Electrode, secondary battery, battery pack and vehicle

Abstract

To provide an electrode capable of achieving a battery with low resistance and long life, and a secondary battery, a battery pack, and a vehicle each including the electrode.SOLUTION: An electrode according to one embodiment of the present invention includes a mixture layer containing a titanium-containing oxide and a conductive agent. The electrode satisfies the following formula (1). In the formula (1), L* is the brightness of the electrode measured on the basis of JISZ8722:2009. ri denotes the particle diameter of the mixture layer at the volume cumulative frequency dx (where i is a natural number from 1 to 9).SELECTED DRAWING: Figure 10

Description

[Technical Field]

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

[0002] Electrode materials in secondary batteries typically expand and contract in volume due to chemical reactions during charging and discharging. For example, in lithium-ion batteries, the volume of the active material changes as lithium ions are inserted and removed from the electrode active material. Negative electrode materials that do not contain lithium in an uncharged state tend to expand in volume as lithium ions are inserted during charging. The electrode itself also exhibits expansion in the thickness and plane directions, often maintaining this expanded state even after further discharging. If the active material itself is an insulating oxide particle, volume expansion can potentially damage the conductive paths between particles. Furthermore, cracks may occur in the active material particles, potentially creating isolated primary particles within the particles. These phenomena increase battery resistance and reduce capacity, and countermeasures must be taken in terms of the active material particle morphology and electrode composition.

[0003] Carbon materials are commonly used as negative electrode materials for lithium-ion batteries, and although their volume expands when lithium ions are inserted, the problem described above does not occur with highly conductive carbon materials. Furthermore, lithium titanate is a typical example of insulating oxide particles that has been commercially available, but the volume of the active material does not change during charging and discharging, so the problem described above does not occur.

[0004] In this sense, electrode designs that are different from conventional ones are required for insulating active materials that change volume during charging and discharging. For example, it has been proposed that the input / output characteristics and cycle characteristics of batteries can be improved by controlling the particle size and pore size distribution within specific ranges in electrodes that contain niobium-titanium composite oxide as the active material.

[0005] On the other hand, in order to optimize the battery characteristics, it is preferable to also control the composition and dispersion state of the conductive agent from the viewpoint of volume change during charge and discharge. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-177977 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide an electrode that can realize a battery with low resistance and long life, and a secondary battery, a battery pack, and a vehicle that include this electrode. [Means for solving the problem]

[0008] According to an embodiment, an electrode is provided that includes a mixture layer containing a titanium-containing oxide and a conductive agent. The titanium-containing oxide includes at least one of a monoclinic niobium titanium composite oxide and an orthorhombic titanium-containing composite oxide. The conductive agent includes acetylene black and carbon nanotubes. The electrode satisfies the following formula (1).

number

[0009] According to another embodiment, a battery pack is provided, which includes a secondary battery according to the embodiment.

[0010] According to another embodiment, a vehicle is provided, the vehicle including a secondary battery or a battery pack according to an embodiment. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment. [Figure 2] FIG. 2 is an enlarged cross-sectional view of part A of the secondary battery shown in FIG. [Figure 3] FIG. 10 is a partially cutaway perspective view schematically showing another example of a secondary battery according to an embodiment. [Figure 4] FIG. 4 is an enlarged cross-sectional view of part B of the secondary battery shown in FIG. [Figure 5] FIG. 1 is a perspective view schematically illustrating an example of a battery pack according to an embodiment. [Figure 6] FIG. 1 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment. [Figure 7] FIG. 7 is a block diagram showing an example of an electrical circuit of the battery pack shown in FIG. 6. [Figure 8] 1 is a cross-sectional view schematically illustrating an example of a vehicle according to an embodiment. [Figure 9] FIG. 10 is a diagram schematically illustrating another example of a vehicle according to an embodiment. [Figure 10] FIG. 2 is a graph showing the volume frequency particle size distribution of the mixture layer of the electrode of Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0012] The following describes the embodiments with reference to the drawings as appropriate. Note that common components throughout the embodiments are designated by the same reference numerals, and redundant explanations will be omitted. The drawings are schematic diagrams for explaining and facilitating understanding of the embodiments, and the shapes, dimensions, ratios, etc. may differ from those of actual devices. However, these can be appropriately modified in design, taking into consideration the following explanation and known techniques. (First embodiment) According to a first embodiment, an electrode is provided that includes a mixture layer (also referred to as an active material-containing layer) that includes an active material containing a titanium-containing oxide, a conductive agent, and a binder. The electrode satisfies the following formula (1):

[0013]

number

[0014] In formula (1), L* is the lightness of the electrode measured in accordance with JIS Z 8722:2009, and ri is the particle diameter at the volume cumulative frequency dx of the mixture layer. i is a natural number from 1 to 9. The volume cumulative frequency dx is the cumulative frequency on a volume basis accumulated from the smallest particle diameter in the mixture layer. 10% of the volume cumulative frequency is defined as d10, and the values ​​range from 10% to 90% in 10% increments. Therefore, the particle diameter at a volume cumulative frequency of 20% (d20) is r2, the particle diameter at a volume cumulative frequency of 30% (d30) is r3, the particle diameter at a volume cumulative frequency of 40% (d40) is r4, the particle diameter at a volume cumulative frequency of 50% (d50) is r5, the particle diameter at a volume cumulative frequency of 60% (d60) is r6, the particle diameter at a volume cumulative frequency of 70% (d70) is r7, the particle diameter at a volume cumulative frequency of 80% (d80) is r8, and the particle diameter at a volume cumulative frequency of 90% (d90) is r9.

[0015] The particle diameter of the mixture layer may be, for example, the particle diameter of the active material particles or the particle diameter of a mixture containing the active material particles and a conductive agent. An example of a mixture containing the active material particles and a conductive agent is one in which at least a portion of the surface of the active material particles is coated with a conductive agent. The active material particles may be single or independent primary particles, secondary particles formed by aggregation of primary particles, or a mixture of primary particles and secondary particles.

[0016] Equation (1) indicates that the relationship between 100 and the electrode lightness (L*) and the sum of the reciprocals of particle diameters at each volumetric frequency is between 7.0 and 11.0. Electrodes that satisfy equation (1) maintain the conductive path even when the active material volume changes during charging and discharging, and also suppress the generation of isolated primary particles due to the disintegration of secondary particles. The electrode lightness (L*) can be used as an indicator of the dispersibility of the conductive agent in electrodes composed of white or near-white active material particles and black or near-black conductive agents. A lower L* indicates better dispersibility, while a higher L* indicates poorer dispersion or insufficient conductive agent addition. The reciprocal sum of particle diameters at each volumetric frequency is an indicator of the total specific surface area of ​​the active material. Dividing the electrode lightness by the reciprocal sum of particle diameters yields a numerical index corresponding to the conductive agent coverage per unit active material surface area. A relationship between the value of this formula and the value of the conductive agent in this graph indicates that the insulating active material surface is sufficiently coated with a conductive agent and that the particle size of the active material is within an appropriate range. In this case, even if cracks occur in the active material secondary particles due to volume changes during charge and discharge, the secondary particles themselves are not large enough compared to the primary particles, making it difficult for isolated primary particles to form, thereby suppressing deterioration of battery performance. In addition, the electrode lightness L* is sufficiently low and the conductive agent uniformly coats the active material surface, forming good conductive paths between the active material particles and reducing battery resistance.

[0017] If the relationship between the sum of the reciprocals of particle diameters at each volume cumulative frequency and 100-electrode brightness L* is greater than 11.0, this indicates either an excessive amount of conductive agent has been added or the particle diameter of the active material is relatively large. If excessive conductive agent is added, there is concern that the electrode density will decrease, resulting in a decrease in the battery's energy density, or that input / output characteristics will deteriorate due to a decrease in the porosity within the electrode. Furthermore, if the particle diameter is large, isolated particles that cannot contribute to charging and discharging are more likely to occur near the center of the secondary particles due to volume changes caused by charging and discharging.

[0018] On the other hand, if the relationship between the above "100 - electrode lightness L*" and the "sum of the reciprocals of particle diameters at each volume cumulative frequency" is less than 7.0, it indicates that the electrode lightness L* is high and the electrode surface color is light (relatively closer to white). A light electrode surface color corresponds to an insufficient amount of conductive agent covering the active material surface, which tends to increase battery resistance. This phenomenon is not only observed when the amount of conductive agent added is low or dispersibility is low, but also occurs when the particle diameter of the active material is small even if these factors are the same. In either case, battery resistance increases when the amount of conductive agent covering the total surface area of ​​the active material is insufficient.

[0019] The numerator of the above equation is "100 - electrode brightness L*" rather than "electrode brightness L*" to more accurately represent the conductive agent coverage rate relative to the active material surface area. If "100 - electrode brightness L*" is used as the numerator, the value of the equation will be small if the conductive agent is poorly dispersed. Poor dispersion corresponds to a lack of conductive agent covering the active material surface. On the other hand, if the active material particle size is excessively small, the value of the equation will also be small, even though there is a similar lack of conductive agent covering the active material surface. If the numerator were "electrode brightness L*," the value of the equation would be large if the conductive agent was poorly dispersed, but small if the active material particle size was small. In this case, even though both are closely correlated phenomena, such as a lack of conductive agent covering the active material surface, the values ​​of the equation would show opposite trends, making it difficult to properly quantify the conductive agent coverage rate on the active material particle surface. For this reason, in this application, the relational expression obtained by dividing "100 - electrode brightness L*" by "the sum of the reciprocals of particle diameters at each volume cumulative frequency" is adopted as an index of the dispersion state.

[0020] The electrodes of the embodiment will be described in detail below.

[0021] The electrode may be a positive electrode or a negative electrode. The electrode may be an electrode for a secondary battery. The electrode may be applicable to batteries with non-aqueous solvents and batteries with aqueous solvents.

[0022] The electrode may further include a current collector on which the mixture layer is laminated or formed.

[0023] Examples of titanium-containing oxides include monoclinic niobium titanium composite oxide and orthorhombic titanium-containing composite oxide. One or more types of titanium-containing oxides can be used. The monoclinic niobium titanium composite oxide and the orthorhombic titanium-containing composite oxide are white, insulating oxide particles.

[0024] Specific examples of monoclinic niobium titanium composite oxides include Nb2TiO7, Nb2Ti2O9, and Nb 10 Ti2O 29 , Nb 14 TiO 37 and Nb 24 TiO 62 Examples of the substituted niobium titanium composite oxide include: The monoclinic niobium titanium composite oxide may be a substituted niobium titanium composite oxide in which at least a portion of Nb and / or Ti has been substituted with a different element. Examples of the substituted element include Na, K, Ca, Co, Ni, Si, P, V, Cr, Mo, Ta, Zr, Mn, Fe, Mg, B, Pb, and Al. The substituted niobium titanium composite oxide may contain one type of substituted element, or may contain two or more types of substituted elements.

[0025] Another example of monoclinic niobium titanium composite oxide is Li x Ti 1-y M3 y+z Nb 2-z O 7-δ Here, M3 is at least one selected from Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0≦x<5, 0≦y<1, 0≦z<2, and −0.3≦δ≦0.3.

[0026] As for orthorhombic titanium-containing composite oxides, Li 2+a M(I) 2-b Ti 6-c M(II) d O 14+σExamples of compounds represented by the formula (I) include compounds represented by the formula (I) above. Here, M(I) is at least one selected from the group consisting of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M(II) is at least one selected from the group consisting of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0≦a≦6, 0≦b<2, 0≦c<6, 0≦d<6, and -0.5≦σ≦0.5. Specific examples of orthorhombic titanium-containing composite oxides include Li 2+a Na2Ti6O 14 (0≦a≦6).

[0027] The average particle diameter (D50) of the active material is preferably 0.1 μm or more and 10 μm or less. This range allows for high lithium diffusivity while minimizing the effects of cracking in the active material particles on capacity loss and increased battery resistance, resulting in favorable battery characteristics. A more preferable average particle diameter (D50) range is 0.5 μm or more and 3 μm or less, achieving an excellent balance between input / output characteristics and lifespan characteristics. On the other hand, if the average particle diameter (D50) is less than 0.1 μm, the surface area of ​​the active material becomes excessively large, potentially requiring the addition of excessive amounts of conductive agent to provide conductivity, or resulting in particles that are incapable of providing conductivity even when added. If the average particle diameter (D50) is greater than 10 μm, the lithium diffusion length within the particles becomes excessive, potentially resulting in reduced input / output characteristics, as well as increased susceptibility to capacity loss and increased battery resistance due to cracking in the active material particles.

[0028] The conductive agent can improve current collection performance and reduce contact resistance between the active material and the current collector. Examples of conductive agents include carbon black such as acetylene black, graphite, vapor-grown carbon fiber (VGCF), and carbonaceous materials such as single-walled carbon nanotubes and multi-walled carbon nanotubes. One of these may be used as the conductive agent, or two or more may be used in combination. The conductive agent may or may not be integrated onto the surface of the active material particles. Preferred conductive agents include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. Such conductive agents can impart uniform conductivity to the surface of active materials with relatively small particle diameters. The single-walled carbon nanotubes and multi-walled carbon nanotubes can each have an average fiber diameter of 1 nm to 30 nm and an average fiber length of 2 μm to 50 μm. Carbon nanotubes with an average fiber diameter and average fiber length within the above ranges can form an excellent conductive path on the surface of insulating active material particles. If the average fiber diameter is less than 1 nm, the fibers tend to aggregate easily and dispersion stability is difficult to maintain, resulting in processability problems. If the average fiber diameter is greater than 30 nm, the amount added tends to be excessive to form a conductive path on the active material surface. Furthermore, if the average fiber length is less than 2 μm, it is difficult to form a long conductive path. Conversely, if the average fiber length is greater than 50 μm, the fluidity of the coating liquid decreases, resulting in poor coatability, resulting in processability problems. The binder is blended to fill gaps between the dispersed active material and bind the active material and the current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-based rubber, styrene-butadiene rubber (SBR), ethylene-propylene rubber, polyacrylic acid compounds, polyamide-imide compounds, carboxymethyl cellulose (CMC), and CMC salts. One of these may be used as the binder, or two or more may be used in combination. When water is used as the solvent for the coating liquid, the addition of carboxymethyl cellulose is preferred from the viewpoints of thickening the coating liquid and stabilizing the dispersion of the active material and conductive agent. A binder containing at least one of SBR and CMC is suitable for mass production of the electrode of the embodiment. The blending ratios of the active material particles, conductive agent, and binder in the mixture layer (active material-containing layer) can be appropriately changed depending on the application of the electrode, but are, for example, as follows: The mixture layer preferably contains the active material particles, conductive agent, and binder in proportions of 70% by weight to 96% by weight, 2% by weight to 28% by weight, and 2% by weight to 28% by weight, respectively. By setting the amount of conductive agent to 2% by weight or more, the current collection performance of the mixture layer can be improved. Furthermore, by setting the amount of binder to 2% by weight or more, sufficient binding between the mixture layer and the current collector can be achieved, resulting in excellent cycle performance. On the other hand, it is preferable to set the amount of conductive agent, binder, and thickener to 28% by weight or less, respectively, in order to achieve high capacity.

[0029] The current collector is made of a material that is electrochemically stable at the potential at which lithium (Li) is inserted into and extracted from the active material. The potential at which lithium (Li) is inserted into and extracted from the active material is, for example, a potential nobler than 1.0 V. For example, when the electrode according to the embodiment functions as a negative electrode, the current collector is preferably made of copper, nickel, stainless steel, aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector having such a thickness can balance the strength and weight of the electrode.

[0030] When aluminum or an aluminum alloy is used as the current collector, the single-sided electrode tends to be easily warped, so the effect of improving cycle life characteristics by providing the mixture layer according to the embodiment can be more effectively enjoyed. Note that the current collector may include a portion on its surface where the mixture layer is not formed. This portion can function as a current collecting tab. An electrode can be fabricated by preparing a slurry in which the active material, conductive agent, and binder are dispersed in a solvent, applying the slurry to a current collector, drying, and pressing. Regarding pressing, the resulting electrode density varies depending on the tap density of the active material and the electrode composition, such as the conductive agent, but generally, pressing increases the uniformity of the coated surface, and compacting to a degree that gives it a gloss is preferred from the viewpoint of reducing the resistance of the ohmic resistance component. The slurry dispersion process can be carried out, for example, by the following method. To uniformly disperse a conductive agent on the surface of insulating active material particles such as titanium-containing oxide, a coating liquid dispersion process is required that breaks down the conductive agent's agglomeration, wets the solvent, and achieves a uniform dispersion state, maintaining a stable dispersion. In particular, the dispersion process significantly affects the dispersion state and battery characteristics of conductive agents with fine particles and high aspect ratios, such as carbon nanotubes. When using a conductive agent such as carbon nanotubes, the dispersibility of the carbon nanotubes can be improved by preparing a dispersion in which the carbon nanotubes are dispersed in a solvent. Examples of dispersion methods include ultrasonic waves and wet high-pressure jet mills, which can break down the agglomeration of carbon nanotube fibers and achieve uniform dispersion. It is also preferable to add a dispersant to stabilize the dispersion during dispersion. The dispersant can be selected based on the slurry solvent; for example, carboxymethyl cellulose and polyvinylpyrrolidone can be used in aqueous solvents. Adding these dispersants can maintain a good dispersion state over the long term.

[0031] In addition to preparing the dispersion liquid as described above, powdered carbon nanotubes and active material can be uniformly dispersed by mixing and dispersing them under high shear or by applying physical shear using media. Examples of the dispersion method mentioned above include a dispersion mechanism such as FILMICS, which uses a high-speed rotating rotor and the stirring energy generated within the thin film space on the device wall for dispersion. When dispersing using FILMICS, mixing carbon nanotubes and active material powder is preferable to dispersing carbon nanotubes alone, as this makes it easier to break down the agglomerates of carbon nanotubes themselves and achieves high dispersibility. An example of the latter is dispersion using a planetary-rotating mixer, where spherical beads made of glass, zirconia, or alumina are mixed as media. Alternatively, dispersion using a bead mill, in which the coating liquid is pumped into a container with a rotating disk filled with the above media, is also effective.

[0032] The methods for measuring the lightness L* of the electrode and the volume cumulative frequency particle size distribution of the mixture layer are described below. <Method for measuring the electrode surface brightness L*> The titanium-containing oxide can be an insulating white active material. The dispersibility of the conductive agent in an electrode containing the insulating white active material and the conductive agent can be evaluated by measuring the brightness of the electrode based on the measurement method described in JIS Z 8722:2009. While the evaluation can also be performed on the slurry, it is preferable to measure the electrode because it allows the measurement of not only the manufacturing process but also the finished battery product.

[0033] The measuring device can be a spectrophotometric colorimeter that measures reflectance at wavelengths across the entire visible light range and calculates tristimulus values. The measured tristimulus values ​​are converted into the L*a*b* color system, and the resulting lightness L* value can be used as an index of the dispersibility of the conductive agent. <Pretreatment of sample for brightness measurement> The sample used for measuring brightness can be an electrode not yet installed in a battery, or an electrode removed from a disassembled battery. When removing an electrode from a battery, it is washed with an organic solvent to remove any remaining lithium salt. The amount of remaining lithium salt can be sufficiently reduced by first impregnating the electrode with a cyclic carbonate, which has high solubility for lithium salt, and then impregnating it with a chain carbonate and washing it. After impregnation, the solvent is removed by reducing the pressure under vacuum. <Method for measuring particle size distribution in the mixture layer> The particle size distribution of the electrode's mixture layer can be measured by redissolving the mixture layer. To avoid overestimating the particle size due to aggregates formed by the binder component, it is preferable to dissolve and remove the binder beforehand. Specifically, the electrode is soaked in N-methylpyrrolidone (NMP) and water for 10 minutes while irradiating with ultrasound. The electrode that peels more from the current collector is used for redissolving the mixture layer. The amount of peeling can be measured by measuring the weight change before and after dissolution for any electrode sample. If the amount of peeling is greater with the water solvent, the sample solution must be pretreated. This is because aqueous slurries often contain binders that form emulsions and are difficult to redissolve in water. For pretreatment, an electrode with a mixture layer area of ​​2 cm x 2 cm is soaked in a 1:9 volumetric toluene / water solution while irradiating with ultrasound for 10 minutes. Thereafter, the aqueous phase, which is the lower layer of the solution that has been left to stand, is removed and redispersed to eliminate the influence of sedimentation, after which the particle size distribution is measured.

[0034] According to the first embodiment described above, an electrode is provided that includes a mixture layer containing a titanium-containing oxide, a conductive agent, and a binder, and satisfies formula (1). The electrode of the embodiment has an appropriate particle size distribution in the mixture layer and an appropriate composition and dispersion state of the conductive agent, so that an increase in battery resistance due to volume changes during charge and discharge can be suppressed, a capacity decrease can be suppressed, and a battery with low resistance and long life can be realized. (Second embodiment) According to a second embodiment, there is provided a secondary battery including a negative electrode, a positive electrode, and an electrolyte. This secondary battery includes the electrode according to the first embodiment as the positive electrode or the negative electrode.

[0035] The secondary battery may further include a separator disposed between the positive electrode and the negative electrode. The negative electrode, positive electrode, and separator may constitute an electrode group. The electrolyte may be held in the electrode group. The secondary battery may further include an exterior member that houses the electrode group and the electrolyte. The secondary battery may further include a negative electrode terminal electrically connected to the negative electrode and a positive electrode terminal electrically connected to the positive electrode.

[0036] The secondary battery may be, for example, a lithium ion secondary battery. The secondary battery also includes a non-aqueous electrolyte secondary battery containing a non-aqueous electrolyte.

[0037] The negative electrode, positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal will be described in detail below. The following example is an example in which the electrode of the embodiment is applied to a negative electrode.

[0038] (1) Negative electrode The negative electrode included in the secondary battery according to the second embodiment can be, for example, the electrode described in the first embodiment.

[0039] (2) Positive electrode The positive electrode may include a positive electrode current collector and a positive electrode mixture layer (also referred to as a positive electrode active material-containing layer). The positive electrode mixture layer may be formed on one or both sides of the positive electrode current collector. The positive electrode mixture layer may include a positive electrode active material, and optionally a conductive agent and a binder.

[0040] The positive electrode active material may be, for example, an oxide or a sulfide. The positive electrode may contain one type of compound alone or two or more types of compounds in combination as the positive electrode active material. Examples of oxides and sulfides include compounds that can insert and extract Li or Li ions.

[0041] Examples of such compounds include manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, and lithium manganese composite oxides (e.g., Li x Mn2O4 or Li xMnO2; 0 < x ≤ 1), lithium nickel composite oxide (e.g., Li x NiO2; 0 < x ≤ 1), lithium cobalt composite oxide (e.g., Li x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxide (e.g., Li x Ni 1-y Co y [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​y O4; where 0 < x ≤ 1 and 0 < y < 2), lithium manganese cobalt composite oxide (e.g., Li x Mn y Co 1-y O2; where 0 < x ≤ 1 and 0 < y < 1), lithium iron phosphate (e.g., Li x FePO4; where 0 < x ≤ 1), and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; where 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, and y + z < 1) are included. When these compounds are used as the positive electrode active material, the positive electrode potential can be increased.

[0043] When a room-temperature molten salt is used as the electrolyte of the battery, it is preferable to use a positive electrode active material containing lithium iron phosphate, Li x VPO4F (0 ≤ x ≤ 1), lithium manganese composite oxide, lithium nickel composite oxide, lithium nickel cobalt composite oxide, or a mixture thereof. Since these compounds have low reactivity with the room-temperature molten salt, the cycle life can be improved. Details of the room-temperature molten salt will be described later.

[0044] The primary particle size of the positive electrode active material is preferably 100 nm or more and 1 μm or less. A positive electrode active material with a primary particle size of 100 nm or more is easy to handle in industrial production. A positive electrode active material with a primary particle size of 1 μm or less can allow the solid-state diffusion of lithium ions to proceed smoothly.

[0045] The specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less. A positive electrode active material with a specific surface area of 0.1 m 2 / g or more can sufficiently secure the sites for lithium ion intercalation and deintercalation. A positive electrode active material with a specific surface area of 10 m 2 / g or less is easy to handle in industrial production and can ensure good charge-discharge cycle performance.

[0046] The binder is blended to fill gaps between the dispersed positive electrode active material and to bind the positive electrode active material and the positive electrode current collector. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine-containing rubber, polyacrylic acid compounds and imide compounds, carboxy methyl cellulose (CMC), and CMC salts. These binders may be used alone or in combination. The conductive agent is blended to improve current collection performance and reduce contact resistance between the positive electrode active material and the positive electrode current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these may be used as the conductive agent, or two or more may be used in combination as the conductive agent. The conductive agent may also be omitted.

[0047] In the positive electrode mixture layer (active material-containing layer), the positive electrode active material and binder are preferably mixed in proportions of 80% by weight to 98% by weight and 2% by weight to 20% by weight, respectively.

[0048] By using a binder amount of 2% by weight or more, sufficient electrode strength can be obtained. Furthermore, the binder can function as an insulator. Therefore, by using a binder amount of 20% by weight or less, the amount of insulator contained in the electrode is reduced, thereby reducing internal resistance.

[0049] When a conductive agent is added, the positive electrode active material, binder, and conductive agent are preferably blended in proportions of 77% by weight or more and 95% by weight or less, 2% by weight or more and 20% by weight or less, and 3% by weight or more and 15% by weight or less, respectively.

[0050] By setting the amount of conductive agent to 3% by weight or more, the above-mentioned effects can be achieved. Furthermore, by setting the amount of conductive agent to 15% by weight or less, the proportion of conductive agent in contact with the electrolyte can be reduced. This low proportion can reduce decomposition of the electrolyte during high-temperature storage.

[0051] 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.

[0052] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by weight or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by weight or less.

[0053] The positive electrode current collector may also include a portion on the surface of which the positive electrode mixture layer is not formed, and this portion can function as a positive electrode current collecting tab.

[0054] The positive electrode can be fabricated, 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 a mixture layer and the current collector. After that, this laminate is pressed. In this manner, the positive electrode is fabricated.

[0055] Alternatively, the positive electrode may be prepared by the following method: First, an active material, a conductive agent, and a binder are mixed to obtain a mixture, and then the mixture is formed into pellets. The pellets are then placed on a current collector to obtain a positive electrode.

[0056] (3) Electrolyte The electrolyte may be, for example, a liquid nonaqueous electrolyte or a gel nonaqueous electrolyte. The liquid nonaqueous electrolyte is prepared by dissolving an electrolyte salt as a solute in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0057] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO), lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoride (LiAsF), lithium trifluoromethanesulfonate (LiCFSO), and lithium bistrifluoromethylsulfonylimide (LiN(CFSO)), and mixtures thereof. The electrolyte salt is preferably one that is difficult to oxidize even at high potentials, and LiPF is most preferred.

[0058] Examples of organic solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); linear carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); linear ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or in combination.

[0059] The gel-like non-aqueous electrolyte is prepared by combining a liquid non-aqueous electrolyte with a polymeric material, such as polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or a mixture thereof.

[0060] Alternatively, in addition to liquid nonaqueous electrolytes and gel nonaqueous electrolytes, room temperature molten salts containing lithium ions (ionic melts), polymer solid electrolytes, inorganic solid electrolytes, and the like may be used as the nonaqueous electrolyte.

[0061] Room-temperature molten salts (ionic melts) refer to organic salts consisting of a combination of organic cations and anions that can exist as a liquid at room temperature (15°C or higher and 25°C or lower). Room-temperature molten salts include room-temperature molten salts that exist as a liquid on their own, room-temperature molten salts that become liquid when mixed with an electrolyte salt, room-temperature molten salts that become liquid when dissolved in an organic solvent, and mixtures of these. Generally, the melting point of room-temperature molten salts used in secondary batteries is 25°C or lower. Furthermore, organic cations generally have a quaternary ammonium skeleton. (4) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a synthetic resin nonwoven fabric. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene, because these porous films melt at a certain temperature and can interrupt current.

[0062] (5) Exterior materials The exterior member may be, for example, a container made of a laminate film or a metal container.

[0063] The thickness of the laminate film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0064] The laminate film is a multilayer film containing multiple resin layers and metal layers interposed between the resin layers. The resin layers include polymeric materials such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). The metal layers are preferably made of aluminum foil or aluminum alloy foil to reduce weight. The laminate film can be molded into the shape of the exterior component by sealing it by heat fusion.

[0065] The thickness of the wall of the metal container is, for example, 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0066] The metal container is made of, for example, aluminum or an aluminum alloy. The aluminum alloy preferably contains elements such as magnesium, zinc, and silicon. If the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, the content of these metals is preferably 100 mass ppm or less.

[0067] The shape of the exterior member is not particularly limited. The shape of the exterior member may be, for example, flat (thin), rectangular, cylindrical, coin-shaped, or button-shaped. The exterior member can be appropriately selected depending on the battery dimensions and the intended use of the battery.

[0068] (6) Negative terminal The negative electrode terminal can be formed from a material that is electrochemically stable at the Li absorption / desorption potential of the negative electrode active material and has electrical conductivity. Specifically, the material for the negative electrode terminal can be copper, nickel, stainless steel, aluminum, or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum or an aluminum alloy is preferably used as the material for the negative electrode terminal. The negative electrode terminal is preferably made of the same material as the negative electrode current collector to reduce contact resistance with the negative electrode current collector.

[0069] (7) Positive terminal The positive electrode terminal has a potential range of 3V to 4.5V relative to the redox potential of lithium (vs. Li / Li + ) and can be formed from a material that is electrically stable and conductive. Examples of materials for the positive electrode terminal include aluminum and aluminum alloys containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. The positive electrode terminal is preferably formed from the same material as the positive electrode current collector in order to reduce contact resistance with the positive electrode current collector.

[0070] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0071] Fig. 1 is a cross-sectional view schematically illustrating an example of a secondary battery according to an embodiment, Fig. 2 is an enlarged cross-sectional view of part A of the secondary battery shown in Fig. 1.

[0072] 1 and 2 includes a bag-shaped exterior member 2 shown in Fig. 1 and 2, an electrode group 1 shown in Fig. 1, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the bag-shaped exterior member 2. The electrolyte (not shown) is held in the electrode group 1.

[0073] The bag-shaped exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0074] As shown in Fig. 1, the electrode group 1 is a flat wound electrode group. As shown in Fig. 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.

[0075] The negative electrode 3 includes a negative electrode current collector 3a and a negative electrode mixture layer (active material-containing layer) 3b. In the portion of the negative electrode 3 that is located at the outermost shell of the wound electrode group 1, the negative electrode mixture layer 3b is formed only on the inner surface side of the negative electrode current collector 3a, as shown in Fig. 2. In the other portions of the negative electrode 3, the negative electrode mixture layer 3b is formed on both sides of the negative electrode current collector 3a.

[0076] The positive electrode 5 includes a positive electrode current collector 5a and positive electrode mixture layers (positive electrode active material-containing layers) 5b formed on both sides of the positive electrode current collector 5a.

[0077] As shown in FIG. 1, the negative electrode terminal 6 and the positive electrode terminal 7 are located near the outer peripheral edge of the wound electrode group 1. The negative electrode terminal 6 is connected to a portion located at the outermost shell of the negative electrode current collector 3a. The positive electrode terminal 7 is connected to a portion located at the outermost shell of the positive electrode current collector 5a. The negative electrode terminal 6 and the positive electrode terminal 7 extend to the outside from an opening of the bag-shaped exterior member 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped exterior member 2, and the opening is closed by heat sealing this.

[0078] The secondary battery according to the embodiment is not limited to the secondary battery having the configuration shown in FIGS. 1 and 2, but may also be a battery having the configuration shown in FIGS. 3 and 4, for example.

[0079] Fig. 3 is a partially cutaway perspective view schematically showing another example of a secondary battery according to an embodiment, Fig. 4 is an enlarged cross-sectional view of part B of the secondary battery shown in Fig. 3. 3 and 4 includes an electrode group 1 shown in Fig. 3 and 4, an exterior member 2 shown in Fig. 3, and an electrolyte (not shown). The electrode group 1 and the electrolyte are housed in the exterior member 2. The electrolyte is held in the electrode group 1.

[0080] The exterior member 2 is made of a laminate film including two resin layers and a metal layer interposed between them.

[0081] The electrode group 1 is a laminated electrode group, as shown in Fig. 4. The laminated electrode group 1 has a structure in which negative electrodes 3 and positive electrodes 5 are alternately laminated with separators 4 interposed therebetween.

[0082] The electrode group 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 includes a negative electrode current collector 3a and a negative electrode mixture layer 3b supported on both sides of the negative electrode current collector 3a. The electrode group 1 also includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 includes a positive electrode current collector 5a and a positive electrode mixture layer 5b supported on both sides of the positive electrode current collector 5a.

[0083] The negative electrode current collector 3a of each negative electrode 3 includes a portion 3c on one side where the negative electrode mixture layer 3b is not supported on any surface. This portion 3c functions as a negative electrode current collector tab. As shown in FIG. 4, the portion 3c functioning as the negative electrode current collector tab does not overlap with the positive electrode 5. The multiple negative electrode current collector tabs (portions 3c) are electrically connected to a strip-shaped negative electrode terminal 6. The tip of the strip-shaped negative electrode terminal 6 is pulled out to the outside of the exterior member 2.

[0084] Although not shown, the positive electrode current collector 5a of each positive electrode 5 includes a portion on one side where the positive electrode mixture layer 5b is not supported on any surface. This portion functions as a positive electrode current collector tab. Like the negative electrode current collector tab (portion 3c), the positive electrode current collector tab does not overlap with the negative electrode 3. The positive electrode current collector tab is located on the opposite side of the electrode group 1 from the negative electrode current collector tab (portion 3c). The positive electrode current collector tab is electrically connected to a strip-shaped positive electrode terminal 7. The tip of the strip-shaped positive electrode terminal 7 is located on the opposite side from the negative electrode terminal 6 and is drawn out to the outside of the exterior member 2.

[0085] The secondary battery according to the embodiment includes the electrode according to the embodiment, and therefore, the secondary battery can suppress an increase in resistance and improve the capacity retention rate during charge / discharge cycles.

[0086] (Third embodiment) According to a third embodiment, there is provided a battery pack, which includes a plurality of secondary batteries according to the embodiment.

[0087] In the battery pack according to the third embodiment, the cells may be electrically connected in series or in parallel, or may be connected in a combination of series and parallel.

[0088] Next, an example of a battery pack according to a third embodiment will be described with reference to the drawings.

[0089] Fig. 5 is a perspective view schematically showing an example of a battery pack according to the third embodiment. The battery pack 200 shown in Fig. 5 includes five cells 100a to 100e, four bus bars 21, a positive electrode lead 22, and a negative electrode lead 23. Each of the five cells 100a to 100e is a secondary battery according to the embodiment.

[0090] For example, the bus bar 21 connects 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 bus bars 21. That is, the battery pack 200 in FIG. 5 is a five-series battery pack.

[0091] 5, the positive electrode terminal 7 of the leftmost cell 100a of the five cells 100a to 100e is connected to a positive electrode lead 22 for external connection. Also, the negative electrode terminal 6 of the rightmost cell 100e of the five cells 100a to 100e is connected to a negative electrode lead 23 for external connection.

[0092] The battery pack according to the embodiment includes the secondary battery according to the embodiment, and therefore, this battery pack can suppress an increase in resistance and exhibit excellent life performance.

[0093] (Fourth embodiment) According to a fourth embodiment, a battery pack is provided. The battery pack includes a battery assembly according to an embodiment. The battery pack may include a secondary battery according to an embodiment instead of the battery assembly according to an embodiment.

[0094] The battery pack according to the embodiment may further include a protection circuit. The protection circuit has a function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device (e.g., electronic device, automobile, etc.) that uses the battery pack as a power source may be used as the protection circuit for the battery pack.

[0095] The battery pack according to the embodiment may further include an external terminal for current supply. The external terminal for current supply is for outputting current from the secondary battery to the outside and / or inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminal for current supply. When charging the battery pack, charging current (including regenerative energy from the power of an automobile or the like) is supplied to the battery pack through the external terminal for current supply.

[0096] Next, an example of a battery pack according to an embodiment will be described with reference to the drawings.

[0097] Fig. 6 is an exploded perspective view schematically showing an example of a battery pack according to an embodiment, and Fig. 7 is a block diagram showing an example of an electric circuit of the battery pack shown in Fig. 6.

[0098] The battery pack 300 shown in FIGS. 6 and 7 includes a container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed wiring board 34, wiring 35, and an insulating plate (not shown).

[0099] The storage container 31 shown in Fig. 6 is a bottomed, prismatic container having a rectangular bottom. The storage container 31 is configured to be able to accommodate a protective sheet 33, a battery pack 200, a printed wiring board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the storage container 31 to accommodate the battery pack 200 and other components. Although not shown, the storage container 31 and the lid 32 are provided with openings or connection terminals for connection to external devices and the like.

[0100] The battery pack 200 includes a plurality of cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0101] The cell 100 has a structure shown in FIGS. 1 and 2. At least one of the cells 100 is a secondary battery according to the embodiment. The cells 100 are stacked in a manner that aligns the negative electrode terminal 6 and the positive electrode terminal 7 extending outward, facing in the same direction. The cells 100 are electrically connected in series as shown in FIG. 7. The cells 100 may be electrically connected in parallel, or may be connected in a combination of series and parallel connections. When the cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0102] The adhesive tape 24 fastens the plurality of cells 100 together. Heat-shrinkable tape may be used to secure the plurality of cells 100 together instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both side surfaces of the battery pack 200, and the heat-shrinkable tape is wrapped around the cells 100, and the heat-shrinkable tape is then thermally shrunk to bind the plurality of cells 100 together.

[0103] One end of the positive electrode lead 22 is connected to the positive electrode terminal 7 of the cell 100 located in the bottom layer of the stack of cells 100. One end of the negative electrode lead 23 is connected to the negative electrode terminal 6 of the cell 100 located in the top layer of the stack of cells 100.

[0104] The printed wiring board 34 is installed along one of the shorter sides of the inner surface of the container 31. The printed wiring board 34 includes a positive connector 341, a negative connector 342, a thermistor 343, a protection circuit 344, wires 345 and 346, an external terminal 347 for supplying current, a positive wire 348a, and a negative wire 348b. One main surface of the printed wiring board 34 faces the surface of the battery pack 200 from which the negative terminal 6 and the positive terminal 7 extend. An insulating plate (not shown) is interposed between the printed wiring board 34 and the battery pack 200.

[0105] A through hole is provided in the positive electrode connector 341. The other end of the positive electrode lead 22 is inserted into this through hole, thereby electrically connecting the positive electrode connector 341 and the positive electrode lead 22. A through hole is provided in the negative electrode connector 342. The other end of the negative electrode lead 23 is inserted into this through hole, thereby electrically connecting the negative electrode connector 342 and the negative electrode lead 23.

[0106] The thermistor 343 is fixed to one main surface of the printed wiring board 34. The thermistor 343 detects the temperature of each of the cells 100 and transmits the detection signal to the protection circuit 344.

[0107] The external terminal 347 for applying current is fixed to the other main surface of the printed wiring board 34. The external terminal 347 for applying current is electrically connected to a device located outside the battery pack 300.

[0108] The protection circuit 344 is fixed to the other main surface of the printed wiring board 34. The protection circuit 344 is connected to an external terminal 347 for supplying current via a positive side wiring 348a. The protection circuit 344 is connected to an external terminal 347 for supplying current via a negative side wiring 348b. The protection circuit 344 is also electrically connected to the positive electrode side connector 341 via a wiring 345. The protection circuit 344 is electrically connected to the negative electrode side connector 342 via a wiring 346. The protection circuit 344 is also electrically connected to each of the plurality of single cells 100 via the wiring 35.

[0109] The protective sheet 33 is disposed on both inner surfaces of the long sides of the container 31 and on the inner surface of the short side that faces the printed wiring board 34 across the battery pack 200. The protective sheet 33 is made of, for example, resin or rubber.

[0110] The protection circuit 344 controls charging and discharging of the plurality of cells 100. Furthermore, the protection circuit 344 cuts off the electrical connection between the protection circuit 344 and an external terminal 347 for supplying electricity to an external device, based on a detection signal transmitted from the thermistor 343 or a detection signal transmitted from each cell 100 or the battery pack 200.

[0111] An example of the detection signal transmitted from the thermistor 343 is a signal indicating that the temperature of the cell 100 is equal to or higher than a predetermined temperature. An example of the detection signal transmitted from each cell 100 or the battery pack 200 is a signal indicating that overcharge, overdischarge, or overcurrent of the cell 100 is detected. When detecting overcharge or the like for each cell 100, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each cell 100.

[0112] The protection circuit 344 may be a circuit included in a device (such as an electronic device or an automobile) that uses the battery pack 300 as a power source.

[0113] Furthermore, as described above, the battery pack 300 includes the external terminal 347 for current application. Therefore, the battery pack 300 can output current from the battery assembly 200 to an external device and input current from the external device to the battery assembly 200 via the external terminal 347 for current application. In other words, when the battery pack 300 is used as a power source, the current from the battery assembly 200 is supplied to the external device through the external terminal 347 for current application. When the battery pack 300 is charged, a charging current from the external device is supplied to the battery pack 300 through the external terminal 347 for current application. When the battery pack 300 is used as an in-vehicle battery, regenerative energy from the vehicle's power can be used as the charging current from the external device.

[0114] The battery pack 300 may include a plurality of assembled batteries 200. In this case, the assembled batteries 200 may be connected in series, in parallel, or in a combination of series and parallel connections. The printed wiring board 34 and the wiring 35 may be omitted. In this case, the positive electrode lead 22 and the negative electrode lead 23 may be used as external terminals for current flow.

[0115] Such a battery pack is used in applications requiring excellent cycle performance when drawing a large current, for example. Specifically, this battery pack is used, for example, as a power source for electronic devices, a stationary battery, or an on-board battery for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an on-board battery.

[0116] The battery pack according to the embodiment includes the secondary battery according to the embodiment or the battery assembly according to the embodiment, and therefore the battery pack can suppress an increase in resistance and exhibit long life performance.

[0117] (Fifth embodiment) According to a fifth embodiment, a vehicle is provided, which is equipped with a battery pack according to the embodiment.

[0118] In the vehicle according to the embodiment, the battery pack recovers, for example, regenerative energy for powering the vehicle, and the vehicle may include a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

[0119] Examples of vehicles according to the embodiment include two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, power-assisted bicycles, and railroad cars.

[0120] The mounting position of the battery pack in the vehicle according to the embodiment is not particularly limited. For example, when the battery pack is mounted in an automobile, the battery pack can be mounted in the engine compartment, the rear of the vehicle body, or under the seat of the vehicle.

[0121] A vehicle according to the embodiment may be equipped with a plurality of battery packs. In this case, the battery packs may be electrically connected in series, in parallel, or in a combination of series and parallel connections.

[0122] Next, an example of a vehicle according to an embodiment will be described with reference to the drawings.

[0123] FIG. 8 is a cross-sectional view that schematically illustrates an example of a vehicle according to an embodiment.

[0124] A vehicle 400 shown in Fig. 8 includes a vehicle body 40 and a battery pack 300 according to the fourth embodiment. In the example shown in Fig. 8, the vehicle 400 is a four-wheeled automobile.

[0125] The vehicle 400 may be equipped with a plurality of battery packs 300. In this case, the battery packs 300 may be connected in series, in parallel, or in a combination of series and parallel connections.

[0126] 8 illustrates an example in which the battery pack 300 is mounted in an engine compartment located in the front of the vehicle body 40. As described above, the battery pack 300 may be mounted, for example, at the rear of the vehicle body 40 or under a seat. This battery pack 300 can be used as a power source for the vehicle 400. In addition, this battery pack 300 can recover regenerative energy for powering the vehicle 400.

[0127] Next, an embodiment of the vehicle according to the embodiment will be described with reference to FIG.

[0128] 9 is a diagram schematically illustrating an example of a vehicle according to the embodiment. A vehicle 400 illustrated in FIG. 9 is an electric vehicle.

[0129] The vehicle 400 shown in FIG. 9 includes a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a higher-level control means 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.

[0130] Vehicle 400 has vehicle power supply 41 mounted, for example, in the engine compartment, the rear of the vehicle body, or under the seat. Note that in vehicle 400 shown in Fig. 9, the mounting location of vehicle power supply 41 is shown schematically.

[0131] The vehicle power supply 41 includes a plurality of (for example, three) battery packs 300a, 300b, and 300c, a battery management unit (BMU) 411, and a communication bus 412.

[0132] The three battery packs 300a, 300b, and 300c are electrically connected in series. The battery pack 300a includes an assembled battery 200a and an assembled battery monitoring device 301a (e.g., VTM: Voltage Temperature Monitoring). The battery pack 300b includes an assembled battery 200b and an assembled battery monitoring device 301b. The battery pack 300c includes an assembled battery 200c and an assembled battery monitoring device 301c. The battery packs 300a, 300b, and 300c can each be removed independently and replaced with another battery pack 300.

[0133] Each of the battery packs 200a to 200c includes a plurality of unit cells connected in series. At least one of the unit cells is the secondary battery according to the second embodiment. Each of the battery packs 200a to 200c is charged and discharged via a positive terminal 413 and a negative terminal 414.

[0134] In order to collect information related to the maintenance of the vehicle power supply 41, the battery management device 411 communicates with the assembled battery monitoring devices 301a to 301c and collects information related to the voltage and temperature of the cells 100 included in the assembled batteries 200a to 200c included in the vehicle power supply 41.

[0135] A communication bus 412 is connected between the battery management unit 411 and the assembled battery monitoring units 301a to 301c. The communication bus 412 is configured so that one set of communication lines is shared by multiple nodes (a battery management unit and one or more assembled battery monitoring units). The communication bus 412 is configured based on, for example, the CAN (Control Area Network) standard.

[0136] The battery pack monitoring devices 301a to 301c measure the voltage and temperature of each of the cells constituting the battery packs 200a to 200c based on commands received through communication from the battery management device 411. However, the temperature can be measured at only a few locations per battery pack, and it is not necessary to measure the temperature of all the cells.

[0137] Vehicle power supply 41 may also have an electromagnetic contactor (for example, switch device 415 shown in FIG. 9) for connecting and disconnecting positive terminal 413 and negative terminal 414. Switch device 415 includes a pre-charge switch (not shown) that is turned on when battery packs 200a to 200c are being charged, and a main switch (not shown) that is turned on when battery output is being supplied to a load. The pre-charge switch and main switch each include a relay circuit (not shown) that is turned on or off by a signal supplied to a coil located near the switch element.

[0138] Inverter 44 converts the input DC voltage into a three-phase AC high voltage for driving the motor. The three-phase output terminals of inverter 44 are connected to the three-phase input terminals of drive motor 45. Inverter 44 controls the output voltage based on a control signal from battery management unit 411 or vehicle ECU 42, which controls the operation of the entire vehicle.

[0139] The drive motor 45 rotates using the electric power supplied from the inverter 44. This rotation is transmitted to the axles and drive wheels W via, for example, a differential gear unit.

[0140] Although not shown, the vehicle 400 also includes a regenerative braking mechanism. The regenerative braking mechanism rotates the drive motor 45 when braking the vehicle 400, and converts 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 direct current. The direct current is input to the vehicle power supply 41.

[0141] One terminal of a connection line L1 is connected to the negative terminal 414 of the vehicle power supply 41 via a current detection unit (not shown) in the battery management device 411. The other terminal of the connection line L1 is connected to the negative input terminal of the inverter 44.

[0142] One terminal of a connection line L2 is connected to the positive terminal 413 of the vehicle power supply 41 via a switch device 415. The other terminal of the connection line L2 is connected to the positive input terminal of the inverter 44.

[0143] The external terminal 43 is connected to the battery management device 411. The external terminal 43 can be connected to, for example, an external power source.

[0144] Vehicle ECU 42 manages the entire vehicle by cooperatively controlling battery management unit 411 together with other devices in response to operational inputs from the driver, etc. Data relating to the maintenance of vehicle power supply 41, such as the remaining capacity of vehicle power supply 41, is transferred between battery management unit 411 and vehicle ECU 42 via a communication line.

[0145] The vehicle according to the embodiment is equipped with the battery pack according to the embodiment, and therefore, according to the embodiment, it is possible to provide a vehicle equipped with a battery pack that has low resistance and can exhibit long life performance. [Example]

[0146] Examples are described below, but the embodiments are not limited to the examples described below. The test results are shown in tables.

[0147] Example 1 <Electrode fabrication> First, for the positive electrode, 90 wt% of LiMn2O4 powder, 5 wt% of acetylene black, and 5 wt% of polyvinylidene fluoride (PVdF) were mixed with N-methylpyrrolidone (NMP) to prepare a slurry. 2 The slurry was applied in an amount of 1000 ml and dried on a hot plate at 120°C to remove the solvent. The back side was similarly coated to produce a double-sided coated positive electrode. The electrode was pressed using a roll press to an electrode density of 2.5 g / cc.

[0148] For the negative electrode, a slurry was prepared by mixing 87 wt% Ti2NbO7 (monoclinic niobium titanium composite oxide) particles with an average particle size of 3.0 μm, 4 wt% acetylene black (AB), 4 wt% multi-walled carbon nanotubes (MWCNT), 5 wt% PVdF, and N-methylpyrrolidone (NMP). The Ti2NbO7 particles are white insulating particles. The multi-walled carbon nanotubes had an average fiber diameter of 10 nm and an average fiber length of 25 μm. For the negative electrode dispersion, 1 mm diameter glass beads were mixed in an amount equivalent to 50% by weight of the active material, and the mixture was mixed at 2000 rpm in a planetary mixer at a solids concentration of 60% for 10 minutes. The glass beads were removed from the mixed slurry by filtration through a 100-mesh filter. The mixture was then spread on 20 μm-thick aluminum foil at 100 g / m. 2 The slurry was applied in an amount of 1000 ml and dried on a hot plate at 120°C to remove the solvent. The back side was similarly coated to produce a double-sided coated negative electrode. The electrode was pressed using a roll press to an electrode density of 2.0 g / cc. <Fabrication of laminated cells> A positive electrode, a 25 μm-thick polyethylene porous film separator, a negative electrode, and a separator were stacked in this order and then spirally wound. This was then hot-pressed at 90°C to produce a flat electrode assembly measuring 30 mm in width and 3.0 mm in thickness. The resulting electrode assembly was placed in a pack made of laminate film and vacuum-dried at 80°C for 24 hours. The laminate film was composed of a 40 μm-thick aluminum foil with a polypropylene layer on both sides, for a total thickness of 0.1 mm. A liquid nonaqueous electrolyte was poured into the laminate film pack containing the electrode assembly. The pack was then completely sealed by heat sealing to produce a nonaqueous electrolyte battery with a 2 Ah capacity and dimensions of 35 mm in width, 3.2 mm in thickness, and 65 mm in height. Example 2 A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the dispersion time in preparing the negative electrode slurry was set to 20 minutes. Example 3 A nonaqueous electrolyte battery was manufactured in the same manner as in Example 1, except that a bead mill was used instead of a planetary centrifugal mixer when preparing the negative electrode slurry. Zirconia beads with a diameter of 1 mm were used as dispersion media for the bead mill. The solution was delivered at 2000 rpm so that the residence time, i.e., the stirring time, was 5 minutes. Example 4 Instead of PVdF, 2.5 wt% each of CMC and SBR was used as the binder for the negative electrode. Therefore, a nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the active material, conductive agent, and binder were mixed in a ratio of TiNbO:AB:MWCNT:CMC:SBR of 87:4:4:2.5:2.5. Example 5 A nonaqueous electrolyte battery was manufactured in the same manner as in Example 1, except that a dispersion in which MWCNT was previously dispersed in NMP using a wet high-pressure jet mill was used instead of a powder. The amount of MWCNT dispersion in the electrode composition shown in Table 1 is a value converted to solid content. Example 6 The electrode composition of the negative electrode was 83 wt% TiNbO particles, 4 wt% acetylene black (AB), 8 wt% multi-walled carbon nanotubes (MWCNT), and 5 wt% PVdF. A bead mill was used to disperse the negative electrode slurry. A nonaqueous electrolyte battery was manufactured in the same manner as in Example 1, except for these points. Zirconia beads with a diameter of 1 mm were used as the dispersion media for the bead mill. The solution was delivered at 3000 rpm so that the residence time, i.e., the stirring time, was 5 minutes. Example 7 A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that Ti2NbO7 particles with an average particle size of 5.0 μm were used. Example 8 For the negative electrode, Li2Na2Ti6O with an average particle size of 3.0 μm 14 A nonaqueous electrolyte battery was manufactured in the same manner as in Example 1, except that particles (orthorhombic titanium-containing composite oxide) were used. 14 The particles are white insulating particles. (Comparative Example 1) A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the dispersion time in preparing the negative electrode slurry was set to 1 minute. (Comparative Example 2) A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that no glass beads were added when preparing the negative electrode slurry. (Comparative Example 3) Instead of PVdF, 5 wt% CMC was used as the binder for the negative electrode. Therefore, the active material, conductive agent, and binder were mixed in a ratio of Ti2NbO7:AB:MWCNT:CMC of 87:4:4:5. A nonaqueous electrolyte battery was manufactured in the same manner as in Example 3, except that the rotation speed of the bead mill dispersion was set to 3000 rpm. Comparative Example 4 A nonaqueous electrolyte battery was produced in the same manner as in Example 4, except that glass beads were not added during dispersion in the planetary / revolutionary mixer. (Comparative Example 5) A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that Ti2NbO7 with an average particle size of 7.0 μm was used. (Comparative Example 6) A nonaqueous electrolyte battery was produced in the same manner as in Example 8, except that no glass beads were added when preparing the negative electrode slurry.

[0149] For the examples and comparative examples, the lightness L* of the electrodes and the particle size distribution of the mixture layer were measured by the methods explained below, and the results are shown in Tables 1 to 3. <Measurement of L* value of negative electrode> The lightness L* of the negative electrode was measured by the method described above. <Measurement of particle size distribution of electrode mixture layer> The electrode was cut into a 2 cm square, i.e., a 2 cm x 2 cm area per side perpendicular to the electrode thickness direction, and immersed in 10 cc of NMP solution. Ultrasonic waves were then applied for approximately 10 minutes. The current collector foil was then removed, and the solution containing the mixture layer was stirred at 2000 rpm for 30 seconds using a planetary mixer. The particle size distribution of the solution was then immediately measured using a laser diffraction / scattering particle size distribution analyzer. The resulting profile was analyzed in reflection mode to obtain particle sizes at volume cumulative frequencies d10, d20, d30, d40, d50, d60, d70, d80, and d90. The volume particle size distribution of the mixture layer in Example 1 is shown in Figure 10. The horizontal axis of Figure 10 represents particle size (μm), and the vertical axis represents volume frequency (arbitrary units). The particle size at volume cumulative frequency d10 of the mixture layer in Example 1 was 0.60 μm, the particle size at d20 was 0.77 μm, the particle size at d30 was 0.96 μm, the particle size at d40 was 1.18 μm, the particle size at d50 was 1.44 μm, the particle size at d60 was 1.79 μm, the particle size at d70 was 2.27 μm, the particle size at d80 was 3.03 μm, and the particle size at d90 was 4.57 μm. The volume cumulative frequency d50 of the mixture layer in each example and comparative example is shown in Tables 1 to 3. Note that the values ​​in parentheses in the active material composition column in Tables 1 to 3 are the average particle size (D50) of the active material particles. <Calculation of the relational expression that expresses the "sum of the reciprocals of particle diameters at each volume cumulative frequency" versus "electrode brightness"> The particle sizes of the volume cumulative frequencies d10, d20, d30, d40, d50, d60, d70, d80, and d90 in the particle size distribution measurement of the mixture layer are designated as r1, r2, r3, r4, r5, r6, r7, r8, and r9, respectively. The values ​​of the relational expression (2) below were calculated from the electrode surface lightness L* and the value of ri (i = a natural number from 1 to 9), and the results are shown in Tables 1 to 3.

[0150]

number

[0151] The capacity retention rate and resistance increase rate of the batteries of the examples and comparative examples during charge / discharge cycles were measured by the following methods, and the results are shown in Tables 1 to 3. The blending amounts of the electrode compositions in Tables 1 to 3 are in weight %. <Charge / discharge test> The battery was charged at a current of 2A with a maximum voltage of 2.85V and a charge time of 3 hours, and then discharged at 2A to 1.6V. This cycle was repeated 100 times at 60°C, and the capacity retention rate and the rate of increase in resistance estimated from a 1C-10C constant current pulse discharge test before and after the cycle test were measured.

[0152] [Table 1]

[0153] [Table 2]

[0154] [Table 3]

[0155] As is clear from Tables 1 to 3, the electrodes of Examples 1 to 8 have a lower resistance increase rate during charge-discharge cycling and a higher capacity retention rate during charge-discharge cycling than the electrodes of Comparative Examples 1 to 6. In Examples 1 to 8, the stirring conditions for the negative electrode slurry were appropriate, which resulted in the loosening of the agglomerates of carbon nanotubes, which are the conductive agent, and the value of the relational expression shown in formula (2) was 7.0 or more and 11.0 or less.

[0156] In Comparative Example 1, the stirring time was insufficient, so the carbon nanotubes serving as the conductive agent remained aggregated, resulting in a high lightness L* of the negative electrode surface, and therefore the value of the relational expression (2) was less than 7.0.

[0157] In Comparative Example 2, stirring with a bead mill was not performed. Therefore, the carbon nanotubes, which are the conductive agent, remained aggregated, and the lightness L* of the negative electrode surface increased. As a result, the value of the relational expression shown in formula (2) was less than 7.0.

[0158] In Comparative Example 3, the particle size of the mixture layer was small, so the value of the relational expression (2) was less than 7.0.

[0159] In Comparative Example 4, stirring with a bead mill was not performed. Therefore, the carbon nanotubes serving as the conductive agent remained aggregated, and the lightness L* of the negative electrode surface increased. As a result, the value of the relational expression shown in formula (2) was less than 7.0.

[0160] In Comparative Example 5, the particle size of the mixture layer was large, so the value of the relational expression (2) was greater than 11.0.

[0161] In Comparative Example 6, stirring with a bead mill was not performed. Therefore, the carbon nanotubes serving as the conductive agent remained aggregated, and the lightness L* of the negative electrode surface increased. As a result, the value of the relational expression shown in formula (2) was less than 7.0.

[0162] According to at least one of the embodiments described above, an electrode is provided that includes a composite layer containing a titanium-containing oxide and a conductive agent, and in which the relationship between "100 - electrode lightness L*" and the "sum of the reciprocals of particle diameters of volume cumulative frequencies" satisfies a specific range. This electrode can suppress an increase in resistance and improve life performance.

[0163] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. The inventions described in the original claims of this application are set forth below. [1] An electrode comprising a mixture layer containing a titanium-containing oxide and a conductive agent, and satisfying the following formula (1):

number

[10] A vehicle equipped with a battery pack described in any one of [7]-[9].

[11] The vehicle according to

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

[0164] 1...electrode group, 2...exterior member, 3...negative electrode, 3a...negative electrode current collector, 3b...negative electrode active material-containing layer, 3c...portion of negative electrode current collector, 4...separator, 5...positive electrode, 5a...positive electrode current collector, 5b...positive electrode active material-containing layer, 6...negative electrode terminal, 7...positive electrode terminal, 21...bus bar, 22...positive electrode side lead, 23...negative electrode side lead, 24...adhesive tape, 31...container, 32...lid, 33...protective sheet, 34...printed wiring board, 35...wiring, 40...vehicle body, 41...vehicle power source, 42...electrical control device, 43...external terminal, 44...inverter, 45...drive motor, 100...secondary battery, 200...battery pack, 100a to 100e...unit battery , 200a... battery pack, 200b... battery pack, 200c... battery pack, 300... battery pack, 300a... battery pack, 300b... battery pack, 300c... battery pack, 301a... battery pack monitoring device, 301b... battery pack monitoring device, 301c... battery pack monitoring device, 341... positive side connector, 342... negative side connector, 343... thermistor, 344... protection circuit, 345... wiring, 346... wiring, 347... external terminal for supplying electricity, 348a... positive side wiring, 348b... negative side wiring, 400... vehicle, 411... battery management device, 412... communication bus, 413... positive terminal, 414... negative terminal, 415... switch device.

Claims

1. a mixture layer containing a titanium-containing oxide and a conductive agent, the titanium-containing oxide includes at least one of a monoclinic niobium-titanium composite oxide and an orthorhombic titanium-containing composite oxide, the conductive agent includes acetylene black and carbon nanotubes; An electrode that satisfies the following formula (1). [Equation 1] In formula (1), L* is the lightness of the electrode measured in accordance with JIS Z8722:2009, ri (i is a natural number from 1 to 9) is the particle diameter at the volume cumulative frequency dx of the mixture layer, and the volume cumulative frequency dx is a cumulative frequency on a volume basis accumulated from the particle with the smallest diameter, and is a value that increases in 10% increments from 10% of the volume cumulative frequency d10 to 90% of the volume cumulative frequency d90.

2. 2. The electrode of claim 1, wherein the lightness (L*) is 35.0≦L*≦50.

0.

3. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, A secondary battery, wherein the positive electrode or the negative electrode is the electrode according to any one of claims 1 to 2.

4. A battery pack comprising the secondary battery according to claim 3.

5. 5. The battery pack according to claim 4, further comprising an external terminal for applying current and a protection circuit.

6. A battery includes a plurality of the secondary batteries, 6. The battery pack according to claim 4, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

7. A vehicle equipped with the battery pack according to any one of claims 4 to 6.

8. 8. The vehicle according to claim 7, further comprising a mechanism for converting kinetic energy of the vehicle into regenerative energy.

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