Electrodes, secondary batteries, battery packs, and vehicles

Abstract

The present invention provides electrodes capable of realizing a secondary battery capable of suppressing gas generation, a secondary battery and battery pack capable of suppressing gas generation, and a vehicle including this battery pack. [Solution] According to the embodiment, an electrode 10 is provided which includes an active material containing a metal oxide and a conductive agent containing a carbon material. The weight of carbon contained in the electrode 10 is 2.5 parts by weight or less per 100 parts by weight of the active material. The brightness L* of the electrode 10 is 40 ≤ L* ≤ 85.

Description

[Technical Field]

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

[0002] Lithium-ion batteries, such as non-aqueous electrolyte batteries, which charge and discharge by the movement of lithium ions between the negative and positive electrodes, are being actively researched as high-energy-density batteries.

[0003] Typical electrodes in secondary batteries such as lithium-ion batteries contain an electrode active material that contributes to charging and discharging through the insertion and removal of lithium ions, as well as a conductive agent to enhance the electrical conductivity of the electrodes. Carbon materials are widely used as conductive agents to be included in electrodes. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-47437 [Patent Document 2] International Publication No. 2015 / 011937 [Patent Document 3] Japanese Patent Publication No. 2016-195003 [Patent Document 4] Japanese Patent Publication No. 2023-139647 [Non-patent literature]

[0005] [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]

[0006] The objective is to provide electrodes that can realize a secondary battery capable of suppressing gas generation, a secondary battery and battery pack capable of suppressing gas generation, and a vehicle including this battery pack. [Means for solving the problem]

[0007] According to the embodiment, an electrode is provided comprising an active material containing a metal oxide and a conductive agent containing a carbon material. The weight of carbon in the electrode is 2.5 parts by weight or less per 100 parts by weight of the active material. The brightness L* of the electrode is 40 ≤ L* ≤ 85.

[0008] In another embodiment, a secondary battery is provided that comprises a positive electrode, a negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode is an electrode according to the above embodiment.

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

[0010] According to other embodiments, a vehicle is provided that is equipped with the battery pack according to the above embodiment. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic cross-sectional view showing an example of an electrode according to the embodiment. [Figure 2] A schematic cross-sectional view showing an example of a secondary battery according to this embodiment. [Figure 3] Figure 2 shows an enlarged cross-sectional view of section A of the secondary battery. [Figure 4] A schematic partial cutaway perspective view showing another example of a secondary battery according to the embodiment. [Figure 5] An enlarged cross-sectional view of section B of the secondary battery shown in Figure 4. [Figure 6] A perspective view showing another example of a stacked electrode group including the electrodes of the embodiment. [Figure 7] A schematic perspective view showing an example of a battery pack according to this embodiment. [Figure 8]An exploded perspective view schematically showing an example of a battery pack according to this embodiment. [Figure 9] A block diagram showing an example of the electrical circuit of the battery pack shown in Figure 8. [Figure 10] A partially transparent view schematically showing an example of a vehicle according to the embodiment. [Figure 11] A schematic diagram showing an example of a control system for the electrical system in a vehicle according to this embodiment. [Figure 12] This figure shows image data of the negative electrode of Example 1 obtained by scanning electron microscopy. [Modes for carrying out the invention]

[0012] (First Embodiment) The embodiments will be described below with reference to the drawings. Common components throughout the embodiments will be denoted by the same reference numerals, and redundant explanations will be omitted. Furthermore, each drawing is a schematic diagram intended to illustrate the embodiments and facilitate understanding; their shapes, dimensions, and ratios may differ from those of the actual device. These can be appropriately modified in accordance with the following description and known technology.

[0013] Electrodes containing metal oxides, such as niobium-containing oxides, as active materials undergo volume changes during the charge-discharge reaction of secondary batteries. One way to prevent this volume change from impairing electron conduction paths within the electrode is to incorporate a large amount of conductive agent. However, to achieve high energy density in a battery, a lower conductive agent content in the electrode is desirable. Therefore, it is difficult to achieve both high charge-discharge cycle performance and high energy density simply by adjusting the conductive agent content of the electrode.

[0014] On the other hand, when using carbon materials as conductive agents, it is generally believed that electrodes with lower brightness (L*) exhibit superior cycle performance. However, electrodes with low brightness (L*) require a large amount of conductive agent. Therefore, there is a need to realize electrodes that can achieve excellent cycle performance with a small amount of conductive agent.

[0015] Examples of carbon materials used as conductive agents include granular carbon materials and fibrous carbon materials. These carbon materials are preferably those with a large specific surface area and small particle or fiber diameter. This allows for improved electrode conductivity with a small amount of additive. When the carbon material is dispersed well around the active material and included in sufficient quantity, the electrode conductivity improves, and the brightness L* decreases. The electrode brightness L* can serve as an indicator of the dispersibility of the carbon material and the electrode's conductivity.

[0016] Ideally, the amount of carbon in the electrode should be low, and the carbon material should be dispersed so as to coat the active material. This state allows for a higher energy density in the battery and improved conductivity of the electrode. The inventors have succeeded in realizing an electrode that significantly contributes to improved battery performance by achieving a good dispersion state under the condition that the amount of carbon in the electrode is 2.5 parts by weight or less per 100 parts by weight of active material. It was also found that a good dispersion state can be achieved by setting the electrode brightness L* to 40 ≤ L* ≤ 85.

[0017] Furthermore, by limiting the amount of carbon in the electrode to 2.5 parts by weight or less when the weight of the active material is 100 parts by weight, the specific surface area of ​​the carbon material can be increased without increasing its bulk, thereby increasing the density of the electrode. As a result, the energy density of the battery can be improved.

[0018] As described above, the electrode of the first embodiment includes an active material containing a metal oxide and a conductive agent containing a carbon material. When the weight of the active material is 100 parts by weight, the weight of carbon contained in the electrode is 2.5 parts by weight or less. Also, the brightness L* of the electrode is 40 ≤ L* ≤ 85.

[0019] The brightness L* is measured according to JIS Z 8722:2009. Furthermore, the electrode brightness L* refers to the brightness L* of the electrode surface.

[0020] The carbon weight in electrodes is measured, for example, by thermogravimetry (TG). When measured by thermogravimetry, the carbon weight of the conductive material can be considered equivalent to the carbon weight in the electrodes. Details of thermogravimetry will be described later.

[0021] By limiting the carbon content of the electrode to 2.5 parts by weight or less per 100 parts by weight of the active material, an electrode with high density and low porosity can be obtained. By setting the brightness L* of the electrode satisfying the carbon content of 2.5 parts by weight or less to 85 or less, the uniformity of the carbon material distribution in the electrode can be increased. As a result, sufficient conductive agent can be secured not only in contact with the active material but also in contact with the current collector, thus reducing electrode resistance. On the other hand, if the brightness L* of the electrode satisfying the carbon content of 2.5 parts by weight or less is reduced, there is a risk that the carbon material will be unevenly distributed on the electrode surface, resulting in a low carbon material content ratio inside the electrode. Therefore, it is desirable to set the lower limit of brightness L* to 40. By setting the brightness L* of the electrode satisfying the carbon content of 2.5 parts by weight or less to 40 or higher, uneven distribution of carbon material on the electrode surface can be suppressed.

[0022] Therefore, by setting the brightness L* of electrodes that satisfy a carbon weight of 2.5 parts by weight or less to 40 to 85, it is possible to ensure high electrode density while also increasing the uniformity of the carbon material distribution in the electrodes. As a result, it is possible to provide electrodes that enable secondary batteries with high energy density, suppressed gas generation, and excellent charge / discharge rate performance and charge / discharge cycle life performance.

[0023] The preferred range for the carbon content in the electrode per 100 parts by weight of the active material is 0.1 parts by weight or more and 2.5 parts by weight or less. Furthermore, the preferred range for the electrode's brightness L* is 51 or more and 80 or less.

[0024] The details of the electrodes in this embodiment will be described below.

[0025] The electrode in question may be, for example, at least one of the positive and negative electrodes of a battery. The electrode may include a current collector and an active material-containing layer. The active material-containing layer may be formed on one or both sides of the current collector. The active material-containing layer may include an active material and a conductive agent, and optionally include a binder. The active material may include a metal oxide. The conductive agent may include a carbon material. The current collector may include portions on its surface where the active material-containing layer is not formed. These portions may function as current-collecting tabs.

[0026] It is desirable that the metal oxide is capable of inserting and removing alkali metals or alkali metal ions such as Li. Furthermore, it is desirable that the metal oxide does not contain Li during synthesis. Even if the metal oxide does not contain Li during synthesis, Li may be stored through charge-discharge reactions. The stored Li may be irreversible. The metal oxide may be white particles. It is also desirable that the metal oxide be a white, insulating oxide. Examples of metal oxides include titanium-containing oxides and niobium-containing oxides. Titanium-containing oxides and niobium-containing oxides can be insulating, white active materials. A single type of metal oxide may be used as the active material, or a mixture of multiple types of metal oxides may be used.

[0027] Examples of titanium-containing oxides include monoclinic titanium oxide, rutile titanium oxide, anatase titanium oxide, and orthorhombic titanium-containing oxide. Each crystalline structure of titanium oxide has a composition of TiO2 before charging and a composition of Li after charging. x It can be represented as TiO2 (where x is 0 ≤ x ≤ 1). Furthermore, the pre-charge structure of monoclinic titanium oxide can be represented as TiO2(B).

[0028] Examples of niobium-containing oxides include niobium pentoxide (Nb2O5) and niobium-titanium-containing oxides. Examples of niobium-titanium-containing oxides include monoclinic niobium-titanium-containing oxides.

[0029] Examples of niobium titanium-containing oxides with a monoclinic structure include Nb2TiO7, Nb2Ti2O9, Nb 10 Ti2O 29 、Nb 14 TiO 37 、Nb 24 TiO 62 is included. The niobium titanium-containing oxide may be a substituted niobium titanium composite oxide in which at least a part of Nb and / or Ti is substituted with a different element. Examples of the substitution 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 substitution element or may contain two or more types of substitution elements. The niobium titanium-containing oxide preferably contains Nb2TiO7 having a monoclinic structure. In this case, an electrode excellent in capacity and rate performance can be obtained.

[0030] Examples of monoclinic niobium titanium-containing oxides include compounds represented by Li x Ti 1-y M1 y Nb 2-z M2 z O 7+δ . Here, M1 is at least one selected from the group consisting of Zr, Si, and Sn. M2 is at least one selected from the group consisting of V, Ta, and Bi. Each subscript in the composition formula satisfies 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3. Specific examples of the monoclinic niobium titanium oxide include Li x Nb2TiO7 (0≦x≦5).

[0031] Other examples of monoclinic niobium titanium oxides include compounds represented by 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. Each subscript in the composition formula satisfies 0≦x≦5, 0≦y<1, 0≦z<2, and -0.3≦δ≦0.3.

[0032] Metal oxides can take the form of primary particles, for example, or secondary particles formed by the aggregation of primary particles. Metal oxides may also be a mixture of primary and secondary particles.

[0033] The metal oxide particles should preferably have an average primary particle diameter of 0.4 μm to 1.5 μm. A more preferable range is 0.7 μm to 1.5 μm.

[0034] The carbon material used as a conductive agent can take various forms, such as granular or fibrous. Either fibrous or granular carbon material may be used as the conductive agent, or a mixture of fibrous and granular carbon materials may be used. Furthermore, carbon materials with shapes different from granular or fibrous may also be used. For example, a layered carbon material coating the active material particles may be included in the conductive agent.

[0035] The conductive agent preferably contains a fibrous carbon material. The fibrous carbon material may come into contact with multiple active material particles or granular carbon particles. Examples of fibrous carbon materials include carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCFs), and carbon nanofibers (CNFs). Examples of CNTs include single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and few-walled carbon nanotubes (FW-CNTs). The fibrous carbon material may be of one type or multiple types.

[0036] The fibrous carbon material preferably has a first portion with a fiber diameter of 60 nm to 500 nm and a second portion with a fiber diameter of 1 nm to 15 nm. The first and second portions may be contained in different fibrous carbon materials. Alternatively, the first and second portions may be different parts of the same fibrous carbon material.

[0037] The first part is formed, for example, from a bundle of aggregated carbon fibers. The fact that the first part is an aggregate of carbon fibers improves current efficiency and leads to a reduction in overall electrode resistance. By making the fiber diameter of the first part 60 nm or larger, a sufficient resistance reduction effect can be obtained. Furthermore, by making the fiber diameter of the first part 500 nm or smaller, the bulkiness of the carbon fiber aggregate can be suppressed, thus ensuring a high energy density. Therefore, by making the fiber diameter of the first part between 60 nm and 500 nm, a sufficient resistance reduction effect can be obtained while avoiding the decrease in energy density caused by the inclusion of carbon fiber aggregates. A more preferable range for the fiber diameter of the first part is between 60 nm and 200 nm.

[0038] The second portion has a finer fiber diameter than the first portion, which promotes the distribution of fibrous carbon material throughout the electrode. By distributing the fibrous carbon material throughout the electrode, localized unreacted or high-resistance areas of the electrode can be reduced. By setting the fiber diameter of the second portion to between 1 nm and 15 nm, the effect of promoting the dispersion of fibrous carbon material can be enhanced. Therefore, it is possible to reduce localized unreacted or high-resistance areas. A more preferable range for the fiber diameter of the second portion is between 2 nm and 10 nm.

[0039] It is desirable that the weight of the fibrous carbon material be between 0.01 parts by weight and 1 part by weight per 100 parts by weight of the active material.

[0040] Examples of granular carbon materials include carbon black such as acetylene black, graphite, Ketjenblack, and coke. The particle size of the granular carbon material should preferably be 30 nm or less. The weight of the granular carbon material should preferably be 1.5 parts by weight or less (including 0 parts by weight) per 100 parts by weight of the active material. The granular carbon material may be of one type or a mixture of two or more types.

[0041] The active material-containing layer may contain a binder. The binder can fill the gaps between the dispersed active material. Furthermore, the binder can bond the active material 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.

[0042] If the active material-containing layer contains a binder, it is desirable that the weight of the binder be between 1 and 5 parts by weight per 100 parts by weight of the active material.

[0043] 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. The current collector is preferably made of 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.

[0044] 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 weight 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 weight or less.

[0045] The density of the active material-containing layer (excluding the current collector) is 1.8 g / cm³. 3 More than 2.8g / cm 3 The following is preferable: The density of the active material-containing layer is 2.1 g / cm³. 3 More than 2.7g / cm 3 The following is more preferable:

[0046] <Manufacturing method> The electrode of the embodiment is manufactured, for example, by the method described below. A dispersion of the fibrous carbon material is prepared by adding, for example, 0.5 wt% of fibrous carbon material and, for example, 0.5 wt% of a water-soluble binder such as CMC to a solvent such as pure water, and stirring with a stirrer such as a homogenizer at, for example, 40 W for 2 hours. This dispersion is then completely dried to re-aggregate the fibrous carbon material. By returning the re-aggregated fibrous carbon material to the dispersion, a dispersion of fibrous carbon material having a first part and a second part can be prepared. This dispersion is mixed with an active material, a binder, and optionally other conductive agents in the presence of a solvent to obtain a slurry. This slurry can be applied to a current collector, dried, and pressed to obtain the electrode of the embodiment.

[0047] <Electrode brightness L*> For lightness measurement samples, electrodes that are not integrated into a battery or electrodes removed from a battery can be used. When removing electrodes from a battery, they should be washed with an organic solvent to ensure no lithium salt remains. First, the electrodes are impregnated with a cyclic carbonate with high lithium salt solubility, and then impregnated with a chain carbonate and washed to sufficiently reduce the amount of lithium salt remaining. After impregnation, the solvent is removed by reducing the pressure under vacuum.

[0048] The lightness L* is measured according to the method described in JIS Z 8722:2009. As the measuring device, a colorimeter based on the spectrophotometric method, which measures the reflectance of each wavelength in the entire visible light region and calculates the tristimulus value, can be used. The lightness L* of the electrode is obtained by converting the measured tristimulus value to the L*a*b* color system.

[0049] Next, we will explain the observation and measurement of the electrode surface using a scanning electron microscope (SEM), as well as the measurement methods for the carbon material and active material contained in the electrode.

[0050] For measurement, electrodes that are not incorporated into a battery or electrodes removed from a battery can be used as samples. When removing electrodes from a battery, they should be washed with an organic solvent to ensure no lithium salt remains. First, impregnate the electrodes in a cyclic carbonate with high lithium salt solubility, then impregnate them in a chain carbonate and wash them to sufficiently reduce the amount of lithium salt remaining. After impregnation, remove the solvent by reducing the pressure under vacuum.

[0051] <SEM observation of electrodes> By observing the surface of the electrode sample with a scanning electron microscope (SEM), the presence of fibrous carbon material, including the first and second parts, and granular carbon material can be confirmed. Furthermore, the fiber diameter of the first part, the fiber diameter of the second part, the particle size of the granular carbon material, and the average primary particle diameter of the active material can be measured.

[0052] SEM images of the electrode surface are acquired, and the obtained SEM images are binarized. During binarization, thresholds are set so that the active material particles and carbon materials such as fibrous carbon materials and granular carbon materials can be distinguished. Software such as Image-J can be used for this purpose.

[0053] Fibrous carbon materials and granular carbon materials differ in shape. Fibrous carbon materials have a high aspect ratio, possessing length relative to their fiber diameter, and may have straight or curved sections. If the aspect ratio is 5 or greater, it is considered a fibrous carbon material. Fibrous carbon materials can come into contact with multiple active material particles or granular carbon material particles. Granular carbon materials have a low aspect ratio, and irregularly shaped particles may exist individually or in clusters. If the aspect ratio is 3 or less, it is considered a granular carbon material. Furthermore, the diameter of a granular carbon material is defined as the diameter of the largest circle inscribed within the particle; for example, the diameter of a single granular particle may be 800 nm or less. Moreover, the diameter of a single granular particle may be 400 nm or less.

[0054] <Fiber diameter of fibrous carbon material> The fiber diameter of the fibrous carbon material is estimated from the binarized image. The first part is the area in the binarized image where the fiber diameter is between 60 nm and 500 nm. Regions with fiber diameters close to 60 nm and 500 nm can be detected from the image. For the fiber diameter in the first part, a 50 nm straight line is drawn along one side of the fiber, a perpendicular line is drawn, and the distance from end to end of the fiber along the perpendicular line is defined as the fiber diameter. Fibrous carbon material can exist on active material particles, on granular particles, and between particles.

[0055] The second portion is the part with a smaller fiber diameter than the first portion, preferably with a fiber diameter of 1 nm to 15 nm. Parts smaller than 60 nm can be detected from the image. Similar to measuring the fiber diameter of the first portion, the fiber diameter of the second portion is determined by drawing a 50 nm straight line along one side of the fiber, drawing a perpendicular line, and measuring the distance from the perpendicular line to the end of the fiber.

[0056] <Particle size of granular carbon material> The particle size of granular carbon material is estimated from the binarized image. The particle size of granular carbon material is determined by identifying areas in the binarized image where the particle size is 30 nm or less. Areas with a particle size close to 30 nm or less can be detected from the image. The particle size of granular carbon material is determined by drawing a 50 nm straight line along one side of the particle, drawing a perpendicular line to it, and measuring the distance from end to end of the particle along the perpendicular line.

[0057] <Average primary particle size of the active material> From the binarized image, 30 primary particles of the active material are selected. After excluding particles with extremely different particle sizes, such as fine powder, the remaining particles are selected randomly. The particle size of the primary particles is determined by drawing a 50 nm straight line along one side of the particle, drawing a perpendicular line to it, and measuring the distance from end to end of the particle along the perpendicular line. The average of the measured particle sizes is calculated and used as the average primary particle diameter of the active material.

[0058] <Method for measuring carbon materials> The amount of carbon material contained in the electrode can be measured by thermogravimetric analysis (TG). The electrode is removed using the same procedure as described for SEM observation. The active material-containing layer of the electrode is peeled off from the current collector, and only the active material-containing layer is collected for TG measurement. By measuring the temperature increase rate at 1-3°C / min, two weight loss points appear at 600-800°C. The lower temperature of the weight loss point indicates fibrous carbon, and the higher temperature indicates granular carbon. The total carbon percentage can be estimated from the weight loss at this time. Similarly, by holding the temperature for 1 hour at the starting point of the decomposition temperature of the carbon material with the lower weight loss point, the weight percentage of fibrous carbon material can be estimated. From the estimated total carbon percentage and the fibrous carbon material percentage, the granular carbon percentage can also be estimated.

[0059] <Composition of the active material> The composition of the active material contained in the electrode can be determined by measuring as described below.

[0060] By combining elemental analysis using a scanning electron microscope (SEM-EDX) equipped with an energy-dispersive X-ray analyzer, X-ray diffraction (XRD) measurement, and inductively coupled plasma (ICP) emission spectroscopy, the composition of the active material contained in the electrode, for example, the active material-containing layer, can be confirmed. SEM-EDX analysis allows us to determine the shape of the components contained in the active material-containing layer and the composition of those components (elements B to U in the periodic table). ICP measurement allows for the quantitative determination of elements in the active material-containing layer. Finally, XRD measurement allows us to confirm the crystal structure of the material contained in the active material-containing layer.

[0061] The cross-section of the electrode extracted as described above is cut out by Ar ion milling. The cut-out cross-section is observed using a scanning electron microscope (SEM). Sample sampling is also carried out in an inert atmosphere such as argon or nitrogen, without exposure to air. Several particles are selected from the 3000x SEM image. At this time, the selection is made so that the particle size distribution of the selected particles is as broad as possible.

[0062] Next, elemental analysis is performed on each selected particle using EDX. This allows us to identify the types and amounts of elements other than Li contained in each selected particle.

[0063] Regarding Li, information about the Li content in the entire active material can be obtained by ICP emission spectroscopy. ICP emission spectroscopy is performed according to the following procedure.

[0064] From the dried electrodes, a powder sample is prepared as follows: The active material-containing layer is peeled off the current collector and ground in a mortar. The ground sample is dissolved in acid to prepare a liquid sample. Hydrochloric acid, nitric acid, sulfuric acid, or hydrogen fluoride can be used as the acid. By subjecting this liquid sample to ICP emission spectroscopy, the concentrations of elements contained in the active material being measured can be determined.

[0065] The crystal structure of the compound contained in each particle selected by SEM can be determined by XRD measurement. The XRD measurement is performed using CuKα radiation as the source in the measurement range of 2θ = 5° to 90°. This measurement allows us to obtain the X-ray diffraction pattern of the compound contained in the selected particle.

[0066] For XRD measurements, we will use the Rigaku SmartLab. 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°.

[0067] If other equipment is used, measurements should be performed using standard Si powder for powder X-ray diffraction to find conditions that yield peak intensity, full width at half maximum, and diffraction angle equivalent to those obtained with the above equipment, and then the sample should be measured under those conditions.

[0068] The XRD measurement conditions should be such that an XRD pattern suitable for Rietveld analysis can be obtained. Specifically, to collect data for Rietveld analysis, the step size should be set to 1 / 3 to 1 / 5 of the minimum full width at half maximum of the diffraction peak, and the measurement time or X-ray intensity should be adjusted as appropriate so that the intensity at the peak position of the most intense reflection is 5000 cps or more.

[0069] The XRD patterns obtained as described above are analyzed using the Rietveld method. In the Rietveld method, the diffraction pattern is calculated from a pre-estimated crystal structure model. The crystal structure model is estimated here based on the analysis results from EDX and ICP. By fitting all of these calculated values ​​with the measured values, parameters related to the crystal structure (lattice constants, atomic coordinates, occupancy, etc.) can be precisely analyzed.

[0070] Rietveld analysis can be used to estimate the content of titanium niobium-containing oxides, for example, when the negative electrode contains multiple active materials. A fitting parameter S is used as a measure to estimate the degree of agreement between the observed intensity and the calculated intensity in Rietveld analysis. The analysis must be performed so that S is less than 1.8. In addition, the standard deviation σj must be taken into consideration when determining the occupancy rate of each site. The fitting parameter S and standard deviation σj defined here shall be estimated using the formula described in Non-Patent Literature 1 ("Practical Aspects of Powder X-ray Analysis," edited by the X-ray Analysis Research Group of the Japan Society for Analytical Chemistry, edited by Izumi Nakai and Fujio Izumi (Asakura Shoten)).

[0071] XRD measurements can be performed by directly attaching the electrode sample to the glass holder of a wide-angle X-ray diffractometer. In this process, it is necessary to pre-measure the XRD spectrum according to the type of metal foil used for the electrode current collector to determine where peaks originating from the current collector appear. It is also important to pre-determine the presence or absence of peaks from conductive agents and binders. If the current collector peak and the active material peak overlap, it is desirable to peel the active material-containing layer from the current collector before measurement. This is to separate the overlapping peaks when quantitatively measuring the peak intensity. Of course, if these factors are known in advance, this step can be omitted.

[0072] For example, if the particles observed by the aforementioned SEM-EDX measurement contain Ti, Nb, and O, and furthermore, if the aforementioned XRD measurement yields an X-ray diffraction pattern attributed to a monoclinic type from the electrode being measured, it indicates that the active material being measured contains particles of monoclinic titanium niobium-containing oxide. If the EDX measurement reveals particles with significantly different Ti and Nb content, it is possible that multiple active materials are present. The amount of elements contained in the active material in the electrode can be determined by ICP emission spectroscopy following the procedure described earlier.

[0073] The amount of active material in the active material-containing layer can be estimated by the following method.

[0074] After cleaning and drying the electrodes removed from the battery using the procedure described earlier, the active material-containing layer is peeled off the current collector and ground in a mortar. The ground sample is placed on a glass sample plate and leveled so that the surface of the sample matches the surface of the glass sample plate. A Si standard sample may also be added to correct the peak position.

[0075] XRD measurements and Rietveld analysis are performed on the powder sample packed into a glass sample plate under the conditions described above. SEM-EDX measurements and ICP measurements are also performed on the powder sample using the procedure described above. Considering the results of the XRD, SEM-EDX, and ICP measurements, the types and proportions of active materials present can be estimated.

[0076] Figure 1 shows an example of an electrode according to the embodiment. Figure 1 schematically shows a cross-section of the electrode.

[0077] The example electrode 10 includes a current collector 10a and active material-containing layers 10b provided on both its front and back surfaces. A portion of the current collector 10a does not have the active material-containing layers 10b provided on either its front or back surface, and this portion can function as a current-collecting tab 10c.

[0078] In the electrode according to the first embodiment, the carbon weight is 2.5 parts by weight or less per 100 parts by weight of the active material. Furthermore, the lightness L* of the electrode is 40 ≤ L* ≤ 85. Therefore, it is possible to provide an electrode that enables the realization of a secondary battery with high energy density, suppressed gas generation, and excellent charge-discharge rate performance and charge-discharge cycle life performance.

[0079] (Second embodiment) According to a second embodiment, a secondary battery is provided that includes a positive electrode, a negative electrode, and an electrolyte. This secondary battery includes an electrode according to the first embodiment as at least one of the positive electrode and the negative electrode. When the electrode according to the first embodiment is included as the negative electrode, the positive electrode may be a different electrode from that of the first embodiment.

[0080] 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.

[0081] Furthermore, the secondary battery may further comprise an outer casing that houses the electrode group and the electrolyte.

[0082] 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.

[0083] 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.

[0084] Hereinafter, the positive electrode, electrolyte, separator, exterior member, negative electrode terminal, and positive electrode terminal of the secondary battery using the electrode of the first embodiment as the negative electrode will be described in detail.

[0085] 1) Positive electrode This positive electrode includes a positive electrode current collector and a positive electrode active material-containing layer carried on or in contact with one side (one main surface) or both sides of the current collector and containing a positive electrode active material. The positive electrode active material-containing layer may contain a binder, a conductive agent, or both.

[0086] Examples of the positive electrode active material include Li x M y O2 (0 < x ≤ 1, 0 < y ≤ 1, M is, for example, Mn), Li x M 2y O4 (0 < x ≤ 1, 0 < y ≤ 1, M is, for example, Mn), lithium phosphate having an olivine structure (for example, Li x M y PO4 (M is at least one element selected from Mn, Ni, Co, Fe, 0 < x ≤ 1.1, 0.8 ≤ y ≤ 1.1), Li x FePO4 (0 < x ≤ 1.1), Li x Fe 1-y Mn y PO4 (0 < x ≤ 1.1, 0 ≤ y ≤ 1), Li x CoPO4 (0 < x ≤ 1.1), Li x MnPO4 (0 < x ≤ 1.1)), lithium nickel cobalt composite oxide (for example, LixNi 1-a Co a O2, 0 < x ≤ 1, 0 < a ≤ 1), lithium cobalt composite oxide (for example, Li x CoO2, 0 < x ≤ 1), lithium nickel manganese cobalt composite oxide (for example, Li x Ni 1-a-b Mn a Co b O2, 0 < x ≤ 1, 0 < 1 - a - b < 1, 0 < a < 1, 0 < b < 1), lithium manganese cobalt composite oxide (for example, Li x Mn 1-a Co aO2, where 0 < x ≤ 1, 0 < a < 1), spinel-type lithium manganese nickel composite oxide (e.g., Li x Mn 2-a Ni a O4, where 0 < x ≤ 1, 0 < a < 2), fluorinated iron sulfate having a tabularite structure (e.g., Li x M y SO4F (0 < x ≤ 1, 0 < y ≤ 1, M is at least one of Fe or Mn), Li x Fe 1-a Mn a SO4F (0 < x ≤ 1, 0 < a ≤ 1), etc. are included. The type of the positive electrode active material can be one type or two or more types.

[0087] The above positive electrode active material can obtain a high voltage of 4 V or more. Lithium nickel manganese cobalt composite oxide can obtain a high voltage of 4 V or more and can increase the energy density of the positive electrode.

[0088] The positive electrode active material particles may be in the form of primary particles, or secondary particles in which the primary particles are aggregated. Also, primary particles and secondary particles may be mixed.

[0089] On the surface of the particles of the positive electrode active material, it is preferable that at least one or more elements selected from Mg, Al, Ti, Nb, Sn, Zr, Ba, B, N, and C are present. Thereby, the oxidative decomposition reaction of the non-aqueous electrolyte under a high-temperature environment can be suppressed, so that the increase in resistance can be suppressed. Therefore, the high-temperature life performance can be improved.

[0090] The positive electrode current collector may contain at least one of aluminum or an aluminum alloy. For the positive electrode current collector, for example, an aluminum foil or an aluminum alloy foil is used. The thickness of the positive electrode current collector can be 20 μm or less. A more preferable range is 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.

[0091] The positive electrode active material-containing layer may contain a conductive agent. Examples of conductive agents include acetylene black, carbon black, and graphite. The number of conductive agents can be one or more.

[0092] The positive electrode active material layer may contain a binder. Examples of binders include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, and acrylic materials. The binder can be one type or two or more types.

[0093] The mixing ratio of the positive electrode active material, conductive agent, and binder is preferably in the range of 80-95% by weight of the positive electrode active material, 3-19% by weight of the conductive agent, and 1-7% by weight of the binder.

[0094] The specific surface area of ​​the positive electrode active material-containing layer, measured by the BET method, is 0.1 to 2 m². 2 It is preferable that the range is within / g. The positive electrode active material-containing layer may be porous.

[0095] The positive electrode is manufactured, for example, by suspending a positive electrode active material, a conductive agent, and a binder in a suitable solvent, applying this suspension to a positive electrode current collector, drying it, and pressing it.

[0096] 2) 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] Polymeric solid electrolytes are prepared by dissolving an electrolyte salt in a polymer material and then solidifying it.

[0103] 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.

[0104] As an oxide-based solid electrolyte, it has a NASICON (Sodium (Na) Super Ionic Conductor) type structure, and its general formula is Li 1+xIt is preferable to use a lithium phosphate solid electrolyte represented by Mα2(PO4)3. Mα in the above general formula is, for example, one or more selected from the group consisting of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is within the range of 0 ≦ x ≦ 2.

[0105] Specific examples of the lithium phosphate solid electrolyte having a NASICON-type structure include LATP compounds represented by Li 1+x Al x Ti 2-x (PO4)3 with 0.1 ≦ x ≦ 0.5; Li 1+x Al y Mβ 2-y (PO4)3 where Mβ is one or more selected from the group consisting of Ti, Ge, Sr, Zr, Sn, and Ca and 0 ≦ x ≦ 1 and 0 ≦ y ≦ 1; Li 1+x Al x Ge 2-x (PO4)3 with 0 ≦ x ≦ 2; and, Li 1+x Al x Zr 2-x (PO4)3 with 0 ≦ x ≦ 2; Li 1+x+y Al x Mγ 2-x Si y P 3-y O 12 represented compounds where Mγ is one or more selected from the group consisting of Ti and Ge and 0 < x ≦ 2, 0 ≦ y < 3; Li 1+2x Zr 1-x Ca x (PO4)3 with 0 ≦ x < 1 can be mentioned.

[0106] In addition, as the oxide-based solid electrolyte, in addition to the above lithium phosphate solid electrolyte, Li x PO y N z represented amorphous LIPON compounds 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); Garnet-type structured 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 La3Zr3O 12 A compound represented by and 0 ≦ x ≦ 0.5; Li 5+x La3Mδ 2-x Zr x O 12 A compound represented by, where Mδ is one or more selected from the group consisting of Nb and Ta, and 0 ≦ x ≦ 2, LLZ compound (for example, Li7La3Zr2O 12 ); And compounds having a perovskite-type structure and represented by La 2 / 3-x Li x TiO3 and 0.3 ≦ x ≦ 0.7.

[0107] One or more of the above compounds can be used as a solid electrolyte. Two or more of the above solid electrolytes may be used.

[0108] 3) Separator The separator is formed from, for example, a porous film containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF), or a non-woven fabric made of synthetic resin. From the viewpoint of safety, it is preferable to use a porous film formed from polyethylene or polypropylene. This is because these porous films melt at a certain temperature and can block the current.

[0109] 4) Exterior member As the exterior member, for example, a container made of a laminate film or a metal container can be used.

[0110] The thickness of the laminating film is, for example, 0.5 mm or less, and preferably 0.2 mm or less.

[0111] 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.

[0112] 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.

[0113] 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 weight or less.

[0114] 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.

[0115] 5) 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.

[0116] 6) 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.

[0117] Next, the secondary battery according to the embodiment will be described in more detail with reference to the drawings.

[0118] Figure 2 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 3.

[0119] The secondary battery 100 shown in Figures 2 and 3 comprises a bag-shaped outer casing member 2 shown in Figure 2, an electrode group 1 shown in Figures 2 and 3, 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.

[0120] The bag-shaped outer packaging member 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0121] As shown in Figure 2, electrode group 1 is a flat, wound electrode group. As shown in Figure 3, 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.

[0122] 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 3. 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.

[0123] The positive electrode 5 includes a positive electrode current collector 5a and positive electrode active material-containing layers 5b formed on both sides thereof.

[0124] As shown in Figure 2, 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.

[0125] The secondary battery according to this embodiment is not limited to the secondary battery with the configuration shown in Figures 2 and 3, but may also be a battery with the configuration shown in Figures 4 and 5, for example.

[0126] Figure 4 is a schematic partially cutaway perspective view showing another example of a secondary battery. Figure 5 is an enlarged cross-sectional view of section B of the secondary battery shown in Figure 4.

[0127] The secondary battery 100 shown in Figures 4 and 5 comprises an electrode group 1 shown in Figures 4 and 5, an outer casing member 2 shown in Figure 4, 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.

[0128] The exterior component 2 consists of a laminate film comprising two resin layers and a metal layer interposed between them.

[0129] As shown in Figure 5, 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.

[0130] 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.

[0131] 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 5, 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.

[0132] 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.

[0133] The stacked electrode group is not limited to the structure shown in Figure 5. Another example of the stacked electrode group 1 is shown in Figure 6. The positive electrode 5, negative electrode 3, positive electrode 5, and negative electrode 3 are arranged in this order, sandwiched between the separators 4 in the zigzag-folded separator 4. The positive electrode current collector tab 5c protrudes from one of the long sides of the zigzag-folded separator 4. The negative electrode current collector tab (not shown) protrudes from the other long side of the zigzag-folded separator 4. Note that the order of the positive electrode 5 and negative electrode 3 is not limited to the case in Figure 6; the order could also be negative electrode 3, positive electrode 5.

[0134] The secondary battery according to the second embodiment includes the electrodes according to the first embodiment. Therefore, such a secondary battery has a high energy density, suppressed gas generation, and excellent charge-discharge rate performance and charge-discharge cycle life performance.

[0135] (Third embodiment) According to the third embodiment, a battery pack is provided. This battery pack comprises a plurality of secondary batteries according to the second embodiment.

[0136] 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.

[0137] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0138] Figure 7 is a schematic perspective view showing an example of a battery pack. The battery pack 200 shown in Figure 7 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.

[0139] 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 7 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.

[0140] 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.

[0141] The battery pack according to the third embodiment comprises a secondary battery according to the second embodiment. Therefore, the battery pack has a high energy density, suppressed gas generation, and excellent charge-discharge rate performance and charge-discharge cycle life performance.

[0142] (Fourth embodiment) According to the fourth embodiment, a battery pack is provided. This battery pack comprises a battery pack according to the third embodiment. This battery pack may also comprise a single secondary battery according to the second embodiment instead of the battery pack according to the third embodiment.

[0143] The battery pack may further include a protection circuit. The protection circuit has the function of controlling the charging and discharging of the secondary battery. Alternatively, a circuit included in a device that uses the battery pack as a power source (e.g., electronic equipment, automobile, etc.) may be used as the protection circuit for the battery pack.

[0144] Furthermore, such a battery pack may also be equipped with external terminals for power supply. These external terminals are for outputting current from the secondary battery to the outside and / or for inputting current from the outside to the secondary battery. In other words, when the battery pack is used as a power source, current is supplied to the outside through the external terminals. Also, when charging the battery pack, the charging current (including regenerative energy from the power of an automobile, etc.) is supplied to the battery pack through the external terminals.

[0145] Next, an example of a battery pack according to the embodiment will be described with reference to the drawings.

[0146] Figure 8 is an exploded perspective view schematically showing an example of a battery pack. Figure 9 is a block diagram showing an example of the electrical circuit of the battery pack shown in Figure 8.

[0147] The battery pack 300 shown in Figures 8 and 9 comprises a housing container 31, a lid 32, a protective sheet 33, a battery pack 200, a printed circuit board 34, wiring 35, and an insulating plate (not shown).

[0148] The container 31 shown in Figure 8 is a rectangular-bottomed rectangular container. The container 31 is configured to accommodate a protective sheet 33, a battery pack 200, a printed circuit board 34, and wiring 35. The lid 32 has a rectangular shape. The lid 32 covers the container 31, thereby housing the battery pack 200 and the other components. The container 31 and the lid 32 are provided with openings or connection terminals for connecting to external devices, etc., although these are not shown in the figures.

[0149] The battery pack 200 comprises multiple individual cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0150] At least one of the multiple single cells 100 is a secondary battery according to the third embodiment. Each of the multiple single cells 100 is electrically connected in series as shown in Figure 9. The multiple single cells 100 may also be electrically connected in parallel, or they may be connected in a combination of series and parallel connections. When the multiple single cells 100 are connected in parallel, the battery capacity increases compared to when they are connected in series.

[0151] The adhesive tape 24 fastens multiple single cells 100 together. Alternatively, heat-shrinkable tape may be used to secure the multiple single cells 100 instead of the adhesive tape 24. In this case, protective sheets 33 are placed on both sides of the battery pack 200, the heat-shrinkable tape is wrapped around it, and then the heat-shrinkable tape is heat-shrinked to bundle the multiple single cells 100 together.

[0152] One end of the positive lead 22 is connected to the battery pack 200. One end of the positive lead 22 is electrically connected to the positive terminal of one or more single cells 100. One end of the negative lead 23 is connected to the battery pack 200. One end of the negative lead 23 is electrically connected to the negative terminal of one or more single cells 100.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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.).

[0162] 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.

[0163] 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.

[0164] 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.

[0165] The battery pack according to the fourth embodiment comprises a secondary battery according to the second embodiment or a battery pack according to the third embodiment. Therefore, the battery pack has a high energy density, suppressed gas generation, and excellent charge / discharge rate performance and charge / discharge cycle life performance.

[0166] (Fifth embodiment) According to the fifth embodiment, a vehicle is provided, which is equipped with the battery pack according to the fourth embodiment.

[0167] In such a vehicle, the battery pack, for example, recovers regenerative energy from the vehicle's power. The vehicle may also include a mechanism (regenerator) that converts the vehicle's kinetic energy into regenerative energy.

[0168] Examples of vehicles include, for example, two-wheeled or four-wheeled hybrid electric vehicles, two-wheeled or four-wheeled electric vehicles, electric assist bicycles, and railway vehicles.

[0169] The mounting location of the battery pack in a vehicle is not particularly limited. For example, when a battery pack is installed in an automobile, it can be mounted in the engine compartment, at the rear of the vehicle, or under the seats.

[0170] A vehicle may be equipped with multiple battery packs. In this case, the batteries contained in each battery pack may be electrically connected in series, in parallel, or a combination of series and parallel connections. For example, if each battery pack contains a battery pack, the battery packs may be electrically connected in series, in parallel, or a combination of series and parallel connections. Alternatively, if each battery pack contains a single battery, the batteries may be electrically connected in series, in parallel, or a combination of series and parallel connections.

[0171] Next, an example of a vehicle according to the embodiment will be described with reference to the drawings.

[0172] Figure 10 is a schematic partial transparency drawing showing an example of a vehicle.

[0173] The vehicle 400 shown in Figure 10 includes a vehicle body 40 and a battery pack 300 according to the fifth embodiment. In the example shown in Figure 10, the vehicle 400 is a four-wheeled automobile.

[0174] 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.

[0175] Figure 10 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.

[0176] Next, an embodiment of the vehicle according to the embodiment will be described with reference to Figure 11.

[0177] Figure 11 is a schematic diagram illustrating an example of a control system for the electrical system in a vehicle. The vehicle 400 shown in Figure 11 is an electric vehicle.

[0178] The vehicle 400 shown in Figure 11 comprises a vehicle body 40, a vehicle power supply 41, a vehicle ECU (ECU: Electric Control Unit) 42 which is a control device higher up than 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.

[0179] Vehicle 400 has a vehicle power supply 41 mounted, for example, in the engine compartment, at the rear of the vehicle body, or under the seats. Note that in the vehicle 400 shown in Figure 11, the mounting location of the vehicle power supply 41 is shown in a schematic manner.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] The vehicle power supply 41 may also have an electromagnetic contactor (for example, a switch device 415 shown in Figure 12) that switches the presence or absence of an electrical connection between the positive terminal 413 and the negative terminal 414. The switch device 415 includes a pre-charge switch (not shown) that turns on when charging is performed on the battery packs 200a to 200c, and a main switch (not shown) that turns on when the output from the battery packs 200a to 200c is supplied to the load. Each of the pre-charge switch and the main switch includes a relay circuit (not shown) that is switched on or off by a signal supplied to a coil located near the switch element. Electromagnetic contactors such as the switch device 415 are controlled based on a control signal from the battery management device 411 or the vehicle ECU 42 that controls the operation of the entire vehicle 400.

[0187] 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.

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] External terminal 43 is connected to battery management device 411. External terminal 43 can be connected to an external power supply, for example.

[0193] 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.

[0194] The vehicle according to the fifth embodiment is equipped with the battery pack according to the fourth embodiment. Therefore, a high-performance vehicle can be provided. [Examples]

[0195] Examples are described below, but the present invention is not limited to the examples listed below unless it exceeds the spirit of the invention.

[0196] (Example 1) In Example 1, a non-aqueous electrolyte battery was manufactured using the following procedure.

[0197] <Fabrication of the negative electrode> As the negative electrode active material, monoclinic titanium niobium composite oxide particles having a composition represented by the formula TiNb2O7 were prepared. Carbon nanotubes (CNTs) and acetylene black (AB) were prepared as conductive agents, and carboxymethylcellulose (CMC) and styrene butadiene rubber (SBR) were prepared as binders. These were mixed in pure water in a weight ratio of negative electrode active material:AB:CNT:CMC:SBR of 96.2:0.5:0.3:2:1 to obtain a slurry. Table 1 shows the amount of fibrous carbon material (parts by weight), the amount of granular carbon material (parts by weight), and the total carbon weight (sum of these carbon materials) per 100 parts by weight of negative electrode active material.

[0198] This slurry was applied to both the front and back main surfaces of a current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. The drying conditions were 70°C with a residence time of 1 minute. Thus, a laminate was obtained containing the current collector and a negative electrode active material-containing layer formed on both sides of the current collector. The amount of negative electrode active material-containing layer applied per side was 100 g / m². 2 The coating amount was adjusted so that it was reduced at both ends of the coated surface. Then, the resulting laminate had a density of 2.7 g / cm³ of the negative electrode active material-containing layer. 3 It was subjected to a roll press in this manner.

[0199] SEM observation was performed on the obtained negative electrode. A representative SEM image is shown in Figure 12. The SEM image shown in Figure 12 is before binarization. As shown in Figure 12, fibrous carbon material 501 or granular carbon material 502 is present between the negative electrode active material particles 500. From the SEM observation, it was confirmed that the fibrous carbon material has a first portion with a fiber diameter W1 of 100-200 nm and a second portion with a fiber diameter W2 of 3-10 nm, and that the particle size of the granular carbon material is 11 nm. The average primary particle diameter of the active material was 1.1 μm. Next, this negative electrode was punched out and subjected to vacuum drying. The brightness L* of the obtained negative electrode is shown in Table 1. <Fabrication of the positive electrode> As the positive electrode active material, Formula LiNi 0.5 Co 0.2Mn 0.3 Particles of lithium nickel cobalt manganese composite oxide represented by O2 were prepared. Acetylene black (AB) was prepared as a conductive agent, and polyvinylidene fluoride (PVdF) was prepared as a binder. These were mixed in a weight ratio of positive electrode active material:AB:PVdF of 90:5:5 to obtain a mixture. Next, the obtained mixture was dispersed in n-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. This slurry was applied to both the front and back main surfaces of a current collector made of aluminum foil with a thickness of 15 μm, and the coating film was dried. Thus, a laminate containing the current collector and positive electrode active material-containing layers formed on both sides of the current collector was obtained. The coating amount per side of the positive electrode active material-containing layer was 125 g / m². 2 With this goal in mind, the coating amount was adjusted so that it was reduced at both ends of the coated surface. Next, the density of the positive electrode active material-containing layer in the center of the coating width of the resulting laminate was 3.05 g / cm³. 3 The material was subjected to a roll press to achieve the desired result. Next, the resulting positive electrode was punched out and subjected to vacuum drying. <Manufacturing of electrode groups> A polyethylene (PE) separator with a thickness of 15 μm was prepared. The separator was folded into a zigzag pattern, and it was stacked with the negative electrode and positive electrode in the order of negative electrode, separator, positive electrode, and separator. The size of the area where the positive and negative electrodes faced each other was 50 mm vertically and 50 mm horizontally. A laminate was obtained using 5 positive electrodes and 6 negative electrodes. The positive and negative electrodes had uncoated areas where the electrode layer (active material-containing layer) was not applied. The uncoated areas of the positive and negative electrodes were located on the short sides of the electrodes. The positive and negative electrodes were stacked with separators in between so that the uncoated areas of the positive and negative electrodes were located on opposite sides of the laminate. The laminate was pressed at room temperature (25°C) by applying a load of 80 kN for 1 minute. Thus, an electrode group was manufactured. <Preparation of non-aqueous electrolytes> A non-aqueous electrolyte was prepared using the following procedure. First, propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a volume ratio of PC:DEC 1:2 to obtain a mixed solvent. Lithium hexafluoride phosphate (LiPF6) was dissolved in this mixed solvent at a concentration of 1 M to obtain a liquid non-aqueous electrolyte. <Battery assembly> The electrode group was housed in a pack made of laminate film and vacuum-dried at 80°C for 10 hours. The laminate film used was a 0.1 mm thick laminate film with polypropylene layers formed on both sides of a 40 μm thick aluminum foil. The electrolyte solution was poured in. After pouring, the laminate was heat-sealed under reduced pressure to manufacture the battery.

[0200] (Examples 2-10) The negative electrode was prepared using the same procedure as in Example 1, except that the composition of the negative electrode active material, the average primary particle diameter of the negative electrode active material, the fiber diameter W1 of the first part of the fibrous carbon material, the fiber diameter W2 of the second part, the particle size of the granular carbon material, the amount of fibrous carbon material (parts by weight) per 100 parts by weight of the negative electrode active material, the amount of granular carbon material (parts by weight) per 100 parts by weight of the negative electrode active material, the total amount of fibrous carbon material and granular carbon material (total carbon weight), and the brightness L* were set as shown in Table 1.

[0201] A non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the obtained negative electrode was used.

[0202] (Example 11) A non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the negative electrode described below was used.

[0203] As a fibrous carbon material, carbon nanotubes consisting only of the second portion and lacking the first portion were prepared. Furthermore, granular carbon material was not used. A slurry was obtained by mixing the negative electrode active material, CNT, CMC, and SBR in pure water in a weight ratio of 96.6:0.4:1:2. Table 1 shows the amount of fibrous carbon material (parts by weight) and the total carbon weight per 100 parts by weight of negative electrode active material.

[0204] This slurry was applied to both the front and back main surfaces of a current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. The drying conditions were 70°C with a residence time of 1 minute. Thus, a laminate was obtained containing the current collector and a negative electrode active material-containing layer formed on both sides of the current collector. The amount of negative electrode active material-containing layer applied per side was 100 g / m².2 The coating amount was adjusted so that it was reduced at both ends of the coated surface. Then, the resulting laminate had a density of 2.7 g / cm³ of the negative electrode active material-containing layer. 3 The material was subjected to a roll press to achieve the desired result. SEM observation of the obtained negative electrode confirmed the presence of CNTs as fibrous carbon material, with fiber diameter W2 having a second portion of the values ​​shown in Table 1. The average primary particle size of the active material was also as shown in Table 1. Next, this negative electrode was punched out and subjected to vacuum drying. The brightness L* of the obtained negative electrode is shown in Table 1.

[0205] (Example 12) A carbon nanotube consisting only of the first part and lacking the second part was prepared as a fibrous carbon material. The negative electrode was manufactured using the same procedure as in Example 1, except that this carbon nanotube was used. A non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the fabricated negative electrode was used.

[0206] (Comparative Example 1) A slurry was obtained by mixing the negative electrode active materials AB:CNT:CMC:SBR in pure water in a weight ratio of 95:1:1:1:2. The amount of fibrous carbon material (parts by weight), total carbon weight, and L* per 100 parts by weight of negative electrode active material are shown in Table 1. The negative electrode was prepared and a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the settings were as shown in Table 1.

[0207] (Comparative Example 2) A slurry was obtained by mixing the negative electrode active material (CNT:CMC:SBR) in pure water in a weight ratio of 96.99:0.01:1:2. The amount of fibrous carbon material (parts by weight) and the total carbon weight (L*) per 100 parts by weight of negative electrode active material are shown in Table 1. The negative electrode was prepared and a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the settings were as shown in Table 1.

[0208] (Comparative Example 3) A slurry was obtained by mixing the negative electrode active materials AB:CNT:CMC:SBR in pure water in a weight ratio of 94:2:1:1:2. The amount of fibrous carbon material (parts by weight) and the total carbon weight (L*) per 100 parts by weight of negative electrode active material are shown in Table 1. The negative electrode was prepared and a non-aqueous electrolyte battery was manufactured using the same procedure as in Example 1, except that the settings were as shown in Table 1.

[0209] Table 1 shows the composition of the negative electrode active material for each example and comparative example, the average primary particle diameter of the negative electrode active material, the fiber diameter W1 of the first part of the fibrous carbon material, the fiber diameter W2 of the second part, the particle size of the granular carbon material, the amount of fibrous carbon material blended per 100 parts by weight of negative electrode active material (parts by weight), the amount of granular carbon material blended per 100 parts by weight of negative electrode active material (parts by weight), the total amount of fibrous carbon material and granular carbon material blended (total carbon weight), and the brightness L* for each example and comparative example. Note that the monoclinic titanium-niobium composite oxide with a composition represented by TiNb2O7, the niobium oxide with a composition represented by Nb2O5, and the monoclinic titanium oxide with a composition represented by TiO2 used in the examples were all white particles.

[0210] <Rating> For each battery in the examples and comparative examples, discharge was performed at 0.2C and 5C respectively as an indicator of rate performance, and the ratio of the 5C discharge capacity to the 0.2C capacity was determined. The test results are shown in Table 2 below.

[0211] For each battery in the examples and comparative examples, SOC100% (3V vs Li / Li + The samples were left to stand at 80°C for 10 days, and the cell volume was measured before and after this period using the Archimedes method. The amount of gas generated was estimated from the difference. The amount of gas generated (cc / Ah) is shown in Table 2.

[0212] For each battery in the examples and comparative examples, a charge-discharge test was performed for 1000 cycles at 25°C and a time rate of 3C. The cycle performance was defined as the percentage retention of the discharge capacity at 1000 cycles relative to the discharge capacity at 1 cycle. The results are shown in Table 2.

[0213] [Table 1]

[0214] [Table 2]

[0215] As shown in Table 2, the non-aqueous electrolyte batteries of Examples 1 to 12 generated less gas during high-temperature storage than the non-aqueous electrolyte batteries of Comparative Examples 1 to 3, while maintaining rate performance and cycle performance. In Comparative Example 1, the fiber diameter of the first portion was larger than 500 nm, resulting in a brightness L* of less than 40. In Comparative Example 2, the fiber diameter of the first portion was smaller than 60 nm and the total carbon weight was low, resulting in a brightness L* exceeding 85. In Comparative Example 3, the fiber diameter of the first portion was larger than 500 nm and the total carbon weight was high, resulting in a brightness L* of less than 40. A comparison of Examples 1, 9, and 10 shows that Example 1, which uses a niobium-titanium-containing oxide as the active material, is superior to Examples 9 and 10 in terms of gas generation amount, rate performance, and cycle performance. A comparison of Examples 1, 11, and 12 shows that Example 1, which uses a fibrous carbon material having a first portion with a fiber diameter of 60 nm to 500 nm and a second portion with a fiber diameter of 1 nm to 15 nm, is superior to Examples 11 and 12 in terms of gas generation amount, rate performance, and cycle performance. A comparison of Example 1 and Example 8 shows that Example 1, which uses granular carbon material with a particle size of 30 nm or less, has superior rate performance and cycle performance compared to Example 8.

[0216] According to the one or more embodiments and examples described above, an electrode is provided. In this electrode, the carbon weight is 2.5 parts by weight or less per 100 parts by weight of the active material. Also, the brightness L* of the electrode is 40 ≤ L* ≤ 85. Therefore, it is possible to provide an electrode that can realize a secondary battery with high energy density, suppressed gas generation, and excellent charge / discharge rate performance and charge / discharge cycle life performance.

[0217] Although some 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 implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

[0218] Some embodiments according to the present invention are appended below.

[0219] (1) An electrode comprising an active material containing a metal oxide and a conductive agent containing a carbon material, where the carbon weight contained in the electrode is 2.5 parts by weight or less with respect to 100 parts by weight of the active material, and the lightness L* of the electrode satisfies 40 ≦ L* ≦ 85.

[0220] (2) The electrode according to (1), wherein the carbon material of the conductive agent includes a fibrous carbon material having a first part with a fiber diameter of 60 nm or more and 500 nm or less and a second part with a fiber diameter of 1 nm or more and 15 nm or less.

[0221] (3) The electrode according to (1) or (2), wherein the carbon material of the conductive agent further includes a granular carbon material having a particle size of 30 nm or less.

[0222] (4) The electrode according to any one of (1) to (3), wherein the metal oxide is white particles.

[0223] (5) The electrode according to any one of (1) to (4), wherein the metal oxide includes at least one of a titanium-containing oxide or a niobium-containing oxide.

[0224] (6) The metal oxide has an average primary particle diameter of 0.4 μm or more and 1.5 μm or less, and is the electrode according to any one of (1) to (5).

[0225] (7) A positive electrode, A negative electrode, And an electrolyte A secondary battery comprising: A secondary battery in which at least one of the positive electrode and the negative electrode is the electrode according to any one of (1) to (6).

[0226] (8) A battery pack comprising the secondary battery according to (7).

[0227] (9) An external terminal for energization, And a protection circuit The battery pack according to (8), further comprising.

[0228] (10) Comprising a plurality of the secondary batteries, The battery pack according to (8) or (9), wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

[0229] (11) A vehicle comprising the battery pack according to any one of (8) to (10).

[0230] (12) The vehicle according to (11), including a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

Explanation of symbols

[0231] 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, 5c…Positive electrode current collector tab, 6…Negative electrode terminal, 7…Positive electrode terminal, 10…Electrode, 10a…Current collector, 10b…Active material containing layer, 10c…Current collector tab, 21…Busbar, 22…Positive electrode side lead, 22a…Other end, 23 ...negative lead, 23a...other end, 24...adhesive tape, 31...container, 32...lid, 33...protective sheet, 34...printed circuit board, 35...wiring, 40...vehicle body, 41...vehicle power supply, 42...electric control device, 43...external terminal, 44...inverter, 45...drive motor, 100...secondary battery, 200...battery pack, 200a...battery pack, 200b...battery pack, 200c...battery pack, 300...battery pack 300a...Battery pack, 300b...Battery pack, 300c...Battery pack, 301a...Battery pack monitoring device, 301b...Battery pack monitoring device, 301c...Battery pack monitoring device, 342...Positive side connector, 343...Negative side connector, 345...Thermistor, 346...Protection circuit, 342a...Wiring, 343a...Wiring, 350...External terminal for power supply, 352...Positive side terminal, 353...Negative side terminal, 348 a...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, 500...Negative active material particles, 501...Fibrous carbon material, 502...Granular carbon material.

Claims

1. An electrode comprising an active material containing a metal oxide and a conductive agent containing a carbon material, The weight of carbon contained in the electrode is 2.5 parts by weight or less per 100 parts by weight of the active material. An electrode in which the brightness L* of the electrode is 40 ≤ L* ≤ 85.

2. The electrode according to claim 1, wherein the carbon material of the conductive agent comprises a fibrous carbon material having a first portion having a fiber diameter of 60 nm or more and 500 nm or less, and a second portion having a fiber diameter of 1 nm or more and 15 nm or less.

3. The electrode according to claim 2, wherein the carbon material of the conductive agent further comprises a granular carbon material with a particle size of 30 nm or less.

4. The electrode according to claim 1, wherein the metal oxide is white particles.

5. The electrode according to claim 1, wherein the metal oxide comprises at least one of a titanium-containing oxide or a niobium-containing oxide.

6. The electrode according to claim 1, wherein the metal oxide has an average primary particle diameter of 0.4 μm or more and 1.5 μm or less.

7. Positive electrode and, The negative electrode and, Electrolytes and A secondary battery comprising, A secondary battery in which at least one of the positive electrode and the negative electrode is an electrode according to any one of claims 1 to 6.

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

9. External terminals for power supply, Protection circuit and The battery pack according to claim 8, further comprising the above.

10. The device comprises multiple secondary batteries, The battery pack according to claim 9, wherein the secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

11. A vehicle comprising the battery pack described in claim 8.

12. The vehicle according to claim 11, which includes a mechanism for converting the kinetic energy of the vehicle into regenerative energy.

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