Niobium titanium oxide, active material, electrodes, secondary batteries, battery packs, and vehicles

Abstract

To provide a niobium titanium-based oxide that can achieve secondary batteries with high capacity and excellent rate characteristics.SOLUTION: According to one embodiment, a niobium titanium-based oxide is provided. The niobium titanium-based oxide satisfies formulae (1) to (3) in an L*a*b* color space as measured in accordance with Japanese Industrial Standards JIS Z8722: 2009: 95.0≤L*≤100 (1), -1.0≤a*≤1.0 (2) and -1.0≤b*≤6.0 (3).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to niobium titanium oxide, active material, electrode, secondary battery, battery pack, and vehicle.

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

[0003] To enable rapid charging and discharging, electrons and lithium ions must be able to move quickly between the positive and negative electrodes. However, in batteries using carbon-based negative electrodes, repeated rapid charging and discharging can cause dendrite deposition of metallic lithium on the electrodes, potentially leading to internal short circuits, overheating, and ignition.

[0004] Therefore, batteries using metal composite oxides as the negative electrode instead of carbonaceous materials have been developed. In particular, batteries using titanium oxide as the negative electrode have the characteristics of enabling stable rapid charging and discharging, and having a longer lifespan compared to those using carbon-based negative electrodes.

[0005] However, titanium oxide has a higher potential relative to metallic lithium than carbonaceous materials, meaning it is nobler. Furthermore, titanium oxide has a low capacity per unit weight. For this reason, batteries using titanium oxide as the negative electrode suffer from a problem of low energy density.

[0006] For example, the electrode potential of titanium oxide is approximately 1.5V (vs. Li / Li) relative to metallic lithium. +) is higher (more noble) than the potential of the carbon-based anode. The potential of titanium oxide is Ti when lithium is electrochemically inserted and removed. 3+ and Tire 4+ Because it is caused by a redox reaction between them, it is electrochemically constrained. Also, 1.5V (vs.Li / Li + There is also the fact that rapid charging and discharging of lithium ions can be performed stably at high electrode potentials. Therefore, it has been difficult to lower the electrode potential in order to improve energy density.

[0007] On the other hand, regarding capacity per unit weight, the theoretical capacity of titanium dioxide (anatase structure) is about 165 mAh / g, while Li4Ti5O 12 The theoretical capacity of spinel-type lithium-titanium composite oxides like the one shown is also around 180 mAh / g. On the other hand, the theoretical capacity of typical graphite-based electrode materials is 385 mAh / g or more. Thus, the capacity density of titanium oxide is significantly lower compared to that of carbon-based anodes. This is because titanium oxide has fewer sites for intercalating lithium in its crystal structure, and lithium is easily stabilized within the structure, resulting in a decrease in effective capacity.

[0008] In light of the above, new electrode materials containing Ti and Nb are being investigated. Such niobium titanium oxide materials are expected to have high charge / discharge capacities. In particular, the composite oxide represented as TiNb2O7 has a high theoretical capacity exceeding 380 mAh / g. Therefore, niobium titanium oxide is Li4Ti5O 12 It is expected to be a high-capacity material that can replace [another material]. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2020-047374 [Patent Document 2] Japanese Patent Publication No. 2021-190250 [Non-patent literature]

[0010] [[Non - Patent Document 1]] M.Gasperin, Journal of Solid State Chemistry 53, pp144 - 147 (1984) [[Non - Patent Document 2]] Y. Zhang, et. al., Electrochimica Acta 330 (2020) 135299 [[Non - Patent Document 3]] Hyunjung Park, et. al., Advanced Energy Materials, 2015 volume 5 Issue 8, 1401945 [[Summary of the Invention]] [[Problems to be Solved by the Invention]]

[0011] An object is to provide a niobium titanium oxide capable of realizing a secondary battery with high capacity and excellent rate characteristics, an active material containing this niobium titanium oxide, an electrode containing this active material, a secondary battery equipped with this electrode, a battery pack equipped with this secondary battery, and a vehicle equipped with this battery pack. [[Means for Solving the Problems]]

[0012] According to an embodiment, a niobium titanium oxide is provided. The niobium titanium oxide satisfies the following formulas (1) to (3) in the L * a * b * color space.

[0013] 95.0≦L * ≦100.0…(1) -1.0≦a * ≦1.0…(2) -1.0≦b * ≦6.0…(3)

[0014] According to another embodiment, an active material containing niobium titanium oxide according to the embodiment is provided.

[0015] According to another embodiment, an electrode containing an active material according to the embodiment is provided.

[0016] In another embodiment, a secondary battery is provided that comprises a positive electrode, a negative electrode, and an electrolyte. The negative electrode is an electrode according to the embodiment.

[0017] According to another embodiment, a battery pack comprising a secondary battery according to the embodiment is provided.

[0018] According to another embodiment, a vehicle is provided that is equipped with a battery pack according to the embodiment. [Brief explanation of the drawing]

[0019] [Figure 1] A schematic diagram showing the crystal structure of niobium titanium oxide (Nb2TiO7). [Figure 2] A schematic diagram showing the crystal structure of Figure 1 when observed from a different direction. [Figure 3] A schematic plan view showing the particles being measured in a transmission electron microscope (TEM) observation. [Figure 4] A schematic cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 5] Figure 4 shows an enlarged cross-sectional view of section A of the secondary battery. [Figure 6] A schematic partial cutaway perspective view showing another example of a secondary battery according to the embodiment. [Figure 7] An enlarged cross-sectional view of section B of the secondary battery shown in Figure 6. [Figure 8] A schematic perspective view showing an example of a battery pack according to this embodiment. [Figure 9] An exploded perspective view schematically showing an example of a battery pack according to this embodiment. [Figure 10] A block diagram showing an example of the electrical circuit of the battery pack shown in Figure 9. [Figure 11]A schematic cross-sectional view showing an example of a vehicle according to this embodiment. [Figure 12] A schematic diagram showing another example of a vehicle according to the embodiment. [Modes for carrying out the invention]

[0020] The embodiments will be described below with reference to the drawings. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each drawing is a schematic diagram intended to illustrate the embodiments and facilitate understanding; their shapes, dimensions, and ratios may differ from those of the actual device. These can be appropriately modified in accordance with the following description and known technology.

[0021] Niobium titanium oxide can be synthesized, for example, by a solid-phase method using Nb and Ti sources as raw materials. The synthesized niobium titanium oxide is then subjected to grinding until it reaches an appropriate particle size. Grinding can form an amorphous phase on the particle surface. The amorphous phase has inferior electronic conductivity and lithium-ion conductivity compared to the portion with the normal crystalline phase. Therefore, secondary batteries using active materials with an amorphous phase tend to have inferior battery capacity and charge / discharge characteristics (rate characteristics).

[0022] The inventors of this invention conducted intensive research to suppress the formation of amorphous phases, which have poor electronic conductivity. As a result, they discovered that in niobium titanium oxide particles with a specific color on the surface, the amorphous phase is either absent or present in only small amounts.

[0023] (First Embodiment) According to the first embodiment, niobium titanium oxide is provided. Niobium titanium oxide is measured according to the Japanese Industrial Standard JIS Z 8722:2009. * a * b * In the color space, the following equations (1) to (3) are satisfied.

[0024] 95.0 ≤ L *≤100.0…(1) -1.0≦a * ≤1.0…(2) -1.0≦b * ≤6.0…(3)

[0025] The color that satisfies all of these equations (1) to (3) is generally a pale yellow. In the case of niobium titanium oxide that satisfies all of the above equations (1) to (3), the band gap is narrower compared to the case that does not satisfy equations (1) to (3). In materials with a narrow band gap, electron excitation occurs more easily. That is, materials with a narrow band gap have high electronic conductivity. In addition, since there are more metal elements involved in the battery reaction, the electrode potential can be lowered, thereby enabling a higher battery voltage. That is, a secondary battery exhibiting high capacity can be realized.

[0026] Methods for producing niobium titanium oxide having a color satisfying the above formulas (1) to (3) will be described in detail later, but one example is the addition of an element (hereinafter referred to as doping element A) that is solidly dissolved in the crystal lattice of niobium titanium oxide without impeding the movement of Li ions and without causing defects. Alternatively, one example is the method of partially depleting the oxygen atoms constituting the crystal lattice, or the method of adding nitrogen atoms to the crystal lattice. These methods may be carried out in appropriate combinations. That is, element A may be added to niobium titanium oxide, and oxygen deficiency and / or nitrogen addition may also be performed.

[0027] When niobium titanium oxide contains an added element A, element A functions as a so-called donor. That is, element A exists within the band gap (forbidden band) between the conduction band and valence band of the niobium titanium oxide, with an energy level within that gap. Electrons at this energy level are easily excited to the conduction band, thus contributing to improved electronic conductivity.

[0028] On the other hand, when niobium titanium oxide has oxygen vacancies or contains added nitrogen atoms, holes are formed at energy levels near the valence band. These holes function as acceptors. Since holes are easily excited to the valence band, they contribute to improved electronic conductivity.

[0029] As described above, in all cases the band gap of niobium titanium oxide is narrowed, making it possible to achieve high capacity and excellent rate characteristics. Furthermore, the inventors have found that the color of niobium titanium oxide changes as the band gap is narrowed. Moreover, the inventors have found that niobium titanium oxide capable of realizing excellent battery characteristics is L * a * b * We discovered that it possesses a specific hue defined by the color space. This hue is, in other words, the hue that satisfies all of the above equations (1) to (3).

[0030] Furthermore, in the present specification and claims, L * a * b * A color space refers to a color space measured according to the Japanese Industrial Standard JIS Z 8722:2009. * a * b * A color space is an index used, for example, to represent the color of an object. * a * b * Color space is an index standardized by the International Commission on Illumination (CIE) in 1976. * a * b * In the color space, L * This represents brightness, a * and b * This represents hue as chromaticity. * A larger value indicates higher brightness. Also, a * and b * The arrow indicates the direction of the color. * The red line indicates the direction, -a * The green line indicates the direction. * The yellow indicates the direction, -b * The blue line indicates the direction.

[0031] Regarding the surface of niobium titanium oxide, L * It is within the range of 95.0 to 100.0. * If the value is less than 95.0, for example, the content of additive element A is too high, or there is an oxygen deficiency or excessive nitrogen addition. In this case, although the electronic conductivity is excellent, the electrode potential is too high, so the energy density tends to decrease. Also, L * The upper limit of L is, by definition, 100. * A value of 99.0 or less is desirable. * If the value exceeds 99.0, it may indicate insufficient content of additive element A, or that there is an oxygen deficiency or insufficient nitrogen addition. In this case, for example, the formation of the amorphous phase cannot be sufficiently suppressed, and therefore the electron conductivity tends to be poor. * Preferably, it is within the range of 95.0 to 99.0, and more preferably within the range of 95.5 to 98.5.

[0032] a * It is within the range of -1.0 to 1.0. * When within this range, the niobium titanium oxide does not undergo phase formation due to the added elements and has a highly crystalline structure. In this case, high rate characteristics can be achieved without hindering lithium ion conduction within the active material particles.

[0033] b * It is within the range of -1.0 to 6.0. * If the value is less than -1.0, for example, the content of additive element A is too high, or there is an oxygen deficiency or excessive nitrogen addition. In this case, although the electronic conductivity is excellent, the electrode potential is too high, so the energy density tends to decrease. Also, b * If the value exceeds 6.0, it indicates that the content of additive element A is insufficient, or that there is insufficient oxygen deficiency or insufficient nitrogen addition. In this case, for example, the formation of the amorphous phase cannot be sufficiently suppressed, and therefore the electron conductivity tends to be poor. b * Preferably, it is within the range of 1.0 to 5.0.

[0034] <Forms of niobium titanium oxide> The form of niobium titanium oxide according to this embodiment is not particularly limited. Niobium titanium oxide may, for example, take the form of primary particles, or it may take the form of secondary particles formed by the aggregation of primary particles. Niobium titanium oxide may also be a mixture of primary and secondary particles. Niobium titanium oxide may have a granular or lumpy form having dimensions larger than what is commonly referred to as a particle.

[0035] Niobium titanium oxide can take the form of a powder, for example, composed of aggregated primary and secondary particles. The average particle size (D50) of niobium titanium oxide powder is in the range of 0.5 μm to 30 μm. Here, "average particle size (D50)" refers to the particle size at which the cumulative volume distribution in the particle size distribution chart obtained by the laser diffraction scattering method described later becomes 50%.

[0036] Based on Japanese Industrial Standard JIS Z 8722:2009, L * a * b * Color space measurements can be performed on niobium titanium oxide in various forms. These measurements can be performed, for example, on primary particles, secondary particles, mixtures of primary and secondary particles, or powders containing these. Specific measurement methods will be described later.

[0037] The niobium titanium oxide according to the embodiment preferably contains the Nb2TiO7 phase as the main phase. The Nb2TiO7 phase is a niobium titanium composite oxide phase represented by Nb2TiO7 as its representative composition. The Nb2TiO7 phase has symmetry of the space group C2 / m and has a crystal structure with atomic coordinates described in Non-Patent Literature 1 (Journal of Solid State Chemistry 53, pp144-147 (1984)). The Nb2TiO7 phase may have a monoclinic crystal structure. The crystal phase of the niobium titanium oxide is not limited to the Nb2TiO7 phase and may further contain Nb-rich phases described later. Whether or not the niobium titanium oxide contains the Nb2TiO7 phase as the main phase is determined based on the fact that the 2θ of the maximum peak in the XRD pattern appears at 26.0±0.1°.

[0038] As an example of the Nb2TiO7 phase, schematic diagrams of the crystal structure of monoclinic Nb2TiO7 are shown in Figures 1 and 2.

[0039] As shown in Figure 1, the crystal structure of monoclinic Nb2TiO7 consists of a skeletal structure 103 composed of metal ions 101 and oxide ions 102. At the positions of the metal ions 101, Nb ions and Ti ions are randomly arranged in a ratio of Nb:Ti = 2:1. The alternating three-dimensional arrangement of these skeletal structure 103 creates voids 104 between them. These voids 104 serve as hosts for lithium ions. Lithium ions can be inserted into this crystal structure from 0 moles to a maximum of 5.0 moles. Therefore, the composition when 0 to 5.0 moles of lithium ions are inserted is Li x It can be expressed as Nb2TiO7(0≦x≦5).

[0040] In Figure 1, regions 105 and 106 are areas having two-dimensional channels in the

[0100] and

[0010] directions. As shown in Figure 2, the monoclinic Nb2TiO7 crystal structure has a void portion 107 in the

[0001] direction. This void portion 107 has a tunnel structure favorable for lithium ion conductivity and forms a conductive path in the

[0001] direction connecting region 105 and region 106. The existence of this conductive path allows lithium ions to move back and forth between region 105 and region 106. Furthermore, niobium titanium oxide has a 1.5V (vs. Li / Li + It has a lithium storage potential of approximately 1 / 2. Therefore, electrodes containing niobium titanium oxide as the active material can realize batteries that enable stable, repeated rapid charging and discharging.

[0041] Furthermore, in the above crystal structure, when lithium ions are inserted into the void portion 104, the metal ions 101 that constitute the framework are reduced to the trivalent state, thereby maintaining the electrical neutrality of the crystal. In niobium titanium oxide, not only are Ti ions reduced from tetravalent to trivalent, but Nb ions are also reduced from pentavalent to trivalent. Therefore, the reduction value per unit weight of active material is large. Consequently, it is possible to maintain the electrical neutrality of the crystal even when many lithium ions are inserted. For this reason, it has a higher energy density compared to compounds such as titanium oxide that contain only tetravalent cations. Also, the Nb2TiO7 phase is Nb 10 Ti2O 29 Phase, Nb 14 TiO 37 Phase and Nb 24 TiO 64 It has superior gravitational energy density compared to the other phases. This is because Nb 10 Ti2O 29 Phase, Nb 14 TiO 37 Phase and Nb 24 TiO 64 This is because the phase contains a large number of Nb atoms per mole, meaning it has a large weight per mole.

[0042] Next, Nb 10 Ti2O 29 Phase, Nb 14TiO 37 phase and Nb 24 TiO 64 phase will be described. In the specification of the present application, these crystal phases may be collectively referred to as the Nb-rich phase. The Nb-rich phase means a niobium titanate phase in which the molar ratio of Nb / Ti is greater than 2.

[0043] The basic skeletal structure of the Nb-rich phase is similar to the crystal structure of monoclinic Nb2TiO7 shown in FIGS. 1 and 2. When lithium ions are inserted into the void portion 104, the metal ions 101 constituting the skeleton are reduced to trivalent, thereby maintaining the electrical neutrality of the crystal. Nb 10 Ti2O 29 When lithium ions are inserted into the phase, the composition can be expressed as LixNb 10 Ti2O 29 (0 ≦ x ≦ 22). When lithium ions are inserted into the Nb 14 TiO 37 phase, the composition can be expressed as LixNb 14 TiO 37 (0 ≦ x ≦ 29). When lithium ions are inserted into the Nb 24 TiO 64 phase, the composition can be expressed as LixNb 24 TiO 64 (0 ≦ x ≦ 49).

[0044] In the Nb 10 Ti2O 29 phase, Nb 14 TiO 37 phase and Nb 24 TiO 64 phase, compared with the Nb2TiO7 phase, the amount of Nb ions reduced from pentavalent to trivalent increases. Therefore, the reduction valence number per mole of the active material is large. Therefore, it is possible to maintain the electrical neutrality of the crystal even when a large amount of lithium ions are inserted. Therefore, Nb 10 Ti2O 29 phase, Nb 14 TiO 37 phase and Nb 24 TiO 64At least one Nb-rich phase selected from the group of phases can maintain a stable crystal structure even when lithium ions are inserted in excess compared to the Nb2TiO7 phase.

[0045] The niobium titanium oxide according to this embodiment may contain, for example, only the Nb2TiO7 phase, or it may contain the Nb2TiO7 phase and the Nb-rich phase. From the viewpoint of gravimetric energy density, as described above, it is preferable that the niobium titanium oxide contains the Nb2TiO7 phase as the main phase.

[0046] Niobium titanium oxide may contain additive element A, which is an element that provides a solid solution without defects in the crystal lattice of niobium titanium oxide. Additive element A is at least one selected from the group consisting of Fe, Cr, W, and Mo. Additive element A provides a solid solution without defects in the crystal lattice of niobium titanium oxide without inhibiting the movement of Li ions. Therefore, additive element A can narrow the band gap of niobium titanium oxide without adversely affecting the operation of the battery.

[0047] When niobium titanium oxide contains Fe as an additive element A, it has the effect of improving the electronic conductivity on the surface and enhancing the rate properties.

[0048] When niobium titanium oxide contains Cr as an additive element A, it has the effect of improving the electron conductivity on the surface and improving the rate properties. Furthermore, Cr 3+ Because it is used for doping, Li + When it detaches (during discharge), Cr 4+ ~Cr 6+ Because there is a range of valence changes up to Li + This promotes the movement of particles and enhances the discharge rate characteristics.

[0049] When niobium titanium oxide contains W as an additive element A, it improves the electron conductivity at the surface and enhances the rate properties. Compared to Ti (3-4 valency) and Nb (3-5 valency), W has a wider valency range of 6-3, allowing it to absorb more Li into a larger crystal.

[0050] When niobium titanium oxide contains Mo as an additive element A, it improves the electron conductivity at the surface and enhances the rate properties. Compared to Ti (3-4 valency) and Nb (3-5 valency), Mo has a wider valency range of 6-3, allowing it to absorb more Li into a larger crystal. Furthermore, due to the low melting point of the raw material, it allows for a lower firing temperature of the material.

[0051] Additive element A may be present in, for example, the primary particles of niobium titanium oxide. Additive element A may be present in some of the multiple particles in the powder constituting the niobium titanium oxide, or it may be present in all of the particles. If the content of additive element A in the niobium titanium oxide particles is high, L * It tends to get smaller, a * and tend to be larger, b * It tends to become smaller.

[0052] It is preferable that primary particles containing additive element A have a concentration gradient of additive element A that increases from the center of gravity of the primary particle toward the surface. Specifically, a primary particle may have a surface region defined as a region from the surface of the primary particle to a depth of 20 nm, and a center of gravity (bulk portion) located inside this surface region. The primary particle has a concentration gradient of additive element A that increases from the center of gravity toward the surface. When a primary particle has such a concentration gradient, the structure of the crystal lattice constituting the particle changes continuously. Therefore, when Li ions move through the crystal lattice, the Li ions can move smoothly along the direction connecting the particle surface and the center of gravity of the particle.

[0053] Since additive element A can be present in trace amounts not only on the surface but also in the bulk portion, electrons that reach the particle interface from outside the particle can quickly move to the particle center.

[0054] Whether the primary particles contain the additive element A can be confirmed by TEM-EDS (Transmission Electron Microscope - Energy dispersive X-ray spectroscopy) which combines a transmission electron microscope and energy dispersive X-ray spectroscopy. According to TEM-EDS, it is also possible to confirm whether there is a continuous concentration gradient of the additive element A in the primary particles. In addition, in each of the above-mentioned surface layer and the centroid, the content AA of the additive element A and the total amount AM of niobium atoms and titanium atoms can be measured.

[0055] <TEM-EDS Observation> In the transmission electron microscope observation, it is desirable to embed the target sample powder in resin etc. and cut out the inside of the specimen by mechanical polishing and ion milling etc. The particle surface of the target sample may be coated with carbon to improve electron conductivity. In that case, the particle surface of the part not coated with carbon will be observed.

[0056] In addition, the same treatment can be performed on the target sample even if it is an electrode body. For example, it can be embedded in resin as an electrode body and the desired location can be observed, or the current collector (metal foil) can be peeled off from the electrode body and observed as electrode powder in which a conductive material and a binder are mixed. By doing so, it is possible to know how the two crystal phases are distributed in the primary particles and to know the composition gradient inside the particles. In addition, by using EDS, the concentration distribution of specific elements in the particles can be measured.

[0057] A specific example will be explained below with reference to Figure 3. Figure 3 is a schematic plan view showing the particle to be measured. First, the centroid of the particle to be measured is considered to be the center of the particle. Next, five measurement points are set at equal intervals on a straight line connecting the center of the particle and an arbitrary point on the particle surface. The multi-wave interference pattern of the particle is examined at three points in the region orthogonal to each measurement point, and the electron diffraction pattern is observed. This observation allows us to know the crystal structure contained in that measurement point. For example, by simulating the electron diffraction pattern in advance, the Nb2TiO7 phase and Nb 10 Ti2O 29 Phase, Nb 14 TiO 37 Phase and Nb 24 TiO 64 It is possible to easily distinguish between this phase and other phases.

[0058] In the surface layer described above, the ratio AA / AM, which is the content of added element A (AA) to the total amount of niobium and titanium atoms (AM), satisfies, for example, 0.02 ≤ AA / AM ≤ 0.10. When the ratio AA / AM satisfies this numerical range, element A is contained in sufficient quantities on the particle surface, allowing for efficient incorporation of electrons from outside the particle into the particle while suppressing capacity reduction.

[0059] In the center of gravity, the ratio AA / AM, which is the amount of additive element A (AA) to the total amount of niobium and titanium atoms (AM), satisfies 0.001 ≤ AA / AM ≤ 0.01. The center of gravity has a larger volume compared to the surface. Therefore, by having additive element A in the center of gravity in such a small amount, it is possible to effectively improve electronic conductivity while suppressing a decrease in battery voltage.

[0060] Within a primary particle, the region defined as the surface and the region defined as the center of gravity are only formally or virtually separated based on a depth of 20 nm. In other words, a layer corresponding to the surface is not attached to the surface of the center of gravity. The surface and the center of gravity can be parts of the primary particle and other parts of the same crystalline phase.

[0061] The crystal lattice that makes up niobium titanium oxide contains oxygen atoms. Some of the oxygen atoms that make up the crystal lattice may be missing. If there are many oxygen vacancies in the niobium titanium oxide particles, L * It tends to get smaller, a * b tends to become smaller. * Regarding this, b* tends to change in the positive direction in the case of a small oxygen deficiency, and in the negative direction when an excessive oxygen deficiency is introduced.

[0062] The niobium titanium oxide according to the embodiment has, for example, an oxygen deficiency in the range of 100 ppm to 10,000 ppm. As an example, the primary particles of niobium titanium oxide may have an oxygen deficiency in the range of 100 ppm to 10,000 ppm. In this specification and claims, the amount of oxygen deficiency is measured by the increase in weight within the range of 200°C to 500°C in thermogravimetry (TG) in air. That is, the increase in weight within that temperature range is considered to be the amount of oxygen deficiency.

[0063] When the amount of oxygen vacancy is within the above range, there is an adequate amount of oxygen vacancy on the particle surface, so the band gap does not narrow too much. Therefore, electrons from outside the particle can be efficiently taken into the particle while suppressing capacity degradation.

[0064] It is preferable that the primary particles have a concentration gradient of oxygen atoms that decreases from the center of gravity of the primary particle toward the surface. When primary particles have a concentration gradient of oxygen vacancies, the structure of the crystal lattice itself that constitutes the particles changes continuously. Therefore, when Li ions move through the crystal lattice, the Li ions can move smoothly along the direction connecting the particle surface and the center of gravity of the particle. The presence of a small amount of oxygen vacancy at the center of gravity suppresses a decrease in battery voltage while effectively increasing electronic conductivity. In the surface layer described above, the ratio AO / AM, which is the oxygen atom content AO to the total amount AM of niobium and titanium atoms, can satisfy, for example, 2 ≤ AO / AM ≤ 2.3. When the ratio AO / AM satisfies 2 ≤ AO / AM ≤ 2.3 for the entire primary particle including the surface layer, the amount of oxygen vacancy due to TG will be greater than 10,000 ppm. When the amount of oxygen vacancy due to TG in niobium titanium oxide is in the range of 100 ppm to 10,000 ppm, and the ratio AO / AM satisfies 2 ≤ AO / AM ≤ 2.3 in the surface layer of the primary particle, oxygen vacancies exist in the surface layer of the niobium titanium oxide particles. Therefore, the primary particle has a concentration gradient for oxygen atoms that decreases from the center of gravity of the primary particle towards the surface. As a result, electrons from outside the particle can be efficiently taken into the particle while suppressing capacity reduction. The ratio AO / AM can be measured by the TEM-EDS described above.

[0065] Nitrogen atoms may be added to niobium titanium oxide. Nitrogen atoms may, for example, be present in the primary particles of the niobium titanium oxide. Nitrogen atoms may be present in some of the particles in the powder constituting the niobium titanium oxide, or in all of the particles. If the amount of nitrogen atoms added to the niobium titanium oxide particles is large, L * It tends to get smaller, a * b tends to get bigger, * It tends to get bigger.

[0066] It is preferable that primary particles containing nitrogen atoms have a concentration gradient of nitrogen atoms that increases from the center of gravity of the primary particle toward the surface. When primary particles have such a nitrogen atom concentration gradient, the structure of the crystal lattice constituting the particle changes continuously. Therefore, when Li ions move through the crystal lattice, they can move smoothly along the direction connecting the particle surface and the center of gravity of the particle. Since nitrogen atoms can be present in trace amounts not only on the surface but also in the bulk portion, electrons that reach the particle interface from outside the particle can quickly move to the particle center.

[0067] In the surface layer described above, the ratio AN / AM, which is the nitrogen atom content AN to the total amount AM of niobium and titanium atoms, satisfies, for example, 0.01 ≤ AN / AM ≤ 0.3. When the ratio AN / AM satisfies this numerical range, there are just enough nitrogen atoms on the particle surface, so the band gap is not too narrow. Therefore, electrons from outside the particle can be efficiently taken into the particle while suppressing capacity degradation.

[0068] In the center of gravity, the ratio AN / AM, which is the nitrogen atom content AN to the total amount of niobium and titanium atoms AM, satisfies 0.0001 ≤ AN / AM ≤ 0.001. The center of gravity has a larger volume compared to the surface. Therefore, the presence of a small amount of nitrogen atoms in the center of gravity effectively enhances electronic conductivity while suppressing a decrease in battery voltage.

[0069] Whether or not primary particles contain nitrogen atoms, and the ratio AN / AM in the surface layer and the center of gravity, can be measured by the TEM-EDS measurement described above.

[0070] It is preferable to subject the niobium titanium oxide to at least one of the above-mentioned treatments: the addition of element A, oxygen deficiency, and nitrogen addition. In any case, the color of the niobium titanium oxide is adjusted so that all of the above formulas (1) to (3) are satisfied.

[0071] In the embodiment, the primary particles of niobium titanium oxide preferably do not contain an amorphous phase. For example, an amorphous phase may exist on the surface of the primary particles in the range of 0 nm to 2 nm (including 0 nm). Since the amorphous phase has poor electronic conductivity, if the primary particles contain an amorphous phase in such a small amount as described above, not only excellent electronic conductivity but also high battery capacity can be achieved. Whether or not the niobium titanium oxide contains an amorphous phase can be confirmed by the TEM observation described above.

[0072] The amorphous phase tends to have more hydroxyl groups on its surface compared to the crystalline phase. Therefore, the amorphous phase is prone to undesirable moisture adsorption. Moisture adsorbed by hydrogen bonding to hydroxyl groups is difficult to remove. Moisture that is not removed by drying will, if the niobium titanium oxide is subjected to charging and discharging, undergo side reactions with electrolytes, etc., contributing to gas generation. Conversely, according to the embodiment of niobium titanium oxide in which the formation of the amorphous phase is suppressed, such moisture is less likely to be present on the particle surface. Therefore, gas generation can be suppressed.

[0073] The amount of moisture adsorbed on the surface of the niobium titanium oxide is measured by the Karl Fischer method. For the niobium titanium oxide according to the embodiment, it is preferable that the amount of moisture adsorbed analyzed by the Karl Fischer method is 800 ppm or less. Here, the Karl Fischer method is used to measure the amount of moisture by coulometric titration using a Karl Fischer moisture meter (VA-06 model, manufactured by Mitsubishi Chemical Analytec Co., Ltd.). Specifically, the sample is heated to 140°C and the measurement is performed under conditions where nitrogen gas is introduced at a flow rate of 200 ml / min. The amount of moisture is calculated from the amount of electricity consumed in the reaction between water and iodine.

[0074] As an example of niobium titanium oxide having a monoclinic Nb2TiO7 phase, Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ Examples of compounds having an average composition represented by the formula are: Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. The subscripts in the composition formula are 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. A specific example of monoclinic titanium niobium oxide is Li x Nb2TiO7 (0≦x≦5) is one example.

[0075] Another example of niobium titanium oxide having a monoclinic Nb2TiO7 phase is Li x Ti1-y M3 y+z Nb 2-z O 7-δ Examples of compounds having an average composition represented by are given by , where M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. In the composition formula, each subscript represents 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3.

[0076] <L * a * b * Color space measurement > L for niobium titanium oxide, according to Japanese Industrial Standard JIS Z 8722:2009 * a * b * For color space measurements, a colorimeter based on a spectrophotometric method can be used, which measures the reflectance at wavelengths across the entire visible light range and calculates the tristimulus value. During measurement, the niobium titanium oxide itself is the object of measurement. For example, during measurement, niobium titanium oxide particles or powder may be sandwiched between transparent films. If niobium titanium oxide is incorporated into the electrode composite layer, the niobium titanium oxide should be isolated using the method described below.

[0077] First, completely discharge the battery. You can discharge the battery to its rated cutoff voltage by discharging it at a current of 0.1C in a 25°C environment.

[0078] Next, the battery is disassembled in a glove box filled with argon to remove the electrode body (or electrode group). This electrode body is washed with a suitable solvent and dried under reduced pressure at 60°C for 12 hours. For example, ethyl methyl carbonate can be used as the washing solvent. In this way, the organic electrolyte contained in the electrode body can be removed. Next, the electrode is cut to obtain two electrode pieces. One of the cut electrode pieces is immersed in a solvent (organic solvents such as alcohol and NMP are preferred) and subjected to ultrasound. This separates the current collector from the electrode constituent material contained in the electrode body. Next, the dispersion solvent in which the electrode constituent material is dispersed is subjected to a centrifuge to separate the active material particles (only niobium titanium oxide powder) from the electrode powder containing conductive agents such as carbon.

[0079] <Powder X-ray diffraction measurement> Powder X-ray diffraction measurements for niobium titanium oxide can be performed, for example, as follows. First, the sample is ground until the average particle size is approximately 5 μm. The ground sample is then packed into a holder portion with a depth of 0.2 mm formed on a glass sample plate. At this time, care should be taken to ensure that the sample is sufficiently packed into the holder portion. Care should also be taken to pack the correct amount of sample to avoid cracks, voids, etc. Next, another glass plate is pressed against the outside to flatten the surface of the sample packed into the holder portion. Care should be taken to ensure that there are no irregularities on the reference surface of the holder due to an excess or deficiency in the amount of packed sample.

[0080] Next, the glass plate filled with the sample is placed in a powder X-ray diffractometer, and a diffraction pattern (XRD pattern; X-Ray Diffraction pattern) is obtained using Cu-Kα rays.

[0081] Furthermore, the orientation of particles may increase depending on the particle shape of the sample. If the orientation of the sample is high, the position of the peak may shift or the intensity ratio may change depending on how the sample is packed. Samples with such significantly high orientation should be measured using a glass capillary. Specifically, the sample is inserted into the capillary, and this capillary is placed on a rotating sample stage for measurement. This measurement method can mitigate the orientation. As for the glass capillary, it is preferable to use a Lindemann glass capillary with a diameter of 1 mm to 6 mmφ.

[0082] When performing powder X-ray diffraction measurements on niobium titanium oxide, which is the active material contained in the electrode, the measurement can be performed as follows, for example. First, to understand the crystalline state of the active material, the lithium ions must be completely removed from the active material. For example, if the active material is used in the negative electrode, the battery must be completely discharged. For instance, the battery can be discharged by repeatedly discharging it at a current of 0.1C in a 25°C environment until the rated cutoff voltage or battery voltage reaches 1.0V, ensuring that the discharge current is less than 1 / 100th of the rated capacity. Even in the discharged state, residual lithium ions may still be present.

[0083] Next, the battery is disassembled in a glove box filled with argon, the electrodes are removed, and washed with a suitable solvent. For example, ethyl methyl carbonate can be used as a suitable solvent. If the electrodes are not washed thoroughly, impurity phases such as lithium carbonate and lithium fluoride may be introduced due to the influence of lithium ions remaining in the electrodes. In that case, it is advisable to use an airtight container that allows the measurement to be performed in an inert gas atmosphere. The washed electrodes are cut to an area approximately the same as the area of ​​the holder of the powder X-ray diffractometer to prepare the measurement sample. This sample is then directly attached to the glass holder and the measurement is performed.

[0084] At this time, peaks derived from the current collector such as metal foil, conductive agent, and binder are measured and grasped in advance using XRD. Of course, if these can be grasped in advance, this operation can be omitted. When the peaks of the current collector and the active material overlap, it is desirable to peel off the active material-containing layer from the current collector for measurement. This is for separating the overlapping peaks when quantitatively measuring the peak intensity. The active material-containing layer may be physically peeled off, but it is easier to peel off by applying ultrasonic waves in a solvent. When ultrasonic treatment is performed to peel off the active material-containing layer from the current collector, the electrode body powder (including the active material, conductive agent, and binder) can be recovered by volatilizing the solvent. By filling the recovered electrode body powder into, for example, a capillary made of Lindemann glass and measuring, powder X-ray diffraction measurement of the active material can be performed. Note that the electrode body powder recovered by ultrasonic treatment can also be used for various analyses other than powder X-ray diffraction measurement.

[0085] As the apparatus for powder X-ray diffraction measurement, for example, SmartLab manufactured by Rigaku Corporation is used. The measurement conditions are as follows: X-ray source: Cu target Output: 45 kV 200 mA Soller slit: 5° for both incident and receiving light Step width (2θ): 0.02 deg Scan speed: 20 deg / min Semiconductor detector: D / teX Ultra 250 Measurement range: 5° ≤ 2θ ≤ 90° Sample plate holder: Flat glass sample plate holder (thickness 0.5 mm).

[0086] When using other apparatuses, perform measurement using a standard Si powder for powder X-ray diffraction so that measurement results equivalent to the above are obtained, and adjust the measurement conditions so that the peak intensity and peak top position match those of the above apparatus.

[0087] <ICP emission spectrometry> The composition of niobium titanium oxide can be analyzed, for example, using inductively coupled plasma (ICP) emission spectroscopy. In this case, the relative abundance (molar ratio) of each element depends on the sensitivity of the analytical instrument used. Therefore, the measured molar ratio may deviate from the actual molar ratio by the error of the measuring instrument. However, even if the value deviates within the error range of the analytical instrument, the performance of the niobium titanium oxide according to this embodiment can still be fully demonstrated.

[0088] To measure the composition of the active material incorporated into a battery using ICP emission spectroscopy, the following procedure is specifically followed.

[0089] First, following the procedure described in the section on powder X-ray diffraction measurement, the electrode containing the active material to be measured is removed from the secondary battery and cleaned. From the cleaned electrode, the portion containing the electrode active material, such as the active material-containing layer, is peeled off. For example, the portion containing the electrode active material can be peeled off by irradiating it with ultrasound. As a specific example, the electrode can be placed in ethyl methyl carbonate in a glass beaker and vibrated in an ultrasonic cleaner to peel off the active material-containing layer containing the electrode active material from the electrode current collector.

[0090] Next, the detached portion is briefly heated in the air (for example, at 500°C for about an hour) to burn off unwanted components such as binder and carbon. By dissolving this residue with acid, a liquid sample containing the active material can be prepared. Hydrochloric acid, nitric acid, sulfuric acid, or hydrogen fluoride can be used as the acid. By subjecting this liquid sample to ICP analysis, the average composition of the active material can be determined.

[0091] <Thermogravimetric analysis> As mentioned above, L * a * b *Isolate the niobium titanium oxide powder using the method described in the section on color space measurement. When measuring thermogravimetric analysis, the obtained powder is heated from room temperature to 500°C at a rate of 5°C / min, and the weight increase is measured. When measuring oxygen deficiency, measure the weight increase within the range of 200°C to 500°C.

[0092] <Measurement of particle size distribution of active material particles using laser diffraction scattering method> As mentioned above, L * a * b * Niobium titanium oxide powder is isolated using the method described in the section on color space measurement. The obtained powder is dispersed in N-methyl-2-pyrrolidone (NMP) solvent and subjected to sonication to obtain a dispersion solution for particle size distribution measurement. The particle size distribution of the constituent particles of this dispersion solution is measured using a laser diffraction distribution analyzer. For example, the Microtrac MT3100II manufactured by Microtrac-Bell Corporation can be used as the measuring device.

[0093] The sonication used to obtain the above-mentioned dispersion solvent is performed using a sample supply system attached to a laser diffraction distribution analyzer. The sonication is performed, for example, at an output of 40W for 300 seconds.

[0094] <Method for producing niobium titanium oxide> The niobium titanium oxide according to this embodiment can be produced, for example, by the synthesis method described below.

[0095] First, the starting materials are mixed. As starting materials containing niobium and titanium, oxides or salts containing Nb and Ti are prepared. For example, Nb2O5 particles and TiO2 particles can be used as starting materials. If the final niobium-titanium oxide contains additive element A, the desired additive element A is added to the Ti source used as a raw material.

[0096] Alternatively, if the goal is to create oxygen deficiencies or incorporate nitrogen atoms in the final niobium titanium oxide, the firing atmosphere during calcination after mixing the Nb and Ti sources should be changed from an atmospheric atmosphere. To create oxygen deficiencies, for example, lowering the oxygen partial pressure and / or increasing the calcination temperature are effective. To add nitrogen atoms, for example, lowering the oxygen partial pressure and calcining under a nitrogen atmosphere at atmospheric pressure is effective. Alternatively, the nitrogen partial pressure may be increased.

[0097] When producing niobium titanium oxide containing additive element A and having oxygen deficiency and / or nitrogen addition, the above-described operations may be carried out in appropriate combinations.

[0098] In solid-phase synthesis, first, a Ti source and a raw material powder containing additive element A are mixed and subjected to grinding and calcination. Grinding and calcination can be carried out, for example, by mixing and grinding in a ball mill for 0.5 to 12 hours, followed by calcination at a temperature of 600°C to 1000°C for 1 to 12 hours. As the raw material for additive element A, for example, an oxide containing at least one element selected from the group consisting of Fe, Cr, W, and Mo as element A can be used. Examples of such raw materials include Fe2O3, Cr2O3, MoO3, and WO3.

[0099] The amount of additive element A mixed can be appropriately changed depending on the desired surface color of the niobium titanium oxide, but for example, the amount should be such that the concentration of additive element A relative to the TiO2 that can be used as a raw material is 500 ppm to 10,000 ppm. When using raw materials with relatively low boiling points such as MoO3 and WO3, the amount of additive element A added may be increased to compensate for the effects of volatilization of these raw materials, so that the final concentration of additive element A in the niobium titanium oxide reaches the target concentration.

[0100] In this way, a Ti source containing additive element A can be obtained. Additive element A is, for example, dissolved in the Ti source.

[0101] It is preferable to make the average particle size of the Ti source powder containing added element A smaller than the average particle size of the Nb source powder. Here, the average particle size may be the median diameter (D50). By making the average particle size of the Ti source smaller than that of the Nb source, during solid-phase diffusion, the Ti source particles first diffuse into the particles acting as the Nb source, and a thermally stable TiNb2O7 phase is formed. Subsequently, added element A diffuses into the interior of the particles with a delay. In this way, it is possible to produce niobium titanium oxide having the TiNb2O7 phase in the interior (center of gravity) and element A unevenly distributed in the surface layer. Element A is not entirely absent in the center of gravity. For example, element A is present in the primary particles such that it has a concentration gradient increasing from the center of gravity towards the surface.

[0102] The ratio D2 / D1 of the average particle size D2 of the Nb-source powder to the average particle size D1 of the Ti-source powder containing additive element A should be, for example, within the range of 5 to 20. By making the average particle size D2 of the Nb-source powder larger than the average particle size D1 of the Ti-source powder, it is possible to make it more difficult for TiO2 to be formed in the particles. Since TiO2 is an insulator, it is desirable to have a small amount of TiO2 contained in the niobium titanium oxide that is formed. The average particle size D1 of the Ti-source powder containing additive element A should be, for example, within the range of 0.01 μm to 0.2 μm. The average particle size D2 of the Nb-source powder should be, for example, within the range of 0.05 μm to 1 μm.

[0103] The mixing and calcination of the Ti source powder and Nb source powder can be carried out, for example, by the method shown below. The Ti source powder may contain the aforementioned additive element A, or it may not contain additive element A. When using Ti source powder that does not contain additive element A, the calcination atmosphere should be a reducing atmosphere or a nitrogen atmosphere, as described later.

[0104] After mixing these raw materials, the resulting mixture is pulverized to obtain a mixture that is as uniform as possible. Next, the resulting mixture is subjected to calcination. Calcination is carried out at a temperature of 800°C to 1200°C for 1 to 10 hours. If oxygen deficiency is to be created in the niobium titanium oxide, the oxygen partial pressure of the calcination atmosphere may be set to, for example, 200 Pa or less, or to 20 Pa to 100 Pa. If nitrogen addition treatment is performed, for example, the oxygen partial pressure of the calcination atmosphere may be set to, for example, within the range of 0.1 Pa to 20 Pa, and the nitrogen partial pressure may be set to atmospheric pressure.

[0105] The niobium titanium oxide obtained after the main calcination may be subjected to appropriate grinding. However, in order to crystallize the amorphous phase that forms on the surface due to grinding, it is preferable to perform a crystallization treatment at a temperature of 600 to 900°C or lower after grinding. Through this process, NTO with the desired hue can be synthesized. The calcination time is preferably 18 hours or less, and it is even more preferable to slowly cool it without any calcination time after heating.

[0106] Furthermore, the niobium titanium oxide synthesized by the above method can be used as an active material incorporated into a secondary battery. In this case, lithium ions may be inserted by charging the battery after its assembly.

[0107] According to the first embodiment, niobium titanium oxide is provided. Niobium titanium oxide is measured according to the Japanese Industrial Standard JIS Z 8722:2009. * a * b * In the color space, the following equations (1) to (3) are satisfied.

[0108] 95.0 ≤ L * ≤100…(1) -1.0≦a * ≤1.0…(2) -1.0≦b * ≤6.0…(3)

[0109] For the reasons described above, the niobium titanium oxide according to this embodiment can realize a secondary battery with high capacity and excellent rate characteristics.

[0110] (Second Embodiment) According to the second embodiment, an active material comprising niobium titanium oxide according to the embodiment is provided. The niobium titanium oxide according to the first embodiment can function as an active material for a secondary battery. The active material may be a negative electrode active material or a positive electrode active material.

[0111] The active material may contain niobium titanium oxide according to the first embodiment in the various particle forms described above. The active material may contain only one type of niobium titanium oxide according to the first embodiment, or it may contain two or more types of niobium titanium oxide according to the first embodiment. The active material may contain one or more types of niobium titanium oxide according to the first embodiment and one or more types of other active materials.

[0112] In the second embodiment, the weight percentage of the niobium titanium oxide according to the first embodiment contained in the active material is preferably 50% by weight or more.

[0113] If the active material according to the second embodiment is the negative electrode active material, other examples of active materials include lithium titanate having a ramsdellite structure (e.g., Li 2+y Li3O7 (0≦y≦3), lithium titanate having a spinel structure (e.g., Li 4+x Ti5O 12 Examples include titanium dioxide (TiO2), anatase-type titanium dioxide, rutile-type titanium dioxide, niobium pentoxide (Nb2O5), hollandite-type titanium composite oxide, orthorhombic titanium composite oxide, and monoclinic niobium titanium oxide.

[0114] As an example of the above orthorhombic titanium-containing composite oxide, Li 2+a M1 2-b Ti 6-c M2 d O 14+σCompounds represented by the following formula are included. Here, M1 is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M2 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. Each subscript in the composition formula satisfies 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. Specific examples of the orthorhombic titanium-containing composite oxide include Li 2+a Na2Ti6O 14 (0≦a≦6) are included.

[0115] In addition, the primary particles of niobium titanate may have a carbon-containing layer on the particle surface of the primary particles. The carbon-containing layer may be attached to the surface of the primary particles or the surface of the secondary particles. Alternatively, the active material particles may include secondary particles formed by aggregation of primary particles having a carbon-containing layer attached to the surface. Since carbon exists between such primary particles, such secondary particles can exhibit excellent conductivity. An embodiment including such secondary particles is preferable because the active material-containing layer can exhibit lower resistance.

[0116] The particle diameter and specific surface area of the active material according to the embodiment will be described.

[0117] <Particle diameter> The average particle diameter of the active material particles, which are primary or secondary particles of niobium titanate, is not particularly limited. The average particle diameter of the active material particles is, for example, in the range of 0.1 μm to 50 μm. The average particle diameter can be changed according to the required battery characteristics. For example, in order to improve the rapid charge / discharge performance, it is preferable to set the average particle diameter to 1.0 μm or less. By doing so, the diffusion distance of lithium ions in the crystal can be reduced, and thus the rapid charge / discharge performance can be improved. The average particle diameter can be determined, for example, by the laser diffraction method.

[0118] <x <BET specific surface area> The BET (Brunauer, Emmett, Teller) specific surface area of ​​the active material according to this embodiment is not particularly limited. However, the BET specific surface area is 5 m². 2 / g or more, 200m 2 It is preferable that the amount be less than / g.

[0119] Specific surface area is 5m 2 If the specific surface area is 200 m² or more, it is possible to secure a contact area with the electrolyte, making it easier to obtain good discharge rate characteristics and shorten the charging time. On the other hand, if the specific surface area is 200 m² 2 If the concentration is less than / g, the reactivity with the electrolyte will not become too high, and the lifespan characteristics can be improved. In addition, the coating properties of the slurry containing the active material used in the manufacture of electrodes, as described later, can be improved.

[0120] Here, the specific surface area is measured by adsorbing molecules with a known adsorption area onto the surface of powder particles at the temperature of liquid nitrogen, and then determining the specific surface area of ​​the sample from the amount adsorbed. The most commonly used method is the BET method, which uses low-temperature, low-humidity physical adsorption of an inert gas. This is the most famous theory for calculating specific surface area, extending the Langmuir theory, which is a monolayer adsorption theory, to multilayer adsorption. The specific surface area obtained by this method is called the BET specific surface area.

[0121] According to the second embodiment, an active material is provided. This active material includes the niobium titanium oxide according to the first embodiment. Therefore, this active material can realize a secondary battery with high capacity and excellent rate characteristics.

[0122] (Third embodiment) According to the third embodiment, an electrode is provided.

[0123] The electrode according to the third embodiment includes the active material according to the second embodiment. This electrode may be a battery electrode containing the active material according to the second embodiment as a battery active material. The electrode as a battery electrode may be, for example, a negative electrode containing the active material according to the second embodiment as a negative electrode active material.

[0124] The electrode according to the third embodiment may include a current collector and an active material-containing layer. The active material-containing layer may be formed on one or both sides of the current collector. The active material-containing layer may include the active material according to the second embodiment and optionally a conductive agent and a binder. As described above, the active material according to the second embodiment may include one or more types of niobium titanium oxide according to the first embodiment and one or more types of other active materials.

[0125] Conductive agents are added to enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. One of these may be used as a conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surface of the active material particles may be coated with a carbon coating or an electronically conductive inorganic material coating.

[0126] A binder is added to fill the gaps between dispersed active materials and to bond the active materials to the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0127] The mixing 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, it is preferable to mix the active material (negative electrode active material), conductive agent, and binder in the following proportions: 68% to 96% by mass, 2% to 30% by mass, and 2% to 30% by mass, respectively. By setting 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 setting the amount of binder to 2% by mass or more, sufficient bonding 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 set the amount of conductive agent and binder to 30% by mass or less each in order to achieve high capacity.

[0128] The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and removed from the active material. For example, when the active material is used as the negative electrode active material, the current collector is preferably made of copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm to 20 μm. A current collector with such a thickness can balance electrode strength and weight reduction.

[0129] Furthermore, the current collector may include portions on its surface where the negative electrode active material-containing layer is not formed. These portions can function as negative electrode current collector tabs.

[0130] Electrodes can be manufactured, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of the active material-containing layer and the current collector. After that, this laminate is pressed. In this way, electrodes are manufactured.

[0131] Alternatively, electrodes may be manufactured by the following method: First, an active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Then, electrodes can be obtained by placing these pellets on a current collector.

[0132] The electrode according to the third embodiment contains the active material according to the second embodiment. Therefore, this electrode can realize a secondary battery with high capacity and excellent rate characteristics.

[0133] (Fourth Embodiment) According to the fourth embodiment, a secondary battery is provided that includes a negative electrode, a positive electrode, and an electrolyte. This secondary battery includes the electrode according to the third embodiment as the negative electrode. In other words, the secondary battery according to the fourth embodiment includes an electrode as the negative electrode that contains the active material according to the second embodiment as the active material for the battery.

[0134] The secondary battery according to the fourth embodiment may further include a separator disposed between the positive electrode and the negative electrode. The negative electrode, positive electrode, and separator can constitute an electrode group. The electrolyte can be held in the electrode group.

[0135] Furthermore, the secondary battery may further comprise an outer casing that houses the electrode group and the electrolyte.

[0136] Furthermore, the secondary battery may further include a negative terminal electrically connected to the negative electrode and a positive terminal electrically connected to the positive electrode.

[0137] The secondary battery in question may be, for example, a lithium secondary battery. Furthermore, the secondary battery may include a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0138] The following provides a detailed explanation of the negative electrode, positive electrode, electrolyte, separator, outer casing, negative electrode terminal, and positive electrode terminal.

[0139] 1) Negative electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode current collector and the negative electrode active material-containing layer may be a current collector and an active material-containing layer that can be included in the electrode according to the third embodiment, respectively. The negative electrode active material-containing layer contains the active material according to the second embodiment as the negative electrode active material.

[0140] Details of the negative electrode that overlap with the details described in the third embodiment are omitted.

[0141] The density of the negative electrode active material layer (excluding the current collector) is 1.8 g / cm³. 3 More than 2.8g / cm 3 The following is preferable. A negative electrode with a density of the negative electrode active material-containing layer within this range exhibits excellent energy density and electrolyte retention. The density of the negative electrode active material-containing layer is 2.1 g / cm³. 3 More than 2.6g / cm 3 The following is more preferable:

[0142] The negative electrode can be manufactured, for example, by the same method as the electrode according to the third embodiment.

[0143] 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 optionally include a positive electrode active material and a conductive agent and a binder.

[0144] For example, oxides or sulfides can be used as the positive electrode active material. The positive electrode may contain one compound alone or a combination of two or more compounds as the positive electrode active material. Examples of oxides and sulfides include compounds that can insert and remove Li or Li ions.

[0145] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, and lithium manganese composite oxide (e.g., Li x Mn2O4 or Li xMnO2; 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.

[0146] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; 0 < x ≤ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≤ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni It should be noted that there seems to be a small error in the original text where the tag number "0000197" is likely a typo in the provided text and should probably be "0000197" in the translation as well. Also, the last line "Ni" at the end of the translation seems to be incomplete in the original text's context. This translation is done based on the best understanding of the provided content with the given rules.y O4; where 0 < x ≤ 1 and 0 < y < 2), lithium manganese cobalt composite oxide (for example, Li x Mn y Co 1-y O2; where 0 < x ≤ 1 and 0 < y < 1), lithium iron phosphate (for example, Li x FePO4; where 0 < x ≤ 1), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; where 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1) are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0147] 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.

[0148] 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 the solid-state diffusion of lithium ions to proceed smoothly.

[0149] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. A positive electrode active material with a specific surface area of 0.1 m 2 / g or more can sufficiently secure the sites for lithium ion intercalation and deintercalation. A positive electrode active material with a specific surface area of 10 m 2 / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance. <00,00830>

[0150] A binder is added to fill the gaps between dispersed positive electrode active materials and to bond the positive electrode active materials to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0151] Conductive agents are added to enhance current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as a conductive agent, or two or more may be used in combination. Conductive agents may also be omitted.

[0152] In the positive electrode active material-containing layer, it is preferable that the positive electrode active material and the binder are blended in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0153] Sufficient electrode strength can be obtained by using a binder amount of 2% by mass or more. Furthermore, the binder can function as an insulator. Therefore, reducing the binder amount to 20% by mass or less reduces the amount of insulator contained in the electrode, thereby reducing internal resistance.

[0154] When a conductive agent is added, it is preferable that the positive electrode active material, binder, and conductive agent are blended in proportions of 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively.

[0155] The above-mentioned effects can be achieved by increasing the amount of conductive agent to 3% by mass or more. Furthermore, by reducing the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This lower proportion reduces the decomposition of the electrolyte under high-temperature storage conditions.

[0156] 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.

[0157] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and 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 in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0158] Furthermore, the positive electrode current collector may include portions on its surface where the positive electrode active material-containing layer is not formed. These portions can function as positive electrode current collector tabs.

[0159] The positive electrode can be manufactured, for example, using a positive electrode active material in the same manner as the electrode according to the third embodiment.

[0160] 3) Electrolyte As the electrolyte, for example, a liquid non-aqueous electrolyte or a gel-type non-aqueous electrolyte can be used. A liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0161] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2), as well as mixtures thereof. The electrolyte salt is preferably resistant to oxidation even at high potentials, with LiPF6 being the most preferred.

[0162] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); and γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as mixed solvents.

[0163] Gel-like non-aqueous electrolytes are prepared by compounding a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0164] Alternatively, in addition to liquid nonaqueous electrolytes and gel-type nonaqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions, polymer solid electrolytes, and inorganic solid electrolytes may be used as nonaqueous electrolytes.

[0165] Room temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as liquids at room temperature (15°C to 25°C). Room temperature molten salts include room temperature molten salts that exist as liquids on their own, room temperature molten salts that become liquid when mixed with an electrolyte salt, room temperature molten salts that become liquid when dissolved in an organic solvent, or mixtures thereof. Generally, the melting point of room temperature molten salts used in secondary batteries is 25°C or lower. Also, organic cations generally have a quaternary ammonium skeleton.

[0166] Polymeric solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and then solidifying it.

[0167] Inorganic solid electrolytes are solid materials that have lithium ion conductivity. Here, "having lithium ion conductivity" means that at 25°C, they have a conductivity of 1 × 10⁻⁶. -6 This refers to exhibiting a lithium ion conductivity of S / cm or higher. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are as follows.

[0168] As an oxide-based solid electrolyte, it has a NASICON (Sodium (Na) Super Ionic Conductor) type structure, and its general formula is Li 1+xIt is preferable to use a lithium phosphate solid electrolyte represented by Mα2(PO4)3. Mα in the above general formula 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.

[0169] Specific examples of the lithium phosphate solid electrolyte having a NASICON-type structure include Li 1+x Al x Ti 2-x (PO4)3 and the LATP compound where 0.1 ≦ x ≦ 0.5; Li 1+x Al y Mβ 2-y (PO4)3 and the compound 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; Li 1+x Al x Ge 2-x (PO4)3 and the compound where 0 ≦ x ≦ 2; and, Li 1+x Al<​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​); Garnet-type structure La 5+x A x La 3-x Mδ2O 12 represented by A is one or more selected from the group consisting of Ca, Sr, and Ba, Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ x ≦ 0.5; Li3Mδ 2-x L2O 12 represented by Mδ is one or more 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 represented by 0 ≦ x ≦ 0.5; Li 5+x La3Mδ 2-x Zr x O 12 represented by Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ x ≦ 2 LLZ compound (for example, Li7La3Zr2O 12 ); and having a perovskite-type structure La 2 / 3-x Li x represented by TiO3 and 0.3 ≦ x ≦ 0.7.

[0171] One or more of the above compounds can be used as a solid electrolyte. Two or more of the above solid electrolytes may be used

[0172] 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 non-woven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and can block the current

[0173] 5) Exterior member As the exterior member, for example, a container made of a laminate film or a metal container can be used

[0174] The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0175] As the laminate film, a multilayer film including a plurality of resin layers and a metal layer interposed between these resin layers is used. The resin layer contains, for example, polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer preferably consists of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be formed into the shape of an exterior member by sealing by heat fusion.

[0176] The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and still more preferably 0.2 mm or less.

[0177] 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. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, its content is preferably 100 mass ppm or less.

[0178] The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), square, cylindrical, coin-shaped, or button-shaped. The exterior member can be appropriately selected according to the battery dimensions and the use of the battery.

[0179] 6) Negative electrode terminal The negative electrode terminal has a potential range of 1.0 V or more and 3.0 V or less with respect to the redox potential of lithium (vs. Li / Li +The negative electrode terminal can be formed from an electrically stable and conductive material. Specifically, examples of materials for the negative electrode terminal include copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable to use aluminum or an aluminum alloy as the material for the negative electrode terminal. It is preferable that the negative electrode terminal be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0180] 7) Positive terminal The positive terminal has a potential range of 3.0V to 4.5V relative to the oxidation-reduction potential of lithium (vs.Li / Li + The positive electrode terminal can be formed from an electrically stable and conductive material. Examples of positive electrode terminal materials include aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the positive electrode terminal be formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0181] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0182] Figure 4 is a schematic cross-sectional view showing an example of a secondary battery according to the fourth embodiment. Figure 5 is an enlarged cross-sectional view of part A of the secondary battery shown in Figure 4.

[0183] The secondary battery 100 shown in Figures 4 and 5 comprises a bag-shaped outer casing member 2 shown in Figures 4 and 5, an electrode group 1 shown in Figure 4, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the bag-shaped outer casing member 2. The electrolyte (not shown) is held by the electrode group 1.

[0184] The bag-shaped outer packaging member 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0185] As shown in Figure 4, electrode group 1 is a flat, wound electrode group. As shown in Figure 5, 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.

[0186] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material containing layer 3b. In the portion of the negative electrode 3 located in the outermost shell of the wound electrode group 1, the negative electrode active material containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a, as shown in Figure 5. 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.

[0187] The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both sides thereof.

[0188] As shown in Figure 4, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer edge of the wound electrode group 1. The negative electrode terminal 6 is connected to the outermost part of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to the outermost part of the positive electrode current collector 5a. These negative electrode terminals 6 and positive electrode terminals 7 extend outward from the opening of the bag-shaped outer casing member 2. A thermoplastic resin layer is installed on the inner surface of the bag-shaped outer casing member 2, and the opening is closed by heat-sealing this layer.

[0189] The secondary battery according to the fourth embodiment is not limited to the secondary battery with the configuration shown in Figures 4 and 5, but may also be a battery with the configuration shown in Figures 6 and 7, for example.

[0190] Figure 6 is a schematic partially cutaway perspective view showing another example of a secondary battery according to the fourth embodiment. Figure 7 is an enlarged cross-sectional view of part B of the secondary battery shown in Figure 6.

[0191] The secondary battery 100 shown in Figures 6 and 7 comprises an electrode group 1 shown in Figures 6 and 7, an outer casing member 2 shown in Figure 6, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the outer casing member 2. The electrolyte is held within the electrode group 1.

[0192] The exterior member 2 is made of a laminated film including two resin layers and a metal layer interposed therebetween.

[0193] As shown in FIG. 7, the electrode group 1 is a laminated electrode group. The laminated electrode group 1 has a structure in which the negative electrode 3 and the positive electrode 5 are alternately laminated with the separator 4 interposed therebetween.

[0194] 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 surfaces 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 surfaces of the positive electrode current collector 5a.

[0195] The negative electrode current collector 3a of each negative electrode 3 includes a portion 3c on one side where the negative electrode active material-containing layer 3b is not supported on either surface. This portion 3c serves as a negative electrode current collecting tab. As shown in FIG. 7, the portion 3c serving as the negative electrode current collecting tab does not overlap with the positive electrode 5. The plurality of negative electrode current collecting tabs (portions 3c) are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is drawn out to the outside of the exterior member 2.

[0196] 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 either surface. This portion serves as a positive electrode current collecting tab. Similar to the negative electrode current collecting tab (portion 3c), the positive electrode current collecting tab does not overlap with the negative electrode 3. The positive electrode current collecting tab is located on the opposite side of the electrode group 1 with respect to the negative electrode current collecting tab (portion 3c). The positive electrode current collecting 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 of the negative electrode terminal 6 and is drawn out to the outside of the exterior member 2.

[0197] The secondary battery according to the fourth embodiment includes the active material according to the second embodiment as a negative electrode active material. Therefore, this secondary battery has a high capacity and exhibits excellent rate characteristics.

[0198] (Fifth embodiment) According to the fifth embodiment, a battery pack is provided. The battery pack according to the fifth embodiment comprises a plurality of secondary batteries according to the fourth embodiment.

[0199] In the battery pack according to the fifth embodiment, each individual cell may be arranged in series or parallel connections, or a combination of series and parallel connections may be used.

[0200] Next, an example of a battery pack according to the fifth embodiment will be described with reference to the drawings.

[0201] Figure 8 is a schematic perspective view showing an example of a battery pack according to the fifth embodiment. The battery pack 200 shown in Figure 8 comprises five single cells 100a to 100e, four busbars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five single cells 100a to 100e is a secondary battery according to the fourth embodiment.

[0202] The busbar 21 connects, for example, the negative terminal 6 of one cell 100a to the positive terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four busbars 21. That is, the battery pack 200 in Figure 8 is a battery pack with five cells connected in series.

[0203] As shown in Figure 8, of the five single cells 100a to 100e, the positive terminal 7 of the leftmost cell 100a is connected to the positive lead 22 for external connection. Also, of the five single cells 100a to 100e, the negative terminal 6 of the rightmost cell 100e is connected to the negative lead 23 for external connection.

[0204] The battery pack according to the fifth embodiment comprises the secondary battery according to the fourth embodiment. Therefore, this battery pack has high capacity and exhibits excellent rate characteristics.

[0205] (Sixth Embodiment) According to the sixth embodiment, a battery pack is provided. This battery pack comprises a battery pack according to the fifth embodiment. This battery pack may also comprise a single secondary battery according to the fourth embodiment instead of the battery pack according to the fifth embodiment.

[0206] The battery pack according to the sixth embodiment may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) may be used as the protection circuit for the battery pack.

[0207] Furthermore, the battery pack according to the sixth embodiment may also be further equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and / or for inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external terminals.

[0208] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0209] Figure 9 is an exploded perspective view schematically showing an example of a battery pack. Figure 10 is a block diagram showing an example of the electrical circuit of the battery pack shown in Figure 9.

[0210] The battery pack 300 shown in Figures 9 and 10 comprises a housing 31, a lid 32, a protective sheet 33, a battery pack 200, a printed circuit board 34, wiring 35, and an insulating plate (not shown).

[0211] The container 31 shown in Figure 9 is a bottomed rectangular container with a rectangular base. The container 31 is configured to accommodate a protective sheet 33, a battery pack 200, a printed circuit board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31, thereby housing the battery pack 200 and the other components. The container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc., although these are not shown in the figures.

[0212] The battery pack 200 comprises multiple individual cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0213] At least one of the multiple single cells 100 is a secondary battery according to the fourth embodiment. Each of the multiple single cells 100 is electrically connected in series as shown in Figure 10. The multiple single cells 100 may also be electrically connected in parallel, or they may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0214] The adhesive tape 24 fastens multiple single cells 100 together. Alternatively, heat-shrinkable tape may be used to secure the multiple single cells 100 instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both sides of the battery pack 200, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to bundle the multiple single cells 100 together.

[0215] One end of the positive lead 22 is connected to the battery pack 200. One end of the positive lead 22 is electrically connected to the positive terminal of one or more single cells 100. One end of the negative lead 23 is connected to the battery pack 200. One end of the negative lead 23 is electrically connected to the negative terminal of one or more single cells 100.

[0216] The printed circuit board 34 is installed along one of the shorter sides of the inner surface of the housing container 31. The printed circuit board 34 includes a positive terminal connector 342, a negative terminal connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energization, a positive side wiring (positive wiring) 348a, and a negative side wiring (negative wiring) 348b. One main surface of the printed circuit board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed circuit board 34 and the battery pack 200.

[0217] The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative connector 343.

[0218] The thermistor 345 is fixed to one main surface of the printed circuit board 34. The thermistor 345 detects the temperature of each of the single cells 100 and transmits the detection signal to the protection circuit 346.

[0219] The external power supply terminal 350 is fixed to the other main surface of the printed circuit board 34. The external power supply terminal 350 is electrically connected to equipment located outside the battery pack 300. The external power supply terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0220] The protection circuit 346 is fixed to the other main surface of the printed circuit board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive side wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative side wiring 348b. The protection circuit 346 is also electrically connected to the positive side connector 342 via wiring 342a. The protection circuit 346 is also electrically connected to the negative side connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via wiring 35.

[0221] The protective sheet 33 is positioned on both inner surfaces in the long-side direction of the housing container 31 and on the inner surface in the short-side direction facing the printed circuit board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0222] The protection circuit 346 controls the charging and discharging of multiple single cells 100. The protection circuit 346 also disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying power to external devices, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual single cell 100 or a battery pack 200.

[0223] An example of a detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of a single cell 100 is above a predetermined temperature. An example of a detection signal transmitted from an individual single cell 100 or a battery pack 200 is a signal indicating that overcharging, over-discharging, or overcurrent has been detected in a single cell 100. When detecting overcharging, etc., in an individual single cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode to be used as a reference electrode is inserted into each individual single cell 100.

[0224] Furthermore, the protection circuit 346 may be a circuit included in a device that uses the battery pack 300 as a power source (for example, an electronic device, an automobile, etc.).

[0225] Furthermore, as described above, the battery pack 300 is equipped with an external terminal 350 for power supply. Therefore, the battery pack 300 can output current from the battery pack 200 to an external device and input current from an external device to the battery pack 200 via the external terminal 350. In other words, when the battery pack 300 is used as a power source, current from the battery pack 200 is supplied to the external device through the external terminal 350. Also, when charging the battery pack 300, charging current from an external device is supplied to the battery pack 300 through the external terminal 350. When this battery pack 300 is used as an on-board battery, the regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0226] The battery pack 300 may have multiple battery packs 200. In this case, the multiple battery packs 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed circuit board 34 and wiring 35 may also be omitted. In this case, the positive lead 22 and the negative lead 23 may be used as the positive terminal 352 and negative terminal 353 of the external terminal 350 for energization, respectively.

[0227] Such battery packs are used in applications where excellent cycle performance is required, for example, when drawing high currents. Specifically, these battery packs are used as power supplies for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

[0228] The battery pack according to the sixth embodiment comprises a secondary battery according to the fourth embodiment or a battery pack according to the fifth embodiment. Therefore, this battery pack has high capacity and exhibits excellent rate characteristics.

[0229] (Seventh Embodiment) According to the seventh embodiment, a vehicle is provided, which comprises a battery pack according to the sixth embodiment.

[0230] In such a vehicle, the battery pack, for example, recovers regenerative energy from the vehicle's power. The vehicle may also include a mechanism (regenerator) that converts the vehicle's kinetic energy into regenerative energy.

[0231] Examples of vehicles include, for example, two-wheeled or four-wheeled hybrid electric vehicles, two-wheeled or four-wheeled electric vehicles, electric assist bicycles, and railway vehicles.

[0232] The mounting location of the battery pack in a vehicle is not particularly limited. For example, when a battery pack is installed in an automobile, it can be mounted in the engine compartment, at the rear of the vehicle, or under the seats.

[0233] A vehicle may be equipped with multiple battery packs. In this case, the batteries contained in each battery pack may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. For example, if each battery pack contains a battery pack, the battery packs may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. Alternatively, if each battery pack contains a single battery, the batteries may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections.

[0234] Next, an example of a vehicle according to the embodiment will be described with reference to the drawings.

[0235] Figure 11 is a schematic partial transparency drawing showing an example of a vehicle.

[0236] The vehicle 400 shown in Figure 11 includes a vehicle body 40 and a battery pack 300 according to the sixth embodiment. In the example shown in Figure 11, the vehicle 400 is a four-wheeled automobile.

[0237] This vehicle 400 may be equipped with multiple battery packs 300. In this case, the batteries contained in the battery pack 300 (for example, single cells or battery packs) may be connected in series, in parallel, or in a combination of series and parallel connections.

[0238] Figure 11 illustrates an example in which the battery pack 300 is mounted in the engine compartment located in front of the vehicle body 40. As described above, the battery pack 300 may also be mounted, for example, in the rear of the vehicle body 40 or under the seats. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy from the vehicle 400's power.

[0239] Next, an embodiment of the vehicle according to the embodiment will be described with reference to Figure 12.

[0240] Figure 12 is a schematic diagram illustrating an example of a control system for the electrical system in a vehicle. The vehicle 400 shown in Figure 12 is an electric vehicle.

[0241] The vehicle 400 shown in Figure 12 comprises a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a control device above the vehicle power supply 41, an external terminal (terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45.

[0242] Vehicle 400 has a vehicle power supply 41 mounted, for example, in the engine compartment, at the rear of the vehicle body, or under the seats. Note that in vehicle 400 shown in Figure 12, the mounting location of the vehicle power supply 41 is shown in a schematic manner.

[0243] The vehicle power supply 41 comprises a plurality (for example, three) of battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0244] Battery pack 300a comprises a battery pack 200a and a battery pack monitoring device 301a (e.g., VTM: Voltage Temperature Monitoring). Battery pack 300b comprises a battery pack 200b and a battery pack monitoring device 301b. Battery pack 300c comprises a battery pack 200c and a battery pack monitoring device 301c. Battery packs 300a to 300c are similar to the aforementioned battery pack 300, and battery packs 200a to 200c are similar to the aforementioned battery pack 200. Battery packs 200a to 200c are electrically connected in series. Battery packs 300a, 300b, and 300c can each be independently removed and replaced with another battery pack 300.

[0245] Each of the battery packs 200a to 200c comprises multiple single cells connected in series. At least one of the multiple single cells is a secondary battery according to the fourth embodiment. Each of the battery packs 200a to 200c is charged and discharged through a positive terminal 413 and a negative terminal 414.

[0246] The battery management device 411 communicates with the battery pack monitoring devices 301a to 301c and collects information such as voltage and temperature for each of the single cells 100 included in the battery packs 200a to 200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information related to the maintenance of the vehicle power supply 41.

[0247] The battery management device 411 and the battery pack monitoring devices 301a to 301c are connected via a communication bus 412. On the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management device 411 and one or more battery pack monitoring devices 301a to 301c). The communication bus 412 is a communication bus configured, for example, based on the CAN (Control Area Network) standard.

[0248] The battery pack monitoring devices 301a to 301c measure the voltage and temperature of each individual cell constituting the battery packs 200a to 200c based on commands communicated from the battery management device 411. However, temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all individual cells.

[0249] The vehicle power supply 41 may also have an electromagnetic contactor (for example, a switch device 415 shown in Figure 12) that switches the presence or absence of an electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that turns on when charging is performed on the battery packs 200a to 200c, and a main switch (not shown) that turns on when the output from the battery packs 200a to 200c is supplied to the 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 located near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

[0250] The inverter 44 converts the input DC voltage into a high voltage of three-phase alternating current (AC) for motor drive. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. The inverter 44 is controlled based on control signals from the battery management device 411 or the vehicle ECU 42 for controlling the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

[0251] The drive motor 45 rotates using power supplied from the inverter 44. The driving force generated by the rotation of the drive motor 45 is transmitted to the axle and drive wheels W, for example, via a differential gear unit.

[0252] Although not shown in the diagram, vehicle 400 is also equipped with a regenerative braking mechanism (regenerator). The regenerative braking mechanism rotates the drive motor 45 when vehicle 400 is braked, converting kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into a DC current. The converted DC current is input to the vehicle power supply 41.

[0253] One terminal of connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of connection line L1 is connected to the negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 within the battery management device 411 is provided on connection line L1 between the negative terminal 414 and the negative input terminal 417.

[0254] One terminal of connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41. The other terminal of connection line L2 is connected to the positive input terminal 418 of the inverter 44. A switch device 415 is provided between the positive terminal 413 and the positive input terminal 418 of connection line L2.

[0255] External terminal 43 is connected to battery management device 411. External terminal 43 can be connected to an external power supply, for example.

[0256] The vehicle ECU 42, in response to operational inputs from the driver and others, coordinates control of the vehicle power supply 41, switch device 415, inverter 44, etc., together with other management and control devices, including the battery management device 411. Through the coordinated control of the vehicle ECU 42, etc., the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, and the entire vehicle 400 is managed. Data related to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line.

[0257] The vehicle according to the seventh embodiment is equipped with the battery pack according to the sixth embodiment. Therefore, according to this embodiment, it is possible to provide a vehicle equipped with a battery pack that has high capacity and can exhibit excellent rate characteristics.

[0258] [Examples] Examples are described below, but the embodiments are not limited to those described below.

[0259] (Example 1) (Preparation of niobium titanium oxide) First, Fe-containing Ti source powder was synthesized by mixing Fe-containing Fe-containing Fe-containing Ti source powder with Ti-containing

[0260] Next, Nb2O5 particles with an average particle size of 0.4 μm, which is larger than that of the Fe-containing Ti source powder, were prepared. The obtained Fe-containing Ti source powder and the Nb-source Nb2O5 particles were thoroughly mixed, and the resulting mixture was calcined at 1000°C for 12 hours. The calcination was carried out in air. In this way, niobium titanium oxide powder was produced.

[0261] (Example 2) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except that Fe2O3 particles were mixed with TiO2 particles to achieve an Fe concentration of 600 ppm.

[0262] (Example 3) Except for the details described below, niobium titanium oxide powder was prepared in the same manner as in Example 1. As the Ti source, TiO2 particles that had not been treated with Fe element mixing were used. In addition, the oxygen partial pressure during firing was set to 85 Pa, and the firing temperature was set to 1000°C.

[0263] (Example 4) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except for the details described below. As the Ti source, TiO2 particles that had not been treated with Fe element mixing were used. In addition, the atmosphere during firing was set to atmospheric pressure nitrogen, and the oxygen partial pressure was set to 3.5 Pa. (Example 5) (Preparation of niobium titanium oxide) First, a Cr-containing Ti source powder was synthesized by mixing TiO2 particles, a Ti source, with Cr2O3 particles, a Cr source. In the synthesis, the TiO2 particles and Cr2O3 particles were first mixed so that the Cr concentration relative to the TiO2 particles was 1000 ppm, and the mixture was subjected to grinding using a ball mill. It is preferable to grind the mixture sufficiently so that the average particle size of the resulting Cr-containing Ti source powder is about 10 nm to 20 nm. The ground mixture was calcined at 900°C to obtain the Cr-containing Ti source powder. Next, Nb2O5 particles with an average particle size of 0.4 μm, which is larger than that of the Cr-containing Ti source powder, were prepared. The obtained Cr-containing Ti source powder and the Nb-source Nb2O5 particles were thoroughly mixed, and the resulting mixture was calcined at 1000°C for 12 hours. The calcination was carried out in air. In this way, niobium titanium oxide powder was produced. (Example 6) (Preparation of niobium titanium oxide) First, a W-containing Ti source powder was synthesized by mixing TiO2 particles, a Ti source, with WO3 particles, a W source. In the synthesis, the TiO2 particles and WO3 particles were first mixed so that the W concentration relative to the TiO2 particles was 1100 ppm, and the mixture was subjected to grinding using a ball mill. It is preferable to grind the mixture sufficiently so that the average particle size of the resulting W-containing Ti source powder is about 10 nm to 20 nm. The ground mixture was calcined at 900°C to obtain the W-containing Ti source powder. Next, Nb2O5 particles with an average particle size of 0.4 μm, which is larger than that of the W-containing Ti source powder, were prepared. The obtained W-containing Ti source powder and the Nb-source Nb2O5 particles were thoroughly mixed, and the resulting mixture was calcined at 1000°C for 12 hours. The calcination was carried out in air. In this way, niobium titanium oxide powder was produced. (Example 7) (Preparation of niobium titanium oxide) First, a Mo-containing Ti source powder was synthesized by mixing TiO2 particles, a Ti source, with MoO3 particles, a Mo source. In the synthesis, the TiO2 particles and MoO3 particles were first mixed so that the Mo concentration relative to the TiO2 particles was 1000 ppm, and the mixture was subjected to grinding using a ball mill. It is preferable to grind the mixture sufficiently so that the average particle size of the resulting Mo-containing Ti source powder is about 10 nm to 20 nm. The ground mixture was calcined at 900°C to obtain the Mo-containing Ti source powder. Next, Nb2O5 particles with an average particle size of 0.4 μm, which is larger than that of the Mo-containing Ti source powder, were prepared. The obtained Mo-containing Ti source powder and the Nb source Nb2O5 particles were thoroughly mixed, and the resulting mixture was calcined at 1000°C for 12 hours. The calcination was carried out in air. In this way, niobium titanium oxide powder was produced. (Example 8) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except for the details described below. Fe2O3 particles were mixed with TiO2 particles so that the Fe concentration was 560 ppm. In addition, the oxygen partial pressure during firing was set to 70 Pa, and the firing temperature was set to 900°C. (Example 9) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except for the details described below. Fe2O3 particles were mixed with TiO2 particles so that the Fe concentration was 620 ppm. In addition, the atmosphere during firing was a nitrogen atmosphere at atmospheric pressure, and the oxygen partial pressure was set to 3.5 Pa. (Example 10) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except that Fe2O3 particles were mixed with TiO2 particles to achieve an Fe concentration of 1950 ppm. (Example 11) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except that Fe2O3 particles were mixed with TiO2 particles to achieve an Fe concentration of 250 ppm.

[0264] (Comparative Example 1) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except that TiO2 particles that had not been treated with Fe element mixing were used as the Ti source.

[0265] (Comparative Example 2) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except for the details described below. Fe2O3 particles were mixed with TiO2 particles so that the Fe concentration was 12,000 ppm. In addition, the oxygen partial pressure during firing was set to 2 Pa, and the firing temperature was set to 1150°C.

[0266] (Comparative Example 3) Niobium titanium oxide powder was prepared in the same manner as in Example 1, except for the details described below. As the Ti source, TiO2 particles that had not been treated with Fe element mixing were used. In addition, the oxygen partial pressure during firing was set to 0.1 Pa, and the firing temperature was set to 1200°C.

[0267] (Comparative Example 4) Niobium titanium oxide powder was prepared in the same manner as in Example 4, except that the atmosphere during firing was at atmospheric pressure with an argon-to-nitrogen pressure ratio of 95:5, and the firing temperature was set to 700°C.

[0268] (Comparative Example 5) Niobium titanium oxide powder was prepared in the same manner as in Example 4, except that the atmosphere during firing was at atmospheric pressure with an argon-to-nitrogen pressure ratio of 67:33, and the firing temperature was set to 700°C.

[0269] <Various analyzes> The niobium titanium oxide powder prepared in each example was subjected to the method described in the first embodiment. * a* b * Color space measurements, powder X-ray diffraction and ICP analysis, TEM-EDS, thermogravimetric analysis, and moisture content measurement by Karl Fischer method were performed. These results are summarized in Table 1.

[0270] <Electrochemical Measurement> First, 100% by mass of niobium titanium oxide powder obtained in each example, 10% by mass of acetylene black as a conductive agent, 5% by mass of carbon nanofiber, and 10% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed with N-methylpyrrolidone (NMP) to obtain a slurry. This slurry was applied to one side of a current collector made of 12 μm thick aluminum foil, dried, and then pressed to obtain an electrode density of 2.4 g / cm³. 3 We fabricated the electrodes.

[0271] Next, an electrolyte was prepared by dissolving a LiPF6-supporting salt at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:2.

[0272] The obtained electrode was used as the working electrode, Li metal as the counter electrode and reference electrode, and a coin cell was fabricated using an electrolyte solution to evaluate its electrochemical properties.

[0273] In this embodiment, since lithium metal is used as the counter electrode in this measurement coin cell, the electrode potential of the embodiment and comparative example is nobler than that of the counter electrode and therefore functions as the positive electrode. For this reason, the definition of charge and discharge is reversed when the electrodes of the embodiment and comparative example are used as the negative electrode. To avoid confusion, in this embodiment, the direction in which lithium ions are inserted into the electrode is called charging, and the direction in which they are removed is called discharging. The active material of this embodiment functions as the negative electrode when combined with a known positive electrode material.

[0274] The fabricated electrochemical measurement cell was charged and discharged within a potential range of 1.0V to 3.0V relative to a metallic lithium electrode. The charge / discharge current was set to 0.2C (time discharge rate), and the 0.2C discharge capacity was confirmed at room temperature. The average discharge voltage was also measured. The 0.2C discharge capacity and average discharge voltage values ​​serve as indicators of energy density.

[0275] Furthermore, the fabricated electrochemical measurement cell was charged and discharged within a potential range of 1.0V to 3.0V relative to the metallic lithium electrode. To investigate the rapid discharge characteristics, after confirming the 0.2C discharge capacity, the cell was charged again with a charging current of 0.2C, and the 15C rapid discharge capacity was confirmed at room temperature. The discharge capacity retention rate (%) was then calculated by dividing the 15C discharge capacity by the 0.2C discharge capacity and multiplying by 100. The 15C / 0.2C discharge capacity retention rate (%) serves as an indicator for evaluating the rapid charge-discharge characteristics.

[0276] Furthermore, a life test was conducted on the cells of the examples and comparative examples under a 45°C environment, involving repeated 0.2C charge-discharge cycles within a potential range of 1.0V to 3.0V relative to the metallic lithium electrode. Under these conditions, 100 charge-discharge cycles were performed (one cycle consisted of charging and discharging), and the discharge capacity retention rate after 100 cycles was investigated. To confirm the discharge capacity retention rate after 100 cycles, charge-discharge was performed again at 0.2C (time discharge rate), and the cycle capacity retention rate (%) was calculated by dividing the discharge capacity after 100 cycles by the initial discharge capacity and multiplying by 100, with the initial discharge capacity set to 100%. The discharge capacity retention rate after 100 cycles serves as an indicator for evaluating the cycle life characteristics. The results are summarized in Table 2.

[0277] Table 3 shows the manufacturing conditions for niobium titanium oxide in each example.

[0278] [Table 1]

[0279] [Table 2]

[0280] [Table 3]

[0281] In Table 1, the "Crystal Phase" column shows the type of crystalline phase identified by powder X-ray diffraction. "Ratio AA / AM" indicates the ratio of the content of additive element A (AA) to the total amount of niobium and titanium atoms (AM). "Ratio AN / AM" indicates the ratio of the content of nitrogen atoms (AN) to the total amount of niobium and titanium atoms (AM). "Ratio AO / AM" indicates the ratio of the content of oxygen atoms (AO) to the total amount of niobium and titanium atoms (AM).

[0282] From the above results, the following can be concluded. As shown in Examples 1 to 11, L * a * b * Niobium titanium oxides that satisfy the following equations (1) to (3) in the color space all achieved high capacity and excellent rate characteristics. In addition, Examples 1-11 also showed high cycle capacity retention rates. 95.0 ≤ L * ≤100…(1) -1.0≦a * ≤1.0…(2) -1.0≦b * ≤6.0…(3)

[0283] hue b * Comparative Example 1, where the value was less than 0.0, was inferior to the example in both energy density and rate characteristics. This is thought to be because the niobium titanium oxide in Comparative Example 1 did not contain additive element A, resulting in a large amount of amorphous phase on the particle surface and a low hue b*.

[0284] The niobium titanium oxide in Comparative Example 2 contains an excess of Fe as an additive element, thus reducing its brightness L *The chromatic potential was low, and the hue b* was excessively high. Therefore, due to the narrow band gap, the rate characteristics were relatively good. On the other hand, the capacitance was poor due to the high electrode potential (negative electrode potential).

[0285] The niobium titanium oxide in Comparative Example 3 contained an excess amount of oxygen deficiency. As a result, the brightness L * In addition to being low, the hue b* was also excessively low. As a result, the capacity, rate characteristics, and cycle life characteristics were all inferior compared to the examples.

[0286] The niobium titanium oxide in Comparative Example 4 contained many nitrogen atoms. Therefore, the brightness L * In addition to having a low hue, the hue b* was excessively high. As a result of synthesis under an excess nitrogen atmosphere, the niobium titanium oxide in Comparative Example 4 further contained a TiN phase as a crystalline phase. Batteries containing a TiN phase in addition to Nb2TiO7 as a crystalline phase were inferior in terms of capacity, rate characteristics, and cycle life characteristics. As is clear from Table 3, etc., the niobium titanium oxide in Comparative Example 5, which was produced under an even more excessive nitrogen atmosphere compared to Comparative Example 4, had a very high hue b*. Also, like Comparative Example 4, it contained a TiN phase. Therefore, Comparative Example 5 was inferior in terms of capacity, rate characteristics, and cycle life characteristics.

[0287] In Examples 1, 5, 7, and 10, the primary particles had a concentration gradient for added element A that increased from the center of gravity of the primary particle towards the surface. In Examples 3, 4, and 8, the amount of oxygen deficiency due to TG was in the range of 100 ppm to 10,000 ppm, and the ratio AO / AM at the surface of the primary particles satisfied 2 ≤ AO / AM ≤ 2.3. Therefore, in Examples 3, 4, and 8, it can be said that oxygen deficiency exists more at the surface than at the center of gravity of the niobium titanium oxide particles.

[0288] According to at least one embodiment and example described above, niobium titanium oxide is provided. Niobium titanium oxide is measured according to the Japanese Industrial Standard JIS Z 8722:2009. * a* b * In the color space, the following equations (1) to (3) are satisfied.

[0289] 95.0 ≤ L * ≤100…(1) -1.0≦a * ≤1.0…(2) -1.0≦b * ≤6.0…(3)

[0290] The above-mentioned niobium titanium oxide has a low amorphous phase content per unit volume and a moderately narrow band gap, making it possible to realize a secondary battery with high capacity and excellent rate characteristics.

[0291] The invention according to the embodiment is described below. [1] L measured according to Japanese Industrial Standard JIS Z 8722:2009 * a * b * In color space, niobium titanium oxide that satisfies the following equations (1) to (3): 95.0 ≤ L * ≤100.0…(1) -1.0≦a * ≤1.0…(2) -1.0≦b * ≤6.0…(3) [2] The primary particles consist of the aforementioned niobium titanium oxide, The primary particles contain at least one element selected from the group consisting of Fe, Cr, W, and Mo as additive element A. The primary particle has a surface layer defined as a region with a depth of 20 nm from the surface of the primary particle, and a center of gravity located inside the surface layer. The primary particles have a concentration gradient with respect to the additive element A that increases from the center of gravity toward the surface layer [1], niobium titanium oxide as described above. [3] In the aforementioned surface layer, the ratio AA / AM of the content AA of the additive element A to the total amount AM of niobium atoms and titanium atoms satisfies 0.02 ≤ AA / AM ≤ 0.10. In the centroid, the ratio AA / AM of the content AA of the additive element A to the total amount AM of niobium atoms and titanium atoms is 0.001 ≤ AA / AM ≤ 0.01, as described in [2]. [4] The niobium titanium oxide described above, wherein, in thermogravimetric analysis in air, the weight increase in the range of 200°C to 500°C is in the range of 100 ppm to 10,000 ppm, as described in any one of [1] to [3]. [5] The primary particles consist of the aforementioned niobium titanium oxide, The primary particles contain nitrogen atoms, The primary particle has a surface layer defined as a region with a depth of 20 nm from the surface of the primary particle, and a center of gravity located inside the surface layer. The primary particles have a concentration gradient with respect to nitrogen atoms that increases from the center of gravity toward the surface layer, according to any one of [1] to [4], the niobium titanium oxide described in [1] to [4]. [6] In the aforementioned surface layer, the ratio AN / AM, which is the nitrogen atom content AN to the total amount AM of niobium atoms and titanium atoms, satisfies 0.01 ≤ AN / AM ≤ 0.3. In the centroid, the ratio AN / AM of the nitrogen atom content AN to the total amount AM of niobium and titanium atoms is such that 0.0001 ≤ AN / AM ≤ 0.001, as described in [5]. [7] A niobium titanium oxide according to any one of [1] to [6], comprising the Nb2TiO7 phase as the main phase. [8] The niobium titanium oxide described in [2], wherein an amorphous phase containing niobium and titanium is present on the surface of the primary particles to a thickness in the range of 0 nm to 2 nm. [9] The niobium titanium oxide contains a monoclinic Nb2TiO7 phase. The aforementioned monoclinic Nb2TiO7 phase has the general formula Li x Ti 1-y M1 y Nb 2-z M2z O 7+δ A composite oxide represented by the general formula Li x Ti 1-y M3 y+z Nb 2-z O 7-δ At least one selected from the group consisting of composite oxides represented by , The aforementioned M1 is at least one selected from the group consisting of Zr, Si, and Sn, the aforementioned M2 is at least one selected from the group consisting of V, Ta, and Bi, and the aforementioned M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The niobium titanium oxide described in any one of [1] to [8], wherein x satisfies 0 ≤ x ≤ 5, y satisfies 0 ≤ y < 1, z satisfies 0 ≤ z < 2, and δ satisfies -0.3 ≤ δ ≤ 0.3.

[10] Niobium titanium oxide as described in any one of [1] to [9], wherein the amount of water adsorbed by the Karl Fischer method is 800 ppm or less.

[11] An active material containing niobium titanium oxide as described in any one of [1] to

[10] .

[12] Equipped with an active material-containing layer, The active material-containing layer is an electrode containing the active material described in

[11] .

[13] Positive electrode and, The negative electrode and, A secondary battery comprising an electrolyte, The negative electrode is a secondary battery having the electrode described in

[12] .

[14] A battery pack comprising the rechargeable battery described in

[13] .

[15] External terminals for power supply, The battery pack described in

[14] further includes a protection circuit.

[16] The battery pack according to

[14] or

[15] , comprising a plurality of the secondary batteries, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

[17] A vehicle equipped with a battery pack as described in any one of

[14] to

[16] .

[18] The vehicle according to

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

[0292] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0293] 1…Electrode group, 2…Outer material, 3…Negative electrode, 3a…Negative electrode current collector, 3b…Negative electrode active material containing layer, 3c…Negative electrode current collector part, 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…Housing container, 32…Lid, 33…Protective sheet, 34 ...printed circuit board, 35...wiring, 40...vehicle body, 41...vehicle power supply, 42...electric control device, 43...external terminal, 44...inverter, 45...drive motor, 50...primary particles, 100...secondary battery, 101...metal ions, 102...oxide ions, 103...skeletal structure, 104...voids, 105, 106...regions, 200...battery pack, 200a...battery pack, 200b...battery pack, 200c...battery pack, 300...battery pack, 300a...battery pack, 300b...battery pack, 300c...battery pack, 301a...battery pack monitoring device, 301b...battery pack monitoring device, 301c...battery pack monitoring device, 342...positive electrode connector, 343...negative electrode connector, 345...thermistor, 346...protection circuit, 342a...wiring, 343a...wiring, 350...for power supply External terminals, 352...positive terminal, 353...negative terminal, 348a...positive wiring, 348b...negative wiring, 400...vehicle, 411...battery management device, 412...communication bus, 413...positive terminal, 414...negative terminal, 415...switch device, 416...current detection unit, 417...negative input terminal, 418...positive input terminal, L1...connection line, L2...connection line, W...drive wheel.

Claims

1. L measured according to Japanese Industrial Standard JIS Z 8722:2009 ＊ a ＊ b ＊ In the color space, niobium titanium oxide that satisfies the following equations (1) to (3): 95.0≦L ＊ ≦100.0…(1) -1.0≦a ＊ ≦1.0…(2) -1.0≦b ＊ ≦6.0…(3)。

2. The primary particles consist of the aforementioned niobium titanium oxide, The primary particles contain at least one element selected from the group consisting of Fe, Cr, W, and Mo as additive element A. The primary particle has a surface layer defined as a region with a depth of 20 nm from the surface of the primary particle, and a center of gravity located inside the surface layer. The niobium titanium oxide according to claim 1, wherein the primary particles have a concentration gradient of the additive element A that increases from the center of gravity toward the surface.

3. In the aforementioned surface layer, the ratio AA / AM of the content of the additive element A to the total amount AM of niobium atoms and titanium atoms satisfies 0.02 ≤ AA / AM ≤ 0.

10. The niobium titanium oxide according to claim 2, wherein in the center of gravity, the ratio AA / AM of the content AA of the additive element A to the total amount AM of niobium atoms and titanium atoms satisfies 0.001 ≤ AA / AM ≤ 0.

01.

4. The niobium titanium oxide according to claim 1 or 2, wherein, in thermogravimetric analysis in air, the weight increase in the range of 200°C to 500°C is in the range of 100 ppm to 10,000 ppm.

5. The primary particles consist of the aforementioned niobium titanium oxide, The primary particles contain nitrogen atoms, The primary particle has a surface layer defined as a region with a depth of 20 nm from the surface of the primary particle, and a center of gravity located inside the surface layer. The niobium titanium oxide according to claim 1, wherein the primary particles have a concentration gradient with respect to nitrogen atoms that increases from the center of gravity toward the surface.

6. In the aforementioned surface layer, the ratio AN / AM of the nitrogen atom content AN to the total amount AM of niobium atoms and titanium atoms satisfies 0.01 ≤ AN / AM ≤ 0.

3. The niobium titanium oxide according to claim 5, wherein in the center of gravity, the ratio AN / AM of the nitrogen atom content AN to the total amount AM of niobium atoms and titanium atoms satisfies 0.0001 ≤ AN / AM ≤ 0.

001.

7. Nb 2 TiO 7 The niobium titanium oxide according to claim 1 or 2, comprising the phase as the main phase.

8. The niobium titanium oxide according to claim 2, wherein an amorphous phase containing niobium and titanium is present on the surface of the primary particles to a thickness in the range of 0 nm to 2 nm.

9. The niobium titanate oxide has a monoclinic Nb 2 TiO 7 phase and The monoclinic type Nb 2 TiO 7 The niobium titanium oxide containing the phase has the general formula Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ A composite oxide represented by the general formula Li x Ti 1-y M3 y+z Nb 2-z O 7-δ At least one selected from the group consisting of composite oxides represented by , The aforementioned M1 is at least one selected from the group consisting of Zr, Si, and Sn, the aforementioned M2 is at least one selected from the group consisting of V, Ta, and Bi, and the aforementioned M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The above x satisfies 0 ≤ x ≤ 5, the above y satisfies 0 ≤ y < 1, the above z satisfies 0 ≤ z < 2, and the above δ satisfies -0.3 ≤ δ ≤ 0.

3. The niobium titanium oxide according to claim 1 or 2.

10. The niobium titanium oxide according to claim 1 or 2, wherein the amount of water adsorbed, as analyzed by the Karl Fischer method, is 800 ppm or less.

11. An active material comprising niobium titanium oxide as described in claim 1 or 2.

12. Equipped with an active material-containing layer, The active material-containing layer is an electrode containing the active material described in claim 11.

13. Positive electrode and, The negative electrode and, A secondary battery comprising an electrolyte, The negative electrode is the electrode described in claim 12, a secondary battery.

14. A battery pack comprising the secondary battery described in claim 13.

15. External terminals for power supply, The battery pack according to claim 14, further comprising a protection circuit.

16. The battery pack according to claim 14, comprising a plurality of the secondary batteries, wherein the secondary batteries are electrically connected in series, parallel, or a combination of series and parallel.

17. A vehicle comprising the battery pack described in claim 14.

18. The vehicle according to claim 17, which includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

Images