Active materials, electrodes, secondary batteries, battery packs, and vehicles

Abstract

The embodiments of the present invention relate to active materials, electrodes, secondary batteries, battery packs, and vehicles. This invention provides an active material and electrodes to achieve a secondary battery with higher output performance and longer lifespan, and provides a secondary battery with higher output performance and longer lifespan, a battery pack, and a vehicle equipped with this battery pack. According to an embodiment, an active material is provided that comprises secondary particles, each secondary particle containing a plurality of primary particles having a niobium oxide component. Each secondary particle includes adjacent portions of the primary particles and necked portions formed by the primary particles adhering to each other. The total circumference L of the primary particles and the sum L of the circumferences of the primary particles after removing the necked portions are also included. cl is a criterion that satisfies 0.1 < (LL) The relationship is cl) / L≦0.6.

Description

Active materials, electrodes, secondary batteries, battery packs, and vehicles Embodiments of the present invention relate to an active material, an electrode, a secondary battery, a battery pack, and a vehicle. In recent years, research and development of high-energy-density batteries has been intensive, particularly for non-aqueous electrolyte secondary batteries such as lithium-ion batteries. These batteries, like non-aqueous electrolyte secondary batteries, are highly anticipated power sources for vehicles like hybrid electric vehicles and electric cars, as well as uninterruptible power supplies like mobile phone base stations. Therefore, in addition to high energy density, these batteries are also required to offer rapid charge and discharge capabilities, along with excellent long-term reliability and other features. For example, batteries capable of rapid charge and discharge are not only required to significantly shorten charging times but also to enhance the power performance of vehicles like hybrid electric vehicles or to effectively recover regenerative energy. To achieve rapid charging and discharging, electrons and lithium ions must move quickly between the positive and negative electrodes. However, batteries using carbon-based negative electrodes, after repeated rapid charging and discharging, can cause the lithium metal on the electrodes to form dendrites, which can cause internal short circuits and lead to overheating and fire. Therefore, batteries using metal composite oxides instead of carbon-based materials to manufacture negative electrodes have been developed. Among them, batteries using titanium oxide as the negative electrode can stably perform rapid charge and discharge and have a longer life than batteries using carbon-based negative electrodes. However, titanium oxide has a higher potential relative to metallic lithium than carbon-based materials, meaning it has a higher potential. Furthermore, titanium oxide has a lower capacitance per unit weight. Therefore, batteries using titanium oxide as a negative electrode suffer from low energy density. For example, the electrode potential of titanium oxide is about 1.5V (vs. Li / Li) based on the standard of metallic lithium. + ), which is higher than the potential of carbon-based negative electrodes (high potential). The potential of titanium oxide is due to the electrochemical insertion and extraction of lithium. 3+ With Ti 4+ The redox reaction between them is limited by electrochemical factors. + ) at such a high electrode potential, rapid charge and discharge of lithium ions can be stably performed. Therefore, it is difficult to lower the electrode potential to increase energy density. On the other hand, regarding the capacitance per unit weight, the theoretical capacitance of titanium dioxide (anatase structure) is about 165 mAh / g, while lithium 4Ti 5O 12The theoretical capacity of this spinel-type lithium-titanium composite oxide is approximately 180 mAh / g. Meanwhile, the theoretical capacity of typical graphite-based electrode materials is over 385 mAh / g. As mentioned above, the capacitance density of titanium oxide is significantly lower than that of carbon-based negative electrodes. This is because titanium oxide's crystal structure has fewer edges capable of absorbing lithium, and lithium tends to be more stable within the structure, thus reducing its actual capacitance. In view of the above situation, new electrode materials containing Ti and Nb are currently under review. Niobium titanium oxide has high charge and discharge capacity and is expected to have a high charge and discharge capacity. For example, the material labeled TiNb 2O The oxide of niobium titanium oxide has a high theoretical capacity of over 380 mAh / g. However, the electronic conductivity of niobium titanium oxide is low, so the output performance is not good. The present invention aims to provide an active material and an electrode to realize a secondary battery with higher output performance and longer life, and to provide a secondary battery with higher output performance and longer life, a battery pack, and a vehicle equipped with the battery pack. According to an embodiment, an active material is provided, comprising secondary particles, each comprising a plurality of primary particles containing niobium oxide. The secondary particles comprise adjacent portions where the primary particles are adjacent to each other, and constricted portions where the primary particles are bonded to each other. The total perimeter L of the primary particles, and the sum of the perimeters L of the primary particles excluding the constricted portions, are: cl , is to satisfy 0.1<(LL cl ) / L≦0.6. According to another embodiment, an electrode including the above-mentioned active material is provided. According to another embodiment, a battery is provided, comprising a positive electrode, a negative electrode containing a negative electrode active material, and an electrolyte. The negative electrode active material comprises secondary particles, wherein the secondary particles comprise a plurality of primary particles containing niobium oxide. The secondary particles comprise a first adjacent portion where the primary particles are adjacent to each other, and a second adjacent portion where the primary particles are in contact with each other across an interface. The total perimeter L of the primary particles, and the sum of the perimeters L of the primary particles excluding the second adjacent portion, are: cl , is to satisfy 0.1≦(LL cl ) / L≦0.6. According to another embodiment, a battery pack is provided, comprising the above-mentioned secondary battery. According to another embodiment, a vehicle is provided that is equipped with the battery pack. According to the active material having the above structure, a secondary battery, a battery pack, and a vehicle equipped with the battery pack can be provided that have higher output performance and longer life. Through hybrid power pulse power characterization (HPPC) experiments, the inventors discovered that the battery impedance of batteries using niobium titanium oxide is primarily due to overvoltage at the solid-liquid interface and lithium (Li) concentration polarization within the active material. These factors are significantly influenced by the particle size of the active material. Even when the particle size distribution of niobium titanium oxide particles is normal, large active material particles significantly increase the impedance. This is particularly true when the particle size distribution is wide, often containing coarse particles, which significantly increase the impedance. The following describes the embodiments with reference to the drawings. Common structures among the embodiments are denoted by the same reference numerals, and repeated descriptions are omitted. Furthermore, the figures are schematic diagrams used to illustrate the embodiments and aid understanding. Their shapes, dimensions, proportions, and other aspects may differ from those of the actual device. These factors can be appropriately modified by referring to the following description and conventional techniques. (First embodiment) The first embodiment provides an active material. The active material includes secondary particles, wherein the secondary particles include niobium oxide. The secondary particles include a plurality of primary particles. The secondary particles include adjacent portions where the primary particles are adjacent to each other and necked portions where the primary particles are bonded to each other. The total perimeter L of the primary particles and the sum of the perimeters L of the primary particles excluding the necked portions are cl , satisfying 0.1<(LL cl ) / L≦0.6. The constricted portion in the active material corresponds to a grain boundary between primary particles, where Li diffusion is higher than in the bulk. The inclusion of the constricted portion allows the active material to exhibit higher Li diffusion. Figure 1 schematically illustrates a cross-section of a secondary particle included in an example of an active material. The secondary particle 12 shown consists of multiple primary particles 11, some of which are bonded together to form a constriction 13. The presence of constriction 13 maintains lithium and electron conductivity between primary particles 11. Because primary particles 11 are active material particles containing niobium oxide, the electrode containing the active material expands and contracts during charge and discharge. This can cause constriction 13 to rupture, but the primary particles 11 that form constriction 13 are not independent of each other. The degree of necking caused by the primary particles 11 in the active material is called the necking ratio N, which represents the total perimeter L of the primary particles 11 and the sum of the perimeters L of the primary particles 11 excluding the necked portion 13. cl The relationship between the two (LL cl ) / L(that is, N=(LL cl ) / L). The details will be explained later. In short, it represents the relationship between the necking ratio N (LL cl ) / L is obtained by observing a range containing more than 100 primary particles 11. If the neck structure of the primary particle 11 in the secondary particle 12 in the active material satisfies 0.1<(LL cl ) / L≦0.6 (0.1<N≦0.6), it is not easy to damage the Li conductivity. Moreover, the electrode containing this active material has a relatively low overvoltage even when charged and discharged at a high speed. Ideal (LL cl ) / L range is 0.2 to 0.6, preferably 0.4 to 0.5. Previous attempts to increase electrode capacitance have included reducing particle size and increasing electrode density. However, increasing electrode density while maintaining a small particle size can lead to compaction of the primary particles due to expansion and contraction during charge and discharge. This compaction of the fine primary particles within the electrode can easily lead to the formation of isolated particles within the center of the secondary particles. The low lithium and electron conductivity between these isolated particles and the surrounding primary particles impairs input and output performance and substantially reduces energy density. Figure 2 illustrates an example. The secondary particle 12 shown contains multiple primary particles 11, but the primary particles 11 do not form a constriction. Furthermore, the center of the secondary particle 12 contains an isolated particle 14—a primary particle isolated from the other primary particles 11. This creates a gap between the isolated particle 14 and the surrounding primary particles 11, increasing the impedance between the isolated particle 14 and the primary particles 11. As an example of niobium-containing oxides, for example, niobium-titanium composite oxides can be cited. As an example of niobium-containing oxides, for example, Nb 2TiO 7. The niobium-containing oxide is not limited thereto, but ideally should have a space group C2 / m symmetry, and at least a portion thereof should have a crystal structure having the atomic coordinates described in the non-patent document M. Gasperin, Journal of Solid State Chemistry 53, pp. 144-147 (1984). Niobium oxides mainly exhibit a monoclinic crystal structure. For example, monoclinic Nb 2TiO 7 crystal structure, when lithium ions are inserted, the metal ions that constitute the crystal structure skeleton will be reduced to trivalent, thereby maintaining the electrical neutrality of the crystal. In the case of niobium titanium oxide, not only the Ti ions will be reduced from tetravalent to trivalent, but the Nb ions will also be reduced from pentavalent to trivalent. Therefore, the number of reduction valences per unit weight of active material is large. Therefore, even if more lithium ions are inserted, the electrical neutrality of the crystal can be maintained. Therefore, compared with compounds such as titanium oxide containing only tetravalent cations, the energy density is higher. In addition, niobium-containing oxide has a 1.5V (to Li / Li + ). Therefore, a battery capable of stable and repeated rapid charge and discharge can be realized by including an electrode containing niobium oxide as an active material. Niobium-containing oxides may be niobium titanium oxides. Niobium titanium oxides, for example, may contain Nb 2TiO 7. Nb 2Ti 2O 9. Nb 10 Ti 2O 29 、Nb 14 TiO 37 and Nb 24 TiO 62 At least one crystalline phase selected from the group consisting of. Niobium titanium oxide can replace at least a portion of Nb and / or Ti with another element to become a substituted niobium titanium oxide. Examples of substitution elements include Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, Al, etc. The substituted niobium titanium oxide can contain one substitution element or two or more substitution elements. The active material particles can contain one niobium titanium oxide or multiple niobium titanium oxides. Niobium titanium oxide is mainly composed of monoclinic niobium titanium oxide Nb 2TiO 7 is preferred. In this case, as described above, an electrode having excellent capacitance and speed performance can be obtained. As examples of monoclinic niobium titanium oxide, Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ A compound represented by . 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 ranges of individual symbols in the chemical formula are 0 ≤ x ≤ 5, 0 ≤ y < 1, 0 ≤ z < 2, and -0.3 ≤ δ ≤ 0.3. As other examples of monoclinic niobium titanium oxide, Ti 1-y M3 y+z Nb 2-z O 7-δ Here, M3 is at least one selected from the group consisting of Mg, Fe, Ni, Co, W, Ta, and Mo. The ranges of individual symbols in the chemical formula are 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. The active material may contain only particles containing niobium oxide, or may contain active materials other than particles containing niobium oxide. The content of niobium oxide particles in the active material is preferably in the range of 75% by weight to 100% by weight. The closer the content of niobium oxide particles in the active material is to 100% by weight, the more desirable it is. As for the active material other than niobium oxide (second active material), for example, lithium titanate having a manganite structure (e.g., Li 2+y Ti 3O 7, 0≦y≦3), lithium titanate with spinel structure (such as Li 4+x Ti 5O 12 , 0≦x≦3), monoclinic titanium dioxide (TiO 2(B)), anatase titanium dioxide, rutile titanium dioxide, philadelphite titanium composite oxide, orthorhombic titanium-containing composite oxide. As examples of the above-mentioned rectangular titanium-containing composite oxide, Li 2+a M I 2-b Ti 6-c M II d O 14+σ Here, M I At least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M II At least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The ranges of individual symbols in the chemical formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, -0.5≦σ≦0.5. Specific examples of rectangular titanium-containing composite oxides include Li 2+a Na 2Ti 6O 14 (0≦a≦6). The average particle size of the primary particles containing niobium oxide is preferably within the range of 0.5 μm to 3 μm, and more preferably within the range of 0.5 μm to 2 μm. By increasing the average particle size to 0.5 μm or more, the electrode density can be increased, thereby allowing the active material particles in the electrode to have better contact with each other, and the active material particles to have good contact with the conductive agent, thereby improving the life performance. In addition, the reaction between the particles containing niobium oxide and the electrolyte is suppressed, thereby improving the rapid charge and discharge performance. In addition, by reducing the average particle size to 3 μm or less, the Li ions in the solid can obtain a moderate diffusion distance, thereby improving the rapid charge and discharge performance. The method for measuring the average particle size will be explained later. The crystallite size of the niobium oxide-containing particles is, for example, within the range of 10 nm to 300 nm, preferably 50 nm to 200 nm, and even more preferably 80 nm to 120 nm. Within this crystallite size range, lithium ion conduction within the crystals is facilitated, improving charge and discharge efficiency and speed performance. <Production Method> The active material can be produced by the following method. First, the starting materials are mixed. As an example of a niobium-containing oxide, oxides or salts containing Li, Ti, and Nb are used as the starting materials for niobium-titanium oxide. Ideally, the starting salt is a carbonate or nitrate salt that decomposes at relatively low temperatures to produce the oxide. The particle size of these starting materials is preferably within the range of 0.1 μm to 10 μm, and more preferably within the range of 0.1 μm to 5 μm. Particles smaller than 0.1 μm are more likely to drift into the atmosphere during mixing, causing compositional variations. Particles larger than 10 μm may result in unreacted products. In addition to the above starting materials containing oxide constituent elements, a material containing at least S is further mixed in as a flux. Examples of materials containing S that can be used as a flux include sulfates such as sodium sulfate. In addition to the material containing S, a material containing P or a material containing K may also be used as a flux. When mixing the starting raw materials, they are mixed in molar ratios to achieve the target composition of the Nb and Ti sources. Flux materials are mixed in amounts such that the molar ratio of S, P, and K to Nb is less than 1. The mixed raw materials are temporarily calcined at a temperature between 500°C and 1000°C for 2 to 5 hours. The temporarily calcined powder is pulverized in a ball mill for 1 hour before the main calcination. The main calcination is carried out in two or more steps at a temperature between 1000°C and 1450°C, lasting a total of 10 to 40 hours. After the main firing, the powder is subjected to a pulverization step. In the pulverization step, it is first subjected to strong pulverization using a roller compactor or hammer mill. Then, it is pulverized continuously for 1 to 5 hours using a wet ball mill. At this time, the crystallinity of the product decreases, so the crystallite diameter becomes smaller. Next, it is subjected to a secondary heat treatment at a temperature equivalent to the temperature during the main firing. The secondary heat treatment lasts, for example, for 0.5 to 5 hours. Ideally, the secondary heat treatment is performed in an electric furnace and the temperature is pre-raised to the target temperature. It is also best to quickly cool the powder after the secondary heat treatment. This can suppress particle growth caused by the heating and cooling of the electric furnace. The ideal cooling conditions after the secondary heat treatment are to reduce the temperature of the fired powder from the firing temperature to below 100°C within 1 hour. As described above, after the pulverization step involving intensive pulverization, a secondary heat treatment, for example, at a temperature equivalent to the main calcination, can restore the crystallinity lost during pulverization, resulting in particles with a larger crystallite diameter. A production method comprising both an intensive pulverization step and a secondary heat treatment step can produce active material particles with high crystallinity and a small average primary particle size. Furthermore, by using a flux containing at least S, the necking ratio N within the above-mentioned range can be observed in the obtained active material. The material used for the flux also affects particle growth. If a substance containing sulfur, such as sulfate, is used as a flux, it is characterized by a low melting point and high volatility, so the flux effect is easily achieved even during low-temperature firing. On the other hand, it is difficult to form a stable crystalline phase similar to the parent phase, so even with a high concentration of sulfur flux, it is difficult to produce an impurity crystal phase. Therefore, the solubility of the solute is low, the effect of promoting particle growth is not significant, and the effect of adding the flux on the secondary particle size is also low. Therefore, it can be expected that the sulfur flux will play an effect of promoting particle necking. When using phosphorus (P) as a flux material, the material has a high melting point, like phosphates. Therefore, to achieve sufficient vapor pressure near the surface of the active material particles to function as a flux, sintering must be performed at a relatively high temperature. Regarding the solubility of the flux (active material), the presence of energetically stable titanium or niobium phosphates facilitates the dissolution of the negative electrode active material (flux). Therefore, high temperatures, where the P flux can fully dissolve, promote particle growth and increase primary particle size. On the other hand, high P flux concentrations can easily generate phosphates of these elements, which can become impurities. Excessive addition can reduce the purity of the active material. As for flux containing K, for example, KCl or KNO 3 This compound with a lower melting point can achieve the same effect as the above-mentioned S. Since the melting points of these substances tend to be lower than those of sulfates, the effect of flux can be expected even in a lower temperature environment. 2O-Nb 2O 5. The presence of a large number of stable phases in the crystal phase diagram allows for a higher solubility of the active material (melt). Therefore, K flux, like P flux, exhibits the function of promoting particle growth. Furthermore, like P flux, K-containing substances are prone to becoming impurities. Impurities such as potassium and phosphorus may form grain boundaries between niobium oxide-containing crystallites. These grain boundaries may contain niobium, as does the parent phase, in addition to the impurity element. Part of these grain boundaries forms a constriction between primary particles. Ideally, the concentration of impurity elements in grain boundaries should be at least 20% higher than that in the parent phase. In other words, impurities retained in grain boundaries enhance the purity of the parent phase, contributing to the enhanced performance of the active material. Furthermore, the niobium titanium oxide synthesized by the above method can be used to insert lithium ions by charging a battery. Alternatively, as described above, a lithium-containing compound such as lithium carbonate can be used as a starting material to synthesize a lithium-containing oxide. The following describes the necking ratio N (relational formula (LL) of the active material in the embodiment. cl ) / L) and other measurement methods. <Measurement of Necking Ratio N> Quantitative evaluation of necking between active materials can be performed by analyzing cross-sectional images of electrodes containing active materials using a scanning electron microscope (SEM). The cross-section of the electrode sample was cut out by Ar ion milling and observed using a SEM. Considering the balance between the number of particles to be measured and resolution, an SEM image magnification of approximately 5000x is ideal. To improve quantitative accuracy, the total number of particles measured should be at least 100. If it is difficult to observe 100 particles in a single SEM image, analyze the particles by combining multiple fields of view to observe a total of 100 or more particles. The detection method selected should clearly observe the periphery of the active material particles and clearly distinguish the active material being measured from other components through contrast. The acquired SEM image can be binarized using analysis software such as ImageJ. First, convert the SEM image to an 8-bit black-and-white image. Then, set a threshold to convert the image to a binary image displaying only brightness levels of 0 (black) and 255 (white). Ideally, the threshold should be set using methods such as discriminant analysis to maximize separation. With the active material particles classified as having a brightness of 255, the resulting binary image is eroded. This process shrinks each enclosed area with a brightness of 255 by only one pixel. This eliminates any connections or noise between adjacent particles, clearly defining the particle boundaries. The resulting image is then subjected to particle analysis to measure the total number of particles n and the total circumference L of the primary particles. Furthermore, assuming all particles are perfectly round, the average particle size D can be calculated as D = L / nπ. Next, the image just binarized is dilated. This dilates each closed area of ​​255 observed by only one pixel. Erode is then performed twice. This closing process fills the fine gaps between particles detected in the original binary image. The same particle analysis is then performed to measure the total number of particles and the sum of the perimeters of the primary particles, excluding the necked-down areas. cl . L clIt represents the total circumference of the primary particle after removing the necking part. This analysis method uses the characteristic that when the necking active material particles are charged and discharged, the volume change will cause the necking part to break. At the beginning, only simple gaps will be generated between adjacent particles. Unlike necking, this does not change before and after the dilate process. On the other hand, the gaps will be filled after the necking position is closed, so the necking cannot be included in the circumference measurement in the closed image. Therefore, LL cl Value (L minus L cl The value of ) represents the reduction of the perimeter by the closing process, which corresponds to the perimeter of the necking. Therefore, the ratio N of the necking area of ​​the particle can be expressed as N=(LL cl ) / L. Cross-sectional SEM measurements involve cutting a portion of the constriction surface along an arbitrary line and measuring that area. Even for the same constriction, the length can vary depending on the area cut. Therefore, in order to quantify the amount of particles using cross-sectional SEM image analysis based solely on information about the total area of ​​the constriction, it is necessary to analyze a sufficient number of particles (100 or more). Figures 3 to 5 show an example of a cross-sectional SEM image and a processed image. Figure 3 shows an example of an SEM image of an electrode cross section. Figure 4 is an image obtained by binarizing the SEM image of Figure 3 and then performing an erode process without performing a dilate process. Figure 5 is a processed image obtained by binarizing the SEM image of Figure 3 and then performing a dilate process and a second erode process (off-processing). In Figure 4, multiple boundaries 16 can be observed between the particles, but they cannot be observed in Figure 5 after the off-processing. As described above, the boundaries 16 that disappear due to the off-processing are equivalent to the necking portion in the active material before charge and discharge. The total length of the periphery 15 of the active material particle in Figure 4 includes the boundary 16 corresponding to the necking portion, so the total periphery L of the primary particle can be obtained by measuring this total length. The position corresponding to the necking portion in Figure 5 has been excluded from the periphery 15, so the total periphery L excluding the necking portion can be obtained by measuring the total length of the periphery 15 in Figure 5. cl . <Confirmation of the Crystal Structure and Crystallite Size of the Active Material> The crystal structure and crystallite size of the active material can be confirmed by, for example, a combination of powder X-ray diffraction measurement (X-ray Diffraction: XRD) and Rietveld analysis. The powder X-ray diffraction measurement method of the active material can be carried out, for example, as follows. First, the active material is crushed as needed to prepare a sample with an average particle size of about less than 5 μm. The average particle size can be determined by the laser diffraction method. The obtained sample is filled in a part of a holder, which is formed on a glass sample plate and has a depth of 0.2 mm. Next, other glass plates are pushed from the outside to flatten the surface of the filled sample. Note that the sample filling amount should be moderate to avoid cracks, gaps, bumps, etc. in the filled sample. Also, be careful to push the glass plate with sufficient pressure. Next, the glass plate filled with the sample is placed in a powder X-ray diffraction device, and an XRD pattern is obtained using Cu-Kα rays. Furthermore, when the sample has a high degree of orientation, different sample filling methods may cause the peak position to shift or change the peak intensity ratio. For samples with such a high degree of orientation, capillary measurements are used. Specifically, the sample is inserted into a capillary, which is then placed on a rotating sample stage for measurement. This measurement method can mitigate the orientation. Lindemann glass is used for the capillary. The active material used as an electrode material in a battery can be measured using the following method. First, the active material in the electrode material (for example, niobium titanium oxide) is brought to a state where lithium ions are completely excluded. For example, when using this active material in the negative electrode, the battery is fully discharged. This allows the crystalline state of the active material to be observed. Sometimes, lithium ions are still present even in the discharged state. Lithium ions remaining in the electrode can affect the powder X-ray diffraction measurement results, causing impurity crystalline phases such as lithium carbonate or lithium fluoride to be mixed in. The mixing of impurity crystalline phases can be prevented by, for example, setting the measurement atmosphere to an inert gas atmosphere or washing the electrode surface. Even if impurity crystalline phases are present, they can be ignored during analysis. Next, disassemble the battery in an argon-filled glove box and remove the electrodes. Clean the removed electrodes with an appropriate solvent, such as ethyl methyl carbonate. Cut the cleaned electrodes into pieces roughly the same size as the holder of the powder X-ray diffraction device, and use them as measurement samples. The cut sample (electrode) is directly attached to a glass holder for measurement. At this time, the peak position caused by the electrode substrate, such as metal foil, is measured in advance. Furthermore, the peaks of other components, such as the conductive agent or adhesive, are also measured in advance. When the substrate peak and the active material peak overlap, it is ideal to peel off the layer containing the active material (for example, the active material-containing layer explained later) from the substrate before measurement. This is because when quantitatively measuring the peak intensity, the overlapping peaks must be separated. For example, the active material layer can be peeled off by irradiating the electrode substrate with ultrasound in a solvent. The XRD pattern obtained in this case must be suitable for Rietveld analysis. To collect data for Rietveld analysis, the measurement time and / or X-ray intensity should be appropriately adjusted so that the step width is 1 / 3 to 1 / 5 of the minimum half-width of the diffraction peak, and the intensity count value at the peak position of the strongest reflection is 5,000 to 10,000. The resulting XRD pattern is analyzed using the Rietveld analysis method. Rietveld analysis calculates the diffraction pattern based on a pre-determined crystal structure model. By perfectly fitting the calculated values ​​to the measured values, parameters related to the crystal structure (lattice constants, atomic coordinates, occupancy, etc.) can be precisely analyzed. This allows the crystal structure characteristics of the synthesized oxide to be investigated. Furthermore, the occupancy of the constituent elements in each location can be examined. To determine the crystallite diameter (crystallite size), select the diffraction ray with the strongest diffraction intensity. For example, for monoclinic niobium titanium oxide, the peak at the (110) plane is measured. The crystallite size can be calculated from the half-width of the obtained peak. Here, the crystallite size is calculated using the Scherrer equation shown in the following mathematical formula 1. Here, K = 0.9, λ = 0.15406nm. e : Half width of the diffraction peak, β o : Corrected value of half-width (0.07˚). <Method for Confirming the Composition of the Active Material> The composition of the active material can be analyzed, for example, using inductively coupled plasma (ICP) emission spectroscopy. The molar ratio of each element in this analysis is related to 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 this numerical deviation is caused by the error range of the analytical instrument, the active material of the embodiments can still fully exert its efficacy. To measure the composition of the active material in a battery using ICP emission spectroscopy, the following procedure is used. First, following the procedures described in the powder X-ray diffraction section, remove the electrode containing the active material to be measured from the secondary battery and clean it. From the cleaned electrode, the portion containing the electrode active material, such as the active material-containing layer, is peeled away. For example, ultrasonic irradiation can be used to peel away the portion containing the electrode active material. Specifically, for example, by placing an electrode in a glass beaker filled with ethyl methyl carbonate and applying vibrations in an ultrasonic cleaner, the active material-containing layer can be peeled away from the electrode current collector. Next, the exfoliated portion is heated briefly in the atmosphere (for example, at 500°C for about an hour) to burn off unnecessary components, such as the binder and conductive agent (e.g., carbon material), described later. The residue is dissolved with an acid to create a liquid sample containing the active material. The acid used can be hydrochloric acid, nitric acid, sulfuric acid, or hydrogen fluoride. This liquid sample is then analyzed by ICP to reveal the composition of the active material. <Method for Confirming Impurity Elements> The concentration of impurity elements in the matrix phase containing niobium oxide and in the grain boundaries between microcrystals was measured as follows. Transmission electron microscopy (TEM) is used to observe the necking areas at the interfaces of the active material particles. Energy dispersive X-ray spectroscopy (EDX) allows the composition of the grain boundaries to be quantified and compared with that of the matrix. This allows the quantitative determination of the impurity elements located at the grain boundaries. The active material according to the first embodiment includes secondary particles containing niobium oxide. The secondary particles include a plurality of primary particles, and include adjacent portions where the primary particles are adjacent to each other and constricted portions where the primary particles are bonded to each other. The total perimeter L of the primary particles and the sum of the perimeters L of the primary particles excluding the constricted portions are: cl , satisfying 0.1<(LL cl ) / L≦0.6. This active material can provide a secondary battery with higher output performance and longer life. (Second embodiment) The second embodiment provides an electrode. The electrode according to the second embodiment includes the active material according to the first embodiment. This electrode can be a battery electrode, including the active material according to the first embodiment as the battery active material. The electrode used as a battery electrode can be, for example, a negative electrode, including the active material according to the first embodiment as the negative electrode active material. The electrode 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 an active material and optionally a conductive agent and a binder. The purpose of adding a conductive agent is to improve current collection performance and suppress the contact resistance between the active material and the current collector. Conductive agents include, for example, vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. One of these can be used as a conductive agent, or a combination of two or more can be used. Alternatively, a carbon coating or an electronically conductive inorganic material coating can be applied to the surface of the active material particles instead of a conductive agent. The purpose of the binder is to fill the gaps between the dispersed active materials and 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 CMC salts. A single binder can be used, or a combination of two or more can be used. The mixing ratio of the active material, the conductive agent, and the binder in the active material containing layer can be appropriately changed according to the purpose of the electrode. For example, when the electrode is used as the negative electrode of a secondary battery, the mixing ratio of the active material (negative electrode active material), the conductive agent, and the binder is preferably 68% by mass or more and 96% by mass or less, 2% by mass or more and 30% by mass or less, and 2% by mass or more and 30% by mass or less, respectively. By making the amount of the conductive agent more than 2% by mass, the current collection performance of the active material containing layer can be improved. Moreover, by making the amount of the binder more than 2% by mass, the active material containing layer and the current collector have sufficient adhesion, and excellent cycle performance can be expected. On the other hand, making the conductive agent and the binder less than 30% by mass, respectively, is better for high capacitance quantization. The material used for the current collector must maintain an electrochemically stable potential when 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 ideally made of copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably between 5 μm and 20 μm. This thickness provides a balance between electrode strength and lightweight design. Furthermore, the surface of the current collector may include a portion where the negative electrode active material-containing layer is not formed. This portion can function as a negative electrode current collector sheet. For example, electrodes can be manufactured using the following method. First, the active material, conductive agent, and binder are stirred in a solvent to prepare a paste. This paste is then applied to one or both sides of a current collector. Next, the applied paste is dried to form a laminate of the active material-containing layer and the current collector. This laminate is then pressed. As described above, the electrode is manufactured. Alternatively, the electrode can be manufactured by the following method. First, the active material, conductive agent, and binder are mixed to obtain a mixture. Next, the mixture is formed into pellets. Next, these pellets are placed on a current collector to obtain an electrode. The electrode according to the second embodiment includes the active material according to the first embodiment. Therefore, the electrode can provide a secondary battery with higher output performance and longer life. (Third embodiment) According to the third embodiment, a secondary battery is provided, comprising a positive electrode, a negative electrode comprising a negative electrode active material, and an electrolyte. The negative electrode active material comprises secondary particles, wherein the secondary particles comprise a plurality of primary particles comprising niobium oxide. The secondary particles comprise a first adjacent portion where the aforementioned primary particles are adjacent to each other, and a second adjacent portion where the aforementioned primary particles are in contact with each other across an interface. The total perimeter L of the primary particles, and the sum of the perimeters L of the primary particles excluding the second adjacent portion, are cl , satisfying 0.1<(LL cl ) / L≦0.6. This secondary battery may be a battery that includes the electrode of the second embodiment as a negative electrode. That is, the secondary battery related to the third embodiment may include an electrode as a negative electrode, and the electrode includes the active material related to the first embodiment as a battery active material. However, as described in the first embodiment, the necked portion of the active material will break due to the volume change caused by charging and discharging. In other words, the second adjacent portion is equivalent to the portion after the necking and breaking. The first adjacent portion is equivalent to the portion where the primary particles are adjacent to each other before the necking and breaking. The above relationship (LL cl ) / L represents the ratio of the second adjacent portion, which corresponds to the necking ratio N. (LL cl The measurement method of ) / L is as described above. The secondary battery may further include a separator disposed between the positive electrode and the negative electrode. The negative electrode, the positive electrode, and the separator may constitute an electrode group. The electrolyte may be retained in the electrode group. Furthermore, the secondary battery may further include an exterior member that houses the electrode group and the electrolyte. Furthermore, the secondary battery may further include a negative electrode terminal electrically connected to the negative electrode, and a positive electrode terminal electrically connected to the positive electrode. The secondary battery may be, for example, a lithium secondary battery. The secondary battery includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte. The negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal are described in detail below. 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 the current collector and active material-containing layer, respectively, included in the electrode of the second embodiment. The negative electrode active material-containing layer may include the active material of the first embodiment as the negative electrode active material. The details of the negative electrode partially overlap with those described in the second embodiment and are therefore omitted. The density of the negative electrode active material containing layer (excluding the current collector) is 1.8 g / cm 3 Above 2.8g / cm 3 The following is the best. When the density of the negative electrode active material containing layer is within this range, the negative electrode has excellent energy density and electrolyte retention. The density of the negative electrode active material containing layer is 2.1g / cm 3 Above 2.6g / cm 3 The following is better. The negative electrode can be produced, for example, by the same method as that of the electrode of the second embodiment. 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 contain a positive electrode active material and optionally a conductive agent and a binder. For example, oxides or sulfides can be used as positive electrode active materials. The positive electrode active material can contain a single compound or a combination of two or more compounds. Examples of oxides and sulfides include compounds that can insert or remove Li or Li ions. As for such compounds, for example, manganese dioxide (MnO 2) Iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (such as Li x Mn 2O 4 or Li x M n O 2,0<x≦1), lithium nickel composite oxide (such as Li x NiO 2,0<x≦1), lithium cobalt composite oxide (such as Li x CoO 2,0<x≦1), lithium nickel cobalt composite oxide (such as Li x Ni 1-y Co y O 2, 0<x≦1, 0<y<1), lithium manganese cobalt composite oxide (such as Li x Mn y Co 1-y O 2, 0<x≦1, 0<y<1), lithium manganese nickel composite oxide with spinel structure (such as Li x Mn 2-y Ni y O 4, 0<x≦1, 0<y<2), lithium phosphorus oxide with olivine structure (such as Li x FePO 4, 0<x≦1, Li x Fe 1-y Mn y PO 4, 0<x≦1, 0<y≦1, Li x CoPO 4,0<x≦1), ferrous sulfate (Fe 2(SO 4) 3) Vanadium oxides (such as V 2O 5) Lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O 2, 0<x≦1, 0<y<1, 0<z<1, y+z<1). Among the above compounds, the most suitable compounds for positive electrode active materials include lithium manganese composite oxides (such as Li x Mn 2O 4,0<x≦1), lithium nickel composite oxide (such as Li x NiO 2,0<x≦1), lithium cobalt composite oxide (such as Li x CoO 2,0<x≦1), lithium nickel cobalt composite oxide (such as Li x Ni 1-y Co y O 2, 0<x≦1, 0<y<1), lithium manganese nickel composite oxide with spinel structure (such as Li x Mn 2-y Ni y O 4, 0<x≦1, 0<y<2), lithium manganese cobalt composite oxide (such as Li x Mn y Co 1-y O 2, 0<x≦1, 0<y<1), lithium iron phosphate (such as Li x FePO 4,0<x≦1), lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O 2, 0<x≦1, 0<y<1, 0<z<1, y+z<1). If these compounds are used as positive electrode active materials, the positive electrode potential can be increased. When using room temperature molten salt as the battery electrolyte, the positive electrode active material contains lithium iron phosphate, Li x VPO 4F (0 ≤ x ≤ 1), lithium-manganese composite oxide, lithium-nickel composite oxide, lithium-nickel-cobalt composite oxide, or mixtures thereof are preferred. These compounds have low reactivity with room-temperature molten salts, thus improving cycle life. The details of room-temperature molten salts will be explained later. The primary particle size of the positive electrode active material is preferably 100 nm or larger and 1 μm or smaller. Positive electrode active materials with a primary particle size of 100 nm or larger are easier to handle in industrial production. Positive electrode active materials with a primary particle size of 1 μm or smaller facilitate the diffusion of lithium ions within the solid. The specific surface area of ​​the positive electrode active material is 0.1m 2 / g above 10m 2 / g or less is preferred. Specific surface area is 0.1m 2 / g or more of positive electrode active material, can fully ensure the storage and release sites of Li ions. 2 / g or less positive electrode active material is easier to handle in industrial production and can ensure good charge and discharge cycle performance. The purpose of the binder is to fill the gaps within the dispersed positive electrode active material and bond the positive electrode active material 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 CMC salts. One or more of these binders can be used, or a combination of two or more can be used. The purpose of adding a conductive agent is to improve current collection performance and reduce the 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 can be used alone, or a combination of two or more can be used. Furthermore, the conductive agent can be omitted. In the positive electrode active material-containing layer, the positive electrode active material and the binder are preferably mixed in a ratio of 80 mass % to 98 mass % and 2 mass % to 20 mass %, respectively. By keeping the binder content at 2% by mass or more, sufficient electrode strength can be achieved. Furthermore, the binder can function as an insulator. Therefore, by setting the binder content to 20% by mass or less, the amount of insulator contained in the electrode is reduced, thereby lowering internal resistance. When a conductive agent is added, the proportions of the positive electrode active material, binder, and conductive agent are preferably 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively. By keeping the conductive agent content at 3% by mass or more, the aforementioned effects are achieved. Furthermore, by keeping the conductive agent content at 15% by mass or less, the proportion of the conductive agent in contact with the electrolyte can be reduced. This low proportion reduces electrolyte decomposition even during high-temperature storage. The positive electrode current collector is preferably aluminum foil or aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si. The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less. Furthermore, the surface of the positive electrode current collector may include a portion where the positive electrode active material-containing layer is not formed. This portion can function as a positive electrode current collector sheet. The positive electrode can be fabricated, for example, using a positive electrode active material using the same method as the electrode of the second embodiment. 3) Electrolytes: For example, liquid non-aqueous electrolytes or gel non-aqueous electrolytes can be used. Liquid non-aqueous electrolytes are prepared by dissolving an electrolyte salt in an organic solvent. The ideal electrolyte salt concentration is between 0.5 mol / L and 2.5 mol / L. Examples of electrolyte salts include lithium perchlorate (LiClO 4) Lithium hexafluorophosphate (LiPF 6) Lithium tetrafluoroborate (LiBF 4) Lithium arsenic hexafluoride (LiAsF 6) Lithium trifluoromethanesulfonate (LiCF 3SO 3) Lithium bis(trifluoromethylsulfonyl)imide (LiN(CF 3SO 2) 2) Lithium salts, and mixtures thereof. Ideally, electrolyte salts are substances that are difficult to oxidize even at high potentials, such as LiPF 6 is ideal. Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2MeTHF), and dioxolane (DOX); chain 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 a mixture. The gel non-aqueous electrolyte is prepared by combining a liquid non-aqueous electrolyte with a polymer material. For example, the polymer material includes polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof. Alternatively, the non-aqueous electrolyte may include, in addition to liquid non-aqueous electrolytes and gel non-aqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions, polymer solid electrolytes, inorganic solid electrolytes, and the like. Room-temperature molten salts (ionic molten salts) are organic salts composed of organic cations and anions that can exist in a liquid state at room temperature (15°C to 25°C). Room-temperature molten salts include those that exist as liquids alone, those that are mixed with electrolyte salts to form liquids, those that are dissolved in organic solvents to form liquids, or mixtures thereof. Generally, room-temperature molten salts used in secondary batteries have a melting point below 25°C. Furthermore, the organic cations typically have a quaternary ammonium skeleton. Polymer solid electrolytes are prepared by dissolving electrolyte salts in polymer materials and solidifying them. Inorganic solid electrolytes are solid materials with lithium ion conductivity. Here, lithium ion conductivity means that the electrolyte has a conductivity of 1×10 -6 S / cm or higher. As for the inorganic solid electrolyte, for example, an oxide-based solid electrolyte or a sulfide-based solid electrolyte can be used. Specific examples of the inorganic solid electrolyte are as follows. As for oxide-based solid electrolytes, ideally, a NASICON (Sodium (Na) Super Ionic Conductor) type structure is used, with a general chemical formula of Li 1+x Mα 2(PO 4) 3. In the above general chemical formula, Mα is, for example, one or more selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The symbol x is within the range of 0 ≤ x ≤ 2. Specific examples of lithium phosphate solid electrolytes having a NASICON structure include Li 1+x Al x Ti 2-x (PO 4) 3 and 0.1≦x≦0.5, LATP compound, Li 1+x Al y Mβ 2-y (PO 4) 3 and Mβ is a compound selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, with 0≦x≦1 and 0≦y≦1, and Li 1+x Al x Ge 2-x (PO 4) 3 and 0≦x≦2, Li 1+x Al x Zr 2-x (PO 4) 3 and 0≦x≦2, Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 and Mγ is a compound selected from the group consisting of Ti and Ge, with 0 < x ≦ 2, 0 ≦ y < 3, and Li 1+2x Zr 1-x Ca x (PO 4) 3 and 0≦x<1. In addition to the above-mentioned lithium phosphate solid electrolyte, the oxide-based solid electrolyte can also be Li x PO y N z To represent an amorphous LIPON compound (for example, Li 2.9 PO 3.3 N 0.46 ), garnet-type structure with La 5+x A x La 3-x Mδ 2O 12 A is one or more selected from the group consisting of Ca, Sr, and Ba, and Mδ is one or more selected from the group consisting of Nb and Ta, and 0≦x≦0.5, and Li 3Mδ 2-x L 2O 12 and Mδ is one or more selected from the group consisting of Nb and Ta, L may contain Zr, and 0≦x≦0.5, and Li 7-3x Al x La 3Zr 3O 12 To represent the compound with 0≦x≦0.5, Li 5+x La 3Mδ 2-x Zr x O 12 and Mδ is an LLZ compound selected from the group consisting of Nb and Ta and 0≦x≦2 (for example, Li 7La 3Zr 2O 12 ), with a perovskite structure based on La 2 / 3-x Li x TiO 3 and 0.3≦x≦0.7. One or more of the above compounds may be used as the solid electrolyte, or two or more of the above solid electrolytes may be used. 4) Separator: The separator is formed from a porous film containing polyethylene (PE), polypropylene (PP), cellulose, polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From a safety perspective, porous films made of polyethylene or polypropylene are preferred. These porous films melt at a certain temperature, thus blocking the flow of electricity. 5) Exterior Components As exterior components, for example, a container made of a laminated film or a metal container can be used. The thickness of the laminated film is, for example, 0.5 mm or less, preferably 0.2 mm or less. The laminated film used is a multilayer film consisting of multiple resin layers with metal layers interposed between them. The resin layers can be made of polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). For lightweighting, the metal layer is preferably made of aluminum foil or aluminum alloy foil. The laminated film can be sealed by heat fusion and formed into the shape of the exterior component. The thickness of the metal container is, for example, 1 mm or less, preferably 0.5 mm or less, and more preferably 0.2 mm or less. The metal container can be made, for example, of 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, the content is preferably 100 ppm by mass or less. The shape of the outer casing is not particularly limited. For example, the outer casing may be flat (thin), square, cylindrical, coin-shaped, or button-shaped. The outer casing may be appropriately selected according to the size of the battery or the intended use of the battery. 6) Negative Terminal: The material forming the negative terminal can be electrochemically stable at the Li absorption and release potential of the negative electrode active material and have conductivity. Specifically, the negative terminal material can include copper, nickel, stainless steel, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum or an aluminum alloy is preferably used as the material for the negative terminal. To reduce contact resistance with the negative electrode current collector, the negative terminal is preferably made of the same material as the negative electrode current collector. 7) Positive terminal The material forming the positive terminal can be a material having a redox potential of 3V to 4.5V for lithium (vs. Li / Li +) is electrically stable and conductive. Examples of materials for the positive terminal 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. To reduce contact resistance with the positive electrode current collector, the positive terminal is preferably formed from the same material as the positive electrode current collector. Next, the secondary battery of this embodiment will be described in detail with reference to the drawings. FIG6 is a cross-sectional view schematically showing an example of a secondary battery. FIG7 is an enlarged cross-sectional view of portion A of the secondary battery shown in FIG6 . The secondary battery 100 shown in FIG6 and FIG7 comprises a bag-shaped outer casing 2 shown in FIG6 , an electrode group 1 shown in FIG6 and FIG7 , and an electrolyte not shown. The electrode group 1 and the electrolyte are housed in the bag-shaped outer casing 2. The electrolyte (not shown) is retained in the electrode group 1. The bag-shaped outer packaging member 2 is composed of a laminated film comprising two resin layers and a metal layer interposed between the resin layers. As shown in Figure 6 , the electrode assembly 1 is a flat, wound-type electrode assembly. As shown in Figure 7 , the flat, wound-type electrode assembly 1 comprises 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. The negative electrode 3 comprises a negative electrode current collector 3a and a negative electrode active material-containing layer 3b. As shown in Figure 7, the portion of the negative electrode 3 located at the outermost portion of the wound electrode assembly 1 has the negative electrode active material-containing layer 3b formed only on the inner surface of the negative electrode current collector 3a. The remaining portion of the negative electrode 3 has the negative electrode active material-containing layer 3b formed on both surfaces of the negative electrode current collector 3a. The positive electrode 5 comprises a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both surfaces of the current collector. As shown in Figure 6, a negative electrode terminal 6 and a positive electrode terminal 7 are located near the outer edges of the wound electrode assembly 1. The negative electrode terminal 6 is connected to the outermost portion of the negative electrode current collector 3a. Furthermore, the positive electrode terminal 7 is connected to the outermost portion of the positive electrode current collector 5a. These negative and positive terminals 6 and 7 extend outward from the opening of the bag-like outer packaging member 2. The inner surface of the bag-like outer packaging member 2 is provided with a thermoplastic resin layer, which is heat-sealed to seal the opening. The secondary battery of this embodiment is not limited to the structure shown in Figures 6 and 7. For example, a battery having the structure shown in Figures 8 and 9 may also be used. Figure 8 is a partially cutaway perspective view schematically showing another example of a secondary battery. Figure 9 is an enlarged cross-sectional view of section B of the secondary battery shown in Figure 8. The secondary battery 100 shown in Figures 8 and 9 comprises an electrode group 1 shown in Figures 8 and 9, an outer casing 2 shown in Figure 8, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the outer casing 2. The electrolyte is retained in the electrode group 1. The exterior member 2 is composed of a laminated film comprising two resin layers and a metal layer interposed between them. The electrode group 1, as shown in Figure 9, is a laminated type. The laminated type electrode group 1 has a separator 4 interposed between the negative electrode 3 and the positive electrode 5, creating an alternating laminate structure. The electrode group 1 includes a plurality of negative electrodes 3. Each of the negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. Furthermore, the electrode group 1 includes a plurality of positive electrodes 5. Each of the positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a. Each negative electrode 3's negative current collector 3a has a portion on one side, on either surface, that is not supported by the negative electrode active material layer 3b. This portion functions as a negative electrode current collector tab 3c. As shown in Figure 9, the negative electrode current collector tab 3c does not overlap with the positive electrode 5. Furthermore, the multiple negative electrode current collector tabs 3c are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is extended to the outside of the exterior member 2. Moreover, although not shown here, the positive electrode collector 5a of each positive electrode 5 has a portion on one side or any surface thereof that does not support the positive electrode active material containing layer 5b. This portion functions as a positive electrode collector sheet. The positive electrode collector sheet is the same as the negative electrode collector sheet 3c and does not overlap with the negative electrode 3. Moreover, the positive electrode collector sheet is located on the opposite side of the electrode group 1 relative to the negative electrode collector sheet 3c. The positive electrode collector sheet is electrically connected to the strip-shaped positive terminal 7. The front end of the strip-shaped positive terminal 7 is located on the opposite side of the negative terminal 6 and is pulled out to the outside of the outer casing 2. The secondary battery according to the third embodiment contains the active material according to the first embodiment. Therefore, the output performance of the secondary battery is higher and the life is longer. (Fourth Embodiment) The fourth embodiment provides an assembled battery. This assembled battery comprises a plurality of secondary batteries according to the third embodiment. In this assembled battery, the individual batteries can be electrically connected in series or in parallel, or in a combination of series and parallel connections. Next, an example of an assembled battery according to this embodiment will be described in detail with reference to the drawings. Figure 10 is a perspective view schematically illustrating an example of an assembled battery. The assembled battery 200 shown in Figure 10 includes five individual batteries 100a through 100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead 23. The five individual batteries 100a through 100e are each a secondary battery according to the third embodiment. For example, busbar 21 connects the negative terminal 6 of one individual battery cell 100a to the positive terminal 7 of the adjacent individual battery cell 100b. As described above, five individual batteries 100 are connected in series using four busbars 21. In other words, the assembled battery 200 in Figure 10 is a five-series assembled battery. For example, an assembled battery comprising multiple individual batteries electrically connected in parallel can be constructed by, for example, connecting multiple negative terminals with a busbar and multiple positive terminals with a busbar, thereby electrically connecting multiple individual batteries. The positive electrode terminal 7 of at least one of the five individual batteries 100a to 100e is electrically connected to a positive-side lead wire 22 for external connection. Furthermore, the negative electrode terminal 6 of at least one of the five individual batteries 100a to 100e is electrically connected to a negative-side lead wire 23 for external connection. The assembled battery according to the fourth embodiment includes the secondary battery according to the third embodiment. Consequently, the assembled battery has higher output performance and a longer life. (Fifth Embodiment) The fifth embodiment provides a battery pack. This battery pack includes the assembled battery according to the fourth embodiment. This battery pack may not include the assembled battery according to the fourth embodiment, but may include a single secondary battery according to the third embodiment. The battery pack may further include a protection circuit. This circuit controls the charge and discharge of the secondary battery. Alternatively, the circuitry within a device that uses the battery pack as a power source (e.g., an electronic device or automobile) may also serve as the battery pack's protection circuit. Furthermore, the battery pack may further include external terminals for power supply. The external terminals for power supply are used to output current from the secondary battery to the outside and / or input current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals for power supply. Furthermore, when charging the battery pack, the charging current (including regenerative power energy of the vehicle, etc.) is supplied to the battery pack through the external terminals for power supply. Next, an example of a battery pack according to this embodiment will be described in detail with reference to the drawings. Fig. 11 is an exploded perspective view schematically showing an example of a battery pack. Fig. 12 is a block diagram showing an example of an electrical circuit of the battery pack shown in Fig. 11. The battery pack 300 shown in FIG. 11 and FIG. 12 includes a storage container 31 , a cover 32 , a protective sheet 33 , assembled batteries 200 , a printed wiring board 34 , wiring 35 , and an insulating plate (not shown). The storage container 31 shown in Figure 11 is a square container with a rectangular bottom. The storage container 31 is configured to accommodate a protective sheet 33, assembled battery 200, printed wiring board 34, and wiring 35. The lid 32 is rectangular in shape. By covering the storage container 31, the lid 32 accommodates the assembled battery 200 and other components. Although not shown, the storage container 31 and lid 32 are provided with openings or connection terminals for connecting to external devices. The assembled battery 200 includes multiple individual batteries 100, a positive electrode lead 22, a negative electrode lead 23, and adhesive tape 24. At least one of the multiple individual batteries 100 is a secondary battery according to the third embodiment. Each of the multiple individual batteries 100 is electrically connected in series, as shown in FIG12 . The multiple individual batteries 100 can also be electrically connected in parallel, or a combination of series and parallel connections. Connecting multiple individual batteries 100 in parallel increases the battery capacity compared to connecting them in series. Adhesive tape 24 is used to secure the individual batteries 100. In addition to adhesive tape 24, heat shrink tape can also be used to secure the individual batteries 100. In this case, protective sheets 33 are placed on both sides of the assembled battery 200. After wrapping the heat shrink tape around them, the heat shrink tape is allowed to shrink, securing the individual batteries 100. One end of the positive electrode lead 22 is connected to the assembled battery 200. One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more individual batteries 100. One end of the negative electrode lead 23 is connected to the assembled battery 200. One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more individual batteries 100. The printed wiring board 34 is located along one of the short sides of the inner side of the storage container 31. It includes a positive-side connector 342, a negative-side connector 343, a thermistor 345, a protective circuit 346, wiring 342a and 343a, external terminals 350 for current flow, a positive-side wiring (positive wiring) 348a, and a negative-side wiring (negative wiring) 348b. One main surface of the printed wiring board 34 faces the assembled battery 200. An insulating plate (not shown) is interposed between the printed wiring board 34 and the assembled battery 200. The positive electrode side connector 342 is electrically connected to the other end 22 a of the positive electrode side lead 22 . The negative electrode side connector 343 is electrically connected to the other end 23 a of the negative electrode side lead 23 . The thermistor 345 is fixed to one main surface of the printed wiring board 34. The thermistor 345 detects the temperature of each battery cell 100 and sends the detection signal to the protection circuit 346. The external terminals 350 for power supply are fixed to the other main surface of the printed wiring board 34. The external terminals 350 for power supply are electrically connected to devices outside the battery pack 300. The external terminals 350 for power supply include a positive terminal 352 and a negative terminal 353. The protection circuit 346 is fixed to the other main surface of the printed wiring board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative wiring 348b. Furthermore, the protection circuit 346 is electrically connected to the positive connector 342 via the wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via the wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the individual batteries 100 via the wiring 35. The protective sheet 33 is disposed on both inner side surfaces in the longitudinal direction of the storage container 31 and on the inner side surface in the transverse direction facing the printed wiring board 34 across the assembled battery 200. The protective sheet 33 is made of, for example, resin or rubber. The protection circuit 346 controls the charging and discharging of the plurality of individual batteries 100. Furthermore, based on the detection signal sent by the thermistor 345 or the detection signal sent by each individual battery 100 or the assembled battery 200, the protection circuit 346 blocks the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352 and negative terminal 353) for powering external devices. For example, the detection signal sent by thermistor 345 can be a signal indicating that the temperature of an individual battery cell 100 has reached a predetermined temperature or above. For example, the detection signal sent by each individual battery cell 100 or assembled battery 200 can be a signal indicating that the individual battery cell 100 is overcharged, overdischarged, or excessively high current. To detect overcharge of each individual battery cell 100, the battery voltage can be measured, or the positive electrode potential or negative electrode potential can be measured. In the latter case, a lithium electrode is inserted into each individual battery cell 100 as a reference electrode. Alternatively, the protection circuit 346 may be a circuit included in a device (e.g., an electronic device, an automobile, etc.) that uses the battery pack 300 as a power source. Furthermore, as described above, the battery pack 300 includes external terminals 350 for power supply. Thus, the battery pack 300 can output current from the assembled battery 200 to an external device via the external terminals 350 for power supply, and input current from the external device to the assembled battery 200. In other words, when the battery pack 300 is used as a power source, the current from the assembled battery 200 is supplied to the external device via the external terminals 350 for power supply. Furthermore, when the battery pack 300 is charged, the charging current from the external device is supplied to the battery pack 300 via the external terminals 350 for power supply. When the battery pack 300 is used as an in-vehicle battery, the charging current from the external device can utilize regenerative energy from the vehicle's power. Alternatively, the battery pack 300 may include multiple assembled batteries 200. In this case, the multiple assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. Furthermore, the printed wiring board 34 and wiring 35 may be omitted. In this case, the positive-side lead wire 22 and the negative-side lead wire 23 may serve as the positive-side terminal 352 and the negative-side terminal 353 of the external terminals 350 for current flow, respectively. This type of battery pack is used, for example, to deliver excellent cycle performance even when high currents are required. Specifically, it is used as a power source for electronic devices, as a stationary battery, and as an onboard battery for various vehicles. An example of an electronic device is a digital camera. This type of battery pack is particularly suitable for onboard use. The battery pack according to the fifth embodiment includes the secondary battery according to the third embodiment or the assembled battery according to the fourth embodiment. Therefore, the battery pack has higher output performance and longer life. (Sixth Embodiment) A sixth embodiment provides a vehicle equipped with the battery pack of the fifth embodiment. The battery pack in the vehicle, for example, recovers regenerative energy that is used to propel the vehicle. The vehicle may include a mechanism that converts the vehicle's kinetic energy into regenerative energy (regenerator). Examples of vehicles include two- to four-wheeled hybrid electric vehicles, two- to four-wheeled electric vehicles, power-assisted bicycles, and rail vehicles. The location where the battery pack is installed in the vehicle is not particularly limited. For example, in the case of an automobile, the battery pack can be installed in the engine compartment, behind the vehicle, or under the seat. 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, in parallel, or in a combination of series and parallel connections. For example, if each battery pack comprises an assembled battery, the assembled batteries may be electrically connected in series, in parallel, or in a combination of series and parallel connections. Alternatively, if each battery pack comprises a single battery, the batteries may be electrically connected in series, in parallel, or in a combination of series and parallel connections. Next, an example of a vehicle according to this embodiment will be described in detail with reference to the drawings. Fig. 13 is a partial perspective view schematically showing an example of a vehicle. The vehicle 400 shown in FIG13 includes a vehicle body 40 and a battery pack 300 according to the fifth embodiment. In the example shown in FIG13 , the vehicle 400 is a four-wheeled vehicle. This vehicle 400 can be equipped with multiple battery packs 300. In this case, the batteries included in the battery pack 300 (e.g., individual batteries or assembled batteries) can be connected in series, in parallel, or in a combination of series and parallel connections. In the example shown in Figure 13, the battery pack 300 is installed in the engine compartment in front of the vehicle body 40. As mentioned above, the battery pack 300 can also be installed, for example, behind the vehicle body 40 or under the seat. This battery pack 300 can be used as a power source for the vehicle 400. Furthermore, this battery pack 300 can recover regenerative energy from the vehicle 400's power. Next, an embodiment of a vehicle according to this embodiment will be described with reference to Fig. 14. Fig. 14 schematically shows an example of a control system for an electrical system in a vehicle. The vehicle 400 shown in Fig. 14 is an electric vehicle. The vehicle 400 shown in Figure 14 includes a vehicle body 40, a vehicle power supply 41, an upper control device of the vehicle power supply 41, namely a vehicle ECU (ECU: Electric Control Unit) 42, an external terminal (a terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45. The vehicle 400 is, for example, a vehicle power supply 41 mounted in an engine room, a rear portion of a vehicle body, or under a seat. The vehicle 400 shown in FIG. 14 schematically illustrates the mounting position of the vehicle power supply 41. The vehicle power supply 41 includes a plurality (eg, three) of battery packs 300 a , 300 b , and 300 c , a battery management unit (BMU) 411 , and a communication bus 412 . Battery pack 300a includes assembled batteries 200a and an assembled battery monitoring device 301a (e.g., VTM: Voltage Temperature Monitoring). Battery pack 300b includes assembled batteries 200b and an assembled battery monitoring device 301b. Battery pack 300c includes assembled batteries 200c and an assembled battery monitoring device 301c. Battery packs 300a-300c are similar to the aforementioned battery pack 300, and assembled batteries 200a-200c are similar to assembled battery 200. Assembled batteries 200a-200c are electrically connected in series. Battery packs 300a, 300b, and 300c can each be independently removed and replaced with another battery pack 300. Each assembled battery 200a-200c includes a plurality of individual batteries connected in series. At least one of the individual batteries is a secondary battery according to the third embodiment. Each assembled battery 200a-200c is charged and discharged via a positive electrode terminal 413 and a negative electrode terminal 414. The battery management device 411 communicates with the assembled battery monitoring devices 301a-301c to collect voltage and temperature information for each individual battery cell 100 included in the assembled batteries 200a-200c of the vehicle power supply 41. In this way, the battery management device 411 can collect information related to the maintenance of the vehicle power supply 41. The battery management device 411 and the assembled battery monitoring devices 301a-301c are connected via a communication bus 412. Communication bus 412 is a single set of communication lines shared by multiple nodes (the battery management device 411 and one or more assembled battery monitoring devices 301a-301c). Communication bus 412 is, for example, based on the CAN (Control Area Network) standard. The assembled battery monitoring devices 301a-301c measure the voltage and temperature of each individual cell comprising the assembled batteries 200a-200c based on communication commands from the battery management device 411. However, it is not necessary to measure the temperature of all individual cells; it is also possible to measure the temperature of only a few locations within a single assembled battery. The vehicle power supply 41 may include an electromagnetic contactor (e.g., the switch device 415 shown in FIG. 14 ) that switches the electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown), which is turned on when charging the assembled batteries 200 a - 200 c, and a main switch (not shown), which is turned on when the output of the assembled batteries 200 a - 200 c begins to be supplied to the load. The pre-charge switch and the main switch each include a relay circuit (not shown) that switches on or off based on a signal supplied by a coil located near the switching element. Electromagnetic contactors such as the switch device 415 are controlled based on a control signal from the battery management unit 411 or a control signal from the vehicle ECU 42 that controls the overall operation of the vehicle 400. The converter 44 converts the input DC voltage into a three-phase AC high voltage for motor driving. The three-phase output terminals of the converter 44 are connected to the three-phase input terminals of the drive motor 45. The converter 44 is controlled based on control signals from the battery management unit 411 or from the vehicle ECU 42, which controls the overall operation of the vehicle. Controlling the converter 44 adjusts its output voltage. The drive motor 45 is rotated by the electric power supplied from the inverter 44. The driving force generated by the rotation of the drive motor 45 is transmitted to the axle and the drive wheels W via, for example, a differential gear unit. Although not shown, vehicle 400 is equipped with a regenerative braking mechanism (regenerative generator). This mechanism rotates drive motor 45 when braking vehicle 400, converting kinetic energy into electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to inverter 44 and converted into direct current. The converted direct current is then input to vehicle power supply 41. Negative terminal 414 of vehicle power supply 41 is connected to one side of connection line L1. The other side of connection line L1 is connected to negative input terminal 417 of converter 44. Current detection unit (current detection circuit) 416 within battery management unit 411 is provided between negative terminal 414 and negative input terminal 417 in connection line L1. Positive terminal 413 of vehicle power supply 41 is connected to one side of connection line L2. The other side of connection line L2 is connected to positive input terminal 418 of converter 44. Switching device 415 is provided between positive terminal 413 and positive input terminal 418 in connection line L2. External terminal 43 is connected to battery management unit 411. External terminal 43 can be connected to an external power source, for example. In response to operational input from the driver, etc., vehicle ECU 42 coordinates and controls other management and control devices, including battery management unit 411, as well as vehicle power supply 41, switching device 415, inverter 44, and the like. Through coordinated control by vehicle ECU 42 and other components, the output power from vehicle power supply 41 and the charging of vehicle power supply 41 are controlled, thereby managing the entire vehicle 400. Data regarding the maintenance of vehicle power supply 41, such as the remaining capacity of vehicle power supply 41, is transmitted between battery management unit 411 and vehicle ECU 42 via a communication line. The vehicle of the sixth embodiment is equipped with the battery pack of the fifth embodiment. As a result, the vehicle has high performance and reliability. [Example] The following examples are described. (Example 1) <Synthesis of active material> First, a commercially available oxide agent Nb was prepared. 2O 5 and TiO 2. Weigh these powders so that the molar ratio of Nb / Ti is 1.0. Add Na 2SO 4. Make the molar ratio of Nb / S 1:0.1. Use a ball mill to mix these for 1 hour. Put the resulting mixture into an electric furnace and temporarily sinter it at 1000°C for 12 hours. Put the temporarily sintered powder into the ball mill again and continue mixing for 1 hour. Put the mixture into the electric furnace again and continue the first formal sintering at 1100°C for 5 hours. After cooling to room temperature, continue to crush it with a ball mill for 1 hour, and then continue the second formal sintering at 1100°C for 5 hours. Take out the powder, crush it vigorously with a hammer mill and a roller compactor, and then continue to crush it with a wet ball mill for 3 hours. Put the resulting powder into an electric furnace that has pre-heated the furnace temperature to 1100°C and continue to heat treat it again for 1 hour. Then quickly take out the powder from the electric furnace and put it into liquid nitrogen to cool. In this way, the active material powder of Example 1 is obtained. <Preparation of negative electrode> Acetylene black (AB) as a conductive agent is mixed with 10 parts by weight of the above active material powder. This mixture is dispersed in NMP (N-methyl-2-pyrrolidone), and then polyvinylidene fluoride (PVdF) as a binder is mixed with 10 parts by weight of the above active material powder to prepare an electrode paste. This paste is applied to a current collector composed of aluminum foil and dried to obtain an electrode coated with an active material-containing layer on both sides of the aluminum foil. The obtained electrode is compacted using a roller pressing device at a specified roller pressing pressure to obtain an electrode density of 2.3 g / cm 3 Next, cut the negative electrode so that the electrode area of ​​the active material containing layer becomes 100mm x 80mm. <Positive electrode production> Instead of using synthesized active material powder, LiNi 0.5 Co 0.2 Mn 0.3 O 2 was used as the positive electrode active material, and AB and PVdF were mixed in the same mixing ratio as the negative electrode to produce an electrode with an electrode density of 2.6 g / cm 3 Next, cut the positive electrode so that the electrode area of ​​the active material containing layer becomes 100mm x 80mm. <Battery Production> Next, the previously produced positive electrode, a separator, a negative electrode, and a separator are repeatedly stacked in this order to obtain a laminate. This laminate is heated and pressed at 90°C to obtain an electrode group with a thickness of 2.0 mm. The obtained electrode group is adhered to the positive and negative terminals. Next, the electrode group is placed in a package made of a laminate film and vacuum-dried at 80°C for 24 hours. The laminate film is composed of polypropylene layers formed on both sides of a 40μm thick aluminum foil, with an overall thickness of 0.1 mm. As mentioned above, a liquid non-aqueous electrolyte is injected into the laminated film package containing the electrode group. The liquid non-aqueous electrolyte used is a mixture of propylene carbonate (PC) and diethyl carbonate (DEC) in a volume ratio of 1:1, in which the electrolyte salt LiPF is dissolved at a concentration of 1M. 6. The package is then completely sealed by heat sealing. This results in a non-aqueous electrolyte battery with a width of 110 mm, a length of 85 mm, and a thickness of 2.2 mm. The fabricated nonaqueous electrolyte battery was charged and discharged within a depth of discharge (DOD) range of 25% to 75%. The charge and discharge current was set at 0.2C (time discharge rate), and the 0.2C discharge capacity was determined at room temperature. The 0.2C discharge capacity is an indicator of energy density. The capacity of the nonaqueous electrolyte battery fabricated in Example 1 was 2000 mAh. (Example 2) Except for changing Na 2SO 4 and a molar ratio of Nb / S of 1:0.5, an active material powder was synthesized in the same manner as in Example 1, and a negative electrode was prepared using the active material powder to produce a non-aqueous electrolyte battery. (Example 3) Except for changing Na 2SO 4 and a molar ratio of Nb / S of 1:1, an active material powder was synthesized in the same manner as in Example 1, and a negative electrode was prepared using the active material powder to produce a non-aqueous electrolyte battery. (Example 4) In addition to adding Na 2SO 4 and K 3PO 4. Active material powder was synthesized in the same manner as in Example 1 except that the molar ratio of Nb / P was set to 1:0.1. This active material powder was used to prepare a negative electrode, thereby producing a non-aqueous electrolyte battery. (Comparative Example 1) Except for not adding flux Na 2SO 4, an active material powder was synthesized by the same method as described in Example 1, and a negative electrode was prepared using this active material powder to produce a non-aqueous electrolyte battery. (Comparative Example 2) In addition to adding FePO 4 to replace Na 2SO 4. Active material powder was synthesized in the same manner as in Example 1 except that the molar ratio of Nb / P was set to 1:0.5. This active material powder was used to prepare a negative electrode, thereby producing a non-aqueous electrolyte battery. (Comparative Example 3) In addition to adding KCl to replace Na 2SO 4. Active material powder was synthesized in the same manner as in Example 1 except that the molar ratio of Nb / K was set to 1:0.5. This active material powder was used to prepare a negative electrode, thereby producing a non-aqueous electrolyte battery. (Comparative Example 4) An active material powder was synthesized in the same manner as in Example 1 except that the temperature of the secondary heat treatment was changed to 1400°C. A negative electrode was produced using the active material powder to fabricate a non-aqueous electrolyte battery. <Powder X-ray Diffraction Measurement> Diffraction patterns were obtained for the active material powders synthesized in each example using the method described in the first embodiment and analyzed using the Rietveld method. The resulting diffraction lines were then used to determine the crystallite size. Table 1 shows the crystallite size of the active material powders for each example. <Measurement of Neck Reduction Ratio N> For each active material powder synthesized in each example, the total perimeter L of the primary particles and the total perimeter L of the primary particles excluding the necking portion were measured using the image analysis tool ImageJ according to the method described in the first embodiment. cl The relationship between cl ) / L, and this relationship is the necking ratio N. Furthermore, assuming the cross-section of the active material particles is a perfect circle, the average particle diameter D (D = L / nπ) is calculated from the total number of particles observed, n, and the total circumference, L. The results are shown in Table 1. <Confirmation of Impurity Elements> The active material powder synthesized in each example was checked for the presence of impurities in the neck portion at the grain boundary between crystallites according to the method described in the first embodiment. <Battery performance evaluation> For the non-aqueous electrolyte batteries prepared in Examples 1-4 and Comparative Examples 1-4, discharge at 10C was used as a rapid discharge performance index to determine the discharge capacity corresponding to 0.2C capacitance. In addition, in order to confirm that stable charge and discharge can be performed, each non-aqueous electrolyte battery was repeatedly charged and discharged for 5000 cycles (charging and discharging is 1 cycle), and the discharge capacity retention rate after 5000 cycles was investigated. The conditions for repeated charge and discharge are that the depth of discharge (DOD) is in the range of 25%-75%, the current value during charging is 10C (time discharge rate), the current value during discharging is 10C (time discharge rate), and the temperature is 45°C. In order to confirm the discharge capacity retention rate after 5000 times, charge and discharge were performed again at 0.2C (time discharge rate), and the discharge capacity after 5000 times was divided by the first discharge capacity and then multiplied by 100. The capacity retention rate (%) can be calculated with the first discharge capacity as 100%. This capacitance retention rate is an indicator of longevity. The above results are summarized in Table 1. As shown in Table 1, the necking ratio N of the active materials synthesized in Examples 1-4 falls within a range greater than 0.1 and less than 0.6. In comparison, the ratio N of Comparative Example 1 is 0.1, while the ratio N of Comparative Examples 2-4 exceeds 0.6. Non-aqueous electrolyte batteries using the active materials of Examples 1-4 as negative electrodes exhibit superior rapid discharge performance (10C / 0.2C capacity ratio) and cycle life performance (discharge capacity retention after 5000 cycles) compared to batteries using the active materials of Comparative Examples 1-4. According to at least one embodiment described above, an active material is provided. The active material comprises secondary particles, each comprising a plurality of primary particles containing niobium oxide. The secondary particles comprise adjacent portions of the primary particles and constricted portions formed by the primary particles adhering to each other. The total perimeter L of the primary particles and the sum of the perimeters L of the primary particles excluding the constricted portions are: cl , satisfying 0.1<(LL cl ) / L≦0.6. This active material can provide an electrode that realizes a secondary battery with higher output performance and longer life, and can also provide a secondary battery with higher output performance and longer life, a battery pack, and a vehicle equipped with the battery pack. Several embodiments of the present invention have been described, but these embodiments are illustrative and are not intended to limit the scope of the invention. These novel embodiments may be implemented in various other forms and may be omitted, replaced, or modified without departing from the spirit of the invention. These embodiments and their variations are intended to be included within the scope and spirit of the invention and are included in the inventions set forth in the claims and their equivalents. The following notes relate to several embodiments of the present invention. (Technical Solution 1) An active material comprising secondary particles, each comprising a plurality of primary particles containing niobium oxide; the secondary particles comprising adjacent portions of the primary particles and a constricted portion formed by the primary particles adhering to each other; a total perimeter L of the primary particles, and a sum of the perimeters L of the primary particles excluding the constricted portion. cl , satisfying 0.1<(LL cl ) / L≦0.6. (Technical Solution 2) According to the above-mentioned Technical Solution 1, the crystallite diameter of the aforementioned niobium oxide is in the range of not less than 10 nm and not more than 300 nm, and the average particle diameter of the aforementioned primary particles is in the range of not less than 0.5 μm and not more than 3 μm; grain boundaries identical to those of the parent phase are formed between the crystallites, and the grain boundaries contain one or more elements selected from the group consisting of niobium, P, K, and Fe. (Technical Solution 3) According to the technical solution 2, the concentration of the element in the grain boundary is higher than the concentration in the matrix by 20% or more. (Technical Solution 4) An electrode comprising the active material according to any one of Technical Solutions 1 to 3. (Technical Solution 5) According to the technical solution 4, the electrode includes an active material-containing layer containing the active material. (Technical Solution 6) A secondary battery comprising a positive electrode; a negative electrode containing a negative electrode active material; and an electrolyte, wherein the negative electrode active material comprises secondary particles, the secondary particles comprising a plurality of primary particles containing niobium oxide; the secondary particles comprising a first adjacent portion in which the primary particles are adjacent to each other, and a second adjacent portion in which the primary particles are in contact with each other across an interface; the total perimeter L of the primary particles, and the sum of the perimeters L of the primary particles excluding the second adjacent portion. cl , is to satisfy 0.1<(LL cl ) / L≦0.6. (Technical Claim 7) A battery pack includes the secondary battery described in Technical Claim 6. (Technical Solution 8) According to the above-mentioned Technical Solution 7, it further includes external terminals for power supply and a protection circuit. (Technical Solution 9) According to the technical solution 7 or 8, a plurality of the aforementioned secondary batteries are provided, and the aforementioned secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel. (Technical Claim 10) A vehicle is equipped with the battery pack described in any one of the technical claims 7 to 9 above. (Technical Solution 11) According to the technical solution 10, a mechanism for converting the kinetic energy of the vehicle into regenerative energy is included. 1: Electrode group 2: Outer casing 3: Negative electrode 3a: Negative electrode current collector 3b: Negative electrode active material containing layer 3c: Negative electrode current collector sheet 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 11: Primary particle 12: Secondary particle 13: Neck portion 14: Isolated particle 15: Periphery 16: Boundary 21: Bus bar 22: Positive electrode side lead wire 23: Negative electrode side lead wire 24: Adhesive tape 31: Storage container 32: Lid 33: Protective sheet 34: Printed wiring board 35: Wiring 40: Vehicle body 41: Vehicle power supply 42: Electrical control device 43: External terminal 44: Inverter 45: Drive motor 100: Secondary battery 200: Assembled battery 200a: Assembled battery 200b: Assembled battery 200c: Assembled Assembled battery 300: Battery pack 300a: Battery pack 300b: Battery pack 300c: Battery pack 301a: Assembled battery monitoring device 301b: Assembled battery monitoring device 301c: Assembled battery monitoring device 342: Positive side connector 343: Negative side connector 345: Thermistor 346: Protection circuit 342a: Wiring 343a: Wiring 350: External terminal for power supply 352: Positive side terminal 353: Negative side terminal 348a: Positive side wiring 348b: Negative side wiring 400: Vehicle 411: Battery management device 412: Communication bus 413: Positive terminal 414: Negative terminal 415: Switching device 416: Current detection unit 417: Negative input terminal 418: Positive input terminal L1: Connection line L2: Connection line W: Drive wheel [Figure 1] is a schematic cross-sectional view of secondary particles included in an example of an active material according to an embodiment. [Figure 2] is a schematic cross-sectional view of an example of a secondary particle of a conventional active material. [Figure 3] is a scanning electron microscope image of a cross-section of an example of an electrode including an active material according to an embodiment. [Figure 4] is a processed image obtained by binarizing and eroding the electron microscope image shown in Figure 3. [Figure 5] is a processed image obtained by binarizing and closing the electron microscope image shown in Figure 3. [Figure 6] is a schematic cross-sectional view of an example of a secondary battery according to an embodiment. [Figure 7] is an enlarged cross-sectional view of section A of the secondary battery shown in Figure 6. [Figure 8] is a partially cutaway perspective view schematically illustrating another example of a secondary battery according to an embodiment. [Figure 9] is an enlarged cross-sectional view of section B of the secondary battery shown in Figure 8. [Figure 10] is a schematic perspective view of an example of an assembled battery according to an embodiment. FIG11 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. FIG12 is a block diagram schematically showing an example of an electrical circuit for the battery pack shown in FIG11. FIG13 is a partial perspective view schematically showing an example of a vehicle according to an embodiment. FIG14 is a diagram schematically showing an example of a control system for an electrical system in a vehicle according to an embodiment. 11: Primary particles 12: Secondary particles 13: Neck part

Claims

1. An active material comprising secondary particles, the secondary particles comprising a plurality of primary particles containing niobium oxide; the aforementioned secondary particles comprising adjacent portions of the aforementioned primary particles and necked portions formed by the aforementioned primary particles adhering to each other; the total perimeter L of the aforementioned primary particles and the sum of the perimeters Lcl of the aforementioned primary particles excluding the aforementioned necked portions satisfying the relationship 0.1 < (LLcl) / L ≤ 0.

6.

2. The active substance as described in claim 1, wherein, The aforementioned niobium oxide-containing microcrystals have a diameter of 10 nm to 300 nm, and the aforementioned primary particles have an average particle size of 0.5 μm to 3 μm; grain boundaries identical to the parent phase are formed between the microcrystals, and these grain boundaries contain one or more elements selected from the group consisting of niobium, P, K, and Fe.

3. The active substance as described in claim 2, wherein, The concentration of the aforementioned elements in the aforementioned grain boundaries is more than 20% higher than the concentration in the aforementioned parent phase.

4. An electrode comprising the active material described in any one of claims 1 to 3.

5. The electrode as described in claim 4, wherein, The aforementioned electrode includes an active material containing the aforementioned active material.

6. A secondary battery comprising a positive electrode; a negative electrode containing a negative electrode active material; and an electrolyte, wherein the negative electrode active material comprises secondary particles, the secondary particles comprising a plurality of primary particles containing niobium oxide; the secondary particles comprising a first adjacent portion of the primary particles being adjacent to each other, and a second adjacent portion of the primary particles being in contact with each other across an interface; the total perimeter L of the primary particles and the sum of the perimeters Lcl of the primary particles excluding the second adjacent portion satisfy the relationship 0.1 < (LLcl) / L ≤ 0.

6.

7. A battery pack having the secondary battery described in claim 6.

8. The battery pack as described in claim 7, wherein, It also includes external terminals for power supply and protection circuitry.

9. The battery pack as described in claim 7, wherein, It has multiple of the aforementioned secondary batteries, which are electrically connected by a combination of series, parallel, series and parallel connections.

10. A vehicle equipped with the battery pack described in claim 7.

11. The vehicle described in claim 10, wherein, It includes a mechanism for converting the kinetic energy of the aforementioned vehicle into regenerative energy.

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