Electrode, secondary battery, battery pack, and vehicle

Abstract

To provide an electrode capable of realizing a secondary battery excellent in life performance and input / output performance, a secondary battery including the electrode, a battery pack including the secondary battery, and a vehicle including the battery pack.SOLUTION: An electrode includes an active material-containing layer. The active material-containing layer includes an active material particle including a first phase and a second phase. The first phase is a niobium-containing oxide phase. The second phase is different from the first phase. In each of divided regions obtained by dividing a square region defined by a first side parallel to a thickness direction and a second side orthogonal to the first side into 16 equal parts in a cross section of the active material-containing layer along the thickness direction, a ratio of an area occupied by the second phase to an area occupied by the first phase is 10% or less. The area occupied by the second phase is an area of one or more regions in which the second phase occupies an area equal to or larger than 2×10-14 m2 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Lithium-ion nonaqueous electrolyte batteries have become widely used as high-energy density batteries in various fields, such as electric vehicles, power storage, and information devices. Accordingly, market demand for nonaqueous electrolyte batteries has increased, and research into them has been actively pursued.

[0003] Among these, lithium-ion nonaqueous electrolyte batteries used as power sources for electric vehicles are required to have a high energy density, i.e., a large discharge capacity per unit mass or unit volume, due to their intended use. Furthermore, they are required to be able to charge efficiently even when a large current is instantaneously input to the battery in order to regenerate kinetic energy during deceleration. Furthermore, they are also required to be able to instantaneously discharge a large output, i.e., a large current, during start-up, sudden start-up, sudden acceleration, etc. In other words, secondary batteries used as power sources for electric vehicles are required to have not only a large capacity but also good short-term input / output characteristics.

[0004] Carbon-based materials have been widely used as the negative electrode active material for lithium-ion nonaqueous electrolyte batteries. However, in recent years, spinel-type lithium titanate, which has a higher Li absorption / desorption potential than carbon-based materials, has attracted attention. This spinel-type lithium titanate exhibits excellent cycle characteristics because it does not undergo volume changes during charge / discharge reactions. Furthermore, this spinel-type lithium titanate is highly safe compared to carbon-based materials, as it is less likely to develop lithium dendrites. Furthermore, being a ceramic, it has the significant advantage of being less susceptible to thermal runaway.

[0005] On the other hand, non-aqueous electrolyte batteries using spinel-type lithium titanate as the negative electrode active material have the problem of low energy density, and a negative electrode material that can achieve high capacity is needed. Therefore, spinel-type lithium titanate Li4Ti5O 12 Larger niobium titanium oxides, such as Nb2TiO7, are being investigated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2022-28793 [Patent Document 2] International Publication No. 2021 / 235289 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-168352 Summary of the Invention [Problem to be solved by the invention]

[0007] The embodiments aim to provide an electrode capable of realizing a secondary battery with excellent life performance and input / output performance, a secondary battery including the electrode, a battery pack including the secondary battery, and a vehicle including the battery pack. [Means for solving the problem]

[0008] According to an embodiment, an electrode is provided. The electrode includes an active material-containing layer. The active material-containing layer includes active material particles including a first phase and a second phase. The first phase is a niobium-containing oxide phase. The second phase is a phase different from the first phase. In a cross section of the active material-containing layer along the thickness direction, a square region defined by a first side parallel to the thickness direction and a second side perpendicular to the first side is equally divided into 16 divided regions, and the ratio of the area occupied by the second phase to the area occupied by the first phase is 10% or less. The area occupied by the second phase is 2×10 -14 m 2 The area of ​​one or more regions occupying an area equal to or greater than the area of ​​the other region.

[0009] According to another embodiment, a secondary battery including an electrode according to the embodiment is provided.

[0010] According to another embodiment, a battery pack including a secondary battery according to the embodiment is provided.

[0011] According to another embodiment, a vehicle equipped with a battery pack according to the embodiment is provided. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram schematically showing an image obtained by binarizing an SEM observation image of a cross section of an electrode according to an example of an embodiment. [Figure 2] FIG. 2 is a diagram schematically showing an image obtained by performing another binarization process on the SEM observation image shown in FIG. 1. [Figure 3] FIG. 2 is a diagram schematically showing an image obtained by further processing the image shown in FIG. 1; [Figure 4] FIG. 2 is an enlarged view of part C1 shown in FIG. [Figure 5] FIG. 2 is an enlarged view of part C2 shown in FIG. [Figure 6] FIG. 2 is a plan view schematically showing an example of an electrode according to the embodiment. [Figure 7] FIG. 7 is a cross-sectional view of the electrode taken along line II-II of FIG. 6. [Figure 8] An enlarged view of part a shown in Figure 7. [Figure 9] 10 is a graph showing a histogram of brightness of an observed image of a cross section of an electrode according to an example of an embodiment. [Figure 10] 10 is a graph showing a five-point moving average of the first derivative of the histogram according to FIG. 9; [Figure 11] FIG. 11 is an enlarged view of the graph shown in FIG. 10. [Figure 12] 10 is a graph showing a five-point moving average of the second derivative of the histogram according to FIG. 9; [Figure 13] FIG. 13 is an enlarged view of the graph shown in FIG. 12. [Figure 14] 1 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment. [Figure 15]FIG. 15 is an enlarged cross-sectional view of part A of the secondary battery shown in FIG. [Figure 16] FIG. 10 is a partially cutaway perspective view schematically showing another example of a secondary battery according to an embodiment. [Figure 17] FIG. 17 is an enlarged cross-sectional view of part B of the secondary battery shown in FIG. [Figure 18] FIG. 1 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. [Figure 19] FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. [Figure 20] FIG. 20 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. [Figure 21] FIG. 1 is a partially see-through view schematically illustrating an example of a vehicle according to an embodiment. [Figure 22] 1 is a diagram illustrating an example of a control system for an electrical system in a vehicle according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0013] (First embodiment) When synthesizing a niobium-containing oxide, a phase other than the niobium-containing oxide may be generated in addition to the niobium-containing oxide phase. Therefore, particles containing a niobium-containing oxide may contain, for example, a niobium-containing oxide phase and a phase other than the niobium-containing oxide phase.

[0014] The present inventors have found that when an active material-containing layer of an electrode contains particles containing a niobium-containing oxide phase and a phase other than the niobium-containing oxide, the particles are prone to cracking when the electrode is subjected to charge-discharge cycles.Furthermore, they have found that, in particles containing a niobium-containing oxide phase and a phase other than the niobium-containing oxide, the greater the volume occupied by the phase other than the niobium-containing oxide, the more likely the particles are to crack.

[0015] The present inventors have considered the reason why cracks occur in particles containing niobium-containing oxide as follows.

[0016] When an electrode including particles containing a niobium-containing oxide in an active material-containing layer is subjected to charge-discharge cycles, lithium ions are desorbed from and inserted into the niobium-containing oxide. The niobium-containing oxide has a high charge-discharge capacity, but undergoes a large volume change due to the desorbing and inserting of lithium ions.

[0017] Therefore, a difference may occur between the volume of the niobium-containing oxide phase and the volume of the phase other than the niobium-containing oxide phase during charging and discharging. This difference is thought to cause stress concentration at the interface between the niobium-containing oxide phase and the phase other than the niobium-containing oxide phase. The stress concentration may cause cracks in the particles containing the niobium-containing oxide.

[0018] Furthermore, in the particles, the larger the volume of the phase other than the niobium-containing oxide, the larger the difference between the volume of the niobium-containing oxide phase and the volume of the phase other than the niobium-containing oxide phase that occurs during charging and discharging tends to be, which is thought to increase the stress generated at the interface between the niobium-containing oxide phase and the phase other than the niobium-containing oxide phase, making the particles more likely to crack.

[0019] When the particles crack, the specific surface area of ​​the particles containing niobium-containing oxide increases, which can increase side reactions. This can reduce the lifespan of the electrode. Furthermore, when the particles containing niobium-containing oxide crack, the conductive path can be broken, causing an increase in resistance. This can reduce the input / output performance of the electrode.

[0020] Based on this result, the inventors conducted further research and achieved the electrode according to the first embodiment.

[0021] According to an embodiment, an electrode is provided. The electrode includes an active material-containing layer. The active material-containing layer includes active material particles including a first phase and a second phase. The first phase is a niobium-containing oxide phase. The second phase is a phase different from the first phase. In a cross section of the active material-containing layer along the thickness direction, a square region defined by a first side parallel to the thickness direction and a second side perpendicular to the first side is equally divided into 16 divided regions, and the ratio of the area occupied by the second phase to the area occupied by the first phase is 10% or less. The area occupied by the second phase is 2×10 -14 m 2 The area of ​​one or more regions occupying an area equal to or greater than the area of ​​the other region.

[0022] In a cross section along the thickness direction of the active material-containing layer, the area of ​​the second phase is 2×10 relative to the area of ​​the first phase. -14 m 2 A small area of ​​one or more regions occupying the above area can be an indicator that the second phase derived from particles having a relatively large volume of the second phase per active material particle is small.

[0023] Active material particles with a relatively large volume of the second phase per particle are prone to cracking when the electrode is charged and discharged. If the active material particles are cracked, the input / output performance of the electrode may be reduced. Therefore, it is preferable that the active material-containing layer have a small number of particles with a relatively large volume of the second phase per particle.

[0024] In the electrode according to the first embodiment, the second phase is 2×10 in each of the 16 divided regions obtained by dividing the square region into 16 equal parts. -14 m 2 The area of ​​one or more regions occupying an area of ​​16 or more is less than 10% of the area occupied by the first phase. In other words, cracking of the active material particles is suppressed in each of the 16 divided regions. Furthermore, it can be said that cracking of the active material particles is suppressed throughout the entire square region. Therefore, in each of the 16 divided regions obtained by equally dividing the square region, the second phase is 2 × 10 -14 m 2The fact that the area of ​​the one or more regions occupying the above area is 10% or less of the area occupied by the first phase is an indicator that cracking of the active material particles is suppressed throughout the active material-containing layer.

[0025] Therefore, according to the embodiment, it is possible to provide an electrode that can realize a secondary battery that is excellent in life performance and input / output performance.

[0026] The electrodes according to the embodiments will be described in further detail with reference to the drawings.

[0027] An electrode according to an embodiment may include an active material-containing layer and a current collector. The current collector may have two main surfaces. The active material-containing layer may be formed on one or both main surfaces of the current collector. The active material-containing layer may include an active material and, optionally, a conductive agent and a binder. The active material includes particles containing a niobium-containing oxide. At least some of the particles containing the niobium-containing oxide are active material particles containing a first phase and a second phase. The particles containing the niobium-containing oxide may include particles consisting of the first phase. The active material particles containing the first phase and the second phase may be primary particles or secondary particles. The active material particles that are secondary particles may be, for example, secondary particles containing primary particles containing the first phase and primary particles containing the second phase.

[0028] The electrode according to the embodiment may be a battery electrode. The niobium-containing oxide contained in the active material may occlude and release carrier ions. That is, the first phase of the active material particles, which is a niobium-containing oxide phase, may occlude and release carrier ions. The second phase may or may not occlude and release carrier ions. The carrier ions may be, for example, alkali metal ions. The electrode according to the embodiment may be an electrode for a lithium battery (lithium ion battery).

[0029] The active material particles contained in the electrode according to the embodiment include a first phase that is a niobium-containing oxide phase and a second phase that is a phase different from the first phase. The second phase may be, for example, a phase formed by the generation of a substance different from the niobium-containing oxide during the synthesis of the niobium-containing oxide, or may be a phase formed by the inclusion of a part of the materials for synthesizing the niobium-containing oxide in the active material particles without reacting.

[0030] In a cross section along the thickness direction of the active material-containing layer, the second phase is 2×10 -14 m 2 The area occupying an area of ​​2×10 or more is sometimes referred to as the large second phase area. -14 m 2 A region occupying an area less than 100 μm may be referred to as a second phase subregion.

[0031] In a cross section of the active material-containing layer taken along the thickness direction, at least a portion of the second phase may be a second-phase large domain. The number of second-phase large domains may be one or more. The cross section of the active material-containing layer taken along the thickness direction may or may not include one or more second-phase small domains.

[0032] In the divided region of the cross section along the thickness direction of the active material-containing layer of the electrode, the second phase is 2 × 10 -14 m 2 When there are multiple regions (second-phase-large regions) occupying an area equal to or larger than this, the total area of ​​the multiple second-phase-large regions is 10% or less of the area occupied by the first phase. In the divided regions of the cross section of the electrode, the ratio of the area occupied by the second-phase-large regions to the area occupied by the first phase may be 0% or more, or may be 2.1% or more.

[0033] Each of the second-phase large regions may be, for example, a region occupied by the second phase in a cross section along the thickness direction of the active material-containing layer, and may be a region separated from other regions by a single contour line. -14 m 2 That's all.

[0034] In a cross section along the thickness direction of the active material-containing layer, the second-phase large region may or may not be included in the active material particle. When the second-phase large region is included in the active material particle, the second-phase large region may be, for example, a region that is located more inward than the first phase in the active material particle. When the second-phase large region is not included in the active material particle, the second-phase large region may be a region occupied by particles separate from the particles containing the niobium-containing oxide. The particles separate from the particles containing the niobium-containing oxide may be, for example, particles consisting of the second phase. Particles consisting of the second phase may also be generated, for example, when the active material particle cracks and the second phase separates from the first phase. When the second-phase large region is not included in the active material particle, the second-phase small region may be included in the active material particle.

[0035] The second phase is 2×10 -14 m 2 The region (second-phase large region) occupying an area of ​​0.7 or more and 1.0 or less has a circularity of, for example, 0.7 or more and 1.0 or less. When one or more second-phase large regions are present in a cross section along the thickness direction of the active material-containing layer, the circularity of each of the one or more second-phase large regions may be within the above range. The second-phase large region having a circularity of 0.7 or more and 1.0 or less may be derived from, for example, a second phase that is generated inside the first phase during synthesis of the niobium-containing oxide.

[0036] During synthesis of the niobium-containing oxide, the second phase may be formed more inward than the first phase. Therefore, the active material particles may include a core of the second phase and an outer shell of the first phase that covers at least a portion of the surface of the core. The core may be, for example, substantially spherical in cross section with a circularity of 0.7 or more and 1.0 or less.

[0037] In such particles, if the volume occupied by the second-phase core is large, the active material particles are prone to cracking. This is because, when the first phase and / or second phase expand or contract, the difference in volume change between the first and second phases is large, which makes it easy for stress to occur at the interface between the outer shell and the core. Furthermore, if the second-phase core is covered by the outer shell of the first phase, there is little room for the stress to escape, making the active material particles even more prone to cracking.

[0038] In an electrode, it is preferable that the area occupied by the second-phase large regions having a circularity of 0.7 to 1.0 is smaller than the area occupied by the first phase, because this makes it less likely for cracks to occur in the active material particles contained in the electrode. Specifically, in each of the 16 divided regions obtained by equally dividing the square region, it is preferable that the area occupied by the second-phase large regions having a circularity of 0.7 to 1.0 is 10% or less of the area occupied by the first phase. In each of the 16 divided regions obtained by equally dividing the square region, the lower limit of the area occupied by the second-phase large regions having a circularity of 0.7 to 1.0 relative to the area occupied by the first phase can be 0%. The upper limit can be 10.0%.

[0039] If the area occupied by the large second phase region is larger than the area occupied by the first phase in a cross section along the thickness direction of the active material-containing layer of the electrode, it can be determined that the electrode is one in which cracking of the active material particles is likely to occur, or is an electrode in which cracking of the active material particles has already occurred.

[0040] In contrast, in the electrode according to the embodiment, in each of the 16 divided regions obtained by dividing the square region into equal parts, the area occupied by the large second-phase region is 10% or less of the area occupied by the first phase, thereby suppressing cracking of the active material particles. By suppressing cracking of the active material particles, an increase in side reactions due to an increase in the specific surface area of ​​the active material can be suppressed, thereby improving the life performance. Furthermore, an increase in resistance due to cracking of the active material particles can be suppressed, thereby improving input / output performance.

[0041] In the square region, the ratio of the area occupied by the large second phase region to the area occupied by the first phase can be 4% or less. When this ratio is 4% or less, it can be said that the ratio of particles in which the volume of the second phase is relatively large per active material particle is low throughout the entire square region. Therefore, it is possible to further suppress the occurrence of cracks in the active material particles. In the square region of the cross section along the thickness direction of the active material-containing layer of the electrode, the second phase is 2 × 10 -14 m 2When there are multiple regions (second-phase large regions) occupying an area of ​​at least 1.5%, the total area of ​​the multiple second-phase large regions may be 4% or less of the area occupied by the first phase. In the square region, the ratio of the area occupied by the second-phase large regions to the area occupied by the first phase may be 0% or more, or may be 1.7% or more.

[0042] FIG. 1 is a diagram schematically showing an image obtained by binarizing an SEM observation image of a cross section of an active material-containing layer of an electrode according to an embodiment.

[0043] Although the image processing method will be described in detail later, Fig. 1 shows a schematic image obtained by binarizing a scanning electron microscope (SEM) image of a cross section of an active material-containing layer by setting a first threshold value and a second threshold value for brightness. In the binarization, areas of the SEM image where the brightness is equal to or greater than the second threshold value and less than the first threshold value are displayed in black.

[0044] In FIG. 1, the lines and hatched areas are areas that are expressed in black in binarization.

[0045] The lines in Figure 1 are a guide to the outline of the first phase, and the hatched area is the area occupied by the second phase.

[0046] The cross section of the active material-containing layer of the electrode according to the embodiment includes a first phase 30a and a second phase 30b, and also includes active material particles 30 that include the first phase 30a and the second phase 30b.

[0047] As shown in Figure 1, such a cross section may include one or more closed regions occupied by the first phase 30a and one or more closed regions occupied by the second phase 30b. In the cross section of the active material-containing layer of the electrode, the closed regions occupied by the first phase can be determined to be derived from the granular first phase. The closed regions occupied by the second phase can be determined to be derived from the granular second phase.

[0048] As shown in Fig. 1, the active material-containing layer of the electrode according to the embodiment may contain a plurality of granular first phases and a plurality of granular second phases. In the active material-containing layer, as shown in part C1, a granular second phase 30b may be contained in the gap between two granular first phases 30a. Furthermore, as shown in part C2, a granular second phase 30b may be contained within one granular first phase 30a. The second phase may contain particles 303b made of the second phase.

[0049] FIG. 2 shows a schematic image of an SEM image of a cross section of an active material-containing layer, binarized by setting a first threshold value for brightness. In the binarization, areas of the SEM image where the brightness is equal to or greater than the first threshold value are expressed in black. The hatched areas in FIG. 2 are areas expressed in black by binarization. The hatched areas are areas occupied by the first phase.

[0050] Fig. 3 is an image obtained by further processing the binarized image shown in Fig. 1. The specific processing method will be described later, but Fig. 3 shows the image obtained by further processing the binarized image shown in Fig. 1, where the area of ​​the lines and regions expressed in black is 2 × 10 -14 m 2 The regions where the second phase is 2×10 or more and the circularity is 0.7 or more and 1.0 or less are extracted and shown by hatching. That is, each of the hatched regions in FIG. 3 is -14 m 2 This is a large second-phase region occupying an area of ​​at least 100 μm. Parts C1 and C2 in Fig. 3 correspond to parts C1 and C2 shown in Fig. 1, respectively. The second phase contained in part C1 is indicated by reference symbol 301b.

[0051] FIG. 4 is an enlarged view of portion C1 shown in FIG. 1. Portion C1 includes a first phase 30a and a second phase 30b. Of the second phases, the second phase included in portion C1 is indicated by reference symbol 301b. The first phase 30a included in portion C1 includes a first portion 301a and a second portion 302a. The second phase 301b is located in the gap between the first portion 301a and the second portion 302a.

[0052] The second phase 301b contained in the C1 portion is shown by hatching in Fig. 3. That is, the second phase 301b contained in the C1 portion is 2 × 10 -14 m 2 The second phase 301b is a large second-phase region occupying an area of ​​at least 1.0. Furthermore, the circularity of the second phase 301b is 0.7 or more and 1.0 or less. From this, it is considered that the first portion 301a, the second portion 302a, and the second phase 301b are formed by cracking of a particle containing a single first phase and a second phase. Specifically, it is considered that the first portion 301a, the second portion 302a, and the second phase 301b are formed by cracking of a particle containing a single first phase outer shell and a second phase core, and in which the volume occupied by the second phase core is relatively large compared to the particle. This is also clear from the fact that the part of the outline of the first portion 301a facing the second portion 302a and the second phase 301b corresponds to the shape of the second portion 302a and the second phase 301b.

[0053] 5 is an enlarged view of part C2 shown in FIG. 1. Part C2 contains active material particles 30 including a first phase 30a and a second phase 30b. The second phase contained in part C2 is indicated by reference symbol 302b. The second phase 302b contained in part C2 is not shown in FIG. 3. In other words, the second phase 302c contained in part C2 has an area of ​​2×10 -14 m 2 That is, the second phase 302c contained in the C2 portion is a second phase small region. Such active material particles are less likely to crack.

[0054] Examples of niobium-containing oxides include niobium titanium oxide and niobium pentoxide (Nb2O5). One or more types of niobium-containing oxides may be used.

[0055] The electrode according to the embodiment preferably contains niobium titanium oxide as the niobium-containing oxide. When niobium titanium oxide is synthesized, a phase different from niobium titanium oxide is likely to be generated. Therefore, when the first phase is a niobium titanium oxide phase, the cracking of the active material particles can be suppressed by reducing the ratio of the area occupied by the second-phase large domains to the area occupied by the first phase in a cross section along the thickness direction of the active material-containing layer.

[0056] An example of niobium titanium oxide is monoclinic niobium titanium oxide.

[0057] An example of monoclinic niobium titanium oxide is Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ 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 composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3. Specific examples of monoclinic niobium titanium oxide include Li x Examples include Nb2TiO7 (0≦x≦5).

[0058] Another example of monoclinic niobium titanium oxide is Li x Ti 1-y M3 y+z Nb 2-z O 7-δ Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

[0059] The second phase is a phase different from the first phase, i.e., it can be a phase of a material different from the niobium-containing oxide.

[0060] Examples of materials different from niobium-containing oxides include, for example, those of the general formula TiO X where x>0. The upper limit of x can be, for example, 2. Examples of such titanium oxides include titanium dioxide (TiO2), anatase-type titanium dioxide, and rutile-type titanium dioxide. The type of material different from the niobium-containing oxide can be one or more. The general formula is TiO Xcan be used as a material for synthesizing a niobium-containing oxide. That is, the titanium oxide phase can be a phase formed when a part of the material for synthesizing the niobium-containing oxide is contained unreacted in the active material particles and / or the active material-containing layer.

[0061] The electrode according to the embodiment may contain particles containing a niobium-containing oxide alone as the active material, or may contain one or more other active materials in addition to the particles containing a niobium-containing oxide. The active material may contain particles containing other active materials in addition to the particles containing a niobium-containing oxide.

[0062] When the active material contains particles containing a niobium-containing oxide and other active materials, it is preferable that the proportion of particles containing a niobium-containing oxide in the active material is high. The higher this proportion, the more likely it is that the cracking of the active material particles will be suppressed by reducing the ratio of the area occupied by the large second-phase region to the area occupied by the first phase in a cross section along the thickness direction of the active material-containing layer. In other words, the higher this proportion, the more likely it is that the effect of improving life performance and input / output performance will be achieved. The proportion of particles containing a niobium-containing oxide in the active material can be, for example, 10 mass% or more.

[0063] Other examples of active materials include lithium titanates with a ramsdellite structure (e.g., Li 2+y Ti3O7, 0≦y≦3), lithium titanates with spinel structure (e.g., Li 4+x Ti5O 12 , 0≦x≦3), titanium dioxide (TiO2), anatase type titanium dioxide, rutile type titanium dioxide, hollandite type titanium composite oxide, and orthorhombic type titanium composite oxide.

[0064] As an example of the above orthorhombic titanium-containing composite oxide, Li 2+a M I 2-b Ti 6-c M II d O 14+σ In this case, MI is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb and K. II is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. Specific examples of orthorhombic titanium-containing composite oxides include Li 2+a Na2Ti6O 14 (0≦a≦6).

[0065] The conductive agent is blended to improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), acetylene black, carbon black, graphite, carbon nanotubes, and carbon nanofibers. One of these may be used as the conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surfaces of the active material particles may be coated with carbon or an electronically conductive inorganic material.

[0066] The binder is blended to fill gaps between the dispersed active materials and to bind the active materials and the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, styrene butadiene rubber (SBR), polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0067] The blending ratios of the active material, conductive agent, and binder in the active material-containing layer can be appropriately changed depending on the application of the electrode. For example, when the electrode is used as the negative electrode of a secondary battery, the active material (negative electrode active material), conductive agent, and binder are preferably blended in proportions of 68% by mass to 96% by mass, 2% by mass to 30% by mass, and 2% by mass to 30% by mass, respectively, so that the total is 100% by mass. By adjusting the amount of conductive agent to 2% by mass or more, the current collection performance of the active material-containing layer can be improved. Furthermore, by adjusting the amount of binder to 2% by mass or more, sufficient binding between the 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 adjust the amount of conductive agent and binder to 30% by mass or less, respectively, in order to achieve high capacity.

[0068] The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and extracted from the active material. For example, when the electrode according to the embodiment is used as a negative electrode, the current collector is preferably made of copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

[0069] The current collector may also include a portion on the surface of which no active material-containing layer is formed, and this portion can function as a current collecting tab.

[0070] [Manufacturing method] The electrode according to the embodiment can be manufactured, for example, by the following method.

[0071] <Preparation of particles containing niobium-containing oxide> In producing particles containing niobium-containing oxide, first, starting materials containing elements to be contained in the niobium-containing oxide of the target composition are mixed to form a raw material powder, which is then sintered to synthesize the niobium-containing oxide. After the sintering, the resulting sintered body is pulverized to obtain particles containing the niobium-containing oxide.

[0072] As the starting material, a powder of an oxide or salt containing elements contained in the niobium-containing oxide of the target composition can be used. The salt used as the starting material is preferably a salt that decomposes at a relatively low temperature to produce an oxide, such as a carbonate or nitrate.

[0073] To obtain the electrode according to the embodiment, it is preferable to adjust the particle size distribution of the raw material powder, pressurize the raw material powder before firing, or pressurize the raw material powder during firing, for example. Any one of these steps may be performed, or two or more steps may be performed in combination.

[0074] The particle size distribution of the raw material powder can be adjusted by mixing multiple starting materials with different particle sizes D50 to obtain the raw material powder. The particle sizes D50 of the multiple starting materials are each within the range of 0.1 μm to 10 μm. The particle size D50 is determined from a particle size distribution chart for each starting material. The D50 of the starting material with the largest particle size D50 is preferably at least two times, more preferably at least three times, and even more preferably at least five times the D50 of the starting material with the smallest particle size D50.

[0075] By adjusting the particle size distribution of the raw material powder as described above, the contact area between the powder particles of the starting material increases, thereby improving reactivity. This facilitates the synthesis of the niobium-containing oxide. This suppresses the generation of particles in which the volume of the second phase per active material particle is relatively large. This reduces the proportion of the area occupied by the large second-phase region in the cross section along the thickness direction of the active material-containing layer.

[0076] The particle size D50 of each starting material is preferably in the range of 0.1 μm or more and 5 μm or less. The larger the particle size D50 of the starting material, the less likely it is to float in the air when mixed. Therefore, composition deviation is less likely to occur, making it easier to obtain niobium oxide with the desired composition. The smaller the particle size D50 of the starting material, the less likely it is to produce unreacted products. Therefore, since the second phase is less likely to be produced, the proportion of the area occupied by the large second-phase region in the cross section along the thickness direction of the active material-containing layer can be reduced.

[0077] An example of a method for pressurizing the raw material powder before firing is a method in which the raw material powder is pressurized after mixing the starting materials and then fired. Pressurization can be carried out at a pressure range of 1 MPa to 100 MPa. Firing can be carried out, for example, at atmospheric pressure and a temperature of 500°C to 1400°C. The firing atmosphere can be, for example, vacuum, air, or an inert gas.

[0078] One example of a method for pressurizing the raw material powder during firing is hot pressing, in which the raw material powder is fired while being pressurized using a hot press. The pressure can be in the range of 1 MPa to 100 MPa, and the temperature can be in the range of 500°C to 1400°C. The firing atmosphere can be, for example, vacuum, air, or an inert gas. In addition to hot pressing, other examples of methods for pressurizing the raw material powder during firing include atmospheric pressure firing and hot isostatic pressing (HIP).

[0079] By applying pressure before and / or during firing, the contact area between the powder particles of the starting material increases, thereby improving reactivity. As a result, the synthesis of the niobium-containing oxide proceeds easily, and the generation of a second phase can be suppressed. Pressurization may be applied either before or during firing, or both before and during firing.

[0080] When the raw material powder is not pressurized either before or during firing, the raw material powder can be fired at atmospheric pressure at a temperature of 900° C. to 1450° C. The firing atmosphere can be, for example, vacuum, air, or an inert gas.

[0081] In this manner, a niobium-containing oxide can be synthesized.

[0082] For example, when synthesizing niobium titanium oxide as the niobium-containing oxide, powder of an oxide or salt containing Li, Ti, or Nb can be used as the starting material. It is preferable to adjust the particle size distribution of the raw material powder. Specifically, it is preferable to use the Nb-containing starting material (Nb source) as the starting material with the largest particle size D50. The particle size D50 of the Nb source is preferably at least twice, more preferably at least three times, and even more preferably at least five times the particle size D50 of the Ti source.

[0083] The sintered body obtained by the synthesis of the niobium-containing oxide is pulverized to obtain particles containing the niobium-containing oxide. The pulverization of the sintered body after firing can be carried out, for example, by subjecting the sintered body to strong pulverization using a hammer mill as coarse pulverization, followed by pulverization using a wet ball mill.

[0084] <Preparation of electrodes> The electrode can be produced, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. Particles containing the niobium-containing oxide synthesized by the above method are blended with the active material. Water, for example, can be used as the solvent for the slurry. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of an active material-containing layer and a current collector. After that, this laminate is pressed. In this manner, an electrode is produced.

[0085] Alternatively, the electrode may be prepared by the following method. First, the active material containing the niobium-containing oxide synthesized by the above method, a conductive agent, and a binder are mixed to obtain a mixture. Next, the mixture is formed into pellets. Next, the pellets are placed on a current collector to obtain an electrode.

[0086] [Measurement method] <Scanning electron microscope observation> A method for observing a cross section of an electrode along its thickness direction using a scanning electron microscope (SEM) will be described.

[0087] When the electrode to be measured is incorporated in a battery, the battery is first disassembled to remove the electrode assembly, and then the electrode assembly is disassembled to remove the electrode to be measured.

[0088] If the removed electrode group is a wound type, the wound electrode group is unwound and the electrode to be measured is removed. For example, if the negative electrode is to be measured, the negative electrode is removed.

[0089] The direction along the winding axis of the electrode to be measured is defined as the width direction of the electrode. The direction perpendicular to the winding axis is defined as the longitudinal direction of the electrode. The region of the electrode that is located in a portion corresponding to one-fourth of the thickness of the wound electrode group is defined as the longitudinal center. In other words, the longitudinal center of the electrode is the region that is located at the midpoint of the line connecting the winding axis of the wound electrode group and the outermost surface of the wound electrode group. The center of the electrode is defined as the portion where the center line of the electrode, which is perpendicular to the width direction of the electrode, passes through the center in the longitudinal direction. The electrode is cut in the thickness direction along a line passing through the center of the electrode. A test specimen is thus obtained. The cross section obtained by cutting is defined as the observation surface. When drawing the center line of the electrode, if there is a portion at the end of the electrode where an active material-containing layer is not provided on the current collector, this portion is ignored when drawing the center line.

[0090] If the removed electrode group is a laminated type, the electrode group is disassembled to remove the electrodes to be measured.

[0091] The center point of the electrode is identified in a plane perpendicular to the thickness direction. The method for identifying the center point will be described with reference to FIG.

[0092] FIG. 6 is a plan view showing an example of an electrode according to an embodiment. The electrode 3 shown in FIG. 6 includes an active material-containing layer 3a and a current collector 3b. The active material-containing layer 3a is laminated on a portion of one main surface of the current collector 3b. The Y-axis direction is the direction along the thickness direction of the electrode. The X-axis direction is the direction perpendicular to the Y-axis direction. The Z-axis direction is the direction perpendicular to both the X-axis direction and the Y-axis direction. The short side direction of the electrode 3 shown in FIG. 6 is along the X-axis, and the long side direction is along the Z-axis.

[0093] Line l1 shown in FIG. 6 is the center line of electrode 3 along the long side direction. Line l2 is the center line of electrode 3 along the short side direction. The point where center line l1 and center line l2 intersect is specified as the center point Cxz of the electrode. When drawing center line l1 and center line l2, if there is a portion at the end of the electrode where active material-containing layer 3a is not provided on current collector 3b, that portion is ignored when drawing the center line.

[0094] The electrode is cut in the thickness direction along a line passing through the center point Cxz identified as above, for example, line II-II. Thus, a test piece is obtained. The cross section obtained by cutting is used as the observation surface.

[0095] When the electrode to be measured is not incorporated into a battery, a test piece can be obtained in the same manner as described for the electrode taken out from the stacked electrode group.

[0096] Next, a method for specifying a square observation area from the observation surface will be described with reference to Fig. 7. Fig. 7 is a cross-sectional view of the electrode shown in Fig. 6 taken along line II-II.

[0097] First, the center point Cxy on the observation surface of the active material-containing layer is identified. I3 shown in Fig. 7 is a virtual line that passes through the center point Cxz described with reference to Fig. 6 and extends along the thickness direction Y. I4 is a virtual line that passes through the center of the active material-containing layer in the thickness direction. The intersection of I3 and I4 is defined as the center point Cxy on the observation surface of the electrode.

[0098] Next, the thickness L of the active material-containing layer 3a 3a is measured as follows:

[0099] First, the observation surface is observed using a scanning electron microscope, with the direction along the thickness direction of the electrode being the vertical direction of the observation field.

[0100] The observation magnification is set so that the horizontal length of the observation field is at least twice the thickness of the active material-containing layer at the thickest part of the active material-containing layer within the observation field.

[0101] The observation position is set so that the entire thickness of the active material-containing layer is included in the vertical direction of the observation field, i.e., the range from the surface of the active material-containing layer in contact with the current collector to the surface of the electrode is completely included in the observation field.

[0102] The area of ​​the active material-containing layer included in the observation field determined as above is measured. For the area measurement, image analysis software such as ImageJ can be used.

[0103] The area of ​​the active material-containing layer included in the observation field is divided by the horizontal length of the observation field to obtain the thickness L of the active material-containing layer. 3a That is, the average thickness of the active material-containing layer included in the observation field is calculated as the thickness L of the active material-containing layer. 3a is obtained as:

[0104] Thickness L of the active material-containing layer 3a 3a The length of one side of the square observation area is defined as La, whichever is smaller: 95% of the length of the square or 40 μm.

[0105] A square region having a side length of La and containing a center point Cxy therein is defined as a square observation region a. The square observation region a is included in the above-mentioned observation field of view.

[0106] Furthermore, a method for determining the region to be observed with a scanning electron microscope will be described with reference to Fig. 8. Fig. 8 is an enlarged view of the square observation region a shown in Fig. 4.

[0107] Virtual lines x1 to x3 extend along the x-axis and divide the observation region a into four equal parts. Virtual lines y1 to y3 extend along the y-axis and divide the observation region a into four equal parts. By dividing the observation region a into four equal parts vertically and horizontally by the virtual lines x1 to x3 and y1 to y3, 16 divided regions a1 to a16 are obtained. Each of the divided regions a1 to a16 may be square.

[0108] Each of the 16 divided regions a1 to a16 is observed using a scanning electron microscope (SEM). An SU8020 (manufactured by Hitachi High-Technologies Corporation) can be used as the SEM. Of the 16 divided regions a1 to a16, a backscattered electron image (BSE image) is acquired for one observation region (e.g., a1) to be observed, at a magnification that occupies 70% or more of the entire observation field. Automatic brightness and contrast adjustment is performed when acquiring the backscattered electron image. Backscattered electron images are acquired for all 16 divided regions a1 to a16 in the same manner.

[0109] <Image analysis> (Method of determining the first threshold) As a preparation for image analysis of the acquired backscattered electron image, a first threshold value is first determined. The method for determining the first threshold value will be described below.

[0110] For the backscattered electron image to be analyzed, a histogram is obtained with brightness as a scale. The lower and upper limits of brightness are 0 and 255, respectively. The histogram scale width is 1, and the frequency is the number of pixels. The scale (brightness) is plotted on the horizontal axis and the frequency (number of pixels) on the vertical axis to create the first graph.

[0111] An example of a first graph of a backscattered electron image acquired for the electrode of the embodiment is shown in Fig. 9. In the first graph shown in Fig. 9, the horizontal axis represents brightness (class) and the vertical axis represents the number of pixels (frequency).

[0112] Further, for the above histogram, the first derivative of the frequency is calculated for each luminance unit. Furthermore, a five-point moving average is calculated for the calculated first derivative. A second graph is created by plotting luminance on the horizontal axis and the five-point moving average of the first derivative of the frequency on the vertical axis. FIG. 10 shows a second graph for the histogram shown in the first graph in FIG. 9. FIG. 11 is an enlarged view of the second graph shown in FIG. 10. In the second graphs shown in FIGS. 10 and 11, the horizontal axis represents luminance (class) and the vertical axis represents the first derivative of the frequency (number of pixels). The points in the second graphs shown in FIGS. 10 and 11 represent the five-point moving average of the first derivative of the frequency.

[0113] Using the first and second graphs thus created, the first threshold value is determined as follows.

[0114] First, among the peaks in the first graph, the peak with the highest luminance at its peak top is identified.

[0115] Here, the peak refers to the part of the graph that exists within the peak region, with the left end (low-luminance end point) being the end point of the region where the vertical axis value continues to approach 0 when viewed from the peak top toward the low-luminance side, and the right end (high-luminance end point) being the end point of the region where the vertical axis value continues to approach 0 when viewed from the peak top toward the high-luminance side.

[0116] In the first graph, the region where the value on the vertical axis continues to approach 0 can be said to be a region where the value on the vertical axis continues to decrease.

[0117] The first graph may have, for example, two or more peaks. The number of peaks that the first graph has may be, for example, two or three.

[0118] Furthermore, the region of the peak in the first graph that is defined by the following one end and the other end may be referred to as the left foot of the peak (the foot on the low-luminance side).

[0119] One end of the left skirt is the luminance at the peak top in the first graph that is lower than the luminance at the peak top in the first graph and that has a positive first derivative of the frequency in the second graph that is closest to the luminance at the peak top in the first graph. The other end of the left skirt is the low-luminance end point of the peak in the first graph.

[0120] Of the peaks in the first graph, the region defined by the following one and other ends is sometimes referred to as the right foot of the peak (the foot on the high-intensity side).

[0121] One end of the right tail is the luminance at the peak top in the first graph that is greater than the luminance at the peak top in the first graph and that is closest in the second graph to the luminance at the peak top in the first graph, where the first derivative of the frequency in the second graph is a negative value. The other end of the right tail is the low-luminance end point of the peak in the first graph.

[0122] The luminance at the peak top of the peak with the highest luminance at the peak top in the first graph is identified. Next, when viewing the second graph shown in Figure 11 from the identified luminance toward the lower luminance side, a point m1 is determined as a point where the first derivative of the frequency is positive and where three consecutive points on the lower luminance side nearest to that point are negative. The luminance at point m1 is determined as a first threshold value.

[0123] The luminance at point m1 may be the luminance at the point where the slope becomes gentler at the left foot of the peak with the highest luminance at its top in graph 1. Specifically, it may be the luminance at the point where the first derivative of the frequency in graph 2 approaches 0 most within the luminance region where the left foot of the peak with the highest luminance at its top in graph 1 exists.

[0124] (Method of determining the second threshold) Next, a method for determining the second threshold will be described below.

[0125] For the histogram related to the first graph described above, the second derivative of the frequency is calculated for each luminance value. A five-point moving average is calculated for the calculated second derivative. A third graph is created by plotting luminance on the horizontal axis and the five-point moving average of the second derivative of the frequency on the vertical axis. FIG. 12 shows a third graph for the histogram shown in the first graph related to FIG. 9. FIG. 13 is an enlarged view of the third graph shown in FIG. 12. In the third graphs shown in FIGS. 12 and 13, the horizontal axis represents luminance (class) and the vertical axis represents the second derivative of the frequency (number of pixels). The points in the third graphs shown in FIGS. 12 and 13 represent the five-point moving average of the second derivative of the frequency.

[0126] The first and third graphs are used to determine the second threshold.

[0127] First, among the peaks in the first graph, the peak with the lowest brightness at its peak top is identified. Next, the range from the brightness at the peak top of that peak to the brightness at the low-brightness end point (left end) of the peak with the highest brightness at its peak top is identified. In the third graph shown in FIGS. 12 and 13, the point where the second derivative of the frequency is maximum within that range is designated m3. When viewing the third graph from m3 toward the high-brightness side, the point where the second derivative of the frequency is 20 or less (including negative values) for the first time is designated m2. The brightness at point m2 is designated as the second threshold.

[0128] (Image analysis) The obtained backscattered electron image is subjected to various image analyses as follows.

[0129] For image analysis, image analysis software such as imageJ is used.

[0130] (Method for measuring the area occupied by the first phase) The acquired backscattered electron image is subjected to Gaussian filter processing. The standard deviation σ value of the Gaussian filter is set to 1. The image that has been subjected to the Gaussian filter processing is then binarized using a first threshold value as the brightness threshold. In the binarization, for example, areas where the brightness is less than the first threshold value can be expressed as white, and areas where the brightness is equal to or greater than the first threshold value can be expressed as black.

[0131] In the image processed by the Gaussian filter, regions where the brightness is equal to or greater than the first threshold, i.e., regions expressed in black, may be regions occupied by niobium-containing oxides, i.e., regions occupied by the first phase.

[0132] Next, the area occupied by the first phase is measured. First, the area expressed in black by the above method (black area) is considered to be the area occupied by the first phase. Furthermore, if there is a hollow black area, that is, an area consisting of a single black area and a white area surrounded by the black area, the white area is also considered to be a black area. The total area of ​​the black areas identified in this way is calculated as the area occupied by the first phase.

[0133] (Method for measuring the area occupied by the second phase) The backscattered electron image is subjected to Gaussian filter processing. The standard deviation σ value of the Gaussian filter is set to 1. The image after Gaussian filter processing is then binarized. The binarization is performed so that the range of brightness equal to or greater than the second threshold and less than the first threshold is detected. For example, regions where the brightness is less than the second threshold and regions where the brightness is equal to or greater than the first threshold can be expressed as white, and regions where the brightness is in the range of equal to or greater than the second threshold and less than the first threshold can be expressed as black.

[0134] The region where the brightness is in the range of not less than the second threshold but less than the first threshold, i.e., the region expressed in black, may be a region occupied by titanium oxide or a contour line of a region occupied by niobium-containing oxide. The titanium oxide may be, for example, a titanium oxide represented by the general formula TiO X where x>0.

[0135] The binarized image obtained as described above is subjected to an open process. This makes it possible to remove linear regions from regions expressed in black, for example. In other words, the outlines of regions occupied by niobium-containing oxides are removed, leaving regions occupied by titanium oxides, i.e., regions occupied by the second phase, as black regions.

[0136] Among the black regions included in the image subjected to the Open process, regions with a circularity of 0.7 or more and 1 or less and an area of 2 × 10 -14 m 2 or more are detected as the second-phase large regions.

[0137] The circularity can be calculated by measuring the area and the length of the contour line for each of the black regions included in the image subjected to the Open process and substituting them into the following formula.

[0138] [[ID=!1]] Formula: (Circularity) = 4π × (Area) / (Length of the contour line) 2 In the case of a hollow-shaped black region, that is, a region composed of a single black region and a white region surrounded by the black region, it is set so that the circularity of the outermost contour line of the hollow-shaped black region is calculated. In the case of a hollow-shaped black region, that is, a region composed of a single black region and a white region surrounded by the black region, the white region is also regarded as a black region. The total area of the black regions specified as above is calculated as the area occupied by the second-phase large regions.

[0139] <EDX Analysis> The composition of the substances contained in the active material layer of the electrode can be specified, for example, by energy dispersive X-ray spectroscopy (EDX). In the SEM observation of the cross-section of the active material layer, EDX analysis is performed at multiple points on the region observed in the same color tone as the region for which the composition is to be specified. The average composition is calculated from the analysis results at each of the multiple points. This average composition is taken as the composition of the region of that color tone.

[0140] Please note that there might be a mistake in the original text where [[ID=!1]] should probably be . I've translated it as is but it might be an error in the source text.According to a first embodiment, an electrode is provided. The electrode includes an active material-containing layer. The active material-containing layer includes active material particles including a first phase and a second phase. The first phase is a niobium-containing oxide phase. The second phase is a phase different from the first phase. In a cross section of the active material-containing layer along the thickness direction, a square region defined by a first side parallel to the thickness direction and a second side perpendicular to the first side is equally divided into 16 divided regions, and the ratio of the area occupied by the second phase to the area occupied by the first phase is 10% or less. The area occupied by the second phase is 2×10 -14 m 2 The area of ​​one or more regions occupying an area equal to or greater than the area of ​​the other region.

[0141] Therefore, according to the embodiment, it is possible to provide an electrode that can realize a secondary battery that is excellent in life performance and input / output performance.

[0142] (Second embodiment) According to a second embodiment, there is provided a secondary battery including a negative electrode, a positive electrode, and an electrolyte. This secondary battery includes the electrode according to the first embodiment as the negative electrode or the positive electrode.

[0143] The secondary battery may further include a separator disposed between the positive electrode and the negative electrode. The negative electrode, the positive electrode, and the separator may constitute an electrode assembly. The electrolyte may be held in the electrode assembly.

[0144] Moreover, such a secondary battery can further include an exterior member that houses the electrode group and the electrolyte.

[0145] Furthermore, such a secondary battery may further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

[0146] Such a secondary battery may be, for example, a lithium secondary battery. The secondary battery also includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0147] The negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal will be described in detail below.

[0148] 1) Negative electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer, which may be the current collector and active material-containing layer that can be included in the electrode according to the first embodiment, respectively.

[0149] Details of the negative electrode that overlap with those described in the first embodiment will be omitted.

[0150] The density of the negative electrode active material-containing layer (excluding the current collector) is 1.8 g / cm 3 More than 2.8g / cm 3 A negative electrode having a negative electrode active material-containing layer with a density within this range is excellent in energy density and electrolyte retention. The density of the negative electrode active material-containing layer is preferably 2.1 g / cm or less. 3 More than 2.6g / cm 3 More preferably, it is:

[0151] The negative electrode can be produced, for example, by the same method as that for the electrode according to the first embodiment.

[0152] 2) Positive electrode 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 include a positive electrode active material and, optionally, a conductive agent and a binder.

[0153] When the electrode according to the first embodiment is used as a negative electrode, the positive electrode may contain, for example, an oxide or a sulfide as the positive electrode active material. The positive electrode may contain, as the positive electrode active material, one type of compound alone or a combination of two or more types of compounds. Examples of oxides and sulfides include compounds capable of inserting and desorbing Li or Li ions.

[0154] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, and lithium manganese composite oxides (e.g., Lix Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≦ 1, Li x Fe 1-y Mn y PO4; 0 < x ≦ 1, 0 < y ≦ 1, Li x CoPO4; 0 < x ≦ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≦ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included.

[0155] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co yO2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; 0 < x ≤ 1), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0156] When a room-temperature molten salt is used as the electrolyte of the battery, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li x VPO4F (0 ≤ x ≤ 1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof. Since these compounds have low reactivity with the room-temperature molten salt, the cycle life can be improved. Details of the room-temperature molten salt will be described later.

[0157] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material with a primary particle size of 1 μm or less can allow smooth solid-state diffusion of lithium ions.

[0158] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. A positive electrode active material having a specific surface area of 0.1 m 2 / g or more can sufficiently secure the lithium ion insertion / extraction sites. A positive electrode active material with a specific surface area of 10 m 2A positive electrode active material having a specific surface area of ​​0.15g / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0159] The binder is blended to fill gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination as the binder.

[0160] The conductive agent is blended to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), acetylene black, carbon black, and graphite. One of these may be used as the conductive agent, or two or more may be used in combination as the conductive agent. The conductive agent may also be omitted.

[0161] In the positive electrode active material-containing layer, the positive electrode active material and the binder are preferably mixed in proportions of 80% by mass to 98% by mass and 2% by mass to 20% by mass, respectively.

[0162] By using a binder amount of 2% by mass or more, sufficient electrode strength can be obtained. Furthermore, the binder can function as an insulator. Therefore, by using a binder amount of 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

[0163] When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably mixed in proportions of 77% by mass or more and 95% by mass or less, 2% by mass or more and 20% by mass or less, and 3% by mass or more and 15% by mass or less, respectively.

[0164] By setting the amount of conductive agent to 3% by mass or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This low proportion can reduce decomposition of the electrolyte during high-temperature storage.

[0165] The positive electrode current collector is preferably an aluminum foil or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0166] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0167] The positive electrode current collector may also include a portion on the surface of which the positive electrode active material-containing layer is not formed, and this portion can function as a positive electrode current collecting tab.

[0168] The positive electrode can be produced, for example, using a positive electrode active material by the same method as that for the electrode according to the first embodiment.

[0169] 3) Electrolyte As the electrolyte, for example, a non-aqueous electrolyte, an aqueous electrolyte, or a combination of a non-aqueous electrolyte and an aqueous electrolyte can be used.

[0170] The nonaqueous electrolyte may be, for example, a liquid or gel nonaqueous electrolyte. The liquid nonaqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0171] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoride (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), and lithium bistrifluoromethylsulfonylimide (LiN(CFSO)), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and LiPF is most preferred.

[0172] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or in combination.

[0173] The gel-like non-aqueous electrolyte is prepared by combining a liquid non-aqueous electrolyte with a polymeric material, such as polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

[0174] Alternatively, the nonaqueous electrolyte may be a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte, or may be a room-temperature molten salt containing lithium ions (ionic melt), a polymer solid electrolyte, or an inorganic solid electrolyte. One or more types of nonaqueous electrolyte may be used. The polymer solid electrolyte or inorganic solid electrolyte may be used in combination with, for example, a liquid nonaqueous electrolyte and / or a gel nonaqueous electrolyte.

[0175] Room-temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C or higher and 25°C or lower). Room-temperature molten salts include room-temperature molten salts that exist as a liquid on their own, room-temperature molten salts that become liquid when mixed with an electrolyte salt, room-temperature molten salts that become liquid when dissolved in an organic solvent, and mixtures of these. Generally, the melting point of room-temperature molten salts used in secondary batteries is 25°C or lower. Furthermore, organic cations generally have a quaternary ammonium skeleton.

[0176] The solid polymer electrolyte is prepared by dissolving an electrolyte salt in a polymer material and solidifying it.

[0177] The inorganic solid electrolyte is a solid substance that has Li-ion conductivity. Here, "having Li-ion conductivity" means that the Li-ion conductivity is 1×10 at 25°C. -6 This refers to a material that exhibits a lithium ion conductivity of 1000 S / cm or more. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are as follows:

[0178] As the oxide-based solid electrolyte, it is preferable to use a lithium phosphate solid electrolyte having a NASICON (Sodium (Na) Super Ionic Conductor) type structure and represented by the general formula Li 1+x Mα2(PO4)3. In the above general formula, Mα is, for example, one or more selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is within the range of 0 ≦ x ≦ 2.

[0179] Specific examples of the lithium phosphate solid electrolyte having a NASICON type structure include LATP compounds represented by Li 1+x Al x Ti 2-x (PO4)3 with 0.1 ≦ x ≦ 0.5; compounds represented by Li 1+x Al y Mβ 2-y (PO4)3 where Mβ is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca and 0 ≦ x ≦ 1 and 0 ≦ y ≦ 1; compounds represented by Li 1+x Al x Ge 2-x (PO4)3 with 0 ≦ x ≦ 2; and compounds represented by Li 1+x Al x Zr 2-x (PO4)3 with 0 ≦ x ≦ 2; Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 where Mγ is one or more selected from the group consisting of Ti and Ge and 0 < x ≦ 2, 0 ≦ y < 3; compounds represented by Li 1+2x Zr 1-x Ca x (PO4)3 with 0 ≦ x < 1 can be mentioned.

[0180] In addition, as the oxide-based solid electrolyte, in addition to the above lithium phosphate solid electrolyte, Li x PO y N zand the amorphous LIPON compound (e.g., Li 2.9 PO 3.3 N 0.46 );La with garnet structure 5+x A x La 3-x MδO 12 A is at least one selected from the group consisting of Ca, Sr, and Ba, Mδ is at least one selected from the group consisting of Nb and Ta, and 0≦x≦0.5; Li3Mδ 2-x L2O 12 wherein Mδ is at least one selected from the group consisting of Nb and Ta, L may contain Zr, and 0≦x≦0.5; Li 7-3x Al x La3Zr3O 12 and 0≦x≦0.5; Li 5+x La3Mδ 2-x Zr x O 12 where Mδ is at least one selected from the group consisting of Nb and Ta, and 0≦x≦2. LLZ compounds (e.g., Li7La3Zr2O 12 ); and La 2 / 3-x Li x Examples include compounds represented by TiO3 where x is 0.3≦x≦0.7.

[0181] One or more of the above compounds can be used as the solid electrolyte, and two or more of the above solid electrolytes can also be used.

[0182] The aqueous electrolyte contains an aqueous solvent and an electrolyte salt. The aqueous electrolyte is, for example, liquid. The liquid aqueous electrolyte is an aqueous solution prepared by dissolving an electrolyte salt as a solute in an aqueous solvent. The aqueous solution preferably contains 1 mol or more of the aqueous solvent per 1 mol of the salt as the solute, and more preferably 3.5 mol or more.

[0183] The aqueous solvent can be a solution containing water. The aqueous solution can be pure water or a mixed solvent of water and an organic solvent. The aqueous solvent contains, for example, 50% or more by volume of water.

[0184] The presence of water in aqueous electrolytes can be confirmed by GC-MS (Gas Chromatography-Mass Spectrometry). Furthermore, the salt concentration and water content in aqueous electrolytes can be measured, for example, by ICP (Inductively Coupled Plasma) optical emission spectrometry. The molar concentration (mol / L) can be calculated by weighing a specified amount of aqueous electrolyte and calculating the salt concentration. Furthermore, the number of moles of solute and solvent can be calculated by measuring the specific gravity of the aqueous electrolyte.

[0185] The aqueous electrolyte may be a gel electrolyte. The gel electrolyte is prepared by mixing the above-mentioned liquid aqueous electrolyte with a polymer compound to form a composite. Examples of the polymer compound include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0186] Examples of electrolyte salts that can be contained in the aqueous electrolyte include lithium chloride (LiCl), lithium bromide (LiBr), lithium hydroxide (LiOH), lithium sulfate (LiSO), lithium nitrate (LiNO), lithium acetate (CHCOOLi), lithium oxalate (LiCO), lithium carbonate (LiCO), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; LiN(SOCF)), lithium bis(fluorosulfonyl)imide (LiFSI; LiN(SOF), and lithium bis(oxalatoborate) (LiBOB: LiB[(OCO)]). The aqueous electrolyte may contain one or more types of electrolyte salts. The aqueous electrolyte preferably contains LiCl. The use of LiCl increases the lithium ion concentration of the aqueous electrolyte. The lithium salt preferably contains at least one of LiSO and LiOH in addition to LiCl.

[0187] The molar concentration of lithium ions in the aqueous electrolyte may be 3 mol / L or more, 6 mol / L or more, or 12 mol / L or more. In one example, the molar concentration of lithium ions in the aqueous electrolyte is 14 mol / L or less. If the concentration of lithium ions in the aqueous electrolyte is high, electrolysis of the aqueous solvent at the negative electrode is likely to be suppressed, and hydrogen generation from the negative electrode tends to be reduced.

[0188] Aqueous electrolytes contain chloride ions (Cl) as anionic species. - ), hydroxide ion (OH - ), sulfate ions (SO4 2- ), nitrate ions (NO3 - ) is preferably contained in the composition.

[0189] The pH of the aqueous electrolyte is preferably 3 or more and 14 or less, and more preferably 4 or more and 13 or less. When separate electrolytes are used for the negative electrode side electrolyte and the positive electrode side electrolyte, the pH of the negative electrode side electrolyte is preferably in the range of 3 or more and 14 or less, and the pH of the positive electrode side electrolyte is preferably in the range of 1 or more and 8 or less.

[0190] When the pH of the negative electrode electrolyte is within the above range, the hydrogen generation potential at the negative electrode is reduced, thereby suppressing hydrogen generation at the negative electrode. This improves the storage performance and cycle life performance of the battery. When the pH of the positive electrode electrolyte is within the above range, the oxygen generation potential at the positive electrode is increased, thereby reducing oxygen generation at the positive electrode. This improves the storage performance and cycle life performance of the battery. The pH of the positive electrode electrolyte is more preferably within the range of 3 or more and 7.5 or less.

[0191] The aqueous electrolyte may contain a surfactant. Examples of surfactants include nonionic surfactants such as polyoxyalkylene alkyl ether, polyethylene glycol, polyvinyl alcohol, thiourea, disodium 3,3'-dithiobis(1-propanephosate), dimercaptothiadiazole, boric acid, oxalic acid, malonic acid, saccharin, sodium naphthalenesulfonate, gelatin, potassium nitrate, aromatic aldehyde, and heterocyclic aldehyde. The surfactants may be used alone or in combination of two or more.

[0192] 4) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene, because these porous films melt at a certain temperature and can interrupt current.

[0193] 5) Exterior materials The exterior member may be, for example, a container made of a laminate film or a metal container.

[0194] The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0195] The laminate film is a multilayer film containing multiple resin layers and metal layers interposed between the resin layers. The resin layers include polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it by heat fusion.

[0196] The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0197] The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of these metals is preferably 100 mass ppm or less.

[0198] The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be appropriately selected depending on the battery dimensions and the intended use of the battery.

[0199] 6) Negative terminal The negative electrode terminal is in the potential range of 1V to 3V with respect to the redox potential of lithium (vs. Li / Li +) and can be formed from a material that is electrically stable and conductive. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The material for the negative electrode terminal is preferably aluminum or an aluminum alloy. The negative electrode terminal is preferably made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0200] 7) Positive terminal The positive electrode terminal has a potential range of 3V to 4.5V relative to the redox potential of lithium (vs. Li / Li + ) and can be formed from a material that is electrically stable and conductive. Examples of materials for the positive electrode terminal include aluminum and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0201] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0202] Fig. 14 is a cross-sectional view schematically showing an example of a secondary battery, and Fig. 15 is an enlarged cross-sectional view of part A of the secondary battery shown in Fig. 14.

[0203] 14 and 15 includes a bag-shaped exterior member 2 shown in Fig. 14, an electrode group 1 shown in Fig. 14 and 15, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the bag-shaped exterior member 2. The electrolyte (not shown) is held in the electrode group 1.

[0204] The bag-shaped exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0205] As shown in Fig. 14, the electrode group 1 is a flat wound electrode group. As shown in Fig. 15, 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.

[0206] 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 at the outermost shell of the wound-type 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 Fig. 15. 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.

[0207] The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both sides of the positive electrode current collector 5a.

[0208] As shown in FIG. 14, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer peripheral edge of the wound electrode group 1. The negative electrode terminal 6 is connected to a portion located at the outermost shell of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to a portion located at the outermost shell of the positive electrode current collector 5a. The negative electrode terminal 6 and the positive electrode terminal 7 extend to the outside from an opening of the bag-shaped exterior member 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped exterior member 2, and the opening is closed by heat sealing this.

[0209] The secondary battery according to the embodiment is not limited to the secondary battery having the configuration shown in FIGS. 14 and 15, but may also be a battery having the configuration shown in FIGS. 16 and 17, for example.

[0210] Fig. 16 is a partially cutaway perspective view schematically showing another example of a secondary battery, and Fig. 17 is an enlarged cross-sectional view of part B of the secondary battery shown in Fig. 16.

[0211] 16 and 17 includes an electrode group 1 shown in Fig. 16 and 17, an exterior member 2 shown in Fig. 16, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 2. The electrolyte is held in the electrode group 1.

[0212] The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0213] The electrode group 1 is a laminated electrode group, as shown in Fig. 17. The laminated electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately laminated with separators 4 interposed therebetween.

[0214] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode 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 includes 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.

[0215] The negative electrode current collector 3a of each negative electrode 3 includes a portion on one side where no negative electrode active material-containing layer 3b is supported on any surface. This portion serves as a negative electrode current collector tab 3c. As shown in FIG. 17 , the negative electrode current collector tab 3c does not overlap with the positive electrode 5. The multiple negative electrode current collector tabs 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 exterior member 2.

[0216] Although not shown, 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. Like the negative electrode current collector tab 3c, the positive electrode current collector tab does not overlap with the negative electrode 3. The positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab 3c. The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is drawn out to the outside of the exterior member 2.

[0217] The secondary battery according to the second embodiment includes the electrode according to the first embodiment, and therefore, the secondary battery can have improved life performance and input / output performance.

[0218] (Third embodiment) According to a third embodiment, there is provided a battery pack, which includes a plurality of secondary batteries according to the second embodiment.

[0219] In such a battery pack, the individual cells may be electrically connected in series or in parallel, or may be connected in a combination of series and parallel.

[0220] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0221] Fig. 18 is a perspective view schematically showing an example of a battery pack. The battery pack 200 shown in Fig. 18 includes five cells 100a to 100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five cells 100a to 100e is a secondary battery according to the second embodiment.

[0222] The bus bar 21 connects, for example, the negative electrode terminal 6 of one cell 100a to the positive electrode terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four bus bars 21. That is, the battery pack 200 in FIG. 18 is a five-series battery pack. Although no example is shown, in a battery pack including a plurality of cells electrically connected in parallel, the plurality of cells can be electrically connected by, for example, connecting the negative electrode terminals to each other by a bus bar and connecting the positive electrode terminals to each other by a bus bar.

[0223] The positive electrode terminal 7 of at least one of the five cells 100a to 100e is electrically connected to a positive electrode lead 22 for external connection. Also, the negative electrode terminal 6 of at least one of the five cells 100a to 100e is electrically connected to a negative electrode lead 23 for external connection.

[0224] The battery pack according to the third embodiment includes the secondary battery according to the second embodiment, and therefore, the life performance and input / output performance can be improved.

[0225] (Fourth embodiment) According to a fourth embodiment, there is provided a battery pack. This battery pack includes the battery assembly according to the third embodiment. This battery pack may include a single secondary battery according to the second embodiment instead of the battery assembly according to the third embodiment.

[0226] Such a battery pack may further include a protection circuit. The protection circuit has a function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) may be used as the protection circuit for the battery pack.

[0227] The battery pack may further include external terminals for current flow. The external terminals for current flow are for outputting current from the secondary battery to the outside and / or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for current flow. When the battery pack is charged, charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminals for current flow.

[0228] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0229] Fig. 19 is an exploded perspective view schematically showing an example of a battery pack, and Fig. 20 is a block diagram showing an example of an electric circuit of the battery pack shown in Fig. 19.

[0230] The battery pack 300 shown in FIGS. 19 and 20 includes a container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

[0231] 19 is a bottomed, square container having a rectangular bottom. The container 31 is configured to be able to accommodate a protective sheet 33, a battery pack 200, a printed wiring board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31 to accommodate the battery pack 200 and other components. Although not shown, the container 31 and the lid 32 are provided with openings or connection terminals for connection to external devices and the like.

[0232] The battery pack 200 includes a plurality of cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0233] At least one of the plurality of cells 100 is a secondary battery according to the second embodiment. The plurality of cells 100 are electrically connected in series as shown in FIG. 20 . The plurality of cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the plurality of cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0234] The adhesive tape 24 fastens the plurality of cells 100 together. Heat-shrinkable tape may be used to secure the plurality of cells 100 together instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both side surfaces of the battery pack 200, and the heat-shrinkable tape is wrapped around the cells 100, and the heat-shrinkable tape is then thermally shrunk to bind the plurality of cells 100 together.

[0235] One end of the positive electrode lead 22 is connected to the battery pack 200. One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more cells 100. One end of the negative electrode lead 23 is connected to the battery pack 200. One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more cells 100.

[0236] The printed wiring board 34 is installed along one of the shorter sides of the inner surface of the container 31. The printed wiring board 34 includes a positive connector 342, a negative connector 343, a thermistor 345, a protection circuit 346, wires 342a and 343a, an external terminal 350 for supplying current, a positive wire (positive wire) 348a, and a negative wire (negative wire) 348b. One main surface of the printed wiring board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

[0237] The other end 22a of the positive electrode lead 22 is electrically connected to the positive electrode connector 342. The other end 23a of the negative electrode lead 23 is electrically connected to the negative electrode connector 343.

[0238] The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 346.

[0239] The external terminals 350 for applying current are fixed to the other main surface of the printed wiring board 34. The external terminals 350 for applying current are electrically connected to devices located outside the battery pack 300. The external terminals 350 for applying current include a positive terminal 352 and a negative terminal 353.

[0240] The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via a positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via a negative wiring 348b. The protection circuit 346 is also electrically connected to the positive connector 342 via a wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via a wiring 343a. The protection circuit 346 is also electrically connected to each of the plurality of single cells 100 via wiring 35.

[0241] The protective sheet 33 is disposed on both inner surfaces of the long sides of the container 31 and on the inner surface of the short side that faces the printed wiring board 34 across the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0242] The protection circuit 346 controls charging and discharging of the plurality of cells 100. Furthermore, the protection circuit 346 cuts off the electrical connection between the protection circuit 346 and external terminals 350 (positive terminal 352, negative terminal 353) for supplying electricity to an external device, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from each cell 100 or the battery pack 200.

[0243] An example of the detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of the cell 100 is equal to or higher than a predetermined temperature. An example of the detection signal transmitted from each cell 100 or the battery pack 200 is a signal indicating that overcharge, overdischarge, or overcurrent of the cell 100 is detected. When detecting overcharge or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

[0244] The protection circuit 346 may be a circuit included in a device (such as an electronic device or an automobile) that uses the battery pack 300 as a power source.

[0245] As described above, the battery pack 300 is also provided with the external terminals 350 for current application. Therefore, the battery pack 300 can output current from the battery assembly 200 to an external device and input current from the external device to the battery assembly 200 via the external terminals 350 for current application. In other words, when the battery pack 300 is used as a power source, the current from the battery assembly 200 is supplied to the external device via the external terminals 350 for current application. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 via the external terminals 350 for current application. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as the charging current from the external device.

[0246] The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive electrode lead 22 and the negative electrode lead 23 may be used as a positive terminal 352 and a negative terminal 353, respectively, of the external terminal 350 for supplying current.

[0247] Such a battery pack is used in applications requiring excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used, for example, as a power source for electronic devices, a stationary battery, or an on-board battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

[0248] The battery pack according to the fourth embodiment includes the secondary battery according to the second embodiment or the battery pack according to the third embodiment, and therefore can improve the lifespan and input / output performance.

[0249] (Fifth embodiment) According to a fifth embodiment, a vehicle is provided, which is equipped with the battery pack according to the fourth embodiment.

[0250] In such a vehicle, the battery pack recovers, for example, regenerative energy for powering the vehicle, and the vehicle may include a mechanism (regenerator) for converting the kinetic energy of the vehicle into regenerative energy.

[0251] Examples of vehicles include two- to four-wheel hybrid electric vehicles, two- to four-wheel electric vehicles, power-assisted bicycles, and rail vehicles.

[0252] The mounting position of the battery pack in a vehicle is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

[0253] A vehicle may be equipped with multiple battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, in parallel, or a combination of series and parallel connections. For example, if each battery pack includes a battery pack, the battery packs may be electrically connected in series, in parallel, or a combination of series and parallel connections. Alternatively, if each battery pack includes a single battery, the batteries may be electrically connected in series, in parallel, or a combination of series and parallel connections.

[0254] Next, an example of a vehicle according to an embodiment will be described with reference to the drawings.

[0255] FIG. 21 is a partially transparent view that schematically illustrates an example of a vehicle.

[0256] A vehicle 400 shown in Fig. 21 includes a vehicle body 40 and a battery pack 300 according to the fourth embodiment. In the example shown in Fig. 21, the vehicle 400 is a four-wheeled automobile.

[0257] The vehicle 400 may be equipped with a plurality of battery packs 300. In this case, the batteries (for example, single cells or assembled batteries) included in the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

[0258] 21 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in the front of the vehicle body 40. As described above, the battery pack 300 may be mounted, for example, at the rear of the vehicle body 40 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for powering the vehicle 400.

[0259] Next, with reference to FIG. 22, an embodiment of the vehicle according to the present invention will be described.

[0260] Fig. 22 is a diagram that schematically illustrates an example of a control system for an electrical system in a vehicle. The vehicle 400 shown in Fig. 22 is an electric vehicle.

[0261] The vehicle 400 shown in Figure 22 comprises a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a higher-level control device of the vehicle power supply 41, an external terminal (terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45.

[0262] The vehicle 400 is equipped with a vehicle power supply 41, for example, in the engine compartment, at the rear of the vehicle body, or under the seat. Note that the location where the vehicle power supply 41 is installed is shown schematically in the vehicle 400 shown in FIG.

[0263] The vehicle power supply 41 includes a plurality of (for example, three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0264] The battery pack 300a includes an assembled battery 200a and an assembled battery monitoring device 301a (for example, VTM: Voltage Temperature Monitoring). The battery pack 300b includes an assembled battery 200b and an assembled battery monitoring device 301b. The battery pack 300c includes an assembled battery 200c and an assembled battery monitoring device 301c. The battery packs 300a to 300c are the same as the battery pack 300 described above, and the assembled batteries 200a to 200c are the same as the assembled battery 200 described above. The assembled batteries 200a to 200c are electrically connected in series. The battery packs 300a, 300b, and 300c can each be removed independently and replaced with another battery pack 300.

[0265] Each of the battery packs 200a to 200c includes a plurality of unit cells connected in series. At least one of the unit cells is the secondary battery according to the second embodiment. Each of the battery packs 200a to 200c is charged and discharged via a positive terminal 413 and a negative terminal 414.

[0266] The battery management device 411 communicates with the assembled battery monitoring devices 301a to 301c and collects information on the voltage, temperature, etc. of each of the cells 100 included in the assembled batteries 200a to 200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information on the maintenance of the vehicle power supply 41.

[0267] The battery management unit 411 and the assembled battery monitoring units 301a to 301c are connected via a communication bus 412. In the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management unit 411 and one or more assembled battery monitoring units 301a to 301c). The communication bus 412 is a communication bus configured based on, for example, the CAN (Control Area Network) standard.

[0268] The battery pack monitoring devices 301a to 301c measure the voltage and temperature of each of the cells constituting the battery packs 200a to 200c based on commands received through communication from the battery management device 411. However, the temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all the cells.

[0269] The vehicle power supply 41 may also have an electromagnetic contactor (for example, a switch device 415 shown in FIG. 22) that switches between electrical connection and disconnection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that is turned on when the assembled batteries 200a-200c are being charged, and a main switch (not shown) that is turned on when the output from the assembled batteries 200a-200c is being supplied to a load. Each of the pre-charge switch and the main switch includes a relay circuit (not shown) that is switched on or off by a signal supplied to a coil disposed near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

[0270] The inverter 44 converts the input DC voltage into a three-phase alternating current (AC) high voltage for driving the motor. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. The inverter 44 is controlled based on control signals from the battery management unit 411 or the vehicle ECU 42, which controls the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

[0271] The drive motor 45 is rotated by the electric power supplied from the inverter 44. The drive force generated by the rotation of the drive motor 45 is transmitted to the axles and drive wheels W via, for example, a differential gear unit.

[0272] Although not shown, vehicle 400 also includes a regenerative braking mechanism (regenerator). When vehicle 400 is braked, regenerative braking mechanism rotates drive motor 45 and converts kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to inverter 44 and converted into direct current. The converted direct current is input to vehicle power supply 41.

[0273] One terminal of a connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of the connection line L1 is connected to a negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 in the battery management device 411 is provided on the connection line L1 between the negative terminal 414 and the negative input terminal 417.

[0274] One terminal of a connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41. The other terminal of the connection line L2 is connected to a positive input terminal 418 of the inverter 44. A switch device 415 is provided on the connection line L2 between the positive terminal 413 and the positive input terminal 418.

[0275] The external terminal 43 is connected to the battery management device 411. The external terminal 43 can be connected to, for example, an external power source.

[0276] In response to operational inputs from the driver or the like, the vehicle ECU 42 coordinates with other management devices and control devices including the battery management device 411 to control the vehicle power supply 41, the switch device 415, the inverter 44, etc. Through the coordinated control of the vehicle ECU 42, etc., the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, thereby managing the entire vehicle 400. Data relating to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line.

[0277] The vehicle according to the fifth embodiment is equipped with the battery pack according to the fourth embodiment. Because the battery pack has excellent life performance and input / output performance, a vehicle with high performance and reliability can be provided.

[0278] [Example] The above embodiment will be described in more detail below based on examples.

[0279] Example 1 (Synthesis of niobium-containing oxides) First, as a niobium-containing oxide, niobium titanium oxide was synthesized as follows.

[0280] Nb2O5 powder with a particle size D50 of 3.0 μm was prepared as the Nb source. TiO2 powder with a particle size D50 of 1.5 μm was prepared as the Ti source. The D50 ratio of the Nb source to the Ti source was 2:1.

[0281] Nb2O5 powder and TiO2 powder were mixed so that the molar ratio of Nb / Ti was 2 to obtain a raw material powder. The raw material powder was fired in the air using a hot press at a pressure of 30 MPa and a temperature of 1000°C to obtain a sintered body. The obtained sintered body was coarsely crushed using a hammer mill and then crushed using a wet ball mill. In this way, niobium titanium oxide powder was obtained.

[0282] (Electrode preparation) A slurry was prepared by dispersing the active material, conductive agent, and binder in a solvent. The proportions of the active material, conductive agent, and binder were 95 mass%, 3 mass%, and 2 mass%, respectively. Niobium titanium oxide powder was used as the active material. A mixture of acetylene black and carbon black was used as the conductive agent. The mass ratio of acetylene black to carbon black in the mixture was 2:1. Styrene butadiene rubber (SBR) was used as the binder. Pure water was used as the solvent.

[0283] Next, the slurry was applied to both sides of a current collector, and the coating was dried to obtain an active material-containing layer. A 12 μm-thick aluminum alloy foil was used as the current collector. The current collector and the active material-containing layer were pressed to obtain an electrode. The active material-containing layer of the electrode had a thickness of 61 μm.

[0284] Example 2 An electrode was produced in the same manner as in Example 1, except that in the synthesis of niobium titanium oxide, the temperature in firing the raw material powder was set to 500°C.

[0285] Example 3 In the synthesis of niobium titanium oxide, Nb2O5 powder with a particle size D50 of 1.3 μm was prepared as the Nb source. TiO2 powder with a particle size D50 of 1.1 μm was prepared as the Ti source. The D50 of the Nb source:D50 of the Ti source was 6:5. Furthermore, the temperature for firing the raw material powder was set to 500°C. Except for the above, an electrode was produced in the same manner as in Example 1.

[0286] Example 4 In the preparation of the electrode, niobium titanium oxide powder and Li4Ti5O 12 The powders were mixed at a ratio of 10% by mass and 90% by mass, respectively, and used. The niobium titanium oxide powder used was obtained in the same manner as described in Example 1. Except for the above, an electrode was produced in the same manner as in Example 1.

[0287] Example 5 Niobium titanium oxide powder was prepared as follows.

[0288] Nb2O5 powder with a particle size D50 of 1.1 μm was prepared as the Nb source. TiO2 powder with a particle size D50 of 2.2 μm was prepared as the Ti source. The D50 ratio of the Nb source to the Ti source was 1:2.

[0289] Nb2O5 powder and TiO2 powder were mixed so that the molar ratio of Nb / Ti was 2 to obtain a raw material powder. The raw material powder was fired in air at a temperature of 700°C using an electric furnace to obtain a sintered body. Note that no pressure was applied during firing. The obtained sintered body was coarsely crushed using a hammer mill and then crushed using a wet ball mill. In this way, niobium titanium oxide powder was obtained.

[0290] Except for the above, the electrode was produced in the same manner as in Example 1.

[0291] (Comparative Example 1) Niobium titanium oxide powder was prepared as follows.

[0292] As the Nb source, Nb2O5 powder with a particle size D50 of 1.6 μm was prepared. As the Ti source, TiO2 powder with a particle size D50 of 11 μm was prepared. The D50 ratio of the Nb source to the Ti source was 1:7.

[0293] Nb2O5 powder and TiO2 powder were mixed so that the molar ratio of Nb / Ti was 2 to obtain a raw material powder. The raw material powder was fired in the air at a temperature of 1000°C using an electric furnace to obtain a sintered body. Note that no pressure was applied during firing. The obtained sintered body was coarsely crushed using a hammer mill and then crushed using a wet ball mill. In this way, niobium titanium oxide powder was obtained.

[0294] Except for the above, the electrode was produced in the same manner as in Example 1.

[0295] For each of the electrodes of Examples 1 to 5 and Comparative Example 1, the maximum ratio of the area occupied by the second-phase large region to the area occupied by the first phase in 16 divided regions obtained by equally dividing a square region in the cross section of the electrode, and the ratio of the area occupied by the second-phase large region to the area occupied by the first phase in the square region were measured by the method described above. The measurement results are shown in Table 1. In each of the electrodes of Examples 1 to 5 and Comparative Example 1, the length of one side of the square observation region was 40 μm. In each of the electrodes of Examples 1 to 5 and Comparative Example 1, the ratio of the length of one side of the square observation region to the thickness of the active material-containing layer was 66 to 83%.

[0296] Furthermore, the performance of each electrode of Examples 1 to 5 and Comparative Example 1 was evaluated by the following method.

[0297] (Preparation of a three-electrode glass cell) A three-electrode glass cell was fabricated, and input / output performance was evaluated. The electrodes fabricated in the examples and comparative examples were used as the working electrodes. The electrodes were square with sides of 2 cm. Lithium metal was used for the counter electrode and reference electrode. The electrolyte used was a mixed solvent of ethylene carbonate and diethyl carbonate in which lithium hexafluorophosphate (LiPF6) was dissolved. The ratio of ethylene carbonate to diethyl carbonate in the mixed solvent was 1:2. The concentration of LiPF6 was 1 mol / L. The amount of electrolyte was 25 mL.

[0298] (Cycle performance evaluation) The three-electrode glass cell was charged at a current density of 1 C in an environment of 25°C until the SOC (State of Charge) reached 100%. It was then discharged at a current density of 1 C until the SOC reached 0%, and the discharge capacity was measured. This cycle was counted as one charge / discharge, and the battery was repeatedly charged / discharged until the discharge capacity retention rate relative to the first discharge capacity reached 80%. The number of cycles required to reach 80% of the discharge capacity relative to the first discharge capacity is an indicator of the long-life performance of the electrode.

[0299] (Input / output performance evaluation) The three-electrode glass cell was charged at a current density of 1 C under a 25°C environment until the state of charge (SOC) reached 100%. It was then discharged at a current density of 0.2 C until the SOC reached 0%, and the discharge capacity W1 was measured. The three-electrode glass cell was then charged again at a current density of 1 C until the SOC reached 100%. It was then discharged at a current density of 5 C until the SOC reached 0%, and the discharge capacity W2 was measured. The capacity ratio W2 / W1 was calculated by dividing the discharge capacity W2 by the discharge capacity W1. The capacity ratio W2 / W1 is an index of the input / output performance of the electrode.

[0300] Table 1 shows the long-life performance (the number of cycles until the discharge capacity retention rate relative to the first discharge capacity becomes 80%) and the input / output performance (W2 / W1) for the electrodes of the examples and comparative examples.

[0301] [Table 1]

[0302] From Table 1, the following becomes clear:

[0303] In Examples 1 to 5, the maximum ratio of the area occupied by the second phase large region to the area occupied by the first phase in the 16 divided regions obtained by equally dividing the square region in the cross section of the electrode was 10% or less in all cases. All of Examples 1 to 5 were superior in long life performance and input / output performance compared to Comparative Example 1.

[0304] Furthermore, in Examples 1 to 4, the ratio of the area occupied by the second phase large domain to the area occupied by the first phase in the square region was 4% or less. Examples 1 to 4 were particularly excellent in long life performance and input / output performance.

[0305] In Comparative Example 1, the maximum value of the ratio of the area occupied by the large second-phase region to the area occupied by the first phase was large for the 16 divided regions obtained by equally dividing the square region. This is thought to be because the particle size D50 of the TiO powder used as the starting material in producing the electrode in Comparative Example 1 was large at 11 μm, which resulted in the generation of unreacted products during firing. More specifically, it is thought that the unreacted products were generated because the particles of the starting material did not all react uniformly during firing.

[0306] According to at least one of these embodiments or examples, an electrode is provided. The electrode includes an active material-containing layer. The active material-containing layer includes active material particles including a first phase and a second phase. The first phase is a niobium-containing oxide phase. The second phase is a phase different from the first phase. In a cross section of the active material-containing layer along the thickness direction, a square region defined by a first side parallel to the thickness direction and a second side perpendicular to the first side is equally divided into 16 divided regions, and the ratio of the area occupied by the second phase to the area occupied by the first phase is 10% or less. The area occupied by the second phase is 2×10 -14 m 2 The area of ​​one or more regions occupying an area of ​​at least 1. Therefore, an electrode with high life performance and input / output performance can be provided.

[0307] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied 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 modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0308] The invention according to the embodiment will be described below.

[0309] [1] An electrode including an active material-containing layer, the active material-containing layer contains active material particles including a first phase and a second phase, the first phase is a niobium-containing oxide phase; the second phase is a different phase from the first phase; In a cross section of the active material-containing layer taken along the thickness direction, a square region defined by a first side parallel to the thickness direction and a second side perpendicular to the first side is equally divided into 16 divided regions, and the ratio of an area occupied by the second phase to an area occupied by the first phase is 10% or less, The area occupied by the second phase is 2×10 -14 m 2 The electrode is an area of ​​one or more regions occupying an area of ​​more than one.

[0310] [2] The electrode according to [1], wherein the ratio of the area occupied by the second phase to the area occupied by the first phase in the square region is 4% or less.

[0311] [3] The electrode according to [1] or [2], wherein the one or more regions of the second phase have a circularity of 0.7 or more and 1.0 or less.

[0312] [4] The electrode according to any one of [1] to [3], wherein the niobium-containing oxide phase is a niobium titanium oxide phase.

[0313] [5] The second phase has the general formula TiO X The electrode according to any one of [1] to [4], wherein x>0.

[0314] [6] a positive electrode; a negative electrode; and an electrolyte, The secondary battery, wherein the negative electrode is the electrode according to any one of [1] to [5].

[0315] [7] A battery pack including the secondary battery according to [6].

[0316] [8] An external terminal for applying current; The battery pack according to [7], further comprising a protection circuit.

[0317] [9] A vehicle equipped with a battery pack described in [7] or [8].

[0318]

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

[0319] 1...electrode group, 2...exterior member, 3...electrode, 3a...current collector, 3b...active material-containing layer, 3c...negative electrode current collecting 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...bus bar, 22...positive electrode side lead, 23...negative electrode side lead, 24...adhesive tape, 31...container, 32...lid, 33...protective sheet, 34...printed wiring board, 35...wiring, 40...vehicle body, 41...vehicle power source, 42...electrical control device, 43...external terminal, 44...inverter, 45...drive motor, 100...secondary battery, 200...assembled battery, 200a...assembled battery, 200b...assembled battery, 200c...assembled battery, 300...battery pack, 300a...battery pack, 300b...battery pack, 300c...battery pack, 301a...assembled battery monitoring device, 301b...assembled battery monitoring device, 301c...assembled battery monitoring device, 342...positive side connector, 343...negative side connector, 345...thermistor, 346...protection circuit, 342a...wiring, 343a...wiring, 350...external terminal for energization, 352...positive side terminal, 353...negative side terminal, 348a...positive side wiring, 348b...negative side wiring, 400...vehicle, 411...battery management device, 412...communication bus, 413...positive side terminal, 414...negative side terminal, 415...switching device, 416...current detection unit, 417...negative side input terminal, 418...positive side input terminal, L1...connecting line, L2...connecting line, W...drive wheel.

Claims

1. An electrode including an active material-containing layer, the active material-containing layer contains active material particles including a first phase and a second phase, the first phase is a niobium-containing oxide phase; the second phase is a different phase from the first phase; In a cross section of the active material-containing layer taken along the thickness direction, a square region defined by a first side parallel to the thickness direction and a second side perpendicular to the first side is equally divided into 16 divided regions, and the ratio of an area occupied by the second phase to an area occupied by the first phase is 10% or less, The area occupied by the second phase is 2 × 10 －１４ m ２ The electrode is an area of ​​one or more regions occupying an area of ​​at least one.

2. 2. The electrode according to claim 1, wherein the ratio of the area occupied by the second phase to the area occupied by the first phase in the square region is 4% or less.

3. 3. The electrode of claim 1, wherein the one or more regions of the second phase have a circularity of 0.7 or greater and 1.0 or less.

4. 3. The electrode according to claim 1, wherein the niobium-containing oxide phase is a niobium titanium oxide phase.

5. The second phase has the general formula TiO Ｘ 3. The electrode of claim 1, wherein x>0.

6. A positive electrode and a negative electrode; and an electrolyte, The secondary battery, wherein the negative electrode is the electrode according to claim 1 or 2.

7. A battery pack comprising the secondary battery according to claim 6.

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

9. A vehicle equipped with the battery pack according to claim 7.

10. The vehicle according to claim 9, further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.

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