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

Abstract

To provide: an active material that can exhibit high energy density and can realize a secondary battery with excellent storage performance at low cost; an electrode including this active material; a secondary battery provided with this electrode; a battery pack provided with this secondary battery; and a vehicle having this battery pack installed thereon.SOLUTION: According to one embodiment, provided is an active material including a niobium titanium-containing oxide phase and a carbon coating layer. The niobium titanium-containing oxide phase contains a niobium titanium-containing oxide having a monoclinic structure and Na, and a Na content therein is 0 ppm or more and 100 ppm or less. The carbon coating layer coats at least a part of the niobium titanium-containing oxide phase, and contains 0.001% or more of carboxyl group.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

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

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

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

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

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

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

[0008] In light of the above, new electrode materials containing Ti and Nb are being investigated. Such niobium titanium oxide materials are expected to have high charge / discharge capacities. In particular, the oxide represented by TiNb2O7 has a high theoretical capacity exceeding 380 mAh / g. Therefore, niobium titanium oxide is Li4Ti5O 12 Although it is expected to be a high-capacitance material to replace [another material], its low electronic conductivity makes it difficult to create conductive channels. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2017-059398 [Patent Document 2] Japanese Patent Publication No. 2018-156897 [Non-patent literature]

[0010] [Non-Patent Document 1] "Practical Aspects of Powder X-ray Radiation Analysis," First Edition (2002), edited by the X-ray Radiation Analysis Research Group of the Japan Society for Analytical Chemistry, authored by Izumi Nakai and Fujio Izumi (Asakura Shoten). [Overview of the project] [Problems that the invention aims to solve]

[0011] The objective is to provide an active material that can realize a secondary battery with high energy density and excellent storage performance at low cost, an electrode containing this active material, a secondary battery equipped with this electrode, a battery pack equipped with this secondary battery, and a vehicle equipped with this battery pack. [Means for solving the problem]

[0012] According to the embodiment, an active material is provided comprising a niobium-titanium-containing oxide phase and a carbon coating layer. The niobium-titanium-containing oxide phase comprises a niobium-titanium-containing oxide having a monoclinic structure and Na, and the Na content is 10 ppm to 60 ppm The carbon coating layer covers at least a portion of the surface of the niobium-titanium oxide phase and contains 0.001% or more of carboxyl groups.

[0013] According to other embodiments, an electrode containing the active material according to the above embodiment is provided.

[0014] In yet another embodiment, a secondary battery is provided comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes the electrode according to the above embodiment.

[0015] In yet another embodiment, a battery pack comprising a secondary battery is provided. The secondary battery of the battery pack includes the secondary battery according to the above embodiment.

[0016] In particular, according to another embodiment, a vehicle is provided that is equipped with the battery pack according to the above embodiment. [Brief explanation of the drawing]

[0017] [Figure 1] A schematic cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 2] An enlarged cross-sectional view of section A of the secondary battery shown in Figure 1. [Figure 3] A partially cutaway perspective view schematically showing another example of a secondary battery according to the embodiment. [Figure 4] Figure 3 shows an enlarged cross-sectional view of section B of the secondary battery. [Figure 5] A schematic perspective view showing an example of a battery pack according to this embodiment. [Figure 6] An exploded perspective view schematically showing an example of a battery pack according to this embodiment. [Figure 7] A block diagram showing an example of the electrical circuit of the battery pack shown in Figure 6. [Figure 8] A partial transparency diagram schematically showing an example of a vehicle according to the embodiment. [Figure 9] A schematic diagram showing an example of a control system for the electrical system in a vehicle according to this embodiment. [Modes for carrying out the invention]

[0018] The embodiments will be described below with reference to the drawings. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each figure is a schematic diagram intended to illustrate the embodiments and facilitate understanding; their shapes, dimensions, and ratios may differ from those of the actual device. These can be appropriately modified based on the following description and known technology. Additionally, the same effects can be obtained even if each constituent element contains impurities that are unavoidable in industrial raw materials or industrial processes.

[0019] (First Embodiment) According to the first embodiment, an active material is provided that includes a niobium titanium-containing oxide phase and a carbon coating layer containing a carboxyl group. The niobium titanium-containing oxide phase has a monoclinic structure. The Na (sodium) content in the niobium titanium-containing oxide phase is 0 ppm or more and 100 ppm or less in terms of mass ratio. The carbon coating layer containing a carboxyl group covers at least a part of the surface of the niobium titanium-containing oxide phase. The carbon coating layer contains 0.001% or more of a carboxyl group.

[0020] In one aspect, the above monoclinic niobium titanium-containing oxide phase includes one or more crystal structures belonging to the Nb2TiO7 phase type crystal structure, Nb 10 Ti2O 29 phase type crystal structure, Nb 14 TiO 37 phase type crystal structure, or Nb 24 TiO 62 phase type crystal structure. In other words, the niobium titanium-containing oxide phase includes the crystal structure of at least one phase selected from the group consisting of the Nb2TiO7 phase, Nb 10 Ti2O 29 phase, Nb 14 TiO 37 phase, and Nb 24 TiO 64 phase. Also, in any of these phases, at least one selected from the group consisting of K, Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al may be contained.

[0021] In another aspect, among the above monoclinic niobium titanium-containing oxide phases, the Nb2TiO7 phase can be represented by the general formula Nb2M1 z Ti 1-z O7. Here, M1 includes at least one selected from the group consisting of K, Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscript z is within the range of 0 < z < 1. Also, when Li is inserted into the Nb2TiO7 phase, the composition is Li a Nb2M1 z Ti 1-zIt can be expressed as O7. Here, the subscript z is as described above, and the subscript a is in the range 0 ≤ a ≤ 5.

[0022] Nb 10 Ti2O 29 The composition of the phase is, for example, the general formula Nb 10-x M1 x Ti 2-y M2 y O 29 It can be expressed as follows: Here, M1 is the same as that for the Nb2TiO7 phase. The subscript x is in the range 0≦x≦5, and the subscript y is in the range 0≦y<1. Also, Nb 10 Ti2O 29 When lithium ions are inserted into the phase, the composition is Li b Nb 10-x M1 x Ti 2-y M2 y O 29 It can be expressed as follows. Here, the subscripts x and y are as described above, and the subscript b is in the range 0 ≤ b ≤ 22.

[0023] Nb 14 TiO 37 The composition of the phase is, for example, the general formula Nb 14-x M1 x Ti 1-y M2 y O 37 It can be expressed as follows: M1, subscript x, and subscript y are Nb 10 Ti2O 29 It is similar to the relative form. M2 is one or more elements similar to those of M1, and M1 and M2 may be the same, or they may be different from each other. Also, Nb 14 TiO 37 When lithium ions are inserted into the phase, the composition is Li c Nb 14-x M1 x Ti 1-y M2 y O 37 It can be expressed as follows. Here, the subscripts x and y are as described above, and the subscript c is in the range 0 ≤ c ≤ 29.

[0024] Nb 24TiO 62 The composition of the phase is, for example, the general formula Nb 24-x M1 x Ti 1-y M2 y O 62 It can be expressed as follows: M1, M2, subscript x, and subscript y are Nb 14 TiO 37 It is similar to the one mentioned above. Also, Nb 24 TiO 62 When lithium ions are inserted into the phase, the composition is Li d Nb 24-x M1 x Ti 1-y M2 y O 62 It can be expressed as follows. Here, the subscripts x and y are as described above, and the subscript d is in the range 0 ≤ d ≤ 49.

[0025] In all embodiments, the active material can be a battery active material. When it is a battery active material, it can be included in an electrode. In the electrode, the active material can be included in an active material-containing layer. The active material-containing layer may further contain a conductive agent and a binder. An electrode containing the active material can be included in a secondary battery, for example, as a negative electrode. The secondary battery can be a lithium secondary battery. When the active material is included in a lithium secondary battery, lithium can be inserted into and removed from the active material.

[0026] When monoclinic niobium-titanium oxide is used as an active material for batteries, the electronic conductivity within the active material layer is insufficient. This leads to a problem where the electronic conductivity network is disrupted by volume changes during charging and discharging, accelerating capacity degradation. While the use of fibrous carbon, such as carbon nanotubes, improves conductivity, its high cost poses a practical challenge. The production of fibrous carbon requires catalytic metals such as Co, Mn, and Fe, which function as growth nuclei. Removing these catalytic metals after growing the fibrous carbon is difficult, contributing to increased costs. Consequently, low-cost fibrous carbon often contains large amounts of residual catalytic metals such as Co, Mn, and Fe. These metal residues are known to dissolve into the electrolyte through electrochemical reactions.

[0027] Furthermore, for example, Mn and Co leaching occurs from nickel-manganese-cobalt cathodes. As a result, at a potential lower than that of lithium titanium oxide (such as the redox potential of monoclinic niobium titanium oxide) and higher than the charging potential of carbon-based anodes, metal ions leached into the electrolyte are reduced and deposited onto the electrode composed of monoclinic niobium titanium oxide over time. Consequently, batteries using monoclinic niobium titanium oxide as the anode active material suffer from a problem of reduced storage performance due to increased self-discharge caused by the reduction and deposition of leached metals onto the anode.

[0028] The active material according to the first embodiment comprises a monoclinic niobium-titanium-containing oxide phase and a carbon coating layer containing carboxyl groups. The carbon coating layer containing carboxyl groups covers at least a portion of the surface of the monoclinic niobium-titanium-containing oxide phase. This provides the effect of adsorbing metal ions such as Co cations and Mn cations that approach the surface of the monoclinic niobium-titanium-containing oxide phase at the carboxyl groups.

[0029] When monoclinic niobium-titanium oxide contains trace amounts of sodium, lithium ion conduction is inhibited at the active material surface. As a result, the reduction deposition reaction is accelerated by overpotential. In addition, sodium ions are adsorbed onto the carboxyl groups, reducing the adsorption capacity of metal ions. Therefore, it is desirable to have a low sodium content in the niobium-titanium oxide phase. For this reason, monoclinic niobium-titanium oxide with a Na content of 100 ppm or less is used as the active material.

[0030] Thus, by having a carbon coating layer containing carboxyl groups on at least a portion of the surface of a monoclinic niobium-titanium oxide phase with a Na content of 100 ppm or less, inexpensive fibrous carbon containing catalyst residues can be used, and metal ions eluted from nickel-cobalt-manganese oxides and the like can also be adsorbed. As a result, electronic conductivity can be ensured as with conventional carbon coatings, and the acceleration of self-discharge due to metal elution, which has been a problem until now, can be suppressed, improving storage performance. The lower limit of the Na content is preferably 10 ppm or more, more preferably 40 ppm or more. The upper limit of the Na content is preferably 80 ppm or less, more preferably 60 ppm or less.

[0031] <Particle size> In an embodiment as an electrode material, the active material may contain multiple active material particles, each containing a niobium-titanium oxide phase and a carbon coating layer. Regarding the active material particles contained in the electrode material, in a particle size distribution chart obtained by laser diffraction scattering, the particle size D at which the volume accumulation frequency reaches 10% from the smallest particle size side is... 10 It is preferable that the particle size is within the range of 0.3 μm to 2.0 μm. 10 When the particle size is 0.3 μm or larger, side reactions between the active material and electrolyte are suppressed, and charge / discharge efficiency and cycle life performance tend to improve. 10 A particle size of 2.0 μm or less tends to result in higher rapid charge and discharge performance. 10 It is more preferable that the particle size is within the range of 0.5 μm to 1.0 μm.

[0032] Furthermore, in the particle size distribution chart, the particle size D at which the volume cumulative frequency reaches 90% is located on the smaller particle size side. 90 It is preferable that the size is within the range of 5 μm or more and 30 μm or less. 90 When the thickness is 5 μm or more, peeling of the active material-containing layer from the current collector becomes less likely in electrodes using electrode materials, and the lifespan performance tends to improve. 90 A particle size of 30 μm or less tends to result in higher rapid charge and discharge performance. 90 It is more preferable that the particle size is within the range of 6 μm to 10 μm.

[0033] D 10 A high value of D means less fine powder, and a low value of D 90 means less coarse particles. That is, it means that the main peak in the particle size distribution tends to be sharp. Although it is not always preferable for the main peak to be sharp, the particle size D at which the volume cumulative frequency becomes 50% of the volume frequency from the small particle size side 50 with respect to D 10 The ratio value, and D 50 with respect to D 90 Based on the ratio value, it is possible to evaluate whether the particle size distribution includes a sharp peak.

[0034] Ratio D 10 / D 50 is in the range of 0.1 or more and 0.6 or less, and the ratio D 50 / D 90 is preferably in the range of 0.2 or more and 0.5 or less. By doing so, active material particles having a small particle size are dispersed in the gaps between active material particles having a large particle size, so that the diffusion distance of carrier ions between active material particles, for example, the migration distance of lithium ions in the electrolyte can be reduced. Therefore, it is possible to achieve both excellent rapid charge-discharge performance and excellent life performance while enhancing the rapid charge-discharge performance. Also, when the ratio D 10 / D 50 is 0.1 or more and the ratio D 50 / D 90 is 0.2 or more, there is less deviation in particle size and it is easy to increase the electrode density. When the ratio D 10 / D 50 is in the range of 0.15 or more and 0.30 or less and the ratio D 50 / D 90 is in the range of 0.20 or more and 0.40 or less, it is more preferable. When the ratio D 10 / D 50 is 0.60 or less and the ratio D 50 / D 90 is 0.50 or less, the flexibility of the electrode can be maintained. Therefore, a battery structure in which the electrode is wound can be easily adopted.

[0035] In addition, the value of D of the active material particles in the embodiment is not particularly limited, but is, for example, in the range of 0.5 μm or more and 30 μm or less. In other words, such an active material may be composed of active material particles having an average primary particle diameter of 0.5 μm or more and 30 μm or less. 50 The value of 50 is not particularly limited, but is, for example, in the range of 0.5 μm or more and 30 μm or less. In other words, such an active material may be composed of active material particles having an average primary particle diameter of 0.5 μm or more and 30 μm or less.

[0036] Also, the above particle size distribution chart may correspond to a histogram of the active material particles contained in the electrode material.

[0037] The aforementioned active material particles may be secondary particles formed from the above primary particles. In this case, the particle diameter of the secondary particles is not particularly restricted.

[0038] <BET specific surface area> If such an active material is, for example, an active material particle in which a niobium titanium-containing oxide phase is in the form of particles and a carbon layer having a carboxyl group is coated on the particle surface of the niobium titanium-containing oxide particle, the BET specific surface area of the active material particle is preferably in the range of 0.8 m 2 / g or more and 50 m 2 / g or less. It is more preferable that the BET specific surface area of the active material particles is 2 m 2 / g or more and 5 m 2 / g or less.

[0039] If the BET specific surface area is 0.8 m 2 / g or more, the contact area between the active material particles and the electrolyte can be ensured, good discharge rate performance can be easily obtained, and the charging time can be shortened. On the other hand, if the BET specific surface area is less than 50 m 2 / g, the reactivity between the active material and the electrolyte does not become too high, and the life performance can be improved. Also, if the BET specific surface area is 5 m 2 / g or less, the side reactivity with the electrolyte can be suppressed, and further longer life can be expected. Also, in this case, the coating property of the slurry containing the active material used for manufacturing the electrode described later can be made good.

[0040] Here, the specific surface area is measured by adsorbing molecules with a known adsorption area onto the surface of powder particles at the temperature of liquid nitrogen, and then determining the specific surface area of ​​the sample from the amount adsorbed. The most commonly used method is the BET method, which involves low-temperature, low-humidity physical adsorption of an inert gas. This BET method is based on the BET theory, the most famous theory for calculating specific surface area, which extends the Langmuir theory, a monolayer adsorption theory, to multilayer adsorption. The specific surface area obtained by this method is called the BET specific surface area.

[0041] The above-described effects can be obtained by having a carbon coating layer containing carboxyl groups present on at least a portion of the surface of the niobium-titanium-containing oxide phase. For example, it is preferable that the carbon coating weight ratio of the oxide phase by the carbon coating layer is 0.5 wt% or more. The carbon coating weight ratio of the carbon coating layer on the oxide phase can be determined from measurement results obtained by the method described later.

[0042] The thickness of the carbon coating layer is not particularly limited, but it is preferably in the range of 0.5 nm to 30 nm. If the thickness is less than 0.5 nm, the coverage by the carbon coating layer is insufficient, and the effect is difficult to obtain. On the other hand, if the thickness is greater than 30 nm, it is undesirable because it hinders Li ion movement.

[0043] The amount of carboxyl groups contained in the carbon coating layer is expressed as the carboxyl group concentration (molecular concentration) in the carbon coating layer, which is determined by the method described later. In the active material in question, the amount of carboxyl groups in the carbon coating layer is such that the carboxyl group concentration is 0.001% or more. A carboxyl group concentration of 0.001% or more allows the material to effectively adsorb and capture Na ions in the electrolyte and eluted metal ions from the positive electrode.

[0044] <Manufacturing method> The active material according to the first embodiment can be produced by the synthesis method described below.

[0045] Monoclinic niobium-titanium oxides can be synthesized as follows: First, the starting materials are mixed. As a starting material containing niobium and titanium, an oxide or salt containing Nb and Ti is prepared. As a starting material containing elements M1 and M2, an oxide or salt containing at least one element selected from the group consisting of K, Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al is prepared. The salt used as a starting material is preferably a salt that decomposes at a relatively low temperature to produce an oxide, such as a carbonate or nitrate.

[0046] These starting materials are mixed in a molar ratio that results in the desired composition. Next, the resulting mixture is pulverized to obtain a mixture that is as homogeneous as possible. Then, the resulting mixture is subjected to calcination (first calcination). Calcination (first calcination) is carried out in two or more stages for a total of 10 to 40 hours at a temperature range of 500°C to 900°C. This allows for the acquisition of highly homogeneous precursor particles.

[0047] Next, the obtained precursor particles are wet-mixed. At this time, a solvent such as deionized water that can dissolve sodium is used for wet mixing, and then the mixed solvent is heated to 60°C. Next, the solvent and precursor particles are separated by sedimentation, and then mixed again in deionized water. This removes the sodium component from the surface of the precursor particles. By performing this desodium treatment, a niobium-titanium oxide phase with a reduced Na content of 100 ppm or less, or with Na removed entirely, can be obtained.

[0048] Next, the precursor particles obtained by wet mixing are subjected to a final calcination (second calcination). The final calcination is preferably carried out at a temperature of 800°C to 1450°C for 1 to 10 hours. More preferably, the final calcination is carried out at a temperature of 1000°C to 1450°C for 2.5 to 3.5 hours. The powder thus obtained is then pulverized. For this pulverization, for example, a roller compactor, a bead mill, and a ball mill can be used.

[0049] By changing the grinding conditions, the D of the electrode material obtained 10 , D 50 and D 90 This can be controlled. For example, by increasing the grinding time, D 10 , D 50 and D 90 There is a tendency to make it smaller. Also, for example, by using a grinding medium with a smaller diameter, D 10 , D 50 and D 90 It tends to be possible to reduce the size. Alternatively, by subjecting the powder to centrifugation, D 10 To collect small particles, D 90 Large particles can be collected. For example, by mixing the collected particles with a separately synthesized electrode material, D 10 , D 50 and D 90 It can be controlled.

[0050] Annealing may be performed after grinding. The annealing temperature should preferably be between 350°C and 800°C. Annealing within this temperature range can alleviate strain within the crystals and stabilize the crystalline state after grinding.

[0051] Next, the surface of the monoclinic niobium-titanium-containing oxide obtained by synthesis as described above is coated with a carbon coating layer containing carboxyl groups. For example, a mixture is obtained by saponifying polyvinyl acetate resin obtained by polymerizing polyvinyl alcohol vinyl acetate monomer, dissolving it in water, and mixing it with the niobium-titanium-containing oxide. This mixture is then granulated and dried, for example, using a spray-drying method, to obtain a granulated body.

[0052] It is preferable to use polyvinyl alcohol (PVA) with a saponification degree of 70% to 98%. If a saponification degree lower than 70% is used, the solubility in water increases. In this case, the precipitation on the oxide surface when the dispersion solvent is dried is slower, and the niobium-titanium-containing oxide tends to aggregate.

[0053] On the other hand, while a lower degree of saponification is preferable for retaining carboxyl groups in the carbon coating layer, a higher degree of saponification results in more stable solution viscosity. From the viewpoint of ensuring a uniform carbon coating layer formed on the oxide surface, a higher degree of saponification is preferable. However, PVA with a degree of saponification higher than 98% has significantly lower solubility in water. Therefore, considering manufacturability, a degree of saponification of 98% or less is preferable. A more preferable range for the degree of saponification is 70% to 85%.

[0054] The resulting granules are heat-treated under a nitrogen atmosphere at a temperature between 500°C and 750°C to carbonize them. During this process, the treatment temperature and time are adjusted according to the degree of saponification of the polyvinyl acetate used, in order to retain the carboxyl groups. Conventional heat treatment methods result in carbonization without the retention of carboxyl groups. Therefore, an example of an appropriate heat treatment method is described below.

[0055] First, as a preheating step for dehydration, the sample is heated in a tubular furnace in a flowing nitrogen atmosphere at 500°C for 30 minutes, and then cooled to room temperature. Next, the sample is transferred to a glass tube, evacuated, and then filled with nitrogen. In this sealed nitrogen atmosphere, a carbonization heat treatment is performed at 400°C to 700°C, and heating is continued until a tar-like viscous liquid adheres to the glass tube (approximately 1 hour).

[0056] By performing heat treatment in this manner, carboxyl groups can be retained during carbonization. Furthermore, the preferred heating temperature varies depending on the degree of saponification, and it is preferable to change the heating temperature as shown in Table 1, for example. This yields an active material containing an oxide (niobium-titanium-containing oxide phase) coated with a carbon layer containing carboxyl groups.

[0057] [Table 1]

[0058] As described above, if heat treatment is applied based on a conventional carbonization method, for example, it is not possible to retain carboxyl groups. By immersing oxide particles coated with a carbon coating layer from which carboxyl groups have been carbonized in this way in a solution containing a compound having carboxyl groups, carboxyl groups can be imparted to the surface of the carbon coating layer. Similarly, immersion in a solution containing a compound having carboxyl groups can also impart carboxyl groups to the surface of the carbon coating layer. When carboxyl groups are imparted in this way, a structure is formed in which carboxyl groups are largely distributed on the surface of the carbon coating layer. In this case, the adsorption of metal ions in the electrolyte mainly occurs on the surface of the coating layer, but the carboxyl groups on the surface of the carbon coating layer may hinder the electronic conductivity between particles.

[0059] In contrast, when carboxyl groups are retained, for example, by firing using the method described above, the carbonized surface (the surface of the carbon coating layer) is sufficiently exposed to the heat source and carbonization progresses, while many carboxyl groups remain at the interface between the carbon coating layer and the niobium-titanium-containing oxide phase. As a result, the surface of the carbon coating layer has high electronic conductivity, and metal ions are adsorbed inside the carbon coating layer. Therefore, both improved lifespan and suppression of self-discharge can be achieved.

[0060] <Method for measuring active material> Next, we will explain how to obtain an X-ray diffraction pattern of a niobium-titanium-containing oxide phase using powder X-ray diffraction, and how to confirm the composition of the niobium-titanium-containing oxide. We will also explain how to measure the amount of carbon, the thickness of the carbon layer, and the amount of carboxyl groups in the carbon coating layer.

[0061] If the active material to be measured is included in the electrode material of a secondary battery, pre-treatment should be performed as follows.

[0062] First, the lithium ions in the oxide phase crystals of the active material are brought to a state as close to complete detachment as possible. For example, if the active material to be measured is contained in the negative electrode, the battery is brought to a completely discharged state. For example, the battery can be discharged to its rated termination voltage at a current of 0.1C in a 25°C environment. However, residual lithium ions may still be present even in the discharged state, but this does not significantly affect the powder X-ray diffraction measurement results described below.

[0063] Next, the battery is disassembled in a glove box filled with argon and the electrodes are removed. The removed electrodes are washed with a suitable solvent and dried under reduced pressure. For example, ethyl methyl carbonate can be used. After washing and drying, it is confirmed that there are no white precipitates such as lithium salts on the surface.

[0064] The cleaned electrodes are processed and treated appropriately according to the respective measurement method to prepare them as measurement samples. For example, when using them for powder X-ray diffraction measurements, the cleaned electrodes are cut to an area approximately the same as the area of ​​the holder of the powder X-ray diffractometer to prepare them as measurement samples.

[0065] Furthermore, the active material is removed from the electrode as needed and used as a measurement sample. For example, when performing compositional analysis or measuring the carbon content, the active material is removed from the cleaned electrode and analyzed, as will be explained later.

[0066] <Method for obtaining X-ray diffraction patterns of oxides using powder X-ray diffraction> The crystalline structure contained in the active material can be confirmed by powder X-ray diffraction (XRD) analysis. By analyzing the measurement results of powder X-ray diffraction, for example, the crystalline structure contained in the niobium-titanium-containing oxide phase of the active material according to the embodiment can be confirmed.

[0067] Powder X-ray diffraction measurements of the active material are performed as follows:

[0068] First, the sample is ground down to an average particle size of approximately 5 μm. Even if the original average particle size is smaller than 5 μm, it is preferable to grind it down using a mortar and pestle or similar device to break down any aggregates. The average particle size can be determined, for example, by laser diffraction.

[0069] The crushed sample is packed into a 0.5 mm deep holder portion formed on a glass sample plate. For example, a glass sample plate manufactured by Rigaku Corporation is used. At this time, care should be taken to ensure that the sample is sufficiently packed into the holder portion. Care should also be taken to prevent cracks and voids from occurring due to insufficient sample packing. Next, another glass plate is used from the outside to press the sample firmly and smooth it out. At this time, care should be taken to ensure that there are no irregularities on the reference surface of the holder due to too much or too little packing.

[0070] Next, the glass plate filled with the sample is placed in a powder X-ray diffractometer, and a diffraction pattern (XRD pattern; X-Ray Diffraction pattern) is obtained using Cu-Kα rays.

[0071] If the active material to be measured is included in the electrode material of a secondary battery, first prepare the sample according to the procedure described above. Then, attach the obtained sample directly to the glass holder and perform the measurement.

[0072] In this process, the position of the peak originating from the electrode substrate, such as metal foil, should be measured in advance. The peaks of other components, such as conductive agents and binders, should also be measured in advance. If the substrate peak and the active material peak overlap, it is desirable to peel off the layer containing the active material (e.g., the active material-containing layer) from the substrate before measurement. This is to separate the overlapping peaks when quantitatively measuring the peak intensity. For example, the active material-containing layer can be peeled off by irradiating the electrode substrate with ultrasound in a solvent.

[0073] Furthermore, if the sample exhibits high orientation, the peak position may shift or the peak intensity ratio may change depending on how the sample is packed. For example, as shown in the Rietveld analysis described later, when packing a sample, orientation may be observed where crystal planes align in a specific direction depending on the particle shape. Alternatively, the effect of orientation may be observed when measuring a sample obtained by removing it from a battery.

[0074] Samples with such high orientation are measured using a capillary (a cylindrical glass tube). Specifically, the sample is inserted into the capillary, and the capillary is placed on a rotating sample stage and measured while rotating. This measurement method allows for obtaining results that mitigate the orientation.

[0075] If the intensity ratio measured by this method differs from the intensity ratio measured using the aforementioned flat plate holder or glass holder, the influence of orientation should be considered, and therefore the measurement result from the rotating sample stage should be adopted.

[0076] For powder X-ray diffraction measurements, we will use, for example, the SmartLab manufactured by Rigaku. The measurement conditions will be as follows: X-ray source: Cu target Output: 45kV, 200mA Solar slit: 5° for both incident and received light. Step size (2θ): 0.02deg Scan speed: 20deg / min Semiconductor detector: D / teX Ultra 250 Sample plate holder: Flat glass sample plate holder (thickness 0.5 mm) Measurement range: 5° ≤ 2θ ≤ 90°.

[0077] If other equipment is used, measurements should be performed using standard Si powder for powder X-ray diffraction to obtain measurement results equivalent to those described above, and the conditions should be adjusted so that the peak intensity and peak top position match those of the above equipment.

[0078] The above conditions for powder X-ray diffraction measurement are those that allow for the acquisition of an XRD pattern applicable to Rietveld analysis. Specifically, to collect data for Rietveld analysis, the step size is set to 1 / 3 to 1 / 5 of the minimum half-width of the diffraction peak, and the measurement time or X-ray intensity is adjusted as appropriate so that the intensity at the peak position of the most intense reflection is 5000 cps or more. For example, Rietveld analysis can be performed based on the method detailed in Non-Patent Document 1.

[0079] By the above method, information regarding the crystal structure of the active material being measured can be obtained. For example, when the active material according to the first embodiment is measured as described above, it can be found that the active material being measured contains an oxide having a monoclinic structure. Furthermore, by measuring as described above, it is possible to investigate the crystallinity and symmetry of the crystal structure of the material being measured, such as a monoclinic system.

[0080] <Method for confirming the composition of niobium-titanium-containing oxides> The composition of the niobium-titanium-containing oxide in the active material can be analyzed, for example, using inductively coupled plasma (ICP) emission spectroscopy. In this case, the relative abundance of each element depends on the sensitivity of the analytical instrument used. Therefore, for example, when the composition of the niobium-titanium-containing oxide phase contained in an example of the active material according to the first embodiment is analyzed using ICP emission spectroscopy, the numerical value may deviate from the elemental ratio described above by the error of the measuring instrument. However, even if the measurement result deviates as described above within the error range of the analytical instrument, the active material in this example can still fully exhibit the effects described above.

[0081] To measure the composition of the active material incorporated into a battery using ICP emission spectroscopy, the following procedure is specifically followed.

[0082] First, following the procedure described earlier, the electrode containing the active material to be measured is removed from the secondary battery and cleaned. The cleaned electrode is then placed in a suitable solvent and irradiated with ultrasound. For example, by placing the electrode in ethyl methyl carbonate in a glass beaker and vibrating it in an ultrasonic cleaner, the active material-containing layer can be detached from the current collector.

[0083] Next, the peeled active material-containing layer is dried under reduced pressure. The resulting active material-containing layer is then crushed in a mortar and pestle to obtain a powder containing the target active material, conductive agent, binder, etc. This powder can be dissolved in an acid to prepare a liquid sample containing the active material. Hydrochloric acid, nitric acid, sulfuric acid, hydrogen fluoride, etc., can be used as the acid. By subjecting this liquid sample to ICP emission spectroscopy, the components of the active material, such as the composition of the niobium-titanium-containing oxide phase, can be determined. The composition of the niobium-titanium-containing oxide phase that can be analyzed by the ICP method includes the composition of the monoclinic niobium-titanium-containing oxide and the Na content in the phase.

[0084] <Method for measuring carbon content> The carbon content in the active material can be measured by, for example, the active material extracted from the electrode as described below. First, the electrode, which has been cleaned as described above, is placed in water to deactivate the active material-containing layer in the water. The active material can then be extracted from the deactivated electrode using a centrifuge or the like. For example, if polyvinylidene fluoride (PVdF) is used as the binder, the extraction process is carried out by washing with N-methyl-2-pyrrolidone (NMP) or the like to remove the binder component, and then removing the conductive agent with a mesh of an appropriate mesh size. If small amounts of these components remain, they can be removed by heat treatment in the air (for example, 250°C for 30 minutes). The active material extracted from the electrode in this way is dried at 150°C for 12 hours, weighed into a container, and then measured using a measuring device (for example, LECO CS-444LS).

[0085] In cases where other active materials are present in the electrode, measurements can be taken as follows.

[0086] The active material extracted from the electrodes is subjected to transmission electron microscopy - energy dispersive X-ray spectroscopy (TEM-EDX) measurements, and the crystal structure of each particle is determined by limited-field diffraction. Particles with diffraction patterns attributed to monoclinic niobium-titanium oxide are selected, and the carbon content of the selected particles is measured. In cases where the niobium-titanium oxide phase does not contain particle morphology, it can be distinguished from other active materials by identifying regions with diffraction patterns attributed to monoclinic niobium-titanium oxide, for example. The carbon content is then measured in the identified regions. Furthermore, when selecting the particles to be measured or identifying the measurement region, carbon mapping can be obtained using EDX to determine the region where carbon is present.

[0087] As described above, the weight of the carbon coating on the surface of the extracted oxide phase can be determined as follows. First, the weight of the active material containing the carbon-coated oxide phase (e.g., oxide particles) is determined and designated as Wc. Next, the active material containing the carbon-coated oxide phase is calcined in air at a temperature of 800°C for 3 hours. This burns off the coating carbon. By determining the weight after calcination, the weight W of the oxide before carbon coating can be obtained. The weight ratio of the carbon coating on the oxide phase can be determined by (Wc-W) / W.

[0088] <Method for measuring carboxyl groups in a carbon coating layer> The amount of carboxyl groups in the carbon coating layer is obtained by first measuring the amount of carbon using X-ray photoelectron spectroscopy (XPS), and then selectively quantitatively analyzing the carboxyl groups using a gas-phase chemical modification method. First, the total amount of carbon (number of atoms) is determined from the quantitative results obtained from peak fitting of C1s in the XPS measurement. totalLet's assume that the COO component concentration [COO] is determined by peak fitting of C1s. The COO component thus obtained contains functional groups other than carboxyl groups, but by chemical modification with trifluoroethanol, it becomes possible to selectively quantify the carboxyl groups. When the amount of carboxyl groups (number of molecules) obtained by this quantification method is denoted as [COOH], [COOH] / C total ×100% is defined as the carboxyl group concentration (molecular concentration) in the carbon coating layer. As mentioned above, the concentration representing the carboxyl group content in the carbon coating layer is 0.001% or more ([COOH] / C total The carboxyl group concentration is (x100%), preferably 0.2% or more, more preferably 1.6% or more, and even more preferably 2.3% or more. It is preferable that the carboxyl group concentration be 10% or less. A concentration of 10% or less enhances the conductivity of the carbon coating layer. The carboxyl group concentration is more preferably 5% or less, and even more preferably 3% or less.

[0089] <Method for measuring the thickness of the carbon coating layer> For measuring the thickness of the carbon coating layer, a transmission electron microscope (TEM) is used, for example.

[0090] Although the carbon coating layer is difficult to observe directly, its thickness can be determined by the following method. First, for example, Ru is deposited onto active material particles, and the particle cross-section is exposed by focused ion beam (FIB) treatment. The gap between the deposited Ru and the oxide phase is identified from the transmission electron microscope image of the cross-section. The point on each particle where the gap is most clearly discernible is selected, and that gap is considered to be the carbon coating layer. The same observation method is performed on 50 randomly selected active material particles, and the average value of the gap width (distance between the deposited Ru and the oxide phase) is taken as the thickness of the carbon coating layer.

[0091] The active material according to the first embodiment comprises a monoclinic niobium-titanium oxide phase containing 0 ppm to 100 ppm of Na and a carbon coating layer containing 0.001% or more of carboxyl groups. The carbon coating layer containing carboxyl groups covers at least a portion of the surface of the niobium-titanium oxide phase. This active material enables the realization of a secondary battery with high energy density and excellent storage performance at a low cost.

[0092] (Second embodiment) According to a second embodiment, an electrode is provided.

[0093] The electrode according to the second embodiment includes the active material according to the first embodiment. This electrode may be a battery electrode containing the active material according to the first embodiment as a battery active material. The electrode as a battery electrode may be, for example, a negative electrode containing the active material according to the first embodiment as a negative electrode active material.

[0094] 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 optionally include an active material and a conductive agent and a binder.

[0095] The active material-containing layer may contain the active material according to the first embodiment alone, or it may contain two or more types of active materials according to the first embodiment. Furthermore, it may contain a mixture of one or more types of active materials according to the first embodiment and one or more other types of active materials. It is desirable that the content ratio of the active material according to the first embodiment to the total mass of the active material according to the first embodiment and the other active materials be 50% by mass or more and 100% by mass or less.

[0096] For example, if the active material according to the first embodiment is included as the negative electrode active material, other examples of active materials include lithium titanate having a ramsdelite structure (e.g., Li 2+y Li3O7 (0≦y≦3), lithium titanate having a spinel structure (e.g., Li 4+x Ti5O 12Examples include titanium dioxide (TiO2), anatase-type titanium dioxide, rutile-type titanium dioxide, niobium pentoxide (Nb2O5), hollandite-type titanium composite oxides, and orthorhombic titanium composite oxides.

[0097] As an example of the above orthorhombic titanium-containing composite oxide, Li 2+a M I 2-b Ti 6-c M II d O 14+σ Examples of compounds represented by are given. Here, M I It is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Cs, Rb, and K. II is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. In the empirical formula, each subscript has the following properties: 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, -0.5≦σ≦0.5.

[0098] Conductive agents are added to enhance current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbonaceous materials such as vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, graphite, carbon nanotubes, and carbon nanofibers. One of these may be used as a conductive agent, or two or more may be used in combination. Alternatively, instead of using a conductive agent, the surface of the active material particles may be further coated with other carbon coatings or electronically conductive inorganic material coatings in addition to the carbon coating layer containing carboxyl groups.

[0099] It is preferable to use one or more fibrous carbon selected from the group consisting of carbon nanotubes and carbon nanofibers as a conductive agent, as this tends to facilitate the maintenance of the electronically conductive network within the active material-containing layer. In this case, as explained in the first embodiment, inexpensive fibrous carbon can also be suitably used because the carboxyl groups of the carbon coating layer of the active material adsorb metal ions derived from the residual catalyst metal.

[0100] A binder is added to fill the gaps between dispersed active materials and to bond the active materials to the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0101] The mixing ratios of the active material, conductive agent, and binder in the active material-containing layer can be appropriately changed depending on the application of the electrode. For example, when the electrode is used as the negative electrode of a secondary battery, it is preferable to mix the active material (negative electrode active material), conductive agent, and binder in the following proportions: 68% to 96% by mass, 2% to 30% by mass, and 2% to 30% by mass, respectively. By setting the amount of conductive agent to 2% by mass or more, the current collection performance of the active material-containing layer can be improved. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient bonding between the active material-containing layer and the current collector can be achieved, and excellent cycle performance can be expected. On the other hand, it is preferable to set the amount of conductive agent and binder to 30% by mass or less each in order to achieve high capacity.

[0102] The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and removed from the active material. For example, when the active material is used as the negative electrode active material, the current collector is preferably made of copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm to 20 μm. A current collector with such a thickness can balance electrode strength and weight reduction.

[0103] Furthermore, the current collector may include portions on its surface where the negative electrode active material-containing layer is not formed. These portions can function as negative electrode current collector tabs.

[0104] Electrodes can be manufactured, for example, by the following method. First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is applied to one or both sides of a current collector. Next, the applied slurry is dried to obtain a laminate of the active material-containing layer and the current collector. After that, this laminate is pressed. In this way, electrodes are manufactured.

[0105] Alternatively, electrodes may be manufactured by the following method: First, an active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is formed into pellets. Then, electrodes can be obtained by placing these pellets on a current collector.

[0106] The electrode according to the second embodiment contains the active material according to the first embodiment. Therefore, such an electrode can realize a secondary battery with high energy density and excellent storage performance at a low cost.

[0107] (Third embodiment) According to the third embodiment, a secondary battery is provided that includes a negative electrode, a positive electrode, and an electrolyte. This secondary battery includes the electrode according to the second embodiment as the negative electrode. In other words, the secondary battery according to the third embodiment includes an electrode as the negative electrode that contains the active material according to the first embodiment as the active material for the battery.

[0108] The secondary battery may further include a separator positioned between the positive electrode and the negative electrode. The negative electrode, positive electrode, and separator can constitute an electrode group. The electrolyte can be held within the electrode group.

[0109] Furthermore, the secondary battery may further comprise an outer casing that houses the electrode group and the electrolyte.

[0110] Furthermore, the secondary battery may further include a negative terminal electrically connected to the negative electrode and a positive terminal electrically connected to the positive electrode.

[0111] The secondary battery in question may be, for example, a lithium secondary battery. Furthermore, the secondary battery may include a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0112] The following provides a detailed explanation of the negative electrode, positive electrode, electrolyte, separator, outer casing, negative electrode terminal, and positive electrode terminal.

[0113] 1) Negative electrode The negative electrode may include a negative electrode current collector and a negative electrode active material-containing layer. The negative electrode current collector and the negative electrode active material-containing layer may be a current collector and an active material-containing layer that can be included in the electrode according to the second embodiment, respectively. The negative electrode active material-containing layer contains the active material according to the first embodiment as the negative electrode active material.

[0114] Details of the negative electrode that overlap with the details described in the second embodiment will be omitted.

[0115] The density of the negative electrode active material layer (excluding the current collector) is 1.8 g / cm³. 3 More than 2.8g / cm 3 The following is preferable. A negative electrode with a density of the negative electrode active material-containing layer within this range exhibits excellent energy density and electrolyte retention. The density of the negative electrode active material-containing layer is 2.1 g / cm³. 3 More than 2.6g / cm 3 The following is more preferable:

[0116] The negative electrode can be produced, for example, by the same method as the electrode according to the second embodiment.

[0117] 2) Positive electrode The positive electrode can include a positive electrode current collector and a positive electrode active material-containing layer. The positive electrode active material-containing layer can be formed on one or both sides of the positive electrode current collector. The positive electrode active material-containing layer can contain a positive electrode active material, and optionally a conductive agent and a binder.

[0118] As the positive electrode active material, for example, an oxide or a sulfide can be used. The positive electrode may contain one type of compound alone as the positive electrode active material, or may contain a combination of two or more types of compounds. Examples of the oxide and the sulfide include compounds into which Li or Li ions can be inserted and desorbed.

[0119] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, lithium manganese composite oxide (e.g., Li x Mn2O4 or Li x MnO2; 0 < x ≦ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≦ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≦ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≦ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≦ 1, 0 < y < 2), lithium phosphate having an olivine structure (e.g., Li x FePO4; 0 < x ≦ 1, Li x Fe 1-y Mn y PO4; 0 < x ≦ 1, 0 < y ≦ 1, Lix CoPO4; 0 < x ≤ 1), iron sulfate (Fe2(SO4)3), vanadium oxide (e.g., V2O5), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included.

[0120] Among the above, examples of more preferable compounds as the positive electrode active material include lithium manganese composite oxide having a spinel structure (e.g., Li x Mn2O4; 0 < x ≤ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≤ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxide having a spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; 0 < x ≤ 1), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1) are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0121] When a room temperature molten salt is used as the electrolyte of the battery, lithium iron phosphate, Li xIt is preferable to use a positive electrode active material containing VPO4F (0 ≤ x ≤ 1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof. These compounds have low reactivity with room-temperature molten salts, thus improving cycle life. Details of room-temperature molten salts will be described later.

[0122] The primary particle size of the positive electrode active material is preferably between 100 nm and 1 μm. Positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. Positive electrode active material with a primary particle size of 1 μm or less allows for smooth diffusion of lithium ions within the solid.

[0123] The specific surface area of ​​the positive electrode active material is 0.1 m². 2 / g or more 10m 2 It is preferable that it is less than or equal to / g. 0.1m 2 A positive electrode active material with a specific surface area of ​​10m or more can adequately secure sites for Li ion intercalation and release. 2 Positive electrode active materials with a specific surface area of ​​less than / g are easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0124] A binder is added to fill the gaps between dispersed positive electrode active materials and to bond the positive electrode active materials to the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these may be used as a binder, or two or more may be used in combination.

[0125] Conductive agents are added to enhance current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as a conductive agent, or two or more may be used in combination. Conductive agents may also be omitted.

[0126] In the positive electrode active material-containing layer, it is preferable that the positive electrode active material and the binder are blended in proportions of 80% to 98% by mass and 2% to 20% by mass, respectively.

[0127] Sufficient electrode strength can be obtained by using a binder amount of 2% by mass or more. Furthermore, the binder can function as an insulator. Therefore, by reducing the binder amount to 20% by mass or less, the amount of insulator contained in the electrode decreases, thus reducing internal resistance.

[0128] When a conductive agent is added, it is preferable that the positive electrode active material, binder, and conductive agent are blended in proportions of 77% to 95% by mass, 2% to 20% by mass, and 3% to 15% by mass, respectively.

[0129] The above-mentioned effects can be achieved by increasing the amount of conductive agent to 3% by mass or more. Furthermore, by reducing the amount of conductive agent to 15% by mass or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This lower proportion reduces the decomposition of the electrolyte under high-temperature storage conditions.

[0130] The positive electrode current collector is preferably an aluminum foil, or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si.

[0131] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, and more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0132] Furthermore, the positive electrode current collector may include portions on its surface where the positive electrode active material-containing layer is not formed. These portions can function as positive electrode current collector tabs.

[0133] The positive electrode can be manufactured, for example, using a positive electrode active material in the same manner as the electrode according to the second embodiment.

[0134] 3) Electrolyte As the electrolyte, for example, a liquid non-aqueous electrolyte or a gel-type non-aqueous electrolyte can be used. A liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0135] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium arsenide hexafluoride (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bistrifluoromethylsulfonylimide (LiN(CF3SO2)2), as well as mixtures thereof. The electrolyte salt is preferably resistant to oxidation even at high potentials, with LiPF6 being the most preferred.

[0136] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); and γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as mixed solvents.

[0137] Gel-like non-aqueous electrolytes are prepared by compounding a liquid non-aqueous electrolyte with a polymer material. Examples of polymer materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0138] Alternatively, in addition to liquid nonaqueous electrolytes and gel-type nonaqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions, polymer solid electrolytes, and inorganic solid electrolytes may be used as nonaqueous electrolytes.

[0139] Room temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as liquids at room temperature (15°C to 25°C). Room temperature molten salts include room temperature molten salts that exist as liquids on their own, room temperature molten salts that become liquid when mixed with an electrolyte salt, room temperature molten salts that become liquid when dissolved in an organic solvent, or mixtures thereof. Generally, the melting point of room temperature molten salts used in secondary batteries is 25°C or lower. Also, organic cations generally have a quaternary ammonium skeleton.

[0140] Polymeric solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and then solidifying it.

[0141] Inorganic solid electrolytes are solid materials that have lithium ion conductivity. Here, "having lithium ion conductivity" means that at 25°C, they have a conductivity of 1 × 10⁻⁶. -6 This refers to exhibiting a lithium ion conductivity of S / cm or higher. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are as follows.

[0142] As an oxide-based solid electrolyte, it has a NASICON (Sodium (Na) Super Ionic Conductor) type structure, and its general formula is Li 1+x It is preferable to use a lithium phosphate solid electrolyte represented by Mα2(PO4)3. In the above general formula, Mα is one or more selected from the group consisting of, for example, titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is in the range of 0 ≤ x ≤ 2.

[0143] A specific example of a lithium phosphate solid electrolyte having a NASICON-type structure is Li 1+x Al x Ti 2-x LATP compounds represented as (PO4)3 where 0.1 ≤ x ≤ 0.5; Li 1+x Al y Mβ 2-yA compound represented by (PO4)3, where Mβ is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca, 0 ≦ x ≦ 1, and 0 ≦ y ≦ 1; Li 1+x Al x Ge 2-x A compound represented by (PO4)3, where 0 ≦ x ≦ 2; and, Li 1+x Al x Zr 2-x A compound represented by (PO4)3, where 0 ≦ x ≦ 2; Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 A compound represented by, where Mγ is one or more selected from the group consisting of Ti and Ge, 0 < x ≦ 2, and 0 ≦ y < 3; Li 1+2x Zr 1-x Ca x Examples of the compound represented by (PO4)3, where 0 ≦ x < 1, can be given.

[0144] In addition, as the oxide-based solid electrolyte, in addition to the above lithium phosphate solid electrolyte, Li x PO y N z An amorphous LIPON compound represented by, where 2.6 ≦ x ≦ 3.5, 1.9 ≦ y ≦ 3.8, and 0.1 ≦ z ≦ 1.3 (for example, Li 2.9 PO 3.3 N 0.46 ); A garnet-type structure La 5+x A x La 3-x Mδ2O 12 A compound represented by, where A is one or more selected from the group consisting of Ca, Sr, and Ba, Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ x ≦ 0.5; Li3Mδ 2-x L2O 12 A compound represented by, where Mδ is one or more selected from the group consisting of Nb and Ta, L may contain Zr, and 0 ≦ x ≦ 0.5; Li 7-3x Al x A compound represented by La3Zr3O 12 where 0 ≦ x ≦ 0.5; Li 5+x La3Mδ 2-x Zr x O12 Represented by , where Mδ is 1 or more selected from the group consisting of Nb and Ta, and 0 ≤ x ≤ 2, it is an LLZ compound (e.g., Li7La3Zr2O 12 ); and having a perovskite-type structure La 2 / 3-x Li x Examples include compounds represented as TiO3 where 0.3 ≤ x ≤ 0.7.

[0145] One or more of the above compounds can be used as a solid electrolyte. Two or more of the above solid electrolytes may also be used.

[0146] 4) Separator The separator is formed from a porous film containing, for example, polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or from a synthetic resin nonwoven fabric. From a safety standpoint, it is preferable to use a porous film made of polyethylene or polypropylene. This is because these porous films can melt at a certain temperature and interrupt the electric current.

[0147] 5) Exterior components For example, the outer packaging material can be a container made of laminate film or a metal container.

[0148] The thickness of the laminating film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

[0149] As the laminate film, a multilayer film is used that includes multiple resin layers and a metal layer interposed between these resin layers. The resin layers include polymer materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layer is preferably made of aluminum foil or aluminum alloy foil for weight reduction. The laminate film can be molded into the shape of an exterior component by sealing it by heat fusion.

[0150] The thickness of the metal container wall is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0151] Metal containers are made from, for example, aluminum or aluminum alloys. Aluminum alloys preferably contain elements such as magnesium, zinc, and silicon. If aluminum alloys contain transition metals such as iron, copper, nickel, and chromium, their content is preferably 100 ppm by mass or less.

[0152] The shape of the exterior components is not particularly limited. For example, the exterior components may be flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior components can be appropriately selected according to the battery dimensions and intended use.

[0153] 6) Negative terminal The negative electrode terminal can be formed from a material that is electrochemically stable at the Li absorption / release potential of the negative electrode active material described above, and is also conductive. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable to use aluminum or an aluminum alloy as the material for the negative electrode terminal. It is preferable that the negative electrode terminal be made of the same material as the negative electrode current collector in order to reduce contact resistance with the negative electrode current collector.

[0154] 7) Positive terminal The positive terminal has a potential range of 3V to 4.5V relative to the oxidation-reduction potential of lithium (vs.Li / Li + The positive electrode terminal can be formed from an electrically stable and conductive material. Examples of positive electrode terminal materials include aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. It is preferable that the positive electrode terminal be formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0155] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0156] Figure 1 is a schematic cross-sectional view showing an example of a secondary battery. Figure 2 is an enlarged cross-sectional view of part A of the secondary battery shown in Figure 1.

[0157] The secondary battery 100 shown in Figures 1 and 2 comprises a bag-shaped outer casing member 2 shown in Figure 1, an electrode group 1 shown in Figures 1 and 2, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the bag-shaped outer casing member 2. The electrolyte (not shown) is held by the electrode group 1.

[0158] The bag-shaped outer packaging member 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0159] As shown in Figure 1, electrode group 1 is a flat, wound electrode group. As shown in Figure 2, the flat, wound electrode group 1 includes a negative electrode 3, a separator 4, and a positive electrode 5. The separator 4 is interposed between the negative electrode 3 and the positive electrode 5.

[0160] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode active material containing layer 3b. In the portion of the negative electrode 3 located in the outermost shell of the wound electrode group 1, the negative electrode active material containing layer 3b is formed only on the inner surface side of the negative electrode current collector 3a, as shown in Figure 2. In the other portions of the negative electrode 3, the negative electrode active material containing layer 3b is formed on both sides of the negative electrode current collector 3a.

[0161] The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both sides thereof.

[0162] As shown in Figure 1, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer edge of the wound electrode group 1. The negative electrode terminal 6 is connected to the outermost part of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to the outermost part of the positive electrode current collector 5a. These negative electrode terminals 6 and positive electrode terminals 7 extend outward from the opening of the bag-shaped outer casing member 2. A thermoplastic resin layer is installed on the inner surface of the bag-shaped outer casing member 2, and the opening is closed by heat fusion of this layer.

[0163] The secondary battery according to this embodiment is not limited to the secondary battery with the configuration shown in Figures 1 and 2, but may also be a battery with the configuration shown in Figures 3 and 4, for example.

[0164] Figure 3 is a schematic partially cutaway perspective view showing another example of a secondary battery. Figure 4 is an enlarged cross-sectional view of section B of the secondary battery shown in Figure 3.

[0165] The secondary battery 100 shown in Figures 3 and 4 comprises an electrode group 1 shown in Figures 3 and 4, an outer casing member 2 shown in Figure 3, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed within the outer casing member 2. The electrolyte is held within the electrode group 1.

[0166] The exterior component 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0167] As shown in Figure 4, electrode group 1 is a stacked electrode group. The stacked electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately stacked with separators 4 interposed between them.

[0168] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 comprises a negative electrode current collector 3a and a negative electrode active material-containing layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 comprises a positive electrode current collector 5a and a positive electrode active material-containing layer 5b supported on both sides of the positive electrode current collector 5a.

[0169] Each negative electrode 3's negative electrode current collector 3a includes a portion on one side where the negative electrode active material-containing layer 3b is not supported on any surface. This portion functions as a negative electrode current collector tab 3c. As shown in Figure 4, the negative electrode current collector tab 3c does not overlap with the positive electrode 5. Furthermore, 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 outer casing member 2.

[0170] Although not shown in the diagram, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode active material-containing layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. The positive electrode current collector tab, like the negative electrode current collector tab 3c, does not overlap with the negative electrode 3. Furthermore, the positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab 3c. The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is extended to the outside of the outer casing member 2.

[0171] The secondary battery according to the third embodiment includes the electrode according to the second embodiment as the negative electrode. Therefore, such a secondary battery exhibits high energy density and excellent storage performance. Furthermore, such a secondary battery can be provided at a low cost.

[0172] (Fourth embodiment) According to the fourth embodiment, a battery pack is provided. This battery pack comprises a plurality of secondary batteries according to the third embodiment.

[0173] In such a battery pack, each individual cell may be arranged in series or parallel connections, or a combination of series and parallel connections may be used.

[0174] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0175] Figure 5 is a schematic perspective view showing an example of a battery pack. The battery pack 200 shown in Figure 5 comprises five single cells 100a to 100e, four busbars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five single cells 100a to 100e is a secondary battery according to the third embodiment.

[0176] The busbar 21 connects, for example, the negative terminal 6 of one cell 100a to the positive terminal 7 of the adjacent cell 100b. In this way, the five cells 100 are connected in series by four busbars 21. That is, the battery pack 200 in Figure 5 is a battery pack with five cells in series. Although not illustrated, in a battery pack containing multiple cells that are electrically connected in parallel, the multiple cells can be electrically connected, for example, by connecting multiple negative terminals to each other and multiple positive terminals to each other by busbars.

[0177] The positive terminal 7 of at least one of the five single cells 100a to 100e is electrically connected to the positive lead 22 for external connection. In addition, the negative terminal 6 of at least one of the five single cells 100a to 100e is electrically connected to the negative lead 23 for external connection.

[0178] The battery pack according to the fourth embodiment comprises the secondary battery according to the third embodiment. Therefore, the battery pack can exhibit a high energy density and excellent storage performance. Furthermore, such a battery pack can be provided at a low cost.

[0179] (Fifth Embodiment) According to the fifth embodiment, a battery pack is provided. This battery pack includes the assembled battery according to the fourth embodiment. This battery pack may include a single secondary battery according to the third embodiment instead of the assembled battery according to the fourth embodiment.

[0180] Such a battery pack can further include a protection circuit. The protection circuit has a function of controlling the charge and discharge of the secondary battery. Alternatively, a circuit included in a device (for example, an electronic device, an automobile, etc.) that uses the battery pack as a power source may be used as the protection circuit of the battery pack.

[0181] Also, such a battery pack can further include external terminals for energization. The external terminals for energization are for outputting a current from the secondary battery to the outside and / or inputting an external current to the secondary battery. In other words, when using the battery pack as a power source, the current is supplied to the outside through the external terminals for energization. Also, when charging the battery pack, the charging current (including the regenerative energy of power such as an automobile) is supplied to the battery pack through the external terminals for energization.

[0182] Next, an example of the battery pack according to the embodiment will be described with reference to the drawings.

[0183] FIG. 6 is an exploded perspective view schematically showing an example of the battery pack. FIG. 7 is a block diagram showing an example of the electrical circuit of the battery pack shown in FIG. 6.

[0184] The battery pack 300 shown in FIGS. 6 and 7 includes a housing container 31, a lid 32, a protection sheet 33, an assembled battery 200, a printed wiring board 34, a wiring 35, and an insulating board (not shown).

[0185] The storage container 31 shown in FIG. 6 is a bottomed rectangular container having a rectangular bottom surface. The storage container 31 is configured to be able to store the protective sheet 33, the assembled battery 200, the printed wiring board 34, and the wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the storage container 31 to store the assembled battery 200 and the like. Although not shown, the storage container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices and the like.

[0186] The assembled battery 200 includes a plurality of single batteries 100, a positive electrode side lead 22, a negative electrode side lead 23, and an adhesive tape 24.

[0187] At least one of the plurality of single batteries 100 is a secondary battery according to the third embodiment. Each of the plurality of single batteries 100 is electrically connected in series as shown in FIG. 7. The plurality of single batteries 100 may be electrically connected in parallel, or may be connected in combination of series connection and parallel connection. When the plurality of single batteries 100 are connected in parallel, the battery capacity increases as compared with the case of series connection.

[0188] The adhesive tape 24 fastens the plurality of single batteries 100. Instead of the adhesive tape 24, a heat shrink tape may be used to fix the plurality of single batteries 100. In this case, the protective sheet 33 is disposed on both side surfaces of the assembled battery 200, and after the heat shrink tape is wound around, the heat shrink tape is heat shrunk to bundle the plurality of single batteries 100.

[0189] One end of the positive electrode side lead 22 is connected to the assembled battery 200. One end of the positive electrode side lead 22 is electrically connected to the positive electrode of one or more single batteries 100. One end of the negative electrode side lead 23 is connected to the assembled battery 200. One end of the negative electrode side lead 23 is electrically connected to the negative electrode of one or more single batteries 100.

[0190] The printed circuit board 34 is installed along one of the shorter sides of the inner surface of the housing container 31. The printed circuit board 34 includes a positive terminal connector 342, a negative terminal connector 343, a thermistor 345, a protection circuit 346, wiring 342a and 343a, an external terminal 350 for energization, a positive side wiring (positive wiring) 348a, and a negative side wiring (negative wiring) 348b. One main surface of the printed circuit board 34 faces one side of the battery pack 200. An insulating plate (not shown) is interposed between the printed circuit board 34 and the battery pack 200.

[0191] The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative connector 343.

[0192] The thermistor 345 is fixed to one main surface of the printed circuit board 34. The thermistor 345 detects the temperature of each of the single cells 100 and transmits the detection signal to the protection circuit 346.

[0193] The external power supply terminal 350 is fixed to the other main surface of the printed circuit board 34. The external power supply terminal 350 is electrically connected to equipment located outside the battery pack 300. The external power supply terminal 350 includes a positive terminal 352 and a negative terminal 353.

[0194] The protection circuit 346 is fixed to the other main surface of the printed circuit board 34. The protection circuit 346 is connected to the positive terminal 352 via the positive side wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via the negative side wiring 348b. The protection circuit 346 is also electrically connected to the positive side connector 342 via wiring 342a. The protection circuit 346 is also electrically connected to the negative side connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple single cells 100 via wiring 35.

[0195] The protective sheet 33 is positioned on both inner surfaces in the long-side direction of the housing container 31 and on the inner surface in the short-side direction facing the printed circuit board 34 via the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0196] The protection circuit 346 controls the charging and discharging of multiple single cells 100. The protection circuit 346 also disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) for supplying power to external devices, based on a detection signal transmitted from the thermistor 345 or a detection signal transmitted from an individual single cell 100 or a battery pack 200.

[0197] An example of a detection signal transmitted from the thermistor 345 is a signal indicating that the temperature of a single cell 100 is above a predetermined temperature. An example of a detection signal transmitted from an individual single cell 100 or a battery pack 200 is a signal indicating that overcharging, over-discharging, or overcurrent has been detected in a single cell 100. When detecting overcharging, etc., in an individual single cell 100, the battery voltage may be detected, or the positive electrode potential or negative electrode potential may be detected. In the latter case, a lithium electrode to be used as a reference electrode is inserted into each individual single cell 100.

[0198] Furthermore, the protection circuit 346 may be a circuit included in a device that uses the battery pack 300 as a power source (for example, an electronic device, an automobile, etc.).

[0199] Furthermore, as described above, the battery pack 300 is equipped with an external terminal 350 for power supply. Therefore, the battery pack 300 can output current from the battery pack 200 to an external device and input current from an external device to the battery pack 200 via the external terminal 350. In other words, when the battery pack 300 is used as a power source, current from the battery pack 200 is supplied to the external device through the external terminal 350. Also, when charging the battery pack 300, charging current from an external device is supplied to the battery pack 300 through the external terminal 350. When this battery pack 300 is used as an on-board battery, the regenerative energy of the vehicle's power can be used as the charging current from the external device.

[0200] The battery pack 300 may have multiple battery packs 200. In this case, the multiple battery packs 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed circuit board 34 and wiring 35 may also be omitted. In this case, the positive lead 22 and the negative lead 23 may be used as the positive terminal 352 and negative terminal 353 of the external terminal 350 for energization, respectively.

[0201] Such battery packs are used in applications where excellent cycle performance is required, for example, when drawing high currents. Specifically, these battery packs are used as power supplies for electronic devices, stationary batteries, and on-board batteries for various vehicles. Examples of electronic devices include digital cameras. These battery packs are particularly suitable for use as on-board batteries.

[0202] The battery pack according to the fifth embodiment comprises a secondary battery according to the third embodiment or a battery pack according to the fourth embodiment. Therefore, the battery pack can exhibit high energy density and excellent storage performance. Furthermore, such a battery pack can be provided at low cost.

[0203] (Sixth embodiment) According to the sixth embodiment, a vehicle is provided. This vehicle is equipped with the battery pack according to the fifth embodiment.

[0204] In such a vehicle, the battery pack, for example, recovers the regenerative energy of the vehicle's power. The vehicle may include a mechanism (Regenerator) that converts the vehicle's kinetic energy into regenerative energy.

[0205] Examples of vehicles include, for example, two - to four - wheel hybrid electric vehicles, two - to four - wheel electric vehicles, assist bicycles, and railway vehicles.

[0206] The mounting position of the battery pack in the vehicle is not particularly limited. For example, when mounting the battery pack in an automobile, the battery pack can be mounted in the vehicle's engine room, behind the vehicle body, or under the seat.

[0207] The vehicle may be equipped with a plurality of battery packs. In this case, the batteries included in each battery pack may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. For example, when each battery pack includes a battery module, the battery modules may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections. Alternatively, when each battery pack includes a single battery, the batteries may be electrically connected in series, electrically connected in parallel, or electrically connected in a combination of series and parallel connections.

[0208] Next, an example of the vehicle according to the embodiment will be described while referring to the drawings.

[0209] FIG. 8 is a partially transparent view schematically showing an example of the vehicle.

[0210] The vehicle 400 shown in Figure 8 includes a vehicle body 40 and a battery pack 300 according to the fifth embodiment. In the example shown in Figure 8, the vehicle 400 is a four-wheeled automobile.

[0211] This vehicle 400 may be equipped with multiple battery packs 300. In this case, the batteries contained in the battery pack 300 (for example, single cells or battery packs) may be connected in series, in parallel, or in a combination of series and parallel connections.

[0212] Figure 8 illustrates an example in which the battery pack 300 is mounted in the engine compartment located in front of the vehicle body 40. As described above, the battery pack 300 may also be mounted, for example, in the rear of the vehicle body 40 or under the seats. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy from the vehicle 400's power.

[0213] Next, an embodiment of the vehicle according to the embodiment will be described with reference to Figure 9.

[0214] Figure 9 is a schematic diagram illustrating an example of a control system for the electrical system in a vehicle. The vehicle 400 shown in Figure 9 is an electric vehicle.

[0215] The vehicle 400 shown in Figure 9 comprises a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a higher-level control device for the vehicle power supply 41, an external terminal (terminal for connecting to an external power supply) 43, an inverter 44, and a drive motor 45.

[0216] Vehicle 400 has its vehicle power supply 41 mounted, for example, in the engine compartment, at the rear of the vehicle body, or under the seats. Note that in the vehicle 400 shown in Figure 9, the mounting location of the vehicle power supply 41 is shown in a schematic manner.

[0217] The vehicle power supply 41 comprises a plurality (for example, three) of battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0218] Battery pack 300a comprises a battery pack 200a and a battery pack monitoring device 301a (e.g., VTM: Voltage Temperature Monitoring). Battery pack 300b comprises a battery pack 200b and a battery pack monitoring device 301b. Battery pack 300c comprises a battery pack 200c and a battery pack monitoring device 301c. Battery packs 300a to 300c are similar to the aforementioned battery pack 300, and battery packs 200a to 200c are similar to the aforementioned battery pack 200. Battery packs 200a to 200c are electrically connected in series. Battery packs 300a, 300b, and 300c can each be independently removed and replaced with another battery pack 300.

[0219] Each of the battery packs 200a to 200c comprises multiple single cells connected in series. At least one of the multiple single cells is a secondary battery according to the third embodiment. Each of the battery packs 200a to 200c is charged and discharged through a positive terminal 413 and a negative terminal 414.

[0220] The battery management device 411 communicates with the battery pack monitoring devices 301a to 301c and collects information such as voltage and temperature for each of the single cells 100 included in the battery packs 200a to 200c included in the vehicle power supply 41. In this way, the battery management device 411 collects information related to the maintenance of the vehicle power supply 41.

[0221] The battery management device 411 and the battery pack monitoring devices 301a to 301c are connected via a communication bus 412. On the communication bus 412, one set of communication lines is shared by multiple nodes (the battery management device 411 and one or more battery pack monitoring devices 301a to 301c). The communication bus 412 is a communication bus configured, for example, based on the CAN (Control Area Network) standard.

[0222] The battery pack monitoring devices 301a to 301c measure the voltage and temperature of each individual cell constituting the battery packs 200a to 200c based on commands communicated from the battery management device 411. However, temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all individual cells.

[0223] The vehicle power supply 41 may also have an electromagnetic contactor (for example, a switch device 415 shown in Figure 9) that switches the presence or absence of an electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that turns on when charging is performed on the battery packs 200a to 200c, and a main switch (not shown) that turns on when the output from the battery packs 200a to 200c is supplied to the load. Each of the pre-charge switch and the main switch includes a relay circuit (not shown) that is switched on or off by a signal supplied to a coil located near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

[0224] The inverter 44 converts the input DC voltage into a high voltage of three-phase alternating current (AC) for motor drive. The three-phase output terminals of the inverter 44 are connected to the three-phase input terminals of the drive motor 45. The inverter 44 is controlled based on control signals from the battery management device 411 or the vehicle ECU 42 for controlling the operation of the entire vehicle. By controlling the inverter 44, the output voltage from the inverter 44 is adjusted.

[0225] The drive motor 45 rotates using power supplied from the inverter 44. The driving force generated by the rotation of the drive motor 45 is transmitted to the axle and drive wheels W, for example, via a differential gear unit.

[0226] Although not shown in the diagram, vehicle 400 is also equipped with a regenerative braking mechanism (regenerator). The regenerative braking mechanism rotates the drive motor 45 when vehicle 400 is braked, converting kinetic energy into regenerative energy as electrical energy. The regenerative energy recovered by the regenerative braking mechanism is input to the inverter 44 and converted into a DC current. The converted DC current is input to the vehicle power supply 41.

[0227] One terminal of connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41. The other terminal of connection line L1 is connected to the negative input terminal 417 of the inverter 44. A current detection unit (current detection circuit) 416 within the battery management device 411 is provided on connection line L1 between the negative terminal 414 and the negative input terminal 417.

[0228] One terminal of connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41. The other terminal of connection line L2 is connected to the positive input terminal 418 of the inverter 44. A switch device 415 is provided between the positive terminal 413 and the positive input terminal 418 of connection line L2.

[0229] External terminal 43 is connected to battery management device 411. External terminal 43 can be connected to an external power supply, for example.

[0230] The vehicle ECU 42, in response to operational inputs from the driver and others, coordinates control of the vehicle power supply 41, switch device 415, inverter 44, etc., together with other management and control devices, including the battery management device 411. Through the coordinated control of the vehicle ECU 42, etc., the output of power from the vehicle power supply 41 and the charging of the vehicle power supply 41 are controlled, and the entire vehicle 400 is managed. Data related to the maintenance of the vehicle power supply 41, such as the remaining capacity of the vehicle power supply 41, is transferred between the battery management device 411 and the vehicle ECU 42 via a communication line.

[0231] The vehicle according to the sixth embodiment is equipped with the battery pack according to the fifth embodiment. Therefore, it can exhibit high performance because it has a battery pack with high energy density. In addition, it is highly reliable because the battery pack has excellent storage performance. [Examples]

[0232] The above embodiments will be described in more detail below based on the examples. The crystalline phases, such as the synthesized monoclinic niobium-titanium-containing oxide (niobium-titanium-containing oxide phase), and the crystal structure were identified and estimated by powder X-ray diffraction using Cu-Kα rays. Furthermore, the composition of the product was analyzed by ICP to confirm that the target product had been obtained.

[0233] (Example 1) The active material was manufactured using the following procedure.

[0234] First, a niobium-titanium-containing oxide having a monoclinic crystal system and represented as Nb2TiO7 was synthesized. The synthesis was carried out by the method described in the first embodiment, including the desodium treatment.

[0235] Next, the obtained oxide powder was composited with a carbon material. Specifically, first, polyvinyl alcohol (PVA) with a degree of saponification of 98% was mixed with pure water as the carbon-containing compound to prepare a 15% by mass aqueous solution of PVA. The oxide powder was mixed and stirred into this aqueous solution to prepare a dispersion. The mass ratio of oxide particles to PVA in this dispersion was 15% by mass. By adding an aqueous ammonia solution to this dispersion, the pH of the dispersion was adjusted to be within the range of pH 11.5 to 12.4.

[0236] Next, a dispersion (pure water) containing the composite obtained in this way, in which the pre-carbonization PVA phase was formed on at least a portion of the surface of the oxide particles, was subjected to spray drying. After that, the obtained powder was collected and dried at 100°C for 12 hours to completely evaporate the solvent, and then carbonization calcination was carried out under a reducing atmosphere.

[0237] First, as a preheating step for dehydration, the sample was heated in a tubular furnace in a flowing nitrogen atmosphere at 500°C for 30 minutes, and then cooled to room temperature. Next, the sample was transferred to a glass tube, vacuumed, and then sealed with nitrogen. Carbonization heat treatment was performed in this sealed nitrogen atmosphere at 500°C for 1 hour, and it was confirmed that a tar-like viscous liquid adhered to the glass tube. The carbonization treatment was completed by cooling to room temperature, and an active material containing a carbon coating layer was obtained.

[0238] Next, the aggregated active material obtained was gently loosened using a mortar. In this way, the evaluation active material according to Example 1 was obtained.

[0239] Furthermore, the state of the coated carbon on the obtained active material was investigated by TEM observation. First, Ru metal was adsorbed onto the surface of the active material by vapor deposition. Then, the sample powder was embedded in resin and thinned by ion milling using a GATAN DualMill600. Using the sample processed in this way, TEM observation was performed on arbitrary primary particles. A Hitachi H-9000UHR III TEM was used, and the evaluation was performed with an acceleration voltage of 300kV and an image magnification of 2,000,000x. In the evaluation active material according to Example 1, the thickness of the carbon coating layer was approximately 2.0 nm, and it was highly smooth and uniformly coated.

[0240] When the BET specific surface area of ​​the active material used for evaluation was measured by nitrogen adsorption, it was found to be 3.1 m². 2 The concentration was [COOH] / g. Furthermore, the weight ratio of the carbon coating layer to the total mass of the active material was determined by the heating method described above, and it was found to be 2.3% by weight. The carboxyl group concentration ([COOH] / C) of the active material for evaluation in Example 1 was determined by the method described above. total The result of multiplying by 100%) was calculated. In Example 1, the carboxyl group concentration was 0.06%.

[0241] Furthermore, the Na content in the niobium-titanium oxide phase was investigated. In Example 1, the Na content was 50 ppm.

[0242] (Example 2- 4,6- 15 and Reference Example 5 ) The oxide synthesized as the niobium-titanium-containing oxide phase was changed to one with the composition shown in Table 2 below. Furthermore, the conditions for compounding the obtained oxide with the carbon coating layer were changed to those shown in Table 3 below. Except for these changes, the evaluation active material was obtained using the same procedure as in Example 1. The obtained evaluation active material was then subjected to the same analysis as in Example 1. The analysis results are shown in Tables 2 and 3.

[0243] (Comparative Example 1) When synthesizing the niobium-titanium oxide Nb2TiO7, the sodium removal treatment was omitted. Furthermore, the conditions for compounding the obtained oxide with the carbon coating layer were changed to those shown in Table 3 below. Aside from these changes, the evaluation active material was obtained using the same procedure as in Example 1. In Comparative Example 1, preheating during the carbon coating treatment was omitted. The obtained evaluation active material was analyzed in the same manner as in Example 1. The analysis results are shown in Tables 2 and 3.

[0244] (Comparative Example 2) When synthesizing the niobium-titanium oxide Nb2TiO7, the sodium removal treatment was omitted. Furthermore, the conditions for compounding the obtained oxide with the carbon coating layer were changed to those shown in Table 3 below. Aside from these changes, the evaluation active material was obtained using the same procedure as in Example 1. The obtained evaluation active material was subjected to the same analysis as in Example 1. The analysis results are shown in Tables 2 and 3.

[0245] (Comparative Example 3) The conditions for compounding the niobium-titanium oxide phase with the carbon coating layer were changed to those shown in Table 3 below. Aside from this change, the evaluation active material was obtained using the same procedure as in Example 1. Furthermore, the obtained evaluation active material was subjected to the same analysis as in Example 1. The analysis results are shown in Tables 2 and 3.

[0246] (Comparative Example 4) As a niobium-titanium-containing oxide phase, instead of monoclinic niobium-titanium-containing oxide, Li2Na 1.5 Ti 5.5 Nb 0.5 O 14 A niobium-titanium-containing oxide having an orthorhombic crystal structure belonging to space group Fmmm was synthesized. No sodium desaturation treatment was performed during synthesis. Furthermore, the conditions for compounding the obtained oxide with the carbon coating layer were changed to those shown in Table 3 below. Except for these changes, the evaluation active material was obtained using the same procedure as in Example 1. The obtained evaluation active material was analyzed in the same manner as in Example 1. The analysis results are shown in Tables 2 and 3.

[0247] (Comparative Example 5) Similar to Comparative Example 4, orthorhombic Li2Na was used instead of monoclinic niobium-titanium-containing oxide as the niobium-titanium-containing oxide phase. 1.5 Ti 5.5 Nb 0.5 O 14 The following was synthesized. In Comparative Example 5, no sodium removal treatment was performed. In addition, the conditions for compounding the obtained oxide with the carbon coating layer were changed to the conditions shown in Table 3 below. Except for these changes, an evaluation active material was obtained using the same procedure as in Example 1. The obtained evaluation active material was subjected to the same analysis as in Example 1. The analysis results are shown in Tables 2 and 3.

[0248] Table 2 below shows Example 1- 4,6- 15 , Reference example 5 The composition, crystal system, and Na content of the niobium-titanium-containing oxide phases obtained in Comparative Examples 1-5 are summarized. Furthermore, the presence or absence of desodium treatment during synthesis is indicated.

[0249] [Table 2]

[0250] Table 3 below shows Example 1- 4,6- 15 , Reference example 5 In Comparative Examples 1-5, the conditions for compounding the niobium-titanium oxide phase with the carbon coating layer and the results of various analyses of the obtained active materials for evaluation are summarized. The compounding conditions include the degree of saponification of the PVA used in the carbon coating treatment, the preheating conditions, and the carbonization conditions. The analytical results include the determined carboxyl group concentration, carbon coating weight percentage, carbon coating layer thickness, and BET specific surface area.

[0251] [Table 3]

[0252] Next, Example 1- 4,6- 15 , Reference example 5 The storage performance of the evaluation active materials obtained in Comparative Examples 1-5 was evaluated as follows.

[0253] A non-aqueous electrolyte battery was fabricated using the following procedure.

[0254] (Fabrication of the negative electrode) The negative electrode was prepared as follows. Example 1- 4,6- 15 , Reference example 5 The particles of the active material obtained in Comparative Examples 1-5 (carbon-coated particles) were used as the negative electrode active material.

[0255] First, the negative electrode active material was pulverized to an average particle size of 5 μm or less to obtain a pulverized material. Next, acetylene black was mixed as a conductive agent at a ratio of 6 parts by mass per 100 parts by mass of the negative electrode active material. Then, as another conductive agent, low-cost carbon fiber, specifically carbon nanotubes containing 852 ppm by mass of cobalt atoms as impurities, was added at a ratio of 4 parts by mass per 100 parts by mass of the negative electrode active material to obtain a mixture. Next, this mixture was dispersed in NMP (N-methyl-2-pyrrolidone) to obtain a dispersion. Polyvinylidene fluoride (PVdF) was mixed into this dispersion as a binder at a ratio of 10 parts by mass per 100 parts by mass of the negative electrode active material to prepare a negative electrode slurry. This slurry was applied to a current collector made of aluminum foil using a blade. After drying this under vacuum at 130°C for 12 hours, the density of the active material-containing layer (excluding the current collector) was 2.2 g / cm³. 3 The negative electrode was obtained by rolling it in such a manner.

[0256] (Fabrication of the positive electrode) The positive electrode was fabricated as follows: Lithium nickel manganese cobalt composite oxide (LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2 was used as the positive electrode active material.

[0257] First, a mixture was obtained by mixing 100 parts by mass of positive electrode active material with 5 parts by mass of acetylene black as a conductive agent. Next, this mixture was dispersed in NMP to obtain a dispersion. To this dispersion, PVdF as a binder was mixed at a ratio of 5 parts by mass relative to the positive electrode active material to prepare a positive electrode slurry. This slurry was applied to a current collector made of aluminum foil using a blade. After drying under vacuum at 130°C for 12 hours, the density of the active material-containing layer (excluding the current collector) was 2.1 g / cm³. 3 The positive electrode was obtained by rolling the material in this manner.

[0258] (Fabrication of electrode groups) The positive and negative electrodes prepared as described above were stacked with a polyethylene separator in between to obtain a laminate. Next, this laminate was wound and pressed to obtain a flattened wound electrode group. The positive and negative electrode terminals were connected to this electrode group.

[0259] (Preparation of non-aqueous electrolytes) A mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 1:1) was prepared. Lithium hexafluoride phosphate (LiPF6) was dissolved in this solvent at a concentration of 1 M. Thus, a non-aqueous electrolyte was prepared.

[0260] (Assembly of non-aqueous electrolyte batteries) A non-aqueous electrolyte battery was fabricated using the electrode group and non-aqueous electrolyte prepared in the manner described above.

[0261] (Storage test) Each non-aqueous electrolyte battery obtained was subjected to a storage test at room temperature. In the storage test, first, the battery was charged and discharged twice at a current of 0.2C (time discharge rate) within a battery voltage range of 1.5V to 3.0V. Next, the battery was charged with a constant current of 0.2C (time discharge rate) until the battery voltage reached 3.0V, and then charged at a constant voltage until the charging current converged to 1 / 20C, resulting in a fully charged battery. This battery was stored in a constant temperature bath at 25°C, and the change in open-circuit voltage was examined. The open-circuit voltage after 12 hours from full charge was V1, and the open-circuit voltage after 30 days was V1. 30When that happens, (V1-V 30 The daily voltage drop rate (mV / Day) was calculated using a 30-day period. The results are shown in Table 4 below.

[0262] Furthermore, the metal ion adsorption rate of carboxyl groups in the carbon coating layer of the negative electrode active material during storage was confirmed as follows. First, the negative electrode was removed by disassembling the battery, washed, and then immersed in water to deactivate the active material-containing layer before the negative electrode active material was extracted. The COO component concentration [COO] was determined from the quantitative results obtained from peak fitting of C1s by XPS measurement on the extracted active material. Next, the amount of carboxyl groups [COOH] was obtained by selectively quantifying the carboxyl groups by chemical modification with trifluoroethanol. Then, using time-of-flight secondary ion mass spectrometry (TOF-SIMS), it was confirmed whether or not carboxylate metal bases such as COOCo (cobalt carboxylate group) were present. If their presence was confirmed, the amount of carboxylate metal bases [COOMe] was calculated from the COO component other than the carboxyl group ([COO]-[COOH]). The ratio of the amount of the metal carboxylate salt [COOMe] to the total COO component concentration [COO] determined before chemical modification with trifluoroethanol ([COOMe] / [COO] × 100%) was calculated as a percentage, and the metal ion adsorption rate was determined. The results are shown in Table 4.

[0263] [Table 4]

[0264] As shown in Table 4, Example 1- 4,6- 15 and Reference Example 5In batteries using the evaluation active material described above as the negative electrode, the daily voltage drop rate during storage tests could be kept below 1.15 mV. In these batteries, which used a negative electrode active material consisting of a monoclinic niobium-titanium oxide phase with a Na content of 100 ppm or less coated with a carbon coating layer containing 0.001% or more carboxyl groups, self-discharge was suppressed even though low-grade carbon nanotubes containing cobalt impurities were included in the conductive agent. In particular, in batteries using the active materials described in Examples 3-6 and 8-15, the daily voltage drop rate could be kept below 0.25 mV. In these examples, the carboxyl group content of the carbon coating layer was 2.3% or more, which provided ample capacity to adsorb metal ions such as the aforementioned impurity cobalt atoms and metals eluted from the positive electrode, as evidenced by the metal ion adsorption rate remaining below 84% during storage tests.

[0265] In contrast, in batteries using the evaluation active material from Comparative Examples 1-5 as the negative electrode, the daily voltage drop rate during storage tests exceeded 2.5 mV.

[0266] In Comparative Examples 1 and 2, on the one hand, a carboxyl group-containing carbon coating layer equivalent to that of Example 7 was obtained, as shown in Table 3. On the other hand, although these comparative examples contained monoclinic Nb2TiO7 in the niobium-titanium-containing oxide phase, as shown in Table 2, the sodium content was high because no sodium removal treatment was performed during its synthesis. As a result, sodium ions originating from the oxide phase of the active material adsorbed onto the carboxyl groups of the carbon coating layer, preventing the battery from exhibiting the ability to adsorb metal ions such as cobalt, and thus failing to suppress self-discharge.

[0267] In Comparative Examples 3 and 5, when the niobium-titanium oxide phase was coated with a carbon coating layer, the carboxyl groups were carbonized and did not remain. As a result, self-discharge occurred in the battery due to the deposition of metal ions such as cobalt. In these comparative examples, the carbon coating layer did not contain carboxyl groups, so the amount of metal ion adsorption is shown as 0% in Table 4.

[0268] Comparative Example 4 is an orthorhombic sodium-containing niobium-titanium composite oxide (Li2Na) with a high sodium content. 1.5 Ti 5.5 Nb 0.5 O 14 Because niobium titanium was used in the oxide phase, the Na content was remarkably high. As a result, Na ions originating from the oxide phase of the active material adsorbed onto the carboxyl groups of the carbon coating layer, preventing the battery from exhibiting the ability to adsorb metal ions such as cobalt, and thus failing to suppress self-discharge. As shown in Table 4, the battery using the active material according to Comparative Example 4 and the Li2Na battery similar to Comparative Example 4 were compared. 1.5 Ti 5.5 Nb 0.5 O 14 The self-discharge rate was similar to that of the battery using the active material in Comparative Example 5, which did not retain carboxyl groups despite using the same material. Thus, when orthorhombic Na-containing titanium composite oxide is used as the main active material, the Na content is so high that self-discharge cannot be suppressed regardless of the presence or absence of carboxyl groups in the coating layer, even when fibrous carbon containing impurities such as Co is used. Note that Li2Na contains a large amount of Na as a constituent element, not just a trace amount. 1.5 Ti 5.5 Nb 0.5 O 14 Performing a desodium treatment on orthorhombic sodium-containing titanium composite oxides such as these is, of course, nonsensical.

[0269] The active material according to at least one embodiment and example described above comprises a niobium-titanium-containing oxide phase having a monoclinic structure and containing 0 ppm to 100 ppm of Na, and a carbon coating layer covering at least a portion thereof and containing 0.001% or more of carboxyl groups. This active material makes it possible to realize a secondary battery that exhibits high energy density and has excellent storage performance, a battery pack equipped with this secondary battery, and a vehicle equipped with this battery pack.

[0270] Several embodiments of the present invention are described below.

[0271] [1] A niobium-titanium-containing oxide phase having a monoclinic structure and containing Na, wherein the Na content is 0 ppm or more and 100 ppm or less, A carbon coating layer that covers at least a portion of the niobium-titanium-containing oxide phase and contains 0.001% or more of carboxyl groups An active material containing the active material.

[0272] [2] The niobium titanium-containing oxide phase is Nb2TiO7 phase, Nb 10 Ti2O 29 Phase, Nb 14 TiO 37 Phase, and Nb 24 TiO 64 The active material according to [1], comprising the crystal structure of at least one phase selected from the group consisting of phases.

[0273] [3] The active material according to [2], wherein the at least one phase contains at least one selected from the group consisting of K, Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al.

[0274] [4] The active material is 0.8m 2 / g or more 50m 2 The active material according to any one of [1] to [3], comprising active material particles having a BET specific surface area of ​​less than / g.

[0275] [5] An electrode containing the active material described in any one of [1] through [4].

[0276] [6] The electrode according to [5], wherein the electrode comprises an active material-containing layer comprising the active material and a conductive agent containing fibrous carbon.

[0277] [7] Positive electrode and, The negative electrode and, Electrolytes and A secondary battery comprising, The negative electrode is a secondary battery comprising the electrode described in [5] or [6].

[0278] [8] The secondary battery according to [7], wherein the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises a lithium phosphate oxide having an olivine structure.

[0279] [9] The secondary battery according to [7] or [8], wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprising at least one selected from the group consisting of a lithium manganese composite oxide having a spinel structure, a lithium cobalt composite oxide, a lithium nickel cobalt composite oxide, a lithium manganese cobalt composite oxide, and a lithium nickel cobalt manganese composite oxide.

[0280] A battery pack comprising a rechargeable battery as described in any one of

[10] [7] through [9].

[0281]

[11] External terminals for power supply, Protection circuit and The battery pack described in

[10] further includes:

[0282]

[12] The battery pack according to

[10] or

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

[0283]

[13] A vehicle equipped with one of the battery packs listed in

[10] through

[12] .

[0284]

[14] The vehicle according to

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

[0285] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0286] 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 tab, 4…Separator, 5…Positive electrode, 5a…Positive electrode current collector, 5b…Positive electrode active material containing layer, 6…Negative electrode terminal, 7…Positive electrode terminal, 21…Bus bar, 22…Positive electrode side lead, 22a…Other end, 23…Negative electrode side lead, 23a…Other end, 24…Adhesive tape, 31…Housing container, 32…Lid, 33…Protective sheet, 34…Printed circuit board, 35…Wiring, 40…Vehicle body, 41…Vehicle power supply, 42…Electrical control device, 43…External terminals, 44…Inverter, 45…Drive motor, 100…Secondary battery, 200…Battery pack, 200a…Battery pack, 200b…Battery pack, 200c…Battery pack, 300…Battery pack, 30 0a...Battery pack, 300b...Battery pack, 300c...Battery pack, 301a...Battery pack monitoring device, 301b...Battery pack monitoring device, 301c...Battery pack monitoring device, 342...Positive side connector, 343...Negative side connector, 345...Thermistor, 346...Protection circuit, 342a...Wiring, 343a...Wiring, 350...External terminal for energization, 352...Positive side terminal, 353...Negative side terminal, 348a...Positive side wiring, 348b...Negative side wiring, 400...Vehicle, 411...Battery management device, 412...Communication bus, 413...Positive terminal, 414...Negative terminal, 415...Switching device, 416...Current detection unit, 417...Negative input terminal, 418...Positive input terminal, L1...Connection line, L2...Connection line, W...Drive wheel.

Claims

1. A niobium-titanium-containing oxide phase having a monoclinic structure and containing Na, wherein the Na content is 10 ppm or more and 60 ppm or less, A carbon coating layer that covers at least a portion of the niobium-titanium-containing oxide phase and contains 0.001% or more of carboxyl groups An active material containing the active material.

2. The niobium titanium-containing oxide phase is Nb 2 TiO 7 phase, Nb 10 Ti 2 O 29 phase, Nb 14 TiO 37 phase, and Nb 24 TiO 64 The active material according to claim 1, comprising a crystal structure of at least one phase selected from the group consisting of phases.

3. The active material according to claim 2, wherein the at least one phase contains at least one selected from the group consisting of K, Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al.

4. The active material is 0.8 m ２ / g or more 50m ２ The active material according to any one of claims 1 to 3, comprising active material particles having a BET specific surface area of ​​less than 1 / g.

5. An electrode comprising the active material according to any one of claims 1 to 3.

6. The electrode according to claim 5, wherein the electrode comprises an active material-containing layer comprising the active material and a conductive agent containing fibrous carbon.

7. Positive electrode and, The negative electrode and, Electrolytes and A secondary battery comprising, The negative electrode is a secondary battery comprising the electrode described in claim 5.

8. The secondary battery according to claim 7, wherein the positive electrode includes a positive electrode active material, and the positive electrode active material includes a lithium phosphate oxide having an olivine structure.

9. The secondary battery according to claim 7, wherein the positive electrode includes a positive electrode active material, and the positive electrode active material includes at least one selected from the group consisting of a lithium manganese composite oxide having a spinel structure, a lithium cobalt composite oxide, a lithium nickel cobalt composite oxide, a lithium manganese cobalt composite oxide, and a lithium nickel cobalt manganese composite oxide.

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

11. External terminals for power supply, Protection circuit and The battery pack according to claim 10, further comprising:

12. The battery pack according to claim 10, comprising a plurality of the secondary batteries, wherein the secondary batteries are electrically connected in series, parallel, or a combination of series and parallel.

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

14. The vehicle according to claim 13, which includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

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