directions. The thickness of the current collector 3a (thickness in the Z-axis direction) is preferably in the range of 5 μm to 20 μm, and more preferably in the range of 5 μm to 15 μm.

[0018] The first active material-containing layer 3b1 can be laminated on one of the first surface 51 and the second surface 52 of the current collector 3a. In Figure 1, the first active material-containing layer 3b1 is laminated on the first surface 51 of the current collector 3a. The second active material-containing layer 3b2 is laminated on the surface of the current collector 3a that is opposite to the surface on which the first active material-containing layer 3b1 is laminated. In Figure 1, the second active material-containing layer 3b2 is laminated on the second surface 52 of the current collector 3a.

[0019] The first active material-containing layer 3b1 has a first back surface 61 that is in contact with the current collector 3a, and a first front surface 62 located on the opposite side of the first back surface 61. The first back surface 61 and the first front surface 62 are two main surfaces of the first active material-containing layer 3b1 that face each other. The first active material-containing layer 3b1 has a sheet shape that extends along the X-axis and Y-axis directions.

[0020] The second active material-containing layer 3b2 has a second back surface 71 that is in contact with the current collector 3a, and a second front surface 72 located on the opposite side from the second back surface 71. The second back surface 71 and the second front surface 72 are two main surfaces of the second active material-containing layer 3b2 that face each other. The second active material-containing layer 3b2 has a sheet shape that extends along the X-axis and Y-axis directions.

[0021] The thickness of the first active material-containing layer 3b1 and the second active material-containing layer 3b2 (thickness in the Z-axis direction) is independently within the range of, for example, 20 μm to 60 μm, and preferably within the range of 40 μm to 56 μm.

[0022] The first active material-containing layer 3b1 includes a region A defined from the first back surface 61 to a point 10% of the total thickness, assuming the total thickness from the first back surface 61 to the first front surface 62 is 100%. The first active material-containing layer 3b1 also includes a region B defined from the point 10% of the total thickness to the first front surface 62.

[0023] The thickness of region A is, for example, within the range of 2.0 μm to 6.0 μm. The thickness of region B is, for example, within the range of 18 μm to 54 μm. The sum of the thicknesses of region A and region B is the total thickness of the first active material-containing layer 3b1.

[0024] Region A contains particles with relatively large particle sizes among the multiple active material particles contained in the first active material-containing layer 3b1. On the other hand, region B contains particles with relatively small particle sizes among the multiple active material particles contained in the first active material-containing layer 3b1. Specifically, in the cross-sectional image obtained by scanning electron microscopy (SEM) observation described later, the cross-sectional area is 0.1 μm². 2 ~0.2μm 2 When the number proportion of particles within the specified range is calculated for each region, the proportion in region A (hereinafter also referred to as "number proportion RA") is lower than the proportion in region B (hereinafter also referred to as "number proportion RB").

[0025] Electrodes having a structure in which an active material-containing layer satisfying this condition is laminated on a current collector can achieve high flexibility. The reason for this is not entirely clear, but the inventors believe it to be as follows: By distributing particles with a relatively large particle size in the vicinity of the current collector, such as in region A, the bonding between the current collector and the active material-containing layer can be reduced. Conversely, if many particles with a relatively small particle size are distributed in region A, the bonding between the current collector and the active material-containing layer becomes excessively high, which tends to reduce the flexibility of the electrode. Because the electrode according to this embodiment has high flexibility, even when it is bent, defects such as cracks are less likely to occur in the active material-containing layer. Therefore, it is possible to suppress the increase in battery resistance and, consequently, achieve high rate characteristics.

[0026] The ratio of the number of items RA to the number of items RB (RA / RB) is not particularly restricted as long as it is less than 1.0, but for example, it is within the range of 0.75 or more and less than 1.0.

[0027] The volume-based average particle diameter D50 of the plurality of first active material particles is in the range of 1.1 μm to 2.5 μm. Since the D50 of the plurality of first active material particles is within this range, the electrode according to the embodiment can achieve both excellent rate characteristics and life characteristics. When the D50 of the plurality of first active material particles is less than 1.1 μm, the specific surface area of the active material particles is excessively large, and thus side reactions due to repeated charge and discharge tend to increase. On the other hand, when the D50 of the plurality of first active material particles exceeds 2.5 μm, the electron conduction path in the active material-containing layer is insufficient, and the rate characteristics may be inferior. The D50 of the plurality of first active material particles is preferably in the range of 1.2 μm to 1.7 μm.

[0028] The second active material-containing layer 3b2 includes a region C defined in a region from the second back surface 71 to a position of 10% of the total thickness when the total thickness from the second back surface 71 to the second front surface 72 is 100%. The second active material-containing layer 3b2 further includes a region D defined in a region from the position of 10% of the total thickness to the second front surface 72.

[0029] The thickness of the region C is, for example, in the range of 2.0 μm to 6.μm. The thickness of the region D is, for example, in the range of 18 μm to 54 μm. The sum of the thickness of the region C and the thickness of the region D is the total thickness of the second active material-containing layer 3b2.

[0030] In the electrode according to the embodiment, as described above, for the first active material-containing layer laminated on one surface of the current collector, the number ratio RA is lower compared to the number ratio RB. This relationship is preferably satisfied in the same manner in the second active material-containing layer laminated on the other surface of the current collector. That is, in the region C, particles having a relatively large particle diameter among the plurality of active material particles included in the second active material-containing layer 3b2 are distributed, and in the region D, particles having a relatively small particle diameter among the plurality of active material particles included in the second active material-containing layer 3b2 are preferably distributed. Specifically, in a cross-sectional image obtained by SEM observation described later, the cross-sectional area is 0.1 μm 2 ~0.2 μm 2When calculating the number ratio of particles within the specified range for each region, it is preferable that the ratio in region C (hereinafter also referred to as "number ratio RC") is lower than the ratio in region D (hereinafter also referred to as "number ratio RD").

[0031] In the first and second active material-containing layers present on both sides of the current collector, if particles with relatively large particle sizes are distributed near the current collector, such as in regions A and C, the electrode exhibits superior flexibility compared to the case where the number ratio RA is lower than the number ratio RB only on one side of the current collector, i.e., the first active material-containing layer. In other words, it is preferable that the number ratio RA is lower than the number ratio RB, and the number ratio RC is lower than the number ratio RD.

[0032] The ratio of the number proportion RC to the number proportion RD, RC / RD, is preferably less than 1.0, and more preferably in the range of 0.75 or more and less than 1.0.

[0033] Furthermore, the volume-based average particle diameter D50 of the multiple second active material particles is preferably within the range of 1.1 μm to 2.5 μm. When the D50 of the multiple second active material particles is within this range, the electrode according to the embodiment can achieve both excellent rate characteristics and lifetime characteristics.

[0034] <Scanning electron microscope (SEM) observation and image processing> Next, we will describe a method for disassembling a secondary battery incorporating the electrodes according to the embodiment, observing the electrode cross-section using a scanning electron microscope (SEM), and processing the images obtained from the SEM observation.

[0035] First, the rechargeable battery is brought to a completely discharged state. For example, the battery can be brought to a completely discharged state by repeatedly discharging it at a current of 0.1C in a 25°C environment until the rated cutoff voltage or battery voltage reaches 1.0V, and ensuring that the discharge current is less than 1 / 100 of the rated capacity. Even in a discharged state, residual lithium ions may still be present.

[0036] A secondary battery containing an electrode in a completely 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 washed with a suitable solvent. For example, ethyl methyl carbonate is a good solvent to use for washing. If the washing is insufficient, it may be difficult to observe the particles due to the influence of residual lithium carbonate or lithium fluoride in the electrode. The electrode to be measured is then cut using an ion milling apparatus. When cutting the electrode, it should be cut along the thickness direction. At least three test pieces should be prepared from the electrode to be measured, and the cutting should be performed at a point that includes the center of a virtual line parallel to the short side of the electrode.

[0037] If the electrode is of the wound type, the specimen shall be cut at a point that includes a section obtained by dividing a virtual line parallel to the long side equally by the number of test specimens. If the electrode is of the stacked type, the number of test specimens shall be obtained by cutting each stacked electrode so as to include the central part of the virtual line parallel to the long side of the electrode.

[0038] If the number of electrodes is less than the intended number of test specimens, multiple pieces may be cut from a single electrode. The cut surfaces of the electrodes are then attached to the SEM sample stage. At this time, conductive tape or similar material should be used to prevent the electrodes from peeling off or floating away from the sample stage. The electrodes (active material-containing layers) attached to the SEM sample stage are observed with an SEM to obtain an SEM image. During SEM measurement, the layer thickness of the active material-containing layer and the positions of regions A and B are observed at a magnification of 1,200x, while the particle number ratio is observed at a magnification of 5,000x. Furthermore, it is preferable to maintain an inert atmosphere when introducing the electrodes into the sample chamber.

[0039] Figure 2 is an SEM image showing a cross-section near the current collector of the electrode according to Embodiment 1, which will be described later. As shown in Figure 2, the SEM image is prepared so that both the first surface 51 and the second surface 52 of the current collector 3a are included in a single field of view. This field of view includes at least a portion of region A contained in the first active material-containing layer 3b1, which is laminated on the first surface 51 of the current collector 3a. The field of view also includes at least a portion of region C contained in the second active material-containing layer 3b2, which is laminated on the second surface 52 of the current collector 3a.

[0040] In Figure 2, the region from the first back surface 61 of the first active material-containing layer 3b1 to approximately 10% of the total thickness of the first active material-containing layer 3b1 is observed. In other words, almost the entire region A is observed in Figure 2. Also in Figure 2, the region from the second back surface 71 of the second active material-containing layer 3b2 to approximately 10% of the total thickness of the second active material-containing layer 3b2 is observed. In other words, almost the entire region C is observed in Figure 2.

[0041] The thickness of the active material-containing layer and the location of the 10% mark of the total thickness shall be determined using a virtual line connecting one end of an SEM image obtained at the aforementioned magnification (for example, 1280 x 960 pixels (25.6 x 19.2 μm, 50 pixels / μm)). Therefore, the thickness of the active material-containing layer shall be the distance from the first back surface to the first surface on the virtual line connecting the first surface at one end of the image to the second surface at the other end. This distance shall be the average of measurements taken at five locations: two locations at the edges of the image parallel to the thickness direction of the active material-containing layer, and three locations that divide the image into four equal parts along the in-plane direction of the active material-containing layer. The 10% mark of the total thickness shall be measured in the same manner.

[0042] Figure 3 is an image obtained by processing the image shown in Figure 2 under the following conditions. The software used for processing the SEM image is Image J, as shown in Non-Patent Document 1.

[0043] First, the SEM image is matched to the actual electrode cross-section size so that the pixel density is 50 pixels / unit (μm). Next, the current collector foil area within the field of view is filled with a black rectangle. Then, the image is binarized using the MaxEntropy algorithm. Furthermore, the white areas (i.e., the particle areas) are separated using the Watershed algorithm. This completes the image processing.

[0044] In the processed image, the total number of active material particles contained in region A and the cross-sectional area of ​​0.1 μm² are shown. 2 ~0.2μm 2 The number of particles within each range is counted. Then, the ratio of the number of particles in the latter range to the number of particles in the former range, i.e., the particle ratio RA, is calculated as a percentage. Similarly, the particle ratio RC is calculated for region C.

[0045] The total number of active material particles contained in region A is, for example, within the range of 100 to 500. In region A, the cross-sectional area is 0.1 μm². 2 ~0.2μm 2 The number of particles within this range is, for example, between 10 and 200. The total number of active material particles contained in region C is, for example, between 100 and 500. In region C, the cross-sectional area is 0.1 μm². 2 ~0.2μm 2 The number of particles within a certain range is, for example, between 10 and 200.

[0046] In addition, although not shown in the diagram, a separate SEM image is prepared showing the entire region B from 10% of the total thickness of the first active material-containing layer 3b1 to the first surface 62. This SEM image is also processed using the same procedure as described above. In the processed image, the number of active material particles contained in the entire region B and the cross-sectional area of ​​0.1 μm² are determined. 2 ~0.2μm 2 The number of particles within the specified range is counted. Then, the ratio of the number of particles to the number of particles, i.e., the particle ratio RB, is calculated as a percentage.

[0047] In addition, a separate SEM image is prepared showing the entire region D from 10% of the total thickness of the second active material-containing layer 3b2 to the second surface 72. This SEM image is also processed using the same procedure as described above. In the processed image, the number of active material particles contained in the entire region D and the cross-sectional area of ​​0.1 μm² are determined. 2 ~0.2μm 2 The number of particles within a given range is counted. Then, the ratio of the number of particles to the number of particles, i.e., the particle ratio RD, is calculated as a percentage.

[0048] The total number of active material particles in region B is, for example, within the range of 900 to 4000. In region B, the cross-sectional area is 0.1 μm². 2 ~0.2μm 2 The number of particles within this range is, for example, between 300 and 3600. The total number of active material particles contained in region D is, for example, between 900 and 4000. In region D, the cross-sectional area is 0.1 μm². 2 ~0.2μm 2 The number of particles within a certain range is, for example, between 300 and 3600.

[0049] Among the first active material particles contained in region A of the first active material-containing layer, those with a cross-sectional area of ​​0.1 μm 2 ~0.2μm 2 The number percentage RA of particles within this range is preferably 10% to 40%. When the number percentage RA is within this range, the effect of reducing the binding between the current collector and the first active material-containing layer is significant, and therefore the effect of increasing the flexibility of the electrode is significant. The number percentage RA is more preferably 30% to 40%.

[0050] Among the first active material particles contained in region B of the first active material-containing layer, those with a cross-sectional area of ​​0.1 μm 2 ~0.2μm 2The number percentage RB of particles within this range is preferably greater than 40% and 90% or less. When the number percentage RB is within this range, the region B, which occupies most of the first active material-containing layer, contains a large number of active material particles with relatively small particle sizes. Therefore, a sufficient electronically conductive network is formed within the layer, enabling the realization of low battery resistance. It is more preferable that the number percentage RB is greater than 40% and 60% or less.

[0051] Among the second active material particles contained in region C of the second active material-containing layer, those with a cross-sectional area of ​​0.1 μm 2 ~0.2μm 2 The particle number ratio RC within this range is preferably 10% to 40%. When the particle number ratio RC is within this range, the effect of reducing the bonding between the current collector and the second active material-containing layer is significant, and therefore the effect of increasing the flexibility of the electrode is significant. The particle number ratio RC is more preferably 30% to 40%.

[0052] Among the second active material particles contained in region D of the second active material-containing layer, those with a cross-sectional area of ​​0.1 μm 2 ~0.2μm 2 The number percentage RD of particles within this range is preferably greater than 40% and 90% or less. When the number percentage RD is within this range, the region D, which occupies most of the second active material-containing layer, contains a large number of active material particles with relatively small particle sizes. Therefore, a sufficient electronically conductive network is formed within the layer, enabling the realization of low battery resistance. It is more preferable that the number percentage RD is greater than 40% and 60% or less.

[0053] The electrode density of the first active material-containing layer and the electrode density of the second active material-containing layer are, independently of each other, for example, 2.2 g / cm³. 3 -2.9 g / cm³ 3 It is within the range, preferably 2.3 / cm 3 -2.8 g / cm³ 3 It is within the range. In this specification and claims, the electrode density of the first active material-containing layer is also referred to as the first electrode density. Similarly, the electrode density of the second active material-containing layer is also referred to as the second electrode density.

[0054] If the electrode density is too low, it is undesirable because the bonding force between the active material-containing layer and the current collector is low, which may result in poor cycle characteristics and low energy density per unit volume. If the electrode density is too high, it is undesirable because it may lead to a decrease in electrode flexibility, as well as a decrease in porosity within the active material-containing layer and an increase in the curvature of the through-holes, which may result in a decrease in rate characteristics and cycle characteristics.

[0055] The electrodes according to this embodiment can function as either a negative electrode or a positive electrode. The negative electrode and the positive electrode will be described in detail below.

[0056] (Negative electrode) The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode active material-containing layer may be formed on one or both sides of the negative electrode current collector. The negative electrode active material-containing layer may optionally include a negative electrode active material and a conductive agent and a binder. When the electrode in the embodiment is a negative electrode, the first active material-containing layer and the second active material-containing layer described above may both be negative electrode active material-containing layers. In this case, the compositions of the first active material-containing layer and the second active material-containing layer may be different from or the same.

[0057] (Negative electrode current collector and tab) The negative electrode current collector has a potential at which lithium (Li) is inserted into and removed from the active material, for example, 1.0V (vs. Li / Li). + A material that is electrochemically stable at a potential that is nobler than ) is used. For example, the current collector is preferably made of copper, nickel, stainless steel or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si.

[0058] Furthermore, the negative electrode current collector may include portions on its surface where the negative electrode active material-containing layer is not formed. These portions can function as negative electrode current collector tabs.

[0059] (Negative electrode active material containing layer) The negative electrode active material includes at least one selected from the group consisting of carbon materials, silicon, silicon oxides, and titanium-containing oxides. Examples of carbon materials include artificial graphite, natural graphite, and fusiform graphite obtained by compacting natural graphite and coating it with carbon.

[0060] Examples of titanium-containing oxides include lithium titanate having a ramsdellite structure (e.g., Li 2+y Li3O7 (0≦y≦3), lithium titanate having a spinel structure (e.g., Li 4+x Ti5O 12 Examples include monoclinic titanium dioxide (TiO2), anatase titanium dioxide, rutile titanium dioxide, hollandite titanium composite oxide, monoclinic niobium titanium composite oxide, and orthorhombic titanium-containing composite oxide. Among these, from the viewpoint of achieving both high capacity and high rate performance, it is preferable that the negative electrode active material contains a titanium-containing oxide.

[0061] In particular, the negative electrode active material preferably contains a niobium-titanium composite oxide. This is because, when using an active material powder containing a niobium-titanium composite oxide, it is preferable to use an aqueous slurry containing styrene-butadiene rubber (SBR) or the like as a binder.

[0062] According to the present inventors, when a negative electrode active material containing niobium-titanium composite oxide is used, it has been found that higher battery performance can be obtained by using SBR, which is known as an aqueous slurry, as a binder, compared with PVdF, which is known as an organic solvent slurry. On the other hand, it has been found that active material-containing layers using SBR as a binder tend to have poor flexibility. Therefore, when the negative electrode active material contains niobium-titanium composite oxide and the negative electrode binder contains SBR, the effect of improving flexibility can be easily obtained by adopting the configuration according to this embodiment.

[0063] Niobium-titanium composite oxides have, for example, a monoclinic crystal structure. An example of a monoclinic niobium-titanium composite oxide is Lix Ti 1-y M1 y Nb 2-z M2 z O 7+δ Examples of compounds represented by the formula are: Here, 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. The subscripts in the compositional formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. A specific example of a monoclinic niobium titanium composite oxide is Li x Nb2TiO7 (0≦x≦5) is one example.

[0064] Another example of monoclinic niobium-titanium composite oxides is Ti 1-y M3 y+z Nb 2-z O 7-δ A compound represented by the formula is shown below. Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. In the compositional formula, each subscript has the following properties: 0≦y<1, 0≦z≦2, and -0.3≦δ≦0.3.

[0065] As an example of orthorhombic titanium-containing composite oxides, Li 2+a M(I) 2-b Ti 6-c M(II) d O 14+σ A compound represented by the formula is shown below. 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. A specific example of an orthorhombic titanium-containing composite oxide is Li 2+a Na2Li6O 14 (0 ≤ a ≤ 6) is one example.

[0066] The average particle size of the primary particles of the negative electrode active material is preferably in the range of 0.001 μm to 1 μm. The average particle size can be determined, for example, by observing the negative electrode active material with a scanning electron microscope (SEM). The particle shape may be granular or fibrous. In the case of fibrous particles, the fiber diameter is preferably 0.1 μm or less. Specifically, the average particle size of the primary particles of the negative electrode active material can be measured from the image observed with an SEM.

[0067] Conductive agents are added to enhance current collection performance and reduce contact resistance between the active material and the 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 a conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surface of the active material particles may be coated with a carbon coating or an electronically conductive inorganic material coating.

[0068] Binding agents are added to fill the gaps between dispersed active materials and to bind the active materials to the negative electrode current collector. Examples of binding agents include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, ethylene propylene rubber, polyacrylic acid compounds, polyimide, polyamide, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binding agent, or two or more may be used in combination. The type of binding agent contained in the active material-containing layer can be estimated by infrared spectroscopy and EDX (Energy Dispersive X-ray Spectroscopy).

[0069] The proportions of the negative electrode active material, conductive agent, and binder in the negative electrode active material-containing layer can be appropriately changed depending on the application of the negative electrode. For example, it is preferable to blend the negative electrode active material, conductive agent, and binder in proportions of 70% to 96% by mass, 2% to 28% by mass, and 2% to 28% by mass, respectively. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the negative electrode active material-containing layer can be improved. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient bonding between the negative electrode active material-containing 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 amount of conductive agent and binder to 28% by mass or less, respectively, in order to achieve high capacity.

[0070] (positive electrode) (Positive electrode current collector and tab) Examples of positive electrode current collectors include foil made of a conductive material. Examples of conductive materials include aluminum and aluminum alloys.

[0071] The positive electrode tab is preferably made from the same material as the positive electrode current collector. Alternatively, the positive electrode tab may be prepared separately from the positive electrode current collector and connected to the positive electrode current collector by welding or other means.

[0072] (Positive electrode active material containing layer) The positive electrode may include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer may be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer may optionally include a positive electrode active material and a conductive agent and a binder. When the electrode in the embodiment is a positive electrode, the first active material-containing layer and the second active material-containing layer described above may both be positive electrode active material-containing layers. In this case, the compositions of the first active material-containing layer and the second active material-containing layer may be different from or the same.

[0073] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain, as the positive electrode active material, one type of compound alone, or may contain a combination of two or more types of compounds. Examples of the oxide and the sulfide include compounds into which Li or Li ions can be inserted and extracted.

[0074] Examples of 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, Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (for example, Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (for example, Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (for example, Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (for example, 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 (for example, 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) are included.

[0075] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxides having a spinel structure (for example, Li x Mn2O4; 0 < x ≦ 1), lithium nickel composite oxides (for example, Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxides (for example, Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxides (for example, Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxides having a spinel structure (for example, Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium manganese cobalt composite oxides (for example, Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium iron phosphate (for example, Li x FePO4; 0 < x ≦ 1), and lithium nickel cobalt manganese composite oxides (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 these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0076] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. The positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. The positive electrode active material with a primary particle size of 1 μm or less can smoothly progress the solid-state diffusion of lithium ions.

[0077] 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. The positive electrode active material having a specific surface area of 0.1 m 2 / g or more can sufficiently secure the occlusion / discharge sites of Li ions. 10 m 2Positive electrode active materials with a specific surface area of ​​less than / g are easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0078] The positive electrode active material-containing layer may contain, in addition to the positive electrode active material, at least one of a binder and a conductive agent. The binder and conductive agent may be the same as those described for the negative electrode active material-containing layer.

[0079] In the positive electrode active material-containing layer, it is preferable that the positive electrode active material and the binder are blended in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0080] Sufficient electrode strength can be obtained by using a binder amount of 2% by mass or more. Furthermore, the binder can function as an insulator. Therefore, reducing the binder amount to 20% by mass or less reduces the amount of insulator contained in the electrode, thereby reducing internal resistance.

[0081] When a conductive agent is added, it is preferable that the positive electrode active material, binder, and conductive agent are blended in proportions of 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively.

[0082] The above-mentioned effects can be achieved by increasing the amount of conductive agent to 3% by mass or more. Furthermore, by reducing 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 lower proportion reduces the decomposition of the electrolyte under high-temperature storage conditions.

[0083] <Method of manufacturing electrodes> Next, a method for manufacturing electrodes according to an embodiment will be described.

[0084] The electrode can be manufactured, for example, by simultaneously applying a first slurry to form region A in the first active material-containing layer 3b1 and a second slurry to form region B to a current collector, and then drying them. In this specification, this is referred to as simultaneous two-layer coating. Alternatively, the electrode can be manufactured by first applying the first slurry to the current collector and drying it to form region A, and then further applying the second slurry and drying it to form region B on region A. In this specification, this is referred to as sequential coating.

[0085] An example of a manufacturing method for simultaneous two-layer coating will be explained with reference to Figures 4 and 5. In the two-layer simultaneous coating process, a first slurry for forming region A and a second slurry for forming region B are simultaneously coated onto at least one of the front and back surfaces of the current collector 3a. The first slurry and the second slurry are prepared, for example, by suspending the aforementioned negative electrode active material, conductive agent, and binder in a suitable solvent. The first slurry and the second slurry may also be prepared by suspending the positive electrode active material, conductive agent, and binder in a suitable solvent.

[0086] For example, the active material particles used in the first slurry have a larger average particle size D50 compared to the active material particles in the second slurry. In other words, the average particle size D50 of the active material particles in the first slurry can be larger than the median diameter of the active material particles in the second slurry. By making the average particle size D50 of the active material particles used in the first slurry and the second slurry different in this way, it is possible to vary the particle size of the active material particles in the first active material-containing layer between region A and region B, for example.

[0087] The average particle size D50 of the active material particles contained in the first slurry can be changed as appropriate, but is within the range of, for example, 1.8 μm to 2.5 μm. The median diameter of the active material particles contained in the second slurry can be changed as appropriate, but is within the range of, for example, 1.0 μm to less than 1.8 μm.

[0088] The coating thickness of the first slurry shall be, for example, within the range of 5 μm to 20 μm. The coating thickness of the second slurry shall be, for example, within the range of 40 μm to 150 μm.

[0089] An example of the coating process is shown in Figures 4 and 5. The coating apparatus 80 includes a tank 82 for containing a first slurry (hereinafter referred to as slurry I) and a tank 83 for containing a second slurry (hereinafter referred to as slurry II), and is configured to simultaneously apply slurry I and slurry II to a substrate such as a current collector. The width perpendicular to the coating direction at the discharge port of slurry I corresponds to the coating width of region A included in the active material-containing layer 3b1. The long current collector 3a, before being cut to predetermined dimensions, is conveyed to the slurry discharge port of the coating apparatus 80 by a conveyor roller 81. In Figure 5, the slurry I discharge port 82a is located upstream of the current collector from the slurry II discharge port 83a. As an example, the width perpendicular to the coating direction of slurry I discharge port 82a is narrower than the width perpendicular to the coating direction of slurry II discharge port 83a. Slurry I is applied from the coating device 80 onto the current collector 3a, except for both ends in the short-side direction. Almost simultaneously, slurry II is applied over it so as to extend beyond the area where slurry I has been applied. Because slurry II is applied over slurry I before slurry I has dried, slurry II can easily conform to the surface shape of slurry I. After the slurry is dried, it is roll-pressed and cut to a predetermined size to obtain electrodes.

[0090] In the case of sequential coating, for example, the first slurry is applied to one or both sides of a long current collector 3a. Next, the applied slurry is dried to obtain a laminate in which region A is laminated on the current collector 3a. Then, the second slurry is applied to region A. At this time, the second slurry may be applied to region A and the current collector 3a with a coating width longer than the length of the already formed region A in the short side direction. After that, the applied second slurry is dried to obtain a laminate consisting of, for example, the current collector 3a, region A and region B. This laminate can be pressed and cut to a predetermined size to obtain electrodes.

[0091] <Powder X-ray diffraction measurement of active material> Powder X-ray diffraction measurements of active materials can be performed, for example, as follows: First, the sample is ground until the average particle size is approximately 5 μm. The ground sample is then packed into a holder portion with a depth of 0.2 mm formed on a glass sample plate. At this time, care should be taken to ensure that the sample is sufficiently packed into the holder portion. Care should also be taken to pack the correct amount of sample to avoid cracks, voids, etc. Next, another glass plate is pressed against the outside to flatten the surface of the sample packed into the holder portion. Care should be taken to ensure that there are no irregularities on the reference surface of the holder due to an excess or deficiency in the amount of packed sample.

[0092] Next, the glass plate filled with the sample is placed in a powder X-ray diffractometer, and a diffraction pattern (XRD pattern; X-Ray Diffraction pattern) is obtained using Cu-Kα rays.

[0093] Furthermore, the orientation of particles may increase depending on the particle shape of the sample. If the orientation of the sample is high, the position of the peak may shift or the intensity ratio may change depending on how the sample is packed. Samples with such significantly high orientation should be measured using a glass capillary. Specifically, the sample is inserted into the capillary, and this capillary is placed on a rotating sample stage for measurement. This measurement method can mitigate the orientation. As for the glass capillary, it is preferable to use a Lindemann glass capillary with a diameter of 1 mm to 6 mmφ.

[0094] When performing powder X-ray diffraction measurements on the active material contained in an electrode, the following method can be used, for example. First, to understand the crystalline state of the active material, the lithium ions must be completely removed from the active material. For example, if the active material is used in the negative electrode, the battery must be completely discharged. For instance, the battery can be discharged by repeatedly discharging it at a current of 0.1C in a 25°C environment until the rated cutoff voltage or battery voltage reaches 1.0V, ensuring that the discharge current is less than 1 / 100th of the rated capacity. Even in the discharged state, residual lithium ions may still be present.

[0095] Next, the battery is disassembled in a glove box filled with argon, the electrodes are removed, and washed with a suitable solvent. For example, ethyl methyl carbonate can be used as a suitable solvent. If the electrodes are not washed thoroughly, impurity phases such as lithium carbonate and lithium fluoride may be introduced due to the influence of lithium ions remaining in the electrodes. In that case, it is advisable to use an airtight container that allows the measurement to be performed in an inert gas atmosphere. The washed electrodes are cut to an area approximately the same as the area of ​​the holder of the powder X-ray diffractometer to prepare the measurement sample. This sample is then directly attached to the glass holder and the measurement is performed.

[0096] At this time, the peaks originating from the current collector (metal foil), conductive agent, and binder should be measured and identified in advance using XRD. Of course, if these are known in advance, this step can be omitted. If the peaks of the current collector and the active material overlap, it is desirable to peel off the active material-containing layer from the current collector and measure it. This is to separate the overlapping peaks when quantitatively measuring the peak intensity. The active material-containing layer can be physically peeled off, but it is easier to peel off by applying ultrasound in a solvent. When ultrasound is used to peel off the active material-containing layer from the current collector, the electrode powder (including the active material, conductive agent, and binder) can be recovered by volatilizing the solvent. The recovered electrode powder can be packed into a capillary, for example, made of Lindemann glass, and measured to perform powder X-ray diffraction measurement of the active material. Note that the electrode powder recovered by ultrasound can also be used for various analyses other than powder X-ray diffraction measurement.

[0097] <Measurement of particle size distribution of active material particles using laser diffraction scattering method> The electrode powder described in the section on powder X-ray diffraction measurement above is calcined to burn off the conductive agent and binder. The remaining active material particles are dispersed in N-methyl-2-pyrrolidone (NMP) solvent and subjected to sonication to obtain a dispersion solution for particle size distribution measurement. The particle size distribution of the constituent particles of this dispersion solution is measured using a laser diffraction distribution analyzer. For example, the Microtrac MT3100II manufactured by Microtrac-Bell Corporation can be used as the measuring device.

[0098] The sonication used to obtain the above-mentioned dispersion solvent is performed using a sample supply system attached to a laser diffraction distribution analyzer. The sonication is performed, for example, at an output of 40W for 300 seconds.

[0099] According to the first embodiment, an electrode is provided. The electrode comprises a current collector having a first surface and a second surface facing the first surface, and a first active material containing layer laminated on one of the first and second surfaces of the current collector and containing a plurality of first active material particles. The first active material containing layer has a first back surface in contact with the current collector and a first front surface located on the opposite side of the first back surface. The volume-based average particle diameter D50 of the plurality of first active material particles is in the range of 1.1 μm to 2.5 μm. The first active material containing layer includes a region A defined from the first back surface to a position 10% of the total thickness, and a region B defined from the position 10% of the total thickness to the first surface, when the total thickness from the first back surface to the first front surface is 100%. In the cross-sectional image obtained by observing the cross-section of the electrode along the stacking direction of the current collector and the first active material-containing layer at 5,000x magnification using a scanning electron microscope, among the multiple first active material particles, those with a cross-sectional area of ​​0.1 μm² 2 ~0.2μm 2 The proportion of particles within this range is lower in region A compared to region B.

[0100] According to the electrode of the first embodiment, a secondary battery can be realized that has high flexibility and excellent rate characteristics.

[0101] (Second Embodiment) According to the second embodiment, a secondary battery is provided that includes a negative electrode, a positive electrode, and an electrolyte. At least one of the positive electrode and the negative electrode included in the secondary battery is the electrode according to the first embodiment.

[0102] A secondary battery may further include a separator positioned between the positive and negative electrodes. The negative electrode, positive electrode, and separator can constitute an electrode group. The electrolyte can be held within the electrode group.

[0103] Furthermore, the secondary battery may further comprise an outer casing that houses the electrode group and the electrolyte.

[0104] Furthermore, the secondary battery may further include a negative terminal electrically connected to the negative electrode and a positive terminal electrically connected to the positive electrode.

[0105] The secondary battery may be, for example, a lithium secondary battery. Alternatively, the secondary battery may be a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0106] The following provides a detailed explanation of the negative electrode, positive electrode, electrolyte, separator, outer casing, negative electrode terminal, and positive electrode terminal.

[0107] (1) Negative electrode The negative electrode of the secondary battery according to the second embodiment may be, for example, the electrode described in the first embodiment. The active material-containing layer included in this electrode may be a negative electrode active material-containing layer. The active material particles included in the electrode may be negative electrode active material particles.

[0108] (2) Positive electrode The positive electrode of the secondary battery according to the second embodiment may be, for example, the electrode described in the first embodiment. The active material-containing layer included in this electrode may be a positive electrode active material-containing layer. The active material particles included in the electrode may be positive electrode active material particles.

[0109] (3) Electrolyte As the electrolyte, for example, a liquid non-aqueous electrolyte or a gel-type non-aqueous electrolyte can be used. A liquid non-aqueous 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.

[0110] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2), as well as mixtures thereof. The electrolyte salt is preferably resistant to oxidation even at high potentials, with LiPF6 being the most preferred.

[0111] 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); and γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as mixed solvents.

[0112] Gel-like non-aqueous electrolytes are prepared by compounding a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0113] Alternatively, in addition to liquid nonaqueous electrolytes and gel-type nonaqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions, polymer solid electrolytes, and inorganic solid electrolytes may be used as nonaqueous electrolytes.

[0114] Room temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as liquids at room temperature (15°C to 25°C). Room temperature molten salts include room temperature molten salts that exist as liquids 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, or mixtures thereof. Generally, the melting point of room temperature molten salts used in secondary batteries is 25°C or lower. Also, organic cations generally have a quaternary ammonium skeleton.

[0115] Polymeric solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and then solidifying it.

[0116] Inorganic solid electrolytes are solid materials that possess lithium ion conductivity.

[0117] The electrolyte may be an aqueous electrolyte containing water.

[0118] Aqueous electrolytes consist of an aqueous solvent and an electrolyte salt. Aqueous electrolytes are, for example, liquid. A 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.

[0119] The aqueous electrolyte may be a gel-like aqueous electrolyte obtained by compounding an aqueous electrolyte solution with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0120] In the aqueous electrolyte, it is preferable that the amount of aqueous solvent is 1 mole or more per mole of solute salt. A more preferable form is when the amount of aqueous solvent is 3.5 moles or more per mole of solute salt.

[0121] The presence of water in an aqueous electrolyte can be confirmed by GC-MS (Gas Chromatography - Mass Spectrometry) measurement. Furthermore, the salt concentration and water content in an aqueous electrolyte can be calculated, for example, by ICP (Inductively Coupled Plasma) emission spectrometry. By weighing a specified amount of the aqueous electrolyte and calculating the salt concentration, the molar concentration (mol / L) can be determined. Additionally, by measuring the specific gravity of the aqueous electrolyte, the number of moles of solute and solvent can be calculated.

[0122] Aqueous electrolytes are prepared, for example, by dissolving an electrolyte salt in an aqueous solvent at a concentration of 1-12 mol / L.

[0123] To suppress the electrolysis of aqueous electrolytes, the pH can be adjusted by adding LiOH or Li2SO4. The pH is preferably between 3 and 13, and more preferably between 4 and 12.

[0124] (4) Separator The separator is formed from a porous film containing, for example, polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or from a synthetic resin nonwoven fabric. From a safety standpoint, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films can melt at a certain temperature and interrupt the electric current.

[0125] A solid electrolyte layer containing solid electrolyte particles can also be used as a separator. The solid electrolyte layer may contain one type of solid electrolyte particle or multiple types of solid electrolyte particles. The solid electrolyte layer may also be a solid electrolyte composite membrane containing solid electrolyte particles. A solid electrolyte composite membrane is, for example, made by forming solid electrolyte particles into a membrane using a polymer material. The solid electrolyte layer may contain at least one selected from the group consisting of plasticizers and electrolyte salts. If the solid electrolyte layer contains electrolyte salts, for example, the alkali metal ion conductivity of the solid electrolyte layer can be further enhanced.

[0126] Examples of polymer materials include polyether-based, polyester-based, polyamine-based, polyethylene-based, silicone-based, and polysulfide-based materials.

[0127] As the solid electrolyte, it is preferable to use an inorganic solid electrolyte. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. As the oxide-based solid electrolyte, it is preferable to use a lithium phosphate solid electrolyte having a NASICON-type structure and represented by the general formula LiM2(PO4)3. In the above general formula, M is preferably at least one element selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), and aluminum (Al). It is more preferable that element M includes one of Ge, Zr, and Ti, and Al.

[0128] As specific examples of the lithium phosphate solid electrolyte having a NASICON structure, LATP (Li 1+x Al x Ti 2-x (PO4)3), Li 1+x Al x Ge 2-x (PO4)3, Li 1+x Al x Zr 2-x (PO4)3 can be mentioned. In the above formula, x is within the range of 0 < x ≦ 5, and preferably within the range of 0.1 ≦ x ≦ 0.5. As the solid electrolyte, it is preferable to use LATP. LATP has excellent water resistance and is less likely to cause hydrolysis in a secondary battery.

[0129] Also, as the oxide-based solid electrolyte, amorphous LIPON (Li 2.9 PO 3.3 N 0.46 ), or garnet-type LLZ (Li7La3Zr2O 12 ) may be used.

[0130] (5) Outer packaging member As the outer packaging member, for example, a container made of a laminate film or a metal container can be used.

[0131] The thickness of the laminate film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

[0132] As the laminate film, a multilayer film including a plurality of resin layers and a metal layer interposed between these resin layers is used. The resin layer contains polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be formed into the shape of the outer packaging member by sealing by heat fusion.

[0133] The thickness of the metal container wall is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0134] Metal containers are made from, for example, aluminum or aluminum alloys. Aluminum alloys preferably contain elements such as magnesium, zinc, and silicon. If aluminum alloys contain transition metals such as iron, copper, nickel, and chromium, their content is preferably 100 ppm by mass or less.

[0135] The shape of the exterior components is not particularly limited. For example, the exterior components may be flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior components can be appropriately selected according to the battery dimensions and intended use.

[0136] (6) Negative terminal The negative electrode terminal can be formed from a material that is electrochemically stable at the Li absorption / release potential of the negative electrode active material described above, and is also conductive. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable to use aluminum or an aluminum alloy as the material for the negative electrode terminal. It is preferable that the negative electrode terminal be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0137] (7) Positive terminal The positive terminal has a potential range of 3V to 4.5V relative to the oxidation-reduction potential of lithium (vs.Li / Li +The positive electrode terminal can be formed from an electrically stable and conductive material. Examples of positive electrode terminal materials include aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the positive electrode terminal be formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0138] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0139] Figure 6 is a schematic cross-sectional view showing an example of a secondary battery according to the embodiment. Figure 7 is an enlarged cross-sectional view of part A of the secondary battery shown in Figure 6.

[0140] The secondary battery 100 shown in Figures 6 and 7 comprises a bag-shaped outer casing member 2 shown in Figure 6, an electrode group 1 shown in Figures 6 and 7, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the bag-shaped outer casing member 2. The electrolyte (not shown) is held by the electrode group 1.

[0141] The bag-shaped outer packaging member 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0142] As shown in Figure 6, electrode group 1 is a flat, wound electrode group. As shown in Figure 7, the flat, wound electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The separator 4 is interposed between the negative electrode 3 and the positive electrode 5.

[0143] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material containing layer 3b. In the portion of the negative electrode 3 located in the outermost shell of the wound electrode group 1, the negative electrode active material containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a, as shown in Figure 7. In the other portions of the negative electrode 3, the negative electrode active material containing layer 3b is formed on both sides of the negative electrode current collector 3a.

[0144] Although not shown in the figures, the negative electrode active material-containing layers 3b formed on both sides of the negative electrode current collector 3a may be the first active material-containing layer 3b1 or the second active material-containing layer 3b2 described in the first embodiment. When the electrode group 1 is a wound electrode group, it is preferable that the first active material-containing layer 3b1 is provided on the inner circumference side of the negative electrode 3 relative to the negative electrode current collector 3a. In a wound electrode group, the radius of curvature on the inner circumference side is smaller than on the outer circumference side of the negative electrode current collector 3a, which is advantageous because it allows for greater flexibility of the active material-containing layer on the inner circumference side. However, as mentioned above, it is preferable that the first active material-containing layer 3b1 and the second active material-containing layer 3b2 are provided on both sides of the negative electrode current collector 3a, respectively.

[0145] The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both sides thereof.

[0146] As shown in Figure 6, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer edge of the wound electrode group 1. The negative electrode terminal 6 is connected to the outermost part of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to the outermost part of the positive electrode current collector 5a. These negative electrode terminals 6 and positive electrode terminals 7 extend outward from the opening of the bag-shaped outer casing member 2. A thermoplastic resin layer is installed on the inner surface of the bag-shaped outer casing member 2, and the opening of the bag-shaped outer casing member 2 is closed by heat fusion of this layer.

[0147] The secondary battery according to this embodiment is not limited to the secondary battery with the configuration shown in Figures 6 and 7, but may also be a battery with the configuration shown in Figures 8 and 9, for example.

[0148] Figure 8 is a schematic partially cutaway perspective view showing another example of a secondary battery according to the embodiment. Figure 9 is an enlarged cross-sectional view of part B of the secondary battery shown in Figure 8.

[0149] The secondary battery 100 shown in Figures 8 and 9 comprises an electrode group 1 shown in Figures 8 and 9, an outer casing member 2 shown in Figure 8, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the outer casing member 2. The electrolyte is held within the electrode group 1.

[0150] The exterior component 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0151] As shown in Figure 9, electrode group 1 is a stacked electrode group. The stacked electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately stacked with separators 4 interposed between them.

[0152] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 comprises a negative electrode current collector 3a and a negative electrode active material-containing 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 comprises a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

[0153] Each negative electrode 3's negative electrode current collector 3a includes a portion 3c on one side where the negative electrode active material-containing layer 3b is not supported on any surface. This portion 3c functions as a negative electrode current collector tab. As shown in Figure 9, the portion 3c acting as a negative electrode current collector tab does not overlap with the positive electrode 5. Furthermore, 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 extended to the outside of the outer casing member 2.

[0154] Although not shown in the diagram, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. The positive electrode current collector tab, like the negative electrode current collector tab (part 3c), does not overlap with the negative electrode 3. Furthermore, the positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab (part 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 extended to the outside of the outer casing member 2.

[0155] The secondary battery according to the second embodiment includes the electrodes according to the first embodiment. Therefore, the secondary battery according to the second embodiment can have high flexibility and achieve excellent rate characteristics.

[0156] (Third embodiment) According to the third embodiment, a battery pack is provided. The battery pack according to the third embodiment comprises a plurality of secondary batteries according to the second embodiment.

[0157] In the battery pack according to this embodiment, each individual cell may be arranged in series or parallel connections, or a combination of series and parallel connections may be used.

[0158] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0159] Figure 10 is a schematic perspective view showing an example of a battery pack according to the embodiment. The battery pack 200 shown in Figure 10 comprises five single cells 100a-100e, four busbars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five single cells 100a-100e is a secondary battery according to the second embodiment.

[0160] The busbar 21 connects, for example, the negative terminal 6 of one cell 100a to the positive terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four busbars 21. That is, the battery pack 200 in Figure 10 is a battery pack with five cells in series. Although not illustrated, in a battery pack containing multiple cells that are electrically connected in parallel, the multiple cells can be electrically connected, for example, by connecting multiple negative terminals to each other and multiple positive terminals to each other by busbars.

[0161] The positive terminal 7 of at least one of the five single cells 100a-100e is electrically connected to the positive lead 22 for external connection. In addition, the negative terminal 6 of at least one of the five single cells 100a-100e is electrically connected to the negative lead 23 for external connection.

[0162] The battery pack according to the third embodiment comprises the secondary battery according to the second embodiment. Therefore, the battery pack according to the third embodiment can have high flexibility and achieve excellent rate characteristics.

[0163] (Fourth Embodiment) According to the fourth embodiment, a battery pack is provided. This battery pack comprises a battery pack according to the third embodiment. This battery pack may also comprise a single secondary battery according to the second embodiment instead of the battery pack according to the third embodiment.

[0164] The battery pack according to this embodiment may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., an electronic device, an automobile, etc.) may be used as the protection circuit for the battery pack.

[0165] Furthermore, the battery pack according to this embodiment may also be further equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and / or for 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 terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external terminals.

[0166] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0167] Figure 11 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. Figure 12 is a block diagram showing an example of the electrical circuit of the battery pack shown in Figure 11.

[0168] The battery pack 300 shown in Figures 11 and 12 comprises a housing 31, a lid 32, a protective sheet 33, a battery pack 200, a printed circuit board 34, wiring 35, and an insulating plate (not shown).

[0169] The container 31 shown in Figure 11 is a rectangular-bottomed rectangular container. The container 31 is configured to accommodate a protective sheet 33, a battery pack 200, a printed circuit board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31, thereby housing the battery pack 200 and the other components. The container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc., although these are not shown in the figures.

[0170] The battery pack 200 comprises multiple individual cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0171] At least one of the multiple single cells 100 is a secondary battery according to the second embodiment. Each of the multiple single cells 100 is electrically connected in series as shown in Figure 12. The multiple single cells 100 may also be electrically connected in parallel, or they may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0172] The adhesive tape 24 fastens multiple single cells 100 together. Alternatively, heat-shrinkable tape may be used to secure the multiple single cells 100 instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both sides of the battery pack 200, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to bundle the multiple single cells 100 together.

[0173] One end of the positive lead 22 is connected to the battery pack 200. One end of the positive lead 22 is electrically connected to the positive terminal of one or more single cells 100. One end of the negative lead 23 is connected to the battery pack 200. One end of the negative lead 23 is electrically connected to the negative terminal of one or more single cells 100.

[0174] The printed circuit board 34 is installed along one of the shorter sides of the inner surface of the housing container 31. The printed circuit board 34 includes a positive terminal connector 342, a negative terminal connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energization, a positive side wiring (positive wiring) 348a, and a negative side wiring (negative wiring) 348b. One main surface of the printed circuit board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed circuit board 34 and the battery pack 200.

[0175] The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative connector 343.

[0176] The thermistor 345 is fixed to one main surface of the printed circuit board 34. The thermistor 345 detects the temperature of each of the single cells 100 and transmits the detection signal to the protection circuit 346.

[0177] The external power supply terminal 350 is fixed to the other main surface of the printed circuit board 34. The external power supply terminal 350 is electrically connected to equipment located outside the battery pack 300. The external power supply terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0178] The protection circuit 346 is fixed to the other main surface of the printed circuit board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via wiring 342a. The protection circuit 346 is also electrically connected to the negative connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via wiring 35.

[0179] The protective sheet 33 is positioned on both inner surfaces in the long-side direction of the housing container 31 and on the inner surface in the short-side direction facing the printed circuit board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0180] The protection circuit 346 controls the charging and discharging of multiple single cells 100. The protection circuit 346 also disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying power to external devices, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual single cell 100 or a battery pack 200.

[0181] An example of a detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of a single cell 100 is above a predetermined temperature. An example of a detection signal transmitted from an individual single cell 100 or a battery pack 200 is a signal indicating that overcharging, over-discharging, or overcurrent has been detected in a single cell 100. When detecting overcharging, etc., in an individual single cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode to be used as a reference electrode is inserted into each individual single cell 100.

[0182] Furthermore, the protection circuit 346 may be a circuit included in a device that uses the battery pack 300 as a power source (for example, an electronic device, an automobile, etc.).

[0183] Furthermore, as described above, the battery pack 300 is equipped with an external terminal 350 for power supply. Therefore, the battery pack 300 can output current from the battery pack 200 to an external device and input current from an external device to the battery pack 200 via the external terminal 350. In other words, when the battery pack 300 is used as a power source, current from the battery pack 200 is supplied to the external device through the external terminal 350. Also, when charging the battery pack 300, charging current from an external device is supplied to the battery pack 300 through the external terminal 350. When this battery pack 300 is used as an on-board battery, the regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0184] The battery pack 300 may comprise multiple battery packs 200. In this case, the multiple battery packs 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed circuit board 34 and wiring 35 may also be omitted. In this case, the positive lead 22 and the negative lead 23 may be used as the positive and negative terminals of the external terminals for energization, respectively.

[0185] Such battery packs are used in applications where excellent cycle performance is required, for example, when drawing high currents. Specifically, these battery packs are used as power supplies for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

[0186] The battery pack according to the fourth embodiment comprises a secondary battery according to the second embodiment or a battery pack according to the third embodiment. Therefore, according to the fourth embodiment, it is possible to provide a battery pack equipped with a secondary battery or battery pack that has high flexibility and excellent rate characteristics.

[0187] (Fifth embodiment) According to the fifth embodiment, a vehicle is provided, which is equipped with a battery pack according to the fourth embodiment.

[0188] In the vehicle according to the fifth embodiment, the battery pack, for example, recovers regenerative energy from the vehicle's power. The vehicle may also include a mechanism that converts the vehicle's kinetic energy into regenerative energy.

[0189] Examples of vehicles according to the fifth embodiment include, for example, two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, electric assist bicycles, and railway vehicles.

[0190] The mounting location of the battery pack in the vehicle according to the fifth embodiment is not particularly limited. For example, when the battery pack is mounted in an automobile, it can be mounted in the engine compartment, at the rear of the vehicle, or under the seats.

[0191] The vehicle according to the fifth embodiment may be equipped with multiple battery packs. In this case, the batteries contained in each battery pack may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. For example, if each battery pack contains a battery pack, the battery packs may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. Alternatively, if each battery pack contains a single battery, the batteries may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections.

[0192] Next, an example of a vehicle according to the fifth embodiment will be described with reference to the drawings.

[0193] Figure 13 is a schematic partial transparency diagram showing an example of a vehicle according to the embodiment.

[0194] The vehicle 400 shown in Figure 13 includes a vehicle body 40 and a battery pack 300 according to this embodiment. In the example shown in Figure 13, the vehicle 400 is a four-wheeled automobile.

[0195] This vehicle 400 may be equipped with multiple battery packs 300. In this case, the batteries contained in the battery pack 300 (for example, single cells or battery packs) may be connected in series, in parallel, or in a combination of series and parallel connections.

[0196] Figure 13 illustrates an example in which the battery pack 300 is mounted in the engine compartment located in front of the vehicle body 40. As described above, the battery pack 300 may also be mounted, for example, in the rear of the vehicle body 40 or under the seats. 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 from the vehicle 400's power.

[0197] Next, an embodiment of the vehicle according to the fifth embodiment will be described with reference to Figure 14.

[0198] Figure 14 is a schematic diagram showing an example of a control system for the electrical system in a vehicle according to the fifth embodiment. The vehicle 400 shown in Figure 14 is an electric vehicle.

[0199] The vehicle 400 shown in Figure 14 comprises a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a control device above 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.

[0200] Vehicle 400 has its vehicle power supply 41 mounted, for example, in the engine compartment, at the rear of the vehicle body, or under the seats. Note that in the vehicle 400 shown in Figure 14, the mounting location of the vehicle power supply 41 is shown in a schematic manner.

[0201] The vehicle power supply 41 comprises a plurality (for example, three) of battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0202] Battery pack 300a comprises a battery pack 200a and a battery pack monitoring device 301a (e.g., VTM: Voltage Temperature Monitoring). Battery pack 300b comprises a battery pack 200b and a battery pack monitoring device 301b. Battery pack 300c comprises a battery pack 200c and a battery pack monitoring device 301c. Battery packs 300a-300c are battery packs similar to the aforementioned battery pack 300, and battery packs 200a-200c are battery packs similar to the aforementioned battery pack 200. Battery packs 200a-200c are electrically connected in series. Battery packs 300a, 300b, and 300c can each be independently removed and replaced with another battery pack 300.

[0203] Each of the battery packs 200a-200c comprises multiple single cells connected in series. At least one of the multiple single cells is a secondary battery according to the second embodiment. The battery packs 200a-200c are charged and discharged through the positive terminal 413 and the negative terminal 414, respectively.

[0204] The battery management device 411 communicates with the battery pack monitoring devices 301a-301c and collects information such as voltage and temperature for each of the single cells 100 included in the battery packs 200a-200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information related to the maintenance of the vehicle power supply 41.

[0205] The battery management device 411 and the battery pack monitoring devices 301a-301c are connected via a communication bus 412. On the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management device 411 and one or more battery pack monitoring devices 301a-301c). The communication bus 412 is a communication bus configured, for example, based on the CAN (Control Area Network) standard.

[0206] The battery pack monitoring devices 301a-301c measure the voltage and temperature of each individual cell constituting the battery packs 200a-200c based on commands communicated from the battery management device 411. However, temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all individual cells.

[0207] The vehicle power supply 41 may also have an electromagnetic contactor (for example, a switch device 415 shown in Figure 14) that switches the presence or absence of an electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a precharge switch (not shown) that turns on when charging is performed on the battery pack 200a-200c, and a main switch (not shown) that turns on when the output from the battery pack 200a-200c is supplied to the load. Each of the precharge switch and the main switch includes a relay circuit (not shown) that is switched on or off by a signal supplied to a coil located 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.

[0208] The inverter 44 converts the input DC voltage into a high voltage of three-phase alternating current (AC) for motor drive. 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 device 411 or the vehicle ECU 42 for controlling the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

[0209] The drive motor 45 rotates using power supplied from the inverter 44. The driving force generated by the rotation of the drive motor 45 is transmitted to the axle and drive wheels W, for example, via a differential gear unit.

[0210] Although not shown in the diagram, vehicle 400 is also equipped with a regenerative braking mechanism (regenerator). The regenerative braking mechanism rotates the drive motor 45 when vehicle 400 is braked, converting kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into a DC current. The converted DC current is input to the vehicle power supply 41.

[0211] One terminal of connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of connection line L1 is connected to the negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 within the battery management device 411 is provided on connection line L1 between the negative terminal 414 and the negative input terminal 417.

[0212] One terminal of connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41. The other terminal of connection line L2 is connected to the positive input terminal 418 of the inverter 44. A switch device 415 is provided between the positive terminal 413 and the positive input terminal 418 of connection line L2.

[0213] External terminal 43 is connected to battery management device 411. External terminal 43 can be connected to an external power supply, for example.

[0214] The vehicle ECU 42, in response to operational inputs from the driver and others, coordinates control of the vehicle power supply 41, switch device 415, inverter 44, etc., together with other management and control devices, including the battery management device 411. 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, and the entire vehicle 400 is managed. Data related 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.

[0215] The vehicle according to the fifth embodiment is equipped with the battery pack according to the fourth embodiment. Therefore, according to the fifth embodiment, it is possible to provide a vehicle equipped with a battery pack that has high flexibility and excellent rate characteristics.

[0216] [Examples] Examples are described below, but the embodiments are not limited to those described below.

[0217] (Example 1) In Example 1, a secondary battery was fabricated using the following procedure.

[0218] <Fabrication of the positive electrode> As the positive electrode active material, LiNi has an average particle diameter of 2 μm for its primary particles. 0.5 Co 0.2 Mn 0.3 A slurry for forming a positive electrode composite layer was prepared by dispersing 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 N-methyl-2-pyrrolidone (NMP) solvent. The above proportions are relative to the mass of the positive electrode composite layer. The prepared slurry was coated onto both sides of a 15 μm thick aluminum alloy foil (99.3% purity), dried, and a laminate was obtained. This laminate was pressed, and the electrode density of the positive electrode composite layer on one side was 3.2 g / cm³. 3 The positive electrode was fabricated.

[0219] <Fabrication of the negative electrode> As described below, a negative electrode was fabricated by a method including sequentially applying two types of slurries onto a current collector by sequential coating and drying them.

[0220] <Preparation of the First Slurry> As the negative electrode active material, monoclinic Nb2TiO7 (NTO) powder with an average particle diameter D50 of 2.0 μm was prepared. As the materials for the composite layer, these active material particles, acetylene black powder as a conductive agent, carboxymethyl cellulose (CMC) sodium salt powder as a thickening agent, and styrene-butadiene rubber (SBR) as a binder were used. The mixing ratio of these materials was NTO:acetylene black:CMC:SBR = 93:5:1:1 in terms of mass ratio. These materials were mixed in the following order while stirring pure water as a solvent to prepare a slurry. After dissolving carboxymethyl cellulose sodium salt in pure water, SBR was further mixed to obtain a dispersion. Acetylene black was dispersed in this dispersion, and finally NTO powder was dispersed, followed by stirring to obtain the first slurry. The first slurry is a slurry for forming a layer corresponding to region A included in the negative electrode active material-containing layer.

[0221] <Preparation of the Second Slurry> As the negative electrode active material, monoclinic Nb2TiO7 (NTO) powder with an average particle diameter D50 of 1.4 μm was prepared. As the materials for the composite layer, these active material particles, acetylene black powder as a conductive agent, carboxymethyl cellulose (CMC) sodium salt powder as a thickening agent, and styrene-butadiene rubber (SBR) as a binder were used. The mixing ratio of these materials was NTO:acetylene black:CMC:SBR = 93:5:1:1 in terms of mass ratio. These materials were mixed in the following order while stirring pure water as a solvent to prepare a slurry. After dissolving carboxymethyl cellulose sodium salt in pure water, SBR was further mixed to obtain a dispersion. Acetylene black was dispersed in this dispersion, and finally NTO powder was dispersed, followed by stirring to obtain the second slurry. The second slurry is a slurry for forming a layer corresponding to region B included in the negative electrode active material-containing layer.

[0222] <Slurry application, drying, and pressing> The first slurry was applied to both sides of a 15 μm thick aluminum alloy foil (99.3% purity) and then dried at 80°C. In this way, a first composite layer with a thickness of approximately 7 μm was created on each side of the aluminum alloy foil, which served as the current collector. Next, the second slurry was applied onto the first composite layer and dried at 80°C to form a second composite layer on top of the first composite layer. The second composite layer was formed such that the combined thickness of the first and second composite layers was 54 μm. Thus, a laminate was obtained in which the first and second composite layers were laminated on both sides of the current collector. This laminate was then pressed to create a negative electrode in which a first active material-containing layer and a second active material-containing layer were laminated on both sides of the current collector. For the obtained negative electrode, the electrode density of the active material-containing layer on one side was 2.6 g / cm³. 3 That was the case.

[0223] <Preparation of electrolytes> A mixed solvent of propylene carbonate and diethyl carbonate in a volume ratio of 1:2 was prepared. Then, LiPF6 was dissolved in this mixed solvent at a concentration of 1.2 M to prepare a liquid non-aqueous electrolyte.

[0224] <Manufacturing of secondary batteries> A wound electrode group was manufactured by winding a cellulose fiber nonwoven fabric with a thickness of 15 μm between the obtained positive and negative electrodes in a flat, spiral shape.

[0225] The fabricated electrode assembly was inserted into a metal can made of aluminum alloy (99% Al purity) with a thickness of 0.25 mm. Next, a liquid non-aqueous electrolyte was poured into the container, and the container was sealed to create a rectangular secondary battery.

[0226] (Example 2) A secondary battery was prepared in the same manner as in Example 1, except that NTO powder with an average particle size D50 of 1.9 μm was used when preparing the first slurry, and NTO powder with an average particle size D50 of 1.2 μm was used when preparing the second slurry.

[0227] (Example 3) A secondary battery was prepared in the same manner as in Example 1, except that NTO powder with an average particle size D50 of 2.5 μm was used when preparing the first slurry, and NTO powder with an average particle size D50 of 2.0 μm was used when preparing the second slurry.

[0228] (Example 4) When fabricating the negative electrode, the electrode density of the active material-containing layer on one side is 2.4 g / cm³. 3 A secondary battery was manufactured in the same manner as in Example 1, except that it was pressed in the manner described above.

[0229] (Example 5) When fabricating the negative electrode, the electrode density of the active material-containing layer on one side is 2.2 g / cm³. 3 A secondary battery was manufactured in the same manner as in Example 1, except that it was pressed in the manner described above.

[0230] (Example 6) When fabricating the negative electrode, a first active material-containing layer was formed on one surface of the negative electrode current collector (here, the first surface) in the same manner as in Example 1, and on the other surface of the negative electrode current collector (here, the second surface), a secondary battery was fabricated in the same manner as in Example 1, except that NTO powder with an average particle size D50 of 1.4 μm was used when fabricating the first slurry, and NTO powder with an average particle size D50 of 2.0 μm was used when fabricating the second slurry.

[0231] (Comparative Example 1) A secondary battery was fabricated in the same manner as in Example 1, except that the preparation of the first composite layer using the first slurry was omitted when fabricating the negative electrode, and an active material-containing layer was fabricated on both sides of the negative electrode current collector using only the second slurry. The thickness of the active material-containing layer formed on both sides of the negative electrode current collector was approximately 54 μm on each side.

[0232] (Comparative Example 2) A secondary battery was prepared in the same manner as in Example 1, except that NTO powder with an average particle size D50 of 1.4 μm was used when preparing the first slurry, and NTO powder with an average particle size D50 of 2.0 μm was used when preparing the second slurry.

[0233] (Comparative Example 3) A secondary battery was fabricated in the same manner as in Example 1, except that NTO powder with an average particle size D50 of 2.0 μm was used when preparing the first slurry, and NTO powder with an average particle size D50 of 0.8 μm was used when preparing the second slurry.

[0234] (Comparative Example 4) A secondary battery was fabricated in the same manner as in Example 1, except that NTO powder with an average particle size D50 of 4.1 μm was used when preparing the first slurry, and NTO powder with an average particle size D50 of 3.2 μm was used when preparing the second slurry.

[0235] <Particle size distribution measurement> For the negative electrodes fabricated in each example, the active material powder was isolated by the method described in the first embodiment, and the particle size distribution of the active material powder was measured. From the obtained particle size distribution chart, the median diameter (D50) of the active material particles contained in the negative electrode was determined.

[0236] <SEM observation, image processing> The secondary batteries fabricated in each example were disassembled, and the cross-section of the negative electrode was observed using SEM by the method described in the first embodiment. Also, the obtained SEM images were subjected to image processing. FIG. 15 is a SEM image observing the vicinity of the negative electrode current collector 3a according to Comparative Example 1. FIG. 16 is an image obtained by subjecting the said image to image processing by the above-mentioned procedure. Comparing FIG. 16 according to Comparative Example 1 with FIG. 3 according to Example 1, it can be seen that in Example 1, there are many particles with a large particle size in both region A and region C.

[0237] From the images obtained for each example, the number ratios RA, RB, RC, and RD were calculated. As an example, in region A according to Example 1 shown in FIG. 3, the number of active material particles contained in the entire region A is 193, and among them, the cross-sectional area is 0.1 μm<Case 2 ~0.2 μm<Case 2The number of particles within the range was 69. When the number ratio RA was calculated from these numerical values, the number ratio RA was 35.8%. The above results are shown in Table 1 and Table 2 below.

[0238] <10-second resistance measurement> After adjusting the state of charge (SOC) of the secondary battery fabricated for each example to 50%, it is discharged for 10 seconds at a constant current of 3C rate (in terms of the negative electrode active material). Taking the difference between the voltage after discharge and the voltage before energization as ΔV, the 10-second resistance [mΩ] is calculated from the following formula. In the following formula, I represents the current value. The value of the 10-second resistance is an index for evaluating the input / output characteristics. (10-second resistance) = ΔV / I <Electrode flexibility evaluation> The negative electrode is taken out from the secondary battery fabricated for each example, and a test piece having a size of 5 cm × 5 cm is cut out from this negative electrode. The obtained piece is folded in half and a pressure is applied with a strength of 15 kN. Then, the case where no breakage occurs is evaluated as "○", and the case where breakage occurs to such an extent that it can be visually discriminated is evaluated as "×".

[0239] The above results are summarized in Table 1 and 2 below. Table 1 and Table 2 summarize the results for the negative electrodes fabricated in the examples and comparative examples.

[0240]

Table 1

[0244] In Comparative Examples 1 and 2, both the first active material-containing layer provided on the first surface side of the current collector and the second active material-containing layer provided on the second surface side of the current collector contained a cross-sectional area of ​​0.1 μm² near the current collector. 2 ~0.2μm 2 The proportion of these particles was higher in the region away from the current collector compared to the region further away. Specifically, both the ratio RA / RB and the ratio RC / RD were 1.0 or higher. For this reason, Comparative Examples 1 and 2 were inferior in both electrode flexibility and 10-second resistance.

[0245] In Comparative Examples 3 and 4, both the ratio RA / RB and the ratio RC / RD were less than 1.0, but the D50 of the active material particles contained in the first and second active material-containing layers were both outside the range of 1.1 μm to 2.5 μm. In Comparative Example 3, where D50 was less than 1.1 μm, the electrode flexibility was poor, resulting in defects in the active material-containing layer. This is thought to be due to increased bonding between the active material-containing layer and the current collector. On the other hand, in Comparative Example 4, where D50 exceeded 2.5 μm, sufficient electrode flexibility was observed, but the resistance was high because the construction of the electronically conductive network between particles was insufficient.

[0246] As shown in Examples 4 and 5, when the electrode density was reduced by adjusting the layer thickness (press pressure), the volumetric energy density tended to be slightly lower, but the 10-second resistance value was lower. As can be seen from the comparison between Example 6 and Example 1, when the ratio RA / RB for the first active material-containing layer, as well as the ratio RC / RD for the second active material-containing layer, was less than 1.0, that is, Example 1 had a lower 10-second resistance.

[0247] An electrode is provided according to at least one embodiment and example described above. The electrode comprises a current collector having a first surface and a second surface facing the first surface, and a first active material containing layer laminated on one of the first and second surfaces of the current collector and containing a plurality of first active material particles. The first active material containing layer has a first back surface in contact with the current collector and a first front surface located on the opposite side of the first back surface. The volume-based average particle diameter D50 of the plurality of first active material particles is in the range of 1.5 μm to 2.5 μm. The first active material containing layer includes a region A defined from the first back surface to a position 10% of the total thickness, and a region B defined from the position 10% of the total thickness to the first surface, when the total thickness from the first back surface to the first front surface is 100%. In the cross-sectional image obtained by observing the cross-section of the electrode along the stacking direction of the current collector and the first active material-containing layer at 5,000x magnification using a scanning electron microscope, among the multiple first active material particles, those with a cross-sectional area of ​​0.1 μm² 2 ~0.2μm 2 The proportion of particles within this range is lower in region A compared to region B.

[0248] This electrode makes it possible to realize a secondary battery that is highly flexible and exhibits excellent rate characteristics.

[0249] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and essence of the invention, as well as in the claims and their equivalents. The invention described in the original claims of this application is listed below. [1] A current collector having a first surface and a second surface facing the first surface, An electrode comprising a first active material-containing layer laminated on one of the first and second surfaces of the current collector, and containing a plurality of first active material particles, The first active material-containing layer has a first back surface that is in contact with the current collector and a first front surface located on the opposite side from the first back surface. The volume-based average particle diameter D50 of the plurality of first active material particles is in the range of 1.1 μm to 2.5 μm. The first active material-containing layer includes a region A defined from the first back surface to a point 10% of the total thickness, and a region B defined from the point 10% of the total thickness to the first surface, when the total thickness from the first back surface to the first front surface is 100%. In the cross-sectional image obtained by observation at 5,000x magnification using a scanning electron microscope, the cross-section of the electrode along the stacking direction of the current collector and the first active material-containing layer, Among the plurality of first active material particles, the cross-sectional area is 0.1 μm 2 ~0.2μm 2 The proportion of particles within the specified range is lower in region A compared to region B. [2] Among the first active material particles contained in region A, the cross-sectional area is 0.1 μm 2 ~0.2μm 2 The electrode described in [1] has a particle number ratio RA within the range of 40% or less. [3] Among the first active material particles contained in region B, the cross-sectional area is 0.1 μm 2 ~0.2μm 2 The electrode described in [1] or [2] has a particle number percentage RB within the range greater than 40%. [4] The electrode according to any one of [1] to [3], wherein the total thickness of the first active material-containing layer is in the range of 20 μm to 60 μm. [5] The density of the first electrode in the first active material-containing layer is 2.2 g / cm³. 3 -2.9 g / cm³ 3 An electrode described in any one of the following items [1] to [4] within the range. [6] The plurality of first active material particles include niobium titanium composite oxide, The aforementioned niobium-titanium composite oxide has the general formula Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ Represented by A composite oxide, and Li x Ti 1-y M3 y+z Nb 2-z O 7-δ The complex oxide represented by At least one selected from the group consisting of, The aforementioned M1 is at least one selected from the group consisting of Zr, Si, and Sn, the aforementioned M2 is at least one selected from the group consisting of V, Ta, and Bi, and the aforementioned M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The electrode described in any one of [1] to [5], wherein x satisfies 0 ≤ x ≤ 5, y satisfies 0 ≤ y < 1, z satisfies 0 ≤ z < 2, and δ satisfies -0.3 ≤ δ ≤ 0.3. [7] The electrode is laminated on the surface of the current collector that has the first active material-containing layer laminated on the surface of the first active material-containing layer that has the first active material-containing layer laminated on the surface of the first active material-containing layer that has the first active material-containing layer laminated on the surface of the current collector that has the first active material-containing layer laminated on the surface The second active material-containing layer has a second back surface that is in contact with the current collector and a second front surface located on the opposite side from the second back surface. The volume-based average particle diameter D50 of the aforementioned plurality of second active material particles is in the range of 1.1 μm to 2.5 μm. The second active material-containing layer includes a region C defined from the second back surface to a point 10% of the total thickness, and a region D defined from the point 10% of the total thickness to the second surface, when the total thickness from the second back surface to the second front surface is 100%. In the cross-sectional image obtained by observation at 5,000 magnification using a scanning electron microscope of the electrode along the stacking direction of the current collector and the second active material-containing layer, Among the plurality of second active material particles, the cross-sectional area is 0.1 μm 2 ~0.2μm 2 The electrode according to any one of the following [1] to [6], wherein the proportion of particles within the range is lower in region C compared to region D. [8] A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, A secondary battery in which at least one of the positive electrode and the negative electrode is an electrode described in any one of items [1] to [7]. A battery pack comprising the rechargeable batteries described in [9] and [8].

[10] External terminals for power supply, Protection circuit and The battery pack described in [9] further comprises the following:

[11] comprising a plurality of the aforementioned secondary batteries, The battery pack described in [9] or

[10] , wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. A vehicle equipped with a battery pack as described in any one of the items

[12] [9] to

[11] .

[13] The vehicle according to

[12] , which includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy. [Explanation of Symbols]

[0250] 1…Electrode group, 2…Outer casing, 3…Electrode (negative electrode), 3a…Current collector (negative electrode current collector), 3b…Active material containing layer (negative electrode active material containing layer), 3b1…First active material containing layer, 3b2…Second active material containing layer, 3c…Negative electrode current collector tab, 4…Separator, 5…Positive electrode, 5a…Positive electrode current collector, 5b…Positive electrode active material containing layer, 6…Negative electrode terminal, 7…Positive electrode terminal, 21…Busbar, 22…Positive electrode side lead, 22a…Other end, 23…Negative electrode side lead, 23a…Other end, 24… 31...Adhesive tape, 32...Container, 33...Lid, 34...Printed circuit board, 35...Wiring, 40...Vehicle body, 41...Vehicle power supply, 42...Electrical control device, 43...External terminals, 44...Inverter, 45...Drive motor, 51...First surface, 52...Second surface, 61...First back surface, 62...First front surface, 71...Second back surface, 72...Second front surface, 80...Coating device, 81...Conveyor roller, 82...Tank, 82a...Slurry I discharge port, 83...Ta 83a…Slurry II discharge port, 100…Secondary battery, 200…Battery pack, 200a…Battery pack, 200b…Battery pack, 200c…Battery pack, 300…Battery pack, 300a…Battery pack, 300b…Battery pack, 300c…Battery pack, 301a…Battery pack monitoring device, 301b…Battery pack monitoring device, 301c…Battery pack monitoring device, 342…Positive side connector, 343…Negative side connector, 345…Thermistor, 346…Protection circuit, 342a...Wiring, 343a...Wiring, 350...External terminal for power supply, 352...Positive terminal, 353...Negative terminal, 348a...Positive wiring, 348b...Negative wiring, 400...Vehicle, 411...Battery management device, 412...Communication bus, 413...Positive terminal, 414...Negative terminal, 415...Switching device, 416...Current detection unit, 417...Negative input terminal, 418...Positive input terminal, L1...Connection line, L2...Connection line, W...Drive wheel.

Claims

1. A current collector having a first surface and a second surface facing the first surface, An electrode comprising a first active material-containing layer laminated on one of the first and second surfaces of the current collector, and containing a plurality of first active material particles, The first active material-containing layer has a first back surface that is in contact with the current collector and a first front surface located on the opposite side from the first back surface. The volume-based average particle diameter D50 of the plurality of first active material particles is in the range of 1.1 μm to 2.5 μm. The first active material-containing layer includes, when the total thickness from the first back surface to the first front surface is 100%, a region A defined from the first back surface to a position 10% of the total thickness, and a region B defined from the position 10% of the total thickness to the first front surface. In the cross-sectional image obtained by observation at 5,000 magnification using a scanning electron microscope of the electrode along the stacking direction of the current collector and the first active material-containing layer, Among the plurality of first active material particles, the cross-sectional area is 0.1 μm 2 ~0.2 μm 2 The proportion of particles within this range is lower in region A compared to region B. The average particle diameter D50 of the first active material particles contained in region A is larger than the average particle diameter D50 of the first active material particles contained in region B. The electrode having a first electrode density in the first active material-containing layer within the range of 2.2 g / cm³ to 2.9 g / cm³.

2. Among the first active material particles contained in region A, the cross-sectional area is 0.1 μm 2 ~0.2 μm 2 The electrode according to claim 1, wherein the number percentage RA of particles within the range is 40% or less.

3. Among the first active material particles contained in region B, the cross-sectional area is 0.1 μm 2 ~0.2 μm 2 The electrode according to claim 1 or 2, wherein the number percentage RB of particles within the range is greater than 40%.

4. The electrode according to any one of claims 1 to 3, wherein the total thickness of the first active material-containing layer is in the range of 20 μm to 60 μm.

5. The plurality of first active material particles include niobium titanium composite oxide, The niobium-titanium composite oxide has the general formula Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ and is represented by A composite oxide, and the general formula Li x Ti 1-y M3 y+z Nb 2-z O 7-δ The complex oxide represented by At least one selected from the group consisting of, The aforementioned M1 is at least one selected from the group consisting of Zr, Si, and Sn, the aforementioned M2 is at least one selected from the group consisting of V, Ta, and Bi, and the aforementioned M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The above x satisfies 0 ≤ x ≤ 5, the above y satisfies 0 ≤ y < 1, the above z satisfies 0 ≤ z < 2, and the above δ satisfies -0.3 ≤ δ ≤ 0.

3. The electrode according to any one of claims 1 to 4.

6. The electrode is laminated on the surface of the current collector that has the first active material-containing layer laminated on the surface The second active material-containing layer has a second back surface that is in contact with the current collector and a second front surface located on the opposite side from the second back surface. The volume-based average particle diameter D50 of the plurality of second active material particles is in the range of 1.1 μm to 2.5 μm. The second active material-containing layer includes a region C defined from the second back surface to a point 10% of the total thickness, and a region D defined from the point 10% of the total thickness to the second surface, when the total thickness from the second back surface to the second front surface is 100%. In the cross-sectional image obtained by observation at 5,000 magnification using a scanning electron microscope of the electrode along the stacking direction of the current collector and the second active material-containing layer, Among the plurality of second active material particles, the cross-sectional area is 0.1 μm ２ ~0.2 μm ２ The proportion of particles within the range is lower in region C compared to region D. The average particle diameter D50 of the second active material particles contained in region C is larger than the average particle diameter D50 of the second active material particles contained in region D. The second electrode density of the second active material-containing layer is 2.2 g / cm³ to 2.9 g / cm³. An electrode according to any one of claims 1 to 5, which is within the range of [the specified range].

7. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, A secondary battery in which at least one of the positive electrode and the negative electrode is the electrode described in any one of claims 1 to 6.

8. A battery pack comprising the secondary battery described in claim 7.

9. External terminals for power supply, Protection circuit and The battery pack according to claim 8, further comprising the above.

10. The device comprises multiple secondary batteries, The battery pack according to claim 8 or 9, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

11. A vehicle equipped with the battery pack described in any one of claims 8 to 10.

12. The vehicle according to claim 11, which includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

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